Boston Properties (BXP) 10-K2 Mar 202019 FY Annual reportFinancial data

Company Profile

Document And Entity Information

Document And Entity Information - USD ($)	12 Months Ended
Document And Entity Information - USD ($)	Dec. 31, 2019	Feb. 21, 2020	Jun. 30, 2019
Entity Information [Line Items]
Document Type	10-K
Document Period End Date	Dec. 31, 2019
Document Annual Report	true
Document Transition Report	false
Entity File Number	1-13087
Entity Registrant Name	BOSTON PROPERTIES, INC.
Entity Central Index Key	0001037540
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	04-2473675
Entity Address, Address Line One	Prudential Center, 800 Boylston Street, Suite 1900
Entity Address, City or Town	Boston
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02199-8103
City Area Code	617
Local Phone Number	236-3300
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 19,902,378,774
Entity Common Stock, Shares Outstanding		155,121,560
Documents Incorporated by Reference [Text Block]	Certain information contained in Boston Properties Inc.’s Proxy Statement relating to its Annual Meeting of Stockholders to be held May 20, 2020 is incorporated by reference in Items 10, 11, 12, 13 and 14 of Part III. Boston Properties, Inc. intends to file such Proxy Statement with the Securities and Exchange Commission not later than 120 days after the end of its fiscal year ended December 31, 2019.
Boston Properties Limited Partnership
Entity Information [Line Items]
Document Type	10-K
Document Period End Date	Dec. 31, 2019
Entity File Number	0-50209
Entity Registrant Name	BOSTON PROPERTIES LIMITED PARTNERSHIP
Entity Central Index Key	0001043121
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	04-3372948
Title of 12(g) Security	Units of Limited Partnership
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		0
Common Stock [Member]
Entity Information [Line Items]
Title of 12(b) Security	Common Stock, par value $.01 per share
Trading Symbol	BXP
Security Exchange Name	NYSE
Entity Listing, Par Value Per Share	$ 0.01
5.25% Series B Cumulative Redeemable Preferred Stock, par value $0.01 per share [Member]
Entity Information [Line Items]
Title of 12(b) Security	Depository Shares Each Representing 1/100th of a share
Trading Symbol	BXP PRB
Security Exchange Name	NYSE
Entity Listing, Par Value Per Share	$ 0.01

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
ASSETS
Real estate, at cost (amounts related to variable interest entities (“VIEs”) of $6,497,031 and $7,481,015 at December 31, 2019 and 2018, respectively)	$ 22,502,976	$ 21,649,896
Right of use assets - finance leases (amount related to VIEs of $21,000 at December 31, 2019)	237,394
Right of use assets - operating leases	148,640
Less: accumulated depreciation (amounts related to VIEs of $(1,058,495) and $(965,500) at December 31, 2019 and 2018, respectively)	(5,266,798)	(4,897,777)
Total real estate	17,622,212	16,752,119
Cash and cash equivalents (amounts related to VIEs of $280,033 and $296,806 at December 31, 2019 and 2018, respectively)	644,950	543,359
Cash held in escrows	46,936	95,832
Investments in securities	36,747	28,198
Tenant and other receivables, net (amounts related to VIEs of $28,918 and $15,519 at December 31, 2019 and 2018, respectively)	112,807	86,629
Related party note receivable	80,000	80,000
Note receivable	15,920	19,468
Accrued rental income, net (amounts related to VIEs of $298,318 and $272,466 at December 31, 2019 and 2018, respectively)	1,038,788	934,896
Deferred charges, net (amounts related to VIEs of $214,769 and $263,402 at December 31, 2019 and 2018, respectively)	689,213	678,724
Prepaid expenses and other assets (amounts related to VIEs of $20,931 and $26,513 at December 31, 2019 and 2018, respectively)	41,685	80,943
Investments in unconsolidated joint ventures	955,647	956,309
Total assets	21,284,905	20,256,477
Liabilities:
Mortgage notes payable, net (amounts related to VIEs of $2,918,806 and $2,929,326 at December 31, 2019 and 2018, respectively)	2,922,408	2,964,572
Unsecured senior notes, net	8,390,459	7,544,697
Unsecured line of credit	0	0
Unsecured term loan, net	498,939	498,488
Lease liabilities - finance leases (amount related to VIEs of $20,189 at December 31, 2019)	224,042
Lease liabilities - operating leases	200,180
Accounts payable and accrued expenses (amounts related to VIEs of $45,777 and $75,786 at December 31, 2019 and 2018, respectively)	377,553	276,645
Dividends and distributions payable	170,713	165,114
Accrued interest payable	90,016	89,267
Other liabilities (amounts related to VIEs of $140,110 and $200,344 at December 31, 2019 and 2018, respectively)	387,994	503,726
Total liabilities	13,262,304	12,042,509
Commitments and contingencies	0	0
Redeemable deferred stock units— 60,676 units outstanding at redemption value at December 31, 2019	8,365
Equity / Capital:
Excess stock, $0.01 par value, 150,000,000 shares authorized, none issued or outstanding	0	0
Preferred stock, $0.01 par value, 50,000,000 shares authorized;
5.25% Series B cumulative redeemable preferred stock / units, liquidation preference $2,500 per share / unit, 80,000 shares / units issued and outstanding at December 31, 2019 and December 31, 2018, respectively	200,000	200,000
Common stock, $0.01 par value, 250,000,000 shares authorized, 154,869,198 and 154,537,378 issued and 154,790,298 and 154,458,478 outstanding at December 31, 2019 and December 31, 2018, respectively	1,548	1,545
Additional paid-in capital	6,294,719	6,407,623
Dividends in excess of earnings	(760,523)	(675,534)
Treasury common stock at cost, 78,900 shares at December 31, 2019 and December 31, 2018	(2,722)	(2,722)
Accumulated other comprehensive loss	(48,335)	(47,741)
Total stockholders' equity attributable to Boston Properties, Inc.	5,684,687	5,883,171
Noncontrolling interests:
Common units of the Operating Partnership	600,860	619,352
Property partnerships	1,728,689	1,711,445
Total equity / capital	8,014,236	8,213,968
Total liabilities and equity / capital	21,284,905	20,256,477
Boston Properties Limited Partnership
ASSETS
Real estate, at cost (amounts related to variable interest entities (“VIEs”) of $6,497,031 and $7,481,015 at December 31, 2019 and 2018, respectively)	22,107,755	21,251,540
Right of use assets - finance leases (amount related to VIEs of $21,000 at December 31, 2019)	237,394
Right of use assets - operating leases	148,640
Less: accumulated depreciation (amounts related to VIEs of $(1,058,495) and $(965,500) at December 31, 2019 and 2018, respectively)	(5,162,908)	(4,800,475)
Total real estate	17,330,881	16,451,065
Cash and cash equivalents (amounts related to VIEs of $280,033 and $296,806 at December 31, 2019 and 2018, respectively)	644,950	543,359
Cash held in escrows	46,936	95,832
Investments in securities	36,747	28,198
Tenant and other receivables, net (amounts related to VIEs of $28,918 and $15,519 at December 31, 2019 and 2018, respectively)	112,807	86,629
Related party note receivable	80,000	80,000
Note receivable	15,920	19,468
Accrued rental income, net (amounts related to VIEs of $298,318 and $272,466 at December 31, 2019 and 2018, respectively)	1,038,788	934,896
Deferred charges, net (amounts related to VIEs of $214,769 and $263,402 at December 31, 2019 and 2018, respectively)	689,213	678,724
Prepaid expenses and other assets (amounts related to VIEs of $20,931 and $26,513 at December 31, 2019 and 2018, respectively)	41,685	80,943
Investments in unconsolidated joint ventures	955,647	956,309
Total assets	20,993,574	19,955,423
Liabilities:
Mortgage notes payable, net (amounts related to VIEs of $2,918,806 and $2,929,326 at December 31, 2019 and 2018, respectively)	2,922,408	2,964,572
Unsecured senior notes, net	8,390,459	7,544,697
Unsecured line of credit	0	0
Unsecured term loan, net	498,939	498,488
Lease liabilities - finance leases (amount related to VIEs of $20,189 at December 31, 2019)	224,042
Lease liabilities - operating leases	200,180
Accounts payable and accrued expenses (amounts related to VIEs of $45,777 and $75,786 at December 31, 2019 and 2018, respectively)	377,553	276,645
Dividends and distributions payable	170,713	165,114
Accrued interest payable	90,016	89,267
Other liabilities (amounts related to VIEs of $140,110 and $200,344 at December 31, 2019 and 2018, respectively)	387,994	503,726
Total liabilities	13,262,304	12,042,509
Commitments and contingencies	0	0
Redeemable deferred stock units— 60,676 units outstanding at redemption value at December 31, 2019	8,365
Redeemable partnership units—16,764,466 and 16,783,558 common units and 1,143,215 and 991,577 long term incentive units outstanding at redemption value at December 31, 2019 and December 31, 2018, respectively	2,468,753	2,000,591
Preferred stock, $0.01 par value, 50,000,000 shares authorized;
5.25% Series B cumulative redeemable preferred stock / units, liquidation preference $2,500 per share / unit, 80,000 shares / units issued and outstanding at December 31, 2019 and December 31, 2018, respectively	193,623	193,623
Boston Properties Limited Partnership partners’ capital—1,726,980 and 1,722,336 general partner units and 153,063,318 and 152,736,142 limited partner units outstanding at December 31, 2019 and December 31, 2018, respectively	3,380,175	4,054,996
Accumulated other comprehensive loss	(48,335)	(47,741)
Total partners’ capital	3,525,463	4,200,878
Noncontrolling interests in property partnerships	1,728,689	1,711,445
Noncontrolling interests:
Total equity / capital	5,254,152	5,912,323
Total liabilities and equity / capital	$ 20,993,574	$ 19,955,423

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
General Partners' Capital Account, Units Outstanding (in units)	1,726,980
Limited Partners' Capital Account, Units Outstanding (in units)	153,063,318
Excess stock, par value	$ 0.01	$ 0.01
Excess stock, shares authorized	150,000,000	150,000,000
Excess stock, shares issued	0	0
Excess stock, shares outstanding	0	0
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	50,000,000	50,000,000
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	250,000,000	250,000,000
Common stock, shares issued	154,869,198	154,537,378
Common stock, shares outstanding	154,790,298	154,458,478
Treasury common stock at cost, shares	78,900	78,900
Real estate, at cost (amounts related to variable interest entities (“VIEs”) of $6,497,031 and $7,481,015 at December 31, 2019 and 2018, respectively)	$ 22,502,976	$ 21,649,896
Right of use assets - finance leases (amount related to VIEs of $21,000 at December 31, 2019)	237,394
Less: accumulated depreciation (amounts related to VIEs of $(1,058,495) and $(965,500) at December 31, 2019 and 2018, respectively)	(5,266,798)	(4,897,777)
Cash and cash equivalents (amounts related to VIEs of $280,033 and $296,806 at December 31, 2019 and 2018, respectively)	644,950	543,359
Cash held in escrows	46,936	95,832
Tenant and other receivables, net (amounts related to VIEs of $28,918 and $15,519 at December 31, 2019 and 2018, respectively)	112,807	86,629
Accrued rental income, net (amounts related to VIEs of $298,318 and $272,466 at December 31, 2019 and 2018, respectively)	1,038,788	934,896
Deferred charges, net (amounts related to VIEs of $214,769 and $263,402 at December 31, 2019 and 2018, respectively)	689,213	678,724
Prepaid expenses and other assets (amounts related to VIEs of $20,931 and $26,513 at December 31, 2019 and 2018, respectively)	41,685	80,943
Mortgage notes payable, net (amounts related to VIEs of $2,918,806 and $2,929,326 at December 31, 2019 and 2018, respectively)	2,922,408	2,964,572
Lease liabilities - finance leases (amount related to VIEs of $20,189 at December 31, 2019)	224,042
Accounts payable and accrued expenses (amounts related to VIEs of $45,777 and $75,786 at December 31, 2019 and 2018, respectively)	377,553	276,645
Other liabilities (amounts related to VIEs of $140,110 and $200,344 at December 31, 2019 and 2018, respectively)	$ 387,994	$ 503,726
Series B Cumulative Redeemable Preferred Stock / Unit [Member]
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	92,000	92,000
Series B Dividend Rate Percentage	5.25%	5.25%
Preferred stock / units, shares / units issued (in shares / units)	80,000	80,000
Series B Liquidation Preference Per Share/ Unit	$ 2,500	$ 2,500
Preferred stock / units, shares / units outstanding (in shares / units)	80,000	80,000
Boston Properties Limited Partnership
Redeemable Partnership Units Common Units Shares Outstanding (in units)	16,764,466	16,783,558
Redeemable Partnership Units Common Units Long Term Incentive Units At Redemption Value Units Outstanding (in units)	1,143,215	991,577
General Partners' Capital Account, Units Outstanding (in units)	1,726,980	1,722,336
Limited Partners' Capital Account, Units Outstanding (in units)	153,063,318	152,736,142
Real estate, at cost (amounts related to variable interest entities (“VIEs”) of $6,497,031 and $7,481,015 at December 31, 2019 and 2018, respectively)	$ 22,107,755	$ 21,251,540
Right of use assets - finance leases (amount related to VIEs of $21,000 at December 31, 2019)	237,394
Less: accumulated depreciation (amounts related to VIEs of $(1,058,495) and $(965,500) at December 31, 2019 and 2018, respectively)	(5,162,908)	(4,800,475)
Cash and cash equivalents (amounts related to VIEs of $280,033 and $296,806 at December 31, 2019 and 2018, respectively)	644,950	543,359
Cash held in escrows	46,936	95,832
Tenant and other receivables, net (amounts related to VIEs of $28,918 and $15,519 at December 31, 2019 and 2018, respectively)	112,807	86,629
Accrued rental income, net (amounts related to VIEs of $298,318 and $272,466 at December 31, 2019 and 2018, respectively)	1,038,788	934,896
Deferred charges, net (amounts related to VIEs of $214,769 and $263,402 at December 31, 2019 and 2018, respectively)	689,213	678,724
Prepaid expenses and other assets (amounts related to VIEs of $20,931 and $26,513 at December 31, 2019 and 2018, respectively)	41,685	80,943
Mortgage notes payable, net (amounts related to VIEs of $2,918,806 and $2,929,326 at December 31, 2019 and 2018, respectively)	2,922,408	2,964,572
Lease liabilities - finance leases (amount related to VIEs of $20,189 at December 31, 2019)	224,042
Accounts payable and accrued expenses (amounts related to VIEs of $45,777 and $75,786 at December 31, 2019 and 2018, respectively)	377,553	276,645
Other liabilities (amounts related to VIEs of $140,110 and $200,344 at December 31, 2019 and 2018, respectively)	$ 387,994	$ 503,726
Boston Properties Limited Partnership \| Series B Cumulative Redeemable Preferred Stock / Unit [Member]
Series B Dividend Rate Percentage	5.25%	5.25%
Preferred stock / units, shares / units issued (in shares / units)	80,000	80,000
Series B Liquidation Preference Per Share/ Unit	$ 2,500	$ 2,500
Preferred stock / units, shares / units outstanding (in shares / units)	80,000	80,000
Variable Interest Entity, Primary Beneficiary [Member]
Real estate, at cost (amounts related to variable interest entities (“VIEs”) of $6,497,031 and $7,481,015 at December 31, 2019 and 2018, respectively)	$ 6,497,031	$ 7,481,015
Right of use assets - finance leases (amount related to VIEs of $21,000 at December 31, 2019)	21,000
Less: accumulated depreciation (amounts related to VIEs of $(1,058,495) and $(965,500) at December 31, 2019 and 2018, respectively)	(1,058,495)	(965,500)
Cash and cash equivalents (amounts related to VIEs of $280,033 and $296,806 at December 31, 2019 and 2018, respectively)	280,033	296,806
Tenant and other receivables, net (amounts related to VIEs of $28,918 and $15,519 at December 31, 2019 and 2018, respectively)	28,918	15,519
Accrued rental income, net (amounts related to VIEs of $298,318 and $272,466 at December 31, 2019 and 2018, respectively)	298,318	272,466
Deferred charges, net (amounts related to VIEs of $214,769 and $263,402 at December 31, 2019 and 2018, respectively)	214,769	263,402
Prepaid expenses and other assets (amounts related to VIEs of $20,931 and $26,513 at December 31, 2019 and 2018, respectively)	20,931	26,513
Mortgage notes payable, net (amounts related to VIEs of $2,918,806 and $2,929,326 at December 31, 2019 and 2018, respectively)	2,918,806	2,929,326
Lease liabilities - finance leases (amount related to VIEs of $20,189 at December 31, 2019)	20,189
Accounts payable and accrued expenses (amounts related to VIEs of $45,777 and $75,786 at December 31, 2019 and 2018, respectively)	45,777	75,786
Other liabilities (amounts related to VIEs of $140,110 and $200,344 at December 31, 2019 and 2018, respectively)	140,110	200,344
Variable Interest Entity, Primary Beneficiary [Member] \| Boston Properties Limited Partnership
Real estate, at cost (amounts related to variable interest entities (“VIEs”) of $6,497,031 and $7,481,015 at December 31, 2019 and 2018, respectively)	6,497,031	7,481,015
Right of use assets - finance leases (amount related to VIEs of $21,000 at December 31, 2019)	21,000
Less: accumulated depreciation (amounts related to VIEs of $(1,058,495) and $(965,500) at December 31, 2019 and 2018, respectively)	(1,058,495)	(965,500)
Cash and cash equivalents (amounts related to VIEs of $280,033 and $296,806 at December 31, 2019 and 2018, respectively)	280,033	296,806
Tenant and other receivables, net (amounts related to VIEs of $28,918 and $15,519 at December 31, 2019 and 2018, respectively)	28,918	15,519
Accrued rental income, net (amounts related to VIEs of $298,318 and $272,466 at December 31, 2019 and 2018, respectively)	298,318	272,466
Deferred charges, net (amounts related to VIEs of $214,769 and $263,402 at December 31, 2019 and 2018, respectively)	214,769	263,402
Prepaid expenses and other assets (amounts related to VIEs of $20,931 and $26,513 at December 31, 2019 and 2018, respectively)	20,931	26,513
Mortgage notes payable, net (amounts related to VIEs of $2,918,806 and $2,929,326 at December 31, 2019 and 2018, respectively)	2,918,806	2,929,326
Lease liabilities - finance leases (amount related to VIEs of $20,189 at December 31, 2019)	20,189
Accounts payable and accrued expenses (amounts related to VIEs of $45,777 and $75,786 at December 31, 2019 and 2018, respectively)	45,777	75,786
Other liabilities (amounts related to VIEs of $140,110 and $200,344 at December 31, 2019 and 2018, respectively)	$ 140,110	$ 200,344

Consolidated Statements Of Oper

Consolidated Statements Of Operations - USD ($) shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue
Lease		$ 2,758,014
Base rent			$ 2,103,723	$ 2,049,368
Recoveries from tenants			402,066	367,500
Total revenue		2,960,562	2,717,076	2,602,076
Expenses
Rental		1,050,010	979,151	929,977
Transaction costs		1,984	1,604	668
General and administrative		140,777	121,722	113,715
Depreciation and amortization		677,764	645,649	617,547
Total expenses		1,914,925	1,791,579	1,693,966
Other income (expense)
Income from unconsolidated joint ventures		46,592	2,222	11,232
Gains on sales of real estate		709	182,356	7,663
Interest and other income		18,939	10,823	5,783
Gains (losses) from investments in securities		6,417	(1,865)	3,678
Impairment losses		(24,038)	(11,812)	0
Interest expense		(412,717)	(378,168)	(374,481)
(Losses) gains from early extinguishments of debt		(29,540)	(16,490)	496
Net income		651,999	712,563	562,481
Net income attributable to noncontrolling interests
Noncontrolling interests in property partnerships		(71,120)	(62,909)	(47,832)
Noncontrolling interest - common units of the Operating Partnership		(59,345)	(66,807)	(52,210)
Net income attributable to the Company		521,534	582,847	462,439
Preferred dividends / distributions		(10,500)	(10,500)	(10,500)
Net income attributable to the Company's common shareholders / unitholders		$ 511,034	$ 572,347	$ 451,939
Basic earnings per common share / unit attributable to the Company
Net income (in dollars per share / unit)		$ 3.31	$ 3.71	$ 2.93
Weighted average number of common shares / units outstanding (in shares / units)		154,582	154,427	154,190
Diluted earnings per common share / unit attributable to the Company
Diluted Earnings: Net income, Per Share Amount (in dollars per share / unit)		$ 3.30	$ 3.70	$ 2.93
Weighted average number of common and common equivalent shares / units outstanding (in shares / units)		154,883	154,682	154,390
Boston Properties Limited Partnership
Revenue
Lease		$ 2,758,014
Base rent			$ 2,103,723	$ 2,049,368
Recoveries from tenants			402,066	367,500
Total revenue		2,960,562	2,717,076	2,602,076
Expenses
Rental		1,050,010	979,151	929,977
Transaction costs		1,984	1,604	668
General and administrative		140,777	121,722	113,715
Depreciation and amortization		669,956	637,891
Total expenses		1,907,117	1,783,821	1,685,826
Other income (expense)
Income from unconsolidated joint ventures		46,592	2,222	11,232
Gains on sales of real estate		858	190,716	8,240
Interest and other income		18,939	10,823	5,783
Gains (losses) from investments in securities		6,417	(1,865)	3,678
Impairment losses		(22,272)	(10,181)	0
Interest expense		(412,717)	(378,168)	(374,481)
(Losses) gains from early extinguishments of debt		(29,540)	(16,490)	496
Net income		661,722	730,312	571,198
Net income attributable to noncontrolling interests
Noncontrolling interests in property partnerships		(71,120)	(62,909)	(47,832)
Net income attributable to the Company		590,602	667,403	523,366
Preferred dividends / distributions		(10,500)	(10,500)	(10,500)
Net income attributable to the Company's common shareholders / unitholders		$ 580,102	$ 656,903	$ 512,866
Basic earnings per common share / unit attributable to the Company
Net income (in dollars per share / unit)		$ 3.37	$ 3.82	$ 2.99
Weighted average number of common shares / units outstanding (in shares / units)		172,200	171,912	171,661
Diluted earnings per common share / unit attributable to the Company
Diluted Earnings: Net income, Per Share Amount (in dollars per share / unit)		$ 3.36	$ 3.81	$ 2.98
Weighted average number of common and common equivalent shares / units outstanding (in shares / units)		172,501	172,167	171,861
Parking and Other [Member]
Revenue
Other revenue		$ 103,534	$ 107,421	$ 105,000
Parking and Other [Member] \| Boston Properties Limited Partnership
Revenue
Other revenue		103,534	107,421	105,000
Hotel [Member]
Revenue
Other revenue	[1]	48,589	49,118	45,603
Expenses
Operating expense		34,004	33,863	32,059
Hotel [Member] \| Boston Properties Limited Partnership
Revenue
Other revenue		48,589	49,118	45,603
Expenses
Operating expense		34,004	33,863	32,059
Real Estate, Other [Member]
Revenue
Other revenue		10,386	9,590	0
Real Estate, Other [Member] \| Boston Properties Limited Partnership
Revenue
Other revenue		10,386	9,590	0
Management Service [Member]
Revenue
Other revenue		40,039	45,158	34,605
Expenses
Operating expense		10,386	9,590	0
Management Service [Member] \| Boston Properties Limited Partnership
Revenue
Other revenue		40,039	45,158	34,605
Expenses
Operating expense		$ 10,386	$ 9,590	$ 0

[1]	Rental Revenue is equal to Total Revenue per the Company’s Consolidated Statements of Operations, less Development and Management Services Revenue and Direct Reimbursements of Payroll and Related Costs from Management Services Contracts Revenue per the Consolidated Statements of Operations.

Consolidated Statements Of Comp

Consolidated Statements Of Comprehensive Income - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net income		$ 651,999	$ 712,563	$ 562,481
Other comprehensive income (loss):
Effective portion of interest rate contracts		(6,751)	(3,096)	(6,133)
Amortization of interest rate contracts	[1]	6,664	6,664	6,033
Other comprehensive income (loss)		(87)	3,568	(100)
Comprehensive Income		651,912	716,131	562,381
Comprehensive income attributable to noncontrolling interests		(130,465)	(129,716)	(100,042)
Other comprehensive income (loss) attributable to noncontrolling interests		(507)	(880)	1,922
Comprehensive income attributable to the Company		520,940	585,535	464,261
Boston Properties Limited Partnership
Net income		661,722	730,312	571,198
Other comprehensive income (loss):
Effective portion of interest rate contracts		(6,751)	(3,096)	(6,133)
Amortization of interest rate contracts	[2]	6,664	6,664	6,033
Other comprehensive income (loss)		(87)	3,568	(100)
Comprehensive Income		661,635	733,880	571,098
Comprehensive income attributable to noncontrolling interests		(71,696)	(63,485)	(45,704)
Comprehensive income attributable to the Company		$ 589,939	$ 670,395	$ 525,394

[1]	Amounts reclassified from comprehensive income primarily to interest expense within Boston Properties, Inc.’s Consolidated Statements of Operations
[2]	Amounts reclassified from comprehensive income primarily to interest expense within Boston Properties Limited Partnership’s Consolidated Statements of Operations.

Consolidated Statements Of Stoc

Consolidated Statements Of Stockholders' Equity - USD ($)	Total	Common Stock [Member]	Preferred Stock [Member]	Additional Paid-In Capital [Member]	Dividends In Excess Of Earnings [Member]	Treasury Stock, At Cost [Member]	Accumulated Other Comprehensive Loss [Member]	Noncontrolling Interests [Member]	Noncontrolling interest - property partnerships [Member]
Equity, shares at Dec. 31, 2016		153,790,000
Equity, value at Dec. 31, 2016	$ 7,931,924,000	$ 1,538,000	$ 200,000,000	$ 6,333,424,000	$ (693,694,000)	$ (2,722,000)	$ (52,251,000)	$ 614,982,000	$ 1,530,647,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of a change in accounting principle	(2,035,000)				(272,000)			(1,763,000)
Redemption of operating partnership units to common stock, shares		495,000
Redemption of operating partnership units to common stock, value	0	$ 5,000		16,911,000				(16,916,000)
Allocated net income for the year	562,481,000				462,439,000			52,210,000	47,832,000
Dividends/distributions declared	(535,310,000)				(480,816,000)			(54,494,000)
Shares issued pursuant to stock purchase plan, shares		6,000
Shares issued pursuant to stock purchase plan, value	795,000			795,000
Net activity from stock option and incentive plan, shares		34,000
Net activity from stock option and incentive plan, value	37,292,000			3,899,000				33,393,000
Proceeds from noncontrolling interest including a contribution related to the repayment of a members' note payable	161,585,000								161,585,000
Contributions from noncontrolling interests in property partnerships	52,009,000								161,585,000
Distributions to noncontrolling interests in property partnerships	(54,176,000)								(54,176,000)
Effective portion of interest rate contracts	(6,133,000)						(3,305,000)	(375,000)	(2,453,000)
Amortization of interest rate contracts	6,033,000						5,127,000	581,000	325,000
Reallocation of noncontrolling interest	0			22,879,000				(22,879,000)
Equity, shares at Dec. 31, 2017		154,325,000
Equity, value at Dec. 31, 2017	8,102,456,000	$ 1,543,000	200,000,000	6,377,908,000	(712,343,000)	(2,722,000)	(50,429,000)	604,739,000	1,683,760,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of a change in accounting principle	5,496,000				4,933,000			563,000
Redemption of operating partnership units to common stock, shares		83,000
Redemption of operating partnership units to common stock, value	0	$ 2,000		2,878,000				(2,880,000)
Allocated net income for the year	712,563,000				582,847,000			66,807,000	62,909,000
Dividends/distributions declared	(613,702,000)				(550,971,000)			(62,731,000)
Shares issued pursuant to stock purchase plan, shares		6,000
Shares issued pursuant to stock purchase plan, value	797,000			797,000
Net activity from stock option and incentive plan, shares		44,000
Net activity from stock option and incentive plan, value	38,590,000			1,729,000				36,861,000
Contributions from noncontrolling interests in property partnerships	46,701,000								46,701,000
Distributions to noncontrolling interests in property partnerships	(82,501,000)								(82,501,000)
Effective portion of interest rate contracts	(3,096,000)						(2,781,000)	(315,000)
Amortization of interest rate contracts	6,664,000						5,469,000	619,000	576,000
Reallocation of noncontrolling interest	$ 0			24,311,000				(24,311,000)
Equity, shares at Dec. 31, 2018	154,458,478	154,458,000
Equity, value at Dec. 31, 2018	$ 8,213,968,000	$ 1,545,000	200,000,000	6,407,623,000	(675,534,000)	(2,722,000)	(47,741,000)	619,352,000	1,711,445,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of a change in accounting principle	(4,379,000)				(3,864,000)			(445,000)	(70,000)
Redemption of operating partnership units to common stock, shares		145,000
Redemption of operating partnership units to common stock, value	0	$ 2,000		4,883,000				(4,885,000)
Allocated net income for the year	651,999,000				521,534,000			59,345,000	71,120,000
Dividends/distributions declared	(671,893,000)				(602,659,000)			(69,234,000)
Shares issued pursuant to stock purchase plan, shares		6,000
Shares issued pursuant to stock purchase plan, value	688,000			688,000
Net activity from stock option and incentive plan, shares		181,000
Net activity from stock option and incentive plan, value	45,000,000	$ 1,000		8,771,000				36,228,000
Sale of an interest in property partnerships	0			(4,216,000)					4,216,000
Acquisition of noncontrolling interest in property partnership	(186,963,000)			(162,462,000)					(24,501,000)
Contributions from noncontrolling interests in property partnerships	35,816,000								35,816,000
Distributions to noncontrolling interests in property partnerships	(69,913,000)								(69,913,000)
Effective portion of interest rate contracts	(6,751,000)						(6,060,000)	(691,000)
Amortization of interest rate contracts	6,664,000						5,466,000	622,000	576,000
Reallocation of noncontrolling interest	$ 0			39,432,000				(39,432,000)
Equity, shares at Dec. 31, 2019	154,790,298	154,790,000
Equity, value at Dec. 31, 2019	$ 8,014,236,000	$ 1,548,000	$ 200,000,000	$ 6,294,719,000	$ (760,523,000)	$ (2,722,000)	$ (48,335,000)	$ 600,860,000	$ 1,728,689,000

Consolidated Statement of Capit

Consolidated Statement of Capital and Noncontrolling Interests Statement - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Common Stock, Shares, Outstanding	154,790,298	154,458,478
Cumulative effect of a change in accounting principle	$ (4,379,000)	$ 5,496,000	$ (2,035,000)
Effective portion of interest rate contracts	(6,751,000)	(3,096,000)	(6,133,000)
Amortization of interest rate contracts	6,664,000	6,664,000	6,033,000
Acquisition of noncontrolling interest in property partnership	(186,963,000)
Sale of an interest in property partnerships	0
Contributions from noncontrolling interests in property partnerships	35,816,000	46,701,000	52,009,000
Distributions to noncontrolling interests in property partnerships	$ (69,913,000)	$ (82,501,000)	$ (54,176,000)
General Partner [Member]
Common Stock, Shares, Outstanding	1,727,000	1,722,000	1,720,000	1,718,000
Contributions, units	3,000	1,000
Conversion of redeemable partnership units	2,000	1,000	2,000
Limited Partner [Member]
Common Stock, Shares, Outstanding	153,063,000	152,736,000	152,606,000	152,072,000
Contributions, units	185,000	49,000	40,000
Conversion of redeemable partnership units	142,000	81,000	494,000
Boston Properties Limited Partnership
Redeemable Noncontrolling Interest, Equity, Preferred, Carrying Amount	$ 2,468,753,000	$ 2,000,591,000
Contributions from noncontrolling interests in property partnerships	35,816,000	46,701,000	$ 52,009,000
Partners' Capital General and Limited Partners) [Member]
Beginning Balance	3,380,175,000	4,054,996,000	3,664,436,000	$ 3,670,345,000
Cumulative effect of a change in accounting principle	(3,864,000)	4,933,000	(272,000)
Contributions, value	17,115,000	1,642,000	4,937,000
Allocated net income for the period	520,757,000	590,096,000	460,656,000
Distributions	(592,159,000)	(540,471,000)	(470,316,000)
Unearned compensation	(7,655,000)	884,000	(243,000)
Conversion of redeemable partnership units, value	4,885,000	2,880,000	16,916,000
Adjustment to reflect redeemable partnership units at redemption value	(447,222,000)	330,596,000	(17,587,000)
Acquisition of noncontrolling interest in property partnership	(162,462,000)
Sale of an interest in property partnerships	(4,216,000)
Preferred Units [Member]
Beginning Balance	193,623,000	193,623,000	193,623,000	193,623,000
Allocated net income for the period	10,500,000	10,500,000	10,500,000
Distributions	(10,500,000)	(10,500,000)	(10,500,000)
Accumulated Other Comprehensive Loss [Member]
Beginning Balance	(48,335,000)	(47,741,000)	(50,429,000)	(52,251,000)
Effective portion of interest rate contracts	(6,060,000)	(2,781,000)	(3,305,000)
Amortization of interest rate contracts	5,466,000	5,469,000	5,127,000
Noncontrolling interest - property partnerships [Member]
Beginning Balance	1,728,689,000	1,711,445,000	1,683,760,000	1,530,647,000
Cumulative effect of a change in accounting principle	(70,000)
Allocated net income for the period	71,120,000	62,909,000	47,832,000
Effective portion of interest rate contracts			(2,453,000)
Amortization of interest rate contracts	576,000	576,000	325,000
Acquisition of noncontrolling interest in property partnership	(24,501,000)
Sale of an interest in property partnerships	4,216,000
Contributions from noncontrolling interests in property partnerships	35,816,000	46,701,000	161,585,000
Distributions to noncontrolling interests in property partnerships	(69,913,000)	(82,501,000)	(54,176,000)
Total Capital [Member]
Beginning Balance	5,254,152,000	5,912,323,000	5,491,390,000	5,342,364,000
Cumulative effect of a change in accounting principle	(3,934,000)	4,933,000	(272,000)
Contributions, value	17,115,000	1,642,000	4,937,000
Allocated net income for the period	602,377,000	663,505,000	518,988,000
Distributions	(602,659,000)	(550,971,000)	(480,816,000)
Unearned compensation	(7,655,000)	884,000	(243,000)
Conversion of redeemable partnership units, value	4,885,000	2,880,000	16,916,000
Adjustment to reflect redeemable partnership units at redemption value	(447,222,000)	330,596,000	(17,587,000)
Effective portion of interest rate contracts	(6,060,000)	(2,781,000)	(5,758,000)
Amortization of interest rate contracts	6,042,000	6,045,000	5,452,000
Acquisition of noncontrolling interest in property partnership	(186,963,000)
Sale of an interest in property partnerships	0
Contributions from noncontrolling interests in property partnerships	35,816,000	46,701,000	161,585,000
Distributions to noncontrolling interests in property partnerships	(69,913,000)	(82,501,000)	(54,176,000)
Noncontrolling interest - Redeemable partnership units [Member]
Redeemable Noncontrolling Interest, Equity, Preferred, Carrying Amount	2,468,753,000	2,000,591,000	2,292,263,000	$ 2,262,040,000
Cumulative effect of a change in accounting principle	(445,000)	563,000	(1,763,000)
Contributions, value	34,217,000	34,680,000	31,743,000
Allocated net income for the period	59,345,000	66,807,000	52,210,000
Distributions	(69,234,000)	(62,731,000)	(54,494,000)
Unearned compensation	2,011,000	2,181,000	1,650,000
Conversion of redeemable partnership units, value	(4,885,000)	(2,880,000)	(16,916,000)
Adjustment to reflect redeemable partnership units at redemption value	447,222,000	(330,596,000)	17,587,000
Effective portion of interest rate contracts	(691,000)	(315,000)	(375,000)
Amortization of interest rate contracts	$ 622,000	$ 619,000	$ 581,000

Consolidated Statements Of Cash

Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net income	$ 651,999	$ 712,563	$ 562,481
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	677,764	645,649	617,547
Amortization of right-of-use assets - operating leases	2,412
Impairment losses	24,038	11,812	0
Non-cash compensation expense	40,958	40,117	35,361
Income from unconsolidated joint ventures	(46,592)	(2,222)	(11,232)
Distributions of net cash flow from operations of unconsolidated joint ventures	17,155	6,703	26,858
(Gains) losses from investments in securities	(6,417)	1,865	(3,678)
Non-cash portion of interest expense	22,254	21,303	(1,284)
Settlement of accreted debt discount on redemption of unsecured senior notes	(763)	(483)	(1,980)
Losses (gains) from early extinguishments of debt	29,540	16,490	(496)
Gains on sales of real estate	(709)	(182,356)	(7,663)
Change in assets and liabilities:
Tenant and other receivables, net	(24,876)	29,204	2,433
Note receivable	4	(13)	0
Accrued rental income, net	(56,817)	(43,662)	(58,355)
Prepaid expenses and other assets	2,965	12,472	51,425
Lease liabilities - operating leases	1,616
Accounts payable and accrued expenses	12,627	1,353	10,482
Accrued interest payable	858	5,237	(160,521)
Other liabilities	(49,569)	4,955	(44,970)
Tenant leasing costs	(117,282)	(130,742)	(104,429)
Total adjustments	529,166	437,682	349,498
Net cash provided by operating activities	1,181,165	1,150,245	911,979
Cash flows from investing activities:
Acquisitions of real estate	(149,031)	0	(15,953)
Construction in progress	(546,060)	(694,791)	(608,404)
Building and other capital improvements	(180,556)	(189,771)	(222,482)
Tenant improvements	(251,831)	(210,034)	(205,331)
Right of use assets - finance leases	(5,152)	0	0
Proceeds from sales of real estate	90,824	455,409	29,810
Capital contributions to unconsolidated joint ventures	(87,392)	(345,717)	(109,015)
Capital distributions from unconsolidated joint ventures	136,807	0	251,000
Cash and cash equivalents deconsolidated	(24,112)	0	0
Deposit on capital lease	0	(13,615)	0
Issuance of related party note receivable	0	(80,000)	0
Issuance of note receivable	0	(19,455)	0
Proceeds from note receivable	3,544	0	0
Investments in securities, net	(2,132)	(902)	(1,669)
Net cash used in investing activities	(1,015,091)	(1,098,876)	(882,044)
Cash flows from financing activities:
Proceeds from mortgage notes payable	0	0	2,300,000
Repayments of mortgage notes payable	(46,173)	(18,634)	(1,317,653)
Proceeds from unsecured senior notes	1,548,106	996,410	847,935
Redemption of unsecured senior notes	(699,237)	(699,517)	(848,020)
Borrowings on unsecured line of credit	380,000	745,000	580,000
Repayments of unsecured line of credit	(380,000)	(790,000)	(535,000)
Proceeds from unsecured term loan	0	500,000	0
Repayments of mezzanine notes payable	0	0	(306,000)
Repayments of outside members’ notes payable	0	0	(70,424)
Payments on finance lease obligations	(502)	0	0
Payments on capital lease obligations	0	(1,353)	(493)
Payments on real estate financing transactions	0	(960)	(2,840)
Deposit on mortgage note payable interest rate lock	0	0	(23,200)
Return of deposit on mortgage note payable interest rate lock	0	0	23,200
Deferred financing costs	(13,213)	(8,362)	(50,705)
Debt prepayment and extinguishment costs	(28,716)	(15,973)	(12,784)
Net proceeds from equity transactions	13,710	(730)	241
Dividends and distributions	(666,294)	(587,628)	(526,578)
Contributions from noncontrolling interests in property partnerships	35,816	46,701	52,009
Distributions to noncontrolling interests in property partnerships	(69,913)	(82,501)	(54,342)
Acquisition of noncontrolling interest in property partnership	(186,963)	0	0
Net cash (used in) provided by financing activities	(113,379)	82,453	55,346
Net increase (decrease) in cash and cash equivalents	52,695	133,822	85,281
Cash and cash equivalents and cash held in escrows, beginning of year	639,191	505,369	420,088
Cash and cash equivalents and cash held in escrows, end of year	691,886	639,191	505,369
Reconciliation of cash and cash equivalents and cash held in escrow
Cash and cash equivalents, beginning of year	543,359	434,767	356,914
Cash held in escrows, beginning of period	95,832	70,602	63,174
Cash and cash equivalents, end of year	644,950	543,359	434,767
Cash held in escrows,end of period	46,936	95,832	70,602
Supplemental disclosures:
Cash paid for interest	439,059	416,019	598,486
Interest capitalized	54,911	65,766	61,070
Non-cash investing and financing activities:
Write-off of fully depreciated real estate	(129,831)	(135,431)	(124,891)
Change in real estate included in accounts payable and accrued expenses	89,245	(44,866)	27,978
Real estate acquired through capital leases	0	12,397	28,962
Real estate acquired through capital lease	287,540	0	0
Prepaid rent reclassified to right of use asset	15,000	0	0
Building and other capital improvements deconsolidated	(12,767)	0	0
Right of use asset - finance lease deconsolidated	(135,004)	0	0
Investment in unconsolidated joint venture recorded on deconsolidation	29,246	0	0
Lease liability - finance lease deconsolidation	119,534	0	0
Outside members’ notes payable contributed to noncontrolling interests in property partnerships	0	0	109,576
Dividends and distributions declared but not paid	170,713	165,114	139,040
Conversions of noncontrolling interests to stockholders’ equity	4,885	2,880	16,916
Issuance of restricted securities to employees and directors	37,622	37,052	35,989
Boston Properties Limited Partnership
Net income	661,722	730,312	571,198
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	669,956	637,891	609,407
Amortization of right-of-use assets - operating leases	2,412
Impairment losses	22,272	10,181	0
Non-cash compensation expense	40,958	40,117	35,361
Income from unconsolidated joint ventures	(46,592)	(2,222)	(11,232)
Distributions of net cash flow from operations of unconsolidated joint ventures	17,155	6,703	26,858
(Gains) losses from investments in securities	(6,417)	1,865	(3,678)
Non-cash portion of interest expense	22,254	21,303	(1,284)
Settlement of accreted debt discount on redemption of unsecured senior notes	(763)	(483)	(1,980)
Losses (gains) from early extinguishments of debt	29,540	16,490	(496)
Gains on sales of real estate	(858)	(190,716)	(8,240)
Change in assets and liabilities:
Tenant and other receivables, net	(24,876)	29,204	2,433
Note receivable	4	(13)	0
Accrued rental income, net	(56,817)	(43,662)	(58,355)
Prepaid expenses and other assets	2,965	12,472	51,425
Lease liabilities - operating leases	1,616
Accounts payable and accrued expenses	12,627	1,353	10,482
Accrued interest payable	858	5,237	(160,521)
Other liabilities	(49,569)	4,955	(44,970)
Tenant leasing costs	(117,282)	(130,742)	(104,429)
Total adjustments	519,443	419,933	340,781
Net cash provided by operating activities	1,181,165	1,150,245	911,979
Cash flows from investing activities:
Acquisitions of real estate	(149,031)	0	(15,953)
Construction in progress	(546,060)	(694,791)	(608,404)
Building and other capital improvements	(180,556)	(189,771)	(222,482)
Tenant improvements	(251,831)	(210,034)	(205,331)
Right of use assets - finance leases	(5,152)	0	0
Proceeds from sales of real estate	90,824	455,409	29,810
Capital contributions to unconsolidated joint ventures	(87,392)	(345,717)	(109,015)
Capital distributions from unconsolidated joint ventures	136,807	0	251,000
Cash and cash equivalents deconsolidated	(24,112)	0	0
Deposit on capital lease	0	(13,615)	0
Issuance of related party note receivable	0	(80,000)	0
Issuance of note receivable	0	(19,455)	0
Proceeds from note receivable	3,544	0	0
Investments in securities, net	(2,132)	(902)	(1,669)
Net cash used in investing activities	(1,015,091)	(1,098,876)	(882,044)
Cash flows from financing activities:
Proceeds from mortgage notes payable	0	0	2,300,000
Repayments of mortgage notes payable	(46,173)	(18,634)	(1,317,653)
Proceeds from unsecured senior notes	1,548,106	996,410	847,935
Redemption of unsecured senior notes	(699,237)	(699,517)	(848,020)
Borrowings on unsecured line of credit	380,000	745,000	580,000
Repayments of unsecured line of credit	(380,000)	(790,000)	(535,000)
Proceeds from unsecured term loan	0	500,000	0
Repayments of mezzanine notes payable	0	0	(306,000)
Repayments of outside members’ notes payable	0	0	(70,424)
Payments on finance lease obligations	(502)
Payments on capital lease obligations		(1,353)	(493)
Payments on real estate financing transactions	0	(960)	(2,840)
Deposit on mortgage note payable interest rate lock	0	0	(23,200)
Return of deposit on mortgage note payable interest rate lock	0	0	23,200
Deferred financing costs	(13,213)	(8,362)	(50,705)
Debt prepayment and extinguishment costs	(28,716)	(15,973)	(12,784)
Net proceeds from equity transactions	13,710	(730)	241
Dividends and distributions	(666,294)	(587,628)	(526,578)
Contributions from noncontrolling interests in property partnerships	35,816	46,701	52,009
Distributions to noncontrolling interests in property partnerships	(69,913)	(82,501)	(54,342)
Acquisition of noncontrolling interest in property partnership	(186,963)	0
Net cash (used in) provided by financing activities	(113,379)	82,453	55,346
Net increase (decrease) in cash and cash equivalents	52,695	133,822	85,281
Cash and cash equivalents and cash held in escrows, beginning of year	639,191	505,369	420,088
Cash and cash equivalents and cash held in escrows, end of year	691,886	639,191	505,369
Reconciliation of cash and cash equivalents and cash held in escrow
Cash and cash equivalents, beginning of year	543,359	434,767	356,914
Cash held in escrows, beginning of period	95,832	70,602	63,174
Cash and cash equivalents, end of year	644,950	543,359	434,767
Cash held in escrows,end of period	46,936	95,832	70,602
Supplemental disclosures:
Cash paid for interest	439,059	416,019	598,486
Interest capitalized	54,911	65,766	61,070
Non-cash investing and financing activities:
Write-off of fully depreciated real estate	(129,253)	(135,431)	(123,714)
Change in real estate included in accounts payable and accrued expenses	89,245	44,866	27,978
Real estate acquired through capital leases	0	12,397	28,962
Real estate acquired through capital lease	287,540	0	0
Prepaid rent reclassified to right of use asset	15,000	0	0
Building and other capital improvements deconsolidated	(12,767)	0	0
Right of use asset - finance lease deconsolidated	(135,004)	0	0
Investment in unconsolidated joint venture recorded on deconsolidation	29,246	0	0
Lease liability - finance lease deconsolidation	119,534	0	0
Outside members’ notes payable contributed to noncontrolling interests in property partnerships	0	0	109,576
Dividends and distributions declared but not paid	170,713	165,114	139,040
Conversions of noncontrolling interests to stockholders’ equity	4,885	2,880	16,916
Issuance Of Restricted Units To Employees And Directors	$ 37,622	$ 37,052	$ 35,989

Organization

Organization	12 Months Ended
Organization	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization	1. Organization Boston Properties, Inc., a Delaware corporation, is a fully integrated, self-administered and self-managed real estate investment trust (“REIT”). Boston Properties, Inc. is the sole general partner of Boston Properties Limited Partnership, its operating partnership and at December 31, 2019 owned an approximate 89.6% ( 89.7% at December 31, 2018 ) general and limited partnership interest in Boston Properties Limited Partnership. Unless stated otherwise or the context requires, the “Company” refers to Boston Properties, Inc. and its subsidiaries, including Boston Properties Limited Partnership and its consolidated subsidiaries. Partnership interests in Boston Properties Limited Partnership include: • common units of partnership interest (also referred to as “OP Units”), • long term incentive units of partnership interest (also referred to as “LTIP Units”), and • preferred units of partnership interest (also referred to as “Preferred Units”). Unless specifically noted otherwise, all references to OP Units exclude units held by Boston Properties, Inc. A holder of an OP Unit may present such OP Unit to Boston Properties Limited Partnership for redemption at any time (subject to restrictions agreed upon at the time of issuance of OP Units to particular holders that may restrict such redemption right for a period of time, generally one year from issuance). Upon presentation of an OP Unit for redemption, Boston Properties Limited Partnership is obligated to redeem the OP Unit for cash equal to the value of a share of common stock of Boston Properties, Inc. (“Common Stock”). In lieu of a cash redemption, Boston Properties, Inc. may elect to acquire the OP Unit for one share of Common Stock. Because the number of shares of Common Stock outstanding at all times equals the number of OP Units that Boston Properties, Inc. owns, one share of Common Stock is generally the economic equivalent of one OP Unit, and the quarterly distribution that may be paid to the holder of an OP Unit equals the quarterly dividend that may be paid to the holder of a share of Common Stock. The Company uses LTIP Units as a form of equity-based award for annual long-term incentive equity compensation. The Company has also issued LTIP Units to employees in the form of (1) 2012 outperformance plan awards (“2012 OPP Units”) and (2) 2013, 2014, 2015, 2016, 2017, 2018 and 2019 multi-year, long-term incentive program awards (also referred to as “MYLTIP Units”), each of which, upon the satisfaction of certain performance and vesting conditions, is convertible into one OP Unit. The three-year measurement periods for the 2012 OPP Units, 2013 MYLTIP Units, 2014 MYLTIP Units, 2015 MYLTIP Units and 2016 MYLTIP Units expired on February 6, 2015, February 4, 2016, February 3, 2017, February 4, 2018 and February 9, 2019, respectively, and Boston Properties, Inc.’s total stockholder return (“TSR”) was sufficient for employees to earn and therefore become eligible to vest in a portion of the awards. Unless and until they are earned, the rights, preferences and privileges of the 2017 MYLTIP Units, 2018 MYLTIP Units and 2019 MYLTIP Units differ from other LTIP Units granted to employees (including the 2012 OPP Units, the 2013 MYLTIP Units, the 2014 MYLTIP Units, the 2015 MYLTIP Units and the 2016 MYLTIP Units, which have been earned). Therefore, unless specifically noted otherwise, all references to LTIP Units exclude the 2017 MYLTIP Units, 2018 MYLTIP Units and 2019 MYLTIP Units. LTIP Units (including the earned 2012 OPP Units, the 2013 MYLTIP Units, the 2014 MYLTIP Units, the 2015 MYLTIP Units and 2016 MYLTIP Units), whether vested or not, will receive the same quarterly per unit distributions as OP Units, which equal per share dividends on Common Stock (See Notes 10 , 16 and 19 ). At December 31, 2019 , there was one series of Preferred Units outstanding (i.e., Series B Preferred Units). The Series B Preferred Units were issued to Boston Properties, Inc. on March 27, 2013 in connection with the issuance of 80,000 shares ( 8,000,000 depositary shares each representing 1/100th of a share) of 5.25% Series B Cumulative Redeemable Preferred Stock (the “Series B Preferred Stock”). Boston Properties, Inc. contributed the net proceeds from the offering to Boston Properties Limited Partnership in exchange for 80,000 Series B Preferred Units having terms and preferences generally mirroring those of the Series B Preferred Stock (See Note 11 ). Properties At December 31, 2019 , the Company owned or had interests in a portfolio of 196 commercial real estate properties (the “Properties”) aggregating approximately 52.0 million net rentable square feet of primarily Class A office properties, including 11 properties under construction/redevelopment totaling approximately 5.5 million net rentable square feet. At December 31, 2019 , the Properties consisted of: • 177 office properties (including nine properties under construction/redevelopment); • twelve retail properties; • six residential properties (including two properties under construction); and • one hotel. The Company considers Class A office properties to be well located buildings that are professionally managed and maintained, attract high-quality tenants and command upper-tier rental rates, and that are modern structures or have been modernized to compete with newer buildings. Basis of Presentation The accompanying consolidated financial statements are presented using the accrual basis of accounting in conformity with accounting principles generally accepted in the United States of America. Boston Properties, Inc. does not have any other significant assets, liabilities or operations, other than its investment in Boston Properties Limited Partnership, nor does it have employees of its own. Boston Properties Limited Partnership, not Boston Properties, Inc., generally executes all significant business relationships other than transactions involving securities of Boston Properties, Inc. All majority-owned subsidiaries and joint ventures over which the Company has financial and operating control and variable interest entities (“VIEs”) in which the Company has determined it is the primary beneficiary are included in the consolidated financial statements. All significant intercompany balances and transactions have been eliminated in consolidation. The Company accounts for all other unconsolidated joint ventures using the equity method of accounting. Accordingly, the Company’s share of the earnings of these joint ventures and companies is included in consolidated net income. Variable Interest Entities (VIEs) Consolidated VIEs are those for which the Company is considered to be the primary beneficiary of a VIE. The primary beneficiary is the entity that has a controlling financial interest in the VIE, which is defined by the entity having both of the following characteristics: (1) the power to direct the activities that, when taken together, most significantly impact the VIE’s performance and (2) the obligation to absorb losses or the right to receive the returns from the VIE that could potentially be significant to the VIE. The Company has determined that it is the primary beneficiary for six of the eight entities that are VIEs (see “ New Accounting Pronouncements Issued but not yet Adopted—Consolidation” within Note 2). Consolidated Variable Interest Entities As of December 31, 2019 , Boston Properties, Inc. has identified six consolidated VIEs, including Boston Properties Limited Partnership. Excluding Boston Properties Limited Partnership, the VIEs consisted of the following five in-service properties: 767 Fifth Avenue (the General Motors Building), Time Square Tower, 601 Lexington Avenue, Atlantic Wharf Office Building and 100 Federal Street. The Company consolidates these VIEs because it is the primary beneficiary. The third parties’ interests in these consolidated entities (i.e., excluding Boston Properties Limited Partnership’s interest) are reflected as noncontrolling interest in property partnerships in the accompanying Consolidated Financial Statements (See Note 10 ). In addition, Boston Properties, Inc.’s only significant asset is its investment in Boston Properties Limited Partnership and, consequently, substantially all of Boston Properties, Inc.’s assets and liabilities are the assets and liabilities of Boston Properties Limited Partnership. Variable Interest Entities Not Consolidated The Company has determined that Platform 16 Holdings LP and the landlord entity for its Platform 16 ground lease are VIEs. The Company does not consolidate these entities as the Company does not have the power to direct the activities that, when taken together, most significantly impact the VIE’s performance and, therefore, the Company is not considered to be the primary beneficiary.

Summary Of Significant Accounti

Summary Of Significant Accounting Policies	12 Months Ended
Summary Of Significant Accounting Policies	Dec. 31, 2019
Accounting Policies [Abstract]
Basis Of Presentation And Summary Of Significant Accounting Policies	2. Summary of Significant Accounting Policies Real Estate Upon acquisitions of real estate, the Company assesses whether the transaction should be accounted for as an asset acquisition or as a business combination by applying a screen to determine whether the integrated set of assets and activities acquired meets the definition of a business. Acquisitions of integrated sets of assets and activities that do not meet the definition of a business are accounted for as asset acquisitions. The Company’s acquisitions of real estate or in-substance real estate generally will not meet the definition of a business because substantially all of the fair value is concentrated in a single identifiable asset or group of similar identifiable assets (i.e. land, buildings, and related intangible assets) or because the acquisition does not include a substantive process in the form of an acquired workforce or an acquired contract that cannot be replaced without significant cost, effort or delay. The Company assesses the fair value of acquired tangible and intangible assets (including land, buildings, tenant improvements, “above-” and “below-market” leases, leasing and assumed financing origination costs, acquired in-place leases, other identified intangible assets and assumed liabilities) and allocates the purchase price to the acquired assets and assumed liabilities, including land and buildings as if vacant. The Company assesses fair value based on estimated cash flow projections that utilize discount and/or capitalization rates that it deems appropriate, as well as available market information. Estimates of future cash flows are based on a number of factors including the historical operating results, known and anticipated trends, and market and economic conditions. The fair value of the tangible assets of an acquired property considers the value of the property as if it were vacant. The Company also considers an allocation of purchase price of other acquired intangibles, including acquired in-place leases that may have a customer relationship intangible value, including (but not limited to) the nature and extent of the existing relationship with the tenants, the tenants’ credit quality and expectations of lease renewals. Based on its acquisitions to date, the Company’s allocation to customer relationship intangible assets has been immaterial. The Company records acquired “above-” and “below-market” leases at their fair values (using a discount rate which reflects the risks associated with the leases acquired) equal to the difference between (1) the contractual amounts to be paid pursuant to each in-place lease and (2) management’s estimate of fair market lease rates for each corresponding in-place lease, measured over a period equal to the remaining term of the lease for above-market leases and the initial term plus the term of any below-market fixed rate renewal options for below-market leases. Acquired “above-” and “below-market” lease values have been reflected within Prepaid Expenses and Other Assets and Other Liabilities, respectively, in the Company’s Consolidated Balance Sheets. Other intangible assets acquired include amounts for in-place lease values that are based on the Company’s evaluation of the specific characteristics of each tenant’s lease. Factors to be considered include estimates of carrying costs during hypothetical expected lease-up periods considering current market conditions, and costs to execute similar leases. In estimating carrying costs, the Company includes real estate taxes, insurance and other operating expenses and estimates of lost rentals at market rates during the expected lease-up periods, depending on local market conditions. In estimating costs to execute similar leases, the Company considers leasing commissions, legal and other related expenses. Management reviews its long-lived assets for impairment following the end of each quarter and when there is an event or change in circumstances that indicates carrying amounts may not be recoverable. An impairment loss is recognized if the carrying amount of an asset is not recoverable and exceeds its fair value. The evaluation of anticipated cash flows is subjective and is based in part on assumptions regarding anticipated hold periods, future occupancy, future rental rates, future capital requirements, discount rates and capitalization rates that could differ materially from actual results in future periods. Because cash flows on properties considered to be “long-lived assets to be held and used” are considered on an undiscounted basis to determine whether an asset has been impaired, the Company’s established strategy of holding properties over the long term directly decreases the likelihood of recording an impairment loss. If the Company’s strategy changes or market conditions otherwise dictate an earlier sale date, an impairment loss may be recognized and such loss could be material. If the Company determines that an impairment has occurred, the affected assets must be reduced to their fair value. Guidance in Accounting Standards Codification (“ASC”) 360 “Property Plant and Equipment” (“ASC 360”) requires that qualifying assets and liabilities and the results of operations that have been sold, or otherwise qualify as “held for sale,” be presented as discontinued operations in all periods presented if the property operations are expected to be eliminated and the Company will not have significant continuing involvement following the sale. Discontinued operations presentation applies only to disposals representing a strategic shift that has (or will have) a major effect on an entity’s operations and financial results (e.g., a disposal of a major geographical area, a major line of business, a major equity method investment or other major parts of an entity). The components of the property’s net income that are reflected as discontinued operations include the net gain (or loss) upon the disposition of the property held for sale, operating results, depreciation and interest expense (if the property is subject to a secured loan). The Company generally considers assets to be “held for sale” when the transaction has been approved by Boston Properties, Inc.’s Board of Directors, or a committee thereof, and there are no known significant contingencies relating to the sale, such that a sale of the property within one year is considered probable. Following the classification of a property as “held for sale,” no further depreciation is recorded on the assets, and the asset is written down to the lower of carrying value or fair market value, less cost to sell. Real estate is stated at depreciated cost. A variety of costs are incurred in the acquisition, development and leasing of properties. The cost of buildings and improvements includes the purchase price of property, legal fees and other acquisition costs. The Company capitalizes acquisition costs that it incurs to effect an asset acquisition and expenses acquisition costs that it incurs to effect a business combination, including legal, due diligence and other closing related costs. Costs directly related to the development of properties are capitalized. Capitalized development costs include interest, internal wages, property taxes, insurance, and other project costs incurred during the period of development. After the determination is made to capitalize a cost, it is allocated to the specific component of the project that benefited from the investment. Determination of when a development project commences and capitalization begins, and when a development project is substantially complete and held available for occupancy and capitalization must cease, involves a degree of judgment. The Company’s capitalization policy on development properties follows the guidance in ASC 835-20 “Capitalization of Interest” and ASC 970 “Real Estate-General.” The costs of land and buildings under development include specifically identifiable costs. Capitalized costs include pre-construction costs necessary to the development of the property, development costs, construction costs, interest costs, real estate taxes, salaries and related costs and other costs incurred during the period of development. The Company begins the capitalization of costs during the pre-construction period, which it defines as activities that are necessary for the development of the property. The Company considers a construction project as substantially complete and held available for occupancy upon the completion of tenant improvements, but no later than one year from cessation of major construction activity. The Company ceases capitalization on the portion (1) substantially completed, (2) occupied or held available for occupancy, and capitalizes only those costs associated with the portion under construction or (3) if activities necessary for the development of the property have been suspended. Interest costs capitalized for the years ended December 31, 2019 , 2018 and 2017 were approximately $54.9 million , $65.8 million and $61.1 million , respectively. Salaries and related costs capitalized for the years ended December 31, 2019 , 2018 and 2017 were approximately $10.4 million , $12.5 million and $13.2 million , respectively. Expenditures for repairs and maintenance are charged to operations as incurred. Significant betterments are capitalized. When assets are sold or retired, their costs and related accumulated depreciation are removed from the accounts with the resulting gains or losses reflected in net income or loss for the period. The Company computes depreciation and amortization on properties using the straight-line method based on estimated useful asset lives. The Company allocates the acquisition cost of real estate to its components and depreciates or amortizes these assets (or liabilities) over their useful lives. The amortization of acquired “above-” and “below-market” leases and acquired in-place leases is recorded as an adjustment to revenue and depreciation and amortization, respectively, in the Consolidated Statements of Operations. Depreciation is computed on a straight-line basis over the estimated useful lives of the assets as follows: Land improvements 25 to 40 years Buildings and improvements 10 to 40 years Tenant improvements Shorter of useful life or terms of related lease Furniture, fixtures, and equipment 3 to 7 years Cash and Cash Equivalents Cash and cash equivalents consist of cash on hand and investments with maturities of three months or less from the date of purchase. The majority of the Company’s cash and cash equivalents are held at major commercial banks which may at times exceed the Federal Deposit Insurance Corporation limit of $250,000 . Cash Held in Escrows Escrows include amounts established pursuant to various agreements for security deposits, property taxes, insurance and other costs. Escrows also include cash held by qualified intermediaries for possible investments in like-kind exchanges in accordance with Section 1031 of the Internal Revenue Code, as amended (the “Code”), in connection with sales of the Company’s properties. Investments in Securities The Company accounts for investments in equity securities at fair value, with gains or losses resulting from changes in fair value recognized currently in earnings. The Company maintains deferred compensation plans that are designed to allow officers and non-employee directors of Boston Properties, Inc. to defer a portion of the officer’s current income or the non-employee director’s current compensation on a pre-tax basis and receive a tax-deferred return on these deferrals based on the performance of specific investments selected by the officer or non-employee director. The Company’s obligation under the plans is that of an unsecured promise to pay the deferred compensation to the plan participants in the future. At December 31, 2019 and 2018 , the Company had maintained approximately $36.7 million and $28.2 million , respectively, in separate accounts, which are not restricted as to their use. The Company recognized gains (losses) of approximately $6.4 million , $(1.9) million and $3.7 million on its investments in the accounts associated with the Company’s deferred compensation plans during the years ended December 31, 2019 , 2018 and 2017 , respectively. Tenant and Other Receivables Tenant and other accounts receivable, other than accrued rents receivable, are expected to be collected within one year. Notes Receivable The Company accounts for notes receivable at their unamortized cost, net of any unamortized deferred fees or costs, premiums or discounts and an allowance for loan losses (see “ New Accounting Pronouncements Issued but not yet Adopted—Financial Instruments - Credit Losses” ). Loan fees and direct costs associated with loans originated by the Company are deferred and amortized over the term of the note as interest income. Deferred Charges Deferred charges include leasing costs and certain financing fees. Leasing costs include acquired intangible in-place lease values and direct and incremental fees and costs incurred in the successful negotiation of leases, including brokerage and other costs which have been deferred and are being amortized on a straight-line basis over the terms of the respective leases. Unamortized leasing costs are charged to expense upon the early termination of the lease. Fully amortized deferred leasing costs are removed from the books upon the expiration of the lease. The Company did not capitalize any external legal costs and internal leasing salaries and related costs for the year ended December 31, 2019 (see “ New Accounting Pronouncements Adopted—Leases ”). Internal leasing salaries and related costs capitalized for the years ended December 31, 2018 and 2017 were approximately $5.4 million and $5.0 million , respectively. Financing fees included in deferred charges consist of external fees and costs incurred to obtain the Company’s revolving facility and if applicable, the delayed draw facility and construction financing arrangements where there are not sufficient amounts outstanding. Such financing costs have been deferred and are being amortized over the terms of the respective financing and included within interest expense. Unamortized financing costs are charged to expense upon the early repayment or significant modification of the financing. Fully amortized deferred financing costs are removed from the books upon the maturity of the debt. External fees and costs incurred to obtain mortgage financings and unsecured senior notes have been deferred and are presented as direct deductions from the carrying amounts of the corresponding debt liability. Such financing costs are being amortized over the terms of the respective financing and included within interest expense. Unamortized financing costs are charged to expense upon the early repayment or significant modification of the financing. Investments in Unconsolidated Joint Ventures The Company consolidates VIEs in which it is considered to be the primary beneficiary. VIEs are entities in which the equity investors do not have sufficient equity at risk to finance their endeavors without additional financial support or that the holders of the equity investment at risk do not have substantive participating rights. The primary beneficiary is defined by the entity having both of the following characteristics: (1) the power to direct the activities that, when taken together, most significantly impact the variable interest entity’s performance, and (2) the obligation to absorb losses and the right to receive the returns from the variable interest entity that could potentially be significant to the VIE. For ventures that are not VIEs, the Company consolidates entities for which it has significant decision making control over the ventures’ operations. The Company’s judgment with respect to its level of influence or control of an entity involves the consideration of various factors including the form of the Company’s ownership interest, its representation in the entity’s governance, the size of its investment (including loans), estimates of future cash flows, its ability to participate in policy making decisions and the rights of the other investors to participate in the decision making process and to replace the Company as manager and/or liquidate the venture, if applicable. The Company’s assessment of its influence or control over an entity affects the presentation of these investments in the Company’s consolidated financial statements. In addition to evaluating control rights, the Company consolidates entities in which the outside partner has no substantive kick-out rights to remove the Company as the managing member. Accounts of the consolidated entity are included in the accounts of the Company and the noncontrolling interest is reflected on the Consolidated Balance Sheets as a component of equity or in temporary equity between liabilities and equity. Investments in unconsolidated joint ventures are recorded initially at cost, and subsequently adjusted for equity in earnings and cash contributions and distributions. Any difference between the carrying amount of these investments on the balance sheet and the underlying equity in net assets is amortized as an adjustment to equity in earnings of unconsolidated joint ventures over the life of the related asset. Under the equity method of accounting, the net equity investment of the Company is reflected within the Consolidated Balance Sheets, and the Company’s share of net income or loss from the joint ventures is included within the Consolidated Statements of Operations. The joint venture agreements may designate different percentage allocations among investors for profits and losses; however, the Company’s recognition of joint venture income or loss generally follows the joint venture’s distribution priorities, which may change upon the achievement of certain investment return thresholds. The Company may account for cash distributions in excess of its investment in an unconsolidated joint venture as income when the Company is not the general partner in a limited partnership and when the Company has neither the requirement nor the intent to provide financial support to the joint venture. The Company classifies distributions received from equity method investees within its Consolidated Statements of Cash Flows using the nature of the distribution approach, which classifies the distributions received on the basis of the nature of the activity or activities of the investee that generated the distribution as either a return on investment (classified as cash inflows from operating activities) or a return of investment (classified as cash inflows from investing activities). The Company’s investments in unconsolidated joint ventures are reviewed for impairment periodically and the Company records impairment charges when events or circumstances change indicating that a decline in the fair values below the carrying amounts has occurred and such decline is other-than-temporary. The evaluation of fair value is subjective and is based in part on assumptions regarding future occupancy, future rental rates, future capital requirements, discount rates and capitalization rates that could differ materially from actual results in future periods . The ultimate realization of the investment in unconsolidated joint ventures is dependent on a number of factors, including the performance of each investment and market conditions. The Company will record an impairment charge if it determines that a decline in the fair value below the carrying amount of an investment in an unconsolidated joint venture is other-than-temporary. To the extent that the Company contributed assets to a joint venture, the Company’s investment in the joint venture was recorded at the Company’s cost basis in the assets that were contributed to the joint venture. To the extent that the Company’s cost basis is different than the basis reflected at the joint venture level, the basis difference is amortized over the life of the related asset and included in the Company’s share of equity in net income of the joint venture. In accordance with the provisions of ASC 610-20 “Gains and Losses from the Derecognition of Nonfinancial Assets” (“ASC 610-20”), the Company will recognize a full gain on both the retained and sold portions of real estate contributed or sold to a joint venture by recognizing its new equity method investment interest at fair value. The combined summarized financial information of the unconsolidated joint ventures is disclosed in Note 5 . Revenue Recognition In general, the Company commences lease/rental revenue recognition when the tenant takes possession of the leased space and the leased space is substantially ready for its intended use. Contractual lease/rental revenue is reported on a straight-line basis over the terms of the respective leases. The impact of the straight-line rent adjustment increased revenue by approximately $58.4 million , $51.9 million and $54.8 million for the years ended December 31, 2019 , 2018 and 2017 , respectively, as the revenue recorded exceeded amounts billed. Accrued rental income, as reported on the Consolidated Balance Sheets, represents cumulative lease/rental income earned in excess of rent payments received pursuant to the terms of the individual lease agreements. The Company maintains an allowance against accrued rental income for future potential tenant credit losses. The credit assessment is based on the estimated accrued rental income that is recoverable over the term of the lease. The Company also maintains an allowance for doubtful accounts for estimated losses resulting from the inability of tenants to make required rent payments. The computation of this allowance is based on the tenants’ payment history and current credit status, as well as certain industry or geographic specific credit considerations. If the Company’s estimates of collectability differ from the cash received, then the timing and amount of the Company’s reported revenue could be impacted. The credit risk is mitigated by the high quality of the Company’s existing tenant base, reviews of prospective tenants’ risk profiles prior to lease execution and consistent monitoring of the Company’s portfolio to identify potential problem tenants. In accordance with ASC 805, the Company recognizes acquired in-place “above-” and “below-market” leases at their fair values as rental revenue over the original term of the respective leases. The impact of the acquired in-place “above-” and “below-market” leases increased revenue by approximately $20.9 million , $23.8 million and $23.5 million for the years ended December 31, 2019 , 2018 and 2017 , respectively. The following table summarizes the scheduled amortization of the Company’s acquired “above-” and “below-market” lease intangibles for each of the five succeeding years (in thousands). Acquired Above-Market Lease Intangibles Acquired Below-Market Lease Intangibles 2020 $ 5,440 $ 10,673 2021 3,054 6,455 2022 357 5,699 2023 183 5,558 2024 135 4,043 Recoveries from tenants, consisting of amounts due from tenants for common area maintenance, real estate taxes and other recoverable costs, are recognized as revenue in the period during which the expenses are incurred (see “ New Accounting Pronouncements Adopted—Leases” ). The Company recognizes these reimbursements on a gross basis, as the Company obtains control of the goods and services before they are transferred to the tenant. The Company also receives reimbursements of payroll and payroll related costs from unconsolidated joint venture entities and third party property owners in connection with management services contracts which the Company reflects on a gross basis instead of on a net basis as the Company has determined that it is the principal and not the agent under these arrangements in accordance with the guidance in ASC 606 “Revenue from Contracts with Customers” (“ASC 606”). The Company’s parking revenue is derived primarily from monthly and transient daily parking. In addition, the Company has certain lease arrangements for parking accounted for under the guidance in ASC 842 “Leases” (“ASC 842”). The monthly and transient daily parking revenue falls within the scope of ASC 606 and is accounted for at the point in time when control of the goods or services transfers to the customer and the Company’s performance obligation is satisfied. The Company’s hotel revenue is derived from room rentals and other sources such as charges to guests for telephone service, movie and vending commissions, meeting and banquet room revenue and laundry services. Hotel revenue is recognized as the hotel rooms are occupied and the services are rendered to the hotel customers. The Company earns management and development fees. Development and management services revenue is earned from unconsolidated joint venture entities and third-party property owners. The Company determined that the performance obligations associated with its development services contracts are satisfied over time and that the Company would recognize its development services revenue under the output method evenly over time from the development commencement date through the substantial completion date of the development management services project due to the stand-ready nature of the contracts. Significant judgments impacting the amount and timing of revenue recognized from the Company’s development services contracts include estimates of total development project costs from which the fees are typically derived and estimates of the period of time until substantial completion of the development project, the period of time over which the development services are required to be performed. The Company recognizes development fees earned from unconsolidated joint venture projects equal to its cost plus profit to the extent of the third party partners’ ownership interest. Property management fees are recorded and earned based on a percentage of collected rents at the properties under management, and not on a straight-line basis, because such fees are contingent upon the collection of rents. Gains on sales of real estate are recognized pursuant to the provisions included in ASC 610-20. Under ASC 610-20, the Company must first determine whether the transaction is a sale to a customer or non-customer. The Company typically sells real estate on a selective basis and not within the ordinary course of its business and therefore expects that its sale transactions will not be contracts with customers. The Company next determines whether it has a controlling financial interest in the property after the sale, consistent with the consolidation model in ASC 810 “Consolidation” (“ASC 810”). If the Company determines that it does not have a controlling financial interest in the real estate, it evaluates whether a contract exists under ASC 606 and whether the buyer has obtained control of the asset that was sold. The Company recognizes a full gain on sale of real estate when the derecognition criteria under ASC 610-20 have been met. Earnings Per Share Basic earnings per share (“EPS”) is computed by dividing net income available to common shareholders, as adjusted for undistributed earnings (if any) of certain securities issued by Boston Properties Limited Partnership, by the weighted average number of shares of Common Stock outstanding during the year. Diluted EPS reflects the potential dilution that could occur from shares issuable in connection with awards under stock-based compensation plans, including upon the exercise of stock options, and securities of Boston Properties Limited Partnership that are exchangeable for Common Stock. Earnings Per Common Unit Basic earnings per common unit is computed by dividing net income available to common unitholders, as adjusted for undistributed earnings (if any) of certain securities issued by Boston Properties Limited Partnership, by the weighted average number of common units outstanding during the year. Diluted earnings per common unit reflects the potential dilution that could occur from units issuable in connection with awards under Boston Properties, Inc.’s stock-based compensation plans, including upon the exercise of stock options, and conversion of preferred units of Boston Properties Limited Partnership. Fair Value of Financial Instruments The carrying values of cash and cash equivalents, marketable securities, escrows, receivables, accounts payable, accrued expenses and other assets and liabilities are reasonable estimates of their fair values because of the short maturities of these instruments. The Company follows the authoritative guidance for fair value measurements when valuing its financial instruments for disclosure purposes. Boston Properties Limited Partnership determines the fair value of its unsecured senior notes using market prices. The inputs used in determining the fair value of Boston Properties Limited Partnership’s unsecured senior notes is categorized at a Level 1 basis (as defined in ASC 820 “Fair Value Measurements and Disclosures” (“ASC 820”)) due to the fact that it uses quoted market rates to value these instruments. However, the inputs used in determining the fair value could be categorized at a Level 2 basis (as defined in ASC 820) if trading volumes are low. The Company determines the fair value of its related party note receivable, note receivable and mortgage notes payable using discounted cash flow analysis by discounting the spread between the future contractual interest payments and hypothetical future interest payments on note receivables / mortgage debt based on current market rates for similar securities. In determining the current market rates, the Company adds its estimates of market spreads to the quoted yields on federal government treasury securities with similar maturity dates to its debt. The inputs used in determining the fair value of the Company’s related party note receivable, note receivable, and mortgage notes payable are categorized at a Level 3 basis (as defined in ASC 820) due to the fact that the Company considers the rates used in the valuation techniques to be unobservable inputs. To the extent that there are outstanding borrowings under the unsecured line of credit or unsecured term loan, the Company utilizes a discounted cash flow methodology in order to estimate the fair value. To the extent that credit spreads have changed since the origination, the net present value of the difference between future contractual interest payments and future interest payments based on the Company’s estimate of a current market rate would represent the difference between the book value and the fair value. The Company’s estimate of a current market rate is based upon the rate, considering current market conditions and Boston Properties Limited Partnership’s specific credit profile, at which it estimates it could obtain similar borrowings. To the extent there are outstanding borrowings, this current market rate is estimated and therefore would be primarily based upon a Level 3 input (see “ New Accounting Pronouncements Issued but not yet Adopted—Fair Value Measurement” ). Because the Company’s valuations of its financial instruments are based on these types of estimates, the actual fair values of its financial instruments may differ materially if the Company’s estimates do not prove to be accurate, and the Company’s estimated fair values for these instruments as of the end of the applicable reporting period are not necessarily indicative of estimated or actual fair values in future reporting periods. The following table presents the aggregate carrying value of the Company’s related party note receivable, note receivable, mortgage notes payable, net, unsecured senior notes, net, unsecured line of credit and unsecured term loan, net and the Company’s corresponding estimate of fair value as of December 31, 2019 and December 31, 2018 (in thousands): December 31, 2019 December 31, 2018 Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value Related party note receivable $ 80,000 $ 81,931 $ 80,000 $ 80,000 Note receivable 15,920 14,978 19,468 19,468 Total $ 95,920 $ 96,909 $ 99,468 $ 99,468 Mortgage notes payable, net $ 2,922,408 $ 2,984,956 $ 2,964,572 $ 2,903,925 Unsecured senior notes, net 8,390,459 8,826,375 7,544,697 7,469,338 Unsecured line of credit — — — — Unsecured term loan, net 498,939 500,561 498,488 500,783 Total $ 11,811,806 $ 12,311,892 $ 11,007,757 $ 10,874,046 The Company uses interest rate swap agreements to manage its interest ra

Real Estate

Real Estate	9 Months Ended
Real Estate	Sep. 30, 2019
Real Estate [Abstract]
Real Estate	3. Real Estate Boston Properties, Inc. Real estate consisted of the following at December 31, 2019 and December 31, 2018 (in thousands): 2019 2018 Land $ 5,111,606 $ 5,072,568 Right of use assets - finance leases 237,394 — Right of use assets - operating leases 148,640 — Land held for future development (1) 254,828 200,498 Buildings and improvements 13,646,054 13,356,751 Tenant improvements 2,656,439 2,396,932 Furniture, fixtures and equipment 44,313 44,351 Construction in progress 789,736 578,796 Total 22,889,010 21,649,896 Less: Accumulated depreciation (5,266,798 ) (4,897,777 ) $ 17,622,212 $ 16,752,119 _______________ (1) Includes pre-development costs. Boston Properties Limited Partnership Real estate consisted of the following at December 31, 2019 and December 31, 2018 (in thousands): 2019 2018 Land $ 5,011,153 $ 4,971,475 Right of use assets - finance leases 237,394 — Right of use assets - operating leases 148,640 — Land held for future development (1) 254,828 200,498 Buildings and improvements 13,351,286 13,059,488 Tenant improvements 2,656,439 2,396,932 Furniture, fixtures and equipment 44,313 44,351 Construction in progress 789,736 578,796 Total 22,493,789 21,251,540 Less: Accumulated depreciation (5,162,908 ) (4,800,475 ) $ 17,330,881 $ 16,451,065 _______________ (1) Includes pre-development costs. Developments/Redevelopments On May 9, 2019, the Company entered into a 15-year lease with Google, LLC for approximately 379,000 net rentable square feet of Class A office space in a build-to-suit development project located at the Company’s 325 Main Street property at Kendall Center in Cambridge, Massachusetts. 325 Main Street consisted of an approximately 115,000 net rentable square foot Class A office property that was demolished and is being developed into an approximately 420,000 net rentable square foot Class A office property, including approximately 41,000 net rentable square feet of retail space. On May 9, 2019, the Company commenced development of the project. Boston Properties, Inc. and Boston Properties Limited Partnership recognized approximately $9.9 million and $9.5 million , respectively, of depreciation expense associated with the acceleration of depreciation on the assets being removed from service and demolished as part of the redevelopment of the property. On June 1, 2019, the Company partially placed in-service 20 CityPoint, a Class A office project with approximately 211,000 net rentable square feet located in Waltham, Massachusetts. On September 30, 2019, the Company commenced the redevelopment of 200 West Street, a Class A office project with approximately 261,000 net rentable square feet located in Waltham, Massachusetts. The redevelopment is a conversion of a 126,000 square foot portion of the property to laboratory space. On October 24, 2019, the Company completed and placed in-service 145 Broadway, a build-to-suit Class A office project with approximately 483,000 net rentable square feet located in Cambridge, Massachusetts. Ground Leases On January 24, 2019, the ground lessor under the Company’s 65 -year ground lease for land totaling approximately 5.6 acres at Platform 16 located in San Jose, California made available for lease to the Company the remaining land parcels. As a result, the Company recognized the remaining portion of the right of use finance lease asset and finance lease liability. The Company entered into the ground lease in 2018, however, at the inception of the ground lease only a portion of the land was available for lease from the lessor, resulting in the Company recognizing only a portion of the ground lease. In the aggregate, the land will support the development of approximately 1.1 million square feet of commercial office space. The ground lease provides the Company with the right to purchase all of the land during a 12-month period commencing February 1, 2020 at a purchase price of approximately $134.8 million . The Company was reasonably certain it would exercise the option to purchase the land and as a result, the Company concluded that the lease should be accounted for as a finance lease. As a result, the Company recorded an approximately $122.6 million right of use asset - finance lease and a lease liability - finance lease on the Company’s Consolidated Balance Sheets reflecting the remaining land parcels made available for lease to the Company. Finance lease assets and liabilities are accounted for at the lower of fair market value or the present value of future lease payments. For land leases classified as finance leases because of a purchase option that the Company views as an economic incentive, the Company follows its existing policy and does not depreciate land because it is assumed to have an indefinite life. See also “ Dispositions ” below and Notes 5 and 19. As of January 24, 2019, the lease payments from the finance lease related to the remaining parcels made available for lease to the Company were as follows (in thousands): Period from January 24, 2019 through December 31, 2019 $ 17,918 2020 109,460 Total expected minimum lease payments 127,378 Interest portion (4,815 ) Present value of expected net lease payments $ 122,563 On July 16, 2019, the Company executed a 75 -year ground lease with The George Washington University for land parcels at 2100 Pennsylvania Avenue located in Washington, DC and commenced development of an approximately 470,000 net rentable square foot Class A office property pursuant to a development agreement that the Company entered into with The George Washington University in 2016. The development agreement provided for the execution of the ground lease upon completion of the entitlement process and relocation of existing tenants. Also in 2016, the Company made a deposit of $15.0 million that, upon execution of the ground lease, is credited against ground rent payable under the ground lease. The present value of the lease payments exceeds substantially all of the fair value of the underlying asset and as a result, the Company has concluded that the ground lease should be accounted for as a finance lease. As a result, the Company recorded an approximately $185.1 million right of use asset - finance lease and an approximately $165.0 million lease liability - finance lease on the Company’s Consolidated Balance Sheets. The difference between the right of use asset - finance lease and lease liability - finance lease is the $15.0 million deposit that was made in 2016 and approximately $5.1 million of initial direct costs. Although the finance lease is for land only, as this was not classified as a finance lease because of a purchase option, the right of use asset will be amortized over the shorter of the useful life of the asset or the lease term. As land is assumed to have an indefinite life, the right of use asset - finance lease will be amortized on a straight-line basis over the 75 -year term. In 2017, the Company entered into a 16-year lease with a tenant for approximately 300,000 net rentable square feet of space at the property. As of July 16, 2019, the lease payments from the finance lease were as follows (in thousands): Period from July 16, 2019 through December 31, 2019 $ — 2020 — 2021 3,863 2022 8,576 2023 8,669 Thereafter 1,358,518 Total expected minimum lease payments 1,379,626 Interest portion (1,214,649 ) Present value of expected net lease payments $ 164,977 Acquisitions On January 10, 2019, the Company acquired land parcels at its Carnegie Center property located in Princeton, New Jersey for a gross purchase price of approximately $51.5 million , which includes an aggregate of approximately $8.6 million of additional amounts that are payable in the future to the seller upon the development or sale of each of the parcels. The land parcels could support approximately 1.7 million square feet of development. On August 27, 2019, the Company acquired 880 and 890 Winter Street located in Waltham, Massachusetts for a gross purchase price of approximately $106.0 million in cash. 880 and 890 Winter Street consists of two Class A office properties aggregating approximately 392,000 net rentable square feet. The following table summarizes the allocation of the purchase price, including transaction costs, of 880 and 890 Winter Street at the date of acquisition (in thousands): Land $ 29,510 Building and improvements 59,788 Tenant improvements 6,024 In-place lease intangibles 11,494 Above-market lease intangibles 246 Below-market lease intangibles (1,092 ) Net assets acquired $ 105,970 The following table summarizes the estimated annual amortization of the acquired in-place lease intangibles, the acquired above-market lease intangibles and the acquired below-market lease intangibles for 880 and 890 Winter Street for the remainder of 2019 and each of the next five succeeding fiscal years (in thousands): Acquired In-Place Lease Intangibles Acquired Above-Market Lease Intangibles Acquired Below- Market Lease Intangibles Period from August 27, 2019 through December 31, 2019 $ 1,801 $ 28 $ (226 ) 2020 4,485 80 (599 ) 2021 2,391 80 (237 ) 2022 1,121 43 (30 ) 2023 179 15 — 2024 60 — — 880 and 890 Winter Street contributed approximately $4.9 million of revenue and approximately ($0.6) million of earnings to the Company for the period from August 27, 2019 through December 31, 2019. Dispositions On January 24, 2019, the Company completed the sale of its 2600 Tower Oaks Boulevard property located in Rockville, Maryland for a gross sale price of approximately $22.7 million . Net cash proceeds totaled approximately $21.4 million , resulting in a loss on sale of real estate totaling approximately $0.6 million . The Company recognized an impairment loss totaling approximately $3.1 million for Boston Properties, Inc. and approximately $1.5 million for Boston Properties Limited Partnership during the year ended December 31, 2018. 2600 Tower Oaks Boulevard is an approximately 179,000 net rentable square foot Class A office property. 2600 Tower Oaks contributed approximately $(0.2) million of net loss to the Company for the period from January 1, 2019 through January 23, 2019 and contributed approximately $(0.6) million and $(0.1) million of net loss to the Company for the years ended December 31, 2018 and 2017, respectively. At March 31, 2019, the Company evaluated the expected hold period of its One Tower Center property located in East Brunswick, New Jersey and, based on a shorter-than-expected hold period, the Company reduced the carrying value of the property to its estimated fair value at March 31, 2019 and recognized an impairment loss totaling approximately $24.0 million for Boston Properties, Inc. and approximately $22.3 million for Boston Properties Limited Partnership. The Company’s estimated fair value was based on a pending offer from a third party to acquire the property and the subsequent execution of a purchase and sale agreement on April 18, 2019 for a gross sale price of $38.0 million . On June 3, 2019, the Company completed the sale of the property. Net cash proceeds totaled approximately $36.6 million , resulting in a loss on sale of real estate totaling approximately $0.8 million . One Tower Center is an approximately 410,000 net rentable square foot Class A office property. One Tower Center contributed approximately $(0.9) million of net loss to the Company for the period from January 1, 2019 through June 2, 2019 and contributed approximately $(2.7) million and $(3.5) million of net loss to the Company for the years ended December 31, 2018 and 2017, respectively. On June 28, 2019, the Company completed the sale of its 164 Lexington Road property located in Billerica, Massachusetts for a gross sale price of $4.0 million . Net cash proceeds totaled approximately $3.8 million , resulting in a gain on sale of real estate totaling approximately $2.5 million for Boston Properties, Inc. and approximately $2.6 million for Boston Properties Limited Partnership. 164 Lexington Road is an approximately 64,000 net rentable square foot Class A office property. 164 Lexington Road contributed approximately $(0.1) million of net loss to the Company for the period from January 1, 2019 through June 27, 2019 and contributed approximately $(0.2) million and $(0.2) million of net loss to the Company for the years ended December 31, 2018 and 2017, respectively. On September 20, 2019, the Company entered into a joint venture with Canada Pension Plan Investment Board (“CPPIB”) to develop Platform 16 located in San Jose, California. Platform 16 consists of a 65 -year ground lease for land totaling approximately 5.6 acres that will support the development of approximately 1.1 million square feet of commercial office space. During 2018, the Company entered into the ground lease, which provides for the right to purchase all of the land during a 12-month period commencing February 1, 2020 at a purchase price of approximately $134.8 million . The Company contributed the ground lease interest and improvements totaling approximately $28.2 million for its initial 55% interest in the joint venture. CPPIB contributed cash totaling approximately $23.1 million for its initial 45% interest in the joint venture. Upon the CPPIB contribution, the Company ceased accounting for the joint venture entity on a consolidated basis and is accounting for the joint venture entity on an unconsolidated basis using the equity method of accounting, as it has reduced its ownership interest and no longer has a controlling financial or operating interest in the joint venture entity (See Note 5 ). The Company did not recognize a gain on the retained or sold interest in the real estate contributed to the joint venture, as the fair value of the real estate approximated its carrying value. On December 20, 2019, the Company completed the sale of the remaining parcel of land at its Washingtonian North property located in Gaithersburg, Maryland for a gross sale price of approximately $7.8 million . Net cash proceeds totaled approximately $7.3 million , resulting in a loss on sale of real estate totaling approximately $0.1 million . The Company recognized an impairment loss totaling approximately $1.8 million

Deferred Charges

Deferred Charges	12 Months Ended
Deferred Charges	Dec. 31, 2019
Deferred Charges [Abstract]
Deferred Charges	4. Deferred Charges Deferred charges consisted of the following at December 31, 2019 and December 31, 2018 (in thousands): 2019 2018 Leasing costs, including lease related intangibles $ 1,155,958 $ 1,191,297 Financing costs 12,728 12,796 1,168,686 1,204,093 Less: Accumulated amortization (479,473 ) (525,369 ) $ 689,213 $ 678,724 The following table summarizes the scheduled amortization of the Company’s acquired in-place lease intangibles for each of the five succeeding years (in thousands). Acquired In-Place Lease Intangibles 2020 $ 17,536 2021 11,001 2022 5,918 2023 4,286 2024 2,510

Investments in Unconsolidated J

Investments in Unconsolidated Joint Ventures	12 Months Ended
Investments in Unconsolidated Joint Ventures	Dec. 31, 2019
Investments In Unconsolidated Joint Ventures [Abstract]
Investments In Unconsolidated Joint Ventures	5. Investments in Unconsolidated Joint Ventures The investments in unconsolidated joint ventures consist of the following at December 31, 2019 and 2018 : Carrying Value of Investment (1) Entity Properties Nominal % Ownership December 31, December 31, (in thousands) Square 407 Limited Partnership Market Square North 50.0 % $ (4,872 ) $ (6,424 ) BP/CRF Metropolitan Square, LLC Metropolitan Square 20.0 % 9,134 2,644 901 New York, LLC 901 New York Avenue 25.0 % (2) (12,113 ) (13,640 ) WP Project Developer LLC Wisconsin Place Land and Infrastructure 33.3 % (3) 36,789 38,214 Annapolis Junction NFM LLC Annapolis Junction 50.0 % (4) 25,391 25,268 540 Madison Venture LLC 540 Madison Avenue 60.0 % (5) 2,953 66,391 500 North Capitol Venture LLC 500 North Capitol Street, NW 30.0 % (5,439 ) (5,026 ) 501 K Street LLC 1001 6th Street 50.0 % (6) 42,496 42,557 Podium Developer LLC The Hub on Causeway - Podium 50.0 % 49,466 69,302 Residential Tower Developer LLC Hub50House 50.0 % 55,092 47,505 Hotel Tower Developer LLC The Hub on Causeway - Hotel Air Rights 50.0 % 9,883 3,022 Office Tower Developer LLC 100 Causeway Street 50.0 % 56,606 23,804 1265 Main Office JV LLC 1265 Main Street 50.0 % 3,780 3,918 BNY Tower Holdings LLC Dock 72 50.0 % 94,804 82,520 BNYTA Amenity Operator LLC Dock 72 50.0 % — N/A CA-Colorado Center Limited Partnership Colorado Center 50.0 % 252,069 253,495 7750 Wisconsin Avenue LLC 7750 Wisconsin Avenue 50.0 % 56,247 69,724 BP-M 3HB Venture LLC 3 Hudson Boulevard 25.0 % 67,499 46,993 SMBP Venture LP Santa Monica Business Park 55.0 % 163,937 180,952 Platform 16 Holdings LP Platform 16 55.0 % (7) 29,501 N/A $ 933,223 $ 931,219 _______________ (1) Investments with deficit balances aggregating approximately $22.4 million and $25.1 million at December 31, 2019 and 2018 , respectively, are included within Other Liabilities in the Company’s Consolidated Balance Sheets. (2) The Company’s economic ownership has increased based on the achievement of certain return thresholds. (3) The Company’s wholly-owned subsidiary that owns Wisconsin Place Office also owns a 33.3% interest in the joint venture entity that owns the land, parking garage and infrastructure of the project. (4) The joint venture owns three in-service buildings and two undeveloped land parcels. (5) T he property was sold on June 27, 2019. As of December 31, 2019, the investment is comprised of undistributed cash. See note below for additional details. (6) Under the joint venture agreement for this land parcel, the partner will be entitled to up to two additional payments from the venture based on increases in total entitled square footage of the project above 520,000 square feet and achieving certain project returns at stabilization. (7) This entity is a VIE (See Note 1 ). Certain of the Company’s unconsolidated joint venture agreements include provisions whereby, at certain specified times, each partner has the right to initiate a purchase or sale of its interest in the joint ventures. With limited exceptions under these provisions, the Company is not compelled to purchase the interest of its outside joint venture partners. Under certain of the Company’s joint venture agreements, if certain return thresholds are achieved the partners or the Company will be entitled to an additional promoted interest or payments. The combined summarized balance sheets of the Company’s unconsolidated joint ventures are as follows: December 31, December 31, (in thousands) ASSETS Real estate and development in process, net (1) $ 3,904,400 $ 3,545,906 Other assets 502,706 543,512 Total assets $ 4,407,106 $ 4,089,418 LIABILITIES AND MEMBERS’/PARTNERS’ EQUITY Mortgage and notes payable, net $ 2,218,853 $ 2,017,609 Other liabilities (2) 749,675 582,006 Members’/Partners’ equity 1,438,578 1,489,803 Total liabilities and members’/partners’ equity $ 4,407,106 $ 4,089,418 Company’s share of equity $ 591,905 $ 622,498 Basis differentials (3) 341,318 308,721 Carrying value of the Company’s investments in unconsolidated joint ventures (4) $ 933,223 $ 931,219 _______________ (1) At December 31, 2019, this amount includes right of use assets - finance leases and right of use assets - operating leases totaling approximately $383.9 million and $12.1 million , respectively. (2) At December 31, 2019, this amount includes lease liabilities - finance leases and lease liabilities - operating leases totaling approximately $510.8 million and $17.3 million , respectively. (3) This amount represents the aggregate difference between the Company’s historical cost basis and the basis reflected at the joint venture level, which is typically amortized over the life of the related assets and liabilities. Basis differentials result from impairments of investments, acquisitions through joint ventures with no change in control and upon the transfer of assets that were previously owned by the Company into a joint venture. In addition, certain acquisition, transaction and other costs may not be reflected in the net assets at the joint venture level. At December 31, 2019 and 2018 , there was an aggregate basis differential of approximately $311.3 million and $316.7 million , respectively, between the carrying value of the Company’s investment in the joint venture that owns Colorado Center and the joint venture’s basis in the assets and liabilities, which differential (excluding land) shall be amortized over the remaining lives of the related assets and liabilities. (4) Investments with deficit balances aggregating approximately $22.4 million and $25.1 million at December 31, 2019 and 2018 , respectively, have been reflected within Other Liabilities in the Company’s Consolidated Balance Sheets. The combined summarized statements of operations of the Company’s unconsolidated joint ventures are as follows: For the year ended December 31, 2019 2018 2017 (in thousands) Total revenue (1) $ 322,817 $ 271,951 $ 222,517 Expenses Operating 122,992 106,610 90,542 Transaction costs 1,000 — — Depreciation and amortization (2) 102,296 103,079 57,079 Total expenses 226,288 209,689 147,621 Other income (expense) Gains on sales of real estate (3) 32,706 16,951 — Interest expense (84,409 ) (71,308 ) (46,371 ) Net income $ 44,826 $ 7,905 $ 28,525 Company’s share of net income $ 24,423 $ 8,084 $ 18,439 Basis differential (3)(4) 22,169 (5,862 ) (7,207 ) Income from unconsolidated joint ventures $ 46,592 $ 2,222 $ 11,232 _______________ (1) Includes straight-line rent adjustments of approximately $32.4 million , $15.9 million and $21.7 million for the years ended December 31, 2019 , 2018 and 2017 , respectively. (2) During the year ended December 31, 2018, the joint venture that owns Metropolitan Square in Washington, DC, commenced a renovation project and recorded accelerated depreciation expense of approximately $22.4 million related to the remaining book value of the assets to be replaced. The Company’s share of the accelerated depreciation expense totaled approximately $4.5 million . (3) For the year ended December 31, 2019, represents the gain on sale of 540 Madison Avenue recognized by the joint venture, as described below. During 2008, the Company recognized an other-than-temporary impairment loss on its investment in the unconsolidated joint venture resulting in a basis differential between the carrying value of the Company’s investment in the joint venture and the joint venture’s basis in the assets and liabilities of the property. As a result of the historical basis difference, the Company recognized a gain on sale of real estate totaling approximately $47.2 million for the year ended December 31, 2019, which consists of its share of the gain on sale reported by the joint venture as well as an adjustment for the basis differential. The gain on sale of real estate is included in Income from Unconsolidated Joint Ventures in the Company’s Consolidated Statements of Operations. (4) Includes straight-line rent adjustments of approximately $2.1 million , $2.4 million and $1.9 million for the years ended December 31, 2019, 2018 and 2017, respectively. Also includes net above-/below-market rent adjustments of approximately $1.7 million , $1.6 million and $2.9 million for the years ended December 31, 2019, 2018 and 2017, respectively. On January 24, 2019, a joint venture in which the Company has a 50% interest extended the loan collateralized by its Annapolis Junction Building Six property. At the time of the extension, the outstanding balance of the loan totaled approximately $13.0 million and was scheduled to mature on November 17, 2019, with a one -year extension option, subject to certain conditions. The extended loan has a total commitment amount of approximately $14.3 million , bears interest at a variable rate equal to LIBOR plus 2.00% per annum and matures on November 17, 2020. Annapolis Junction Building Six is a Class A office property with approximately 119,000 net rentable square feet located in Annapolis, Maryland. On April 26, 2019, a joint venture in which the Company has a 50% interest obtained construction financing with a total commitment of $255.0 million collateralized by its 7750 Wisconsin Avenue development project located in Bethesda, Maryland. The construction financing bears interest at a variable rate equal to LIBOR plus 1.25% per annum and matures on April 26, 2023, with two , one -year extension options, subject to certain conditions. As of December 31, 2019, approximately $64.5 million has been drawn under the loan. 7750 Wisconsin Avenue is a 734,000 net rentable square foot build-to-suit Class A office project and below-grade parking garage. On May 28, 2019, joint ventures in which the Company has a 50% interest and that own The Hub on Causeway - Podium and 100 Causeway Street development projects entered into an infrastructure development assistance agreement (the “IDAA”) with the Commonwealth of Massachusetts and the City of Boston. Per the IDAA, The Hub on Causeway - Podium development project would be reimbursed for certain costs of public infrastructure improvements using the proceeds of up to $30.0 million in aggregate principal amount of municipal bonds issued by the Commonwealth of Massachusetts. On September 16, 2019, the joint venture received the full reimbursement of costs for the public infrastructure improvements totaling approximately $28.8 million , which has been reflected as a reduction to the carrying value of the real estate of The Hub on Causeway - Podium property. The construction loan agreement for The Hub on Causeway - Podium was modified to require the joint venture to pay down the construction loan principal balance using the proceeds received from the reimbursement of costs of the public infrastructure improvements and on September 16, 2019, the joint venture that owns The Hub on Causeway - Podium development project paid down the construction loan principal balance in the amount of approximately $28.8 million . On November 22, 2019, the joint venture that owns The Hub on Causeway - Podium development project completed and fully placed in-service The Hub on Causeway - Podium development project, an approximately 382,000 net rentable square foot project containing retail and office space located in Boston, Massachusetts. On June 27, 2019, a joint venture in which the Company has a 60% interest completed the sale of 540 Madison Avenue in New York City for a gross sale price of approximately $310.3 million , including the assumption by the buyer of the mortgage loan collateralized by the property totaling $120.0 million . The mortgage loan bore interest at a variable rate equal to LIBOR plus 1.10% per annum and was scheduled to mature on June 5, 2023. Net cash proceeds totaled approximately $178.7 million , of which the Company’s share was approximately $107.1 million , after the payment of transaction costs. During 2008, the Company recognized an other-than-temporary impairment loss on its investment in the unconsolidated joint venture. As a result, the Company recognized a gain on sale of real estate totaling approximately $47.2 million , which is included in Income from Unconsolidated Joint Ventures in the accompanying Consolidated Statements of Operations. 540 Madison Avenue is an approximately 284,000 net rentable square foot Class A office property. On September 5, 2019, a joint venture in which the Company has a 50% interest obtained construction financing with a total commitment of $400.0 million collateralized by its 100 Causeway Street development project located in Boston, Massachusetts. The construction financing bears interest at a variable rate equal to LIBOR plus 1.50% per annum (LIBOR plus 1.375% per annum upon stabilization, as defined in the loan agreement) and matures on September 5, 2023, with two , one -year extension options, subject to certain conditions. As of December 31, 2019, approximately $81.1 million has been drawn under the loan. 100 Causeway Street is an approximately 632,000 net rentable square foot Class A office project. On September 20, 2019, the Company entered into a joint venture with CPPIB to develop Platform 16 located in San Jose, California. Platform 16 consists of a 65 -year ground lease for land totaling approximately 5.6 acres that will support the development of approximately 1.1 million square feet of commercial office space (See Note 19). The Company contributed the ground lease interest and improvements totaling approximately $28.2 million for its initial 55% interest in the joint venture (See Note 3 ). CPPIB contributed cash totaling approximately $23.1 million for its initial 45% interest in the joint venture. The Company will provide customary development, property management and leasing services to the joint venture. On October 1, 2019, a joint venture in which the Company has a 50% interest partially placed in-service Dock 72, a Class A office project with approximately 670,000 net rentable square feet located in Brooklyn, New York. On October 1, 2019, a joint venture in which the Company has a 50% interest partially placed in-service Hub50House, an approximately 320,000 square foot project comprised of 440 residential units located in Boston, Massachusetts. On December 6, 2019, a joint venture in which the Company has a 50% interest extended the mortgage loan collateralized by Annapolis Junction Building Seven and Building Eight. At the time of the extension, the outstanding balance of the loan totaled approximately $34.8 million , bore interest at a variable rate equal to LIBOR plus 2.35% per annum and was scheduled to mature on December 7, 2019, with three , one -year extension options, subject to certain conditions. The extended loan matures on March 6, 2020. Annapolis Junction Building Seven and Building Eight are Class A office properties with approximately 127,000 and 126,000 net rentable square feet, respectively, located in Annapolis, Maryland.

Mortgage Notes Payable, Net

Mortgage Notes Payable, Net	12 Months Ended
Mortgage Notes Payable, Net	Dec. 31, 2019
Loans Payable [Abstract]
Mortgage Notes Payable, Net	6. Mortgage Notes Payable, Net The Company had outstanding mortgage notes payable totaling approximately $2.9 billion and $3.0 billion as of December 31, 2019 and 2018 , respectively, each collateralized by one or more buildings and related land included in real estate assets. The mortgage notes payable are generally due in monthly installments and mature at various dates through June 9, 2027. Fixed rate mortgage notes payable totaled approximately $2.9 billion and $3.0 billion at December 31, 2019 and 2018 , respectively, with contractual interest rates ranging from 3.43% to 6.94% per annum at December 31, 2019 and 3.43% to 7.69% at December 31, 2018 (with a weighted-average interest rate of 3.73% and 3.77% per annum at December 31, 2019 and 2018 , respectively). There were no variable rate mortgage loans at December 31, 2019 and 2018 . On December 19, 2019, the Company used available cash to repay the bond financing collateralized by its New Dominion Technology Park, Building One property totaling approximately $26.5 million . The bond financing bore interest at a weighted-average fixed rate of approximately 7.69% per annum and was scheduled to mature on January 15, 2021. The Company recognized a loss from early extinguishment of debt totaling approximately $1.5 million , which amount included the payment of a prepayment penalty totaling approximately $1.4 million . New Dominion Technology Park, Building One is an approximately 235,000 net rentable square foot Class A office property located in Herndon, Virginia (See Note 19 ). No mortgage loans at December 31, 2019 and December 31, 2018 had been accounted for at fair value. Prior to December 31, 2017, the Company had mortgage loans that were accounted for at fair value and the impact of recording them at fair value resulted in a decrease to interest expense of approximately $19.6 million for the year ended December 31, 2017 . Contractual aggregate principal payments of mortgage notes payable at December 31, 2019 are as follows (in thousands): Principal Payments 2020 $ 17,168 2021 17,276 2022 614,710 2023 — 2024 — Thereafter 2,300,000 Total aggregate principal payments 2,949,154 Deferred financing costs, net (26,746 ) Total carrying value of mortgage notes payable, net $ 2,922,408

Unsecured Senior Notes

Unsecured Senior Notes	12 Months Ended
Unsecured Senior Notes	Dec. 31, 2019
Debt Disclosure [Abstract]
Unsecured Senior Notes	7. Unsecured Senior Notes The following summarizes the unsecured senior notes outstanding as of December 31, 2019 (dollars in thousands): Coupon/ Stated Rate Effective Rate(1) Principal Amount Maturity Date(2) 10 Year Unsecured Senior Notes 4.125 % 4.289 % $ 850,000 May 15, 2021 11 Year Unsecured Senior Notes 3.850 % 3.954 % 1,000,000 February 1, 2023 10.5 Year Unsecured Senior Notes 3.125 % 3.279 % 500,000 September 1, 2023 10.5 Year Unsecured Senior Notes 3.800 % 3.916 % 700,000 February 1, 2024 7 Year Unsecured Senior Notes 3.200 % 3.350 % 850,000 January 15, 2025 10 Year Unsecured Senior Notes 3.650 % 3.766 % 1,000,000 February 1, 2026 10 Year Unsecured Senior Notes 2.750 % 3.495 % 1,000,000 October 1, 2026 10 Year Unsecured Senior Notes 4.500 % 4.628 % 1,000,000 December 1, 2028 10 Year Unsecured Senior Notes 3.400 % 3.505 % 850,000 June 21, 2029 10.5 Year Unsecured Senior Notes 2.900 % 2.984 % 700,000 March 15, 2030 Total principal 8,450,000 Net unamortized discount (17,451 ) Deferred financing costs, net (42,090 ) Total $ 8,390,459 _______________ (1) Yield on issuance date including the effects of discounts on the notes, settlements of interest rate contracts and the amortization of financing costs. (2) No principal amounts are due prior to maturity. On June 21, 2019, Boston Properties Limited Partnership completed a public offering of $850.0 million in aggregate principal amount of its 3.400% unsecured senior notes due 2029. The notes were priced at 99.815% of the principal amount to yield an effective rate (including financing fees) of approximately 3.505% per annum to maturity. The notes will mature on June 21, 2029, unless earlier redeemed. The aggregate net proceeds from the offering were approximately $841.4 million after deducting underwriting discounts and transaction expenses. On September 3, 2019, Boston Properties Limited Partnership completed a public offering of $700.0 million in aggregate principal amount of its 2.900% unsecured senior notes due 2030. The notes were priced at 99.954% of the principal amount to yield an effective rate (including financing fees) of approximately 2.984% per annum to maturity. The notes will mature on March 15, 2030, unless earlier redeemed. The aggregate net proceeds from the offering were approximately $693.8 million after deducting underwriting discounts and transaction expenses. On September 18, 2019, Boston Properties Limited Partnership completed the redemption of $700.0 million in aggregate principal amount of its 5.625% senior notes due November 15, 2020. The redemption price was approximately $740.7 million . The redemption price included approximately $13.5 million of accrued and unpaid interest to, but not including, the redemption date. Excluding the accrued and unpaid interest, the redemption price was approximately 103.90% of the principal amount being redeemed. The Company recognized a loss from early extinguishment of debt totaling approximately $28.0 million , which amount included the payment of the redemption premium totaling approximately $27.3 million . The indenture relating to the unsecured senior notes contains certain financial restrictions and requirements, including (1) a leverage ratio not to exceed 60%, (2) a secured debt leverage ratio not to exceed 50%, (3) an interest coverage ratio of greater than 1.50, and (4) an unencumbered asset value of not less than 150% of unsecured debt. At December 31, 2019, Boston Properties Limited Partnership was in compliance with each of these financial restrictions and requirements.

Unsecured Credit Facility

Unsecured Credit Facility	12 Months Ended
Unsecured Credit Facility	Dec. 31, 2019
Line of Credit Facility [Abstract]
Unsecured Credit Facility [Text Block]	8. Unsecured Credit Facility On April 24, 2017, Boston Properties Limited Partnership amended and restated its unsecured revolving credit agreement (as amended and restated, the “2017 Credit Facility”). Among other things, the 2017 Credit Facility (1) increased the total commitment of the revolving line of credit (the “Revolving Facility”) from $1.0 billion to $1.5 billion , (2) extended the maturity date from July 26, 2018 to April 24, 2022, (3) reduced the per annum variable interest rates, and (4) added a $500.0 million delayed draw term loan facility (the “Delayed Draw Facility”) that permitted Boston Properties Limited Partnership to draw upon it provided that amounts drawn and subsequently repaid may not be borrowed again. In addition, Boston Properties Limited Partnership may increase the total commitment under the 2017 Credit Facility by up to $500.0 million through increases in the Revolving Facility or the Delayed Draw Facility, or both, subject to syndication of the increase and other conditions. On April 24, 2018, Boston Properties Limited Partnership exercised its option to draw $500.0 million on its Delayed Draw Facility. The Delayed Draw Facility bears interest at a variable rate equal to LIBOR plus 0.90% per annum based on Boston Properties Limited Partnership’s current credit rating and matures on April 24, 2022. At Boston Properties Limited Partnership’s option, loans under the Revolving Facility and Delayed Draw Facility will bear interest at a rate per annum equal to (1) (a) in the case of loans denominated in Dollars, Euro or Sterling, LIBOR, and (b) in the case of loans denominated in Canadian Dollars, CDOR, in each case, plus a margin ranging from 77.5 to 155 basis points for the Revolving Commitment and 85 to 175 basis points for the Delayed Draw Facility, based on Boston Properties Limited Partnership’s credit rating or (2) an alternate base rate equal to the greatest of (x) the Administrative Agent’s prime rate, (y) the Federal Funds rate plus 0.50% or (z) LIBOR for a one-month period plus 1.00%, in each case, plus a margin ranging from 0 to 55 basis points for the Revolving Facility and 0 to 75 basis points for the Delayed Draw Facility, based on Boston Properties Limited Partnership’s credit rating. The 2017 Credit Facility also contains a competitive bid option for up to 65% of the Revolving Facility that allows banks that are part of the lender consortium to bid to make loan advances to Boston Properties Limited Partnership at a reduced interest rate. In addition, Boston Properties Limited Partnership is obligated to pay (1) in quarterly installments a facility fee on the total commitment under the Revolving Facility at a rate per annum ranging from 0.10% to 0.30% based on Boston Properties Limited Partnership’s credit rating, (2) an annual fee on the undrawn amount of each letter of credit equal to the LIBOR margin on the Revolving Facility and (3) a fee on the unused commitments under the Delayed Draw Facility equal to 0.15% per annum. Based on Boston Properties Limited Partnership’s December 31, 2019 credit rating, (1) the applicable Eurocurrency margins for the Revolving Facility and Delayed Draw Facility are 0.825% and 0.90% , respectively, (2) the alternate base rate margin is zero basis points for each of the Revolving Facility and Delayed Draw Facility and (3) the facility fee on the Revolving Facility commitment is 0.125% per annum. At December 31, 2019 and 2018, Boston Properties Limited Partnership had $500.0 million of borrowings outstanding under its Delayed Draw Facility and no amounts outstanding under its Revolving Facility. The 2017 Credit Facility contains customary representations and warranties, affirmative and negative covenants and events of default provisions, including failure to pay indebtedness, breaches of covenants, and bankruptcy and other insolvency events, which could result in the acceleration of all amounts and cancellation of all commitments outstanding under the Credit Agreement. Among other covenants, the 2017 Credit Facility requires that Boston Properties Limited Partnership maintain on an ongoing basis: (1) a leverage ratio not to exceed 60%, however, the leverage ratio may increase to no greater than 65% provided that it is reduced back to 60% within one year, (2) a secured debt leverage ratio not to exceed 55%, (3) a fixed charge coverage ratio of at least 1.40, (4) an unsecured debt leverage ratio not to exceed 60%, however, the unsecured debt leverage ratio may increase to no greater than 65% provided that it is reduced to 60% within one year, (5) an unsecured debt interest coverage ratio of at least 1.75 and (6) limitations on permitted investments. At December 31, 2019, Boston Properties Limited Partnership was in compliance with each of these financial and other covenant requirements.

Commitments And Contingencies

Commitments And Contingencies	12 Months Ended
Commitments And Contingencies	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments And Contingencies	9. Commitments and Contingencies General In the normal course of business, the Company guarantees its performance of services or indemnifies third parties against its negligence. In addition, in the normal course of business, the Company guarantees to certain tenants the obligations of its subsidiaries for the payment of tenant improvement allowances and brokerage commissions in connection with their leases and limited costs arising from delays in delivery of their premises. The Company has letter of credit and performance obligations related to lender and development requirements that total approximately $21.0 million . Certain of the Company’s joint venture agreements include provisions whereby, at certain specified times, each partner has the right to initiate a purchase or sale of its interest in the joint ventures. With limited exception, under these provisions, the Company is not compelled to purchase the interest of its outside joint venture partners. From time to time, under certain of the Company’s joint venture agreements, if certain return thresholds are achieved, either the Company or its partners may be entitled to an additional promoted interest or payments. See also Note 10 . From time to time, the Company (or ventures in which the Company has an ownership interest) has agreed, and may in the future agree, to (1) guarantee portions of the principal, interest and other amounts in connection with their borrowings, (2) provide customary environmental indemnifications and nonrecourse carve-outs (e.g., guarantees against fraud, misrepresentation and bankruptcy) in connection with their borrowings and (3) provide guarantees to lenders, tenants and other third parties for the completion of development projects. The Company has agreements with its outside partners whereby the partners agree to reimburse the joint venture for their share of any payments made under the guarantee. In some cases, the Company earns a fee from the applicable joint venture for providing the guarantee. In connection with the refinancing of 767 Fifth Avenue’s (the General Motors Building) secured loan by the Company’s consolidated joint venture entity, 767 Venture, LLC, the Company guaranteed the consolidated entity’s obligation to fund various reserves for tenant improvement costs and allowances, leasing commissions and free rent obligations in lieu of cash deposits. As of December 31, 2019 , the maximum funding obligation under the guarantee was approximately $70.2 million . The Company earns a fee from the joint venture for providing the guarantee and has an agreement with the outside partners to reimburse the joint venture for their share of any payments made under the guarantee. As of December 31, 2019 , no amounts related to the guarantee are recorded as liabilities in the Company’s consolidated financial statements. Pursuant to the lease agreement with Marriott, the Company has guaranteed the completion of the office building and parking garage on behalf of its 7750 Wisconsin Avenue joint venture and has also agreed to provide any financing guaranty that may be required with respect to third-party construction financing. The Company earns fees from the joint venture for providing the guarantees and any amounts the Company pays under the guarantee(s) will be deemed to be capital contributions by the Company to the joint venture. The Company has also agreed to fund construction costs through capital contributions to the joint venture in the event of unavailability or insufficiency of third-party construction financing. In addition, the Company has guaranteed to Marriott, as hotel manager, the completion of a hotel being developed by an affiliate of The Bernstein Companies (the Company’s partner in the 7750 Wisconsin Avenue joint venture) adjacent to the office property, for which the Company earns a fee from the affiliate of The Bernstein Companies. In addition, the Company entered into agreements with affiliates of The Bernstein Companies whereby the Company could be required to act as a mezzanine and/or mortgage lender and finance the construction of the hotel property. To secure such financing arrangements, affiliates of The Bernstein Companies are required to provide certain security, which varies depending on the specific loan, by pledges of their equity interest in the office property, a fee mortgage on the hotel property, or both. As of December 31, 2019 , no amounts related to the contingent aspect of any of the guarantees are recorded as liabilities in the Company’s consolidated financial statements. In connection with the sale and development of the Company’s 6595 Springfield Center Drive development project, the Company has guaranteed the completion of the project and the payment of certain cost overruns in accordance with the development management agreement with the buyer. Although the project has been sold and the lease with the Federal Government tenant has been assigned to the buyer, pursuant to the terms of the Federal Government lease, the Federal Government tenant is not obligated to release the prior owner/landlord from such landlord’s obligations under the lease until completion of the construction. As a result, the entity which previously owned the land remains liable to the Federal Government tenant for the completion of the construction obligations under the lease. The buyer is obligated to fund the balance of the costs to meet such construction obligations, subject to the Company’s obligation to fund cost overruns (if any), as noted above. An affiliate of the buyer has provided a guaranty of the obligations of the buyer to fund such construction costs and the buyer has agreed to use commercially reasonable efforts to require the construction lender to provide certain remedies to the Company in the event the buyer does not fund such construction obligations. As of December 31, 2019 , no amounts related to the contingent aspect of the guarantee are recorded as a liability in the Company’s consolidated financial statements (See Note 3 ). In connection with the redevelopment of the Company’s 325 Main Street property located in Cambridge, Massachusetts, the Company is required, pursuant to the local zoning ordinance, to commence construction of a residential building of at least 200,000 square feet with 25% of the project designated as income-restricted (with a minimum of 20% of the square footage devoted to home ownership units) prior to the occupancy of the 325 Main Street property. 325 Main Street consisted of an approximately 115,000 net rentable square foot Class A office property that was demolished and is being developed into an approximately 420,000 net rentable square foot Class A office property, including approximately 41,000 net rentable square feet of retail space (See Note 3 ). In 2009, the Company filed a general unsecured creditor’s claim against Lehman Brothers, Inc. for approximately $45.3 million related to its rejection of a lease at 399 Park Avenue in New York City. On January 10, 2014, the trustee for the liquidation of the business of Lehman Brothers allowed the Company’s claim in the amount of approximately $45.2 million . During the years 2014 through 2018, the Company received distributions aggregating approximately $18.0 million , leaving a remaining claim of approximately $27.2 million . The Company will continue to evaluate whether to attempt to sell the remaining claim or wait until the trustee distributes proceeds from the Lehman Brothers estate. Given the inherent uncertainties in bankruptcy proceedings, there can be no assurance as to the timing or amount of additional proceeds, if any, that the Company may ultimately realize on the remaining claim, whether by sale to a third party or by one or more distributions from the trustee. Accordingly, the Company has not recorded any estimated recoveries associated with this gain contingency within its Consolidated Financial Statements at December 31, 2019 . Concentrations of Credit Risk Management of the Company performs ongoing credit evaluations of tenants and may require tenants to provide some form of credit support such as corporate guarantees and/or other financial guarantees. Although the Company’s properties are geographically diverse and the tenants operate in a variety of industries, to the extent the Company has a significant concentration of rental revenue from any single tenant, the inability of that tenant to make its lease payments could have an adverse effect on the Company. Insurance The Company’s property insurance program per occurrence limits are $1.0 billion for its portfolio insurance program, including coverage for acts of terrorism other than nuclear, biological, chemical or radiological terrorism (“Terrorism Coverage”). The Company also carries $250 million of Terrorism Coverage for 601 Lexington Avenue, New York, New York (“601 Lexington Avenue”) in excess of the $1.0 billion of coverage in the Company’s property insurance program. Certain properties, including the General Motors Building located at 767 Fifth Avenue in New York, New York (“767 Fifth Avenue”), are currently insured in separate insurance programs. The property insurance program per occurrence limits for 767 Fifth Avenue are $1.625 billion , including Terrorism Coverage. The Company also currently carries nuclear, biological, chemical and radiological terrorism insurance coverage for acts of terrorism certified under the Federal Terrorism Risk Insurance Act (as amended, “TRIA”) (“NBCR Coverage”), which is provided by IXP as a direct insurer, for the properties in the Company’s portfolio, including 767 Fifth Avenue, but excluding certain other properties owned in joint ventures with third parties or which the Company manages. The per occurrence limit for NBCR Coverage is $1.0 billion . Under TRIA, after the payment of the required deductible and coinsurance, the NBCR Coverage provided by IXP is backstopped by the Federal Government if the aggregate industry insured losses resulting from a certified act of terrorism exceed a “program trigger.” In 2019, the program trigger was $180 million and the coinsurance was 19% , however, both will increase in subsequent years pursuant to TRIA. If the Federal Government pays out for a loss under TRIA, it is mandatory that the Federal Government recoup the full amount of the loss from insurers offering TRIA coverage after the payment of the loss pursuant to a formula in TRIA. The Company may elect to terminate the NBCR Coverage if the Federal Government seeks recoupment for losses paid under TRIA, if TRIA is not extended after its expiration on December 31, 2027, if there is a change in its portfolio or for any other reason. The Company intends to continue to monitor the scope, nature and cost of available terrorism insurance. The Company also currently carries earthquake insurance on its properties located in areas known to be subject to earthquakes. In addition, this insurance is subject to a deductible in the amount of 3% of the value of the affected property. Specifically, the Company currently carries earthquake insurance which covers its San Francisco and Los Angeles regions with a $240 million per occurrence limit, and a $240 million annual aggregate limit, $20 million of which is provided by IXP, as a direct insurer. The amount of the Company’s earthquake insurance coverage may not be sufficient to cover losses from earthquakes. In addition, the amount of earthquake coverage could impact the Company’s ability to finance properties subject to earthquake risk. The Company may discontinue earthquake insurance or change the structure of its earthquake insurance program on some or all of its properties in the future if the premiums exceed the Company’s estimation of the value of the coverage. IXP, a captive insurance company which is a wholly-owned subsidiary of the Company, acts as a direct insurer with respect to a portion of the Company’s earthquake insurance coverage for its Greater San Francisco and Los Angeles properties and the Company’s NBCR Coverage. Insofar as the Company owns IXP, it is responsible for its liquidity and capital resources, and the accounts of IXP are part of the Company’s consolidated financial statements. In particular, if a loss occurs which is covered by the Company’s NBCR Coverage but is less than the applicable program trigger under TRIA, IXP would be responsible for the full amount of the loss without any backstop by the Federal Government. IXP would also be responsible for any recoupment charges by the Federal Government in the event losses are paid out and its insurance policy is maintained after the payout by the Federal Government. If the Company experiences a loss and IXP is required to pay under its insurance policy, the Company would ultimately record the loss to the extent of the required payment. Therefore, insurance coverage provided by IXP should not be considered as the equivalent of third-party insurance, but rather as a modified form of self-insurance. In addition, Boston Properties Limited Partnership has issued a guarantee to cover liabilities of IXP in the amount of $20.0 million . The Company continues to monitor the state of the insurance market in general, and the scope and costs of coverage for acts of terrorism and California earthquake risk in particular, but the Company cannot anticipate what coverage will be available on commercially reasonable terms in future policy years. There are other types of losses, such as from wars, for which the Company cannot obtain insurance at all or at a reasonable cost. With respect to such losses and losses from acts of terrorism, earthquakes or other catastrophic events, if the Company experiences a loss that is uninsured or that exceeds policy limits, the Company could lose the capital invested in the damaged properties, as well as the anticipated future revenues from those properties. Depending on the specific circumstances of each affected property, it is possible that the Company could be liable for mortgage indebtedness or other obligations related to the property. Any such loss could materially and adversely affect the Company’s business and financial condition and results of operations. Legal Matters The Company is subject to various legal proceedings and claims that arise in the ordinary course of business. These matters are generally covered by insurance. Management believes that the final outcome of such matters will not have a material adverse effect on the financial position, results of operations or liquidity of the Company. State and Local Tax Matters Because Boston Properties, Inc. is organized and qualifies as a REIT, it is generally not subject to federal income taxes, but is subject to certain state and local taxes. In the normal course of business, certain entities through which the Company owns real estate either have undergone, or are currently undergoing, tax audits. Although the Company believes that it has substantial arguments in favor of its positions in the ongoing audits, in some instances there is no controlling precedent or interpretive guidance on the specific point at issue. Collectively, tax deficiency notices received to date from the jurisdictions conducting the ongoing audits have not been material. However, there can be no assurance that future audits will not occur with increased frequency or that the ultimate result of such audits will not have a material adverse effect on the Company’s results of operations. Environmental Matters It is the Company’s policy to retain independent environmental consultants to conduct or update Phase I environmental assessments (which generally do not involve invasive techniques such as soil or ground water sampling) and asbestos surveys in connection with the Company’s acquisition of properties. These pre-purchase environmental assessments have not revealed environmental conditions that the Company believes will have a material adverse effect on its business, assets, financial condition, results of operations or liquidity, and the Company is not otherwise aware of environmental conditions with respect to its properties that the Company believes would have such a material adverse effect. However, from time to time environmental conditions at the Company’s properties have required and may in the future require environmental testing and/or regulatory filings, as well as remedial action. In February 1999, the Company (through a joint venture) acquired from Exxon Corporation a property in Massachusetts that was formerly used as a petroleum bulk storage and distribution facility and was known by the state regulatory authority to contain soil and groundwater contamination. The Company developed an office park on the property. The Company engaged a specially licensed environmental consultant to oversee the management of contaminated soil and groundwater that was disturbed in the course of construction. Under the property acquisition agreement, Exxon agreed to (1) bear the liability arising from releases or discharges of oil and hazardous substances which occurred at the site prior to the Company’s ownership, (2) continue monitoring and/or remediating such releases and discharges as necessary and appropriate to comply with applicable requirements, and (3) indemnify the Company for certain losses arising from preexisting site conditions. Any indemnity claim may be subject to various defenses, and there can be no assurance that the amounts paid under the indemnity, if any, would be sufficient to cover the liabilities arising from any such releases and discharges. Environmental investigations at some of the Company’s properties and certain properties owned by affiliates of the Company have identified groundwater contamination migrating from off-site source properties. In each case the Company engaged a licensed environmental consultant to perform the necessary investigations and assessments and to prepare any required submittals to the regulatory authorities. In each case the environmental consultant concluded that the properties qualify under the regulatory program or the regulatory practice for a status which eliminates certain deadlines for conducting response actions at a site. The Company also believes that these properties qualify for liability relief under certain statutory provisions or regulatory practices regarding upgradient releases. Although the Company believes that the current or former owners of the upgradient source properties may bear responsibility for some or all of the costs of addressing the identified groundwater contamination, the Company will take such further response actions (if any) that it deems necessary or advisable. Other than periodic testing at some of these properties, no such additional response actions are anticipated at this time. Some of the Company’s properties and certain properties owned by the Company’s affiliates are located in urban, industrial and other previously developed areas where fill or current or historical uses of the areas have caused site contamination. Accordingly, it is sometimes necessary to institute special soil and/or groundwater handling procedures and/or include particular building design features in connection with development, construction and other property operations in order to achieve regulatory closure and/or ensure that contaminated materials are addressed in an appropriate manner. In these situations, it is the Company’s practice to investigate the nature and extent of detected contamination, including potential issues associated with contaminant migration, assess potential liability risks and estimate the costs of required response actions and special handling procedures. The Company then uses this information as part of its decision-making process with respect to the acquisition, deal structure and/or development of the property. For example, the Company owns a parcel in Massachusetts which was formerly used as a quarry/asphalt batching facility. Pre-purchase testing indicated that the site contained relatively low levels of certain contaminants. The Company has developed an office park on this property. Prior to and during redevelopment activities, the Company engaged a specially licensed environmental consultant to monitor environmental conditions at the site and prepare necessary regulatory submittals based on the results of an environmental risk characterization. A submittal has been made to the regulatory authorities in order to achieve regulatory closure at this site. The submittal included an environmental deed restriction that mandates compliance with certain protective measures in a portion of the site where low levels of residual soil contamination have been left in place in accordance with applicable laws. The Company expects that resolution of the environmental matters relating to the above will not have a material impact on its business, assets, financial condition, results of operations or liquidity. However, the Company cannot assure you that it has identified all environmental liabilities at its properties, that all necessary remediation actions have been or will be undertaken at the Company’s properties or that the Company will be indemnified, in full or at all, in the event that such environmental liabilities arise.

Noncontrolling Interests

Noncontrolling Interests	12 Months Ended
Noncontrolling Interests	Dec. 31, 2019
Noncontrolling Interest [Abstract]
Noncontrolling Interests	10. Noncontrolling Interests Noncontrolling interests relate to the interests in Boston Properties Limited Partnership not owned by Boston Properties, Inc. and interests in consolidated property partnerships not wholly-owned by the Company. As of December 31, 2019 , the noncontrolling interests in Boston Properties Limited Partnership consisted of 16,764,466 OP Units, 1,143,215 LTIP Units (including 118,067 2012 OPP Units, 68,659 2013 MYLTIP Units, 23,100 2014 MYLTIP Units, 28,724 2015 MYLTIP Units and 98,706 2016 MYLTIP Units), 394,921 2017 MYLTIP Units, 336,195 2018 MYLTIP Units and 220,734 2019 MYLTIP Units held by parties other than Boston Properties, Inc. Noncontrolling Interest—Common Units During the years ended December 31, 2019 and 2018 , 144,481 and 83,136 OP Units, respectively, were presented by the holders for redemption (including 92,678 and 48,389 OP Units, respectively, issued upon conversion of LTIP Units, 2012 OPP Units, 2013 MYLTIP Units, 2014 MYLTIP Units and 2016 MYLTIP Units) and were redeemed by Boston Properties, Inc. in exchange for an equal number of shares of Common Stock. At December 31, 2019 , Boston Properties Limited Partnership had outstanding 394,921 2017 MYLTIP Units, 336,195 2018 MYLTIP Units and 220,734 2019 MYLTIP Units (See Note 16 ). Prior to the applicable measurement date (February 6, 2020 for 2017 MYLTIP Units (See Note 19 ), February 5, 2021 for 2018 MYLTIP Units and February 4, 2022 for 2019 MYLTIP Units), holders of MYLTIP Units will be entitled to receive per unit distributions equal to one-tenth ( 10% ) of the regular quarterly distributions payable on an OP Unit, but will not be entitled to receive any special distributions. After the measurement date, the number of MYLTIP Units, both vested and unvested, that MYLTIP award recipients have earned, if any, based on the establishment of a performance pool, will be entitled to receive distributions in an amount per unit equal to distributions, both regular and special, payable on an OP Unit. On February 3, 2017, the measurement period for the Company’s 2014 MYLTIP awards ended and, based on Boston Properties, Inc.’s relative TSR performance, the final awards were determined to be 27.7% of target or an aggregate of approximately $3.5 million (after giving effect to employee separations and the unallocated reserve). As a result, an aggregate of 447,386 2014 MYLTIP Units that had been previously granted were automatically forfeited. On February 4, 2018, the measurement period for the Company’s 2015 MYLTIP awards ended and, based on Boston Properties, Inc.’s relative TSR performance, the final awards were determined to be 22.0% of target or an aggregate of approximately $3.6 million (after giving effect to employee separations). As a result, an aggregate of 337,847 2015 MYLTIP Units that had been previously granted were automatically forfeited. On February 9, 2019, the measurement period for the Company’s 2016 MYLTIP awards ended and, based on Boston Properties, Inc.’s relative TSR performance, the final awards were determined to be 69.5% of target or an aggregate of approximately $13.6 million (after giving effect to employee separations). As a result, an aggregate of 364,980 2016 MYLTIP Units that had been previously granted were automatically forfeited. The following table presents Boston Properties Limited Partnership’s distributions on the OP Units and LTIP Units (including the 2012 OPP Units, 2013 MYLTIP Units, 2014 MYLTIP Units and 2015 MYLTIP Units and, after the February 9, 2019 measurement date, the 2016 MYLTIP Units) and its distributions on the 2016 MYLTIP Units (prior to the February 9, 2019 measurement date), 2017 MYLTIP Units, 2018 MYLTIP Units and 2019 MYLTIP Units (after the February 5, 2019 issuance date) that occurred during the year ended December 31, 2019: Record Date Payment Date Distributions per OP Unit and LTIP Unit Distributions per MYLTIP Unit December 31, 2019 January 30, 2020 $0.98 $0.098 September 30, 2019 October 31, 2019 $0.95 $0.095 June 28, 2019 July 31, 2019 $0.95 $0.095 March 29, 2019 April 30, 2019 $0.95 $0.095 December 31, 2018 January 30, 2019 $0.95 $0.095 The following table presents Boston Properties Limited Partnership’s distributions on the OP Units and LTIP Units (including the 2012 OPP Units, 2013 MYLTIP Units, 2014 MYLTIP Units and, after the February 4, 2018 measurement date, the 2015 MYLTIP Units) and its distributions on the 2015 MYLTIP Units (prior to the February 4, 2018 measurement date), 2016 MYLTIP Units, 2017 MYLTIP Units and 2018 MYLTIP Units (after the February 6, 2018 issuance date) that occurred during the year ended December 31, 2018: Record Date Payment Date Distributions per OP Unit and LTIP Unit Distributions per MYLTIP Unit December 31, 2018 January 30, 2019 $0.95 $0.095 September 28, 2018 October 31, 2018 $0.95 $0.095 June 29, 2018 July 31, 2018 $0.80 $0.080 March 29, 2018 April 30, 2018 $0.80 $0.080 December 29, 2017 January 30, 2018 $0.80 $0.080 A holder of an OP Unit may present the OP Unit to Boston Properties Limited Partnership for redemption at any time (subject to restrictions agreed upon at the time of issuance of OP Units to particular holders that may restrict such redemption right for a period of time, generally one year from issuance). Upon presentation of an OP Unit for redemption, Boston Properties Limited Partnership must redeem the OP Unit for cash equal to the then value of a share of common stock of Boston Properties, Inc. Boston Properties, Inc. may, in its sole discretion, elect to assume and satisfy the redemption obligation by paying either cash or issuing one share of Common Stock. The value of the OP Units (not owned by Boston Properties, Inc. and LTIP Units (including the 2012 OPP Units, 2013 MYLTIP Units, 2014 MYLTIP Units, 2015 MYLTIP Units and 2016 MYLTIP Units) assuming that all conditions had been met for the conversion thereof) had all of such units been redeemed at December 31, 2019 was approximately $2.5 billion based on the last reported price of a share of Common Stock on the New York Stock Exchange of $137.86 per share on December 31, 2019 . Noncontrolling Interests—Property Partnerships The noncontrolling interests in property partnerships consist of the outside equity interests in ventures that are consolidated with the financial results of the Company because the Company exercises control over the entities that own the properties. The equity interests in these ventures that are not owned by the Company, totaling approximately $1.7 billion at December 31, 2019 and 2018 , are included in Noncontrolling Interests—Property Partnerships on the accompanying Consolidated Balance Sheets. On May 12, 2016, the partners in the Company’s consolidated entity that owns Salesforce Tower located in San Francisco, California amended the venture agreement. Under the original venture agreement, if the Company elected to fund the construction of Salesforce Tower without a construction loan (or a construction loan of less than 50% of project costs) and the venture commenced vertical construction of the project, then the partner’s capital funding obligation would be limited, in which event the Company would fund up to 2.5% of the total project costs (i.e., 50% of the partner’s 5% interest in the venture) in the form of a loan to the partner. This loan would bear interest at the then prevailing market interest rates for construction loans. Under the amended venture agreement, the partners agreed to structure this funding by the Company as preferred equity rather than a loan. The preferred equity contributed by the Company earned a preferred return equal to LIBOR plus 3.00% per annum and was payable to the Company out of any distributions to which the partner would otherwise be entitled until such preferred equity and preferred return was repaid to the Company. The Company contributed an aggregate of approximately $22.6 million of preferred equity to the venture. Also, under the amended venture agreement, (a) from and after the stabilization date, the partner had the right to cause the Company to purchase all (but not less than all) of the partner’s interest and (b) from and after the third anniversary of the stabilization date, the Company had the right to acquire all (but not less than all) of the partner’s interest, in each case, at an agreed upon purchase price or appraised value. In addition, if certain threshold returns were achieved the partner may be entitled to receive an additional promoted interest with respect to cash flow distributions. The term stabilization date was defined in the agreement to generally mean the first date after completion upon which Salesforce Tower is (1) at least 90% leased and (2) 50% occupied by tenants that are paying rent. Salesforce Tower is an approximately 1,421,000 net rentable square foot Class A office property. On January 18, 2019, the Company and its partner further amended the venture agreement. Per the amendment, the partner exercised its right to cause the Company to purchase, on April 1, 2019, its 5% ownership interest and promoted profits interest in the venture for cash totaling approximately $210.9 million , which amount was reduced by approximately $24.1 million , consisting of the repayment of the Company’s preferred equity and preferred return as provided for in the amended venture agreement. On April 1, 2019, the Company completed the acquisition of its partner’s 5% ownership interest and promoted profits interest in the consolidated entity for cash totaling approximately $210.9 million , which amount was reduced by approximately $24.1 million to $186.8 million to reflect the repayment of the Company’s preferred equity and preferred return in the venture, as described above. The Company now owns 100% of Salesforce Tower. The Company has accounted for the transaction as an equity transaction for financial reporting purposes and has reflected the difference between the fair value of the total consideration paid and the related carrying value of the noncontrolling interest - property partnership totaling approximately $162.5 million as a decrease to Additional Paid-in Capital and Partners’ Capital in the Consolidated Balance Sheets of Boston Properties, Inc. and Boston Properties Limited Partnership, respectively. On June 6, 2017, in conjunction with the refinancing of the indebtedness of the Company’s consolidated entity in which it has a 60% interest and that owns 767 Fifth Avenue (the General Motors Building) located in New York City, the members of the consolidated entity amended the limited liability company agreement to provide for the contribution of the remaining unpaid principal balance of the members’ notes payable totaling approximately $273.9 million (of which the Company’s share of approximately $164.4 million is eliminated in consolidation) to equity in the consolidated entity, resulting in an increase of approximately $109.6 million

Stockholders' Equity _ Partners

Stockholders' Equity / Partners' Capital	12 Months Ended
Stockholders' Equity / Partners' Capital	Dec. 31, 2019
Equity [Abstract]
Stockholders' Equity / Partners' Capital	11. Stockholders’ Equity / Partners’ Capital Boston Properties, Inc. As of December 31, 2019 , Boston Properties, Inc. had 154,790,298 shares of Common Stock outstanding. As of December 31, 2019 , Boston Properties, Inc. owned 1,726,980 general partnership units and 153,063,318 limited partnership units in Boston Properties Limited Partnership. On June 2, 2017, Boston Properties, Inc. renewed its “at the market” (“ATM”) stock offering program through which it may sell from time to time up to an aggregate of $600.0 million of its common stock through sales agents over a three -year period. This program replaced the Company’s prior $600.0 million ATM stock offering program that was scheduled to expire on June 3, 2017. The Company intends to use the net proceeds from any offering for general business purposes, which may include investment opportunities and debt reduction. No shares of common stock have been issued under this ATM stock offering program. During the year ended December 31, 2019 , Boston Properties, Inc. issued 145,088 shares of Common Stock upon the exercise of options to purchase Common Stock. During the year ended December 31, 2018, there were no options to purchase Common Stock exercised. During the years ended December 31, 2019 and 2018 , Boston Properties, Inc. issued 144,481 and 83,136 shares of Common Stock, respectively, in connection with the redemption of an equal number of redeemable OP Units from limited partners. The following table presents Boston Properties, Inc.’s dividends per share and Boston Properties Limited Partnership’s distributions per OP Unit and LTIP Unit paid or payable in 2019 and 2018 : Record Date Payment Date Dividend (Per Share) Distribution (Per Unit) December 31, 2019 January 30, 2020 $0.98 $0.98 September 30, 2019 October 31, 2019 $0.95 $0.95 June 28, 2019 July 31, 2019 $0.95 $0.95 March 29, 2019 April 30, 2019 $0.95 $0.95 December 31, 2018 January 30, 2019 $0.95 $0.95 September 28, 2018 October 31, 2018 $0.95 $0.95 June 29, 2018 July 31, 2018 $0.80 $0.80 March 29, 2018 April 30, 2018 $0.80 $0.80 December 29, 2017 January 30, 2018 $0.80 $0.80 Preferred Stock As of December 31, 2019 , Boston Properties, Inc. had 80,000 shares ( 8,000,000 depositary shares each representing 1/100th of a share) outstanding of its 5.25% Series B Cumulative Redeemable Preferred Stock with a liquidation preference of $2,500.00 per share ( $25.00 per depositary share). Boston Properties, Inc. pays cumulative cash dividends on the Series B Preferred Stock at a rate of 5.25% per annum of the $2,500.00 liquidation preference per share. Boston Properties, Inc. did not redeem the Series B Preferred Stock prior to March 27, 2018, except in certain circumstances relating to the preservation of Boston Properties, Inc.’s REIT status. On and after March 27, 2018, Boston Properties, Inc., at its option, may redeem the Series B Preferred Stock for a cash redemption price of $2,500.00 per share ( $25.00 per depositary share), plus all accrued and unpaid dividends. The Series B Preferred Stock is not redeemable by the holders, has no maturity date and is not convertible into any other security of Boston Properties, Inc. or its affiliates. The following table presents Boston Properties Inc.’s dividends per share on its outstanding Series B Preferred Stock paid or payable in 2019 and 2018 : Record Date Payment Date Dividend (Per Share) February 4, 2020 February 18, 2020 $32.8125 November 1, 2019 November 15, 2019 $32.8125 August 2, 2019 August 15, 2019 $32.8125 May 3, 2019 May 15, 2019 $32.8125 February 4, 2019 February 15, 2019 $32.8125 November 2, 2018 November 15, 2018 $32.8125 August 3, 2018 August 15, 2018 $32.8125 May 4, 2018 May 15, 2018 $32.8125 February 2, 2018 February 15, 2018 $32.8125

Future Minimum Rents

Future Minimum Rents	12 Months Ended
Future Minimum Rents	Dec. 31, 2019
Future Minimum Rents [Abstract]
Future Minimum Rents [Text Block]	12. Future Minimum Rents On January 1, 2019, the Company adopted ASU 2016-02, “Leases” (see “ New Accounting Pronouncements Adopted—Leases ” section of Note 2 ). The Company’s properties are leased to tenants under operating leases with initial term expiration dates ranging from 2020 to 2049. The future contractual minimum lease payments to be received (excluding operating expense reimbursements) by the Company as of December 31, 2018, under non-cancelable operating leases which expire on various dates through 2049: Years Ending December 31, (in thousands) 2019 $ 2,088,171 2020 2,106,963 2021 2,015,031 2022 1,838,699 2023 1,736,636 Thereafter 12,295,464 The future contractual lease payments to be received (excluding operating expense reimbursements) by the Company as of December 31, 2019, under non-cancelable operating leases which expire on various dates through 2049: Years Ending December 31, (in thousands) 2020 $ 2,205,675 2021 2,222,643 2022 2,126,968 2023 2,068,871 2024 1,974,144 Thereafter 13,892,504 No single tenant represented more than 10.0% of the Company’s total rental revenue for the years ended December 31, 2018 and 2017 and no single tenant represented more than 10.0% of the Company’s total lease revenue for the year ended December 31, 2019 .

Segment Information

Segment Information	12 Months Ended
Segment Information	Dec. 31, 2019
Segment Reporting [Abstract]
Segment Reporting Disclosure [Text Block]	13. Segment Information The following tables present reconciliations of Net Income Attributable to Boston Properties, Inc. Common Shareholders to the Company’s share of Net Operating Income and Net Income Attributable to Boston Properties Limited Partnership Common Unitholders to the Company’s share of Net Operating Income for the years ended December 31, 2019 , 2018 and 2017 . Boston Properties, Inc. Year ended December 31, 2019 2018 2017 (in thousands) Net income attributable to Boston Properties, Inc. common shareholders $ 511,034 $ 572,347 $ 451,939 Add: Preferred dividends 10,500 10,500 10,500 Noncontrolling interest—common units of the Operating Partnership 59,345 66,807 52,210 Noncontrolling interests in property partnerships 71,120 62,909 47,832 Interest expense 412,717 378,168 374,481 Losses (gains) from early extinguishments of debt 29,540 16,490 (496 ) Impairment losses 24,038 11,812 — Net operating income from unconsolidated joint ventures 97,716 79,893 64,008 Depreciation and amortization expense 677,764 645,649 617,547 Transaction costs 1,984 1,604 668 Payroll and related costs from management services contracts 10,386 9,590 — General and administrative expense 140,777 121,722 113,715 Less: Net operating income attributable to noncontrolling interests in property partnerships 183,989 177,365 174,245 Gains (losses) from investments in securities 6,417 (1,865 ) 3,678 Interest and other income 18,939 10,823 5,783 Gains on sales of real estate 709 182,356 7,663 Income from unconsolidated joint ventures 46,592 2,222 11,232 Direct reimbursements of payroll and related costs from management services contracts 10,386 9,590 — Development and management services revenue 40,039 45,158 34,605 Company’s share of Net Operating Income $ 1,739,850 $ 1,551,842 $ 1,495,198 Boston Properties Limited Partnership Year ended December 31, 2019 2018 2017 (in thousands) Net income attributable to Boston Properties Limited Partnership common unitholders $ 580,102 $ 656,903 $ 512,866 Add: Preferred distributions 10,500 10,500 10,500 Noncontrolling interests in property partnerships 71,120 62,909 47,832 Interest expense 412,717 378,168 374,481 Losses (gains) from early extinguishments of debt 29,540 16,490 (496 ) Impairment losses 22,272 10,181 — Net operating income from unconsolidated joint ventures 97,716 79,893 64,008 Depreciation and amortization expense 669,956 637,891 609,407 Transaction costs 1,984 1,604 668 Payroll and related costs from management services contracts 10,386 9,590 — General and administrative expense 140,777 121,722 113,715 Less: Net operating income attributable to noncontrolling interests in property partnerships 183,989 177,365 174,245 Gains (losses) from investments in securities 6,417 (1,865 ) 3,678 Interest and other income 18,939 10,823 5,783 Gains on sales of real estate 858 190,716 8,240 Income from unconsolidated joint ventures 46,592 2,222 11,232 Direct reimbursements of payroll and related costs from management services contracts 10,386 9,590 — Development and management services revenue 40,039 45,158 34,605 Company’s share of Net Operating Income $ 1,739,850 $ 1,551,842 $ 1,495,198 Net operating income (“NOI”) is a non-GAAP financial measure equal to net income attributable to Boston Properties, Inc. common shareholders and net income attributable to Boston Properties Limited Partnership common unitholders, as applicable, the most directly comparable GAAP financial measures, plus (1) preferred dividends/distributions, net income attributable to noncontrolling interests, interest expense, losses (gains) from early extinguishments of debt, impairment losses, depreciation and amortization expense, transaction costs, payroll and related costs from management services contracts and corporate general and administrative expense less (2) gains (losses) from investments in securities, interest and other income, gains on sales of real estate, income from unconsolidated joint ventures, direct reimbursements of payroll and related costs from management services contracts and development and management services revenue. The Company believes NOI is useful to investors as a performance measure and believes it provides useful information to investors regarding its results of operations and financial condition because, when compared across periods, it reflects the impact on operations from trends in occupancy rates, rental rates, operating costs and acquisition and development activity on an unleveraged basis, providing perspective not immediately apparent from net income attributable to Boston Properties, Inc. common shareholders and net income attributable to Boston Properties Limited Partnership common unitholders. For example, interest expense is not necessarily linked to the operating performance of a real estate asset and is often incurred at the corporate level as opposed to the property level. Similarly, interest expense may be incurred at the property level even though the financing proceeds may be used at the corporate level (e.g., used for other investment activity). In addition, depreciation and amortization expense, because of historical cost accounting and useful life estimates, may distort operating performance measures at the property level. NOI presented by the Company may not be comparable to NOI reported by other REITs or real estate companies that define NOI differently. Asset information by segment is not reported because the Company does not use this measure to assess performance. Therefore, depreciation and amortization expense is not allocated among segments. Preferred dividends/distributions, interest expense, losses (gains) from early extinguishments of debt, impairment losses, depreciation and amortization expense, transaction costs, payroll and related costs from management services contracts, corporate general and administrative expense, gains (losses) from investments in securities, interest and other income, gains on sales of real estate, direct reimbursements of payroll and related costs from management services contracts and development and management services revenue are not included in NOI and are provided as reconciling items to the Company’s reconciliations of its share of NOI to net income attributable to common shareholders/unitholders. The Company’s segments are based on the Company’s method of internal reporting which classifies its operations by geographic area. The Company’s segments by geographic area are Boston, Los Angeles, New York, San Francisco and Washington, DC. The Company also presents information for each segment by property type, including Office, Residential and Hotel. Beginning in 2019, the Company modified the presentation of its geographic area classification for all periods presented to include the Los Angeles geographic area to align with its method of internal reporting. The Company expanded its presence in the Los Angeles geographic area with its equity method investment in Santa Monica Business Park located in Santa Monica, California. As of December 31, 2019 , the Company has equity interests in a portfolio of 27 office and retail properties in the Los Angeles geographic area aggregating approximately 2.3 million net rentable square feet, all of which are owned through investments in unconsolidated joint ventures. The Company began presenting the Los Angeles geographic area as a reportable segment to align with its method of internal reporting given the increased significance as a result of commencing a full reporting period of ownership of the Santa Monica Business Park portfolio. The inclusion of the Los Angeles geographic area has also resulted in a change in the reported measure of segment profit or loss from NOI to the Company’s share of NOI. This change has been reflected in all periods presented and the impact of the change can been seen within the tables below. The Company has not presented rental revenue and rental expenses for properties owned through investments in unconsolidated joint ventures, including those in the Los Angeles geographic area, as the Company accounts for these properties using the equity method of accounting. Information by geographic area and property type (dollars in thousands): For the year ended December 31, 2019 : Boston Los Angeles New York San Francisco Washington, DC Total Rental Revenue: (1) Office $ 895,098 $ — $ 1,011,912 $ 533,189 $ 384,435 $ 2,824,634 Residential 13,786 — — — 23,128 36,914 Hotel 48,589 — — — — 48,589 Total 957,473 — 1,011,912 533,189 407,563 2,910,137 % of Grand Totals 32.90 % — % 34.78 % 18.32 % 14.00 % 100.00 % Rental Expenses: Office 322,282 — 389,532 177,994 144,217 1,034,025 Residential 5,071 — — — 10,914 15,985 Hotel 34,004 — — — — 34,004 Total 361,357 — 389,532 177,994 155,131 1,084,014 % of Grand Totals 33.34 % — % 35.93 % 16.42 % 14.31 % 100.00 % Net operating income $ 596,116 $ — $ 622,380 $ 355,195 $ 252,432 $ 1,826,123 % of Grand Totals 32.64 % — % 34.09 % 19.45 % 13.82 % 100.00 % Less: Net operating income attributable to noncontrolling interests in property partnerships (40,109 ) — (143,432 ) (448 ) — (183,989 ) Add: Company’s share of net operating income from unconsolidated joint ventures 5,494 61,338 4,174 — 26,710 97,716 Company’s share of net operating income $ 561,501 $ 61,338 $ 483,122 $ 354,747 $ 279,142 $ 1,739,850 % of Grand Totals 32.27 % 3.53 % 27.77 % 20.39 % 16.04 % 100.00 % _______________ (1) Rental Revenue is equal to Total Revenue per the Company’s Consolidated Statements of Operations, less Development and Management Services Revenue and Direct Reimbursements of Payroll and Related Costs from Management Services Contracts Revenue per the Consolidated Statements of Operations. For the year ended December 31, 2018 : Boston Los Angeles New York San Francisco Washington, DC Total Rental Revenue: (1) Office $ 838,341 $ — $ 959,050 $ 397,180 $ 396,088 $ 2,590,659 Residential 6,694 — — — 15,857 22,551 Hotel 49,118 — — — — 49,118 Total 894,153 — 959,050 397,180 411,945 2,662,328 % of Grand Totals 33.59 % — % 36.02 % 14.92 % 15.47 % 100.00 % Rental Expenses: Office 315,653 — 377,992 130,016 142,886 966,547 Residential 3,632 — — — 8,972 12,604 Hotel 33,863 — — — — 33,863 Total 353,148 — 377,992 130,016 151,858 1,013,014 % of Grand Totals 34.86 % — % 37.32 % 12.83 % 14.99 % 100.00 % Net operating income $ 541,005 $ — $ 581,058 $ 267,164 $ 260,087 $ 1,649,314 % of Grand Totals 32.80 % — % 35.23 % 16.20 % 15.77 % 100.00 % Less: Net operating income attributable to noncontrolling interests in property partnerships (33,862 ) — (143,562 ) 59 — (177,365 ) Add: Company’s share of net operating income from unconsolidated joint ventures 2,866 42,750 6,590 — 27,687 79,893 Company’s share of net operating income $ 510,009 $ 42,750 $ 444,086 $ 267,223 $ 287,774 $ 1,551,842 % of Grand Totals 32.86 % 2.75 % 28.63 % 17.22 % 18.54 % 100.00 % _______________ (1) Rental Revenue is equal to total Revenue per the Company’s Consolidated Statements of Operations, less Development and Management Services Revenue and Direct Reimbursements of Payroll and Related Costs from Management Services Contracts Revenue per the Consolidated Statements of Operations. For the year ended December 31, 2017 : Boston Los Angeles New York San Francisco Washington, DC Total Rental Revenue: (1) Office $ 776,279 $ — $ 969,371 $ 345,519 $ 414,103 $ 2,505,272 Residential 4,745 — — — 11,851 16,596 Hotel 45,603 — — — — 45,603 Total 826,627 — 969,371 345,519 425,954 2,567,471 % of Grand Totals 32.20 % — % 37.75 % 13.46 % 16.59 % 100.00 % Rental Expenses: Office 301,097 — 372,810 105,253 144,515 923,675 Residential 2,044 — — — 4,258 6,302 Hotel 32,059 — — — — 32,059 Total 335,200 — 372,810 105,253 148,773 962,036 % of Grand Totals 34.84 % — % 38.76 % 10.94 % 15.46 % 100.00 % Net operating income $ 491,427 $ — $ 596,561 $ 240,266 $ 277,181 $ 1,605,435 % of Grand Totals 30.61 % — % 37.15 % 14.97 % 17.27 % 100.00 % Less: Net operating income attributable to noncontrolling interests in property partnerships (31,857 ) — (142,916 ) 528 — (174,245 ) Add: Company’s share of net operating income from unconsolidated joint ventures 1,962 26,816 8,832 — 26,398 64,008 Company’s share of net operating income $ 461,532 $ 26,816 $ 462,477 $ 240,794 $ 303,579 $ 1,495,198 % of Grand Totals 30.87 % 1.79 % 30.94 % 16.10 % 20.30 % 100.00 % _______________ (1) Rental Revenue is equal to total Revenue per the Company’s Consolidated Statements of Operations, less Development and Management Services Revenue and Direct Reimbursements of Payroll and Related Costs from Management Services Contracts Revenue per the Consolidated Statements of Operations.

Earnings Per Share _ Common Uni

Earnings Per Share / Common Unit	12 Months Ended
Earnings Per Share / Common Unit	Dec. 31, 2019
Earnings Per Share [Abstract]
Earnings Per Share / Common Unit	14. Earnings Per Share / Common Unit Boston Properties, Inc. The following table provides a reconciliation of both the net income attributable to Boston Properties, Inc. common shareholders and the number of common shares used in the computation of basic earnings per share (“EPS”), which is calculated by dividing net income attributable to Boston Properties, Inc. common shareholders by the weighted-average number of common shares outstanding during the period. Unvested share-based payment awards that contain non-forfeitable rights to dividends or dividend equivalents (whether paid or unpaid) are also participating securities. As such, unvested restricted common stock of Boston Properties, Inc. and Boston Properties Limited Partnership’s LTIP Units, 2012 OPP Units and MYLTIP Units are considered participating securities. Participating securities are included in the computation of basic EPS of Boston Properties, Inc. using the two -class method. Participating securities are included in the computation of diluted EPS of Boston Properties, Inc. using the if-converted method if the impact is dilutive. Because the 2012 OPP Units, 2013 MYLTIP Units, 2014 MYLTIP Units, 2015 MYLTIP Units and 2016 MYLTIP Units required, and the 2017-2019 MYLTIP Units require, Boston Properties, Inc. to outperform absolute and relative return thresholds, unless such thresholds have been met by the end of the applicable reporting period, Boston Properties, Inc. excludes such units from the diluted EPS calculation. Other potentially dilutive common shares, including stock options, restricted stock and other securities of Boston Properties Limited Partnership that are exchangeable for Boston Properties, Inc.’s Common Stock, and the related impact on earnings, are considered when calculating diluted EPS. For the Year Ended December 31, 2019 Income (Numerator) Shares (Denominator) Per Share Amount (in thousands, except for per share amounts) Basic Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 511,034 154,582 $ 3.31 Effect of Dilutive Securities: Stock Based Compensation — 301 (0.01 ) Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 511,034 154,883 $ 3.30 For the Year ended December 31, 2018 Income (Numerator) Shares (Denominator) Per Share Amount (in thousands, except for per share amounts) Basic Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 572,347 154,427 $ 3.71 Allocation of undistributed earnings to participating securities (101 ) — — Net income attributable to Boston Properties, Inc. common shareholders $ 572,246 154,427 $ 3.71 Effect of Dilutive Securities: Stock Based Compensation — 255 (0.01 ) Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 572,246 154,682 $ 3.70 For the Year ended December 31, 2017 Income (Numerator) Shares (Denominator) Per Share Amount (in thousands, except for per share amounts) Basic Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 451,939 154,190 $ 2.93 Effect of Dilutive Securities: Stock Based Compensation — 200 — Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 451,939 154,390 $ 2.93 Boston Properties Limited Partnership The following table provides a reconciliation of both the net income attributable to Boston Properties Limited Partnership common unitholders and the number of common units used in the computation of basic earnings per common unit, which is calculated by dividing net income attributable to Boston Properties Limited Partnership common unitholders by the weighted-average number of common units outstanding during the period. Unvested share-based payment awards that contain non-forfeitable rights to dividends or dividend equivalents (whether paid or unpaid) are also participating securities. As such, unvested restricted common stock of Boston Properties, Inc. and Boston Properties Limited Partnership’s LTIP Units, 2012 OPP Units and MYLTIP Units are considered participating securities. Participating securities are included in the computation of basic earnings per common unit using the two -class method. Participating securities are included in the computation of diluted earnings per common unit using the if-converted method if the impact is dilutive. Because the 2012 OPP Units, 2013 MYLTIP Units, 2014 MYLTIP Units, 2015 MYLTIP Units and 2016 MYLTIP Units required, and the 2017-2019 MYLTIP Units require, Boston Properties, Inc. to outperform absolute and relative return thresholds, unless such thresholds have been met by the end of the applicable reporting period, Boston Properties Limited Partnership excludes such units from the diluted earnings per common unit calculation. Other potentially dilutive common units and the related impact on earnings are considered when calculating diluted earnings per common unit. Included in the number of units (the denominator) below are approximately 17,618,000 , 17,485,000 and 17,471,000 redeemable common units for the years ended December 31, 2019 , 2018 and 2017 , respectively. For the Year Ended December 31, 2019 Income (Numerator) Units (Denominator) Per Unit Amount (in thousands, except for per unit amounts) Basic Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 580,102 172,200 $ 3.37 Effect of Dilutive Securities: Stock Based Compensation — 301 (0.01 ) Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 580,102 172,501 $ 3.36 For the Year ended December 31, 2018 Income (Numerator) Units (Denominator) Per Unit Amount (in thousands, except for per unit amounts) Basic Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 656,903 171,912 $ 3.82 Allocation of undistributed earnings to participating securities (113 ) — — Net income attributable to Boston Properties Limited Partnership common unitholders $ 656,790 171,912 $ 3.82 Effect of Dilutive Securities: Stock Based Compensation — 255 (0.01 ) Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 656,790 172,167 $ 3.81 For the Year ended December 31, 2017 Income (Numerator) Units (Denominator) Per Unit Amount (in thousands, except for per unit amounts) Basic Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 512,866 171,661 $ 2.99 Effect of Dilutive Securities: Stock Based Compensation — 200 (0.01 ) Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 512,866 171,861 $ 2.98

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
Employee Benefit Plans	Dec. 31, 2019
Employee Benefit Plans [Abstract]
Compensation and Employee Benefit Plans [Text Block]	15. Employee Benefit Plans Effective January 1, 1985, the predecessor of the Company adopted a 401(k) Savings Plan (the “Plan”) for its employees. Upon formation, the Company adopted the Plan and the terms of the Plan. Under the Plan, as amended, the Company’s matching contribution equals 200% of the first 3% of participant’s eligible earnings contributed (utilizing earnings that are not in excess of an amount established by the IRS ( $280,000 , $275,000 and $270,000 in 2019 , 2018 and 2017 , respectively), indexed for inflation) with no vesting requirement. The Company’s aggregate matching contribution for the years ended December 31, 2019 , 2018 and 2017 was approximately $4.2 million , $4.1 million and $4.1 million , respectively. The Company also maintains a deferred compensation plan that is designed to allow officers of Boston Properties, Inc. to defer a portion of the officer’s current income on a pre-tax basis and receive a tax-deferred return on these deferrals based on the performance of specific investments selected by the officer. The Company’s obligation under the plan is that of an unsecured promise to pay the deferred compensation to the plan participants in the future. At December 31, 2019 and 2018 , the Company had maintained approximately $36.0 million and $28.2 million , respectively, in a separate account, which is not restricted as to its use. The Company’s liability under the plan is equal to the total amount of compensation deferred by the plan participants and earnings on the deferred compensation pursuant to investments elected by the plan participants. The Company’s liability as of December 31, 2019 and 2018 was approximately $36.0 million and $28.2 million , respectively, which are included in the accompanying Consolidated Balance Sheets.

Stock Option and Incentive Plan

Stock Option and Incentive Plan	12 Months Ended
Stock Option and Incentive Plan	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock Option and Incentive Plan	16. Stock Option and Incentive Plan At Boston Properties, Inc.’s 2012 annual meeting of stockholders held on May 15, 2012, its stockholders approved the Boston Properties, Inc. 2012 Stock Option and Incentive Plan (the “2012 Plan”). The 2012 Plan replaced the 1997 Stock Option and Incentive Plan (the “1997 Plan”). The material terms of the 2012 Plan include, among other things: (1) the maximum number of shares of common stock reserved and available for issuance under the 2012 Plan is the sum of (i) 13,000,000 newly authorized shares, plus (ii) the number of shares available for grant under the 1997 Stock Plan immediately prior to the effective date of the 2012 Plan, plus (iii) any shares underlying grants under the 1997 Plan that are forfeited, canceled or terminated (other than by exercise) in the future; (2) “full-value” awards (i.e., awards other than stock options) are multiplied by a 2.32 conversion ratio to calculate the number of shares available under the 2012 Plan that are used for each full-value award, as opposed to a 1.0 conversion ratio for each stock option awarded under the 2012 Plan; (3) shares tendered or held back for taxes will not be added back to the reserved pool under the 2012 Plan; (4) stock options may not be re-priced without stockholder approval; and (5) the term of the 2012 Plan is for 10 years from the date of stockholder approval. On February 5, 2019, Boston Properties, Inc.’s Compensation Committee approved the 2019 MYLTIP awards under the 2012 Plan to certain officers and employees of Boston Properties, Inc. The 2019 MYLTIP awards utilize Boston Properties, Inc.’s TSR over a three-year measurement period, on an annualized, compounded basis, as the performance metric. Earned awards will be based on Boston Properties, Inc.’s TSR relative to the Nareit Office Index, adjusted to include Vornado Realty Trust. Earned awards will range from zero to a maximum of 220,734 LTIP Units depending on Boston Properties, Inc.’s TSR relative to the Nareit Office Index, adjusted to include Vornado Realty Trust, with a target of approximately 110,367 LTIP Units and linear interpolation between zero and maximum. Earned awards (if any) will vest 50% on February 4, 2022 and 50% on February 4, 2023, based on continued employment. Vesting will be accelerated in the event of a change in control, termination of employment by Boston Properties, Inc. without cause, or termination of employment by the award recipient for good reason, death, disability or retirement. If there is a change of control prior to February 4, 2022, earned awards will be calculated based on TSR performance up to the date of the change of control. The 2019 MYLTIP awards are in the form of LTIP Units issued on the grant date which (i) are subject to forfeiture to the extent awards are not earned and (ii) prior to the performance measurement date are only entitled to one-tenth (10%) of the regular quarterly distributions payable on common partnership units. Under ASC 718 “Compensation - Stock Compensation”, the 2019 MYLTIP awards have an aggregate value of approximately $13.5 million , which amount will generally be amortized into earnings over the four year plan period under the graded vesting method. On February 9, 2019, the measurement period for the Company’s 2016 MYLTIP awards ended and, based on Boston Properties, Inc.’s relative TSR performance, the final awards were determined to be 69.5% of target or an aggregate of approximately $13.6 million (after giving effect to employee separations). As a result, an aggregate of 364,980 2016 MYLTIP Units that had been previously granted were automatically forfeited. On February 4, 2018, the measurement period for the Company’s 2015 MYLTIP awards ended and, based on Boston Properties, Inc.’s relative TSR performance, the final awards were determined to be 22.0% of target or an aggregate of approximately $3.6 million (after giving effect to employee separations). As a result, an aggregate of 337,847 2015 MYLTIP Units that had been previously granted were automatically forfeited. On February 3, 2017, the measurement period for the Company’s 2014 MYLTIP awards ended and, based on Boston Properties, Inc.’s relative TSR performance, the final awards were determined to be 27.7% of target or an aggregate of approximately $3.5 million (after giving effect to employee separations and the unallocated reserve). As a result, an aggregate of 447,386 2014 MYLTIP Units that had been previously granted were automatically forfeited. Boston Properties, Inc. issued 26,503 , 20,320 and 37,414 shares of restricted common stock and Boston Properties Limited Partnership issued 181,919 , 205,838 and 113,918 LTIP Units to employees and non-employee directors under the 2012 Plan during the years ended December 31, 2019 , 2018 and 2017 , respectively. Boston Properties, Inc. did not issue any non-qualified stock options under the 2012 Plan during the years ended December 31, 2019 , 2018 and 2017. Boston Properties Limited Partnership issued 220,734 2019 MYLTIP Units, 342,659 2018 MYLTIP Units and 400,000 2017 MYLTIP Units to employees under the 2012 Plan during the years ended December 31, 2019 , 2018 and 2017 , respectively. Employees and non-employee directors paid $0.01 per share of restricted common stock and $0.25 per LTIP Unit, OPP Unit and MYLTIP Unit. When issued, LTIP Units are not economically equivalent in value to a share of Common Stock, but over time can increase in value to one-for-one parity with Common Stock if there is sufficient appreciation in the value of the Company’s assets. The aggregate value of the LTIP Units is included in noncontrolling interests in the Consolidated Balance Sheets. Grants of restricted stock and LTIP Units to employees vest in four equal annual installments. Restricted stock is measured at fair value on the date of grant based on the number of shares granted and the closing price of Boston Properties, Inc.’s Common Stock on the date of grant as quoted on the New York Stock Exchange. Such value is recognized as an expense ratably over the corresponding employee service period. Non-qualified stock options, which are valued using the Black-Scholes option-pricing model, are recognized as an expense ratably over the corresponding employee service period. As the 2012 OPP Awards, 2013 MYLTIP Awards, 2014 MYLTIP Awards, 2015 MYLTIP Awards, 2016 MYLTIP Awards, 2017 MYLTIP Awards, 2018 MYLTIP Awards and 2019 MYLTIP Awards are subject to both a service condition and a market condition, the Company recognizes the compensation expense related to the 2012 OPP Awards, 2013 MYLTIP Awards, 2014 MYLTIP Awards, 2015 MYLTIP Awards 2016 MYLTIP Awards, 2017 MYLTIP Awards, 2018 MYLTIP Awards and 2019 MYLTIP Awards under the graded vesting attribution method. Under the graded vesting attribution method, each portion of the award that vests at a different date is accounted for as a separate award and recognized over the period appropriate to that portion so that the compensation cost for each portion should be recognized in full by the time that portion vests. The Company recognizes forfeitures as they occur on its awards of stock-based compensation. Dividends paid on both vested and unvested shares of restricted stock are charged directly to Dividends in Excess of Earnings in Boston Properties, Inc.’s Consolidated Balance Sheets and Partners’ Capital in Boston Properties Limited Partnership’s Consolidated Balance Sheets. Aggregate stock-based compensation expense associated with restricted stock, non-qualified stock options, LTIP Units, 2013 MYLTIP Units, 2014 MYLTIP Units, 2015 MYLTIP Units, 2016 MYLTIP Units, 2017 MYLTIP Units, 2018 MYLTIP Units and 2019 MYLTIP Units was approximately $39.8 million , $38.0 million and $33.2 million for the years ended December 31, 2019 , 2018 and 2017 , respectively. At December 31, 2019 , there was (1) an aggregate of approximately $23.3 million of unrecognized compensation expense related to unvested restricted stock and LTIP Units and (2) an aggregate of approximately $12.4 million of unrecognized compensation expense related to unvested 2017 MYLTIP Units, 2018 MYLTIP Units and 2019 MYLTIP Units that is expected to be recognized over a weighted-average period of approximately 2.4 years . The shares of restricted stock were valued at approximately $3.5 million ( $131.27 per share weighted-average), $2.4 million ( $119.27 per share weighted-average) and $4.9 million ( $130.32 per share weighted-average) for the years ended December 31, 2019 , 2018 and 2017 , respectively. LTIP Units were valued using a Monte Carlo simulation method model in accordance with the provisions of ASC 718. LTIP Units issued during the years ended December 31, 2019 , 2018 and 2017 were valued at approximately $22.1 million , $22.7 million and $13.6 million , respectively. The weighted-average per unit fair value of LTIP Unit grants in 2019 , 2018 and 2017 was $121.50 , $110.29 and $119.41 , respectively. The per unit fair value of each LTIP Unit granted in 2019 , 2018 and 2017 was estimated on the date of grant using the following assumptions; an expected life of 5.7 years , 5.7 years and 5.7 years , a risk-free interest rate of 2.68% , 2.63% and 2.14% and an expected price volatility of 27.0% , 27.0% and 28.0% , respectively. There were no non-qualified stock options granted during the years ended December 31, 2019 , 2018 and 2017 . A summary of the status of Boston Properties, Inc.’s stock options as of December 31, 2019 , 2018 and 2017 and changes during the years then ended are presented below: Shares Weighted-Average Exercise Price Outstanding at December 31, 2016 547,129 $ 96.38 Exercised (6,688 ) $ 99.15 Outstanding at December 31, 2017 540,441 $ 96.35 Exercised — $ — Outstanding at December 31, 2018 540,441 $ 96.35 Exercised (145,088 ) $ 96.27 Outstanding at December 31, 2019 395,353 $ 96.37 The following table summarizes information about Boston Properties, Inc.’s stock options outstanding at December 31, 2019 : Options Outstanding Options Exercisable Number Outstanding at 12/31/19 Weighted-Average Remaining Contractual Life Exercise Price Number Exercisable at 12/31/19 Exercise Price 81,458 1.1 years $ 86.86 81,458 $ 86.86 54,282 3.3 years $ 95.69 54,282 $ 95.69 142,422 3.1 years $ 98.46 142,422 $ 98.46 117,191 2.1 years $ 100.77 117,191 $ 100.77 The total intrinsic value of the outstanding and exercisable stock options as of December 31, 2019 was approximately $16.4 million . In addition, Boston Properties, Inc. had 540,441 options exercisable at a weighted-average exercise price of $96.35 at December 31, 2018 and 2017. Boston Properties, Inc. adopted the 1999 Non-Qualified Employee Stock Purchase Plan (the “Stock Purchase Plan”) to encourage the ownership of Common Stock by eligible employees. The Stock Purchase Plan became effective on January 1, 1999 with an aggregate maximum of 250,000 shares of Common Stock available for issuance. The Stock Purchase Plan provides for eligible employees to purchase on the business day immediately following the end of the biannual purchase periods (i.e., January 1-June 30 and July 1-December 31) shares of Common Stock at a purchase price equal to 85% of the average closing prices of the Common Stock during the last ten business days of the purchase period. Boston Properties, Inc. issued 5,862 , 6,268 and 6,317 shares with the weighted-average purchase price equal to $104.11 per share, $107.20 per share and $105.97 per share under the Stock Purchase Plan during the years ended December 31, 2019 , 2018 and 2017 , respectively.

Related Party Transactions

Related Party Transactions	12 Months Ended
Related Party Transactions	Dec. 31, 2019
Related Party Transaction [Line Items]
Related Party Transactions Disclosure [Text Block]	17. Related Party Transactions A firm controlled by Mr. Raymond A. Ritchey’s brother was paid aggregate leasing commissions of approximately $21,000 , $921,000 and $368,000 for the years ended December 31, 2019 , 2018 and 2017 , respectively, related to certain exclusive leasing arrangements for certain Northern Virginia properties. Mr. Ritchey is a Senior Executive Vice President of Boston Properties, Inc. In accordance with Boston Properties, Inc.’s 2012 Plan, and as approved by its Board of Directors, seven non-employee directors made elections to receive deferred stock units in lieu of cash fees for 2019 . As a result of these elections, the aggregate cash fees otherwise payable to a non-employee director during a fiscal quarter are converted into a number of deferred stock units equal to the aggregate cash fees divided by the last reported sales price of a share of Boston Properties, Inc.’s Common Stock on the last trading of the applicable fiscal quarter. The deferred stock units are also credited with dividend equivalents as dividends are paid by Boston Properties, Inc. The deferred stock units may be settled in shares of Common Stock upon the cessation of such director’s service on the Board of Directors of Boston Properties, Inc. The Company modified the terms of the non-employee director compensation program to provide, subject to certain conditions, the non-employee directors holding deferred stock units with the ability to elect, following cessation of their service on the Company’s Board of Directors, to diversify their investment elections into non-employer securities on a pre-tax basis and receive tax-deferred returns on such deferrals, which will ultimately be settled in cash. The Company’s obligation under the plan is that of an unsecured promise to pay the deferred compensation to the non-employee director in the future. At December 31, 2019, the Company had maintained approximately $0.7 million in a separate account, which is not restricted as to its use. The Company’s liability under the plan is equal to the total amount of compensation deferred by the non-employee director and earnings on the deferred compensation pursuant to investments elected by the non-employee director. The Company’s liability as of December 31, 2019 was approximately $0.7 million , which is included in the accompanying Consolidated Balance Sheets. The modification of the terms of the non-employee director compensation program required a change to the classification of these deferred stock units from permanent equity to temporary equity on the Consolidated Balance Sheets of Boston Properties, Inc. and Boston Properties Limited Partnership within Redeemable Deferred Stock Units (See Note 2 ). On May 21, 2019, in connection with the cessation of a director’s service on the Board of Directors of Boston Properties, Inc., Boston Properties, Inc. issued 17,949 shares of Common Stock in settlement of a portion of the director’s outstanding deferred stock units. In addition, on September 3, 2019, the Company converted 4,917 of such director’s deferred stock units as a result of such director’s election to diversify their investment elections into non-employer securities. On May 23, 2018, in connection with the cessation of a director’s service on the Board of Directors of Boston Properties, Inc., Boston Properties, Inc. issued 36,836 shares of Common Stock in settlement of the director’s outstanding deferred stock units. At December 31, 2019 and 2018 , Boston Properties, Inc. had outstanding 60,676 and 74,966 deferred stock units, respectively.

Selected Interim Financial Info

Selected Interim Financial Information (unaudited)	12 Months Ended
Selected Interim Financial Information (unaudited)	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information [Text Block]	18. Selected Interim Financial Information (unaudited) Boston Properties, Inc. The tables below reflect Boston Properties, Inc.’s selected quarterly information for the years ended December 31, 2019 and 2018 . 2019 Quarter Ended March 31, June 30, September 30, December 31, (in thousands, except for per share amounts) Total revenue $ 725,767 $ 733,741 $ 743,553 $ 757,501 Net income $ 131,159 $ 203,461 $ 141,370 $ 176,009 Net income attributable to Boston Properties, Inc. common shareholders $ 98,105 $ 164,318 $ 107,771 $ 140,824 Income attributable to Boston Properties, Inc. per share—basic $ 0.63 $ 1.06 $ 0.70 $ 0.91 Income attributable to Boston Properties, Inc. per share—diluted $ 0.63 $ 1.06 $ 0.70 $ 0.91 2018 Quarter Ended March 31, June 30, September 30, December 31, (in thousands, except for per share amounts) Total revenue $ 661,151 $ 664,484 $ 686,284 $ 705,157 Net income $ 216,312 $ 160,565 $ 150,445 $ 185,241 Net income attributable to Boston Properties, Inc. common shareholders $ 176,021 $ 128,681 $ 119,118 $ 148,529 Income attributable to Boston Properties, Inc. per share—basic $ 1.14 $ 0.83 $ 0.77 $ 0.96 Income attributable to Boston Properties, Inc. per share—diluted $ 1.14 $ 0.83 $ 0.77 $ 0.96 Boston Properties Limited Partnership The tables below reflect Boston Properties Limited Partnership’s selected quarterly information for the years ended December 31, 2019 and 2018 . 2019 Quarter Ended March 31, June 30, September 30, December 31, (in thousands, except for per unit amounts) Total revenue $ 725,767 $ 733,741 $ 743,553 $ 757,501 Net income $ 134,837 $ 205,822 $ 143,212 $ 177,851 Net income attributable to Boston Properties Limited Partnership common unitholders $ 113,382 $ 185,715 $ 122,117 $ 158,888 Income attributable to Boston Properties Limited Partnership per unit—basic $ 0.66 $ 1.08 $ 0.71 $ 0.92 Income attributable to Boston Properties Limited Partnership per unit—diluted $ 0.66 $ 1.08 $ 0.71 $ 0.92 2018 Quarter Ended March 31, June 30, September 30, December 31, (in thousands, except for per unit amounts) Total revenue $ 661,151 $ 664,484 $ 686,284 $ 705,157 Net income $ 220,766 $ 162,986 $ 153,676 $ 192,884 Net income attributable to Boston Properties Limited Partnership common unitholders $ 200,907 $ 145,961 $ 136,201 $ 173,834 Income attributable to Boston Properties Limited Partnership per unit—basic $ 1.17 $ 0.85 $ 0.79 $ 1.01 Income attributable to Boston Properties Limited Partnership per unit—diluted $ 1.17 $ 0.85 $ 0.79 $ 1.01

Subsequent Events

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2018
Subsequent Events [Abstract]
Subsequent Events	19. Subsequent Events On January 28, 2020, the Company entered into a joint venture with a third party to own, operate and develop properties at its Gateway Commons complex located in South San Francisco, California. The Company contributed its 601, 611 and 651 Gateway properties and development rights with an agreed upon value aggregating approximately $350.0 million for its 50% interest in the joint venture. 601, 611 and 651 Gateway consist of three Class A office properties aggregating approximately 768,000 net rentable square feet. The partner contributed three properties and development rights with an agreed upon value aggregating approximately $280.8 million at closing and will contribute cash totaling approximately $69.2 million in the future for its 50% ownership interest in the joint venture. On January 28, 2020 , a joint venture in which the Company has a 55% interest commenced development of the first phase of its Platform 16 project located in San Jose, California. The first phase of the Platform 16 development project consists of an approximately 390,000 net rentable square foot Class A office building and a below-grade parking garage. On February 20, 2020, the joint venture acquired the land under the ground lease for a purchase price totaling approximately $134.8 million . The joint venture had previously made a deposit totaling $15.0 million , which deposit was credited against the purchase price. Platform 16 consists of a parcel of land totaling approximately 5.6 acres that will support the development of approximately 1.1 million square feet of commercial office space (See Notes 3 and 5). On January 28, 2020, the Company exercised its option to acquire real property at 425 Fourth Street located in San Francisco, California for a purchase price totaling approximately $134.1 million . 425 Fourth Street will support the development of approximately 804,000 square feet of primarily commercial office space. The Company expects to complete the acquisition during the second quarter of 2020. On January 31, 2020 and February 4, 2020, Boston Properties, Inc. issued an aggregate of 24,503 shares of restricted Common Stock and Boston Properties Limited Partnership issued an aggregate of 196,927 LTIP Units under the 2012 Plan to certain employees of Boston Properties, Inc. On February 4, 2020, Boston Properties, Inc.’s Compensation Committee approved the 2020 Multi-Year Long-Term Incentive Program (the “2020 MYLTIP”) awards under Boston Properties, Inc.’s 2012 Plan to certain officers and employees of Boston Properties, Inc. Earned awards will range from zero to a maximum of 203,278 LTIP Units depending on Boston Properties, Inc.’s TSR relative to the FTSE Nareit Office Index, adjusted to include Vornado Realty Trust, with a target of approximately 101,638 LTIP Units and linear interpolation between zero and maximum. Under ASC 718, the 2020 MYLTIP awards have an aggregate value of approximately $13.7 million . On February 6, 2020, the measurement period for the Company’s 2017 MYLTIP awards ended and, based on Boston Properties, Inc.’s relative TSR performance, the final awards were determined to be 83.8% of target or an aggregate of approximately $17.6 million (after giving effect to employee separations). As a result, an aggregate of 270,942 2017 MYLTIP Units that had been previously granted were automatically forfeited. On February 20, 2020 , the Company completed the sale of its New Dominion Technology Park located in Herndon, Virginia for a gross sale price of $256.0 million . New Dominion Technology Park is comprised of two Class A office properties aggregating approximately 493,000 net rentable square feet (See Note 6

Real Estate and Accumulated Dep

Real Estate and Accumulated Depreciation	12 Months Ended
Real Estate and Accumulated Depreciation	Dec. 31, 2019
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate and Accumulated Depreciation Disclosure [Text Block]	Item 15. Exhibits and Financial Statement Schedules (a) Financial Statement Schedule Boston Properties, Inc. Schedule 3 - Real Estate and Accumulated Depreciation December 31, 2019 (dollars in thousands) Property Name Type Location Encumbrances Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Land Building 767 Fifth Avenue (the General Motors Building) Office New York, NY $ 2,274,028 $ 1,796,252 $ 1,532,654 $ 202,612 $ 1,796,252 $ 1,735,266 $ — $ — $ 3,531,518 $ 313,158 1968/2019 2013 (1) Prudential Center Office Boston, MA — 92,077 948,357 556,458 115,638 1,478,578 2,676 — 1,596,892 596,740 1965/1993/2002/2016-2017 1998/1999/2000 (1) Embarcadero Center Office San Francisco, CA — 179,697 847,410 415,228 195,987 1,246,348 — — 1,442,335 633,711 1970/1989 1998-1999 (1) 399 Park Avenue Office New York, NY — 339,200 700,358 300,519 354,107 985,970 — — 1,340,077 358,960 1961/2018 2002 (1) 601 Lexington Avenue Office New York, NY 644,778 241,600 494,782 454,902 289,639 688,550 — 213,095 1,191,284 289,482 1977/1997 2001 (1) Salesforce Tower Office San Francisco, CA — 200,349 946,205 — 200,349 946,205 — — 1,146,554 38,727 2018 2013 (1) 200 Clarendon Street and Garage Office Boston, MA — 219,543 667,884 210,160 250,134 829,529 17,924 — 1,097,587 214,533 1976 2010 (1) 250 West 55th Street Office New York, NY — 285,263 603,167 51,928 285,263 655,095 — — 940,358 116,857 2014 2007 (1) 100 Federal Street Office Boston, MA — 131,067 435,954 102,984 131,067 538,938 — — 670,005 122,799 1971-1975/2017 2012 (1) Times Square Tower Office New York, NY — 165,413 380,438 113,222 169,193 489,880 — — 659,073 217,303 2004 2000 (1) Carnegie Center Office Princeton, NJ — 142,666 316,856 152,280 94,240 462,882 54,680 — 611,802 208,331 1983-2016 1998/1999/2000/2007/2014/2017/2019 (1) Atlantic Wharf Office Boston, MA — 63,988 454,537 18,709 63,988 473,246 — — 537,234 131,828 2011 2007 (1) 510 Madison Avenue Office New York, NY — 103,000 253,665 25,495 103,000 279,160 — — 382,160 72,213 2012 2010 (1) Fountain Square Office Reston, VA — 56,853 306,298 12,140 56,853 318,438 — — 375,291 78,498 1986-1990 2012 (1) 599 Lexington Avenue Office New York, NY — 81,040 100,507 188,572 87,852 282,267 — — 370,119 183,291 1986 1997 (1) 680 Folsom Street Office San Francisco, CA — 72,545 219,766 7,907 72,545 227,673 — — 300,218 46,777 2014 2012 (1) 2200 Pennsylvania Avenue Office Washington, DC — — 183,541 113,627 109,038 188,130 — — 297,168 59,190 2011 2008 (1) 145 Broadway Office Cambridge, MA — 121 273,013 23,246 23,367 273,013 — — 296,380 1,511 2019 1997 (1) South of Market and Democracy Tower Office Reston, VA — 13,603 237,479 26,415 13,687 263,810 — — 277,497 99,478 2008-2009 2003 (1) 601 Massachusetts Avenue Office Washington, DC — 95,310 165,173 3,945 95,322 169,106 — — 264,428 24,502 2016 2008 (1) Bay Colony Corporate Center Office Waltham, MA — 18,789 148,451 80,077 18,789 228,528 — — 247,317 79,824 1985-1989 2011 (1) Gateway Center Office San Francisco, CA — 28,255 139,245 61,791 30,627 198,664 — — 229,291 106,680 1984/1986/2002 1999 (1) 535 Mission Street Office San Francisco, CA — 40,933 148,378 3,276 40,933 151,654 — — 192,587 26,293 2015 2013 (1) Reservoir Place Office Waltham, MA — 18,605 104,124 53,718 20,108 156,339 — — 176,447 70,870 1955/1987/2017 1997/1998 (1) Mountain View Research Park Office Mountain View, CA — 95,066 68,373 12,704 95,066 81,077 — — 176,143 19,807 1977-1981/2007-2013 2013 (1) 1330 Connecticut Avenue Office Washington, DC — 25,982 82,311 36,847 27,135 118,005 — — 145,140 32,775 1984/2018 2004 (1) Boston Properties, Inc. Schedule 3 - Real Estate and Accumulated Depreciation December 31, 2019 (dollars in thousands) Property Name Type Location Encumbrances Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Land Building Kingstowne Towne Center Office Alexandria, VA — 18,021 109,038 3,376 18,062 112,373 — — 130,435 44,294 2003-2006 2007 (1) One Freedom Square Office Reston, VA — 9,929 84,504 34,372 11,293 117,512 — — 128,805 59,006 2000 2003 (1) Capital Gallery Office Washington, DC — 4,725 29,565 88,704 8,662 114,332 — — 122,994 71,631 1981/2006 2007 (1) Weston Corporate Center Office Weston, MA — 25,753 92,312 (123 ) 25,854 92,088 — — 117,942 29,227 2010 2001 (1) Two Freedom Square Office Reston, VA — 13,930 77,739 23,209 15,420 99,458 — — 114,878 50,668 2001 2003 (1) One and Two Reston Overlook Office Reston, VA — 16,456 66,192 24,181 16,179 90,650 — — 106,829 51,503 1999 2000 (1) Discovery Square Office Reston, VA — 11,198 71,782 20,905 12,533 91,352 — — 103,885 43,619 2001 2003 (1) 140 Kendrick Street Office Needham, MA — 18,095 66,905 17,574 19,092 83,482 — — 102,574 35,721 2000 2004 (1) 355 Main Street Office Cambridge, MA — 18,863 53,346 27,582 21,173 78,618 — — 99,791 26,439 1981/1996/2013 2006 (1) 880 & 890 Winter Street Office Waltham, MA — 29,510 65,812 — 29,510 65,812 — — 95,322 1,458 1998-1999 2019 (1) 10 CityPoint Office Waltham, MA — 1,953 85,752 4,697 2,290 90,112 — — 92,402 10,928 2016 1997 (1) 90 Broadway Office Cambridge, MA — 19,104 52,078 19,857 20,785 70,254 — — 91,039 23,621 1983/1998/2013 2006 (1) 230 CityPoint Office Waltham, MA — 13,189 49,823 22,057 13,807 71,262 — — 85,069 29,255 1992 2005 (1) 77 CityPoint Office Waltham, MA — 13,847 60,383 10,556 14,023 70,763 — — 84,786 27,172 2008 2001 (1) Waltham Weston Corporate Center Office Waltham, MA — 10,385 60,694 13,165 11,097 73,147 — — 84,244 35,567 2003 1999 (1) 3625-3635 Peterson Way Office Santa Clara, CA — 63,206 14,879 752 63,206 14,879 752 — 78,837 11,172 1979 2016 (1) 2440 West El Camino Real Office Mountain View, CA — 16,741 51,285 5,454 16,741 56,739 — — 73,480 13,090 1987/2003 2011 (1) 191 Spring Street Office Lexington, MA — 2,850 59,751 7,695 3,151 67,145 — — 70,296 21,917 1971/1995/2018 1997 (1) 300 Binney Street Office Cambridge, MA — 18,080 51,262 140 18,080 51,402 — — 69,482 11,146 2013 2009 (1) Wisconsin Place Office Chevy Chase, MD — — 53,349 14,924 — 68,273 — — 68,273 25,934 2009 2004 (1) Reston Corporate Center Office Reston, VA — 9,135 50,857 6,236 10,148 56,080 — — 66,228 29,860 1984 1998 (1) New Dominion Technology Park, Bldg. Two Office Herndon, VA — 5,584 51,868 4,157 6,510 55,099 — — 61,609 26,894 2004 1998 (1) 255 Main Street Office Cambridge, MA — 134 25,110 34,124 548 58,820 — — 59,368 33,543 1987 1997 (1) University Place Office Cambridge, MA 3,602 — 37,091 16,001 7,418 45,674 — — 53,092 29,423 1985 1998 (1) New Dominion Technology Park, Bldg. One Office Herndon, VA — 3,880 43,227 3,927 4,583 46,451 — — 51,034 29,141 2001 1998 (1) Sumner Square Office Washington, DC — 624 28,745 21,344 3,535 47,178 — — 50,713 27,093 1985 1999 (1) 200 West Street Office Waltham, MA — 16,148 24,983 8,211 16,813 30,425 — 2,104 49,342 17,001 1999 1997 (1) North First Business Park Office San Jose, CA — 23,398 13,069 4,571 23,377 17,661 — — 41,038 16,411 1981 2007 (1) 150 Broadway Office Cambridge, MA — 850 25,042 8,540 1,323 33,109 — — 34,432 19,875 1999 1997 (1) 105 Broadway Office Cambridge, MA — 1,299 12,943 11,406 2,395 23,253 — — 25,648 11,870 1990 1997 (1) Lexington Office Park Office Lexington, MA — 998 1,426 18,547 1,264 19,707 — — 20,971 14,312 1982 1997 (1) 201 Spring Street Office Lexington, MA — 2,849 15,303 1,172 3,124 16,200 — — 19,324 8,587 1997 1997 (1) The Point Office Waltham, MA — 6,395 10,040 421 6,492 10,364 — — 16,856 1,349 2015 2007 (1) 33 Hayden Avenue Office Lexington, MA — 266 3,234 12,898 425 15,973 — — 16,398 5,678 1979 1997 (1) 690 Folsom Street Office San Francisco, CA — 3,219 11,038 1,157 3,219 12,195 — — 15,414 2,284 2015 2012 (1) Boston Properties, Inc. Schedule 3 - Real Estate and Accumulated Depreciation December 31, 2019 (dollars in thousands) Property Name Type Location Encumbrances Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Land Building 92-100 Hayden Avenue Office Lexington, MA — 594 6,748 7,529 802 14,069 — — 14,871 12,041 1985 1997 (1) 181 Spring Street Office Lexington, MA — 1,066 9,520 2,177 1,160 11,603 — — 12,763 5,597 1999 1997 (1) 195 West Street Office Waltham, MA — 1,611 6,652 4,218 1,858 10,623 — — 12,481 8,352 1990 1997 (1) 7501 Boston Boulevard, Building Seven Office Springfield, VA — 665 9,273 816 791 9,963 — — 10,754 5,393 1997 1997 (1) 7435 Boston Boulevard, Building One Office Springfield, VA — 392 3,822 4,983 659 8,538 — — 9,197 6,344 1982 1997 (1) 7450 Boston Boulevard, Building Three Office Springfield, VA — 1,165 4,681 2,591 1,430 7,007 — — 8,437 3,575 1987 1998 (1) 32 Hartwell Avenue Office Lexington, MA — 168 1,943 6,115 314 7,912 — — 8,226 1,975 1968/1979/1987 1997 (1) 250 Binney Street Office Cambridge, MA — 110 4,483 3,593 273 7,913 — — 8,186 5,829 1983 1997 (1) 8000 Grainger Court, Building Five Office Springfield, VA — 366 4,282 3,198 601 7,245 — — 7,846 5,752 1984 1997 (1) 453 Ravendale Drive Office Mountain View, CA — 5,477 1,090 676 5,477 1,766 — — 7,243 690 1977 2012 (1) 7300 Boston Boulevard, Building Thirteen Office Springfield, VA — 608 4,773 1,007 661 5,727 — — 6,388 1,984 2002 1997 (1) 17 Hartwell Avenue Office Lexington, MA — 26 150 6,064 65 6,175 — — 6,240 1,966 1968 1997 (1) 7601 Boston Boulevard, Building Eight Office Springfield, VA — 200 878 5,060 551 5,587 — — 6,138 4,689 1986 1997 (1) 7500 Boston Boulevard, Building Six Office Springfield, VA — 138 3,749 1,640 367 5,160 — — 5,527 4,237 1985 1997 (1) 8000 Corporate Court, Building Eleven Office Springfield, VA — 136 3,071 1,596 774 4,029 — — 4,803 3,191 1989 1997 (1) 7375 Boston Boulevard, Building Ten Office Springfield, VA — 23 2,685 1,032 93 3,647 — — 3,740 2,606 1988 1997 (1) 7374 Boston Boulevard, Building Four Office Springfield, VA — 241 1,605 1,828 398 3,276 — — 3,674 2,779 1984 1997 (1) 7451 Boston Boulevard, Building Two Office Springfield, VA — 249 1,542 1,667 613 2,845 — — 3,458 2,610 1982 1997 (1) Signature at Reston Residential Reston, VA — 27,076 190,580 393 27,076 190,973 — — 218,049 8,773 2018 2013 (1) Proto Kendall Square Residential Cambridge, MA — 9,243 127,248 2,939 9,245 130,185 — — 139,430 4,566 2018 2015 (1) The Avant at Reston Town Center Residential Reston, VA — 20,350 91,995 830 20,350 92,825 — — 113,175 14,728 2014 2010 (1) The Lofts at Atlantic Wharf Residential Boston, MA — 3,529 54,891 1,897 3,529 56,788 — — 60,317 12,639 2011 2007 (1) Boston Marriott Cambridge Hotel Cambridge, MA — 478 37,918 35,813 1,201 73,008 — — 74,209 46,605 1986/2017 1997 (1) Kendall Center Green Garage Garage Cambridge, MA — — 35,035 7,329 103 42,261 — — 42,364 13,512 1984 2006 (1) Kendall Center Yellow Garage Garage Cambridge, MA — 1,256 15,697 1,552 1,434 17,071 — — 18,505 6,031 2006 2004 (1) Kendall Center Blue Garage Garage Cambridge, MA — 1,163 11,633 2,151 1,579 13,368 — — 14,947 9,728 1990 1997 (1) The Skylyne (MacArthur Station Residences) Development Oakland, CA — — — 226,526 29,807 — — 196,719 226,526 — N/A N/A N/A 2100 Pennsylvania Avenue Development Washington, DC — — — 224,380 185,129 — — 39,251 224,380 1,024 N/A N/A N/A Reston Gateway Development Reston, VA — — — 150,632 — — — 150,632 150,632 — N/A 1998 N/A 17Fifty Presidents Street Development Reston, VA — — — 99,816 — — — 99,816 99,816 — N/A 2013 N/A Boston Properties, Inc. Schedule 3 - Real Estate and Accumulated Depreciation December 31, 2019 (dollars in thousands) Property Name Type Location Encumbrances Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Land Building 20 CityPoint Development Waltham, MA — 4,721 52,039 20,007 4,721 52,039 — 20,007 76,767 1,136 N/A 2007 N/A 325 Main Street Development Cambridge, MA — 174 — 68,903 965 — — 68,112 69,077 — N/A 1997 N/A North First Master Plan Land San Jose, CA — 35,004 — 3,932 — — 38,936 — 38,936 — N/A 2007 N/A Plaza at Almaden Land San Jose, CA — — — 34,889 — — 34,889 — 34,889 — N/A 2006 N/A 425 Fourth Street Land San Francisco, CA — — — 22,074 — — 22,074 — 22,074 — N/A N/A N/A Springfield Metro Center Land Springfield, VA — — — 19,844 — — 19,844 — 19,844 — N/A 2007 N/A Reston Gateway Master Plan Land Reston, VA — — — 18,292 — — 18,292 — 18,292 — N/A 1998 N/A 214 Third Avenue Land Waltham, MA — — — 17,692 — — 17,692 — 17,692 — N/A 2006 N/A 103 Fourth Avenue Land Waltham, MA — — — 12,826 — — 12,826 — 12,826 — N/A 2007 N/A Crane Meadow Land Marlborough, MA — — — 8,866 — — 8,866 — 8,866 — N/A 2000 N/A Broad Run Business Park Land Loudoun County, VA — — — 2,396 — — 2,396 — 2,396 — N/A 1998 N/A Kendall Center Master Plan Land Cambridge, MA — — — 1,693 — — 1,693 — 1,693 — N/A 1997 N/A Weston Quarry Land Weston, MA — — — 1,249 — — 1,249 — 1,249 — N/A 2001 N/A Reston Overlook Master Plan Land Reston, VA — — — 39 — — 39 — 39 — N/A 2000 N/A $ 2,922,408 (2 ) $ 5,024,060 $ 13,057,336 $ 4,763,301 $ 5,474,337 (3 ) $ 16,325,796 (4 ) $ 254,828 (5 ) $ 789,736 $ 22,844,697 $ 5,239,179 Note: Total Real Estate does not include Furniture, Fixtures and Equipment totaling approximately $44,313 . Accumulated Depreciation does not include approximately $27,619 of accumulated depreciation related to Furniture, Fixtures and Equipment. The aggregate cost and accumulated depreciation for tax purposes was approximately $18.6 billion and $4.0 billion , respectively. (1) Depreciation of the buildings and improvements are calculated over lives ranging from the life of the lease to 40 years. (2) Includes unamortized deferred financing costs totaling approximately $(26.7) million . (3) Includes Right of Use Assets - Finance Leases and Right of Use Assets - Operating Leases of approximately $214,091 and $148,640 , respectively. (4) Includes Right of Use Assets - Finance Leases of approximately $23,303 . (5) Includes pre-development costs. Boston Properties, Inc. Real Estate and Accumulated Depreciation December 31, 2019 , 2018 and 2017 (dollars in thousands) A summary of activity for real estate and accumulated depreciation is as follows: 2019 2018 2017 Real Estate: Balance at the beginning of the year $ 21,605,545 $ 21,058,714 $ 20,114,576 Additions to/improvements of real estate 1,671,898 1,043,379 1,099,286 Assets sold/written-off (432,746 ) (496,548 ) (155,148 ) Balance at the end of the year $ 22,844,697 $ 21,605,545 $ 21,058,714 Accumulated Depreciation: Balance at the beginning of the year $ 4,871,102 $ 4,566,570 $ 4,201,891 Depreciation expense 564,938 533,342 497,059 Assets sold/written-off (196,861 ) (228,810 ) (132,380 ) Balance at the end of the year $ 5,239,179 $ 4,871,102 $ 4,566,570 Note: Real Estate and Accumulated Depreciation amounts do not include Furniture, Fixtures and Equipment.
Boston Properties Limited Partnership
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate and Accumulated Depreciation Disclosure [Text Block]	Boston Properties Limited Partnership Schedule 3—Real Estate and Accumulated Depreciation December 31, 2019 (dollars in thousands) Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Property Name Type Location Encumbrances Land Building 767 Fifth Avenue (the General Motors Building) Office New York, NY $ 2,274,028 $ 1,796,252 $ 1,532,654 $ 202,612 $ 1,796,252 $ 1,735,266 $ — $ — $ 3,531,518 $ 313,158 1968/2019 2013 (1) Prudential Center Office Boston, MA — 92,077 948,357 496,088 100,540 1,433,306 2,676 — 1,536,522 580,797 1965/1993/2002/2016-2017 1998/1999/2000 (1) Embarcadero Center Office San Francisco, CA — 179,697 847,410 352,847 180,420 1,199,534 — — 1,379,954 617,163 1970/1989 1998-1999 (1) 399 Park Avenue Office New York, NY — 339,200 700,358 240,911 339,200 941,269 — — 1,280,469 343,191 1961/2018 2002 (1) 601 Lexington Avenue Office New York, NY 644,778 241,600 494,782 417,816 279,281 661,822 — 213,095 1,154,198 280,028 1977/1997 2001 (1) Salesforce Tower Office San Francisco, CA — 200,349 946,205 — 200,349 946,205 — — 1,146,554 38,727 2018 2013 (1) 200 Clarendon Street and Garage Office Boston, MA — 219,543 667,884 210,160 250,134 829,529 17,924 — 1,097,587 214,533 1976 2010 (1) 250 West 55th Street Office New York, NY — 285,263 603,167 51,928 285,263 655,095 — — 940,358 116,857 2014 2007 (1) 100 Federal Street Office Boston, MA — 131,067 435,954 102,984 131,067 538,938 — — 670,005 122,799 1971-1975/2017 2012 (1) Times Square Tower Office New York, NY — 165,413 380,438 75,243 159,694 461,400 — — 621,094 207,272 2004 2000 (1) Carnegie Center Office Princeton, NJ — 142,666 316,856 137,317 90,498 451,661 54,680 — 596,839 204,380 1983-2016 1998/1999/2000/2007/2014/2017/2019 (1) Atlantic Wharf Office Boston, MA — 63,988 454,537 18,709 63,988 473,246 — — 537,234 131,828 2011 2007 (1) 510 Madison Avenue Office New York, NY — 103,000 253,665 25,495 103,000 279,160 — — 382,160 72,213 2012 2010 (1) Fountain Square Office Reston, VA — 56,853 306,298 12,140 56,853 318,438 — — 375,291 78,498 1986-1990 2012 (1) 599 Lexington Avenue Office New York, NY — 81,040 100,507 161,330 81,040 261,837 — — 342,877 176,101 1986 1997 (1) 680 Folsom Street Office San Francisco, CA — 72,545 219,766 7,907 72,545 227,673 — — 300,218 46,777 2014 2012 (1) 2200 Pennsylvania Avenue Office Washington, DC — — 183,541 113,627 109,038 188,130 — — 297,168 59,190 2011 2008 (1) 145 Broadway Office Cambridge, MA — 121 273,013 23,043 23,164 273,013 — — 296,177 1,511 2019 1997 (1) South of Market and Democracy Tower Office Reston, VA — 13,603 237,479 26,079 13,603 263,558 — — 277,161 99,406 2008-2009 2003 (1) 601 Massachusetts Avenue Office Washington, DC — 95,310 165,173 3,933 95,310 169,106 — — 264,416 24,502 2016 2008 (1) Bay Colony Corporate Center Office Waltham, MA — 18,789 148,451 80,077 18,789 228,528 — — 247,317 79,824 1985-1989 2011 (1) Gateway Center Office San Francisco, CA — 28,255 139,245 55,402 29,029 193,873 — — 222,902 104,993 1984/1986/2002 1999 (1) 535 Mission Street Office San Francisco, CA — 40,933 148,378 3,276 40,933 151,654 — — 192,587 26,293 2015 2013 (1) Mountain View Research Park Office Mountain View, CA — 95,066 68,373 12,704 95,066 81,077 — — 176,143 19,807 1977-1981/2007-2013 2013 (1) Reservoir Place Office Waltham, MA — 18,605 104,124 49,643 19,089 153,283 — — 172,372 69,794 1955/1987/2017 1997/1998 (1) 1330 Connecticut Avenue Office Washington, DC — 25,982 82,311 32,234 25,982 114,545 — — 140,527 31,553 1984/2018 2004 (1) Kingstowne Towne Center Office Alexandria, VA — 18,021 109,038 3,212 18,021 112,250 — — 130,271 44,258 2003-2006 2007 (1) One Freedom Square Office Reston, VA — 9,929 84,504 28,735 9,883 113,285 — — 123,168 57,516 2000 2003 (1) Weston Corporate Center Office Weston, MA — 25,753 92,312 (123 ) 25,854 92,088 — — 117,942 29,227 2010 2001 (1) Capital Gallery Office Washington, DC — 4,725 29,565 78,573 6,128 106,735 — — 112,863 68,953 1981/2006 2007 (1) Two Freedom Square Office Reston, VA — 13,930 77,739 16,997 13,866 94,800 — — 108,666 49,028 2001 2003 (1) Boston Properties Limited Partnership Schedule 3—Real Estate and Accumulated Depreciation December 31, 2019 (dollars in thousands) Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Property Name Type Location Encumbrances Land Building One and Two Reston Overlook Office Reston, VA — 16,456 66,192 19,763 15,074 87,337 — — 102,411 50,336 1999 2000 (1) 355 Main Street Office Cambridge, MA — 18,863 53,346 27,284 21,098 78,395 — — 99,493 26,362 1981/1996/2013 2006 (1) 140 Kendrick Street Office Needham, MA — 18,095 66,905 13,584 18,095 80,489 — — 98,584 34,667 2000 2004 (1) Discovery Square Office Reston, VA — 11,198 71,782 15,360 11,146 87,194 — — 98,340 42,152 2001 2003 (1) 880 & 890 Winter Street Office Waltham, MA — 29,510 65,812 — 29,510 65,812 — — 95,322 1,458 1998-1999 2019 (1) 10 CityPoint Office Waltham, MA — 1,953 85,752 4,534 2,127 90,112 — — 92,239 10,928 2016 1997 (1) 90 Broadway Office Cambridge, MA — 19,104 52,078 19,678 20,741 70,119 — — 90,860 23,581 1983/1998/2013 2006 (1) 77 CityPoint Office Waltham, MA — 13,847 60,383 10,451 13,997 70,684 — — 84,681 27,148 2008 2001 (1) 230 CityPoint Office Waltham, MA — 13,189 49,823 20,440 13,403 70,049 — — 83,452 28,831 1992 2005 (1) Waltham Weston Corporate Center Office Waltham, MA — 10,385 60,694 10,178 10,350 70,907 — — 81,257 34,777 2003 1999 (1) 3625-3635 Peterson Way Office Santa Clara, CA — 63,206 14,879 752 63,206 14,879 752 — 78,837 11,172 1979 2016 (1) 2440 West El Camino Real Office Mountain View, CA — 16,741 51,285 5,454 16,741 56,739 — — 73,480 13,090 1987/2003 2011 (1) 191 Spring Street Office Lexington, MA — 2,850 59,751 7,063 2,850 66,814 — — 69,664 21,801 1971/1995/2018 1997 (1) 300 Binney Street Office Cambridge, MA — 18,080 51,262 140 18,080 51,402 — — 69,482 11,146 2013 2009 (1) Wisconsin Place Office Chevy Chase, MD — — 53,349 14,924 — 68,273 — — 68,273 25,934 2009 2004 (1) Reston Corporate Center Office Reston, VA — 9,135 50,857 3,625 9,496 54,121 — — 63,617 29,170 1984 1998 (1) New Dominion Technology Park, Bldg. Two Office Herndon, VA — 5,584 51,868 412 5,574 52,290 — — 57,864 25,900 2004 1998 (1) 255 Main Street Office Cambridge, MA — 134 25,110 32,468 134 57,578 — — 57,712 33,108 1987 1997 (1) University Place Office Cambridge, MA 3,602 — 37,091 14,551 7,055 44,587 — — 51,642 29,044 1985 1998 (1) Sumner Square Office Washington, DC — 624 28,745 19,264 3,015 45,618 — — 48,633 26,547 1985 1999 (1) New Dominion Technology Park, Bldg. One Office Herndon, VA — 3,880 43,227 1,117 3,880 44,344 — — 48,224 28,398 2001 1998 (1) 200 West Street Office Waltham, MA — 16,148 24,983 5,550 16,148 28,429 — 2,104 46,681 16,298 1999 1997 (1) North First Business Park Office San Jose, CA — 23,398 13,069 4,548 23,371 17,644 — — 41,015 16,411 1981 2007 (1) 150 Broadway Office Cambridge, MA — 850 25,042 6,535 822 31,605 — — 32,427 19,342 1999 1997 (1) 105 Broadway Office Cambridge, MA — 1,299 12,943 9,300 1,868 21,674 — — 23,542 11,312 1990 1997 (1) Lexington Office Park Office Lexington, MA — 998 1,426 17,783 1,073 19,134 — — 20,207 14,114 1982 1997 (1) 201 Spring Street Office Lexington, MA — 2,849 15,303 73 2,849 15,376 — — 18,225 8,295 1997 1997 (1) The Point Office Waltham, MA — 6,395 10,040 421 6,492 10,364 — — 16,856 1,349 2015 2007 (1) 33 Hayden Avenue Office Lexington, MA — 266 3,234 12,261 266 15,495 — — 15,761 5,510 1979 1997 (1) 690 Folsom Street Office San Francisco, CA — 3,219 11,038 1,157 3,219 12,195 — — 15,414 2,284 2015 2012 (1) 92-100 Hayden Avenue Office Lexington, MA — 594 6,748 6,800 619 13,523 — — 14,142 11,847 1985 1997 (1) 181 Spring Street Office Lexington, MA — 1,066 9,520 1,800 1,066 11,320 — — 12,386 5,498 1999 1997 (1) 195 West Street Office Waltham, MA — 1,611 6,652 3,229 1,611 9,881 — — 11,492 8,087 1990 1997 (1) 7501 Boston Boulevard, Building Seven Office Springfield, VA — 665 9,273 311 665 9,584 — — 10,249 5,257 1997 1997 (1) Boston Properties Limited Partnership Schedule 3—Real Estate and Accumulated Depreciation December 31, 2019 (dollars in thousands) Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Property Name Type Location Encumbrances Land Building 7435 Boston Boulevard, Building One Office Springfield, VA — 392 3,822 4,290 486 8,018 — — 8,504 6,162 1982 1997 (1) 7450 Boston Boulevard, Building Three Office Springfield, VA — 1,165 4,681 2,177 1,327 6,696 — — 8,023 3,462 1987 1998 (1) 32 Hartwell Avenue Office Lexington, MA — 168 1,943 5,529 168 7,472 — — 7,640 1,819 1968/1979/1987 1997 (1) 250 Binney Street Office Cambridge, MA — 110 4,483 2,939 110 7,422 — — 7,532 5,660 1983 1997 (1) 8000 Grainger Court, Building Five Office Springfield, VA — 366 4,282 2,604 453 6,799 — — 7,252 5,597 1984 1997 (1) 453 Ravendale Drive Office Mountain View, CA — 5,477 1,090 676 5,477 1,766 — — 7,243 690 1977 2012 (1) 7300 Boston Boulevard, Building Thirteen Office Springfield, VA — 608 4,773 795 608 5,568 — — 6,176 1,928 2002 1997 (1) 17 Hartwell Avenue Office Lexington, MA — 26 150 5,907 26 6,057 — — 6,083 1,924 1968 1997 (1) 7601 Boston Boulevard, Building Eight Office Springfield, VA — 200 878 4,367 378 5,067 — — 5,445 4,507 1986 1997 (1) 7500 Boston Boulevard, Building Six Office Springfield, VA — 138 3,749 1,107 234 4,760 — — 4,994 4,097 1985 1997 (1) 8000 Corporate Court, Building Eleven Office Springfield, VA — 136 3,071 1,245 686 3,766 — — 4,452 3,094 1989 1997 (1) 7375 Boston Boulevard, Building Ten Office Springfield, VA — 23 2,685 851 47 3,512 — — 3,559 2,562 1988 1997 (1) 7374 Boston Boulevard, Building Four Office Springfield, VA — 241 1,605 1,445 303 2,988 — — 3,291 2,681 1984 1997 (1) 7451 Boston Boulevard, Building Two Office Springfield, VA — 249 1,542 1,354 535 2,610 — — 3,145 2,526 1982 1997 (1) Signature at Reston Residential Reston, VA — 27,076 190,580 393 27,076 190,973 — — 218,049 8,773 2018 2013 (1) Proto Kendall Square Residential Cambridge, MA — 9,243 127,248 2,939 9,245 130,185 — — 139,430 4,566 2018 2015 (1) The Avant at Reston Town Center Residential Reston, VA — 20,350 91,995 830 20,350 92,825 — — 113,175 14,728 2014 2010 (1) The Lofts at Atlantic Wharf Residential Boston, MA — 3,529 54,891 1,897 3,529 56,788 — — 60,317 12,639 2011 2007 (1) Boston Marriott Cambridge Hotel Cambridge, MA — 478 37,918 32,922 478 70,840 — — 71,318 45,842 1986/2017 1997 (1) Kendall Center Green Garage Garage Cambridge, MA — — 35,035 6,915 — 41,950 — — 41,950 13,404 1984 2006 (1) Kendall Center Yellow Garage Garage Cambridge, MA — 1,256 15,697 840 1,256 16,537 — — 17,793 5,847 2006 2004 (1) Kendall Center Blue Garage Garage Cambridge, MA — 1,163 11,633 486 1,163 12,119 — — 13,282 9,290 1990 1997 (1) The Skylyne (MacArthur Station Residences) Development Oakland, CA — — — 226,526 29,807 — — 196,719 226,526 — N/A N/A N/A 2100 Pennsylvania Avenue Development Washington, DC — — — 224,380 185,129 — — 39,251 224,380 1,024 N/A N/A N/A Reston Gateway Development Reston, VA — — — 150,632 — — — 150,632 150,632 — N/A 1998 N/A 17Fifty Presidents Street Development Reston, VA — — — 99,816 — — — 99,816 99,816 — N/A 2013 N/A 20 CityPoint Development Waltham, MA — 4,721 52,039 20,007 4,721 52,039 — 20,007 76,767 1,136 N/A 2007 N/A 325 Main Street Development Cambridge, MA — 174 — 68,710 772 — — 68,112 68,884 — N/A 1997 N/A North First Master Plan Land San Jose, CA — 35,004 — 3,932 — — 38,936 — 38,936 — N/A 2007 N/A Plaza at Almaden Land San Jose, CA — — — 34,889 — — 34,889 — 34,889 — N/A 2006 N/A Boston Properties Limited Partnership Schedule 3—Real Estate and Accumulated Depreciation December 31, 2019 (dollars in thousands) Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Property Name Type Location Encumbrances Land Building 425 Fourth Street Land San Francisco, CA — — — 22,074 — — 22,074 — 22,074 — N/A N/A N/A Springfield Metro Center Land Springfield, VA — — — 19,844 — — 19,844 — 19,844 — N/A 2007 N/A Reston Gateway Master Plan Land Reston, VA — — — 18,292 — — 18,292 — 18,292 — N/A 1998 N/A 214 Third Avenue Land Waltham, MA — — — 17,692 — — 17,692 — 17,692 — N/A 2006 N/A 103 Fourth Avenue Land Waltham, MA — — — 12,826 — — 12,826 — 12,826 — N/A 2007 N/A Crane Meadow Land Marlborough, MA — — — 8,866 — — 8,866 — 8,866 — N/A 2000 N/A Broad Run Business Park Land Loudoun County, VA — — — 2,396 — — 2,396 — 2,396 — N/A 1998 N/A Kendall Center Master Plan Land Cambridge, MA — — — 1,693 — — 1,693 — 1,693 — N/A 1997 N/A Weston Quarry Land Weston, MA — — — 1,249 — — 1,249 — 1,249 — N/A 2001 N/A Reston Overlook Master Plan Land Reston, VA — — — 39 — — 39 — 39 — N/A 2000 N/A $ 2,922,408 (2 ) $ 5,024,060 $ 13,057,336 $ 4,368,080 $ 5,373,884 (3 ) $ 16,031,028 (4 ) $ 254,828 (5 ) $ 789,736 $ 22,449,476 $ 5,135,289 Note: Total Real Estate does not include Furniture, Fixtures and Equipment totaling approximately $44,313 . Accumulated Depreciation does not include approximately $27,619 of accumulated depreciation related to Furniture, Fixtures and Equipment. The aggregate cost and accumulated depreciation for tax purposes was approximately $20.7 billion and $4.5 billion , respectively. (1) Depreciation of the buildings and improvements are calculated over lives ranging from the life of the lease to 40 years. (2) Includes unamortized deferred financing costs totaling approximately $(26.7) million . (3) Includes Right of Use Assets - Finance Leases and Right of Use Assets - Operating Leases of approximately $214,091 and $148,640 , respectively. (4) Includes Right of Use Assets - Finance Leases of approximately $23,303 . (5) Includes pre-development costs. Boston Properties Limited Partnership Real Estate and Accumulated Depreciation December 31, 2019 , 2018 and 2017 (dollars in thousands) A summary of activity for real estate and accumulated depreciation is as follows: 2019 2018 2017 Real Estate: Balance at the beginning of the year $ 21,207,189 $ 20,647,236 $ 19,701,185 Additions to/improvements of real estate 1,671,898 1,043,379 1,099,286 Assets sold/written-off (429,611 ) (483,426 ) (153,235 ) Balance at the end of the year $ 22,449,476 $ 21,207,189 $ 20,647,236 Accumulated Depreciation: Balance at the beginning of the year $ 4,773,800 $ 4,473,895 $ 4,116,020 Depreciation expense 557,130 525,584 488,919 Assets sold/written-off (195,641 ) (225,679 ) (131,044 ) Balance at the end of the year $ 5,135,289 $ 4,773,800 $ 4,473,895 Note: Real Estate and Accumulated Depreciation amounts do not include Furniture, Fixtures and Equipment.

Real Estate and Accumulated D_2

Real Estate and Accumulated Depreciation Activity of Real Estate and Accumulated Depreciation (Notes)	12 Months Ended
	Dec. 31, 2019
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation Disclosure [Abstract]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation Disclosure [Text Block]	Item 15. Exhibits and Financial Statement Schedules (a) Financial Statement Schedule Boston Properties, Inc. Schedule 3 - Real Estate and Accumulated Depreciation December 31, 2019 (dollars in thousands) Property Name Type Location Encumbrances Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Land Building 767 Fifth Avenue (the General Motors Building) Office New York, NY $ 2,274,028 $ 1,796,252 $ 1,532,654 $ 202,612 $ 1,796,252 $ 1,735,266 $ — $ — $ 3,531,518 $ 313,158 1968/2019 2013 (1) Prudential Center Office Boston, MA — 92,077 948,357 556,458 115,638 1,478,578 2,676 — 1,596,892 596,740 1965/1993/2002/2016-2017 1998/1999/2000 (1) Embarcadero Center Office San Francisco, CA — 179,697 847,410 415,228 195,987 1,246,348 — — 1,442,335 633,711 1970/1989 1998-1999 (1) 399 Park Avenue Office New York, NY — 339,200 700,358 300,519 354,107 985,970 — — 1,340,077 358,960 1961/2018 2002 (1) 601 Lexington Avenue Office New York, NY 644,778 241,600 494,782 454,902 289,639 688,550 — 213,095 1,191,284 289,482 1977/1997 2001 (1) Salesforce Tower Office San Francisco, CA — 200,349 946,205 — 200,349 946,205 — — 1,146,554 38,727 2018 2013 (1) 200 Clarendon Street and Garage Office Boston, MA — 219,543 667,884 210,160 250,134 829,529 17,924 — 1,097,587 214,533 1976 2010 (1) 250 West 55th Street Office New York, NY — 285,263 603,167 51,928 285,263 655,095 — — 940,358 116,857 2014 2007 (1) 100 Federal Street Office Boston, MA — 131,067 435,954 102,984 131,067 538,938 — — 670,005 122,799 1971-1975/2017 2012 (1) Times Square Tower Office New York, NY — 165,413 380,438 113,222 169,193 489,880 — — 659,073 217,303 2004 2000 (1) Carnegie Center Office Princeton, NJ — 142,666 316,856 152,280 94,240 462,882 54,680 — 611,802 208,331 1983-2016 1998/1999/2000/2007/2014/2017/2019 (1) Atlantic Wharf Office Boston, MA — 63,988 454,537 18,709 63,988 473,246 — — 537,234 131,828 2011 2007 (1) 510 Madison Avenue Office New York, NY — 103,000 253,665 25,495 103,000 279,160 — — 382,160 72,213 2012 2010 (1) Fountain Square Office Reston, VA — 56,853 306,298 12,140 56,853 318,438 — — 375,291 78,498 1986-1990 2012 (1) 599 Lexington Avenue Office New York, NY — 81,040 100,507 188,572 87,852 282,267 — — 370,119 183,291 1986 1997 (1) 680 Folsom Street Office San Francisco, CA — 72,545 219,766 7,907 72,545 227,673 — — 300,218 46,777 2014 2012 (1) 2200 Pennsylvania Avenue Office Washington, DC — — 183,541 113,627 109,038 188,130 — — 297,168 59,190 2011 2008 (1) 145 Broadway Office Cambridge, MA — 121 273,013 23,246 23,367 273,013 — — 296,380 1,511 2019 1997 (1) South of Market and Democracy Tower Office Reston, VA — 13,603 237,479 26,415 13,687 263,810 — — 277,497 99,478 2008-2009 2003 (1) 601 Massachusetts Avenue Office Washington, DC — 95,310 165,173 3,945 95,322 169,106 — — 264,428 24,502 2016 2008 (1) Bay Colony Corporate Center Office Waltham, MA — 18,789 148,451 80,077 18,789 228,528 — — 247,317 79,824 1985-1989 2011 (1) Gateway Center Office San Francisco, CA — 28,255 139,245 61,791 30,627 198,664 — — 229,291 106,680 1984/1986/2002 1999 (1) 535 Mission Street Office San Francisco, CA — 40,933 148,378 3,276 40,933 151,654 — — 192,587 26,293 2015 2013 (1) Reservoir Place Office Waltham, MA — 18,605 104,124 53,718 20,108 156,339 — — 176,447 70,870 1955/1987/2017 1997/1998 (1) Mountain View Research Park Office Mountain View, CA — 95,066 68,373 12,704 95,066 81,077 — — 176,143 19,807 1977-1981/2007-2013 2013 (1) 1330 Connecticut Avenue Office Washington, DC — 25,982 82,311 36,847 27,135 118,005 — — 145,140 32,775 1984/2018 2004 (1) Boston Properties, Inc. Schedule 3 - Real Estate and Accumulated Depreciation December 31, 2019 (dollars in thousands) Property Name Type Location Encumbrances Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Land Building Kingstowne Towne Center Office Alexandria, VA — 18,021 109,038 3,376 18,062 112,373 — — 130,435 44,294 2003-2006 2007 (1) One Freedom Square Office Reston, VA — 9,929 84,504 34,372 11,293 117,512 — — 128,805 59,006 2000 2003 (1) Capital Gallery Office Washington, DC — 4,725 29,565 88,704 8,662 114,332 — — 122,994 71,631 1981/2006 2007 (1) Weston Corporate Center Office Weston, MA — 25,753 92,312 (123 ) 25,854 92,088 — — 117,942 29,227 2010 2001 (1) Two Freedom Square Office Reston, VA — 13,930 77,739 23,209 15,420 99,458 — — 114,878 50,668 2001 2003 (1) One and Two Reston Overlook Office Reston, VA — 16,456 66,192 24,181 16,179 90,650 — — 106,829 51,503 1999 2000 (1) Discovery Square Office Reston, VA — 11,198 71,782 20,905 12,533 91,352 — — 103,885 43,619 2001 2003 (1) 140 Kendrick Street Office Needham, MA — 18,095 66,905 17,574 19,092 83,482 — — 102,574 35,721 2000 2004 (1) 355 Main Street Office Cambridge, MA — 18,863 53,346 27,582 21,173 78,618 — — 99,791 26,439 1981/1996/2013 2006 (1) 880 & 890 Winter Street Office Waltham, MA — 29,510 65,812 — 29,510 65,812 — — 95,322 1,458 1998-1999 2019 (1) 10 CityPoint Office Waltham, MA — 1,953 85,752 4,697 2,290 90,112 — — 92,402 10,928 2016 1997 (1) 90 Broadway Office Cambridge, MA — 19,104 52,078 19,857 20,785 70,254 — — 91,039 23,621 1983/1998/2013 2006 (1) 230 CityPoint Office Waltham, MA — 13,189 49,823 22,057 13,807 71,262 — — 85,069 29,255 1992 2005 (1) 77 CityPoint Office Waltham, MA — 13,847 60,383 10,556 14,023 70,763 — — 84,786 27,172 2008 2001 (1) Waltham Weston Corporate Center Office Waltham, MA — 10,385 60,694 13,165 11,097 73,147 — — 84,244 35,567 2003 1999 (1) 3625-3635 Peterson Way Office Santa Clara, CA — 63,206 14,879 752 63,206 14,879 752 — 78,837 11,172 1979 2016 (1) 2440 West El Camino Real Office Mountain View, CA — 16,741 51,285 5,454 16,741 56,739 — — 73,480 13,090 1987/2003 2011 (1) 191 Spring Street Office Lexington, MA — 2,850 59,751 7,695 3,151 67,145 — — 70,296 21,917 1971/1995/2018 1997 (1) 300 Binney Street Office Cambridge, MA — 18,080 51,262 140 18,080 51,402 — — 69,482 11,146 2013 2009 (1) Wisconsin Place Office Chevy Chase, MD — — 53,349 14,924 — 68,273 — — 68,273 25,934 2009 2004 (1) Reston Corporate Center Office Reston, VA — 9,135 50,857 6,236 10,148 56,080 — — 66,228 29,860 1984 1998 (1) New Dominion Technology Park, Bldg. Two Office Herndon, VA — 5,584 51,868 4,157 6,510 55,099 — — 61,609 26,894 2004 1998 (1) 255 Main Street Office Cambridge, MA — 134 25,110 34,124 548 58,820 — — 59,368 33,543 1987 1997 (1) University Place Office Cambridge, MA 3,602 — 37,091 16,001 7,418 45,674 — — 53,092 29,423 1985 1998 (1) New Dominion Technology Park, Bldg. One Office Herndon, VA — 3,880 43,227 3,927 4,583 46,451 — — 51,034 29,141 2001 1998 (1) Sumner Square Office Washington, DC — 624 28,745 21,344 3,535 47,178 — — 50,713 27,093 1985 1999 (1) 200 West Street Office Waltham, MA — 16,148 24,983 8,211 16,813 30,425 — 2,104 49,342 17,001 1999 1997 (1) North First Business Park Office San Jose, CA — 23,398 13,069 4,571 23,377 17,661 — — 41,038 16,411 1981 2007 (1) 150 Broadway Office Cambridge, MA — 850 25,042 8,540 1,323 33,109 — — 34,432 19,875 1999 1997 (1) 105 Broadway Office Cambridge, MA — 1,299 12,943 11,406 2,395 23,253 — — 25,648 11,870 1990 1997 (1) Lexington Office Park Office Lexington, MA — 998 1,426 18,547 1,264 19,707 — — 20,971 14,312 1982 1997 (1) 201 Spring Street Office Lexington, MA — 2,849 15,303 1,172 3,124 16,200 — — 19,324 8,587 1997 1997 (1) The Point Office Waltham, MA — 6,395 10,040 421 6,492 10,364 — — 16,856 1,349 2015 2007 (1) 33 Hayden Avenue Office Lexington, MA — 266 3,234 12,898 425 15,973 — — 16,398 5,678 1979 1997 (1) 690 Folsom Street Office San Francisco, CA — 3,219 11,038 1,157 3,219 12,195 — — 15,414 2,284 2015 2012 (1) Boston Properties, Inc. Schedule 3 - Real Estate and Accumulated Depreciation December 31, 2019 (dollars in thousands) Property Name Type Location Encumbrances Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Land Building 92-100 Hayden Avenue Office Lexington, MA — 594 6,748 7,529 802 14,069 — — 14,871 12,041 1985 1997 (1) 181 Spring Street Office Lexington, MA — 1,066 9,520 2,177 1,160 11,603 — — 12,763 5,597 1999 1997 (1) 195 West Street Office Waltham, MA — 1,611 6,652 4,218 1,858 10,623 — — 12,481 8,352 1990 1997 (1) 7501 Boston Boulevard, Building Seven Office Springfield, VA — 665 9,273 816 791 9,963 — — 10,754 5,393 1997 1997 (1) 7435 Boston Boulevard, Building One Office Springfield, VA — 392 3,822 4,983 659 8,538 — — 9,197 6,344 1982 1997 (1) 7450 Boston Boulevard, Building Three Office Springfield, VA — 1,165 4,681 2,591 1,430 7,007 — — 8,437 3,575 1987 1998 (1) 32 Hartwell Avenue Office Lexington, MA — 168 1,943 6,115 314 7,912 — — 8,226 1,975 1968/1979/1987 1997 (1) 250 Binney Street Office Cambridge, MA — 110 4,483 3,593 273 7,913 — — 8,186 5,829 1983 1997 (1) 8000 Grainger Court, Building Five Office Springfield, VA — 366 4,282 3,198 601 7,245 — — 7,846 5,752 1984 1997 (1) 453 Ravendale Drive Office Mountain View, CA — 5,477 1,090 676 5,477 1,766 — — 7,243 690 1977 2012 (1) 7300 Boston Boulevard, Building Thirteen Office Springfield, VA — 608 4,773 1,007 661 5,727 — — 6,388 1,984 2002 1997 (1) 17 Hartwell Avenue Office Lexington, MA — 26 150 6,064 65 6,175 — — 6,240 1,966 1968 1997 (1) 7601 Boston Boulevard, Building Eight Office Springfield, VA — 200 878 5,060 551 5,587 — — 6,138 4,689 1986 1997 (1) 7500 Boston Boulevard, Building Six Office Springfield, VA — 138 3,749 1,640 367 5,160 — — 5,527 4,237 1985 1997 (1) 8000 Corporate Court, Building Eleven Office Springfield, VA — 136 3,071 1,596 774 4,029 — — 4,803 3,191 1989 1997 (1) 7375 Boston Boulevard, Building Ten Office Springfield, VA — 23 2,685 1,032 93 3,647 — — 3,740 2,606 1988 1997 (1) 7374 Boston Boulevard, Building Four Office Springfield, VA — 241 1,605 1,828 398 3,276 — — 3,674 2,779 1984 1997 (1) 7451 Boston Boulevard, Building Two Office Springfield, VA — 249 1,542 1,667 613 2,845 — — 3,458 2,610 1982 1997 (1) Signature at Reston Residential Reston, VA — 27,076 190,580 393 27,076 190,973 — — 218,049 8,773 2018 2013 (1) Proto Kendall Square Residential Cambridge, MA — 9,243 127,248 2,939 9,245 130,185 — — 139,430 4,566 2018 2015 (1) The Avant at Reston Town Center Residential Reston, VA — 20,350 91,995 830 20,350 92,825 — — 113,175 14,728 2014 2010 (1) The Lofts at Atlantic Wharf Residential Boston, MA — 3,529 54,891 1,897 3,529 56,788 — — 60,317 12,639 2011 2007 (1) Boston Marriott Cambridge Hotel Cambridge, MA — 478 37,918 35,813 1,201 73,008 — — 74,209 46,605 1986/2017 1997 (1) Kendall Center Green Garage Garage Cambridge, MA — — 35,035 7,329 103 42,261 — — 42,364 13,512 1984 2006 (1) Kendall Center Yellow Garage Garage Cambridge, MA — 1,256 15,697 1,552 1,434 17,071 — — 18,505 6,031 2006 2004 (1) Kendall Center Blue Garage Garage Cambridge, MA — 1,163 11,633 2,151 1,579 13,368 — — 14,947 9,728 1990 1997 (1) The Skylyne (MacArthur Station Residences) Development Oakland, CA — — — 226,526 29,807 — — 196,719 226,526 — N/A N/A N/A 2100 Pennsylvania Avenue Development Washington, DC — — — 224,380 185,129 — — 39,251 224,380 1,024 N/A N/A N/A Reston Gateway Development Reston, VA — — — 150,632 — — — 150,632 150,632 — N/A 1998 N/A 17Fifty Presidents Street Development Reston, VA — — — 99,816 — — — 99,816 99,816 — N/A 2013 N/A Boston Properties, Inc. Schedule 3 - Real Estate and Accumulated Depreciation December 31, 2019 (dollars in thousands) Property Name Type Location Encumbrances Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Land Building 20 CityPoint Development Waltham, MA — 4,721 52,039 20,007 4,721 52,039 — 20,007 76,767 1,136 N/A 2007 N/A 325 Main Street Development Cambridge, MA — 174 — 68,903 965 — — 68,112 69,077 — N/A 1997 N/A North First Master Plan Land San Jose, CA — 35,004 — 3,932 — — 38,936 — 38,936 — N/A 2007 N/A Plaza at Almaden Land San Jose, CA — — — 34,889 — — 34,889 — 34,889 — N/A 2006 N/A 425 Fourth Street Land San Francisco, CA — — — 22,074 — — 22,074 — 22,074 — N/A N/A N/A Springfield Metro Center Land Springfield, VA — — — 19,844 — — 19,844 — 19,844 — N/A 2007 N/A Reston Gateway Master Plan Land Reston, VA — — — 18,292 — — 18,292 — 18,292 — N/A 1998 N/A 214 Third Avenue Land Waltham, MA — — — 17,692 — — 17,692 — 17,692 — N/A 2006 N/A 103 Fourth Avenue Land Waltham, MA — — — 12,826 — — 12,826 — 12,826 — N/A 2007 N/A Crane Meadow Land Marlborough, MA — — — 8,866 — — 8,866 — 8,866 — N/A 2000 N/A Broad Run Business Park Land Loudoun County, VA — — — 2,396 — — 2,396 — 2,396 — N/A 1998 N/A Kendall Center Master Plan Land Cambridge, MA — — — 1,693 — — 1,693 — 1,693 — N/A 1997 N/A Weston Quarry Land Weston, MA — — — 1,249 — — 1,249 — 1,249 — N/A 2001 N/A Reston Overlook Master Plan Land Reston, VA — — — 39 — — 39 — 39 — N/A 2000 N/A $ 2,922,408 (2 ) $ 5,024,060 $ 13,057,336 $ 4,763,301 $ 5,474,337 (3 ) $ 16,325,796 (4 ) $ 254,828 (5 ) $ 789,736 $ 22,844,697 $ 5,239,179 Note: Total Real Estate does not include Furniture, Fixtures and Equipment totaling approximately $44,313 . Accumulated Depreciation does not include approximately $27,619 of accumulated depreciation related to Furniture, Fixtures and Equipment. The aggregate cost and accumulated depreciation for tax purposes was approximately $18.6 billion and $4.0 billion , respectively. (1) Depreciation of the buildings and improvements are calculated over lives ranging from the life of the lease to 40 years. (2) Includes unamortized deferred financing costs totaling approximately $(26.7) million . (3) Includes Right of Use Assets - Finance Leases and Right of Use Assets - Operating Leases of approximately $214,091 and $148,640 , respectively. (4) Includes Right of Use Assets - Finance Leases of approximately $23,303 . (5) Includes pre-development costs. Boston Properties, Inc. Real Estate and Accumulated Depreciation December 31, 2019 , 2018 and 2017 (dollars in thousands) A summary of activity for real estate and accumulated depreciation is as follows: 2019 2018 2017 Real Estate: Balance at the beginning of the year $ 21,605,545 $ 21,058,714 $ 20,114,576 Additions to/improvements of real estate 1,671,898 1,043,379 1,099,286 Assets sold/written-off (432,746 ) (496,548 ) (155,148 ) Balance at the end of the year $ 22,844,697 $ 21,605,545 $ 21,058,714 Accumulated Depreciation: Balance at the beginning of the year $ 4,871,102 $ 4,566,570 $ 4,201,891 Depreciation expense 564,938 533,342 497,059 Assets sold/written-off (196,861 ) (228,810 ) (132,380 ) Balance at the end of the year $ 5,239,179 $ 4,871,102 $ 4,566,570 Note: Real Estate and Accumulated Depreciation amounts do not include Furniture, Fixtures and Equipment.

Organization (Policies)

Organization (Policies)	12 Months Ended
Organization (Policies)	Dec. 31, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements are presented using the accrual basis of accounting in conformity with accounting principles generally accepted in the United States of America. Boston Properties, Inc. does not have any other significant assets, liabilities or operations, other than its investment in Boston Properties Limited Partnership, nor does it have employees of its own. Boston Properties Limited Partnership, not Boston Properties, Inc., generally executes all significant business relationships other than transactions involving securities of Boston Properties, Inc. All majority-owned subsidiaries and joint ventures over which the Company has financial and operating control and variable interest entities (“VIEs”) in which the Company has determined it is the primary beneficiary are included in the consolidated financial statements. All significant intercompany balances and transactions have been eliminated in consolidation. The Company accounts for all other unconsolidated joint ventures using the equity method of accounting. Accordingly, the Company’s share of the earnings of these joint ventures and companies is included in consolidated net income.
Variable Interest Entities (VIEs)	Variable Interest Entities (VIEs)

Summary Of Significant Accoun_2

Summary Of Significant Accounting Policies (Policies)	12 Months Ended
Summary Of Significant Accounting Policies (Policies)	Dec. 31, 2019
Accounting Policies [Abstract]
Real Estate	Real Estate Upon acquisitions of real estate, the Company assesses whether the transaction should be accounted for as an asset acquisition or as a business combination by applying a screen to determine whether the integrated set of assets and activities acquired meets the definition of a business. Acquisitions of integrated sets of assets and activities that do not meet the definition of a business are accounted for as asset acquisitions. The Company’s acquisitions of real estate or in-substance real estate generally will not meet the definition of a business because substantially all of the fair value is concentrated in a single identifiable asset or group of similar identifiable assets (i.e. land, buildings, and related intangible assets) or because the acquisition does not include a substantive process in the form of an acquired workforce or an acquired contract that cannot be replaced without significant cost, effort or delay. The Company assesses the fair value of acquired tangible and intangible assets (including land, buildings, tenant improvements, “above-” and “below-market” leases, leasing and assumed financing origination costs, acquired in-place leases, other identified intangible assets and assumed liabilities) and allocates the purchase price to the acquired assets and assumed liabilities, including land and buildings as if vacant. The Company assesses fair value based on estimated cash flow projections that utilize discount and/or capitalization rates that it deems appropriate, as well as available market information. Estimates of future cash flows are based on a number of factors including the historical operating results, known and anticipated trends, and market and economic conditions. The fair value of the tangible assets of an acquired property considers the value of the property as if it were vacant. The Company also considers an allocation of purchase price of other acquired intangibles, including acquired in-place leases that may have a customer relationship intangible value, including (but not limited to) the nature and extent of the existing relationship with the tenants, the tenants’ credit quality and expectations of lease renewals. Based on its acquisitions to date, the Company’s allocation to customer relationship intangible assets has been immaterial. The Company records acquired “above-” and “below-market” leases at their fair values (using a discount rate which reflects the risks associated with the leases acquired) equal to the difference between (1) the contractual amounts to be paid pursuant to each in-place lease and (2) management’s estimate of fair market lease rates for each corresponding in-place lease, measured over a period equal to the remaining term of the lease for above-market leases and the initial term plus the term of any below-market fixed rate renewal options for below-market leases. Acquired “above-” and “below-market” lease values have been reflected within Prepaid Expenses and Other Assets and Other Liabilities, respectively, in the Company’s Consolidated Balance Sheets. Other intangible assets acquired include amounts for in-place lease values that are based on the Company’s evaluation of the specific characteristics of each tenant’s lease. Factors to be considered include estimates of carrying costs during hypothetical expected lease-up periods considering current market conditions, and costs to execute similar leases. In estimating carrying costs, the Company includes real estate taxes, insurance and other operating expenses and estimates of lost rentals at market rates during the expected lease-up periods, depending on local market conditions. In estimating costs to execute similar leases, the Company considers leasing commissions, legal and other related expenses. Management reviews its long-lived assets for impairment following the end of each quarter and when there is an event or change in circumstances that indicates carrying amounts may not be recoverable. An impairment loss is recognized if the carrying amount of an asset is not recoverable and exceeds its fair value. The evaluation of anticipated cash flows is subjective and is based in part on assumptions regarding anticipated hold periods, future occupancy, future rental rates, future capital requirements, discount rates and capitalization rates that could differ materially from actual results in future periods. Because cash flows on properties considered to be “long-lived assets to be held and used” are considered on an undiscounted basis to determine whether an asset has been impaired, the Company’s established strategy of holding properties over the long term directly decreases the likelihood of recording an impairment loss. If the Company’s strategy changes or market conditions otherwise dictate an earlier sale date, an impairment loss may be recognized and such loss could be material. If the Company determines that an impairment has occurred, the affected assets must be reduced to their fair value. Guidance in Accounting Standards Codification (“ASC”) 360 “Property Plant and Equipment” (“ASC 360”) requires that qualifying assets and liabilities and the results of operations that have been sold, or otherwise qualify as “held for sale,” be presented as discontinued operations in all periods presented if the property operations are expected to be eliminated and the Company will not have significant continuing involvement following the sale. Discontinued operations presentation applies only to disposals representing a strategic shift that has (or will have) a major effect on an entity’s operations and financial results (e.g., a disposal of a major geographical area, a major line of business, a major equity method investment or other major parts of an entity). The components of the property’s net income that are reflected as discontinued operations include the net gain (or loss) upon the disposition of the property held for sale, operating results, depreciation and interest expense (if the property is subject to a secured loan). The Company generally considers assets to be “held for sale” when the transaction has been approved by Boston Properties, Inc.’s Board of Directors, or a committee thereof, and there are no known significant contingencies relating to the sale, such that a sale of the property within one year is considered probable. Following the classification of a property as “held for sale,” no further depreciation is recorded on the assets, and the asset is written down to the lower of carrying value or fair market value, less cost to sell. Real estate is stated at depreciated cost. A variety of costs are incurred in the acquisition, development and leasing of properties. The cost of buildings and improvements includes the purchase price of property, legal fees and other acquisition costs. The Company capitalizes acquisition costs that it incurs to effect an asset acquisition and expenses acquisition costs that it incurs to effect a business combination, including legal, due diligence and other closing related costs. Costs directly related to the development of properties are capitalized. Capitalized development costs include interest, internal wages, property taxes, insurance, and other project costs incurred during the period of development. After the determination is made to capitalize a cost, it is allocated to the specific component of the project that benefited from the investment. Determination of when a development project commences and capitalization begins, and when a development project is substantially complete and held available for occupancy and capitalization must cease, involves a degree of judgment. The Company’s capitalization policy on development properties follows the guidance in ASC 835-20 “Capitalization of Interest” and ASC 970 “Real Estate-General.” The costs of land and buildings under development include specifically identifiable costs. Capitalized costs include pre-construction costs necessary to the development of the property, development costs, construction costs, interest costs, real estate taxes, salaries and related costs and other costs incurred during the period of development. The Company begins the capitalization of costs during the pre-construction period, which it defines as activities that are necessary for the development of the property. The Company considers a construction project as substantially complete and held available for occupancy upon the completion of tenant improvements, but no later than one year from cessation of major construction activity. The Company ceases capitalization on the portion (1) substantially completed, (2) occupied or held available for occupancy, and capitalizes only those costs associated with the portion under construction or (3) if activities necessary for the development of the property have been suspended. Interest costs capitalized for the years ended December 31, 2019 , 2018 and 2017 were approximately $54.9 million , $65.8 million and $61.1 million , respectively. Salaries and related costs capitalized for the years ended December 31, 2019 , 2018 and 2017 were approximately $10.4 million , $12.5 million and $13.2 million , respectively. Expenditures for repairs and maintenance are charged to operations as incurred. Significant betterments are capitalized. When assets are sold or retired, their costs and related accumulated depreciation are removed from the accounts with the resulting gains or losses reflected in net income or loss for the period. The Company computes depreciation and amortization on properties using the straight-line method based on estimated useful asset lives. The Company allocates the acquisition cost of real estate to its components and depreciates or amortizes these assets (or liabilities) over their useful lives. The amortization of acquired “above-” and “below-market” leases and acquired in-place leases is recorded as an adjustment to revenue and depreciation and amortization, respectively, in the Consolidated Statements of Operations. Depreciation is computed on a straight-line basis over the estimated useful lives of the assets as follows: Land improvements 25 to 40 years Buildings and improvements 10 to 40 years Tenant improvements Shorter of useful life or terms of related lease Furniture, fixtures, and equipment 3 to 7 years
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents consist of cash on hand and investments with maturities of three months or less from the date of purchase. The majority of the Company’s cash and cash equivalents are held at major commercial banks which may at times exceed the Federal Deposit Insurance Corporation limit of $250,000 .
Cash Held in Escrows	Cash Held in Escrows Escrows include amounts established pursuant to various agreements for security deposits, property taxes, insurance and other costs. Escrows also include cash held by qualified intermediaries for possible investments in like-kind exchanges in accordance with Section 1031 of the Internal Revenue Code, as amended (the “Code”), in connection with sales of the Company’s properties.
Investments in Securities	Investments in Securities The Company accounts for investments in equity securities at fair value, with gains or losses resulting from changes in fair value recognized currently in earnings. The Company maintains deferred compensation plans that are designed to allow officers and non-employee directors of Boston Properties, Inc. to defer a portion of the officer’s current income or the non-employee director’s current compensation on a pre-tax basis and receive a tax-deferred return on these deferrals based on the performance of specific investments selected by the officer or non-employee director. The Company’s obligation under the plans is that of an unsecured promise to pay the deferred compensation to the plan participants in the future. At December 31, 2019 and 2018 , the Company had maintained approximately $36.7 million and $28.2 million , respectively, in separate accounts, which are not restricted as to their use. The Company recognized gains (losses) of approximately $6.4 million , $(1.9) million and $3.7 million on its investments in the accounts associated with the Company’s deferred compensation plans during the years ended December 31, 2019 , 2018 and 2017 , respectively.
Tenant and Other Receivables and Notes Receivables	Tenant and Other Receivables Tenant and other accounts receivable, other than accrued rents receivable, are expected to be collected within one year. Notes Receivable The Company accounts for notes receivable at their unamortized cost, net of any unamortized deferred fees or costs, premiums or discounts and an allowance for loan losses (see “ New Accounting Pronouncements Issued but not yet Adopted—Financial Instruments - Credit Losses” ). Loan fees and direct costs associated with loans originated by the Company are deferred and amortized over the term of the note as interest income.
Deferred Charges	Deferred Charges Deferred charges include leasing costs and certain financing fees. Leasing costs include acquired intangible in-place lease values and direct and incremental fees and costs incurred in the successful negotiation of leases, including brokerage and other costs which have been deferred and are being amortized on a straight-line basis over the terms of the respective leases. Unamortized leasing costs are charged to expense upon the early termination of the lease. Fully amortized deferred leasing costs are removed from the books upon the expiration of the lease. The Company did not capitalize any external legal costs and internal leasing salaries and related costs for the year ended December 31, 2019 (see “ New Accounting Pronouncements Adopted—Leases ”). Internal leasing salaries and related costs capitalized for the years ended December 31, 2018 and 2017 were approximately $5.4 million and $5.0 million , respectively. Financing fees included in deferred charges consist of external fees and costs incurred to obtain the Company’s revolving facility and if applicable, the delayed draw facility and construction financing arrangements where there are not sufficient amounts outstanding. Such financing costs have been deferred and are being amortized over the terms of the respective financing and included within interest expense. Unamortized financing costs are charged to expense upon the early repayment or significant modification of the financing. Fully amortized deferred financing costs are removed from the books upon the maturity of the debt. External fees and costs incurred to obtain mortgage financings and unsecured senior notes have been deferred and are presented as direct deductions from the carrying amounts of the corresponding debt liability. Such financing costs are being amortized over the terms of the respective financing and included within interest expense. Unamortized financing costs are charged to expense upon the early repayment or significant modification of the financing.
Investments in Unconsolidated Joint Ventures	Investments in Unconsolidated Joint Ventures The Company consolidates VIEs in which it is considered to be the primary beneficiary. VIEs are entities in which the equity investors do not have sufficient equity at risk to finance their endeavors without additional financial support or that the holders of the equity investment at risk do not have substantive participating rights. The primary beneficiary is defined by the entity having both of the following characteristics: (1) the power to direct the activities that, when taken together, most significantly impact the variable interest entity’s performance, and (2) the obligation to absorb losses and the right to receive the returns from the variable interest entity that could potentially be significant to the VIE. For ventures that are not VIEs, the Company consolidates entities for which it has significant decision making control over the ventures’ operations. The Company’s judgment with respect to its level of influence or control of an entity involves the consideration of various factors including the form of the Company’s ownership interest, its representation in the entity’s governance, the size of its investment (including loans), estimates of future cash flows, its ability to participate in policy making decisions and the rights of the other investors to participate in the decision making process and to replace the Company as manager and/or liquidate the venture, if applicable. The Company’s assessment of its influence or control over an entity affects the presentation of these investments in the Company’s consolidated financial statements. In addition to evaluating control rights, the Company consolidates entities in which the outside partner has no substantive kick-out rights to remove the Company as the managing member. Accounts of the consolidated entity are included in the accounts of the Company and the noncontrolling interest is reflected on the Consolidated Balance Sheets as a component of equity or in temporary equity between liabilities and equity. Investments in unconsolidated joint ventures are recorded initially at cost, and subsequently adjusted for equity in earnings and cash contributions and distributions. Any difference between the carrying amount of these investments on the balance sheet and the underlying equity in net assets is amortized as an adjustment to equity in earnings of unconsolidated joint ventures over the life of the related asset. Under the equity method of accounting, the net equity investment of the Company is reflected within the Consolidated Balance Sheets, and the Company’s share of net income or loss from the joint ventures is included within the Consolidated Statements of Operations. The joint venture agreements may designate different percentage allocations among investors for profits and losses; however, the Company’s recognition of joint venture income or loss generally follows the joint venture’s distribution priorities, which may change upon the achievement of certain investment return thresholds. The Company may account for cash distributions in excess of its investment in an unconsolidated joint venture as income when the Company is not the general partner in a limited partnership and when the Company has neither the requirement nor the intent to provide financial support to the joint venture. The Company classifies distributions received from equity method investees within its Consolidated Statements of Cash Flows using the nature of the distribution approach, which classifies the distributions received on the basis of the nature of the activity or activities of the investee that generated the distribution as either a return on investment (classified as cash inflows from operating activities) or a return of investment (classified as cash inflows from investing activities). The Company’s investments in unconsolidated joint ventures are reviewed for impairment periodically and the Company records impairment charges when events or circumstances change indicating that a decline in the fair values below the carrying amounts has occurred and such decline is other-than-temporary. The evaluation of fair value is subjective and is based in part on assumptions regarding future occupancy, future rental rates, future capital requirements, discount rates and capitalization rates that could differ materially from actual results in future periods . The ultimate realization of the investment in unconsolidated joint ventures is dependent on a number of factors, including the performance of each investment and market conditions. The Company will record an impairment charge if it determines that a decline in the fair value below the carrying amount of an investment in an unconsolidated joint venture is other-than-temporary. To the extent that the Company contributed assets to a joint venture, the Company’s investment in the joint venture was recorded at the Company’s cost basis in the assets that were contributed to the joint venture. To the extent that the Company’s cost basis is different than the basis reflected at the joint venture level, the basis difference is amortized over the life of the related asset and included in the Company’s share of equity in net income of the joint venture. In accordance with the provisions of ASC 610-20 “Gains and Losses from the Derecognition of Nonfinancial Assets” (“ASC 610-20”), the Company will recognize a full gain on both the retained and sold portions of real estate contributed or sold to a joint venture by recognizing its new equity method investment interest at fair value.
Revenue Recognition	Revenue Recognition In general, the Company commences lease/rental revenue recognition when the tenant takes possession of the leased space and the leased space is substantially ready for its intended use. Contractual lease/rental revenue is reported on a straight-line basis over the terms of the respective leases. The impact of the straight-line rent adjustment increased revenue by approximately $58.4 million , $51.9 million and $54.8 million for the years ended December 31, 2019 , 2018 and 2017 , respectively, as the revenue recorded exceeded amounts billed. Accrued rental income, as reported on the Consolidated Balance Sheets, represents cumulative lease/rental income earned in excess of rent payments received pursuant to the terms of the individual lease agreements. The Company maintains an allowance against accrued rental income for future potential tenant credit losses. The credit assessment is based on the estimated accrued rental income that is recoverable over the term of the lease. The Company also maintains an allowance for doubtful accounts for estimated losses resulting from the inability of tenants to make required rent payments. The computation of this allowance is based on the tenants’ payment history and current credit status, as well as certain industry or geographic specific credit considerations. If the Company’s estimates of collectability differ from the cash received, then the timing and amount of the Company’s reported revenue could be impacted. The credit risk is mitigated by the high quality of the Company’s existing tenant base, reviews of prospective tenants’ risk profiles prior to lease execution and consistent monitoring of the Company’s portfolio to identify potential problem tenants. In accordance with ASC 805, the Company recognizes acquired in-place “above-” and “below-market” leases at their fair values as rental revenue over the original term of the respective leases. The impact of the acquired in-place “above-” and “below-market” leases increased revenue by approximately $20.9 million , $23.8 million and $23.5 million for the years ended December 31, 2019 , 2018 and 2017 , respectively. The following table summarizes the scheduled amortization of the Company’s acquired “above-” and “below-market” lease intangibles for each of the five succeeding years (in thousands). Acquired Above-Market Lease Intangibles Acquired Below-Market Lease Intangibles 2020 $ 5,440 $ 10,673 2021 3,054 6,455 2022 357 5,699 2023 183 5,558 2024 135 4,043 Recoveries from tenants, consisting of amounts due from tenants for common area maintenance, real estate taxes and other recoverable costs, are recognized as revenue in the period during which the expenses are incurred (see “ New Accounting Pronouncements Adopted—Leases” ). The Company recognizes these reimbursements on a gross basis, as the Company obtains control of the goods and services before they are transferred to the tenant. The Company also receives reimbursements of payroll and payroll related costs from unconsolidated joint venture entities and third party property owners in connection with management services contracts which the Company reflects on a gross basis instead of on a net basis as the Company has determined that it is the principal and not the agent under these arrangements in accordance with the guidance in ASC 606 “Revenue from Contracts with Customers” (“ASC 606”). The Company’s parking revenue is derived primarily from monthly and transient daily parking. In addition, the Company has certain lease arrangements for parking accounted for under the guidance in ASC 842 “Leases” (“ASC 842”). The monthly and transient daily parking revenue falls within the scope of ASC 606 and is accounted for at the point in time when control of the goods or services transfers to the customer and the Company’s performance obligation is satisfied. The Company’s hotel revenue is derived from room rentals and other sources such as charges to guests for telephone service, movie and vending commissions, meeting and banquet room revenue and laundry services. Hotel revenue is recognized as the hotel rooms are occupied and the services are rendered to the hotel customers. The Company earns management and development fees. Development and management services revenue is earned from unconsolidated joint venture entities and third-party property owners. The Company determined that the performance obligations associated with its development services contracts are satisfied over time and that the Company would recognize its development services revenue under the output method evenly over time from the development commencement date through the substantial completion date of the development management services project due to the stand-ready nature of the contracts. Significant judgments impacting the amount and timing of revenue recognized from the Company’s development services contracts include estimates of total development project costs from which the fees are typically derived and estimates of the period of time until substantial completion of the development project, the period of time over which the development services are required to be performed. The Company recognizes development fees earned from unconsolidated joint venture projects equal to its cost plus profit to the extent of the third party partners’ ownership interest. Property management fees are recorded and earned based on a percentage of collected rents at the properties under management, and not on a straight-line basis, because such fees are contingent upon the collection of rents. Gains on sales of real estate are recognized pursuant to the provisions included in ASC 610-20. Under ASC 610-20, the Company must first determine whether the transaction is a sale to a customer or non-customer. The Company typically sells real estate on a selective basis and not within the ordinary course of its business and therefore expects that its sale transactions will not be contracts with customers. The Company next determines whether it has a controlling financial interest in the property after the sale, consistent with the consolidation model in ASC 810 “Consolidation” (“ASC 810”). If the Company determines that it does not have a controlling financial interest in the real estate, it evaluates whether a contract exists under ASC 606 and whether the buyer has obtained control of the asset that was sold. The Company recognizes a full gain on sale of real estate when the derecognition criteria under ASC 610-20 have been met.
Earnings Per Share and Earnings Per Common Unit	Earnings Per Share Basic earnings per share (“EPS”) is computed by dividing net income available to common shareholders, as adjusted for undistributed earnings (if any) of certain securities issued by Boston Properties Limited Partnership, by the weighted average number of shares of Common Stock outstanding during the year. Diluted EPS reflects the potential dilution that could occur from shares issuable in connection with awards under stock-based compensation plans, including upon the exercise of stock options, and securities of Boston Properties Limited Partnership that are exchangeable for Common Stock. Earnings Per Common Unit Basic earnings per common unit is computed by dividing net income available to common unitholders, as adjusted for undistributed earnings (if any) of certain securities issued by Boston Properties Limited Partnership, by the weighted average number of common units outstanding during the year. Diluted earnings per common unit reflects the potential dilution that could occur from units issuable in connection with awards under Boston Properties, Inc.’s stock-based compensation plans, including upon the exercise of stock options, and conversion of preferred units of Boston Properties Limited Partnership.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The carrying values of cash and cash equivalents, marketable securities, escrows, receivables, accounts payable, accrued expenses and other assets and liabilities are reasonable estimates of their fair values because of the short maturities of these instruments. The Company follows the authoritative guidance for fair value measurements when valuing its financial instruments for disclosure purposes. Boston Properties Limited Partnership determines the fair value of its unsecured senior notes using market prices. The inputs used in determining the fair value of Boston Properties Limited Partnership’s unsecured senior notes is categorized at a Level 1 basis (as defined in ASC 820 “Fair Value Measurements and Disclosures” (“ASC 820”)) due to the fact that it uses quoted market rates to value these instruments. However, the inputs used in determining the fair value could be categorized at a Level 2 basis (as defined in ASC 820) if trading volumes are low. The Company determines the fair value of its related party note receivable, note receivable and mortgage notes payable using discounted cash flow analysis by discounting the spread between the future contractual interest payments and hypothetical future interest payments on note receivables / mortgage debt based on current market rates for similar securities. In determining the current market rates, the Company adds its estimates of market spreads to the quoted yields on federal government treasury securities with similar maturity dates to its debt. The inputs used in determining the fair value of the Company’s related party note receivable, note receivable, and mortgage notes payable are categorized at a Level 3 basis (as defined in ASC 820) due to the fact that the Company considers the rates used in the valuation techniques to be unobservable inputs. To the extent that there are outstanding borrowings under the unsecured line of credit or unsecured term loan, the Company utilizes a discounted cash flow methodology in order to estimate the fair value. To the extent that credit spreads have changed since the origination, the net present value of the difference between future contractual interest payments and future interest payments based on the Company’s estimate of a current market rate would represent the difference between the book value and the fair value. The Company’s estimate of a current market rate is based upon the rate, considering current market conditions and Boston Properties Limited Partnership’s specific credit profile, at which it estimates it could obtain similar borrowings. To the extent there are outstanding borrowings, this current market rate is estimated and therefore would be primarily based upon a Level 3 input (see “ New Accounting Pronouncements Issued but not yet Adopted—Fair Value Measurement” ). Because the Company’s valuations of its financial instruments are based on these types of estimates, the actual fair values of its financial instruments may differ materially if the Company’s estimates do not prove to be accurate, and the Company’s estimated fair values for these instruments as of the end of the applicable reporting period are not necessarily indicative of estimated or actual fair values in future reporting periods. The following table presents the aggregate carrying value of the Company’s related party note receivable, note receivable, mortgage notes payable, net, unsecured senior notes, net, unsecured line of credit and unsecured term loan, net and the Company’s corresponding estimate of fair value as of December 31, 2019 and December 31, 2018 (in thousands): December 31, 2019 December 31, 2018 Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value Related party note receivable $ 80,000 $ 81,931 $ 80,000 $ 80,000 Note receivable 15,920 14,978 19,468 19,468 Total $ 95,920 $ 96,909 $ 99,468 $ 99,468 Mortgage notes payable, net $ 2,922,408 $ 2,984,956 $ 2,964,572 $ 2,903,925 Unsecured senior notes, net 8,390,459 8,826,375 7,544,697 7,469,338 Unsecured line of credit — — — — Unsecured term loan, net 498,939 500,561 498,488 500,783 Total $ 11,811,806 $ 12,311,892 $ 11,007,757 $ 10,874,046 The Company uses interest rate swap agreements to manage its interest rate risk. The valuation of these instruments is determined using widely accepted valuation techniques, including discounted cash flow analysis on the expected cash flows of each derivative. This analysis reflects the contractual terms of the derivatives, including the period to maturity, and uses observable market-based inputs, including interest rate curves. To comply with the provisions of ASC 820, the Company incorporates credit valuation adjustments to appropriately reflect both its own nonperformance risk and the respective counterparty’s nonperformance risk in the fair value measurements. Although the Company determined that the majority of the inputs used to value its derivatives fall within Level 2 of the fair value hierarchy, the credit valuation adjustments associated with its derivatives utilize Level 3 inputs, such as estimates of current credit spreads to evaluate the likelihood of default by the Company and its counterparties. The Company assessed the significance of the impact of the credit valuation adjustments on the overall valuation of its derivative positions and determined that the credit valuation adjustments were not significant to the overall valuation of its derivatives. As a result, the Company has determined that its derivative valuations in their entirety are classified in Level 2 of the fair value hierarchy.
Derivative Instruments and Hedging Activities	Derivative Instruments and Hedging Activities Derivative instruments and hedging activities require management to make judgments on the nature of its derivatives and their effectiveness as hedges. These judgments determine if the changes in fair value of the derivative instruments are reported in the Consolidated Statements of Operations as a component of net income or as a component of comprehensive income and as a component of equity on the Consolidated Balance Sheets. While management believes its judgments are reasonable, a change in a derivative’s effectiveness as a hedge could materially affect expenses, net income and equity. The Company accounts for both the effective and ineffective portions of changes in the fair value of a derivative in other comprehensive income (loss) and subsequently reclassifies the fair value of the derivative to earnings over the term that the hedged transaction affects earnings and in the same line item as the hedged transaction within the statements of operations.
Stock-Based Employee Compensation Plans	Stock-Based Employee Compensation Plans At December 31, 2019
Use of Estimates in the Preparation of Financial Statements	Use of Estimates in the Preparation of Financial Statements The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America (“GAAP”) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. These estimates include such items as depreciation and allowances for doubtful accounts. Actual results could differ from those estimates.
Lessee, Leases	For leases in which the Company is the lessee (generally ground leases), on January 1, 2019, the Company recognized a right-of-use asset and a lease liability of approximately $151.8 million and $199.3 million , respectively. The lease liability was equal to the present value of the minimum lease payments in accordance with Topic ASC 840. In addition, the Company did not know the rate implicit in any of its ground leases that were classified as operating leases, and accordingly used the Company’s incremental borrowing rate (“IBR”) to determine the net present value of the minimum lease payments. In order to determine the IBR, the Company utilized a market-based approach to estimate the incremental borrowing rate for each individual lease. The approach required significant judgment. Therefore, the Company utilized different data sets to estimate base IBRs via an analysis of the following weighted-components: • the interpolated rates from yields on outstanding U.S. Treasury issuances for up to 30 years and for years 31 and beyond, longer-term publicly traded educational institution debt issued by high credit quality educational institutions with maturity dates up to 2116, • observable mortgage rates spread over U.S. Treasury issuances, and • unlevered property yields and discount rates. The Company then applied adjustments to account for considerations related to term and interpolated the IBR. The Company has four non-cancelable ground lease obligations, which were classified as operating leases, with various initial term expiration dates through 2114. The Company recognizes ground rent expense on a straight-line basis over the term of the respective ground lease agreements. None of the amounts disclosed below for these ground leases contain variable payments, extension options or residual value guarantees. One of the ground leases does have an extension option. However, lease payments for this ground lease are based on fair market value and as such have not been included in the analysis below.
Lessor, Leases	ASU 2018-11 provides lessors a practical expedient to not separate nonlease components from the associated lease component if certain criteria stated above are met for each class of underlying assets. The guidance in Topic 842 defines “underlying asset” as “an asset that is the subject of a lease for which a right to use that asset has been conveyed to a lessee. The underlying asset could be a physically distinct portion of a single asset.” Based on the above guidance, t he Company considers real estate assets as a class of underlying assets and will not be further delineating it into specific uses of the real estate asset as the risk profiles are similar in nature. Lease components are elements of an arrangement that provide the customer with the right to use an identified asset. Nonlease components are distinct elements of a contract that are not related to securing the use of the leased asset and revenue is recognized in accordance with ASC 606. The Company considers common area maintenance (CAM) and service income associated with tenant work orders to be nonlease components because they represent delivery of a separate service but are not considered a cost of securing the identified asset. In the case of the Company’s business, the identified asset would be the leased real estate (office, retail or residential). The Company assessed and concluded that the timing and pattern of transfer for nonlease components and the associated lease component are the same. The Company determined that the predominant component was the lease component and as such its leases will continue to qualify as operating leases and the Company has made a policy election to account for and present the lease component and the nonlease component as a single component in the revenue section of the Consolidated Statements of Operations labeled Lease. Prior to the adoption of Topic 842, nonlease components had been included within Recoveries from Tenants Revenue, Parking and Other Revenue and Development and Management Services Revenue on the Company’s Consolidated Statements of Operations. In addition, under ASU 2016-02, lessors will only capitalize incremental direct leasing costs. As a result, starting January 1, 2019, the Company no longer capitalizes non-incremental legal costs and internal leasing wages. These costs are expensed as incurred. The expensing of these items is included within General and Administrative Expense on the Consolidated Statements of Operations.
New Accounting Pronouncements	New Accounting Pronouncements Adopted Leases General Adoption In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2016-02, which sets out the principles for the recognition, measurement, presentation and disclosure of leases for both parties to a contract (i.e., lessees and lessors). ASU 2016-02 requires lessees to apply a dual approach, classifying leases as either finance or operating leases based on the principle of whether or not the lease for accounting purposes is effectively a financed purchase of the leased asset by the lessee. This classification will determine whether the lease expense is recognized based on an effective interest method or on a straight-line basis over the term of the lease. A lessee is also required to record a right-of-use asset and a lease liability for all leases with a term of greater than 12 months regardless of their classification. Leases with a term of 12 months or less will be accounted for similar to the prior guidance in ASC 840 -“Leases” (“Topic 840”). ASU 2016-02 requires lessors to account for leases using an approach that is substantially equivalent to Topic 840 for sales-type leases, direct financing leases and operating leases. ASU 2016-02 supersedes previous leasing standards. On July 30, 2018, the FASB issued ASU 2018-11, “Leases (Topic 842): Targeted Improvements” (“ASU 2018-11”), that (1) simplifies transition requirements for both lessees and lessors by adding an option that permits an organization to apply the transition provisions of the new standard at its adoption date instead of at the earliest comparative period presented in its financial statements and (2) allows lessors to elect, as a practical expedient, by class of underlying asset, to not separate nonlease components from the associated lease component and, instead, to account for those components as a single component if the nonlease components otherwise would be accounted for under the revenue guidance in ASC 606 that was adopted on January 1, 2018, and both of the following are met: (1) the timing and pattern of transfer of the nonlease component(s) and associated lease components are the same; and (2) the lease component, if accounted for separately, would be classified as an operating lease. If the nonlease component or components associated with the lease component are the predominant component of the combined component, an entity is required to account for the combined component in accordance with ASC 606. The Company adopted ASU 2016-02 and ASU 2018-11 effective January 1, 2019. For purposes of transition, the Company elected the practical expedient package, which has been applied consistently to all of its leases, but did not elect the hindsight practical expedient. The practical expedient package did not require the Company to reassess the following: (i) whether an expired or existing contract meets the definition of a lease; (ii) the lease classification at the adoption date for existing leases; and (iii) whether costs previously capitalized as initial direct costs would continue to be amortized. This allows the Company to continue to account for its ground leases as operating leases. However, as of January 1, 2019, any new or modified ground leases may be classified as financing leases unless they meet certain conditions. The Company also elected to apply the transition provisions as of the adoption date, January 1, 2019, and not change its comparative statements. The Company recorded an adjustment to the opening balance of retained earnings related to initial direct costs that, as of January 1, 2019, had not started to amortize and are no longer allowed to be capitalized in accordance with ASU 2016-02, totaling approximately $3.9 million to Dividends in Excess of Earnings of Boston Properties, Inc. and Partners’ Capital of Boston Properties Limited Partnership, approximately $0.4 million to Noncontrolling interests - Common Units of Boston Properties, Inc. and Noncontrolling Interest - Redeemable Partnership Units of Boston Properties Limited Partnership and $70,000 to Noncontrolling Interests - Property Partnerships of Boston Properties, Inc. and Noncontrolling Interests in Property Partnerships of Boston Properties Limited Partnership on the corresponding Consolidated Balance Sheets. The Company made the policy election, when it is the lessee, to not apply the revenue recognition requirements of Topic 842 to short-term leases. This policy election is made by class of underlying assets and as described below, the Company considers real estate to be a class of underlying assets, and will not be further delineating it into specific uses of the real estate asset as the risk profiles are similar in nature. The Company will recognize the lease payments in net income on a straight-line basis over the lease term. Lease payments from operating leases are recognized on a straight-line basis over the term of the leases. The cumulative difference between lease revenue recognized under this method and the contractual lease payment terms is recorded as deferred rent receivable on the Company’s Consolidated Balance Sheets. The Company reviews its trade accounts receivable, including its straight-line rent receivable, related to base rents, straight-line rent, expense reimbursements and other revenues for collectability. The Company analyzes its accounts receivable, customer creditworthiness and current economic trends when evaluating the adequacy of the collectability of the lessee’s total accounts receivable balance on a lease-by-lease basis. In addition, tenants in bankruptcy are analyzed and considerations are made in connection with the expected recovery of pre-petition and post-petition claims. If a lessee’s accounts receivable balance is considered uncollectible, the Company will write-off the receivable balances associated with the lease to Lease revenue and cease to recognize lease income, including straight-line rent, unless cash is received. If the Company subsequently determines that it is probable it will collect substantially all the remaining lessee’s lease payments under the lease term, the Company will then reinstate the straight-line balance, adjusting for the amount related to the period when the lease payments were considered not probable. The Company’s reported net earnings are directly affected by management’s estimate of the collectability of its trade accounts receivable. In January 2018, the FASB issued ASU 2018-01, “Leases (Topic 842): Land Easement Practical Expedient for Transition to Topic 842” (“ASU 2018-01”), which provides an optional transition practical expedient to not evaluate, under Topic 842, existing or expired land easements that were not previously accounted for as leases under the leases guidance in Topic 840. An entity that elects this practical expedient should evaluate new or modified land easements under Topic 842 beginning at the date that the entity adopts Topic 842. An entity that does not elect this practical expedient should evaluate all existing or expired land easements in connection with the adoption of the new lease requirements in Topic 842 to assess whether they meet the definition of a lease. The effective date and transition requirements for ASU 2018-01 are the same as the effective date and transition requirements in ASU 2016-02. The Company adopted ASU 2018-01 on January 1, 2019. Lessee For leases in which the Company is the lessee (generally ground leases), on January 1, 2019, the Company recognized a right-of-use asset and a lease liability of approximately $151.8 million and $199.3 million , respectively. The lease liability was equal to the present value of the minimum lease payments in accordance with Topic ASC 840. In addition, the Company did not know the rate implicit in any of its ground leases that were classified as operating leases, and accordingly used the Company’s incremental borrowing rate (“IBR”) to determine the net present value of the minimum lease payments. In order to determine the IBR, the Company utilized a market-based approach to estimate the incremental borrowing rate for each individual lease. The approach required significant judgment. Therefore, the Company utilized different data sets to estimate base IBRs via an analysis of the following weighted-components: • the interpolated rates from yields on outstanding U.S. Treasury issuances for up to 30 years and for years 31 and beyond, longer-term publicly traded educational institution debt issued by high credit quality educational institutions with maturity dates up to 2116, • observable mortgage rates spread over U.S. Treasury issuances, and • unlevered property yields and discount rates. The Company then applied adjustments to account for considerations related to term and interpolated the IBR. The Company has four non-cancelable ground lease obligations, which were classified as operating leases, with various initial term expiration dates through 2114. The Company recognizes ground rent expense on a straight-line basis over the term of the respective ground lease agreements. None of the amounts disclosed below for these ground leases contain variable payments, extension options or residual value guarantees. One of the ground leases does have an extension option. However, lease payments for this ground lease are based on fair market value and as such have not been included in the analysis below. The Company has four finance lease obligations with various initial term expiration dates through 2094, see Note 3 . The following table provides lease cost information for the Company’s operating and finance leases for the year ended December 31, 2019 (in thousands): Lease costs Operating lease costs $ 14,573 Finance lease costs Amortization of right of use asset (1) $ 29 Interest on lease liabilities (2) $ 47 _______________ (1) The finance leases relate to either land, buildings or assets that remain in development. For land leases classified as finance leases because of a purchase option that the Company views as an economic incentive, the Company follows its existing policy and does not depreciate land because it is assumed to have an indefinite life. For all other finance leases, the Company would amortize the right of use asset over the shorter of the useful life of the asset or the lease term. If the finance lease relates to a property under development, the amortization of the right of use asset may be eligible for capitalization. For assets under development, depreciation may commence once the asset is placed in-service and depreciation would be recognized in accordance with the Company’s policy. (2) Three of the finance leases relate to assets under development and as such, the entire interest amount was capitalized. The following table provides other quantitative information for the Company’s operating and finance leases as of December 31, 2019 : December 31, 2019 Other information Weighted-average remaining lease term (in years) Operating leases 51 Finance leases 71 Weighted-average discount rate Operating leases 5.7 % Finance leases 6.2 % The following table provides a maturity analysis for the Company’s future contractual minimum lease payments to be made by the Company as of December 31, 2018, under non-cancelable ground leases which expire on various dates through 2114: Years Ending December 31, (in thousands) 2019 $ 11,425 2020 18,425 2021 25,310 2022 8,894 2023 9,084 Thereafter 567,232 The following table provides a maturity analysis for the Company’s future minimum lease payments, as of December 31, 2018, related to the four capital leases, through 2036: Years Ending December 31, (in thousands) 2019 $ 1,441 2020 12,682 2021 2,123 2022 1,253 2023 944 Thereafter 73,241 Total expected minimum lease payments 91,684 Interest portion (27,497 ) Present value of expected net minimum lease payments $ 64,187 The following table provides a maturity analysis for the Company’s lease liabilities related to its operating and finance leases as of December 31, 2019 (in thousands): Operating Finance 2020 $ 10,050 $ 834 2021 24,973 5,960 2022 18,041 10,208 2023 10,322 9,708 2024 (1) 9,277 48,518 Thereafter 557,954 1,383,242 Total lease payments 630,617 1,458,470 Less: interest portion (430,437 ) (1,234,428 ) Present value of lease payments $ 200,180 $ 224,042 _______________ (1) Finance lease payments in 2024 include approximately $38.7 million related to a purchase option that the Company is reasonably certain it will exercise. Lessor The Company leases primarily Class A office, retail and residential space to tenants. These leases may contain extension and termination options that are predominately at the sole discretion of the tenant, provided certain conditions are satisfied. In a few instances, the leases also contain purchase options, which would be exercisable at fair market value. Also, certain of the Company’s leases include rental payments that are based on a percentage of the tenant sales in excess of contractual amounts. ASU 2018-11 provides lessors a practical expedient to not separate nonlease components from the associated lease component if certain criteria stated above are met for each class of underlying assets. The guidance in Topic 842 defines “underlying asset” as “an asset that is the subject of a lease for which a right to use that asset has been conveyed to a lessee. The underlying asset could be a physically distinct portion of a single asset.” Based on the above guidance, t he Company considers real estate assets as a class of underlying assets and will not be further delineating it into specific uses of the real estate asset as the risk profiles are similar in nature. Lease components are elements of an arrangement that provide the customer with the right to use an identified asset. Nonlease components are distinct elements of a contract that are not related to securing the use of the leased asset and revenue is recognized in accordance with ASC 606. The Company considers common area maintenance (CAM) and service income associated with tenant work orders to be nonlease components because they represent delivery of a separate service but are not considered a cost of securing the identified asset. In the case of the Company’s business, the identified asset would be the leased real estate (office, retail or residential). The Company assessed and concluded that the timing and pattern of transfer for nonlease components and the associated lease component are the same. The Company determined that the predominant component was the lease component and as such its leases will continue to qualify as operating leases and the Company has made a policy election to account for and present the lease component and the nonlease component as a single component in the revenue section of the Consolidated Statements of Operations labeled Lease. Prior to the adoption of Topic 842, nonlease components had been included within Recoveries from Tenants Revenue, Parking and Other Revenue and Development and Management Services Revenue on the Company’s Consolidated Statements of Operations. In addition, under ASU 2016-02, lessors will only capitalize incremental direct leasing costs. As a result, starting January 1, 2019, the Company no longer capitalizes non-incremental legal costs and internal leasing wages. These costs are expensed as incurred. The expensing of these items is included within General and Administrative Expense on the Consolidated Statements of Operations. The following table summarizes the components of lease revenue recognized during the year ended December 31, 2019 included within the Company’s Consolidated Statements of Operations (in thousands): Lease Revenue Fixed contractual payments $ 2,261,260 Variable lease payments 496,754 $ 2,758,014 The Company’s properties are leased to tenants under operating leases with initial term expiration dates ranging from 2020 to 2049. For the future contractual lease payments to be received by the Company, refer to Note 12 . New Accounting Pronouncements Issued but not yet Adopted Financial Instruments - Credit Losses In June 2016, the FASB issued ASU 2016-13, “Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments” (“ASU 2016-13”). ASU 2016-13 is intended to provide financial statement users with more decision-useful information about the expected credit losses on financial instruments and other commitments to extend credit held by a reporting entity at each reporting date by replacing the current incurred loss impairment methodology with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. In November 2018, the FASB issued ASU 2018-19, “Codification Improvements to Topic 326, Financial Instruments - Credit Losses” (“ASU 2018-19”). ASU 2018-19 clarifies that receivables arising from operating leases are not within the scope of ASC 326-20, “Financial Instruments - Credit Losses - Measured at Amortized Cost,” which addresses financial assets measured at amortized cost basis, including net investments in leases arising from sales-type and direct financing leases. Instead, impairment of receivables arising from operating leases should be accounted for in accordance with ASC 842. ASU 2016-13 and ASU 2018-19 are effective for the Company for reporting periods beginning after December 15, 2019, with early adoption permitted. ASU 2016-13 and ASU 2018-19 are applicable to the Company with respect to (1) certain of its accounts receivable, except for amounts arising from operating leases accounted for under ASC 842, (2) its related party note receivable, (3) its note receivable and (4) certain of its off-balance sheet credit exposures. The Company adopted ASU 2016-13 and ASU 2018-19 effective January 1, 2020 using the modified retrospective approach. The adoption of ASU 2016-13 and ASU 2018-19 did not have a material impact on the Company’s consolidated financial statements. Fair Value Measurement In August 2018, the FASB issued ASU 2018-13, “Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement” (“ASU 2018-13”). ASU 2018-13 is intended to improve the effectiveness of disclosures required by entities regarding recurring and nonrecurring fair value measurements. ASU 2018-13 is effective for the Company for reporting periods beginning after December 15, 2019, with early adoption permitted. The adoption of ASU 2018-13 will not have a material impact on the Company’s consolidated financial statements. Derivatives and Hedging In October 2018, the FASB issued ASU 2018-16, “Derivatives and Hedging (Topic 815): Inclusion of the Secured Overnight Financing Rate (SOFR) Overnight Index Swap (OIS) Rate as a Benchmark Interest Rate for Hedge Accounting Purposes” (“ASU 2018-16”). ASU 2018-16 permits the use of the overnight index swap rate based on the Secured Overnight Financing Rate (“SOFR”) to be used as a U.S. benchmark interest rate for purposes of applying hedge accounting under ASC 815. ASU 2018-16 is effective for the Company, which has already adopted ASU 2017-12, for reporting periods beginning after December 15, 2018 and is required to be adopted on a prospective basis for qualifying new or re-designated hedging relationships entered into on or after the date of adoption. The adoption of ASU 2018-16 will not have a material impact on the Company’s consolidated financial statements. Consolidation In October 2018, the FASB issued ASU 2018-17, “Consolidation (Topic 810): Targeted Improvements to Related Party Guidance for Variable Interest Entities” (“ASU 2018-17”). ASU 2018-17 is intended to improve the accounting when considering indirect interests held through related parties under common control for determining whether fees paid to decision makers and service providers are variable interests. ASU 2018-17 is effective for the Company for reporting periods beginning after December 15, 2019, with early adoption permitted. The adoption of ASU 2018-17 will not have a material impact on the Company’s consolidated financial statements.
Equity Offering Costs	Equity Offering Costs Underwriting commissions and offering costs have been reflected as a reduction of additional paid-in capital.
Treasury Stock	Treasury Stock Boston Properties, Inc.’s share repurchases are reflected as treasury stock utilizing the cost method of accounting and are presented as a reduction to consolidated stockholders’ equity.
Dividends	Dividends Earnings and profits, which determine the taxability of dividends to stockholders, will differ from income reported for financial reporting purposes due to the differences for federal income tax purposes in the treatment of gains/losses on the sale of real property, revenue and expense recognition, compensation expense, and in the estimated useful lives and basis used to compute depreciation.
Income Taxes	Income Taxes Boston Properties, Inc. has elected to be treated as a REIT under Sections 856 through 860 of the Code, commencing with its taxable year ended December 31, 1997. As a result, it generally will not be subject to federal corporate income tax on its taxable income that is distributed to its stockholders. A REIT is subject to a number of organizational and operational requirements, including a requirement that it currently distribute at least 90% of its annual taxable income (with certain adjustments). Boston Properties, Inc.’s policy is to distribute at least 100% of its taxable income. Accordingly, the only provision for federal income taxes in the accompanying consolidated financial statements relates to Boston Properties, Inc.’s consolidated taxable REIT subsidiaries. Boston Properties, Inc.’s taxable REIT subsidiaries did not have significant tax provisions or deferred income tax items. Boston Properties, Inc. has no uncertain tax positions recognized as of December 31, 2019 and 2018 . The Company owns a hotel property that it leases to one of its taxable REIT subsidiaries and that is managed by Marriott International, Inc. The hotel taxable REIT subsidiary, a wholly owned subsidiary of Boston Properties Limited Partnership, is the lessee pursuant to the lease for the hotel property. As lessor, Boston Properties Limited Partnership is entitled to a percentage of gross receipts from the hotel property. Marriott International, Inc. continues to manage the hotel property under the Marriott name and under terms of a management agreement. The hotel taxable REIT subsidiary is subject to tax at the federal and state level and, accordingly, Boston Properties, Inc. has recorded a tax provision in its Consolidated Statements of Operations for the years ended December 31, 2019 , 2018 and 2017 . Certain entities included in Boston Properties, Inc.’s consolidated financial statements are subject to certain state and local taxes. These taxes are recorded as operating expenses in the accompanying consolidated financial statements. Boston Properties Limited Partnership Income Taxes The partners are required to report their respective share of Boston Properties Limited Partnership’s taxable income or loss on their respective tax returns and are liable for any related taxes thereon. Accordingly, the only provision for federal income taxes in the accompanying consolidated financial statements relates to Boston Properties Limited Partnership’s consolidated taxable REIT subsidiaries. Boston Properties Limited Partnership’s taxable REIT subsidiaries did not have significant tax provisions or deferred income tax items. Boston Properties Limited Partnership has no uncertain tax positions recognized as of December 31, 2019 and 2018 . The Company owns a hotel property which is managed through a taxable REIT subsidiary. The hotel taxable REIT subsidiary, a wholly owned subsidiary Boston Properties Limited Partnership, is the lessee pursuant to the lease for the hotel property. As lessor, Boston Properties Limited Partnership is entitled to a percentage of gross receipts from the hotel property. Marriott International, Inc. continues to manage the hotel property under the Marriott name and under terms of a management agreement. The hotel taxable REIT subsidiary is subject to tax at the federal and state level and, accordingly, Boston Properties Limited Partnership has recorded a tax provision in its Consolidated Statements of Operations for the years ended December 31, 2019 , 2018 and 2017 . Certain entities included in Boston Properties Limited Partnership’s consolidated financial statements are subject to certain state and local taxes. These taxes are recorded as operating expenses in the accompanying consolidated financial statements.

Summary Of Significant Accoun_3

Summary Of Significant Accounting Policies (Tables)	12 Months Ended
Summary Of Significant Accounting Policies (Tables)	Dec. 31, 2019
Summary Of Significant Accounting Policies [Line Items]
Property, Plant and Equipment [Table Text Block]	Depreciation is computed on a straight-line basis over the estimated useful lives of the assets as follows: Land improvements 25 to 40 years Buildings and improvements 10 to 40 years Tenant improvements Shorter of useful life or terms of related lease Furniture, fixtures, and equipment 3 to 7 years
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]	The following table summarizes the scheduled amortization of the Company’s acquired “above-” and “below-market” lease intangibles for each of the five succeeding years (in thousands). Acquired Above-Market Lease Intangibles Acquired Below-Market Lease Intangibles 2020 $ 5,440 $ 10,673 2021 3,054 6,455 2022 357 5,699 2023 183 5,558 2024 135 4,043 The following table summarizes the scheduled amortization of the Company’s acquired in-place lease intangibles for each of the five succeeding years (in thousands). Acquired In-Place Lease Intangibles 2020 $ 17,536 2021 11,001 2022 5,918 2023 4,286 2024 2,510
Fair Value, by Balance Sheet Grouping [Table Text Block]	The following table presents the aggregate carrying value of the Company’s related party note receivable, note receivable, mortgage notes payable, net, unsecured senior notes, net, unsecured line of credit and unsecured term loan, net and the Company’s corresponding estimate of fair value as of December 31, 2019 and December 31, 2018 (in thousands): December 31, 2019 December 31, 2018 Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value Related party note receivable $ 80,000 $ 81,931 $ 80,000 $ 80,000 Note receivable 15,920 14,978 19,468 19,468 Total $ 95,920 $ 96,909 $ 99,468 $ 99,468 Mortgage notes payable, net $ 2,922,408 $ 2,984,956 $ 2,964,572 $ 2,903,925 Unsecured senior notes, net 8,390,459 8,826,375 7,544,697 7,469,338 Unsecured line of credit — — — — Unsecured term loan, net 498,939 500,561 498,488 500,783 Total $ 11,811,806 $ 12,311,892 $ 11,007,757 $ 10,874,046
Lease, Cost [Table Text Block]	The following table provides lease cost information for the Company’s operating and finance leases for the year ended December 31, 2019 (in thousands): Lease costs Operating lease costs $ 14,573 Finance lease costs Amortization of right of use asset (1) $ 29 Interest on lease liabilities (2) $ 47 _______________ (1) The finance leases relate to either land, buildings or assets that remain in development. For land leases classified as finance leases because of a purchase option that the Company views as an economic incentive, the Company follows its existing policy and does not depreciate land because it is assumed to have an indefinite life. For all other finance leases, the Company would amortize the right of use asset over the shorter of the useful life of the asset or the lease term. If the finance lease relates to a property under development, the amortization of the right of use asset may be eligible for capitalization. For assets under development, depreciation may commence once the asset is placed in-service and depreciation would be recognized in accordance with the Company’s policy. (2) Three of the finance leases relate to assets under development and as such, the entire interest amount was capitalized. The following table provides other quantitative information for the Company’s operating and finance leases as of December 31, 2019 : December 31, 2019 Other information Weighted-average remaining lease term (in years) Operating leases 51 Finance leases 71 Weighted-average discount rate Operating leases 5.7 % Finance leases 6.2 %
Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block]	The following table provides a maturity analysis for the Company’s future contractual minimum lease payments to be made by the Company as of December 31, 2018, under non-cancelable ground leases which expire on various dates through 2114: Years Ending December 31, (in thousands) 2019 $ 11,425 2020 18,425 2021 25,310 2022 8,894 2023 9,084 Thereafter 567,232
Schedule of Future Minimum Lease Payments for Capital Leases [Table Text Block]	The following table provides a maturity analysis for the Company’s future minimum lease payments, as of December 31, 2018, related to the four capital leases, through 2036: Years Ending December 31, (in thousands) 2019 $ 1,441 2020 12,682 2021 2,123 2022 1,253 2023 944 Thereafter 73,241 Total expected minimum lease payments 91,684 Interest portion (27,497 ) Present value of expected net minimum lease payments $ 64,187
Lessee, Operating and Finance Lease Liability [Table Text Block]	The following table provides a maturity analysis for the Company’s lease liabilities related to its operating and finance leases as of December 31, 2019 (in thousands): Operating Finance 2020 $ 10,050 $ 834 2021 24,973 5,960 2022 18,041 10,208 2023 10,322 9,708 2024 (1) 9,277 48,518 Thereafter 557,954 1,383,242 Total lease payments 630,617 1,458,470 Less: interest portion (430,437 ) (1,234,428 ) Present value of lease payments $ 200,180 $ 224,042 _______________ (1) Finance lease payments in 2024 include approximately $38.7 million related to a purchase option that the Company is reasonably certain it will exercise.
Operating Lease, Lease Income [Table Text Block]	The following table summarizes the components of lease revenue recognized during the year ended December 31, 2019 included within the Company’s Consolidated Statements of Operations (in thousands): Lease Revenue Fixed contractual payments $ 2,261,260 Variable lease payments 496,754 $ 2,758,014
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes, Table [Table Text Block]	The tax treatment of common dividends per share for federal income tax purposes is as follows: For the year ended December 31, 2019 2018 2017 Per Share % Per Share % Per Share % Ordinary income $ 2.99 94.84 % $ 2.79 78.17 % $ 2.86 98.29 % Capital gain income 0.16 5.16 % 0.78 21.83 % 0.05 1.71 % Total $ 3.15 (1) 100.00 % $ 3.57 (2) 100.00 % $ 2.91 (3) 100.00 % _____________ (1) The fourth quarter 2019 regular quarterly dividend was $0.98 per common share of which approximately $0.04 per common share was allocable to 2019 and approximately $0.94 per common share is allocable to 2020. (2) The fourth quarter 2018 regular quarterly dividend was $0.95 per common share of which approximately $0.69 per common share was allocable to 2018 and approximately $0.26 per common share is allocable to 2019. (3) The fourth quarter 2017 regular quarterly dividend was $0.80 per common share of which approximately $0.47 per common share was allocable to 2017 and approximately $0.33 per common share is allocable to 2018. The following table presents Boston Properties, Inc.’s dividends per share and Boston Properties Limited Partnership’s distributions per OP Unit and LTIP Unit paid or payable in 2019 and 2018 : Record Date Payment Date Dividend (Per Share) Distribution (Per Unit) December 31, 2019 January 30, 2020 $0.98 $0.98 September 30, 2019 October 31, 2019 $0.95 $0.95 June 28, 2019 July 31, 2019 $0.95 $0.95 March 29, 2019 April 30, 2019 $0.95 $0.95 December 31, 2018 January 30, 2019 $0.95 $0.95 September 28, 2018 October 31, 2018 $0.95 $0.95 June 29, 2018 July 31, 2018 $0.80 $0.80 March 29, 2018 April 30, 2018 $0.80 $0.80 December 29, 2017 January 30, 2018 $0.80 $0.80
Finance Lease, Liability, Maturity [Table Text Block]	The following table provides a maturity analysis for the Company’s lease liabilities related to its operating and finance leases as of December 31, 2019 (in thousands): Operating Finance 2020 $ 10,050 $ 834 2021 24,973 5,960 2022 18,041 10,208 2023 10,322 9,708 2024 (1) 9,277 48,518 Thereafter 557,954 1,383,242 Total lease payments 630,617 1,458,470 Less: interest portion (430,437 ) (1,234,428 ) Present value of lease payments $ 200,180 $ 224,042 _______________ (1) Finance lease payments in 2024 include approximately $38.7 million related to a purchase option that the Company is reasonably certain it will exercise.

Real Estate (Tables)

Real Estate (Tables)	Aug. 27, 2019	Jul. 16, 2019	Jan. 24, 2019	Dec. 31, 2019
Real Estate Properties [Line Items]
Schedule of Real Estate Properties				Boston Properties, Inc. Real estate consisted of the following at December 31, 2019 and December 31, 2018 (in thousands): 2019 2018 Land $ 5,111,606 $ 5,072,568 Right of use assets - finance leases 237,394 — Right of use assets - operating leases 148,640 — Land held for future development (1) 254,828 200,498 Buildings and improvements 13,646,054 13,356,751 Tenant improvements 2,656,439 2,396,932 Furniture, fixtures and equipment 44,313 44,351 Construction in progress 789,736 578,796 Total 22,889,010 21,649,896 Less: Accumulated depreciation (5,266,798 ) (4,897,777 ) $ 17,622,212 $ 16,752,119 _______________ (1) Includes pre-development costs.
Finance Lease, Liability, Maturity [Table Text Block]				The following table provides a maturity analysis for the Company’s lease liabilities related to its operating and finance leases as of December 31, 2019 (in thousands): Operating Finance 2020 $ 10,050 $ 834 2021 24,973 5,960 2022 18,041 10,208 2023 10,322 9,708 2024 (1) 9,277 48,518 Thereafter 557,954 1,383,242 Total lease payments 630,617 1,458,470 Less: interest portion (430,437 ) (1,234,428 ) Present value of lease payments $ 200,180 $ 224,042 _______________ (1) Finance lease payments in 2024 include approximately $38.7 million related to a purchase option that the Company is reasonably certain it will exercise.
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]				The following table summarizes the scheduled amortization of the Company’s acquired “above-” and “below-market” lease intangibles for each of the five succeeding years (in thousands). Acquired Above-Market Lease Intangibles Acquired Below-Market Lease Intangibles 2020 $ 5,440 $ 10,673 2021 3,054 6,455 2022 357 5,699 2023 183 5,558 2024 135 4,043 The following table summarizes the scheduled amortization of the Company’s acquired in-place lease intangibles for each of the five succeeding years (in thousands). Acquired In-Place Lease Intangibles 2020 $ 17,536 2021 11,001 2022 5,918 2023 4,286 2024 2,510
880 & 890 Winter Street [Member]
Real Estate Properties [Line Items]
Schedule of Business Acquisitions, by Acquisition [Table Text Block]	The following table summarizes the allocation of the purchase price, including transaction costs, of 880 and 890 Winter Street at the date of acquisition (in thousands): Land $ 29,510 Building and improvements 59,788 Tenant improvements 6,024 In-place lease intangibles 11,494 Above-market lease intangibles 246 Below-market lease intangibles (1,092 ) Net assets acquired $ 105,970
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]	The following table summarizes the estimated annual amortization of the acquired in-place lease intangibles, the acquired above-market lease intangibles and the acquired below-market lease intangibles for 880 and 890 Winter Street for the remainder of 2019 and each of the next five succeeding fiscal years (in thousands): Acquired In-Place Lease Intangibles Acquired Above-Market Lease Intangibles Acquired Below- Market Lease Intangibles Period from August 27, 2019 through December 31, 2019 $ 1,801 $ 28 $ (226 ) 2020 4,485 80 (599 ) 2021 2,391 80 (237 ) 2022 1,121 43 (30 ) 2023 179 15 — 2024 60 — —
Platform 16
Real Estate Properties [Line Items]
Finance Lease, Liability, Maturity [Table Text Block]			As of January 24, 2019, the lease payments from the finance lease related to the remaining parcels made available for lease to the Company were as follows (in thousands): Period from January 24, 2019 through December 31, 2019 $ 17,918 2020 109,460 Total expected minimum lease payments 127,378 Interest portion (4,815 ) Present value of expected net lease payments $ 122,563
2100 Pennsylvania Avenue
Real Estate Properties [Line Items]
Finance Lease, Liability, Maturity [Table Text Block]		As of July 16, 2019, the lease payments from the finance lease were as follows (in thousands): Period from July 16, 2019 through December 31, 2019 $ — 2020 — 2021 3,863 2022 8,576 2023 8,669 Thereafter 1,358,518 Total expected minimum lease payments 1,379,626 Interest portion (1,214,649 ) Present value of expected net lease payments $ 164,977
Boston Properties Limited Partnership
Real Estate Properties [Line Items]
Schedule of Real Estate Properties				Boston Properties Limited Partnership Real estate consisted of the following at December 31, 2019 and December 31, 2018 (in thousands): 2019 2018 Land $ 5,011,153 $ 4,971,475 Right of use assets - finance leases 237,394 — Right of use assets - operating leases 148,640 — Land held for future development (1) 254,828 200,498 Buildings and improvements 13,351,286 13,059,488 Tenant improvements 2,656,439 2,396,932 Furniture, fixtures and equipment 44,313 44,351 Construction in progress 789,736 578,796 Total 22,493,789 21,251,540 Less: Accumulated depreciation (5,162,908 ) (4,800,475 ) $ 17,330,881 $ 16,451,065 _______________ (1) Includes pre-development costs.

Deferred Charges (Tables)

Deferred Charges (Tables)	12 Months Ended
Deferred Charges (Tables)	Dec. 31, 2019
Deferred Charges [Abstract]
Deferred Charges	Deferred charges consisted of the following at December 31, 2019 and December 31, 2018 (in thousands): 2019 2018 Leasing costs, including lease related intangibles $ 1,155,958 $ 1,191,297 Financing costs 12,728 12,796 1,168,686 1,204,093 Less: Accumulated amortization (479,473 ) (525,369 ) $ 689,213 $ 678,724
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]	The following table summarizes the scheduled amortization of the Company’s acquired “above-” and “below-market” lease intangibles for each of the five succeeding years (in thousands). Acquired Above-Market Lease Intangibles Acquired Below-Market Lease Intangibles 2020 $ 5,440 $ 10,673 2021 3,054 6,455 2022 357 5,699 2023 183 5,558 2024 135 4,043 The following table summarizes the scheduled amortization of the Company’s acquired in-place lease intangibles for each of the five succeeding years (in thousands). Acquired In-Place Lease Intangibles 2020 $ 17,536 2021 11,001 2022 5,918 2023 4,286 2024 2,510

Investments in Unconsolidated_2

Investments in Unconsolidated Joint Ventures (Tables)	12 Months Ended
Investments in Unconsolidated Joint Ventures (Tables)	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Investments In Unconsolidated Joint Ventures	The investments in unconsolidated joint ventures consist of the following at December 31, 2019 and 2018 : Carrying Value of Investment (1) Entity Properties Nominal % Ownership December 31, December 31, (in thousands) Square 407 Limited Partnership Market Square North 50.0 % $ (4,872 ) $ (6,424 ) BP/CRF Metropolitan Square, LLC Metropolitan Square 20.0 % 9,134 2,644 901 New York, LLC 901 New York Avenue 25.0 % (2) (12,113 ) (13,640 ) WP Project Developer LLC Wisconsin Place Land and Infrastructure 33.3 % (3) 36,789 38,214 Annapolis Junction NFM LLC Annapolis Junction 50.0 % (4) 25,391 25,268 540 Madison Venture LLC 540 Madison Avenue 60.0 % (5) 2,953 66,391 500 North Capitol Venture LLC 500 North Capitol Street, NW 30.0 % (5,439 ) (5,026 ) 501 K Street LLC 1001 6th Street 50.0 % (6) 42,496 42,557 Podium Developer LLC The Hub on Causeway - Podium 50.0 % 49,466 69,302 Residential Tower Developer LLC Hub50House 50.0 % 55,092 47,505 Hotel Tower Developer LLC The Hub on Causeway - Hotel Air Rights 50.0 % 9,883 3,022 Office Tower Developer LLC 100 Causeway Street 50.0 % 56,606 23,804 1265 Main Office JV LLC 1265 Main Street 50.0 % 3,780 3,918 BNY Tower Holdings LLC Dock 72 50.0 % 94,804 82,520 BNYTA Amenity Operator LLC Dock 72 50.0 % — N/A CA-Colorado Center Limited Partnership Colorado Center 50.0 % 252,069 253,495 7750 Wisconsin Avenue LLC 7750 Wisconsin Avenue 50.0 % 56,247 69,724 BP-M 3HB Venture LLC 3 Hudson Boulevard 25.0 % 67,499 46,993 SMBP Venture LP Santa Monica Business Park 55.0 % 163,937 180,952 Platform 16 Holdings LP Platform 16 55.0 % (7) 29,501 N/A $ 933,223 $ 931,219 _______________ (1) Investments with deficit balances aggregating approximately $22.4 million and $25.1 million at December 31, 2019 and 2018 , respectively, are included within Other Liabilities in the Company’s Consolidated Balance Sheets. (2) The Company’s economic ownership has increased based on the achievement of certain return thresholds. (3) The Company’s wholly-owned subsidiary that owns Wisconsin Place Office also owns a 33.3% interest in the joint venture entity that owns the land, parking garage and infrastructure of the project. (4) The joint venture owns three in-service buildings and two undeveloped land parcels. (5) T he property was sold on June 27, 2019. As of December 31, 2019, the investment is comprised of undistributed cash. See note below for additional details. (6) Under the joint venture agreement for this land parcel, the partner will be entitled to up to two additional payments from the venture based on increases in total entitled square footage of the project above 520,000 square feet and achieving certain project returns at stabilization. (7) This entity is a VIE (See Note 1 ).
Schedule Of Balance Sheets Of The Unconsolidated Joint Ventures [Text Block]	The combined summarized balance sheets of the Company’s unconsolidated joint ventures are as follows: December 31, December 31, (in thousands) ASSETS Real estate and development in process, net (1) $ 3,904,400 $ 3,545,906 Other assets 502,706 543,512 Total assets $ 4,407,106 $ 4,089,418 LIABILITIES AND MEMBERS’/PARTNERS’ EQUITY Mortgage and notes payable, net $ 2,218,853 $ 2,017,609 Other liabilities (2) 749,675 582,006 Members’/Partners’ equity 1,438,578 1,489,803 Total liabilities and members’/partners’ equity $ 4,407,106 $ 4,089,418 Company’s share of equity $ 591,905 $ 622,498 Basis differentials (3) 341,318 308,721 Carrying value of the Company’s investments in unconsolidated joint ventures (4) $ 933,223 $ 931,219 _______________ (1) At December 31, 2019, this amount includes right of use assets - finance leases and right of use assets - operating leases totaling approximately $383.9 million and $12.1 million , respectively. (2) At December 31, 2019, this amount includes lease liabilities - finance leases and lease liabilities - operating leases totaling approximately $510.8 million and $17.3 million , respectively. (3) This amount represents the aggregate difference between the Company’s historical cost basis and the basis reflected at the joint venture level, which is typically amortized over the life of the related assets and liabilities. Basis differentials result from impairments of investments, acquisitions through joint ventures with no change in control and upon the transfer of assets that were previously owned by the Company into a joint venture. In addition, certain acquisition, transaction and other costs may not be reflected in the net assets at the joint venture level. At December 31, 2019 and 2018 , there was an aggregate basis differential of approximately $311.3 million and $316.7 million , respectively, between the carrying value of the Company’s investment in the joint venture that owns Colorado Center and the joint venture’s basis in the assets and liabilities, which differential (excluding land) shall be amortized over the remaining lives of the related assets and liabilities. (4) Investments with deficit balances aggregating approximately $22.4 million and $25.1 million at December 31, 2019 and 2018 , respectively, have been reflected within Other Liabilities in the Company’s Consolidated Balance Sheets.
Statements Of Operations Of The Joint Ventures	The combined summarized statements of operations of the Company’s unconsolidated joint ventures are as follows: For the year ended December 31, 2019 2018 2017 (in thousands) Total revenue (1) $ 322,817 $ 271,951 $ 222,517 Expenses Operating 122,992 106,610 90,542 Transaction costs 1,000 — — Depreciation and amortization (2) 102,296 103,079 57,079 Total expenses 226,288 209,689 147,621 Other income (expense) Gains on sales of real estate (3) 32,706 16,951 — Interest expense (84,409 ) (71,308 ) (46,371 ) Net income $ 44,826 $ 7,905 $ 28,525 Company’s share of net income $ 24,423 $ 8,084 $ 18,439 Basis differential (3)(4) 22,169 (5,862 ) (7,207 ) Income from unconsolidated joint ventures $ 46,592 $ 2,222 $ 11,232 _______________ (1) Includes straight-line rent adjustments of approximately $32.4 million , $15.9 million and $21.7 million for the years ended December 31, 2019 , 2018 and 2017 , respectively. (2) During the year ended December 31, 2018, the joint venture that owns Metropolitan Square in Washington, DC, commenced a renovation project and recorded accelerated depreciation expense of approximately $22.4 million related to the remaining book value of the assets to be replaced. The Company’s share of the accelerated depreciation expense totaled approximately $4.5 million . (3) For the year ended December 31, 2019, represents the gain on sale of 540 Madison Avenue recognized by the joint venture, as described below. During 2008, the Company recognized an other-than-temporary impairment loss on its investment in the unconsolidated joint venture resulting in a basis differential between the carrying value of the Company’s investment in the joint venture and the joint venture’s basis in the assets and liabilities of the property. As a result of the historical basis difference, the Company recognized a gain on sale of real estate totaling approximately $47.2 million for the year ended December 31, 2019, which consists of its share of the gain on sale reported by the joint venture as well as an adjustment for the basis differential. The gain on sale of real estate is included in Income from Unconsolidated Joint Ventures in the Company’s Consolidated Statements of Operations. (4) Includes straight-line rent adjustments of approximately $2.1 million , $2.4 million and $1.9 million for the years ended December 31, 2019, 2018 and 2017, respectively. Also includes net above-/below-market rent adjustments of approximately $1.7 million , $1.6 million and $2.9 million for the years ended December 31, 2019, 2018 and 2017, respectively.

Mortgage Notes Payable, Net Sch

Mortgage Notes Payable, Net Schedule of Aggregate Principal Payments On Mortgage Notes (Tables)	12 Months Ended
	Dec. 31, 2019
Mortgage Notes Payable [Abstract]
Schedule of Aggregate Principal Payments On Mortgage Notes [Table Text Block]	Contractual aggregate principal payments of mortgage notes payable at December 31, 2019 are as follows (in thousands): Principal Payments 2020 $ 17,168 2021 17,276 2022 614,710 2023 — 2024 — Thereafter 2,300,000 Total aggregate principal payments 2,949,154 Deferred financing costs, net (26,746 ) Total carrying value of mortgage notes payable, net $ 2,922,408

Unsecured Senior Notes (Tables)

Unsecured Senior Notes (Tables)	12 Months Ended
Unsecured Senior Notes (Tables)	Dec. 31, 2019
Debt Disclosure [Abstract]
Schedule of Senior Notes	The following summarizes the unsecured senior notes outstanding as of December 31, 2019 (dollars in thousands): Coupon/ Stated Rate Effective Rate(1) Principal Amount Maturity Date(2) 10 Year Unsecured Senior Notes 4.125 % 4.289 % $ 850,000 May 15, 2021 11 Year Unsecured Senior Notes 3.850 % 3.954 % 1,000,000 February 1, 2023 10.5 Year Unsecured Senior Notes 3.125 % 3.279 % 500,000 September 1, 2023 10.5 Year Unsecured Senior Notes 3.800 % 3.916 % 700,000 February 1, 2024 7 Year Unsecured Senior Notes 3.200 % 3.350 % 850,000 January 15, 2025 10 Year Unsecured Senior Notes 3.650 % 3.766 % 1,000,000 February 1, 2026 10 Year Unsecured Senior Notes 2.750 % 3.495 % 1,000,000 October 1, 2026 10 Year Unsecured Senior Notes 4.500 % 4.628 % 1,000,000 December 1, 2028 10 Year Unsecured Senior Notes 3.400 % 3.505 % 850,000 June 21, 2029 10.5 Year Unsecured Senior Notes 2.900 % 2.984 % 700,000 March 15, 2030 Total principal 8,450,000 Net unamortized discount (17,451 ) Deferred financing costs, net (42,090 ) Total $ 8,390,459 _______________ (1) Yield on issuance date including the effects of discounts on the notes, settlements of interest rate contracts and the amortization of financing costs. (2) No principal amounts are due prior to maturity.

Noncontrolling Interests (Table

Noncontrolling Interests (Tables)	12 Months Ended
Noncontrolling Interests (Tables)	Dec. 31, 2019
Noncontrolling Interest [Line Items]
Distribution Declared to OP, LTIP, OPP and MYLTIP Units [Table Text Block]	The tax treatment of common dividends per share for federal income tax purposes is as follows: For the year ended December 31, 2019 2018 2017 Per Share % Per Share % Per Share % Ordinary income $ 2.99 94.84 % $ 2.79 78.17 % $ 2.86 98.29 % Capital gain income 0.16 5.16 % 0.78 21.83 % 0.05 1.71 % Total $ 3.15 (1) 100.00 % $ 3.57 (2) 100.00 % $ 2.91 (3) 100.00 % _____________ (1) The fourth quarter 2019 regular quarterly dividend was $0.98 per common share of which approximately $0.04 per common share was allocable to 2019 and approximately $0.94 per common share is allocable to 2020. (2) The fourth quarter 2018 regular quarterly dividend was $0.95 per common share of which approximately $0.69 per common share was allocable to 2018 and approximately $0.26 per common share is allocable to 2019. (3) The fourth quarter 2017 regular quarterly dividend was $0.80 per common share of which approximately $0.47 per common share was allocable to 2017 and approximately $0.33 per common share is allocable to 2018. The following table presents Boston Properties, Inc.’s dividends per share and Boston Properties Limited Partnership’s distributions per OP Unit and LTIP Unit paid or payable in 2019 and 2018 : Record Date Payment Date Dividend (Per Share) Distribution (Per Unit) December 31, 2019 January 30, 2020 $0.98 $0.98 September 30, 2019 October 31, 2019 $0.95 $0.95 June 28, 2019 July 31, 2019 $0.95 $0.95 March 29, 2019 April 30, 2019 $0.95 $0.95 December 31, 2018 January 30, 2019 $0.95 $0.95 September 28, 2018 October 31, 2018 $0.95 $0.95 June 29, 2018 July 31, 2018 $0.80 $0.80 March 29, 2018 April 30, 2018 $0.80 $0.80 December 29, 2017 January 30, 2018 $0.80 $0.80
Noncontrolling Interests [Member]
Noncontrolling Interest [Line Items]
Distribution Declared to OP, LTIP, OPP and MYLTIP Units [Table Text Block]	The following table presents Boston Properties Limited Partnership’s distributions on the OP Units and LTIP Units (including the 2012 OPP Units, 2013 MYLTIP Units, 2014 MYLTIP Units and 2015 MYLTIP Units and, after the February 9, 2019 measurement date, the 2016 MYLTIP Units) and its distributions on the 2016 MYLTIP Units (prior to the February 9, 2019 measurement date), 2017 MYLTIP Units, 2018 MYLTIP Units and 2019 MYLTIP Units (after the February 5, 2019 issuance date) that occurred during the year ended December 31, 2019: Record Date Payment Date Distributions per OP Unit and LTIP Unit Distributions per MYLTIP Unit December 31, 2019 January 30, 2020 $0.98 $0.098 September 30, 2019 October 31, 2019 $0.95 $0.095 June 28, 2019 July 31, 2019 $0.95 $0.095 March 29, 2019 April 30, 2019 $0.95 $0.095 December 31, 2018 January 30, 2019 $0.95 $0.095 The following table presents Boston Properties Limited Partnership’s distributions on the OP Units and LTIP Units (including the 2012 OPP Units, 2013 MYLTIP Units, 2014 MYLTIP Units and, after the February 4, 2018 measurement date, the 2015 MYLTIP Units) and its distributions on the 2015 MYLTIP Units (prior to the February 4, 2018 measurement date), 2016 MYLTIP Units, 2017 MYLTIP Units and 2018 MYLTIP Units (after the February 6, 2018 issuance date) that occurred during the year ended December 31, 2018: Record Date Payment Date Distributions per OP Unit and LTIP Unit Distributions per MYLTIP Unit December 31, 2018 January 30, 2019 $0.95 $0.095 September 28, 2018 October 31, 2018 $0.95 $0.095 June 29, 2018 July 31, 2018 $0.80 $0.080 March 29, 2018 April 30, 2018 $0.80 $0.080 December 29, 2017 January 30, 2018 $0.80 $0.080

Stockholders' Equity _ Partne_2

Stockholders' Equity / Partners' Capital (Tables)	12 Months Ended
Stockholders' Equity / Partners' Capital (Tables)	Dec. 31, 2019
Class of Stock [Line Items]
Dividends Declared [Table Text Block]	The tax treatment of common dividends per share for federal income tax purposes is as follows: For the year ended December 31, 2019 2018 2017 Per Share % Per Share % Per Share % Ordinary income $ 2.99 94.84 % $ 2.79 78.17 % $ 2.86 98.29 % Capital gain income 0.16 5.16 % 0.78 21.83 % 0.05 1.71 % Total $ 3.15 (1) 100.00 % $ 3.57 (2) 100.00 % $ 2.91 (3) 100.00 % _____________ (1) The fourth quarter 2019 regular quarterly dividend was $0.98 per common share of which approximately $0.04 per common share was allocable to 2019 and approximately $0.94 per common share is allocable to 2020. (2) The fourth quarter 2018 regular quarterly dividend was $0.95 per common share of which approximately $0.69 per common share was allocable to 2018 and approximately $0.26 per common share is allocable to 2019. (3) The fourth quarter 2017 regular quarterly dividend was $0.80 per common share of which approximately $0.47 per common share was allocable to 2017 and approximately $0.33 per common share is allocable to 2018. The following table presents Boston Properties, Inc.’s dividends per share and Boston Properties Limited Partnership’s distributions per OP Unit and LTIP Unit paid or payable in 2019 and 2018 : Record Date Payment Date Dividend (Per Share) Distribution (Per Unit) December 31, 2019 January 30, 2020 $0.98 $0.98 September 30, 2019 October 31, 2019 $0.95 $0.95 June 28, 2019 July 31, 2019 $0.95 $0.95 March 29, 2019 April 30, 2019 $0.95 $0.95 December 31, 2018 January 30, 2019 $0.95 $0.95 September 28, 2018 October 31, 2018 $0.95 $0.95 June 29, 2018 July 31, 2018 $0.80 $0.80 March 29, 2018 April 30, 2018 $0.80 $0.80 December 29, 2017 January 30, 2018 $0.80 $0.80
Series B Preferred Stock [Member]
Class of Stock [Line Items]
Dividends Declared [Table Text Block]	The following table presents Boston Properties Inc.’s dividends per share on its outstanding Series B Preferred Stock paid or payable in 2019 and 2018 : Record Date Payment Date Dividend (Per Share) February 4, 2020 February 18, 2020 $32.8125 November 1, 2019 November 15, 2019 $32.8125 August 2, 2019 August 15, 2019 $32.8125 May 3, 2019 May 15, 2019 $32.8125 February 4, 2019 February 15, 2019 $32.8125 November 2, 2018 November 15, 2018 $32.8125 August 3, 2018 August 15, 2018 $32.8125 May 4, 2018 May 15, 2018 $32.8125 February 2, 2018 February 15, 2018 $32.8125

Future Minimum Rents (Tables)

Future Minimum Rents (Tables)	12 Months Ended
Future Minimum Rents (Tables)	Dec. 31, 2019
Future Minimum Rents [Abstract]
Lessor, Operating Lease, Payments to be Received, Maturity Table [Table Text Block]	The future contractual minimum lease payments to be received (excluding operating expense reimbursements) by the Company as of December 31, 2018, under non-cancelable operating leases which expire on various dates through 2049: Years Ending December 31, (in thousands) 2019 $ 2,088,171 2020 2,106,963 2021 2,015,031 2022 1,838,699 2023 1,736,636 Thereafter 12,295,464 The future contractual lease payments to be received (excluding operating expense reimbursements) by the Company as of December 31, 2019, under non-cancelable operating leases which expire on various dates through 2049: Years Ending December 31, (in thousands) 2020 $ 2,205,675 2021 2,222,643 2022 2,126,968 2023 2,068,871 2024 1,974,144 Thereafter 13,892,504

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
Segment Information (Tables)	Dec. 31, 2019
Segment Reporting [Abstract]
Schedule Of Reconciliation Of Net Operating Income To Net Income	Boston Properties, Inc. Year ended December 31, 2019 2018 2017 (in thousands) Net income attributable to Boston Properties, Inc. common shareholders $ 511,034 $ 572,347 $ 451,939 Add: Preferred dividends 10,500 10,500 10,500 Noncontrolling interest—common units of the Operating Partnership 59,345 66,807 52,210 Noncontrolling interests in property partnerships 71,120 62,909 47,832 Interest expense 412,717 378,168 374,481 Losses (gains) from early extinguishments of debt 29,540 16,490 (496 ) Impairment losses 24,038 11,812 — Net operating income from unconsolidated joint ventures 97,716 79,893 64,008 Depreciation and amortization expense 677,764 645,649 617,547 Transaction costs 1,984 1,604 668 Payroll and related costs from management services contracts 10,386 9,590 — General and administrative expense 140,777 121,722 113,715 Less: Net operating income attributable to noncontrolling interests in property partnerships 183,989 177,365 174,245 Gains (losses) from investments in securities 6,417 (1,865 ) 3,678 Interest and other income 18,939 10,823 5,783 Gains on sales of real estate 709 182,356 7,663 Income from unconsolidated joint ventures 46,592 2,222 11,232 Direct reimbursements of payroll and related costs from management services contracts 10,386 9,590 — Development and management services revenue 40,039 45,158 34,605 Company’s share of Net Operating Income $ 1,739,850 $ 1,551,842 $ 1,495,198 Boston Properties Limited Partnership Year ended December 31, 2019 2018 2017 (in thousands) Net income attributable to Boston Properties Limited Partnership common unitholders $ 580,102 $ 656,903 $ 512,866 Add: Preferred distributions 10,500 10,500 10,500 Noncontrolling interests in property partnerships 71,120 62,909 47,832 Interest expense 412,717 378,168 374,481 Losses (gains) from early extinguishments of debt 29,540 16,490 (496 ) Impairment losses 22,272 10,181 — Net operating income from unconsolidated joint ventures 97,716 79,893 64,008 Depreciation and amortization expense 669,956 637,891 609,407 Transaction costs 1,984 1,604 668 Payroll and related costs from management services contracts 10,386 9,590 — General and administrative expense 140,777 121,722 113,715 Less: Net operating income attributable to noncontrolling interests in property partnerships 183,989 177,365 174,245 Gains (losses) from investments in securities 6,417 (1,865 ) 3,678 Interest and other income 18,939 10,823 5,783 Gains on sales of real estate 858 190,716 8,240 Income from unconsolidated joint ventures 46,592 2,222 11,232 Direct reimbursements of payroll and related costs from management services contracts 10,386 9,590 — Development and management services revenue 40,039 45,158 34,605 Company’s share of Net Operating Income $ 1,739,850 $ 1,551,842 $ 1,495,198
Schedule Of Segment Information By Geographic Area And Property Type	Information by geographic area and property type (dollars in thousands): For the year ended December 31, 2019 : Boston Los Angeles New York San Francisco Washington, DC Total Rental Revenue: (1) Office $ 895,098 $ — $ 1,011,912 $ 533,189 $ 384,435 $ 2,824,634 Residential 13,786 — — — 23,128 36,914 Hotel 48,589 — — — — 48,589 Total 957,473 — 1,011,912 533,189 407,563 2,910,137 % of Grand Totals 32.90 % — % 34.78 % 18.32 % 14.00 % 100.00 % Rental Expenses: Office 322,282 — 389,532 177,994 144,217 1,034,025 Residential 5,071 — — — 10,914 15,985 Hotel 34,004 — — — — 34,004 Total 361,357 — 389,532 177,994 155,131 1,084,014 % of Grand Totals 33.34 % — % 35.93 % 16.42 % 14.31 % 100.00 % Net operating income $ 596,116 $ — $ 622,380 $ 355,195 $ 252,432 $ 1,826,123 % of Grand Totals 32.64 % — % 34.09 % 19.45 % 13.82 % 100.00 % Less: Net operating income attributable to noncontrolling interests in property partnerships (40,109 ) — (143,432 ) (448 ) — (183,989 ) Add: Company’s share of net operating income from unconsolidated joint ventures 5,494 61,338 4,174 — 26,710 97,716 Company’s share of net operating income $ 561,501 $ 61,338 $ 483,122 $ 354,747 $ 279,142 $ 1,739,850 % of Grand Totals 32.27 % 3.53 % 27.77 % 20.39 % 16.04 % 100.00 % _______________ (1) Rental Revenue is equal to Total Revenue per the Company’s Consolidated Statements of Operations, less Development and Management Services Revenue and Direct Reimbursements of Payroll and Related Costs from Management Services Contracts Revenue per the Consolidated Statements of Operations. For the year ended December 31, 2018 : Boston Los Angeles New York San Francisco Washington, DC Total Rental Revenue: (1) Office $ 838,341 $ — $ 959,050 $ 397,180 $ 396,088 $ 2,590,659 Residential 6,694 — — — 15,857 22,551 Hotel 49,118 — — — — 49,118 Total 894,153 — 959,050 397,180 411,945 2,662,328 % of Grand Totals 33.59 % — % 36.02 % 14.92 % 15.47 % 100.00 % Rental Expenses: Office 315,653 — 377,992 130,016 142,886 966,547 Residential 3,632 — — — 8,972 12,604 Hotel 33,863 — — — — 33,863 Total 353,148 — 377,992 130,016 151,858 1,013,014 % of Grand Totals 34.86 % — % 37.32 % 12.83 % 14.99 % 100.00 % Net operating income $ 541,005 $ — $ 581,058 $ 267,164 $ 260,087 $ 1,649,314 % of Grand Totals 32.80 % — % 35.23 % 16.20 % 15.77 % 100.00 % Less: Net operating income attributable to noncontrolling interests in property partnerships (33,862 ) — (143,562 ) 59 — (177,365 ) Add: Company’s share of net operating income from unconsolidated joint ventures 2,866 42,750 6,590 — 27,687 79,893 Company’s share of net operating income $ 510,009 $ 42,750 $ 444,086 $ 267,223 $ 287,774 $ 1,551,842 % of Grand Totals 32.86 % 2.75 % 28.63 % 17.22 % 18.54 % 100.00 % _______________ (1) Rental Revenue is equal to total Revenue per the Company’s Consolidated Statements of Operations, less Development and Management Services Revenue and Direct Reimbursements of Payroll and Related Costs from Management Services Contracts Revenue per the Consolidated Statements of Operations. For the year ended December 31, 2017 : Boston Los Angeles New York San Francisco Washington, DC Total Rental Revenue: (1) Office $ 776,279 $ — $ 969,371 $ 345,519 $ 414,103 $ 2,505,272 Residential 4,745 — — — 11,851 16,596 Hotel 45,603 — — — — 45,603 Total 826,627 — 969,371 345,519 425,954 2,567,471 % of Grand Totals 32.20 % — % 37.75 % 13.46 % 16.59 % 100.00 % Rental Expenses: Office 301,097 — 372,810 105,253 144,515 923,675 Residential 2,044 — — — 4,258 6,302 Hotel 32,059 — — — — 32,059 Total 335,200 — 372,810 105,253 148,773 962,036 % of Grand Totals 34.84 % — % 38.76 % 10.94 % 15.46 % 100.00 % Net operating income $ 491,427 $ — $ 596,561 $ 240,266 $ 277,181 $ 1,605,435 % of Grand Totals 30.61 % — % 37.15 % 14.97 % 17.27 % 100.00 % Less: Net operating income attributable to noncontrolling interests in property partnerships (31,857 ) — (142,916 ) 528 — (174,245 ) Add: Company’s share of net operating income from unconsolidated joint ventures 1,962 26,816 8,832 — 26,398 64,008 Company’s share of net operating income $ 461,532 $ 26,816 $ 462,477 $ 240,794 $ 303,579 $ 1,495,198 % of Grand Totals 30.87 % 1.79 % 30.94 % 16.10 % 20.30 % 100.00 % _______________ (1) Rental Revenue is equal to total Revenue per the Company’s Consolidated Statements of Operations, less Development and Management Services Revenue and Direct Reimbursements of Payroll and Related Costs from Management Services Contracts Revenue per the Consolidated Statements of Operations.

Earnings Per Share _ Common U_2

Earnings Per Share / Common Unit (Tables)	12 Months Ended
Earnings Per Share / Common Unit (Tables)	Dec. 31, 2019
Entity Information [Line Items]
Computation Of Basic And Diluted Earnings Per Share / Unit	For the Year Ended December 31, 2019 Income (Numerator) Shares (Denominator) Per Share Amount (in thousands, except for per share amounts) Basic Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 511,034 154,582 $ 3.31 Effect of Dilutive Securities: Stock Based Compensation — 301 (0.01 ) Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 511,034 154,883 $ 3.30 For the Year ended December 31, 2018 Income (Numerator) Shares (Denominator) Per Share Amount (in thousands, except for per share amounts) Basic Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 572,347 154,427 $ 3.71 Allocation of undistributed earnings to participating securities (101 ) — — Net income attributable to Boston Properties, Inc. common shareholders $ 572,246 154,427 $ 3.71 Effect of Dilutive Securities: Stock Based Compensation — 255 (0.01 ) Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 572,246 154,682 $ 3.70 For the Year ended December 31, 2017 Income (Numerator) Shares (Denominator) Per Share Amount (in thousands, except for per share amounts) Basic Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 451,939 154,190 $ 2.93 Effect of Dilutive Securities: Stock Based Compensation — 200 — Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 451,939 154,390 $ 2.93
Boston Properties Limited Partnership
Entity Information [Line Items]
Computation Of Basic And Diluted Earnings Per Share / Unit	Included in the number of units (the denominator) below are approximately 17,618,000 , 17,485,000 and 17,471,000 redeemable common units for the years ended December 31, 2019 , 2018 and 2017 , respectively. For the Year Ended December 31, 2019 Income (Numerator) Units (Denominator) Per Unit Amount (in thousands, except for per unit amounts) Basic Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 580,102 172,200 $ 3.37 Effect of Dilutive Securities: Stock Based Compensation — 301 (0.01 ) Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 580,102 172,501 $ 3.36 For the Year ended December 31, 2018 Income (Numerator) Units (Denominator) Per Unit Amount (in thousands, except for per unit amounts) Basic Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 656,903 171,912 $ 3.82 Allocation of undistributed earnings to participating securities (113 ) — — Net income attributable to Boston Properties Limited Partnership common unitholders $ 656,790 171,912 $ 3.82 Effect of Dilutive Securities: Stock Based Compensation — 255 (0.01 ) Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 656,790 172,167 $ 3.81 For the Year ended December 31, 2017 Income (Numerator) Units (Denominator) Per Unit Amount (in thousands, except for per unit amounts) Basic Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 512,866 171,661 $ 2.99 Effect of Dilutive Securities: Stock Based Compensation — 200 (0.01 ) Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 512,866 171,861 $ 2.98

Stock Option and Incentive Pl_2

Stock Option and Incentive Plan (Tables)	12 Months Ended
Stock Option and Incentive Plan (Tables)	Dec. 31, 2018
Stock Option and Incentive Plan and Stock Purchase Plan [Abstract]
Share-based Compensation, Stock Options, Activity [Table Text Block]	A summary of the status of Boston Properties, Inc.’s stock options as of December 31, 2019 , 2018 and 2017 and changes during the years then ended are presented below: Shares Weighted-Average Exercise Price Outstanding at December 31, 2016 547,129 $ 96.38 Exercised (6,688 ) $ 99.15 Outstanding at December 31, 2017 540,441 $ 96.35 Exercised — $ — Outstanding at December 31, 2018 540,441 $ 96.35 Exercised (145,088 ) $ 96.27 Outstanding at December 31, 2019 395,353 $ 96.37
Schedule of Stock Options Outstanding [Table Text Block]	The following table summarizes information about Boston Properties, Inc.’s stock options outstanding at December 31, 2019 : Options Outstanding Options Exercisable Number Outstanding at 12/31/19 Weighted-Average Remaining Contractual Life Exercise Price Number Exercisable at 12/31/19 Exercise Price 81,458 1.1 years $ 86.86 81,458 $ 86.86 54,282 3.3 years $ 95.69 54,282 $ 95.69 142,422 3.1 years $ 98.46 142,422 $ 98.46 117,191 2.1 years $ 100.77 117,191 $ 100.77

Selected Interim Financial In_2

Selected Interim Financial Information (unaudited) (Tables)	3 Months Ended
Selected Interim Financial Information (unaudited) (Tables)	Mar. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information [Table Text Block]	Boston Properties, Inc. The tables below reflect Boston Properties, Inc.’s selected quarterly information for the years ended December 31, 2019 and 2018 . 2019 Quarter Ended March 31, June 30, September 30, December 31, (in thousands, except for per share amounts) Total revenue $ 725,767 $ 733,741 $ 743,553 $ 757,501 Net income $ 131,159 $ 203,461 $ 141,370 $ 176,009 Net income attributable to Boston Properties, Inc. common shareholders $ 98,105 $ 164,318 $ 107,771 $ 140,824 Income attributable to Boston Properties, Inc. per share—basic $ 0.63 $ 1.06 $ 0.70 $ 0.91 Income attributable to Boston Properties, Inc. per share—diluted $ 0.63 $ 1.06 $ 0.70 $ 0.91 2018 Quarter Ended March 31, June 30, September 30, December 31, (in thousands, except for per share amounts) Total revenue $ 661,151 $ 664,484 $ 686,284 $ 705,157 Net income $ 216,312 $ 160,565 $ 150,445 $ 185,241 Net income attributable to Boston Properties, Inc. common shareholders $ 176,021 $ 128,681 $ 119,118 $ 148,529 Income attributable to Boston Properties, Inc. per share—basic $ 1.14 $ 0.83 $ 0.77 $ 0.96 Income attributable to Boston Properties, Inc. per share—diluted $ 1.14 $ 0.83 $ 0.77 $ 0.96 Boston Properties Limited Partnership The tables below reflect Boston Properties Limited Partnership’s selected quarterly information for the years ended December 31, 2019 and 2018 . 2019 Quarter Ended March 31, June 30, September 30, December 31, (in thousands, except for per unit amounts) Total revenue $ 725,767 $ 733,741 $ 743,553 $ 757,501 Net income $ 134,837 $ 205,822 $ 143,212 $ 177,851 Net income attributable to Boston Properties Limited Partnership common unitholders $ 113,382 $ 185,715 $ 122,117 $ 158,888 Income attributable to Boston Properties Limited Partnership per unit—basic $ 0.66 $ 1.08 $ 0.71 $ 0.92 Income attributable to Boston Properties Limited Partnership per unit—diluted $ 0.66 $ 1.08 $ 0.71 $ 0.92 2018 Quarter Ended March 31, June 30, September 30, December 31, (in thousands, except for per unit amounts) Total revenue $ 661,151 $ 664,484 $ 686,284 $ 705,157 Net income $ 220,766 $ 162,986 $ 153,676 $ 192,884 Net income attributable to Boston Properties Limited Partnership common unitholders $ 200,907 $ 145,961 $ 136,201 $ 173,834 Income attributable to Boston Properties Limited Partnership per unit—basic $ 1.17 $ 0.85 $ 0.79 $ 1.01 Income attributable to Boston Properties Limited Partnership per unit—diluted $ 1.17 $ 0.85 $ 0.79 $ 1.01

Real Estate and Accumulated D_3

Real Estate and Accumulated Depreciation Real Estate and Accumulated Depreciation (Tables)	12 Months Ended
	Dec. 31, 2019
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate and Accumulated Depreciation, By Property [Table Text Block]	Boston Properties, Inc. Schedule 3 - Real Estate and Accumulated Depreciation December 31, 2019 (dollars in thousands) Property Name Type Location Encumbrances Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Land Building 767 Fifth Avenue (the General Motors Building) Office New York, NY $ 2,274,028 $ 1,796,252 $ 1,532,654 $ 202,612 $ 1,796,252 $ 1,735,266 $ — $ — $ 3,531,518 $ 313,158 1968/2019 2013 (1) Prudential Center Office Boston, MA — 92,077 948,357 556,458 115,638 1,478,578 2,676 — 1,596,892 596,740 1965/1993/2002/2016-2017 1998/1999/2000 (1) Embarcadero Center Office San Francisco, CA — 179,697 847,410 415,228 195,987 1,246,348 — — 1,442,335 633,711 1970/1989 1998-1999 (1) 399 Park Avenue Office New York, NY — 339,200 700,358 300,519 354,107 985,970 — — 1,340,077 358,960 1961/2018 2002 (1) 601 Lexington Avenue Office New York, NY 644,778 241,600 494,782 454,902 289,639 688,550 — 213,095 1,191,284 289,482 1977/1997 2001 (1) Salesforce Tower Office San Francisco, CA — 200,349 946,205 — 200,349 946,205 — — 1,146,554 38,727 2018 2013 (1) 200 Clarendon Street and Garage Office Boston, MA — 219,543 667,884 210,160 250,134 829,529 17,924 — 1,097,587 214,533 1976 2010 (1) 250 West 55th Street Office New York, NY — 285,263 603,167 51,928 285,263 655,095 — — 940,358 116,857 2014 2007 (1) 100 Federal Street Office Boston, MA — 131,067 435,954 102,984 131,067 538,938 — — 670,005 122,799 1971-1975/2017 2012 (1) Times Square Tower Office New York, NY — 165,413 380,438 113,222 169,193 489,880 — — 659,073 217,303 2004 2000 (1) Carnegie Center Office Princeton, NJ — 142,666 316,856 152,280 94,240 462,882 54,680 — 611,802 208,331 1983-2016 1998/1999/2000/2007/2014/2017/2019 (1) Atlantic Wharf Office Boston, MA — 63,988 454,537 18,709 63,988 473,246 — — 537,234 131,828 2011 2007 (1) 510 Madison Avenue Office New York, NY — 103,000 253,665 25,495 103,000 279,160 — — 382,160 72,213 2012 2010 (1) Fountain Square Office Reston, VA — 56,853 306,298 12,140 56,853 318,438 — — 375,291 78,498 1986-1990 2012 (1) 599 Lexington Avenue Office New York, NY — 81,040 100,507 188,572 87,852 282,267 — — 370,119 183,291 1986 1997 (1) 680 Folsom Street Office San Francisco, CA — 72,545 219,766 7,907 72,545 227,673 — — 300,218 46,777 2014 2012 (1) 2200 Pennsylvania Avenue Office Washington, DC — — 183,541 113,627 109,038 188,130 — — 297,168 59,190 2011 2008 (1) 145 Broadway Office Cambridge, MA — 121 273,013 23,246 23,367 273,013 — — 296,380 1,511 2019 1997 (1) South of Market and Democracy Tower Office Reston, VA — 13,603 237,479 26,415 13,687 263,810 — — 277,497 99,478 2008-2009 2003 (1) 601 Massachusetts Avenue Office Washington, DC — 95,310 165,173 3,945 95,322 169,106 — — 264,428 24,502 2016 2008 (1) Bay Colony Corporate Center Office Waltham, MA — 18,789 148,451 80,077 18,789 228,528 — — 247,317 79,824 1985-1989 2011 (1) Gateway Center Office San Francisco, CA — 28,255 139,245 61,791 30,627 198,664 — — 229,291 106,680 1984/1986/2002 1999 (1) 535 Mission Street Office San Francisco, CA — 40,933 148,378 3,276 40,933 151,654 — — 192,587 26,293 2015 2013 (1) Reservoir Place Office Waltham, MA — 18,605 104,124 53,718 20,108 156,339 — — 176,447 70,870 1955/1987/2017 1997/1998 (1) Mountain View Research Park Office Mountain View, CA — 95,066 68,373 12,704 95,066 81,077 — — 176,143 19,807 1977-1981/2007-2013 2013 (1) 1330 Connecticut Avenue Office Washington, DC — 25,982 82,311 36,847 27,135 118,005 — — 145,140 32,775 1984/2018 2004 (1) Boston Properties, Inc. Schedule 3 - Real Estate and Accumulated Depreciation December 31, 2019 (dollars in thousands) Property Name Type Location Encumbrances Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Land Building Kingstowne Towne Center Office Alexandria, VA — 18,021 109,038 3,376 18,062 112,373 — — 130,435 44,294 2003-2006 2007 (1) One Freedom Square Office Reston, VA — 9,929 84,504 34,372 11,293 117,512 — — 128,805 59,006 2000 2003 (1) Capital Gallery Office Washington, DC — 4,725 29,565 88,704 8,662 114,332 — — 122,994 71,631 1981/2006 2007 (1) Weston Corporate Center Office Weston, MA — 25,753 92,312 (123 ) 25,854 92,088 — — 117,942 29,227 2010 2001 (1) Two Freedom Square Office Reston, VA — 13,930 77,739 23,209 15,420 99,458 — — 114,878 50,668 2001 2003 (1) One and Two Reston Overlook Office Reston, VA — 16,456 66,192 24,181 16,179 90,650 — — 106,829 51,503 1999 2000 (1) Discovery Square Office Reston, VA — 11,198 71,782 20,905 12,533 91,352 — — 103,885 43,619 2001 2003 (1) 140 Kendrick Street Office Needham, MA — 18,095 66,905 17,574 19,092 83,482 — — 102,574 35,721 2000 2004 (1) 355 Main Street Office Cambridge, MA — 18,863 53,346 27,582 21,173 78,618 — — 99,791 26,439 1981/1996/2013 2006 (1) 880 & 890 Winter Street Office Waltham, MA — 29,510 65,812 — 29,510 65,812 — — 95,322 1,458 1998-1999 2019 (1) 10 CityPoint Office Waltham, MA — 1,953 85,752 4,697 2,290 90,112 — — 92,402 10,928 2016 1997 (1) 90 Broadway Office Cambridge, MA — 19,104 52,078 19,857 20,785 70,254 — — 91,039 23,621 1983/1998/2013 2006 (1) 230 CityPoint Office Waltham, MA — 13,189 49,823 22,057 13,807 71,262 — — 85,069 29,255 1992 2005 (1) 77 CityPoint Office Waltham, MA — 13,847 60,383 10,556 14,023 70,763 — — 84,786 27,172 2008 2001 (1) Waltham Weston Corporate Center Office Waltham, MA — 10,385 60,694 13,165 11,097 73,147 — — 84,244 35,567 2003 1999 (1) 3625-3635 Peterson Way Office Santa Clara, CA — 63,206 14,879 752 63,206 14,879 752 — 78,837 11,172 1979 2016 (1) 2440 West El Camino Real Office Mountain View, CA — 16,741 51,285 5,454 16,741 56,739 — — 73,480 13,090 1987/2003 2011 (1) 191 Spring Street Office Lexington, MA — 2,850 59,751 7,695 3,151 67,145 — — 70,296 21,917 1971/1995/2018 1997 (1) 300 Binney Street Office Cambridge, MA — 18,080 51,262 140 18,080 51,402 — — 69,482 11,146 2013 2009 (1) Wisconsin Place Office Chevy Chase, MD — — 53,349 14,924 — 68,273 — — 68,273 25,934 2009 2004 (1) Reston Corporate Center Office Reston, VA — 9,135 50,857 6,236 10,148 56,080 — — 66,228 29,860 1984 1998 (1) New Dominion Technology Park, Bldg. Two Office Herndon, VA — 5,584 51,868 4,157 6,510 55,099 — — 61,609 26,894 2004 1998 (1) 255 Main Street Office Cambridge, MA — 134 25,110 34,124 548 58,820 — — 59,368 33,543 1987 1997 (1) University Place Office Cambridge, MA 3,602 — 37,091 16,001 7,418 45,674 — — 53,092 29,423 1985 1998 (1) New Dominion Technology Park, Bldg. One Office Herndon, VA — 3,880 43,227 3,927 4,583 46,451 — — 51,034 29,141 2001 1998 (1) Sumner Square Office Washington, DC — 624 28,745 21,344 3,535 47,178 — — 50,713 27,093 1985 1999 (1) 200 West Street Office Waltham, MA — 16,148 24,983 8,211 16,813 30,425 — 2,104 49,342 17,001 1999 1997 (1) North First Business Park Office San Jose, CA — 23,398 13,069 4,571 23,377 17,661 — — 41,038 16,411 1981 2007 (1) 150 Broadway Office Cambridge, MA — 850 25,042 8,540 1,323 33,109 — — 34,432 19,875 1999 1997 (1) 105 Broadway Office Cambridge, MA — 1,299 12,943 11,406 2,395 23,253 — — 25,648 11,870 1990 1997 (1) Lexington Office Park Office Lexington, MA — 998 1,426 18,547 1,264 19,707 — — 20,971 14,312 1982 1997 (1) 201 Spring Street Office Lexington, MA — 2,849 15,303 1,172 3,124 16,200 — — 19,324 8,587 1997 1997 (1) The Point Office Waltham, MA — 6,395 10,040 421 6,492 10,364 — — 16,856 1,349 2015 2007 (1) 33 Hayden Avenue Office Lexington, MA — 266 3,234 12,898 425 15,973 — — 16,398 5,678 1979 1997 (1) 690 Folsom Street Office San Francisco, CA — 3,219 11,038 1,157 3,219 12,195 — — 15,414 2,284 2015 2012 (1) Boston Properties, Inc. Schedule 3 - Real Estate and Accumulated Depreciation December 31, 2019 (dollars in thousands) Property Name Type Location Encumbrances Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Land Building 92-100 Hayden Avenue Office Lexington, MA — 594 6,748 7,529 802 14,069 — — 14,871 12,041 1985 1997 (1) 181 Spring Street Office Lexington, MA — 1,066 9,520 2,177 1,160 11,603 — — 12,763 5,597 1999 1997 (1) 195 West Street Office Waltham, MA — 1,611 6,652 4,218 1,858 10,623 — — 12,481 8,352 1990 1997 (1) 7501 Boston Boulevard, Building Seven Office Springfield, VA — 665 9,273 816 791 9,963 — — 10,754 5,393 1997 1997 (1) 7435 Boston Boulevard, Building One Office Springfield, VA — 392 3,822 4,983 659 8,538 — — 9,197 6,344 1982 1997 (1) 7450 Boston Boulevard, Building Three Office Springfield, VA — 1,165 4,681 2,591 1,430 7,007 — — 8,437 3,575 1987 1998 (1) 32 Hartwell Avenue Office Lexington, MA — 168 1,943 6,115 314 7,912 — — 8,226 1,975 1968/1979/1987 1997 (1) 250 Binney Street Office Cambridge, MA — 110 4,483 3,593 273 7,913 — — 8,186 5,829 1983 1997 (1) 8000 Grainger Court, Building Five Office Springfield, VA — 366 4,282 3,198 601 7,245 — — 7,846 5,752 1984 1997 (1) 453 Ravendale Drive Office Mountain View, CA — 5,477 1,090 676 5,477 1,766 — — 7,243 690 1977 2012 (1) 7300 Boston Boulevard, Building Thirteen Office Springfield, VA — 608 4,773 1,007 661 5,727 — — 6,388 1,984 2002 1997 (1) 17 Hartwell Avenue Office Lexington, MA — 26 150 6,064 65 6,175 — — 6,240 1,966 1968 1997 (1) 7601 Boston Boulevard, Building Eight Office Springfield, VA — 200 878 5,060 551 5,587 — — 6,138 4,689 1986 1997 (1) 7500 Boston Boulevard, Building Six Office Springfield, VA — 138 3,749 1,640 367 5,160 — — 5,527 4,237 1985 1997 (1) 8000 Corporate Court, Building Eleven Office Springfield, VA — 136 3,071 1,596 774 4,029 — — 4,803 3,191 1989 1997 (1) 7375 Boston Boulevard, Building Ten Office Springfield, VA — 23 2,685 1,032 93 3,647 — — 3,740 2,606 1988 1997 (1) 7374 Boston Boulevard, Building Four Office Springfield, VA — 241 1,605 1,828 398 3,276 — — 3,674 2,779 1984 1997 (1) 7451 Boston Boulevard, Building Two Office Springfield, VA — 249 1,542 1,667 613 2,845 — — 3,458 2,610 1982 1997 (1) Signature at Reston Residential Reston, VA — 27,076 190,580 393 27,076 190,973 — — 218,049 8,773 2018 2013 (1) Proto Kendall Square Residential Cambridge, MA — 9,243 127,248 2,939 9,245 130,185 — — 139,430 4,566 2018 2015 (1) The Avant at Reston Town Center Residential Reston, VA — 20,350 91,995 830 20,350 92,825 — — 113,175 14,728 2014 2010 (1) The Lofts at Atlantic Wharf Residential Boston, MA — 3,529 54,891 1,897 3,529 56,788 — — 60,317 12,639 2011 2007 (1) Boston Marriott Cambridge Hotel Cambridge, MA — 478 37,918 35,813 1,201 73,008 — — 74,209 46,605 1986/2017 1997 (1) Kendall Center Green Garage Garage Cambridge, MA — — 35,035 7,329 103 42,261 — — 42,364 13,512 1984 2006 (1) Kendall Center Yellow Garage Garage Cambridge, MA — 1,256 15,697 1,552 1,434 17,071 — — 18,505 6,031 2006 2004 (1) Kendall Center Blue Garage Garage Cambridge, MA — 1,163 11,633 2,151 1,579 13,368 — — 14,947 9,728 1990 1997 (1) The Skylyne (MacArthur Station Residences) Development Oakland, CA — — — 226,526 29,807 — — 196,719 226,526 — N/A N/A N/A 2100 Pennsylvania Avenue Development Washington, DC — — — 224,380 185,129 — — 39,251 224,380 1,024 N/A N/A N/A Reston Gateway Development Reston, VA — — — 150,632 — — — 150,632 150,632 — N/A 1998 N/A 17Fifty Presidents Street Development Reston, VA — — — 99,816 — — — 99,816 99,816 — N/A 2013 N/A Boston Properties, Inc. Schedule 3 - Real Estate and Accumulated Depreciation December 31, 2019 (dollars in thousands) Property Name Type Location Encumbrances Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Land Building 20 CityPoint Development Waltham, MA — 4,721 52,039 20,007 4,721 52,039 — 20,007 76,767 1,136 N/A 2007 N/A 325 Main Street Development Cambridge, MA — 174 — 68,903 965 — — 68,112 69,077 — N/A 1997 N/A North First Master Plan Land San Jose, CA — 35,004 — 3,932 — — 38,936 — 38,936 — N/A 2007 N/A Plaza at Almaden Land San Jose, CA — — — 34,889 — — 34,889 — 34,889 — N/A 2006 N/A 425 Fourth Street Land San Francisco, CA — — — 22,074 — — 22,074 — 22,074 — N/A N/A N/A Springfield Metro Center Land Springfield, VA — — — 19,844 — — 19,844 — 19,844 — N/A 2007 N/A Reston Gateway Master Plan Land Reston, VA — — — 18,292 — — 18,292 — 18,292 — N/A 1998 N/A 214 Third Avenue Land Waltham, MA — — — 17,692 — — 17,692 — 17,692 — N/A 2006 N/A 103 Fourth Avenue Land Waltham, MA — — — 12,826 — — 12,826 — 12,826 — N/A 2007 N/A Crane Meadow Land Marlborough, MA — — — 8,866 — — 8,866 — 8,866 — N/A 2000 N/A Broad Run Business Park Land Loudoun County, VA — — — 2,396 — — 2,396 — 2,396 — N/A 1998 N/A Kendall Center Master Plan Land Cambridge, MA — — — 1,693 — — 1,693 — 1,693 — N/A 1997 N/A Weston Quarry Land Weston, MA — — — 1,249 — — 1,249 — 1,249 — N/A 2001 N/A Reston Overlook Master Plan Land Reston, VA — — — 39 — — 39 — 39 — N/A 2000 N/A $ 2,922,408 (2 ) $ 5,024,060 $ 13,057,336 $ 4,763,301 $ 5,474,337 (3 ) $ 16,325,796 (4 ) $ 254,828 (5 ) $ 789,736 $ 22,844,697 $ 5,239,179 Note: Total Real Estate does not include Furniture, Fixtures and Equipment totaling approximately $44,313 . Accumulated Depreciation does not include approximately $27,619 of accumulated depreciation related to Furniture, Fixtures and Equipment. The aggregate cost and accumulated depreciation for tax purposes was approximately $18.6 billion and $4.0 billion , respectively. (1) Depreciation of the buildings and improvements are calculated over lives ranging from the life of the lease to 40 years. (2) Includes unamortized deferred financing costs totaling approximately $(26.7) million . (3) Includes Right of Use Assets - Finance Leases and Right of Use Assets - Operating Leases of approximately $214,091 and $148,640 , respectively. (4) Includes Right of Use Assets - Finance Leases of approximately $23,303 . (5) Includes pre-development costs.
Activity of Real Estate and Accumulated Depreciation [Table Text Block]	A summary of activity for real estate and accumulated depreciation is as follows: 2019 2018 2017 Real Estate: Balance at the beginning of the year $ 21,605,545 $ 21,058,714 $ 20,114,576 Additions to/improvements of real estate 1,671,898 1,043,379 1,099,286 Assets sold/written-off (432,746 ) (496,548 ) (155,148 ) Balance at the end of the year $ 22,844,697 $ 21,605,545 $ 21,058,714 Accumulated Depreciation: Balance at the beginning of the year $ 4,871,102 $ 4,566,570 $ 4,201,891 Depreciation expense 564,938 533,342 497,059 Assets sold/written-off (196,861 ) (228,810 ) (132,380 ) Balance at the end of the year $ 5,239,179 $ 4,871,102 $ 4,566,570 Note: Real Estate and Accumulated Depreciation amounts do not include Furniture, Fixtures and Equipment.
Boston Properties Limited Partnership
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate and Accumulated Depreciation, By Property [Table Text Block]	Boston Properties Limited Partnership Schedule 3—Real Estate and Accumulated Depreciation December 31, 2019 (dollars in thousands) Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Property Name Type Location Encumbrances Land Building 767 Fifth Avenue (the General Motors Building) Office New York, NY $ 2,274,028 $ 1,796,252 $ 1,532,654 $ 202,612 $ 1,796,252 $ 1,735,266 $ — $ — $ 3,531,518 $ 313,158 1968/2019 2013 (1) Prudential Center Office Boston, MA — 92,077 948,357 496,088 100,540 1,433,306 2,676 — 1,536,522 580,797 1965/1993/2002/2016-2017 1998/1999/2000 (1) Embarcadero Center Office San Francisco, CA — 179,697 847,410 352,847 180,420 1,199,534 — — 1,379,954 617,163 1970/1989 1998-1999 (1) 399 Park Avenue Office New York, NY — 339,200 700,358 240,911 339,200 941,269 — — 1,280,469 343,191 1961/2018 2002 (1) 601 Lexington Avenue Office New York, NY 644,778 241,600 494,782 417,816 279,281 661,822 — 213,095 1,154,198 280,028 1977/1997 2001 (1) Salesforce Tower Office San Francisco, CA — 200,349 946,205 — 200,349 946,205 — — 1,146,554 38,727 2018 2013 (1) 200 Clarendon Street and Garage Office Boston, MA — 219,543 667,884 210,160 250,134 829,529 17,924 — 1,097,587 214,533 1976 2010 (1) 250 West 55th Street Office New York, NY — 285,263 603,167 51,928 285,263 655,095 — — 940,358 116,857 2014 2007 (1) 100 Federal Street Office Boston, MA — 131,067 435,954 102,984 131,067 538,938 — — 670,005 122,799 1971-1975/2017 2012 (1) Times Square Tower Office New York, NY — 165,413 380,438 75,243 159,694 461,400 — — 621,094 207,272 2004 2000 (1) Carnegie Center Office Princeton, NJ — 142,666 316,856 137,317 90,498 451,661 54,680 — 596,839 204,380 1983-2016 1998/1999/2000/2007/2014/2017/2019 (1) Atlantic Wharf Office Boston, MA — 63,988 454,537 18,709 63,988 473,246 — — 537,234 131,828 2011 2007 (1) 510 Madison Avenue Office New York, NY — 103,000 253,665 25,495 103,000 279,160 — — 382,160 72,213 2012 2010 (1) Fountain Square Office Reston, VA — 56,853 306,298 12,140 56,853 318,438 — — 375,291 78,498 1986-1990 2012 (1) 599 Lexington Avenue Office New York, NY — 81,040 100,507 161,330 81,040 261,837 — — 342,877 176,101 1986 1997 (1) 680 Folsom Street Office San Francisco, CA — 72,545 219,766 7,907 72,545 227,673 — — 300,218 46,777 2014 2012 (1) 2200 Pennsylvania Avenue Office Washington, DC — — 183,541 113,627 109,038 188,130 — — 297,168 59,190 2011 2008 (1) 145 Broadway Office Cambridge, MA — 121 273,013 23,043 23,164 273,013 — — 296,177 1,511 2019 1997 (1) South of Market and Democracy Tower Office Reston, VA — 13,603 237,479 26,079 13,603 263,558 — — 277,161 99,406 2008-2009 2003 (1) 601 Massachusetts Avenue Office Washington, DC — 95,310 165,173 3,933 95,310 169,106 — — 264,416 24,502 2016 2008 (1) Bay Colony Corporate Center Office Waltham, MA — 18,789 148,451 80,077 18,789 228,528 — — 247,317 79,824 1985-1989 2011 (1) Gateway Center Office San Francisco, CA — 28,255 139,245 55,402 29,029 193,873 — — 222,902 104,993 1984/1986/2002 1999 (1) 535 Mission Street Office San Francisco, CA — 40,933 148,378 3,276 40,933 151,654 — — 192,587 26,293 2015 2013 (1) Mountain View Research Park Office Mountain View, CA — 95,066 68,373 12,704 95,066 81,077 — — 176,143 19,807 1977-1981/2007-2013 2013 (1) Reservoir Place Office Waltham, MA — 18,605 104,124 49,643 19,089 153,283 — — 172,372 69,794 1955/1987/2017 1997/1998 (1) 1330 Connecticut Avenue Office Washington, DC — 25,982 82,311 32,234 25,982 114,545 — — 140,527 31,553 1984/2018 2004 (1) Kingstowne Towne Center Office Alexandria, VA — 18,021 109,038 3,212 18,021 112,250 — — 130,271 44,258 2003-2006 2007 (1) One Freedom Square Office Reston, VA — 9,929 84,504 28,735 9,883 113,285 — — 123,168 57,516 2000 2003 (1) Weston Corporate Center Office Weston, MA — 25,753 92,312 (123 ) 25,854 92,088 — — 117,942 29,227 2010 2001 (1) Capital Gallery Office Washington, DC — 4,725 29,565 78,573 6,128 106,735 — — 112,863 68,953 1981/2006 2007 (1) Two Freedom Square Office Reston, VA — 13,930 77,739 16,997 13,866 94,800 — — 108,666 49,028 2001 2003 (1) Boston Properties Limited Partnership Schedule 3—Real Estate and Accumulated Depreciation December 31, 2019 (dollars in thousands) Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Property Name Type Location Encumbrances Land Building One and Two Reston Overlook Office Reston, VA — 16,456 66,192 19,763 15,074 87,337 — — 102,411 50,336 1999 2000 (1) 355 Main Street Office Cambridge, MA — 18,863 53,346 27,284 21,098 78,395 — — 99,493 26,362 1981/1996/2013 2006 (1) 140 Kendrick Street Office Needham, MA — 18,095 66,905 13,584 18,095 80,489 — — 98,584 34,667 2000 2004 (1) Discovery Square Office Reston, VA — 11,198 71,782 15,360 11,146 87,194 — — 98,340 42,152 2001 2003 (1) 880 & 890 Winter Street Office Waltham, MA — 29,510 65,812 — 29,510 65,812 — — 95,322 1,458 1998-1999 2019 (1) 10 CityPoint Office Waltham, MA — 1,953 85,752 4,534 2,127 90,112 — — 92,239 10,928 2016 1997 (1) 90 Broadway Office Cambridge, MA — 19,104 52,078 19,678 20,741 70,119 — — 90,860 23,581 1983/1998/2013 2006 (1) 77 CityPoint Office Waltham, MA — 13,847 60,383 10,451 13,997 70,684 — — 84,681 27,148 2008 2001 (1) 230 CityPoint Office Waltham, MA — 13,189 49,823 20,440 13,403 70,049 — — 83,452 28,831 1992 2005 (1) Waltham Weston Corporate Center Office Waltham, MA — 10,385 60,694 10,178 10,350 70,907 — — 81,257 34,777 2003 1999 (1) 3625-3635 Peterson Way Office Santa Clara, CA — 63,206 14,879 752 63,206 14,879 752 — 78,837 11,172 1979 2016 (1) 2440 West El Camino Real Office Mountain View, CA — 16,741 51,285 5,454 16,741 56,739 — — 73,480 13,090 1987/2003 2011 (1) 191 Spring Street Office Lexington, MA — 2,850 59,751 7,063 2,850 66,814 — — 69,664 21,801 1971/1995/2018 1997 (1) 300 Binney Street Office Cambridge, MA — 18,080 51,262 140 18,080 51,402 — — 69,482 11,146 2013 2009 (1) Wisconsin Place Office Chevy Chase, MD — — 53,349 14,924 — 68,273 — — 68,273 25,934 2009 2004 (1) Reston Corporate Center Office Reston, VA — 9,135 50,857 3,625 9,496 54,121 — — 63,617 29,170 1984 1998 (1) New Dominion Technology Park, Bldg. Two Office Herndon, VA — 5,584 51,868 412 5,574 52,290 — — 57,864 25,900 2004 1998 (1) 255 Main Street Office Cambridge, MA — 134 25,110 32,468 134 57,578 — — 57,712 33,108 1987 1997 (1) University Place Office Cambridge, MA 3,602 — 37,091 14,551 7,055 44,587 — — 51,642 29,044 1985 1998 (1) Sumner Square Office Washington, DC — 624 28,745 19,264 3,015 45,618 — — 48,633 26,547 1985 1999 (1) New Dominion Technology Park, Bldg. One Office Herndon, VA — 3,880 43,227 1,117 3,880 44,344 — — 48,224 28,398 2001 1998 (1) 200 West Street Office Waltham, MA — 16,148 24,983 5,550 16,148 28,429 — 2,104 46,681 16,298 1999 1997 (1) North First Business Park Office San Jose, CA — 23,398 13,069 4,548 23,371 17,644 — — 41,015 16,411 1981 2007 (1) 150 Broadway Office Cambridge, MA — 850 25,042 6,535 822 31,605 — — 32,427 19,342 1999 1997 (1) 105 Broadway Office Cambridge, MA — 1,299 12,943 9,300 1,868 21,674 — — 23,542 11,312 1990 1997 (1) Lexington Office Park Office Lexington, MA — 998 1,426 17,783 1,073 19,134 — — 20,207 14,114 1982 1997 (1) 201 Spring Street Office Lexington, MA — 2,849 15,303 73 2,849 15,376 — — 18,225 8,295 1997 1997 (1) The Point Office Waltham, MA — 6,395 10,040 421 6,492 10,364 — — 16,856 1,349 2015 2007 (1) 33 Hayden Avenue Office Lexington, MA — 266 3,234 12,261 266 15,495 — — 15,761 5,510 1979 1997 (1) 690 Folsom Street Office San Francisco, CA — 3,219 11,038 1,157 3,219 12,195 — — 15,414 2,284 2015 2012 (1) 92-100 Hayden Avenue Office Lexington, MA — 594 6,748 6,800 619 13,523 — — 14,142 11,847 1985 1997 (1) 181 Spring Street Office Lexington, MA — 1,066 9,520 1,800 1,066 11,320 — — 12,386 5,498 1999 1997 (1) 195 West Street Office Waltham, MA — 1,611 6,652 3,229 1,611 9,881 — — 11,492 8,087 1990 1997 (1) 7501 Boston Boulevard, Building Seven Office Springfield, VA — 665 9,273 311 665 9,584 — — 10,249 5,257 1997 1997 (1) Boston Properties Limited Partnership Schedule 3—Real Estate and Accumulated Depreciation December 31, 2019 (dollars in thousands) Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Property Name Type Location Encumbrances Land Building 7435 Boston Boulevard, Building One Office Springfield, VA — 392 3,822 4,290 486 8,018 — — 8,504 6,162 1982 1997 (1) 7450 Boston Boulevard, Building Three Office Springfield, VA — 1,165 4,681 2,177 1,327 6,696 — — 8,023 3,462 1987 1998 (1) 32 Hartwell Avenue Office Lexington, MA — 168 1,943 5,529 168 7,472 — — 7,640 1,819 1968/1979/1987 1997 (1) 250 Binney Street Office Cambridge, MA — 110 4,483 2,939 110 7,422 — — 7,532 5,660 1983 1997 (1) 8000 Grainger Court, Building Five Office Springfield, VA — 366 4,282 2,604 453 6,799 — — 7,252 5,597 1984 1997 (1) 453 Ravendale Drive Office Mountain View, CA — 5,477 1,090 676 5,477 1,766 — — 7,243 690 1977 2012 (1) 7300 Boston Boulevard, Building Thirteen Office Springfield, VA — 608 4,773 795 608 5,568 — — 6,176 1,928 2002 1997 (1) 17 Hartwell Avenue Office Lexington, MA — 26 150 5,907 26 6,057 — — 6,083 1,924 1968 1997 (1) 7601 Boston Boulevard, Building Eight Office Springfield, VA — 200 878 4,367 378 5,067 — — 5,445 4,507 1986 1997 (1) 7500 Boston Boulevard, Building Six Office Springfield, VA — 138 3,749 1,107 234 4,760 — — 4,994 4,097 1985 1997 (1) 8000 Corporate Court, Building Eleven Office Springfield, VA — 136 3,071 1,245 686 3,766 — — 4,452 3,094 1989 1997 (1) 7375 Boston Boulevard, Building Ten Office Springfield, VA — 23 2,685 851 47 3,512 — — 3,559 2,562 1988 1997 (1) 7374 Boston Boulevard, Building Four Office Springfield, VA — 241 1,605 1,445 303 2,988 — — 3,291 2,681 1984 1997 (1) 7451 Boston Boulevard, Building Two Office Springfield, VA — 249 1,542 1,354 535 2,610 — — 3,145 2,526 1982 1997 (1) Signature at Reston Residential Reston, VA — 27,076 190,580 393 27,076 190,973 — — 218,049 8,773 2018 2013 (1) Proto Kendall Square Residential Cambridge, MA — 9,243 127,248 2,939 9,245 130,185 — — 139,430 4,566 2018 2015 (1) The Avant at Reston Town Center Residential Reston, VA — 20,350 91,995 830 20,350 92,825 — — 113,175 14,728 2014 2010 (1) The Lofts at Atlantic Wharf Residential Boston, MA — 3,529 54,891 1,897 3,529 56,788 — — 60,317 12,639 2011 2007 (1) Boston Marriott Cambridge Hotel Cambridge, MA — 478 37,918 32,922 478 70,840 — — 71,318 45,842 1986/2017 1997 (1) Kendall Center Green Garage Garage Cambridge, MA — — 35,035 6,915 — 41,950 — — 41,950 13,404 1984 2006 (1) Kendall Center Yellow Garage Garage Cambridge, MA — 1,256 15,697 840 1,256 16,537 — — 17,793 5,847 2006 2004 (1) Kendall Center Blue Garage Garage Cambridge, MA — 1,163 11,633 486 1,163 12,119 — — 13,282 9,290 1990 1997 (1) The Skylyne (MacArthur Station Residences) Development Oakland, CA — — — 226,526 29,807 — — 196,719 226,526 — N/A N/A N/A 2100 Pennsylvania Avenue Development Washington, DC — — — 224,380 185,129 — — 39,251 224,380 1,024 N/A N/A N/A Reston Gateway Development Reston, VA — — — 150,632 — — — 150,632 150,632 — N/A 1998 N/A 17Fifty Presidents Street Development Reston, VA — — — 99,816 — — — 99,816 99,816 — N/A 2013 N/A 20 CityPoint Development Waltham, MA — 4,721 52,039 20,007 4,721 52,039 — 20,007 76,767 1,136 N/A 2007 N/A 325 Main Street Development Cambridge, MA — 174 — 68,710 772 — — 68,112 68,884 — N/A 1997 N/A North First Master Plan Land San Jose, CA — 35,004 — 3,932 — — 38,936 — 38,936 — N/A 2007 N/A Plaza at Almaden Land San Jose, CA — — — 34,889 — — 34,889 — 34,889 — N/A 2006 N/A Boston Properties Limited Partnership Schedule 3—Real Estate and Accumulated Depreciation December 31, 2019 (dollars in thousands) Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Property Name Type Location Encumbrances Land Building 425 Fourth Street Land San Francisco, CA — — — 22,074 — — 22,074 — 22,074 — N/A N/A N/A Springfield Metro Center Land Springfield, VA — — — 19,844 — — 19,844 — 19,844 — N/A 2007 N/A Reston Gateway Master Plan Land Reston, VA — — — 18,292 — — 18,292 — 18,292 — N/A 1998 N/A 214 Third Avenue Land Waltham, MA — — — 17,692 — — 17,692 — 17,692 — N/A 2006 N/A 103 Fourth Avenue Land Waltham, MA — — — 12,826 — — 12,826 — 12,826 — N/A 2007 N/A Crane Meadow Land Marlborough, MA — — — 8,866 — — 8,866 — 8,866 — N/A 2000 N/A Broad Run Business Park Land Loudoun County, VA — — — 2,396 — — 2,396 — 2,396 — N/A 1998 N/A Kendall Center Master Plan Land Cambridge, MA — — — 1,693 — — 1,693 — 1,693 — N/A 1997 N/A Weston Quarry Land Weston, MA — — — 1,249 — — 1,249 — 1,249 — N/A 2001 N/A Reston Overlook Master Plan Land Reston, VA — — — 39 — — 39 — 39 — N/A 2000 N/A $ 2,922,408 (2 ) $ 5,024,060 $ 13,057,336 $ 4,368,080 $ 5,373,884 (3 ) $ 16,031,028 (4 ) $ 254,828 (5 ) $ 789,736 $ 22,449,476 $ 5,135,289 Note: Total Real Estate does not include Furniture, Fixtures and Equipment totaling approximately $44,313 . Accumulated Depreciation does not include approximately $27,619 of accumulated depreciation related to Furniture, Fixtures and Equipment. The aggregate cost and accumulated depreciation for tax purposes was approximately $20.7 billion and $4.5 billion , respectively. (1) Depreciation of the buildings and improvements are calculated over lives ranging from the life of the lease to 40 years. (2) Includes unamortized deferred financing costs totaling approximately $(26.7) million . (3) Includes Right of Use Assets - Finance Leases and Right of Use Assets - Operating Leases of approximately $214,091 and $148,640 , respectively. (4) Includes Right of Use Assets - Finance Leases of approximately $23,303 . (5) Includes pre-development costs.
Activity of Real Estate and Accumulated Depreciation [Table Text Block]	A summary of activity for real estate and accumulated depreciation is as follows: 2019 2018 2017 Real Estate: Balance at the beginning of the year $ 21,207,189 $ 20,647,236 $ 19,701,185 Additions to/improvements of real estate 1,671,898 1,043,379 1,099,286 Assets sold/written-off (429,611 ) (483,426 ) (153,235 ) Balance at the end of the year $ 22,449,476 $ 21,207,189 $ 20,647,236 Accumulated Depreciation: Balance at the beginning of the year $ 4,773,800 $ 4,473,895 $ 4,116,020 Depreciation expense 557,130 525,584 488,919 Assets sold/written-off (195,641 ) (225,679 ) (131,044 ) Balance at the end of the year $ 5,135,289 $ 4,773,800 $ 4,473,895 Note: Real Estate and Accumulated Depreciation amounts do not include Furniture, Fixtures and Equipment.

Organization (Details)

Organization (Details) ft² in Millions	12 Months Ended
Organization (Details) ft² in Millions	Dec. 31, 2019ft²Real_Estate_Propertiesyrshares	Dec. 31, 2018shares
Real Estate Properties [Line Items]
General and limited partnership interest in the operating partnership (percent)	89.60%	89.70%
Restriction on redemption of OP units from date of issuance (years) \| yr	1
One OP unit is equivalent to one share of Common Stock (in shares) \| shares	1
OP unit conversion rate (in shares) \| shares	1
Number Of series Of preferred units outstanding	1
Number of VIEs - Consolidated	6
Number of VIEs - Total	8
Commercial Real Estate Properties [Member]
Real Estate Properties [Line Items]
Number of real estate properties	196
Net Rentable Area (in sf) \| ft²	52
Total Properties Under Construction [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	11
Net Rentable Area (in sf) \| ft²	5.5
Total Office Properties [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	177
Number of VIEs - Consolidated	5
Office Properties Under Construction [Member]
Real Estate Properties [Line Items]
Number of real estate properties	9
Retail Properties [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	12
Residential Properties [Member]
Real Estate Properties [Line Items]
Number of real estate properties	6
Residential Properties Under Construction [Member]
Real Estate Properties [Line Items]
Number of real estate properties	2
Hotel Property [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	1
Series B Cumulative Redeemable Preferred Stock / Unit [Member]
Real Estate Properties [Line Items]
Preferred Stock, Dividend Rate, Percentage	5.25%
Preferred stock / units, shares / units outstanding (in shares / units) \| shares	80,000	80,000
Depositary shares of Series B Cumulative Redeemable Preferred [Member]
Real Estate Properties [Line Items]
Preferred stock / units, shares / units outstanding (in shares / units) \| shares	8,000,000
Series B Preferred Units [Member]
Real Estate Properties [Line Items]
Preferred stock / units, shares / units outstanding (in shares / units) \| shares	80,000

Summary Of Significant Accoun_4

Summary Of Significant Accounting Policies (Narrative) (Details)	3 Months Ended	12 Months Ended
	Dec. 31, 2019USD ($)	Dec. 31, 2019USD ($)yr	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Jan. 01, 2019USD ($)
Entity Information [Line Items]
Probable Sale Term of Property After Classified As Held For Sale (Years) \| yr		1
Interest costs capitalized		$ 54,911,000	$ 65,766,000	$ 61,070,000
Salaries And Related Costs Capitalized		10,400,000	12,500,000	13,200,000
Cash FDIC Insured Limit	$ 250,000	250,000
Separate Unrestricted Cash For Deferred Compensation Plans	36,700,000	36,700,000	28,200,000
Gains (losses) from investments in securities		6,417,000	(1,865,000)	3,678,000
Internal Leasing Salaries And Related Costs Capitalized			5,400,000	5,000,000
Straight-line rent adjustments		58,400,000	51,900,000	54,800,000
Above and below market rent adjustments, net		$ 20,900,000	23,800,000	23,500,000
REIT Annual Taxable Income Distribution Requirement Percentage, Minimum		90.00%
Company Annual Taxable Income Distribution Percentage		100.00%
Cumulative effect of a change in accounting principle		$ 4,379,000	(5,496,000)	2,035,000
Right of use assets - operating leases	148,640,000	148,640,000			$ 151,800,000
Operating Lease, Liability	200,180,000	200,180,000			$ 199,300,000
Redeemable Noncontrolling Interest, Equity, Carrying Amount	8,365,000	8,365,000
Accounts Payable and Accrued Liabilities	$ 377,553,000	377,553,000	276,645,000
Lessee, Finance Lease, Description	four
Boston Properties Limited Partnership
Entity Information [Line Items]
Interest costs capitalized		54,911,000	65,766,000	61,070,000
Gains (losses) from investments in securities		6,417,000	(1,865,000)	3,678,000
Right of use assets - operating leases	$ 148,640,000	148,640,000
Operating Lease, Liability	200,180,000	200,180,000
Redeemable Noncontrolling Interest, Equity, Carrying Amount	8,365,000	8,365,000
Accounts Payable and Accrued Liabilities	377,553,000	377,553,000	276,645,000
deferred compenstation for directors [Member]
Entity Information [Line Items]
Change in classification of director deferred compensation plan		8,400,000
Redeemable Noncontrolling Interest, Equity, Carrying Amount	8,100,000	8,100,000
Accounts Payable and Accrued Liabilities	$ 300,000	300,000
Dividends In Excess Of Earnings [Member]
Entity Information [Line Items]
Cumulative effect of a change in accounting principle		3,864,000	(4,933,000)	272,000
Noncontrolling Interests [Member]
Entity Information [Line Items]
Cumulative effect of a change in accounting principle		445,000	$ (563,000)	$ 1,763,000
Noncontrolling interest - property partnerships [Member]
Entity Information [Line Items]
Cumulative effect of a change in accounting principle		$ 70,000

Summary Of Significant Accoun_5

Summary Of Significant Accounting Policies Schedule of Estimated Useful Lives (Details)	12 Months Ended
	Dec. 31, 2019
Land Improvements [Member] \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (years)	25 years
Land Improvements [Member] \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (years)	40 years
Building and Building Improvements [Member] \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (years)	10 years
Building and Building Improvements [Member] \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (years)	40 years
Tenant Improvement [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life, description	Shorter of useful life or terms of related lease
Furniture, fixtures and equipment [Member] \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (years)	3 years
Furniture, fixtures and equipment [Member] \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (years)	7 years

Summary Of Significant Accoun_6

Summary Of Significant Accounting Policies Schedule of Finite Lived Intangible Assets Future Amortization Expense (Details) $ in Thousands	Dec. 31, 2019USD ($)
Finite-Lived Intangible Assets [Line Items]
2020	$ 17,536
2021	11,001
2022	5,918
2023	4,286
2024	2,510
Acquired Above-Market Lease Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
2020	5,440
2021	3,054
2022	357
2023	183
2024	135
Acquired Below-Market Lease Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
2020	10,673
2021	6,455
2022	5,699
2023	5,558
2024	$ 4,043

Summary Of Significant Accoun_7

Summary Of Significant Accounting Policies (Carrying Value Of Indebtedness And Corresponding Estimate Of Fair Value) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Summary Of Significant Accounting Policies [Line Items]
Related party note receivable	$ 80,000	$ 80,000
Note receivable	15,920	19,468
Mortgage notes payable, net	2,922,408	2,964,572
Unsecured senior notes, net	8,390,459	7,544,697
Unsecured line of credit	0	0
Unsecured term loan, net	498,939	498,488
Total	2,949,154
Carrying Amount [Member]
Summary Of Significant Accounting Policies [Line Items]
Related party note receivable	80,000	80,000
Note receivable	15,920	19,468
Total	95,920	99,468
Mortgage notes payable, net	2,922,408	2,964,572
Unsecured senior notes, net	8,390,459	7,544,697
Unsecured line of credit	0	0
Unsecured term loan, net	498,939	498,488
Total	11,811,806	11,007,757
Estimated Fair Value [Member]
Summary Of Significant Accounting Policies [Line Items]
Related party note receivable	81,931	80,000
Note receivable	14,978	19,468
Total	96,909	99,468
Mortgage notes payable, net	2,984,956	2,903,925
Unsecured senior notes, net	8,826,375	7,469,338
Unsecured line of credit	0	0
Unsecured term loan, net	500,561	500,783
Total	$ 12,311,892	$ 10,874,046

Summary Of Significant Accoun_8

Summary Of Significant Accounting Policies Lessee, Lease Costs and Other Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)
Leases [Abstract]
Finance leases under development	3
Operating lease costs	$ 14,573
Amortization of right of use asset	29	[1]
Interest on lease liabilities	$ 47	[2]
Operating Lease, Weighted Average Remaining Lease Term	51 years
Finance Lease, Weighted Average Remaining Lease Term	71 years
Operating Lease, Weighted Average Discount Rate, Percent	5.70%
Finance Lease, Weighted Average Discount Rate, Percent	6.20%

[1]	The finance leases relate to either land, buildings or assets that remain in development. For land leases classified as finance leases because of a purchase option that the Company views as an economic incentive, the Company follows its existing policy and does not depreciate land because it is assumed to have an indefinite life. For all other finance leases, the Company would amortize the right of use asset over the shorter of the useful life of the asset or the lease term. If the finance lease relates to a property under development, the amortization of the right of use asset may be eligible for capitalization. For assets under development, depreciation may commence once the asset is placed in-service and depreciation would be recognized in accordance with the Company’s policy.
[2]	Three of the finance leases relate to assets under development and as such, the entire interest amount was capitalized.

Summary Of Significant Accoun_9

Summary Of Significant Accounting Policies Future Minimum Lease Payments for Ground Leases (Details) $ in Thousands	Dec. 31, 2018USD ($)
Leases [Abstract]
2019	$ 11,425
2020	18,425
2021	25,310
2022	8,894
2023	9,084
Thereafter	$ 567,232

Summary Of Significant Accou_10

Summary Of Significant Accounting Policies Future Minimum Lease Payments, Capital Leases (Details) $ in Thousands	Dec. 31, 2018USD ($)
Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2019	$ 1,441
2020	12,682
2021	2,123
2022	1,253
2023	944
Thereafter	73,241
Total expected minimum lease payments	91,684
Interest portion	(27,497)
Present value of expected net minimum lease payments	$ 64,187

Summary Of Significant Accou_11

Summary Of Significant Accounting Policies Lease Liability Maturity Schedule (Details) - USD ($) $ in Thousands		Dec. 31, 2019	Jan. 01, 2019
Leases [Abstract]
Lessee, Finance Lease, Option to Extend, Reasonably Certain 2024		$ 38,700
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2020		10,050
2021		24,973
2022		18,041
2023		10,322
2024		9,277
Thereafter		557,954
Total lease payments		630,617
Less: interest portion		(430,437)
Present value of lease payments		200,180	$ 199,300
Finance Lease Liabilities, Payments, Due [Abstract]
2020		834
2021		5,960
2022		10,208
2023		9,708
2024	[1]	48,518
Thereafter		1,383,242
Total expected minimum lease payments		1,458,470
Interest portion		(1,234,428)
Present value of lease payments		$ 224,042

[1]	Finance lease payments in 2024 include approximately $38.7 million related to a purchase option that the Company is reasonably certain it will exercise.

Summary Of Significant Accou_12

Summary Of Significant Accounting Policies Lessor, Lease Income Table (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)
Leases [Abstract]
Fixed contractual payments	$ 2,261,260
Variable lease payments	496,754
Lease	$ 2,758,014

Summary Of Significant Accou_13

Summary Of Significant Accounting Policies Schedule of Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017		Dec. 17, 2019
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes [Line Items]
Dividends treatment for federal tax purposes.	$ 3.15	[1]	$ 3.57	[2]	$ 2.91	[3]
Dividends Treatment For Federal Tax Purposes, Percentage	100.00%		100.00%		100.00%
Dividends Payable, Amount Per Share							$ 0.98
Dividend Declared
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes [Line Items]
Dividends Payable, Amount Per Share	$ 0.98		$ 0.95		$ 0.80
Allocated to fiscal 2020
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes [Line Items]
Dividends Payable, Amount Per Share	0.94
Allocated to fiscal 2019
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes [Line Items]
Special dividend / distribution (per share / common unit amount)	0.04
Dividends Payable, Amount Per Share			0.26
Allocated to fiscal 2018
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes [Line Items]
Special dividend / distribution (per share / common unit amount)			0.69
Dividends Payable, Amount Per Share					0.33
Allocated to fiscal 2017
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes [Line Items]
Special dividend / distribution (per share / common unit amount)					0.47
Capital Gains Income
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes [Line Items]
Dividends treatment for federal tax purposes.	$ 0.16		$ 0.78		$ 0.05
Dividends Treatment For Federal Tax Purposes, Percentage	5.16%		21.83%		1.71%
Ordinary Income
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes [Line Items]
Dividends treatment for federal tax purposes.	$ 2.99		$ 2.79		$ 2.86
Dividends Treatment For Federal Tax Purposes, Percentage	94.84%		78.17%		98.29%

[1]	The fourth quarter 2019 regular quarterly dividend was $0.98 per common share of which approximately $0.04 per common share was allocable to 2019 and approximately $0.94 per common share is allocable to 2020.
[2]	The fourth quarter 2018 regular quarterly dividend was $0.95 per common share of which approximately $0.69 per common share was allocable to 2018 and approximately $0.26 per common share is allocable to 2019.
[3]	The fourth quarter 2017 regular quarterly dividend was $0.80 per common share of which approximately $0.47 per common share was allocable to 2017 and approximately $0.33 per common share is allocable to 2018.

Real Estate Schedule of Real Es

Real Estate Schedule of Real Estate Properties (Details) - USD ($) $ in Thousands		Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Real Estate Properties [Line Items]
Land		$ 5,111,606		$ 5,072,568
Right-of-use assets - finance leases		237,394
Right of use assets - operating leases		148,640	$ 151,800
Land held for future development	[1]	254,828		200,498
Buildings and improvements		13,646,054		13,356,751
Tenant improvements		2,656,439		2,396,932
Furniture, Fixtures and Equipment		44,313		44,351
Construction in progress		789,736		578,796
Total		22,889,010		21,649,896
Less: accumulated depreciation		(5,266,798)		(4,897,777)
Total real estate		17,622,212		16,752,119
Boston Properties Limited Partnership
Real Estate Properties [Line Items]
Land		5,011,153		4,971,475
Right-of-use assets - finance leases		237,394
Right of use assets - operating leases		148,640
Land held for future development	[1]	254,828		200,498
Buildings and improvements		13,351,286		13,059,488
Tenant improvements		2,656,439		2,396,932
Furniture, Fixtures and Equipment		44,313		44,351
Construction in progress		789,736		578,796
Total		22,493,789		21,251,540
Less: accumulated depreciation		(5,162,908)		(4,800,475)
Total real estate		$ 17,330,881		$ 16,451,065

[1]	Includes pre-development costs.

Real Estate (Narrative) (Detail

Real Estate (Narrative) (Details) $ in Thousands	Dec. 20, 2019USD ($)	Sep. 20, 2019USD ($)ft²a	Jul. 16, 2019USD ($)ft²	Jun. 28, 2019USD ($)ft²	Jun. 03, 2019USD ($)ft²	May 09, 2019USD ($)ft²	Jan. 24, 2019USD ($)ft²a	Jan. 23, 2019USD ($)	Dec. 31, 2019USD ($)ft²		Sep. 30, 2019USD ($)ft²	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2019USD ($)ft²		Jun. 02, 2019USD ($)	Jun. 27, 2019USD ($)	Dec. 31, 2019USD ($)ft²		Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Oct. 24, 2019ft²	Aug. 27, 2019USD ($)ft²Real_Estate_Properties	Jun. 01, 2019ft²	Apr. 18, 2019USD ($)	Jan. 10, 2019USD ($)ft²
Real Estate Properties [Line Items]
Accelerated depreciation																						$ 677,764		$ 645,649	$ 617,547
Right-of-use assets - finance leases									$ 237,394									$ 237,394				237,394
Lease liabilities - finance leases									224,042									$ 224,042				224,042
Proceeds from sales of real estate																						90,824		455,409	29,810
Gains (loss) on sales of real estate																						709		182,356	7,663
Payments to Acquire Equity Method Investments																						87,392		345,717	109,015
Revenues									$ 757,501		$ 743,553	$ 733,741	$ 725,767	$ 705,157	$ 686,284	$ 664,484	$ 661,151					$ 2,960,562		2,717,076	2,602,076
2600 Tower Oaks Boulevard [Member]
Real Estate Properties [Line Items]
Net Rentable Area (in sf) \| ft²							179,000
Contractual Sales Price							$ 22,700
Proceeds from sales of real estate							21,400
Gains (loss) on sales of real estate							$ (600)
Impairment losses																								3,100
Operating Income (Loss)								$ (200)																(600)	(100)
One Tower Center [Member]
Real Estate Properties [Line Items]
Net Rentable Area (in sf) \| ft²					410,000
Contractual Sales Price																													$ 38,000
Proceeds from sales of real estate					$ 36,600
Gains (loss) on sales of real estate					$ (800)
Impairment losses													24,000
Operating Income (Loss)																				$ (900)				(2,700)	(3,500)
164 Lexington Road [Member]
Real Estate Properties [Line Items]
Net Rentable Area (in sf) \| ft²				64,000
Contractual Sales Price				$ 4,000
Proceeds from sales of real estate				3,800
Gains (loss) on sales of real estate				2,500
Operating Income (Loss)																					$ (100)			(200)	(200)
Washingtonian North [Member]
Real Estate Properties [Line Items]
Contractual Sales Price	$ 7,800
Proceeds from sales of real estate	7,300
Gains (loss) on sales of real estate	$ (100)
Impairment losses																								1,800
325 Main Street
Real Estate Properties [Line Items]
Term of Lease Signed (in years)						15-year
Net Rentable Area (in sf) \| ft²						115,000			115,000									115,000				115,000
Accelerated depreciation						$ 9,900
20 CityPoint
Real Estate Properties [Line Items]
Net Rentable Area (in sf) \| ft²																												211,000
200 West Street
Real Estate Properties [Line Items]
Net Rentable Area (in sf) \| ft²											261,000
145 Broadway
Real Estate Properties [Line Items]
Net Rentable Area (in sf) \| ft²																										483,000
Platform 16
Real Estate Properties [Line Items]
Net Rentable Area (in sf) \| ft²							1,100,000
Lessee, Finance Lease, Term of Contract							65 years
Area of Land \| a							5.6
Finance lease fixed purchase price							$ 134,800
Right-of-use assets - finance leases							122,600
Lease liabilities - finance leases							$ 122,563
2100 Pennsylvania Avenue
Real Estate Properties [Line Items]
Term of Lease Signed (in years)			16-year
Square Footage Of Signed Lease \| ft²			300,000
Net Rentable Area (in sf) \| ft²			470,000
Lessee, Finance Lease, Term of Contract			75 years
Right-of-use assets - finance leases			$ 185,100
Prepaid Rent			15,000
Lease liabilities - finance leases			164,977
Finance lease - right of use asset -prepaid rent			15,000
Finance lease - right of use asset - initial direct costs			$ 5,100
Lessee, finance lease, term of amortization			75 years
Carnegie Center
Real Estate Properties [Line Items]
Net Rentable Area (in sf) \| ft²																														1,700,000
Aggregate purchase price																														$ 51,500
Deferred purchase price																														$ 8,600
880 & 890 Winter Street [Member]
Real Estate Properties [Line Items]
Net Rentable Area (in sf) \| ft²																											392,000
Aggregate purchase price																											$ 106,000
Number of real estate properties \| Real_Estate_Properties																											2
Operating Income (Loss)																		$ (600)
Revenues																		4,900
Boston Properties Limited Partnership
Real Estate Properties [Line Items]
Accelerated depreciation																						$ 669,956		637,891
Right-of-use assets - finance leases									$ 237,394									237,394				237,394
Lease liabilities - finance leases									224,042									$ 224,042				224,042
Proceeds from sales of real estate																						90,824		455,409	29,810
Gains (loss) on sales of real estate																						858		190,716	8,240
Impairment losses																									0
Payments to Acquire Equity Method Investments																						87,392		345,717	109,015
Revenues									$ 757,501		$ 743,553	$ 733,741	725,767	$ 705,157	$ 686,284	$ 664,484	$ 661,151					$ 2,960,562		2,717,076	$ 2,602,076
Boston Properties Limited Partnership \| 2600 Tower Oaks Boulevard [Member]
Real Estate Properties [Line Items]
Impairment losses																								$ 1,500
Boston Properties Limited Partnership \| One Tower Center [Member]
Real Estate Properties [Line Items]
Impairment losses													$ 22,300
Boston Properties Limited Partnership \| 164 Lexington Road [Member]
Real Estate Properties [Line Items]
Gains (loss) on sales of real estate				$ 2,600
Boston Properties Limited Partnership \| 325 Main Street
Real Estate Properties [Line Items]
Accelerated depreciation						$ 9,500
Future Office Building [Member] \| 325 Main Street
Real Estate Properties [Line Items]
Square Footage Of Signed Lease \| ft²						379,000
Net Rentable Area (in sf) \| ft²						420,000			420,000									420,000				420,000
Future Retail Building [Member] \| 325 Main Street
Real Estate Properties [Line Items]
Net Rentable Area (in sf) \| ft²						41,000			41,000									41,000				41,000
Office Properties Under Construction [Member] \| 200 West Street
Real Estate Properties [Line Items]
Net Rentable Area (in sf) \| ft²											126,000
Platform 16
Real Estate Properties [Line Items]
Net Rentable Area (in sf) \| ft²		1,100,000
Lessee, Finance Lease, Term of Contract		65 years
Area of Land \| a		5.6
Finance lease fixed purchase price		$ 134,800
Payments to Acquire Equity Method Investments		$ 28,200
Ownership Percentage		55.00%							55.00%	[1]								55.00%	[1]			55.00%	[1]
Joint Venture Partner [Member] \| Platform 16
Real Estate Properties [Line Items]
Payments to Acquire Equity Method Investments		$ 23,100
Ownership Percentage		45.00%

[1]	This entity is a VIE (See Note 1 ).

Real Estate Finance Lease Liabi

Real Estate Finance Lease Liability, Maturity (Details) - USD ($) $ in Thousands		Dec. 31, 2019	Jul. 16, 2019	Jan. 24, 2019
Capital Leased Assets [Line Items]
2019		$ 834
2020		5,960
2021		10,208
2022		9,708
2023	[1]	48,518
Thereafter		1,383,242
Total expected minimum lease payments		1,458,470
Interest portion		(1,234,428)
Present value of lease payments		$ 224,042
Platform 16
Capital Leased Assets [Line Items]
2019				$ 17,918
2020				109,460
Total expected minimum lease payments				127,378
Interest portion				(4,815)
Present value of lease payments				$ 122,563
2100 Pennsylvania Avenue
Capital Leased Assets [Line Items]
2019			$ 0
2020			0
2021			3,863
2022			8,576
2023			8,669
Thereafter			1,358,518
Total expected minimum lease payments			1,379,626
Interest portion			(1,214,649)
Present value of lease payments			$ 164,977

[1]	Finance lease payments in 2024 include approximately $38.7 million related to a purchase option that the Company is reasonably certain it will exercise.

Real Estate Asset Acquisition -

Real Estate Asset Acquisition - 880 & 890 Winter Street (Details) - 880 & 890 Winter Street [Member] $ in Thousands	Aug. 27, 2019USD ($)
Business Acquisition [Line Items]
Land	$ 29,510
Building and improvements	59,788
Tenant improvements	6,024
Net assets acquired	105,970
In-place lease intangibles
Business Acquisition [Line Items]
Lease intangibles	11,494
Above-market lease intangibles
Business Acquisition [Line Items]
Lease intangibles	246
Below-market lease intangibles
Business Acquisition [Line Items]
Lease intangibles	$ (1,092)

Real Estate Asset Acquisition_2

Real Estate Asset Acquisition - Lease Intangibles Amortization (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Aug. 27, 2019
Acquired Finite-Lived Intangible Assets [Line Items]
Period from August 27, 2019 through December 31, 2019	$ 17,536
2020	11,001
2021	5,918
2022	4,286
2023	$ 2,510
880 & 890 Winter Street [Member] \| Acquired In-Place Lease Intangibles [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Period from August 27, 2019 through December 31, 2019		$ 1,801
2020		4,485
2021		2,391
2022		1,121
2023		179
2024		60
880 & 890 Winter Street [Member] \| Acquired Above-Market Lease Intangibles [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Period from August 27, 2019 through December 31, 2019		28
2020		80
2021		80
2022		43
2023		15
2024		0
880 & 890 Winter Street [Member] \| Acquired Below-Market Lease Intangibles [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Period from August 27, 2019 through December 31, 2019		(226)
2020		(599)
2021		(237)
2022		(30)
2023		0
2024		$ 0

Deferred Charges (Details)

Deferred Charges (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred Charges [Abstract]
Leasing costs, including lease related intangibles	$ 1,155,958	$ 1,191,297
Financing costs	12,728	12,796
Deferred charges, gross	1,168,686	1,204,093
Less: Accumulated amortization	(479,473)	(525,369)
Deferred charges, total	$ 689,213	$ 678,724

Deferred Charges Schedule of Ac

Deferred Charges Schedule of Acquired In-Place Lease Intangibles (Details) $ in Thousands	Dec. 31, 2019USD ($)
Deferred Charges [Abstract]
2020	$ 17,536
2021	11,001
2022	5,918
2023	4,286
2024	$ 2,510

Investments in Unconsolidated_3

Investments in Unconsolidated Joint Ventures (Investments in Unconsolidated Joint Ventures) (Details) $ in Thousands		12 Months Ended
		Dec. 31, 2019USD ($)ft²Land_ParcelsBuildingspayments		Sep. 20, 2019	Sep. 05, 2019	Jun. 27, 2019	Dec. 31, 2018USD ($)
Schedule of Equity Method Investments [Line Items]
Other Liabilities		$ 387,994					$ 503,726
Investments in unconsolidated joint ventures		955,647					956,309
Investments In Affiliates Subsidiaries Associates And Joint Ventures net	[1]	933,223					931,219
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Other Liabilities		$ 22,400					25,100
Square 407 Limited Partnership [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Market Square North
Ownership Percentage		50.00%
Other Liabilities	[1]	$ 4,872					6,424
BP/CRF Metropolitan Square LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Metropolitan Square
Ownership Percentage		20.00%
Investments in unconsolidated joint ventures	[1]	$ 9,134					2,644
901 New York Avenue LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		901 New York Avenue
Ownership Percentage	[2]	25.00%
Other Liabilities	[1]	$ 12,113					13,640
WP Project Developer LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Wisconsin Place Land and Infrastructure
Ownership Percentage	[3]	33.30%
Investments in unconsolidated joint ventures	[1]	$ 36,789					38,214
Annapolis Junction NFM, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Annapolis Junction
Ownership Percentage	[4]	50.00%
Investments in unconsolidated joint ventures	[1]	$ 25,391					25,268
Number of real estate properties \| Buildings		3
Parcels of undeveloped land \| Land_Parcels		2
540 Madison Venture LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		540 Madison Avenue
Ownership Percentage		60.00%	[5]			60.00%
Investments in unconsolidated joint ventures	[1]	$ 2,953					66,391
500 North Capitol Venture LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		500 North Capitol Street, NW
Ownership Percentage		30.00%
Other Liabilities	[1]	$ 5,439					5,026
501 K Street LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		1001 6th Street
Ownership Percentage	[6]	50.00%
Investments in unconsolidated joint ventures	[1]	$ 42,496					42,557
Potential additonal payments to joint venture partner \| payments		2
Minimum square footage to make a potential additional payment to joint venture partner (in sqft) \| ft²		520,000
Podium Developer LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		The Hub on Causeway - Podium
Ownership Percentage		50.00%
Investments in unconsolidated joint ventures	[1]	$ 49,466					69,302
Residential Tower Developer LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Hub50House
Ownership Percentage		50.00%
Investments in unconsolidated joint ventures	[1]	$ 55,092					47,505
Hotel Tower Developer LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		The Hub on Causeway - Hotel Air Rights
Ownership Percentage		50.00%
Investments in unconsolidated joint ventures	[1]	$ 9,883					3,022
Office Tower Developer LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		100 Causeway Street
Ownership Percentage		50.00%			50.00%
Investments in unconsolidated joint ventures	[1]	$ 56,606					23,804
1265 Main Office JV LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		1265 Main Street
Ownership Percentage		50.00%
Investments in unconsolidated joint ventures	[1]	$ 3,780					3,918
BNY Tower Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Dock 72
Ownership Percentage		50.00%
Investments in unconsolidated joint ventures	[1]	$ 94,804					82,520
BNYA Amenity Operator LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Dock 72
Ownership Percentage		50.00%
Investments in unconsolidated joint ventures	[1]	$ 0
CA-Colorado Center Limited Partnership [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Colorado Center
Ownership Percentage		50.00%
Investments in unconsolidated joint ventures	[1]	$ 252,069					253,495
7750 Wisconsin Avenue LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		7750 Wisconsin Avenue
Ownership Percentage		50.00%
Investments in unconsolidated joint ventures	[1]	$ 56,247					69,724
BP-M 3HB Venture LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		3 Hudson Boulevard
Ownership Percentage		25.00%
Investments in unconsolidated joint ventures	[1]	$ 67,499					46,993
SMBP Venture LP [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Santa Monica Business Park
Ownership Percentage		55.00%
Investments in unconsolidated joint ventures	[1]	$ 163,937					$ 180,952
Platform 16 Holdings LP [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Platform 16
Ownership Percentage		55.00%	[7]	55.00%
Investments in unconsolidated joint ventures	[1]	$ 29,501
Entity Owning Land And Infrastructure Of Project [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		33.30%

[1]	Investments with deficit balances aggregating approximately $22.4 million and $25.1 million at December 31, 2019 and 2018 , respectively, are included within Other Liabilities in the Company’s Consolidated Balance Sheets.
[2]	The Company’s economic ownership has increased based on the achievement of certain return thresholds.
[3]	The Company’s wholly-owned subsidiary that owns Wisconsin Place Office also owns a 33.3% interest in the joint venture entity that owns the land, parking garage and infrastructure of the project.
[4]	The joint venture owns three in-service buildings and two undeveloped land parcels.
[5]	T he property was sold on June 27, 2019. As of December 31, 2019, the investment is comprised of undistributed cash. See note below for additional details.
[6]	Under the joint venture agreement for this land parcel, the partner will be entitled to up to two additional payments from the venture based on increases in total entitled square footage of the project above 520,000 square feet and achieving certain project returns at stabilization.
[7]	This entity is a VIE (See Note 1 ).

Investments in Unconsolidated_4

Investments in Unconsolidated Joint Ventures (Balance Sheets of the Unconsolidated Joint Ventures) (Details) - USD ($) $ in Thousands		Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
ASSETS
Real estate and development in process, net		$ 17,622,212		$ 16,752,119
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Mortgage and notes payable, net		2,922,408		2,964,572
Other Liabilities		387,994		503,726
Total liabilities and equity / capital		21,284,905		20,256,477
Carying value of the Company's investment in unconsolidated joint ventures		955,647		956,309
Right-of-use assets - finance leases		237,394
Right of use assets - operating leases		148,640	$ 151,800
Lease liabilities - finance leases		224,042
Lease liabilities - operating leases		200,180	$ 199,300
Unconsolidated Joint Ventures [Member]
ASSETS
Real estate and development in process, net	[1]	3,904,400		3,545,906
Other assets		502,706		543,512
Total assets		4,407,106		4,089,418
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Mortgage and notes payable, net		2,218,853		2,017,609
Other Liabilities	[2]	749,675		582,006
Members'/Partners' equity		1,438,578		1,489,803
Total liabilities and equity / capital		4,407,106		4,089,418
Company's share of equity		591,905		622,498
Basis differentials	[3]	341,318		308,721
Carying value of the Company's investment in unconsolidated joint ventures	[4]	933,223		931,219
Right-of-use assets - finance leases		383,900
Right of use assets - operating leases		12,100
Lease liabilities - finance leases		510,800
Lease liabilities - operating leases		17,300
Colorado Center [Member]
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Basis differentials		311,300		316,700
Unconsolidated Joint Ventures [Member]
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Other Liabilities		$ 22,400		$ 25,100

[1]	At December 31, 2019, this amount includes right of use assets - finance leases and right of use assets - operating leases totaling approximately $383.9 million and $12.1 million , respectively.
[2]	At December 31, 2019, this amount includes lease liabilities - finance leases and lease liabilities - operating leases totaling approximately $510.8 million and $17.3 million , respectively.
[3]	This amount represents the aggregate difference between the Company’s historical cost basis and the basis reflected at the joint venture level, which is typically amortized over the life of the related assets and liabilities. Basis differentials result from impairments of investments, acquisitions through joint ventures with no change in control and upon the transfer of assets that were previously owned by the Company into a joint venture. In addition, certain acquisition, transaction and other costs may not be reflected in the net assets at the joint venture level. At December 31, 2019 and 2018 , there was an aggregate basis differential of approximately $311.3 million and $316.7 million , respectively, between the carrying value of the Company’s investment in the joint venture that owns Colorado Center and the joint venture’s basis in the assets and liabilities, which differential (excluding land) shall be amortized over the remaining lives of the related assets and liabilities.
[4]	Investments with deficit balances aggregating approximately $22.4 million and $25.1 million at December 31, 2019 and 2018 , respectively, have been reflected within Other Liabilities in the Company’s Consolidated Balance Sheets.

Investments in Unconsolidated_5

Investments in Unconsolidated Joint Ventures (Statements of Operations of the Joint Ventures) (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Total revenue		$ 757,501	$ 743,553	$ 733,741	$ 725,767	$ 705,157	$ 686,284	$ 664,484	$ 661,151	$ 2,960,562		$ 2,717,076		$ 2,602,076
Expenses
Transaction costs										1,984		1,604		668
Depreciation and amortization										677,764		645,649		617,547
Total expenses										1,914,925		1,791,579		1,693,966
Other income (expense)
Gains on sales of real estate										709		182,356		7,663
Interest expense										(412,717)		(378,168)		(374,481)
Net income										651,999		712,563		562,481
Income from unconsolidated joint ventures										46,592		2,222		11,232
Straight-line rent adjustments										58,400		51,900		54,800
Above and below market rent adjustments, net										20,900		23,800		23,500
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Total revenue	[1]									322,817		271,951		222,517
Expenses
Operating										122,992		106,610		90,542
Transaction costs										1,000		0		0
Depreciation and amortization										102,296		103,079	[2]	57,079
Total expenses										226,288		209,689		147,621
Other income (expense)
Gains on sales of real estate										32,706		16,951		0
Interest expense										(84,409)		(71,308)		(46,371)
Net income										44,826		7,905		28,525
Company's share of net income										24,423		8,084		18,439
Basis differential	[4]									22,169	[3]	(5,862)		(7,207)
Income from unconsolidated joint ventures										46,592		2,222		11,232
Straight-line rent adjustments										32,400		15,900		21,700
Metropolitan Square [Member]
Expenses
Depreciation and amortization												22,400
Metropolitan Square [Member] \| Boston Properties, Inc. [Member]
Expenses
Depreciation and amortization												4,500
540 Madison Avenue [Member]
Other income (expense)
Gain on sale of real estate										47,200
Colorado Center [Member]
Other income (expense)
Straight-line rent adjustments										2,100		2,400		1,900
Above and below market rent adjustments, net										$ 1,700		$ 1,600		$ 2,900

[1]	Includes straight-line rent adjustments of approximately $32.4 million , $15.9 million and $21.7 million for the years ended December 31, 2019 , 2018 and 2017 , respectively.
[2]	During the year ended December 31, 2018, the joint venture that owns Metropolitan Square in Washington, DC, commenced a renovation project and recorded accelerated depreciation expense of approximately $22.4 million related to the remaining book value of the assets to be replaced. The Company’s share of the accelerated depreciation expense totaled approximately $4.5 million .
[3]	For the year ended December 31, 2019, represents the gain on sale of 540 Madison Avenue recognized by the joint venture, as described below. During 2008, the Company recognized an other-than-temporary impairment loss on its investment in the unconsolidated joint venture resulting in a basis differential between the carrying value of the Company’s investment in the joint venture and the joint venture’s basis in the assets and liabilities of the property. As a result of the historical basis difference, the Company recognized a gain on sale of real estate totaling approximately $47.2 million for the year ended December 31, 2019, which consists of its share of the gain on sale reported by the joint venture as well as an adjustment for the basis differential. The gain on sale of real estate is included in Income from Unconsolidated Joint Ventures in the Company’s Consolidated Statements of Operations.
[4]	Includes straight-line rent adjustments of approximately $2.1 million , $2.4 million and $1.9 million for the years ended December 31, 2019, 2018 and 2017, respectively. Also includes net above-/below-market rent adjustments of approximately $1.7 million , $1.6 million and $2.9 million

Investment in unconsolidated Jo

Investment in unconsolidated Joint Ventures (Narrative) (Details) $ in Thousands

Dec. 06, 2019USD ($)ft²yr

Sep. 20, 2019USD ($)ft²a

Sep. 16, 2019USD ($)

Sep. 05, 2019USD ($)ft²yr

Jun. 27, 2019USD ($)ft²

Apr. 26, 2019USD ($)ft²yr

Jan. 24, 2019USD ($)ft²

Dec. 31, 2019USD ($)

Dec. 31, 2018USD ($)

Dec. 31, 2017USD ($)

Nov. 22, 2019ft²

Oct. 01, 2019ft²apartments

May 28, 2019USD ($)

Schedule of Equity Method Investments [Line Items]

Mortgage notes payable, net

$ 2,922,408

$ 2,964,572

Payments to Acquire Equity Method Investments

87,392

$ 345,717

$ 109,015

Annapolis Junction Building Six [Member]

Schedule of Equity Method Investments [Line Items]

Ownership Percentage

50.00%

Mortgage notes payable, net

$ 13,000

Extension Option (in years)

Debt instrument, borrowing capacity

$ 14,300

Debt Instrument, Basis Spread on Variable Rate

2.00%

Net Rentable Area (in sf) | ft²

119,000

7750 Wisconsin Avenue [Member]

Schedule of Equity Method Investments [Line Items]

Ownership Percentage

50.00%

Extension Option (in years) | yr

Proceeds from Construction Loans Payable

$ 64,500

Debt Instrument, Basis Spread on Variable Rate

1.25%

Net Rentable Area (in sf) | ft²

734,000

Construction Loan Facility Borrowing Capacity

$ 255,000

Number of extensions

The Hub on Causeway - Podium and 100 Causeway Street [Member]

Schedule of Equity Method Investments [Line Items]

Ownership Percentage

50.00%

Maximum proceeds from a state infrastructure development program

$ 30,000

Net proceeds from a state infrastructure development program

$ 28,800

Hub on Causeway - Podium [Member]

Schedule of Equity Method Investments [Line Items]

Net Rentable Area (in sf) | ft²

382,000

Repayments of Construction Loans Payable

$ 28,800

540 Madison Avenue [Member]

Schedule of Equity Method Investments [Line Items]

Ownership Percentage

60.00%

[1]

60.00%

[1]

Debt Instrument, Basis Spread on Variable Rate

1.10%

Net Rentable Area (in sf) | ft²

284,000

Contractual Sales Price

$ 310,300

Loans Assumed

120,000

Proceeds from Sale of Equity Method Investments

178,700

Gain on sale of investment in unconsolidated joint venture

$ 47,200

100 Causeway Street [Member]

Schedule of Equity Method Investments [Line Items]

Ownership Percentage

50.00%

Extension Option (in years) | yr

Proceeds from Construction Loans Payable

$ 81,100

Debt Instrument, Basis Spread on Variable Rate

1.50%

Net Rentable Area (in sf) | ft²

632,000

Construction Loan Facility Borrowing Capacity

$ 400,000

Number of extensions

Platform 16

Schedule of Equity Method Investments [Line Items]

Ownership Percentage

55.00%

[2]

55.00%

[2]

Net Rentable Area (in sf) | ft²

1,100,000

Lessee, Finance Lease, Term of Contract

65 years

Area of Land | a

5.6

Payments to Acquire Equity Method Investments

$ 28,200

Dock 72 [Member]

Schedule of Equity Method Investments [Line Items]

Ownership Percentage

50.00%

Net Rentable Area (in sf) | ft²

670,000

Annapolis Junction building seven and eight [Member]

Schedule of Equity Method Investments [Line Items]

Ownership Percentage

50.00%

Mortgage notes payable, net

$ 34,800

Extension Option (in years) | yr

Debt Instrument, Basis Spread on Variable Rate

2.35%

Number of extensions

Annapolis Junction Building Seven [Member]

Schedule of Equity Method Investments [Line Items]

Net Rentable Area (in sf) | ft²

127,000

Annapolis Junction Building Eight [Member]

Schedule of Equity Method Investments [Line Items]

Net Rentable Area (in sf) | ft²

126,000

Joint Venture Partner [Member] | Platform 16

Schedule of Equity Method Investments [Line Items]

Ownership Percentage

45.00%

Payments to Acquire Equity Method Investments

$ 23,100

Residential Properties [Member] | Hub50House [Member]

Schedule of Equity Method Investments [Line Items]

Ownership Percentage

50.00%

Net Rentable Area (in sf) | ft²

320,000

Number of Units in Real Estate Property | apartments

440

Company's Share [Member] | 540 Madison Avenue [Member]

Schedule of Equity Method Investments [Line Items]

Proceeds from Sale of Equity Method Investments

$ 107,100

Stabilization as defined in the agreement [Member] | 100 Causeway Street [Member]

Schedule of Equity Method Investments [Line Items]

Debt Instrument, Basis Spread on Variable Rate

1.375%

[1]

T he property was sold on June 27, 2019. As of December 31, 2019, the investment is comprised of undistributed cash. See note below for additional details.

[2]

This entity is a VIE (See Note 1 ).

Mortgage Notes Payable, Net S_2

Mortgage Notes Payable, Net Schedule Of Aggregate Principal Payments On Mortgage Notes (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Mortgage Notes Payable [Abstract]
2020	$ 17,168
2021	17,276
2022	614,710
2023	0
2024	0
Thereafter	2,300,000
Total	2,949,154
Deferred finance costs, net	(26,700)
Total carrying value of mortgage notes payable, net	$ 2,922,408	$ 2,964,572

Mortgage Notes Payable, Net (Na

Mortgage Notes Payable, Net (Narrative) (Details) $ in Thousands	Dec. 19, 2019USD ($)ft²	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Mortgage Notes Payable [Line Items]
Mortgage notes payable, net (amounts related to VIEs of $2,918,806 and $2,929,326 at December 31, 2019 and 2018, respectively)		$ 2,922,408	$ 2,964,572
Number Of Mortgage Loans Accounted For Fair Value		0	0
Repayments of Secured Debt		$ 46,173	$ 18,634	$ 1,317,653
Losses (gains) from early extinguishments of debt		29,540	16,490	(496)
Payment for Debt Extinguishment or Debt Prepayment Cost		$ 28,716	15,973	12,784
Interest Expense Decrease Due To Recording Mortgage Loans At Fair Value				$ 19,600
Minimum [Member]
Mortgage Notes Payable [Line Items]
Number Real Estate Assets Used For Mortgage Loan Collateral		1
Fixed Rate Mortgages [Member]
Mortgage Notes Payable [Line Items]
Mortgage notes payable, net (amounts related to VIEs of $2,918,806 and $2,929,326 at December 31, 2019 and 2018, respectively)		$ 2,900,000	$ 3,000,000
Debt, Weighted Average Interest Rate		3.73%	3.77%
Fixed Rate Mortgages [Member] \| Minimum [Member]
Mortgage Notes Payable [Line Items]
Coupon/Stated Rate		3.43%	3.43%
Fixed Rate Mortgages [Member] \| Maximum [Member]
Mortgage Notes Payable [Line Items]
Coupon/Stated Rate		6.94%	7.69%
Variable Rate Mortgages [Member]
Mortgage Notes Payable [Line Items]
Number of variable rate mortgage loans		0	0
New Dominion Technology Park, Bldg. One [Member]
Mortgage Notes Payable [Line Items]
Coupon/Stated Rate	7.69%
Repayments of Secured Debt	$ 26,500
Losses (gains) from early extinguishments of debt	1,500
Payment for Debt Extinguishment or Debt Prepayment Cost	$ 1,400
Net Rentable Area (in sf) \| ft²	235,000

Unsecured Senior Notes Schedule

Unsecured Senior Notes Schedule of Unsecured Senior Notes (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019		Sep. 03, 2019	Jun. 21, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Deferred finance costs, net		$ (26,700)
Total		8,390,459				$ 7,544,697
Boston Properties Limited Partnership
Debt Instrument [Line Items]
Deferred finance costs, net		(26,700)
Total		8,390,459				$ 7,544,697
Boston Properties Limited Partnership \| Senior Notes [Member]
Debt Instrument [Line Items]
Principal Amount		8,450,000
Net unamortized discount		(17,451)
Deferred finance costs, net		(42,090)
Total		$ 8,390,459
Boston Properties Limited Partnership \| Senior Notes [Member] \| Unsecured Senior Notes 4.289%
Debt Instrument [Line Items]
Coupon/Stated Rate		4.125%
Effective Rate	[1]	4.289%
Principal Amount		$ 850,000
Maturity date	[2]	May 15, 2021
Boston Properties Limited Partnership \| Senior Notes [Member] \| Unsecured Senior Notes 3.954%
Debt Instrument [Line Items]
Coupon/Stated Rate		3.85%
Effective Rate	[1]	3.954%
Principal Amount		$ 1,000,000
Maturity date	[2]	Feb. 1, 2023
Boston Properties Limited Partnership \| Senior Notes [Member] \| Unsecured Senior Notes 3.279%
Debt Instrument [Line Items]
Coupon/Stated Rate		3.125%
Effective Rate	[1]	3.279%
Principal Amount		$ 500,000
Maturity date	[2]	Sep. 1, 2023
Boston Properties Limited Partnership \| Senior Notes [Member] \| Unsecured Senior Notes 3.916%
Debt Instrument [Line Items]
Coupon/Stated Rate		3.80%
Effective Rate	[1]	3.916%
Principal Amount		$ 700,000
Maturity date	[2]	Feb. 1, 2024
Boston Properties Limited Partnership \| Senior Notes [Member] \| Unsecured Senior Notes 3.35%
Debt Instrument [Line Items]
Coupon/Stated Rate		3.20%
Effective Rate	[1]	3.35%
Principal Amount		$ 850,000
Maturity date	[2]	Jan. 15, 2025
Boston Properties Limited Partnership \| Senior Notes [Member] \| Unsecured Senior Note 3.766%
Debt Instrument [Line Items]
Coupon/Stated Rate		3.65%
Effective Rate	[1]	3.766%
Principal Amount		$ 1,000,000
Maturity date	[2]	Feb. 1, 2026
Boston Properties Limited Partnership \| Senior Notes [Member] \| Unsecured Senior Note 3.495%
Debt Instrument [Line Items]
Coupon/Stated Rate		2.75%
Effective Rate	[1]	3.495%
Principal Amount		$ 1,000,000
Maturity date	[2]	Oct. 1, 2026
Boston Properties Limited Partnership \| Senior Notes [Member] \| Unsecured Senior Note 4.628%
Debt Instrument [Line Items]
Coupon/Stated Rate		4.50%
Effective Rate	[1]	4.628%
Principal Amount		$ 1,000,000
Maturity date	[2]	Dec. 1, 2028
Boston Properties Limited Partnership \| Senior Notes [Member] \| Unsecured Senior Note 3.505%
Debt Instrument [Line Items]
Coupon/Stated Rate		3.40%			3.40%
Effective Rate		3.505%	[1]		3.505%
Principal Amount		$ 850,000			$ 850,000
Maturity date	[2]	Jun. 21, 2029
Boston Properties Limited Partnership \| Senior Notes [Member] \| Unsecured Senior Note 2.984%
Debt Instrument [Line Items]
Coupon/Stated Rate		2.90%		2.90%
Effective Rate		2.984%	[1]	2.984%
Principal Amount		$ 700,000		$ 700,000
Maturity date	[2]	Mar. 15, 2030

[1]	Yield on issuance date including the effects of discounts on the notes, settlements of interest rate contracts and the amortization of financing costs.
[2]	No principal amounts are due prior to maturity.

Unsecured Senior Notes Unsecure

Unsecured Senior Notes Unsecured Senior Notes (Narrative) (Details) - USD ($) $ in Thousands	Sep. 18, 2019	Sep. 03, 2019	Jun. 21, 2019	Dec. 31, 2019		Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Proceeds from unsecured senior notes				$ 1,548,106		$ 996,410	$ 847,935
Redemption of unsecured senior notes				699,237		699,517	848,020
Losses (gains) from early extinguishments of debt				29,540		16,490	(496)
Boston Properties Limited Partnership
Debt Instrument [Line Items]
Proceeds from unsecured senior notes				1,548,106		996,410	847,935
Redemption of unsecured senior notes				699,237		699,517	848,020
Losses (gains) from early extinguishments of debt				29,540		$ 16,490	$ (496)
Boston Properties Limited Partnership \| Senior Notes [Member]
Debt Instrument [Line Items]
Principal Amount				$ 8,450,000
Debt Instrument, Covenant Description				The indenture relating to the unsecured senior notes contains certain financial restrictions and requirements, including (1) a leverage ratio not to exceed 60%, (2) a secured debt leverage ratio not to exceed 50%, (3) an interest coverage ratio of greater than 1.50, and (4) an unencumbered asset value of not less than 150% of unsecured debt.
Debt Instrument, Covenant Compliance				At December 31, 2019, Boston Properties Limited Partnership was in compliance with each of these financial restrictions and requirements.
Boston Properties Limited Partnership \| Senior Notes [Member] \| Unsecured Senior Note 3.505%
Debt Instrument [Line Items]
Principal Amount			$ 850,000	$ 850,000
Coupon/Stated Rate			3.40%	3.40%
Senior Notes Pricing			99.815%
Effective Rate			3.505%	3.505%	[1]
Proceeds from unsecured senior notes			$ 841,400
Boston Properties Limited Partnership \| Senior Notes [Member] \| Unsecured Senior Note 2.984%
Debt Instrument [Line Items]
Principal Amount		$ 700,000		$ 700,000
Coupon/Stated Rate		2.90%		2.90%
Senior Notes Pricing		99.954%
Effective Rate		2.984%		2.984%	[1]
Proceeds from unsecured senior notes		$ 693,800
Boston Properties Limited Partnership \| Senior Notes [Member] \| Unsecured Senior Note 5.708%
Debt Instrument [Line Items]
Coupon/Stated Rate	5.625%
Debt Instrument, Face Amount	$ 700,000
Redemption of unsecured senior notes	740,700
Accrued and Unpaid Interest	$ 13,500
Redemption Price, Percentage	103.90%
Losses (gains) from early extinguishments of debt	$ 28,000
Redemption Premium	$ 27,300

[1]	Yield on issuance date including the effects of discounts on the notes, settlements of interest rate contracts and the amortization of financing costs.

Unsecured Credit Facility (Deta

Unsecured Credit Facility (Details) - USD ($) $ in Thousands	Apr. 24, 2017	Dec. 31, 2019	Dec. 31, 2018	Apr. 24, 2018	Apr. 23, 2017
Line of Credit Facility [Line Items]
Unsecured term loan, net		$ 498,939	$ 498,488
Document Period End Date		Dec. 31, 2019
Long-term Line of Credit		$ 0	0
Line of Credit Facility, Covenant Compliance		At December 31, 2019, Boston Properties Limited Partnership was in compliance with each of these financial and other covenant requirements.
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 1,500,000				$ 1,000,000
Potential increase to line of credit	$ 500,000
Competitive bid quote	65.00%
Long-term Line of Credit		$ 0	0
Line of Credit Facility, Covenant Terms		Among other covenants, the 2017 Credit Facility requires that Boston Properties Limited Partnership maintain on an ongoing basis: (1) a leverage ratio not to exceed 60%, however, the leverage ratio may increase to no greater than 65% provided that it is reduced back to 60% within one year, (2) a secured debt leverage ratio not to exceed 55%, (3) a fixed charge coverage ratio of at least 1.40, (4) an unsecured debt leverage ratio not to exceed 60%, however, the unsecured debt leverage ratio may increase to no greater than 65% provided that it is reduced to 60% within one year, (5) an unsecured debt interest coverage ratio of at least 1.75 and (6) limitations on permitted investments.
Delayed Draw Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 500,000
Unsecured term loan, net				$ 500,000
Margin added to Calculated Interest Rate				0.90%
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.15%
Long-term Line of Credit		$ 500,000	$ 500,000
Line of Credit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate Description	At Boston Properties Limited Partnership’s option, loans under the Revolving Facility and Delayed Draw Facility will bear interest at a rate per annum equal to (1) (a) in the case of loans denominated in Dollars, Euro or Sterling, LIBOR, and (b) in the case of loans denominated in Canadian Dollars, CDOR, in each case, plus a margin ranging from 77.5 to 155 basis points for the Revolving Commitment and 85 to 175 basis points for the Delayed Draw Facility, based on Boston Properties Limited Partnership’s credit rating or (2) an alternate base rate equal to the greatest of (x) the Administrative Agent’s prime rate, (y) the Federal Funds rate plus 0.50% or (z) LIBOR for a one-month period plus 1.00%, in each case, plus a margin ranging from 0 to 55 basis points for the Revolving Facility and 0 to 75 basis points for the Delayed Draw Facility, based on Boston Properties Limited Partnership’s credit rating.
Minimum [Member] \| Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.10%
Maximum [Member] \| Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.30%
Current credit rating [Member] \| Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Margin added to Calculated Interest Rate		0.825%
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage		0.125%
Current credit rating [Member] \| Delayed Draw Facility [Member]
Line of Credit Facility [Line Items]
Margin added to Calculated Interest Rate		0.90%

Commitments And Contingencies (

Commitments And Contingencies (Details)	12 Months Ended
Commitments And Contingencies (Details)	Dec. 31, 2019USD ($)ft²	Dec. 31, 2009USD ($)	May 09, 2019ft²	Apr. 26, 2019ft²	Dec. 31, 2018USD ($)	Jan. 10, 2014USD ($)
Commitments And Contingencies [Line Items]
Letter of credit and performance obligations	$ 21,000,000
Property insurance program per occurrence limits	1,000,000,000
Per occurrence limit for NBCR Coverage	1,000,000,000
Value of program trigger	$ 180,000,000
Coinsurance of program trigger	19.00%
Deductible in insurance as a percentage of the value of the affected property, San Francisco and Los Angeles	3.00%
Per occurrence limit of the earthquake insurance which covers San Francisco and Los Angeles regions	$ 240,000,000
Annual aggregate limit of the earthquake insurance which covers San Francisco and Los Angeles regions	240,000,000
Amount of earthquake insurance provided by IXP, LLC as direct insurer San Francisco and Los Angeles	20,000,000
767 Venture, LLC [Member]
Commitments And Contingencies [Line Items]
Maximum funding obligation	70,200,000
Property insurance program per occurrence limits	1,625,000,000
7750 Wisconsin Avenue [Member]
Commitments And Contingencies [Line Items]
Liabilities for Contingent Guarantees	0
Net Rentable Area (in sf) \| ft²				734,000
Lehman [Member]
Commitments And Contingencies [Line Items]
Bankruptcy claim, amount filed by general creditor		$ 45,300,000
Bankruptcy claim amount allowed by court to creditor						$ 45,200,000
Bankruptcy Claims, Amount of Claims Settled					$ 18,000,000
Bankruptcy remaining claim amount allowed by court to creditor	27,200,000
6595 Springfield Center Drive [Member]
Commitments And Contingencies [Line Items]
Liabilities for Contingent Guarantees	$ 0
325 Main Street
Commitments And Contingencies [Line Items]
Net Rentable Area (in sf) \| ft²	115,000		115,000
601 Lexington Avenue
Commitments And Contingencies [Line Items]
Coverage For Acts Of Terrorism Under TRIA Covered in Excess of Amount Covered by IXP	$ 250,000,000
Boston Properties Limited Partnership
Commitments And Contingencies [Line Items]
Operating partnership guarantee to cover liabilities of IXP	$ 20,000,000
Future Residential Building [Member] \| 325 Main Street
Commitments And Contingencies [Line Items]
Net Rentable Area (in sf) \| ft²	200,000
Affordable Housing requirement	25.00%
Future Office Building [Member] \| 325 Main Street
Commitments And Contingencies [Line Items]
Net Rentable Area (in sf) \| ft²	420,000		420,000
Future Retail Building [Member] \| 325 Main Street
Commitments And Contingencies [Line Items]
Net Rentable Area (in sf) \| ft²	41,000		41,000
Home Ownership Units [Member] \| Future Residential Building [Member] \| 325 Main Street
Commitments And Contingencies [Line Items]
Affordable Housing requirement	20.00%

Noncontrolling Interests (Narra

Noncontrolling Interests (Narrative) (Details) - Boston Properties Limited Partnership	Dec. 31, 2019shares
Noncontrolling Interest [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Operating Partnership (OP) Units (in shares)	16,764,466
Long-Term Incentive Plan (LTIP) Units (in shares)	1,143,215
OPP Units 2012 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Outperformance awards in LTIP Units (in shares)	118,067
MYLTIP 2013
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
2013 MYLTIP	68,659
MYLTIP 2014
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
2014 MYLTIP	23,100
MYLTIP 2015 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
2015 MYLTIP	28,724
MYLTIP 2016 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
2016 MYLTIP	98,706
MYLTIP 2017 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
2017 MYLTIP	394,921
MYLTIP 2018
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
2018 MYLTIP	336,195
MYLTIP 2019 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
2019 MYLTIPS	220,734

(Common Units) (Narrative) (Det

(Common Units) (Narrative) (Details) $ / shares in Units, $ in Thousands	Feb. 09, 2019USD ($)shares	Feb. 04, 2018USD ($)shares	Feb. 03, 2017USD ($)shares	Dec. 31, 2019USD ($)sharesyr$ / shares	Dec. 31, 2018USD ($)shares
OP Units [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
OP Units for redemption (in shares)				144,481	83,136
Redemption of OP units issued on conversion of LTIP, OPP and MYLTIP units (in shares)				92,678	48,389
MYLTIP Units distribution as percentage of OP Unit distribution prior to measurement date				10.00%
Restriction on redemption of OP Unit to Common Stock (in years) \| yr				1
Redemption of OP Unit equivalent to Common Stock (in shares)				1
Common units of operating partnership if converted value \| $				$ 2,500,000
Closing price of common stock (in dollars per share) \| $ / shares				$ 137.86
MYLTIP 2014
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Final awards percentage of target			27.70%
Value of MYLTIP Awards \| $			$ 3,500
MYLTIP Units forfeited			447,386
MYLTIP 2015 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Final awards percentage of target		22.00%
Value of MYLTIP Awards \| $		$ 3,600
MYLTIP Units forfeited		337,847
MYLTIP 2016 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Final awards percentage of target	69.50%
Value of MYLTIP Awards \| $	$ 13,600
2016 MYLTIP Units forfeited	364,980
Boston Properties Limited Partnership
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Common units of operating partnership if converted value \| $				$ 2,468,753	$ 2,000,591
Boston Properties Limited Partnership \| MYLTIP 2017 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
2017 MYLTIP				394,921
Boston Properties Limited Partnership \| MYLTIP 2018
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
2018 MYLTIP				336,195
Boston Properties Limited Partnership \| MYLTIP 2019 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
2019 MYLTIPS				220,734

Noncontrolling Interests Common

Noncontrolling Interests Common Units Distributions (Details) - Boston Properties Limited Partnership - $ / shares	Oct. 31, 2019	Jul. 31, 2019	Apr. 30, 2019	Jan. 30, 2019	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2018	Jan. 30, 2018	Dec. 17, 2019
Dividends Payable [Line Items]
Distributions Declared To OP And LTIP Units Per Unit									$ 0.98
Distributions Declared To MYLTIP Units Per Unit									$ 0.098
Distributions made to OP and LTIP units per unit (in dollars per share)	$ 0.95	$ 0.95	$ 0.95	$ 0.95	$ 0.95	$ 0.80	$ 0.80	$ 0.80
Distributions Made To MYLTIP Units Per Unit	$ 0.095	$ 0.095	$ 0.095	$ 0.095	$ 0.095	$ 0.080	$ 0.080	$ 0.080

Noncontrolling Interests (Prope

Noncontrolling Interests (Property Partnerships) (Narrative) (Details) $ in Thousands	Apr. 01, 2019USD ($)	May 12, 2016ft²	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Jun. 06, 2017USD ($)
Noncontrolling Interest [Line Items]
Noncontrolling Interest in Limited Partnerships			$ 1,728,689	$ 1,711,445
Payments to Noncontrolling Interests			69,913	$ 82,501	$ 54,342
Acquisition of noncontrolling interest in property partnership			(186,963)
Salesforce Tower \| Consolidated Properties [Member]
Noncontrolling Interest [Line Items]
Portion of costs funded (in percentage)		50.00%
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners		5.00%
Debt Instrument, Basis Spread on Variable Rate		3.00%
Stabilization definition for Salesforce Tower		The term stabilization date was defined in the agreement to generally mean the first date after completion upon which Salesforce Tower is (1) at least 90% leased and (2) 50% occupied by tenants that are paying rent.
Net Rentable Area (in sf) \| ft²		1,421,000
Salesforce Tower \| Boston Properties, Inc. [Member] \| Consolidated Properties [Member]
Noncontrolling Interest [Line Items]
Costs funded (in percentage)		2.50%
Preferred equity funded			$ 22,600
Salesforce Tower
Noncontrolling Interest [Line Items]
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners	5.00%
Payments to Noncontrolling Interests	$ 210,900
Repayment of Preferred Equity	24,100
Net Payments To Minority Shareholders	186,800
Acquisition of noncontrolling interest in property partnership	$ 162,500
767 Fifth Avenue (the General Motors Building) [Member] \| Consolidated Properties [Member]
Noncontrolling Interest [Line Items]
Noncontrolling Interest in Limited Partnerships						$ 109,600
Noncontrolling Interest, Ownership Percentage by Parent						60.00%
Unpaid principal balance of the members' notes payable contributed to equity						$ 273,900
Consolidation, Eliminations [Member] \| 767 Fifth Avenue (the General Motors Building) [Member] \| Consolidated Properties [Member]
Noncontrolling Interest [Line Items]
Unpaid principal balance of the members' notes payable contributed to equity						$ 164,400

Stockholders' Equity _ Partne_3

Stockholders' Equity / Partners' Capital Narrative (Details) $ / shares in Units, $ in Millions	Jun. 02, 2017USD ($)yr	Dec. 31, 2019$ / sharesshares	Dec. 31, 2018$ / sharesshares	Dec. 31, 2017shares	Mar. 27, 2018$ / shares	Jun. 03, 2014USD ($)
Class of Stock [Line Items]
Common Stock, Shares, Outstanding		154,790,298	154,458,478
General Partners' Capital Account, Units Outstanding (in units)		1,726,980
Limited Partners' Capital Account, Units Outstanding (in units)		153,063,318
Options exercised		145,088	0	6,688
Shares of Common Stock issued in connection with redemption of an equal number of OP Units (in shares)		144,481	83,136
ATM Program [Member]
Class of Stock [Line Items]
At The Market Stock Offering Program Aggregate Value Of Common Stock \| $	$ 600					$ 600
At Market Stock Offering Program Maximum Length Of Sale (in years) \| yr	3
Series B Cumulative Redeemable Preferred Stock / Unit [Member]
Class of Stock [Line Items]
Series B, Shares Outstanding (in shares)		80,000	80,000
Series B, Dividend Rate, Percentage		5.25%
Series B, Liquidation Preference Per Share (dollars per share) \| $ / shares		$ 2,500	$ 2,500		$ 2,500
Depositary shares of Series B Cumulative Redeemable Preferred [Member]
Class of Stock [Line Items]
Series B, Shares Outstanding (in shares)		8,000,000
Series B, Liquidation Preference Per Share (dollars per share) \| $ / shares		$ 25			$ 25
Boston Properties Limited Partnership
Class of Stock [Line Items]
General Partners' Capital Account, Units Outstanding (in units)		1,726,980	1,722,336
Limited Partners' Capital Account, Units Outstanding (in units)		153,063,318	152,736,142
Boston Properties Limited Partnership \| Series B Cumulative Redeemable Preferred Stock / Unit [Member]
Class of Stock [Line Items]
Series B, Shares Outstanding (in shares)		80,000	80,000
Series B, Liquidation Preference Per Share (dollars per share) \| $ / shares		$ 2,500	$ 2,500

Stockholders' Equity _ Partne_4

Stockholders' Equity / Partners' Capital Dividends / Distributions (Details) - $ / shares	Nov. 15, 2019	Oct. 31, 2019	Aug. 15, 2019	Jul. 31, 2019	May 15, 2019	Apr. 30, 2019	Feb. 15, 2019	Jan. 30, 2019	Nov. 15, 2018	Oct. 31, 2018	Aug. 15, 2018	Jul. 31, 2018	May 15, 2018	Apr. 30, 2018	Feb. 15, 2018	Jan. 30, 2018	Dec. 17, 2019
Dividends / Distributions [Line Items]
Dividends Payable, Amount Per Share / Unit																	$ 0.98
Common Stock / Unit, Dividends / Distributions, Per Share / Unit, Cash Paid		$ 0.95		$ 0.95		$ 0.95		$ 0.95		$ 0.95		$ 0.80		$ 0.80		$ 0.80
Boston Properties Limited Partnership
Dividends / Distributions [Line Items]
Dividends Payable, Amount Per Share / Unit																	0.98
Common Stock / Unit, Dividends / Distributions, Per Share / Unit, Cash Paid		$ 0.95		$ 0.95		$ 0.95		$ 0.95		$ 0.95		$ 0.80		$ 0.80		$ 0.80
Series B Cumulative Redeemable Preferred Stock / Unit [Member]
Dividends / Distributions [Line Items]
Dividends Payable, Amount Per Share / Unit																	$ 32.8125
Common Stock / Unit, Dividends / Distributions, Per Share / Unit, Cash Paid	$ 32.8125		$ 32.8125		$ 32.8125		$ 32.8125		$ 32.8125		$ 32.8125		$ 32.8125		$ 32.8125

Future Minimum Rents Narrative

Future Minimum Rents Narrative (Details) - tenants	12 Months Ended
Future Minimum Rents Narrative (Details) - tenants	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Future Minimum Rent [Line Items]
Number Of Tenants Above Concentration Amount.	0	0	0
Concentration Risk, Percentage	10.00%	10.00%	10.00%

Future Minimum Rents Future min

Future Minimum Rents Future minimum rent under non-cancelable operating leases (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Future minimum rent [Abstract]
2020	$ 2,205,675	$ 2,088,171
2021	2,222,643	2,106,963
2022	2,126,968	2,015,031
2023	2,068,871	1,838,699
2024	1,974,144	1,736,636
Thereafter	$ 13,892,504	$ 12,295,464

Future Minimum Rents Future M_2

Future Minimum Rents Future Minimum Rents for non-cancelable leases for 2018 (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Future minimum rent [Abstract]
2019	$ 2,205,675	$ 2,088,171
2020	2,222,643	2,106,963
2021	2,126,968	2,015,031
2022	2,068,871	1,838,699
2023	1,974,144	1,736,636
Thereafter	$ 13,892,504	$ 12,295,464

Segment Information (Schedule O

Segment Information (Schedule Of Reconciliation Of Net Operating Income To Net Income) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net income attributable to the Company's common shareholders / unitholders	$ 511,034	$ 572,347		$ 451,939
Preferred dividends / distributions	(10,500)	(10,500)		(10,500)
Noncontrolling interest-common units of the Operating Partnership	(59,345)	(66,807)		(52,210)
Noncontrolling interest in property partnerships	(71,120)	(62,909)		(47,832)
Interest expense	(412,717)	(378,168)		(374,481)
Gains (losses) from early extinguishments of debt	29,540	16,490		(496)
Company's share of net operating income from joint ventures	(1,826,123)	(1,649,314)		(1,605,435)
Depreciation and amortization expense	(677,764)	(645,649)		(617,547)
Transaction costs	(1,984)	(1,604)		(668)
General and administrative expense	(140,777)	(121,722)		(113,715)
Gains (losses) from investments in securities	(6,417)	1,865		(3,678)
Interest and other income	(18,939)	(10,823)		(5,783)
Income from unconsolidated joint ventures	(46,592)	(2,222)		(11,232)
Business Intersegment, Eliminations [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net income attributable to the Company's common shareholders / unitholders	511,034	572,347		451,939
Preferred dividends / distributions	10,500	10,500		10,500
Noncontrolling interest-common units of the Operating Partnership	59,345	66,807		52,210
Noncontrolling interest in property partnerships	71,120	62,909		47,832
Interest expense	412,717	378,168		374,481
Gains (losses) from early extinguishments of debt	29,540	16,490		(496)
Impairment losses	24,038	11,812		0
Depreciation and amortization expense	677,764	645,649		617,547
Transaction costs	1,984	1,604		668
Payroll and related costs from management services contracts	10,386	9,590		0
General and administrative expense	140,777	121,722		113,715
Gains (losses) from investments in securities	6,417	(1,865)		3,678
Interest and other income	18,939	10,823		5,783
Gains on sales of real estate	709	182,356		7,663
Income from unconsolidated joint ventures	46,592	2,222		11,232
Other revenue	10,386	9,590		0
Net Operating Income	1,739,850	1,551,842		1,495,198
Boston Properties Limited Partnership
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net income attributable to the Company's common shareholders / unitholders	580,102	656,903		512,866
Preferred dividends / distributions	(10,500)	(10,500)		(10,500)
Noncontrolling interest in property partnerships	(71,120)	(62,909)		(47,832)
Interest expense	(412,717)	(378,168)		(374,481)
Gains (losses) from early extinguishments of debt	29,540	16,490		(496)
Impairment losses				0
Depreciation and amortization expense	(669,956)	(637,891)
Transaction costs	(1,984)	(1,604)		(668)
General and administrative expense	(140,777)	(121,722)		(113,715)
Gains (losses) from investments in securities	(6,417)	1,865		(3,678)
Interest and other income	(18,939)	(10,823)		(5,783)
Income from unconsolidated joint ventures	(46,592)	(2,222)		(11,232)
Boston Properties Limited Partnership \| Business Intersegment, Eliminations [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net income attributable to the Company's common shareholders / unitholders	580,102	656,903		512,866
Preferred dividends / distributions	10,500	10,500		10,500
Noncontrolling interest in property partnerships	71,120	62,909		47,832
Interest expense	412,717	378,168		374,481
Gains (losses) from early extinguishments of debt	29,540	16,490		496
Impairment losses	22,272	10,181		0
Depreciation and amortization expense	669,956	637,891		609,407
Transaction costs	1,984	1,604		668
Payroll and related costs from management services contracts	10,386	9,590		0
General and administrative expense	140,777	121,722		113,715
Gains (losses) from investments in securities	6,417	(1,865)		3,678
Interest and other income	18,939	10,823		5,783
Gains on sales of real estate	858	190,716		8,240
Income from unconsolidated joint ventures	46,592	2,222		11,232
Other revenue	10,386	9,590		0
Net Operating Income	1,739,850	1,551,842		1,495,198
Unconsolidated Joint Ventures [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Interest expense	(84,409)	(71,308)		(46,371)
Company's share of net operating income from joint ventures	(97,716)	(79,893)		(64,008)
Depreciation and amortization expense	(102,296)	(103,079)	[1]	(57,079)
Transaction costs	(1,000)	0		0
Income from unconsolidated joint ventures	(46,592)	(2,222)		(11,232)
Unconsolidated Joint Ventures [Member] \| Business Intersegment, Eliminations [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Company's share of net operating income from joint ventures	(97,716)	(79,893)		(64,008)
Unconsolidated Joint Ventures [Member] \| Boston Properties Limited Partnership \| Business Intersegment, Eliminations [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Company's share of net operating income from joint ventures	(97,716)	(79,893)		(64,008)
Management Service [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Payroll and related costs from management services contracts	(10,386)	(9,590)		0
Other revenue	(40,039)	(45,158)		(34,605)
Management Service [Member] \| Business Intersegment, Eliminations [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Other revenue	40,039	45,158		34,605
Management Service [Member] \| Boston Properties Limited Partnership
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Payroll and related costs from management services contracts	(10,386)	(9,590)		0
Other revenue	(40,039)	(45,158)		(34,605)
Management Service [Member] \| Boston Properties Limited Partnership \| Business Intersegment, Eliminations [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Other revenue	40,039	45,158		34,605
Noncontrolling interest - property partnerships [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Company's share of net operating income from joint ventures	183,989	177,365		174,245
Noncontrolling interest - property partnerships [Member] \| Business Intersegment, Eliminations [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Company's share of net operating income from joint ventures	183,989	177,365		174,245
Noncontrolling interest - property partnerships [Member] \| Boston Properties Limited Partnership \| Business Intersegment, Eliminations [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Company's share of net operating income from joint ventures	$ 183,989	$ 177,365		$ 174,245

[1]	During the year ended December 31, 2018, the joint venture that owns Metropolitan Square in Washington, DC, commenced a renovation project and recorded accelerated depreciation expense of approximately $22.4 million related to the remaining book value of the assets to be replaced. The Company’s share of the accelerated depreciation expense totaled approximately $4.5 million .

Segment Information (Schedule_2

Segment Information (Schedule Of Segment Reporting By Geographic Area And Property Type) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	[1]	$ 2,824,634	$ 2,590,659	$ 2,505,272
Rental Revenue: Residential	[1]	36,914	22,551	16,596
Rental Revenue Total	[1]	$ 2,910,137	$ 2,662,328	$ 2,567,471
Rental Revenue: % of Grand Totals	[1]	100.00%	100.00%	100.00%
Rental Expenses: Class A Office		$ 1,034,025	$ 966,547	$ 923,675
Rental Expenses: Residential		15,985	12,604	6,302
Rental Expenses: Total		$ 1,084,014	$ 1,013,014	$ 962,036
Rental Expenses: % Of Grand Totals		100.00%	100.00%	100.00%
Net Operating Income: % of Grand Totals		100.00%	100.00%	100.00%
Net Operating Income		$ 1,826,123	$ 1,649,314	$ 1,605,435
Company's Share of Net Operating Income: % of Grand Totals		100.00%	100.00%	100.00%
Boston [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	[1]	$ 895,098	$ 838,341	$ 776,279
Rental Revenue: Residential	[1]	13,786	6,694	4,745
Rental Revenue Total	[1]	$ 957,473	$ 894,153	$ 826,627
Rental Revenue: % of Grand Totals	[1]	32.90%	33.59%	32.20%
Rental Expenses: Class A Office		$ 322,282	$ 315,653	$ 301,097
Rental Expenses: Residential		5,071	3,632	2,044
Rental Expenses: Total		$ 361,357	$ 353,148	$ 335,200
Rental Expenses: % Of Grand Totals		33.34%	34.86%	34.84%
Net Operating Income: % of Grand Totals		32.64%	32.80%	30.61%
Net Operating Income		$ 596,116	$ 541,005	$ 491,427
Company's Share of Net Operating Income: % of Grand Totals		32.27%	32.86%	30.87%
Los Angeles [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	[1]	$ 0	$ 0	$ 0
Rental Revenue: Residential	[1]	0	0	0
Rental Revenue Total	[1]	$ 0	$ 0	$ 0
Rental Revenue: % of Grand Totals	[1]	0.00%	0.00%	0.00%
Rental Expenses: Class A Office		$ 0	$ 0	$ 0
Rental Expenses: Residential		0	0	0
Rental Expenses: Total		$ 0	$ 0	$ 0
Rental Expenses: % Of Grand Totals		0.00%	0.00%	0.00%
Net Operating Income: % of Grand Totals		0.00%	0.00%	0.00%
Net Operating Income		$ 0	$ 0	$ 0
Company's Share of Net Operating Income: % of Grand Totals		3.53%	2.75%	1.79%
New York [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	[1]	$ 1,011,912	$ 959,050	$ 969,371
Rental Revenue: Residential	[1]	0	0	0
Rental Revenue Total	[1]	$ 1,011,912	$ 959,050	$ 969,371
Rental Revenue: % of Grand Totals	[1]	34.78%	36.02%	37.75%
Rental Expenses: Class A Office		$ 389,532	$ 377,992	$ 372,810
Rental Expenses: Residential		0	0	0
Rental Expenses: Total		$ 389,532	$ 377,992	$ 372,810
Rental Expenses: % Of Grand Totals		35.93%	37.32%	38.76%
Net Operating Income: % of Grand Totals		34.09%	35.23%	37.15%
Net Operating Income		$ 622,380	$ 581,058	$ 596,561
Company's Share of Net Operating Income: % of Grand Totals		27.77%	28.63%	30.94%
San Francisco [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	[1]	$ 533,189	$ 397,180	$ 345,519
Rental Revenue: Residential	[1]	0	0	0
Rental Revenue Total	[1]	$ 533,189	$ 397,180	$ 345,519
Rental Revenue: % of Grand Totals	[1]	18.32%	14.92%	13.46%
Rental Expenses: Class A Office		$ 177,994	$ 130,016	$ 105,253
Rental Expenses: Residential		0	0	0
Rental Expenses: Total		$ 177,994	$ 130,016	$ 105,253
Rental Expenses: % Of Grand Totals		16.42%	12.83%	10.94%
Net Operating Income: % of Grand Totals		19.45%	16.20%	14.97%
Net Operating Income		$ 355,195	$ 267,164	$ 240,266
Company's Share of Net Operating Income: % of Grand Totals		20.39%	17.22%	16.10%
Washington, DC [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	[1]	$ 384,435	$ 396,088	$ 414,103
Rental Revenue: Residential	[1]	23,128	15,857	11,851
Rental Revenue Total	[1]	$ 407,563	$ 411,945	$ 425,954
Rental Revenue: % of Grand Totals	[1]	14.00%	15.47%	16.59%
Rental Expenses: Class A Office		$ 144,217	$ 142,886	$ 144,515
Rental Expenses: Residential		10,914	8,972	4,258
Rental Expenses: Total		$ 155,131	$ 151,858	$ 148,773
Rental Expenses: % Of Grand Totals		14.31%	14.99%	15.46%
Net Operating Income: % of Grand Totals		13.82%	15.77%	17.27%
Net Operating Income		$ 252,432	$ 260,087	$ 277,181
Company's Share of Net Operating Income: % of Grand Totals		16.04%	18.54%	20.30%
Hotel [Member]
Segment Reporting Information [Line Items]
Other revenue	[1]	$ 48,589	$ 49,118	$ 45,603
Payroll and related costs from management services contracts		34,004	33,863	32,059
Hotel [Member] \| Boston [Member]
Segment Reporting Information [Line Items]
Other revenue	[1]	48,589	49,118	45,603
Payroll and related costs from management services contracts		34,004	33,863	32,059
Hotel [Member] \| Los Angeles [Member]
Segment Reporting Information [Line Items]
Other revenue	[1]	0	0	0
Payroll and related costs from management services contracts		0	0	0
Hotel [Member] \| New York [Member]
Segment Reporting Information [Line Items]
Other revenue	[1]	0	0	0
Payroll and related costs from management services contracts		0	0	0
Hotel [Member] \| San Francisco [Member]
Segment Reporting Information [Line Items]
Other revenue	[1]	0	0	0
Payroll and related costs from management services contracts		0	0	0
Hotel [Member] \| Washington, DC [Member]
Segment Reporting Information [Line Items]
Other revenue	[1]	0	0	0
Payroll and related costs from management services contracts		0	0	0
Noncontrolling interest - property partnerships [Member]
Segment Reporting Information [Line Items]
Net Operating Income		(183,989)	(177,365)	(174,245)
Noncontrolling interest - property partnerships [Member] \| Boston [Member]
Segment Reporting Information [Line Items]
Net Operating Income		(40,109)	(33,862)	(31,857)
Noncontrolling interest - property partnerships [Member] \| Los Angeles [Member]
Segment Reporting Information [Line Items]
Net Operating Income		0	0	0
Noncontrolling interest - property partnerships [Member] \| New York [Member]
Segment Reporting Information [Line Items]
Net Operating Income		(143,432)	(143,562)	(142,916)
Noncontrolling interest - property partnerships [Member] \| San Francisco [Member]
Segment Reporting Information [Line Items]
Net Operating Income		(448)	59	528
Noncontrolling interest - property partnerships [Member] \| Washington, DC [Member]
Segment Reporting Information [Line Items]
Net Operating Income		0	0	0
Unconsolidated Joint Ventures [Member]
Segment Reporting Information [Line Items]
Net Operating Income		97,716	79,893	64,008
Unconsolidated Joint Ventures [Member] \| Boston [Member]
Segment Reporting Information [Line Items]
Net Operating Income		5,494	2,866	1,962
Unconsolidated Joint Ventures [Member] \| Los Angeles [Member]
Segment Reporting Information [Line Items]
Net Operating Income		61,338	42,750	26,816
Unconsolidated Joint Ventures [Member] \| New York [Member]
Segment Reporting Information [Line Items]
Net Operating Income		4,174	6,590	8,832
Unconsolidated Joint Ventures [Member] \| San Francisco [Member]
Segment Reporting Information [Line Items]
Net Operating Income		0	0	0
Unconsolidated Joint Ventures [Member] \| Washington, DC [Member]
Segment Reporting Information [Line Items]
Net Operating Income		26,710	27,687	26,398
Company's Share [Member]
Segment Reporting Information [Line Items]
Net Operating Income		1,739,850	1,551,842	1,495,198
Company's Share [Member] \| Boston [Member]
Segment Reporting Information [Line Items]
Net Operating Income		561,501	510,009	461,532
Company's Share [Member] \| Los Angeles [Member]
Segment Reporting Information [Line Items]
Net Operating Income		61,338	42,750	26,816
Company's Share [Member] \| New York [Member]
Segment Reporting Information [Line Items]
Net Operating Income		483,122	444,086	462,477
Company's Share [Member] \| San Francisco [Member]
Segment Reporting Information [Line Items]
Net Operating Income		354,747	267,223	240,794
Company's Share [Member] \| Washington, DC [Member]
Segment Reporting Information [Line Items]
Net Operating Income		$ 279,142	$ 287,774	$ 303,579

[1]	Rental Revenue is equal to Total Revenue per the Company’s Consolidated Statements of Operations, less Development and Management Services Revenue and Direct Reimbursements of Payroll and Related Costs from Management Services Contracts Revenue per the Consolidated Statements of Operations.

Segment Information Narrative (

Segment Information Narrative (Details) - Los Angeles [Member] ft² in Millions	Dec. 31, 2019ft²Buildings
Segment Reporting Information [Line Items]
Number of real estate properties \| Buildings	27
Net Rentable Area (in sf) \| ft²	2.3

Earnings Per Share _ Common U_3

Earnings Per Share / Common Unit (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Basic Earnings:
Net income attributable to the company's common shareholders / unitholders									$ 511,034	$ 572,347	$ 451,939
Net income attributable to the company's common shareholders / unitholders (in shares / units)									154,582,000	154,427,000	154,190,000
Net income attributable to the company's common shareholders / unitholders (in dollars per share / unit)	$ 0.91	$ 0.70	$ 1.06	$ 0.63	$ 0.96	$ 0.77	$ 0.83	$ 1.14	$ 3.31	$ 3.71	$ 2.93
Allocation of undistributed earnings to participating securities										$ (101)
Allocation of undistributed earnings to participating securities (in shares / units)										0
Allocation of undistributed earnings to participating securities (in dollars per share / unit)										$ 0
Net income attributable to the company's common shareholders / unitholders, after allocation of undistributed earnings to participating securities										$ 572,246
Net income attributable to the company's common shareholders / unitholders, after allocation of undistributed earnings to participating securities (in shares / units)										154,427,000
Net income attributable to the company's common shareholders / unitholders, after allocation of undistributed earnings to participating securities (in dollars per share / unit)										$ 3.71
Effect of Dilutive Securities:
Stock Based Compensation									$ 0	$ 0	$ 0
Stock Based Compensation (in shares / units)									301,000	255,000	200,000
Weighted Average Number Diluted Shares Outstanding Adjustment (per share)									$ (0.01)	$ (0.01)	$ 0
Diluted Earnings:
Diluted Earnings: Net income attributable to the Company's common shareholders / unitholders									$ 511,034	$ 572,246	$ 451,939
Diluted Earnings: Net income attributable to the Company's common shareholders / unitholders (in shares / units)									154,883,000	154,682,000	154,390,000
Diluted Earnings: Net income, Per Share Amount (in dollars per share / unit)	0.91	0.70	1.06	0.63	0.96	0.77	0.83	1.14	$ 3.30	$ 3.70	$ 2.93
Boston Properties Limited Partnership
Redeemable Common Units									17,618,000	17,485,000	17,471,000
Basic Earnings:
Net income attributable to the company's common shareholders / unitholders									$ 580,102	$ 656,903	$ 512,866
Net income attributable to the company's common shareholders / unitholders (in shares / units)									172,200,000	171,912,000	171,661,000
Net income attributable to the company's common shareholders / unitholders (in dollars per share / unit)	0.92	0.71	1.08	0.66	1.01	0.79	0.85	1.17	$ 3.37	$ 3.82	$ 2.99
Allocation of undistributed earnings to participating securities										$ (113)
Allocation of undistributed earnings to participating securities (in shares / units)										0
Allocation of undistributed earnings to participating securities (in dollars per share / unit)										$ 0
Net income attributable to the company's common shareholders / unitholders, after allocation of undistributed earnings to participating securities										$ 656,790
Net income attributable to the company's common shareholders / unitholders, after allocation of undistributed earnings to participating securities (in shares / units)										171,912,000
Net income attributable to the company's common shareholders / unitholders, after allocation of undistributed earnings to participating securities (in dollars per share / unit)										$ 3.82
Effect of Dilutive Securities:
Stock Based Compensation									$ 0	$ 0	$ 0
Stock Based Compensation (in shares / units)									301,000	255,000	200,000
Weighted Average Number Diluted Shares Outstanding Adjustment (per share)									$ (0.01)	$ (0.01)	$ (0.01)
Diluted Earnings:
Diluted Earnings: Net income attributable to the Company's common shareholders / unitholders									$ 580,102	$ 656,790	$ 512,866
Diluted Earnings: Net income attributable to the Company's common shareholders / unitholders (in shares / units)									172,501,000	172,167,000	171,861,000
Diluted Earnings: Net income, Per Share Amount (in dollars per share / unit)	$ 0.92	$ 0.71	$ 1.08	$ 0.66	$ 1.01	$ 0.79	$ 0.85	$ 1.17	$ 3.36	$ 3.81	$ 2.98

Employee Benefit Plans (Details

Employee Benefit Plans (Details) - USD ($)	12 Months Ended			240 Months Ended
Employee Benefit Plans (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019
Related Party Transaction [Line Items]
Employer Matching Contribution, Percent of Match	200.00%
Employer Matching Contribution, Percent of Employees' Gross Pay				3.00%
Maximum Eligible Earnings As Established By IRS For Matching Contributions	$ 280,000	$ 275,000	$ 270,000
Employer Contribution Amount	4,200,000	4,100,000	$ 4,100,000
Separate Unrestricted Cash For Deferred Compensation Plans	36,700,000	28,200,000		$ 36,700,000
Deferred Compensation Liability	36,000,000	28,200,000		36,000,000
Officer [Member]
Related Party Transaction [Line Items]
Separate Unrestricted Cash For Deferred Compensation Plans	$ 36,000,000	$ 28,200,000		$ 36,000,000

Stock Option and Incentive Pl_3

Stock Option and Incentive Plan (Narrative) (Details) $ / shares in Units, $ in Millions	Feb. 09, 2019USD ($)shares	Feb. 05, 2019USD ($)shares	Feb. 04, 2018USD ($)shares	Feb. 03, 2017USD ($)shares	May 15, 2012shares	Dec. 31, 2018$ / sharesshares	Dec. 31, 2017$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number Exercisable						540,441	540,441
Exercisable, Weighted Average Exercise Price \| $ / shares						$ 96.35	$ 96.35
2012 Stock Option and Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Additional Shares Authorized					13,000,000
Other Than Stock Options Awards Conversion Ratio					2.32
Stock Option Awards Conversion Ratio					1
Stock Option and Incentive Plan Term Period					10 years
MYLTIP 2019 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period		4 years
TSR measurement (in years)		three-year
Minimum earned awards		0
Maximum Earned Awards		220,734
Earned wards - Target		110,367
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights		Earned awards (if any) will vest 50% on February 4, 2022 and 50% on February 4, 2023, based on continued employment. Vesting will be accelerated in the event of a change in control, termination of employment by Boston Properties, Inc. without cause, or termination of employment by the award recipient for good reason, death, disability or retirement. If there is a change of control prior to February 4, 2022, earned awards will be calculated based on TSR performance up to the date of the change of control. The 2019 MYLTIP awards are in the form of LTIP Units issued on the grant date which (i) are subject to forfeiture to the extent awards are not earned and (ii) prior to the performance measurement date are only entitled to one-tenth (10%) of the regular quarterly distributions payable on common partnership units.
Value of MYLTIP Awards \| $		$ 13.5
MYLTIP Value Amortized Into Earnings, Years		four year
MYLTIP 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value of MYLTIP Awards \| $				$ 3.5
Final awards percentage of target				27.70%
MYLTIP Units forfeited				447,386
MYLTIP 2016 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value of MYLTIP Awards \| $	$ 13.6
Stock Issued During Period, Shares, Share-based Compensation, Forfeited	364,980
Final awards percentage of target	69.50%
MYLTIP 2015 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value of MYLTIP Awards \| $			$ 3.6
Final awards percentage of target			22.00%
MYLTIP Units forfeited			337,847

Stock Option and Incentive Pl_4

Stock Option and Incentive Plan (Restricted Stock) (Narrative) (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)d$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares	Dec. 31, 2017USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued	154,869,198	154,537,378
Stock based compensation expense \| $	$ 39,800		$ 33,200
Common Stock, Value, Issued \| $	1,548	$ 1,545
Intrinsic Value of stock options \| $	$ 16,400
Number Exercisable		540,441	540,441
Exercisable, Weighted Average Exercise Price \| $ / shares		$ 96.35	$ 96.35
Non-qualified stock options issued	0	0	0
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued	26,503	20,320	37,414
Employee and director payment per share (in dollars per share) \| $ / shares	$ 0.01
Common Stock, Value, Issued \| $	$ 3,500	$ 2,400	$ 4,900
Common Stock Weighted Average Price (in dollars per share) \| $ / shares	$ 131.27	$ 119.27	$ 130.32
LTIP Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value Of LTIP Units Issued \| $	$ 22,100	$ 22,700	$ 13,600
Weighted Average Per Unit Fair Value (in dollars per share) \| $ / shares	$ 121.50	$ 110.29	$ 119.41
Expected life assumed to calculate per unit fair value per LTIP unit (in years)	5 years 8 months 12 days	5 years 8 months 12 days	5 years 8 months 12 days
Risk-free rate	2.68%	2.63%	2.14%
Expected price volatility	27.00%	27.00%	28.00%
LTIP and MYLTIP Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee and director payment per share (in dollars per share) \| $ / shares	$ 0.25
Unvested Restricted stock and LTIP Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expenses \| $	$ 23,300
Unvested 2017 - 2019 MYLTIP Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expenses \| $	$ 12,400
Weighted-average period (years)	2 years 4 months 24 days
Non-Qualified Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock available for issuance	250,000
Payment Award Discount From Market Price Based on Ten Business Day Average	85.00%
Number Of Days Used In Calculation, Average Closing Prices Of Common Stock \| d	10
Number of shares issued	5,862	6,268	6,317
Weighted Average Purchase Price of Shares (in dollars per share) \| $ / shares	$ 104.11	$ 107.20	$ 105.97
Boston Properties Limited Partnership \| LTIP Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
LTIP units issued (in shares)	181,919	205,838	113,918
Boston Properties Limited Partnership \| MYLTIP 2019 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
MYLTIP units issued (in shares)	220,734
Boston Properties Limited Partnership \| MYLTIP 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
MYLTIP units issued (in shares)		342,659
Boston Properties Limited Partnership \| MYLTIP 2017 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
MYLTIP units issued (in shares)			400,000

Stock Option and Incentive Pl_5

Stock Option and Incentive Plan Schedule of Stock Options Status (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning Outstanding, Shares	540,441	540,441	547,129
Beginning Outstanding, Weighted Average Exercise Price	$ 96.35	$ 96.35	$ 96.38
Exercised, Shares	(145,088)	0	(6,688)
Exercised, Weighted Averge Exercise Price	$ 96.27	$ 0	$ 99.15
Ending Outstanding, Shares	395,353	540,441	540,441
Ending Outstanding, Weighted Average Exercise Price	$ 96.37	$ 96.35	$ 96.35

Stock Option and Incentive Pl_6

Stock Option and Incentive Plan Schedule of Stock Options Outstanding (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number Outstanding at period end	395,353	540,441	540,441	547,129
Outstanding, Weighted Average Exercise Price	$ 96.37	$ 96.35	$ 96.35	$ 96.38
Number Exercisable		540,441	540,441
Exercisable, Weighted Average Exercise Price		$ 96.35	$ 96.35
Exercise Price of $86.86 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number Outstanding at period end	81,458
Weighted Average Remaining Contractual Life (Years)	1 year 1 month 6 days
Outstanding, Weighted Average Exercise Price	$ 86.86
Number Exercisable	81,458
Exercisable, Weighted Average Exercise Price	$ 86.86
Exercise Price of $95.69 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number Outstanding at period end	54,282
Weighted Average Remaining Contractual Life (Years)	3 years 3 months 18 days
Outstanding, Weighted Average Exercise Price	$ 95.69
Number Exercisable	54,282
Exercisable, Weighted Average Exercise Price	$ 95.69
Exercise Price of $98.46 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number Outstanding at period end	142,422
Weighted Average Remaining Contractual Life (Years)	3 years 1 month 6 days
Outstanding, Weighted Average Exercise Price	$ 98.46
Number Exercisable	142,422
Exercisable, Weighted Average Exercise Price	$ 98.46
Exercise Price of $100.77 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number Outstanding at period end	117,191
Weighted Average Remaining Contractual Life (Years)	2 years 1 month 6 days
Outstanding, Weighted Average Exercise Price	$ 100.77
Number Exercisable	117,191
Exercisable, Weighted Average Exercise Price	$ 100.77

Related Party Transactions (Det

Related Party Transactions (Details)	Sep. 03, 2019shares	Dec. 31, 2019USD ($)nonemployeedirectorsshares	Dec. 31, 2018USD ($)shares	Dec. 31, 2017USD ($)	May 21, 2019shares	May 23, 2018shares
Related Party Transaction [Line Items]
Number Of Non Employee Directors Electing To Receive Deferred Stock Units \| nonemployeedirectors		7
Shares issued \| shares		154,869,198	154,537,378
Deferred Stock Units Outstanding		60,676	74,966
Separate Unrestricted Cash For Deferred Compensation Plans		$ 36,700,000	$ 28,200,000
Company's liability for Directors		377,553,000	276,645,000
Brother of Senior Executive Vice President [Member]
Related Party Transaction [Line Items]
Aggregate leasing commissions paid to related parties		21,000	$ 921,000	$ 368,000
deferred compenstation for directors [Member]
Related Party Transaction [Line Items]
Separate Unrestricted Cash For Deferred Compensation Plans		700,000
Company's liability for Directors		$ 700,000
Director Cessation [Member]
Related Party Transaction [Line Items]
Shares issued \| shares					17,949	36,836
Common Stock converted (Shares) \| shares	4,917

Selected Interim Financial In_3

Selected Interim Financial Information (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Total revenue	$ 757,501	$ 743,553	$ 733,741	$ 725,767	$ 705,157	$ 686,284	$ 664,484	$ 661,151	$ 2,960,562	$ 2,717,076	$ 2,602,076
Net income	176,009	141,370	203,461	131,159	185,241	150,445	160,565	216,312
Net income attributable to the Company	$ 140,824	$ 107,771	$ 164,318	$ 98,105	$ 148,529	$ 119,118	$ 128,681	$ 176,021	$ 521,534	$ 582,847	$ 462,439
Income attributable to the Company (in dollars per share / unit) - Basic	$ 0.91	$ 0.70	$ 1.06	$ 0.63	$ 0.96	$ 0.77	$ 0.83	$ 1.14	$ 3.31	$ 3.71	$ 2.93
Income attributable to the Company (in dollars per share / unit) - Diluted	$ 0.91	$ 0.70	$ 1.06	$ 0.63	$ 0.96	$ 0.77	$ 0.83	$ 1.14	$ 3.30	$ 3.70	$ 2.93
Boston Properties Limited Partnership
Total revenue	$ 757,501	$ 743,553	$ 733,741	$ 725,767	$ 705,157	$ 686,284	$ 664,484	$ 661,151	$ 2,960,562	$ 2,717,076	$ 2,602,076
Net income	177,851	143,212	205,822	134,837	192,884	153,676	162,986	220,766
Net income attributable to the Company	$ 158,888	$ 122,117	$ 185,715	$ 113,382	$ 173,834	$ 136,201	$ 145,961	$ 200,907	$ 590,602	$ 667,403	$ 523,366
Income attributable to the Company (in dollars per share / unit) - Basic	$ 0.92	$ 0.71	$ 1.08	$ 0.66	$ 1.01	$ 0.79	$ 0.85	$ 1.17	$ 3.37	$ 3.82	$ 2.99
Income attributable to the Company (in dollars per share / unit) - Diluted	$ 0.92	$ 0.71	$ 1.08	$ 0.66	$ 1.01	$ 0.79	$ 0.85	$ 1.17	$ 3.36	$ 3.81	$ 2.98

Subsequent Events (Details)

Subsequent Events (Details) $ in Thousands	Feb. 20, 2020USD ($)ft²Buildings	Feb. 06, 2020USD ($)shares	Feb. 04, 2020USD ($)shares	Jan. 28, 2020USD ($)ft²aBuildings	Sep. 20, 2019USD ($)ft²a	Dec. 31, 2019USD ($)shares		Dec. 31, 2018USD ($)shares	Dec. 31, 2017USD ($)	Jan. 31, 2020shares
Subsequent Event [Line Items]
Common stock, shares issued \| shares						154,869,198		154,537,378
Payments to Acquire Equity Method Investments						$ 87,392		$ 345,717	$ 109,015
MYLTIPS 2020 [Member]
Subsequent Event [Line Items]
MYLTIP Value Amortized Into Earnings, Years			four-year
Value of MYTIP to be recognized as expense during the first year of issuance			$ 7,900
Subsequent Event [Member] \| MYLTIPS 2020 [Member]
Subsequent Event [Line Items]
Value of MYLTIP Awards			$ 13,700
Subsequent Event [Member] \| MYLTIPS 2020 [Member] \| NAREIT Office Index adjusted [Member]
Subsequent Event [Line Items]
Target Tier \| shares			101,638
Subsequent Event [Member] \| MYLTIP 2017 [Member]
Subsequent Event [Line Items]
Value of MYLTIP Awards		$ 17,600
Final awards percentage of target		83.80%
MYLTIP Units forfeited \| shares		270,942
Subsequent Event [Member] \| Minimum [Member] \| MYLTIPS 2020 [Member] \| NAREIT Office Index adjusted [Member]
Subsequent Event [Line Items]
Minimum earned awards \| shares			0
Subsequent Event [Member] \| Maximum [Member] \| MYLTIPS 2020 [Member] \| NAREIT Office Index adjusted [Member]
Subsequent Event [Line Items]
Maximum Earned Awards \| shares			203,278
Subsequent Event [Member] \| Restricted Stock [Member]
Subsequent Event [Line Items]
Common stock, shares issued \| shares										24,503
Subsequent Event [Member] \| LTIP Units [Member]
Subsequent Event [Line Items]
LTIP units issued (in shares) \| shares			196,927
New Dominion Technology Park [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Contractual Sales Price	$ 256,000
number of buildings \| Buildings	2
Net Rentable Area (in sf) \| ft²	493,000
Gateway Commons Complex [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Ownership Percentage				50.00%
number of buildings \| Buildings				3
Net Rentable Area (in sf) \| ft²				768,000
Payments to Acquire Equity Method Investments				$ 350,000
Platform 16
Subsequent Event [Line Items]
Ownership Percentage					55.00%	55.00%	[1]
Net Rentable Area (in sf) \| ft²					1,100,000
Finance lease fixed purchase price					$ 134,800
Area of Land \| a					5.6
Payments to Acquire Equity Method Investments					$ 28,200
Platform 16 \| Subsequent Event [Member]
Subsequent Event [Line Items]
Ownership Percentage				55.00%
Net Rentable Area (in sf) \| ft²				1,100,000
Finance lease fixed purchase price				$ 134,800
Prepaid purchase price				$ 15,000
Area of Land \| a				5.6
Joint Venture Partner [Member] \| Gateway Commons Complex [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Ownership Percentage				50.00%
number of buildings \| Buildings				3
Payments to Acquire Equity Method Investments				$ 280,800
Future payment to acquire interest in equity method investment				$ 69,200
Joint Venture Partner [Member] \| Platform 16
Subsequent Event [Line Items]
Ownership Percentage					45.00%
Payments to Acquire Equity Method Investments					$ 23,100
425 Fourth Street \| Subsequent Event [Member]
Subsequent Event [Line Items]
Net Rentable Area (in sf) \| ft²				804,000
Aggregate purchase price				$ 134,100
Future Office Building [Member] \| Platform 16 \| Subsequent Event [Member]
Subsequent Event [Line Items]
Net Rentable Area (in sf) \| ft²				390,000

[1]	This entity is a VIE (See Note 1 ).

Real Estate and Accumulated D_4

Real Estate and Accumulated Depreciation Schedule of Real Estate and Accumulated Depreciation (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	[1]	$ 2,922,408
Original Land		5,024,060
Original Building		13,057,336
Costs Capitalized Subsequent to Acquisition		4,763,301
Land and improvements	[2]	5,474,337
Buildings and Improvements	[3]	16,325,796
Land Held for Development	[4]	254,828
Development and Construction in Progress		789,736
Total		22,844,697
Accumulated Depreciation		5,239,179
Furniture, Fixtures and Equipment		44,313		$ 44,351
Real Estate Aggregate Cost For Tax Purposes		18,600,000
Real Estate Aggregate Accumulated Depreciation For Tax Purposes		$ 4,000,000
Real Estate and Accumulated Depreciation, Life Used for Depreciation		40 years
Unamortized deferred finance costs		$ (26,700)
Right-of-use assets - finance leases		237,394
Right of use assets - operating leases		$ 148,640	$ 151,800
767 Fifth Avenue (the General Motors Building)
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		767 Fifth Avenue (the General Motors Building)
Type		Office
Location		New York, NY
Encumbrances		$ 2,274,028
Original Land		1,796,252
Original Building		1,532,654
Costs Capitalized Subsequent to Acquisition		202,612
Land and improvements		1,796,252
Buildings and Improvements		1,735,266
Land Held for Development		0
Development and Construction in Progress		0
Total		3,531,518
Accumulated Depreciation		$ 313,158
Year(s) Built / Renovated		1968/2019
Year(s) Acquired		2013
Depreciable Lives (Years)	[5]	(1)
Prudential Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Prudential Center
Type		Office
Location		Boston, MA
Encumbrances		$ 0
Original Land		92,077
Original Building		948,357
Costs Capitalized Subsequent to Acquisition		556,458
Land and improvements		115,638
Buildings and Improvements		1,478,578
Land Held for Development		2,676
Development and Construction in Progress		0
Total		1,596,892
Accumulated Depreciation		$ 596,740
Year(s) Built / Renovated		1965/1993/2002/2016-2017
Year(s) Acquired		1998/1999/2000
Depreciable Lives (Years)	[5]	(1)
Embarcadero Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Embarcadero Center
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		179,697
Original Building		847,410
Costs Capitalized Subsequent to Acquisition		415,228
Land and improvements		195,987
Buildings and Improvements		1,246,348
Land Held for Development		0
Development and Construction in Progress		0
Total		1,442,335
Accumulated Depreciation		$ 633,711
Year(s) Built / Renovated		1970/1989
Year(s) Acquired		1998-1999
Depreciable Lives (Years)	[5]	(1)
399 Park Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		399 Park Avenue
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		339,200
Original Building		700,358
Costs Capitalized Subsequent to Acquisition		300,519
Land and improvements		354,107
Buildings and Improvements		985,970
Land Held for Development		0
Development and Construction in Progress		0
Total		1,340,077
Accumulated Depreciation		$ 358,960
Year(s) Built / Renovated		1961/2018
Year(s) Acquired		2002
Depreciable Lives (Years)	[5]	(1)
601 Lexington Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		601 Lexington Avenue
Type		Office
Location		New York, NY
Encumbrances		$ 644,778
Original Land		241,600
Original Building		494,782
Costs Capitalized Subsequent to Acquisition		454,902
Land and improvements		289,639
Buildings and Improvements		688,550
Land Held for Development		0
Development and Construction in Progress		213,095
Total		1,191,284
Accumulated Depreciation		$ 289,482
Year(s) Built / Renovated		1977/1997
Year(s) Acquired		2001
Depreciable Lives (Years)	[5]	(1)
Salesforce Tower
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Salesforce Tower
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		200,349
Original Building		946,205
Costs Capitalized Subsequent to Acquisition		0
Land and improvements		200,349
Buildings and Improvements		946,205
Land Held for Development		0
Development and Construction in Progress		0
Total		1,146,554
Accumulated Depreciation		$ 38,727
Year(s) Built / Renovated		2018
Year(s) Acquired		2013
Depreciable Lives (Years)	[5]	(1)
200 Clarendon Street and Garage
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		200 Clarendon Street and Garage
Type		Office
Location		Boston, MA
Encumbrances		$ 0
Original Land		219,543
Original Building		667,884
Costs Capitalized Subsequent to Acquisition		210,160
Land and improvements		250,134
Buildings and Improvements		829,529
Land Held for Development		17,924
Development and Construction in Progress		0
Total		1,097,587
Accumulated Depreciation		$ 214,533
Year(s) Built / Renovated		1976
Year(s) Acquired		2010
Depreciable Lives (Years)	[5]	(1)
250 West 55th Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		250 West 55th Street
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		285,263
Original Building		603,167
Costs Capitalized Subsequent to Acquisition		51,928
Land and improvements		285,263
Buildings and Improvements		655,095
Land Held for Development		0
Development and Construction in Progress		0
Total		940,358
Accumulated Depreciation		$ 116,857
Year(s) Built / Renovated		2014
Year(s) Acquired		2007
Depreciable Lives (Years)	[5]	(1)
100 Federal Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		100 Federal Street
Type		Office
Location		Boston, MA
Encumbrances		$ 0
Original Land		131,067
Original Building		435,954
Costs Capitalized Subsequent to Acquisition		102,984
Land and improvements		131,067
Buildings and Improvements		538,938
Land Held for Development		0
Development and Construction in Progress		0
Total		670,005
Accumulated Depreciation		$ 122,799
Year(s) Built / Renovated		1971-1975/2017
Year(s) Acquired		2012
Depreciable Lives (Years)	[5]	(1)
Times Square Tower
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Times Square Tower
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		165,413
Original Building		380,438
Costs Capitalized Subsequent to Acquisition		113,222
Land and improvements		169,193
Buildings and Improvements		489,880
Land Held for Development		0
Development and Construction in Progress		0
Total		659,073
Accumulated Depreciation		$ 217,303
Year(s) Built / Renovated		2004
Year(s) Acquired		2000
Depreciable Lives (Years)	[5]	(1)
Carnegie Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Carnegie Center
Type		Office
Location		Princeton, NJ
Encumbrances		$ 0
Original Land		142,666
Original Building		316,856
Costs Capitalized Subsequent to Acquisition		152,280
Land and improvements		94,240
Buildings and Improvements		462,882
Land Held for Development		54,680
Development and Construction in Progress		0
Total		611,802
Accumulated Depreciation		$ 208,331
Year(s) Built / Renovated		1983-2016
Year(s) Acquired		1998/1999/2000/2007/2014/2017/2019
Depreciable Lives (Years)	[5]	(1)
Atlantic Wharf
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Atlantic Wharf
Type		Office
Location		Boston, MA
Encumbrances		$ 0
Original Land		63,988
Original Building		454,537
Costs Capitalized Subsequent to Acquisition		18,709
Land and improvements		63,988
Buildings and Improvements		473,246
Land Held for Development		0
Development and Construction in Progress		0
Total		537,234
Accumulated Depreciation		$ 131,828
Year(s) Built / Renovated		2011
Year(s) Acquired		2007
Depreciable Lives (Years)	[5]	(1)
510 Madison Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		510 Madison Avenue
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		103,000
Original Building		253,665
Costs Capitalized Subsequent to Acquisition		25,495
Land and improvements		103,000
Buildings and Improvements		279,160
Land Held for Development		0
Development and Construction in Progress		0
Total		382,160
Accumulated Depreciation		$ 72,213
Year(s) Built / Renovated		2012
Year(s) Acquired		2010
Depreciable Lives (Years)	[5]	(1)
Fountain Square
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Fountain Square
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		56,853
Original Building		306,298
Costs Capitalized Subsequent to Acquisition		12,140
Land and improvements		56,853
Buildings and Improvements		318,438
Land Held for Development		0
Development and Construction in Progress		0
Total		375,291
Accumulated Depreciation		$ 78,498
Year(s) Built / Renovated		1986-1990
Year(s) Acquired		2012
Depreciable Lives (Years)	[5]	(1)
599 Lexington Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		599 Lexington Avenue
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		81,040
Original Building		100,507
Costs Capitalized Subsequent to Acquisition		188,572
Land and improvements		87,852
Buildings and Improvements		282,267
Land Held for Development		0
Development and Construction in Progress		0
Total		370,119
Accumulated Depreciation		$ 183,291
Year(s) Built / Renovated		1986
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
680 Folsom Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		680 Folsom Street
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		72,545
Original Building		219,766
Costs Capitalized Subsequent to Acquisition		7,907
Land and improvements		72,545
Buildings and Improvements		227,673
Land Held for Development		0
Development and Construction in Progress		0
Total		300,218
Accumulated Depreciation		$ 46,777
Year(s) Built / Renovated		2014
Year(s) Acquired		2012
Depreciable Lives (Years)	[5]	(1)
2200 Pennsylvania Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		2200 Pennsylvania Avenue
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		0
Original Building		183,541
Costs Capitalized Subsequent to Acquisition		113,627
Land and improvements		109,038
Buildings and Improvements		188,130
Land Held for Development		0
Development and Construction in Progress		0
Total		297,168
Accumulated Depreciation		$ 59,190
Year(s) Built / Renovated		2011
Year(s) Acquired		2008
Depreciable Lives (Years)	[5]	(1)
145 Broadway
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		145 Broadway
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		121
Original Building		273,013
Costs Capitalized Subsequent to Acquisition		23,246
Land and improvements		23,367
Buildings and Improvements		273,013
Land Held for Development		0
Development and Construction in Progress		0
Total		296,380
Accumulated Depreciation		$ 1,511
Year(s) Built / Renovated		2019
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
South of Market and Democracy Tower
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		South of Market and Democracy Tower
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		13,603
Original Building		237,479
Costs Capitalized Subsequent to Acquisition		26,415
Land and improvements		13,687
Buildings and Improvements		263,810
Land Held for Development		0
Development and Construction in Progress		0
Total		277,497
Accumulated Depreciation		$ 99,478
Year(s) Built / Renovated		2008-2009
Year(s) Acquired		2003
Depreciable Lives (Years)	[5]	(1)
601 Massachusetts Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		601 Massachusetts Avenue
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		95,310
Original Building		165,173
Costs Capitalized Subsequent to Acquisition		3,945
Land and improvements		95,322
Buildings and Improvements		169,106
Land Held for Development		0
Development and Construction in Progress		0
Total		264,428
Accumulated Depreciation		$ 24,502
Year(s) Built / Renovated		2016
Year(s) Acquired		2008
Depreciable Lives (Years)	[5]	(1)
Bay Colony Corporate Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Bay Colony Corporate Center
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		18,789
Original Building		148,451
Costs Capitalized Subsequent to Acquisition		80,077
Land and improvements		18,789
Buildings and Improvements		228,528
Land Held for Development		0
Development and Construction in Progress		0
Total		247,317
Accumulated Depreciation		$ 79,824
Year(s) Built / Renovated		1985-1989
Year(s) Acquired		2011
Depreciable Lives (Years)	[5]	(1)
Gateway Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Gateway Center
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		28,255
Original Building		139,245
Costs Capitalized Subsequent to Acquisition		61,791
Land and improvements		30,627
Buildings and Improvements		198,664
Land Held for Development		0
Development and Construction in Progress		0
Total		229,291
Accumulated Depreciation		$ 106,680
Year(s) Built / Renovated		1984/1986/2002
Year(s) Acquired		1999
Depreciable Lives (Years)	[5]	(1)
535 Mission Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		535 Mission Street
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		40,933
Original Building		148,378
Costs Capitalized Subsequent to Acquisition		3,276
Land and improvements		40,933
Buildings and Improvements		151,654
Land Held for Development		0
Development and Construction in Progress		0
Total		192,587
Accumulated Depreciation		$ 26,293
Year(s) Built / Renovated		2015
Year(s) Acquired		2013
Depreciable Lives (Years)	[5]	(1)
Reservoir Place
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reservoir Place
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		18,605
Original Building		104,124
Costs Capitalized Subsequent to Acquisition		53,718
Land and improvements		20,108
Buildings and Improvements		156,339
Land Held for Development		0
Development and Construction in Progress		0
Total		176,447
Accumulated Depreciation		$ 70,870
Year(s) Built / Renovated		1955/1987/2017
Year(s) Acquired		1997/1998
Depreciable Lives (Years)	[5]	(1)
Mountain View Research Park
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Mountain View Research Park
Type		Office
Location		Mountain View, CA
Encumbrances		$ 0
Original Land		95,066
Original Building		68,373
Costs Capitalized Subsequent to Acquisition		12,704
Land and improvements		95,066
Buildings and Improvements		81,077
Land Held for Development		0
Development and Construction in Progress		0
Total		176,143
Accumulated Depreciation		$ 19,807
Year(s) Built / Renovated		1977-1981/2007-2013
Year(s) Acquired		2013
Depreciable Lives (Years)	[5]	(1)
1330 Connecticut Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		1330 Connecticut Avenue
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		25,982
Original Building		82,311
Costs Capitalized Subsequent to Acquisition		36,847
Land and improvements		27,135
Buildings and Improvements		118,005
Land Held for Development		0
Development and Construction in Progress		0
Total		145,140
Accumulated Depreciation		$ 32,775
Year(s) Built / Renovated		1984/2018
Year(s) Acquired		2004
Depreciable Lives (Years)	[5]	(1)
Kingstowne Towne Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kingstowne Towne Center
Type		Office
Location		Alexandria, VA
Encumbrances		$ 0
Original Land		18,021
Original Building		109,038
Costs Capitalized Subsequent to Acquisition		3,376
Land and improvements		18,062
Buildings and Improvements		112,373
Land Held for Development		0
Development and Construction in Progress		0
Total		130,435
Accumulated Depreciation		$ 44,294
Year(s) Built / Renovated		2003-2006
Year(s) Acquired		2007
Depreciable Lives (Years)	[5]	(1)
One Freedom Square
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		One Freedom Square
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		9,929
Original Building		84,504
Costs Capitalized Subsequent to Acquisition		34,372
Land and improvements		11,293
Buildings and Improvements		117,512
Land Held for Development		0
Development and Construction in Progress		0
Total		128,805
Accumulated Depreciation		$ 59,006
Year(s) Built / Renovated		2000
Year(s) Acquired		2003
Depreciable Lives (Years)	[5]	(1)
Capital Gallery
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Capital Gallery
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		4,725
Original Building		29,565
Costs Capitalized Subsequent to Acquisition		88,704
Land and improvements		8,662
Buildings and Improvements		114,332
Land Held for Development		0
Development and Construction in Progress		0
Total		122,994
Accumulated Depreciation		$ 71,631
Year(s) Built / Renovated		1981/2006
Year(s) Acquired		2007
Depreciable Lives (Years)	[5]	(1)
Weston Corporate Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Weston Corporate Center
Type		Office
Location		Weston, MA
Encumbrances		$ 0
Original Land		25,753
Original Building		92,312
Costs Capitalized Subsequent to Acquisition		(123)
Land and improvements		25,854
Buildings and Improvements		92,088
Land Held for Development		0
Development and Construction in Progress		0
Total		117,942
Accumulated Depreciation		$ 29,227
Year(s) Built / Renovated		2010
Year(s) Acquired		2001
Depreciable Lives (Years)	[5]	(1)
Two Freedom Square
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Two Freedom Square
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		13,930
Original Building		77,739
Costs Capitalized Subsequent to Acquisition		23,209
Land and improvements		15,420
Buildings and Improvements		99,458
Land Held for Development		0
Development and Construction in Progress		0
Total		114,878
Accumulated Depreciation		$ 50,668
Year(s) Built / Renovated		2001
Year(s) Acquired		2003
Depreciable Lives (Years)	[5]	(1)
One and Two Reston Overlook
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		One and Two Reston Overlook
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		16,456
Original Building		66,192
Costs Capitalized Subsequent to Acquisition		24,181
Land and improvements		16,179
Buildings and Improvements		90,650
Land Held for Development		0
Development and Construction in Progress		0
Total		106,829
Accumulated Depreciation		$ 51,503
Year(s) Built / Renovated		1999
Year(s) Acquired		2000
Depreciable Lives (Years)	[5]	(1)
Discovery Square
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Discovery Square
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		11,198
Original Building		71,782
Costs Capitalized Subsequent to Acquisition		20,905
Land and improvements		12,533
Buildings and Improvements		91,352
Land Held for Development		0
Development and Construction in Progress		0
Total		103,885
Accumulated Depreciation		$ 43,619
Year(s) Built / Renovated		2001
Year(s) Acquired		2003
Depreciable Lives (Years)	[5]	(1)
140 Kendrick Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		140 Kendrick Street
Type		Office
Location		Needham, MA
Encumbrances		$ 0
Original Land		18,095
Original Building		66,905
Costs Capitalized Subsequent to Acquisition		17,574
Land and improvements		19,092
Buildings and Improvements		83,482
Land Held for Development		0
Development and Construction in Progress		0
Total		102,574
Accumulated Depreciation		$ 35,721
Year(s) Built / Renovated		2000
Year(s) Acquired		2004
Depreciable Lives (Years)	[5]	(1)
355 Main Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		355 Main Street
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		18,863
Original Building		53,346
Costs Capitalized Subsequent to Acquisition		27,582
Land and improvements		21,173
Buildings and Improvements		78,618
Land Held for Development		0
Development and Construction in Progress		0
Total		99,791
Accumulated Depreciation		$ 26,439
Year(s) Built / Renovated		1981/1996/2013
Year(s) Acquired		2006
Depreciable Lives (Years)	[5]	(1)
880 & 890 Winter Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		880 & 890 Winter Street
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		29,510
Original Building		65,812
Costs Capitalized Subsequent to Acquisition		0
Land and improvements		29,510
Buildings and Improvements		65,812
Land Held for Development		0
Development and Construction in Progress		0
Total		95,322
Accumulated Depreciation		$ 1,458
Year(s) Built / Renovated		1998-1999
Year(s) Acquired		2019
Depreciable Lives (Years)	[5]	(1)
10 CityPoint
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		10 CityPoint
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		1,953
Original Building		85,752
Costs Capitalized Subsequent to Acquisition		4,697
Land and improvements		2,290
Buildings and Improvements		90,112
Land Held for Development		0
Development and Construction in Progress		0
Total		92,402
Accumulated Depreciation		$ 10,928
Year(s) Built / Renovated		2016
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
90 Broadway
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		90 Broadway
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		19,104
Original Building		52,078
Costs Capitalized Subsequent to Acquisition		19,857
Land and improvements		20,785
Buildings and Improvements		70,254
Land Held for Development		0
Development and Construction in Progress		0
Total		91,039
Accumulated Depreciation		$ 23,621
Year(s) Built / Renovated		1983/1998/2013
Year(s) Acquired		2006
Depreciable Lives (Years)	[5]	(1)
230 CityPoint
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		230 CityPoint
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		13,189
Original Building		49,823
Costs Capitalized Subsequent to Acquisition		22,057
Land and improvements		13,807
Buildings and Improvements		71,262
Land Held for Development		0
Development and Construction in Progress		0
Total		85,069
Accumulated Depreciation		$ 29,255
Year(s) Built / Renovated		1992
Year(s) Acquired		2005
Depreciable Lives (Years)	[5]	(1)
77 CityPoint
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		77 CityPoint
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		13,847
Original Building		60,383
Costs Capitalized Subsequent to Acquisition		10,556
Land and improvements		14,023
Buildings and Improvements		70,763
Land Held for Development		0
Development and Construction in Progress		0
Total		84,786
Accumulated Depreciation		$ 27,172
Year(s) Built / Renovated		2008
Year(s) Acquired		2001
Depreciable Lives (Years)	[5]	(1)
Waltham Weston Corporate Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Waltham Weston Corporate Center
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		10,385
Original Building		60,694
Costs Capitalized Subsequent to Acquisition		13,165
Land and improvements		11,097
Buildings and Improvements		73,147
Land Held for Development		0
Development and Construction in Progress		0
Total		84,244
Accumulated Depreciation		$ 35,567
Year(s) Built / Renovated		2003
Year(s) Acquired		1999
Depreciable Lives (Years)	[5]	(1)
3625-3635 Peterson Way
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		3625-3635 Peterson Way
Type		Office
Location		Santa Clara, CA
Encumbrances		$ 0
Original Land		63,206
Original Building		14,879
Costs Capitalized Subsequent to Acquisition		752
Land and improvements		63,206
Buildings and Improvements		14,879
Land Held for Development		752
Development and Construction in Progress		0
Total		78,837
Accumulated Depreciation		$ 11,172
Year(s) Built / Renovated		1979
Year(s) Acquired		2016
Depreciable Lives (Years)	[5]	(1)
2440 West El Camino Real
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		2440 West El Camino Real
Type		Office
Location		Mountain View, CA
Encumbrances		$ 0
Original Land		16,741
Original Building		51,285
Costs Capitalized Subsequent to Acquisition		5,454
Land and improvements		16,741
Buildings and Improvements		56,739
Land Held for Development		0
Development and Construction in Progress		0
Total		73,480
Accumulated Depreciation		$ 13,090
Year(s) Built / Renovated		1987/2003
Year(s) Acquired		2011
Depreciable Lives (Years)	[5]	(1)
191 Spring Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		191 Spring Street
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		2,850
Original Building		59,751
Costs Capitalized Subsequent to Acquisition		7,695
Land and improvements		3,151
Buildings and Improvements		67,145
Land Held for Development		0
Development and Construction in Progress		0
Total		70,296
Accumulated Depreciation		$ 21,917
Year(s) Built / Renovated		1971/1995/2018
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
300 Binney Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		300 Binney Street
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		18,080
Original Building		51,262
Costs Capitalized Subsequent to Acquisition		140
Land and improvements		18,080
Buildings and Improvements		51,402
Land Held for Development		0
Development and Construction in Progress		0
Total		69,482
Accumulated Depreciation		$ 11,146
Year(s) Built / Renovated		2013
Year(s) Acquired		2009
Depreciable Lives (Years)	[5]	(1)
Wisconsin Place
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Wisconsin Place
Type		Office
Location		Chevy Chase, MD
Encumbrances		$ 0
Original Land		0
Original Building		53,349
Costs Capitalized Subsequent to Acquisition		14,924
Land and improvements		0
Buildings and Improvements		68,273
Land Held for Development		0
Development and Construction in Progress		0
Total		68,273
Accumulated Depreciation		$ 25,934
Year(s) Built / Renovated		2009
Year(s) Acquired		2004
Depreciable Lives (Years)	[5]	(1)
Reston Corporate Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reston Corporate Center
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		9,135
Original Building		50,857
Costs Capitalized Subsequent to Acquisition		6,236
Land and improvements		10,148
Buildings and Improvements		56,080
Land Held for Development		0
Development and Construction in Progress		0
Total		66,228
Accumulated Depreciation		$ 29,860
Year(s) Built / Renovated		1984
Year(s) Acquired		1998
Depreciable Lives (Years)	[5]	(1)
New Dominion Technology Park, Bldg. Two
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		New Dominion Technology Park, Bldg. Two
Type		Office
Location		Herndon, VA
Encumbrances		$ 0
Original Land		5,584
Original Building		51,868
Costs Capitalized Subsequent to Acquisition		4,157
Land and improvements		6,510
Buildings and Improvements		55,099
Land Held for Development		0
Development and Construction in Progress		0
Total		61,609
Accumulated Depreciation		$ 26,894
Year(s) Built / Renovated		2004
Year(s) Acquired		1998
Depreciable Lives (Years)	[5]	(1)
255 Main Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		255 Main Street
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		134
Original Building		25,110
Costs Capitalized Subsequent to Acquisition		34,124
Land and improvements		548
Buildings and Improvements		58,820
Land Held for Development		0
Development and Construction in Progress		0
Total		59,368
Accumulated Depreciation		$ 33,543
Year(s) Built / Renovated		1987
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
University Place
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		University Place
Type		Office
Location		Cambridge, MA
Encumbrances		$ 3,602
Original Land		0
Original Building		37,091
Costs Capitalized Subsequent to Acquisition		16,001
Land and improvements		7,418
Buildings and Improvements		45,674
Land Held for Development		0
Development and Construction in Progress		0
Total		53,092
Accumulated Depreciation		$ 29,423
Year(s) Built / Renovated		1985
Year(s) Acquired		1998
Depreciable Lives (Years)	[5]	(1)
New Dominion Technology Park, Bldg. One
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		New Dominion Technology Park, Bldg. One
Type		Office
Location		Herndon, VA
Encumbrances		$ 0
Original Land		3,880
Original Building		43,227
Costs Capitalized Subsequent to Acquisition		3,927
Land and improvements		4,583
Buildings and Improvements		46,451
Land Held for Development		0
Development and Construction in Progress		0
Total		51,034
Accumulated Depreciation		$ 29,141
Year(s) Built / Renovated		2001
Year(s) Acquired		1998
Depreciable Lives (Years)	[5]	(1)
Sumner Square
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Sumner Square
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		624
Original Building		28,745
Costs Capitalized Subsequent to Acquisition		21,344
Land and improvements		3,535
Buildings and Improvements		47,178
Land Held for Development		0
Development and Construction in Progress		0
Total		50,713
Accumulated Depreciation		$ 27,093
Year(s) Built / Renovated		1985
Year(s) Acquired		1999
Depreciable Lives (Years)	[5]	(1)
200 West Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		200 West Street
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		16,148
Original Building		24,983
Costs Capitalized Subsequent to Acquisition		8,211
Land and improvements		16,813
Buildings and Improvements		30,425
Land Held for Development		0
Development and Construction in Progress		2,104
Total		49,342
Accumulated Depreciation		$ 17,001
Year(s) Built / Renovated		1999
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
North First Business Park
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		North First Business Park
Type		Office
Location		San Jose, CA
Encumbrances		$ 0
Original Land		23,398
Original Building		13,069
Costs Capitalized Subsequent to Acquisition		4,571
Land and improvements		23,377
Buildings and Improvements		17,661
Land Held for Development		0
Development and Construction in Progress		0
Total		41,038
Accumulated Depreciation		$ 16,411
Year(s) Built / Renovated		1981
Year(s) Acquired		2007
Depreciable Lives (Years)	[5]	(1)
150 Broadway
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		150 Broadway
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		850
Original Building		25,042
Costs Capitalized Subsequent to Acquisition		8,540
Land and improvements		1,323
Buildings and Improvements		33,109
Land Held for Development		0
Development and Construction in Progress		0
Total		34,432
Accumulated Depreciation		$ 19,875
Year(s) Built / Renovated		1999
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
105 Broadway
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		105 Broadway
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		1,299
Original Building		12,943
Costs Capitalized Subsequent to Acquisition		11,406
Land and improvements		2,395
Buildings and Improvements		23,253
Land Held for Development		0
Development and Construction in Progress		0
Total		25,648
Accumulated Depreciation		$ 11,870
Year(s) Built / Renovated		1990
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
Lexington Office Park
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Lexington Office Park
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		998
Original Building		1,426
Costs Capitalized Subsequent to Acquisition		18,547
Land and improvements		1,264
Buildings and Improvements		19,707
Land Held for Development		0
Development and Construction in Progress		0
Total		20,971
Accumulated Depreciation		$ 14,312
Year(s) Built / Renovated		1982
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
201 Spring Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		201 Spring Street
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		2,849
Original Building		15,303
Costs Capitalized Subsequent to Acquisition		1,172
Land and improvements		3,124
Buildings and Improvements		16,200
Land Held for Development		0
Development and Construction in Progress		0
Total		19,324
Accumulated Depreciation		$ 8,587
Year(s) Built / Renovated		1997
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
The Point
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		The Point
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		6,395
Original Building		10,040
Costs Capitalized Subsequent to Acquisition		421
Land and improvements		6,492
Buildings and Improvements		10,364
Land Held for Development		0
Development and Construction in Progress		0
Total		16,856
Accumulated Depreciation		$ 1,349
Year(s) Built / Renovated		2015
Year(s) Acquired		2007
Depreciable Lives (Years)	[5]	(1)
33 Hayden Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		33 Hayden Avenue
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		266
Original Building		3,234
Costs Capitalized Subsequent to Acquisition		12,898
Land and improvements		425
Buildings and Improvements		15,973
Land Held for Development		0
Development and Construction in Progress		0
Total		16,398
Accumulated Depreciation		$ 5,678
Year(s) Built / Renovated		1979
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
690 Folsom Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		690 Folsom Street
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		3,219
Original Building		11,038
Costs Capitalized Subsequent to Acquisition		1,157
Land and improvements		3,219
Buildings and Improvements		12,195
Land Held for Development		0
Development and Construction in Progress		0
Total		15,414
Accumulated Depreciation		$ 2,284
Year(s) Built / Renovated		2015
Year(s) Acquired		2012
Depreciable Lives (Years)	[5]	(1)
92-100 Hayden Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		92-100 Hayden Avenue
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		594
Original Building		6,748
Costs Capitalized Subsequent to Acquisition		7,529
Land and improvements		802
Buildings and Improvements		14,069
Land Held for Development		0
Development and Construction in Progress		0
Total		14,871
Accumulated Depreciation		$ 12,041
Year(s) Built / Renovated		1985
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
181 Spring Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		181 Spring Street
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		1,066
Original Building		9,520
Costs Capitalized Subsequent to Acquisition		2,177
Land and improvements		1,160
Buildings and Improvements		11,603
Land Held for Development		0
Development and Construction in Progress		0
Total		12,763
Accumulated Depreciation		$ 5,597
Year(s) Built / Renovated		1999
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
195 West Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		195 West Street
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		1,611
Original Building		6,652
Costs Capitalized Subsequent to Acquisition		4,218
Land and improvements		1,858
Buildings and Improvements		10,623
Land Held for Development		0
Development and Construction in Progress		0
Total		12,481
Accumulated Depreciation		$ 8,352
Year(s) Built / Renovated		1990
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
7501 Boston Boulevard, Building Seven
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		7501 Boston Boulevard, Building Seven
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		665
Original Building		9,273
Costs Capitalized Subsequent to Acquisition		816
Land and improvements		791
Buildings and Improvements		9,963
Land Held for Development		0
Development and Construction in Progress		0
Total		10,754
Accumulated Depreciation		$ 5,393
Year(s) Built / Renovated		1997
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
7435 Boston Boulevard, Building One
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		7435 Boston Boulevard, Building One
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		392
Original Building		3,822
Costs Capitalized Subsequent to Acquisition		4,983
Land and improvements		659
Buildings and Improvements		8,538
Land Held for Development		0
Development and Construction in Progress		0
Total		9,197
Accumulated Depreciation		$ 6,344
Year(s) Built / Renovated		1982
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
7450 Boston Boulevard, Building Three
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		7450 Boston Boulevard, Building Three
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		1,165
Original Building		4,681
Costs Capitalized Subsequent to Acquisition		2,591
Land and improvements		1,430
Buildings and Improvements		7,007
Land Held for Development		0
Development and Construction in Progress		0
Total		8,437
Accumulated Depreciation		$ 3,575
Year(s) Built / Renovated		1987
Year(s) Acquired		1998
Depreciable Lives (Years)	[5]	(1)
32 Hartwell Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		32 Hartwell Avenue
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		168
Original Building		1,943
Costs Capitalized Subsequent to Acquisition		6,115
Land and improvements		314
Buildings and Improvements		7,912
Land Held for Development		0
Development and Construction in Progress		0
Total		8,226
Accumulated Depreciation		$ 1,975
Year(s) Built / Renovated		1968/1979/1987
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
250 Binney Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		250 Binney Street
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		110
Original Building		4,483
Costs Capitalized Subsequent to Acquisition		3,593
Land and improvements		273
Buildings and Improvements		7,913
Land Held for Development		0
Development and Construction in Progress		0
Total		8,186
Accumulated Depreciation		$ 5,829
Year(s) Built / Renovated		1983
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
8000 Grainger Court, Building Five
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		8000 Grainger Court, Building Five
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		366
Original Building		4,282
Costs Capitalized Subsequent to Acquisition		3,198
Land and improvements		601
Buildings and Improvements		7,245
Land Held for Development		0
Development and Construction in Progress		0
Total		7,846
Accumulated Depreciation		$ 5,752
Year(s) Built / Renovated		1984
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
453 Ravendale Drive
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		453 Ravendale Drive
Type		Office
Location		Mountain View, CA
Encumbrances		$ 0
Original Land		5,477
Original Building		1,090
Costs Capitalized Subsequent to Acquisition		676
Land and improvements		5,477
Buildings and Improvements		1,766
Land Held for Development		0
Development and Construction in Progress		0
Total		7,243
Accumulated Depreciation		$ 690
Year(s) Built / Renovated		1977
Year(s) Acquired		2012
Depreciable Lives (Years)	[5]	(1)
7300 Boston Boulevard, Building Thirteen
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		7300 Boston Boulevard, Building Thirteen
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		608
Original Building		4,773
Costs Capitalized Subsequent to Acquisition		1,007
Land and improvements		661
Buildings and Improvements		5,727
Land Held for Development		0
Development and Construction in Progress		0
Total		6,388
Accumulated Depreciation		$ 1,984
Year(s) Built / Renovated		2002
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
17 Hartwell Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		17 Hartwell Avenue
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		26
Original Building		150
Costs Capitalized Subsequent to Acquisition		6,064
Land and improvements		65
Buildings and Improvements		6,175
Land Held for Development		0
Development and Construction in Progress		0
Total		6,240
Accumulated Depreciation		$ 1,966
Year(s) Built / Renovated		1968
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
7601 Boston Boulevard, Building Eight
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		7601 Boston Boulevard, Building Eight
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		200
Original Building		878
Costs Capitalized Subsequent to Acquisition		5,060
Land and improvements		551
Buildings and Improvements		5,587
Land Held for Development		0
Development and Construction in Progress		0
Total		6,138
Accumulated Depreciation		$ 4,689
Year(s) Built / Renovated		1986
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
7500 Boston Boulevard, Building Six
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		7500 Boston Boulevard, Building Six
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		138
Original Building		3,749
Costs Capitalized Subsequent to Acquisition		1,640
Land and improvements		367
Buildings and Improvements		5,160
Land Held for Development		0
Development and Construction in Progress		0
Total		5,527
Accumulated Depreciation		$ 4,237
Year(s) Built / Renovated		1985
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
8000 Corporate Court, Building Eleven
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		8000 Corporate Court, Building Eleven
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		136
Original Building		3,071
Costs Capitalized Subsequent to Acquisition		1,596
Land and improvements		774
Buildings and Improvements		4,029
Land Held for Development		0
Development and Construction in Progress		0
Total		4,803
Accumulated Depreciation		$ 3,191
Year(s) Built / Renovated		1989
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
7375 Boston Boulevard, Building Ten
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		7375 Boston Boulevard, Building Ten
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		23
Original Building		2,685
Costs Capitalized Subsequent to Acquisition		1,032
Land and improvements		93
Buildings and Improvements		3,647
Land Held for Development		0
Development and Construction in Progress		0
Total		3,740
Accumulated Depreciation		$ 2,606
Year(s) Built / Renovated		1988
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
7374 Boston Boulevard, Building Four
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		7374 Boston Boulevard, Building Four
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		241
Original Building		1,605
Costs Capitalized Subsequent to Acquisition		1,828
Land and improvements		398
Buildings and Improvements		3,276
Land Held for Development		0
Development and Construction in Progress		0
Total		3,674
Accumulated Depreciation		$ 2,779
Year(s) Built / Renovated		1984
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
7451 Boston Boulevard, Building Two
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		7451 Boston Boulevard, Building Two
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		249
Original Building		1,542
Costs Capitalized Subsequent to Acquisition		1,667
Land and improvements		613
Buildings and Improvements		2,845
Land Held for Development		0
Development and Construction in Progress		0
Total		3,458
Accumulated Depreciation		$ 2,610
Year(s) Built / Renovated		1982
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
Signature at Reston
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Signature at Reston
Type		Residential
Location		Reston, VA
Encumbrances		$ 0
Original Land		27,076
Original Building		190,580
Costs Capitalized Subsequent to Acquisition		393
Land and improvements		27,076
Buildings and Improvements		190,973
Land Held for Development		0
Development and Construction in Progress		0
Total		218,049
Accumulated Depreciation		$ 8,773
Year(s) Built / Renovated		2018
Year(s) Acquired		2013
Depreciable Lives (Years)	[5]	(1)
Proto Kendall Square
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Proto Kendall Square
Type		Residential
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		9,243
Original Building		127,248
Costs Capitalized Subsequent to Acquisition		2,939
Land and improvements		9,245
Buildings and Improvements		130,185
Land Held for Development		0
Development and Construction in Progress		0
Total		139,430
Accumulated Depreciation		$ 4,566
Year(s) Built / Renovated		2018
Year(s) Acquired		2015
Depreciable Lives (Years)	[5]	(1)
The Avant at Reston Town Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		The Avant at Reston Town Center
Type		Residential
Location		Reston, VA
Encumbrances		$ 0
Original Land		20,350
Original Building		91,995
Costs Capitalized Subsequent to Acquisition		830
Land and improvements		20,350
Buildings and Improvements		92,825
Land Held for Development		0
Development and Construction in Progress		0
Total		113,175
Accumulated Depreciation		$ 14,728
Year(s) Built / Renovated		2014
Year(s) Acquired		2010
Depreciable Lives (Years)	[5]	(1)
The Lofts at Atlantic Wharf
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		The Lofts at Atlantic Wharf
Type		Residential
Location		Boston, MA
Encumbrances		$ 0
Original Land		3,529
Original Building		54,891
Costs Capitalized Subsequent to Acquisition		1,897
Land and improvements		3,529
Buildings and Improvements		56,788
Land Held for Development		0
Development and Construction in Progress		0
Total		60,317
Accumulated Depreciation		$ 12,639
Year(s) Built / Renovated		2011
Year(s) Acquired		2007
Depreciable Lives (Years)	[5]	(1)
Boston Marriott Cambridge
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Boston Marriott Cambridge
Type		Hotel
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		478
Original Building		37,918
Costs Capitalized Subsequent to Acquisition		35,813
Land and improvements		1,201
Buildings and Improvements		73,008
Land Held for Development		0
Development and Construction in Progress		0
Total		74,209
Accumulated Depreciation		$ 46,605
Year(s) Built / Renovated		1986/2017
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
Kendall Center Green Garage
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kendall Center Green Garage
Type		Garage
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		0
Original Building		35,035
Costs Capitalized Subsequent to Acquisition		7,329
Land and improvements		103
Buildings and Improvements		42,261
Land Held for Development		0
Development and Construction in Progress		0
Total		42,364
Accumulated Depreciation		$ 13,512
Year(s) Built / Renovated		1984
Year(s) Acquired		2006
Depreciable Lives (Years)	[5]	(1)
Kendall Center Yellow Garage
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kendall Center Yellow Garage
Type		Garage
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		1,256
Original Building		15,697
Costs Capitalized Subsequent to Acquisition		1,552
Land and improvements		1,434
Buildings and Improvements		17,071
Land Held for Development		0
Development and Construction in Progress		0
Total		18,505
Accumulated Depreciation		$ 6,031
Year(s) Built / Renovated		2006
Year(s) Acquired		2004
Depreciable Lives (Years)	[5]	(1)
Kendall Center Blue Garage
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kendall Center Blue Garage
Type		Garage
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		1,163
Original Building		11,633
Costs Capitalized Subsequent to Acquisition		2,151
Land and improvements		1,579
Buildings and Improvements		13,368
Land Held for Development		0
Development and Construction in Progress		0
Total		14,947
Accumulated Depreciation		$ 9,728
Year(s) Built / Renovated		1990
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
The Skylyne (MacArthur Station Residences)
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		The Skylyne (MacArthur Station Residences)
Type		Development
Location		Oakland, CA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		226,526
Land and improvements		29,807
Buildings and Improvements		0
Land Held for Development		0
Development and Construction in Progress		196,719
Total		226,526
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		N/A
Depreciable Lives (Years)		N/A
2100 Pennsylvania Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		2100 Pennsylvania Avenue
Type		Development
Location		Washington, DC
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		224,380
Land and improvements		185,129
Buildings and Improvements		0
Land Held for Development		0
Development and Construction in Progress		39,251
Total		224,380
Accumulated Depreciation		$ 1,024
Year(s) Built / Renovated		N/A
Year(s) Acquired		N/A
Depreciable Lives (Years)		N/A
Reston Gateway
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reston Gateway
Type		Development
Location		Reston, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		150,632
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		0
Development and Construction in Progress		150,632
Total		150,632
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1998
Depreciable Lives (Years)		N/A
17Fifty Presidents Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		17Fifty Presidents Street
Type		Development
Location		Reston, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		99,816
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		0
Development and Construction in Progress		99,816
Total		99,816
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2013
Depreciable Lives (Years)		N/A
20 CityPoint
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		20 CityPoint
Type		Development
Location		Waltham, MA
Encumbrances		$ 0
Original Land		4,721
Original Building		52,039
Costs Capitalized Subsequent to Acquisition		20,007
Land and improvements		4,721
Buildings and Improvements		52,039
Land Held for Development		0
Development and Construction in Progress		20,007
Total		76,767
Accumulated Depreciation		$ 1,136
Year(s) Built / Renovated		N/A
Year(s) Acquired		2007
Depreciable Lives (Years)		N/A
325 Main Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		325 Main Street
Type		Development
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		174
Original Building		0
Costs Capitalized Subsequent to Acquisition		68,903
Land and improvements		965
Buildings and Improvements		0
Land Held for Development		0
Development and Construction in Progress		68,112
Total		69,077
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1997
Depreciable Lives (Years)		N/A
North First Master Plan
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		North First Master Plan
Type		Land
Location		San Jose, CA
Encumbrances		$ 0
Original Land		35,004
Original Building		0
Costs Capitalized Subsequent to Acquisition		3,932
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		38,936
Development and Construction in Progress		0
Total		38,936
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2007
Depreciable Lives (Years)		N/A
Plaza at Almaden
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Plaza at Almaden
Type		Land
Location		San Jose, CA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		34,889
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		34,889
Development and Construction in Progress		0
Total		34,889
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2006
Depreciable Lives (Years)		N/A
425 Fourth Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		425 Fourth Street
Type		Land
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		22,074
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		22,074
Development and Construction in Progress		0
Total		22,074
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		N/A
Depreciable Lives (Years)		N/A
Springfield Metro Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Springfield Metro Center
Type		Land
Location		Springfield, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		19,844
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		19,844
Development and Construction in Progress		0
Total		19,844
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2007
Depreciable Lives (Years)		N/A
Reston Gateway Master Plan
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reston Gateway Master Plan
Type		Land
Location		Reston, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		18,292
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		18,292
Development and Construction in Progress		0
Total		18,292
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1998
Depreciable Lives (Years)		N/A
214 Third Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		214 Third Avenue
Type		Land
Location		Waltham, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		17,692
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		17,692
Development and Construction in Progress		0
Total		17,692
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2006
Depreciable Lives (Years)		N/A
103 Fourth Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		103 Fourth Avenue
Type		Land
Location		Waltham, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		12,826
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		12,826
Development and Construction in Progress		0
Total		12,826
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2007
Depreciable Lives (Years)		N/A
Crane Meadow
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Crane Meadow
Type		Land
Location		Marlborough, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		8,866
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		8,866
Development and Construction in Progress		0
Total		8,866
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2000
Depreciable Lives (Years)		N/A
Broad Run Business Park
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Broad Run Business Park
Type		Land
Location		Loudoun County, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		2,396
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		2,396
Development and Construction in Progress		0
Total		2,396
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1998
Depreciable Lives (Years)		N/A
Kendall Center Master Plan
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kendall Center Master Plan
Type		Land
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		1,693
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		1,693
Development and Construction in Progress		0
Total		1,693
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1997
Depreciable Lives (Years)		N/A
Weston Quarry
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Weston Quarry
Type		Land
Location		Weston, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		1,249
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		1,249
Development and Construction in Progress		0
Total		1,249
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2001
Depreciable Lives (Years)		N/A
Reston Overlook Master Plan
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reston Overlook Master Plan
Type		Land
Location		Reston, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		39
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		39
Development and Construction in Progress		0
Total		39
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2000
Depreciable Lives (Years)		N/A
Minimum [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate and Accumulated Depreiation Life used for Depreciation		life of the lease
Maximum [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate and Accumulated Depreciation, Life Used for Depreciation		40 years
Furniture and Fixtures [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Accumulated Depreciation		$ 27,619
Land and Land Improvements [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Right-of-use assets - finance leases		214,091
Building and Building Improvements [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Right-of-use assets - finance leases		$ 23,303

[1]	Includes unamortized deferred financing costs totaling approximately $(26.7) million .
[2]	Includes Right of Use Assets - Finance Leases and Right of Use Assets - Operating Leases of approximately $214,091 and $148,640 , respectively.
[3]	Includes Right of Use Assets - Finance Leases of approximately $23,303 .
[4]	Includes pre-development costs.
[5]	Depreciation of the buildings and improvements are calculated over lives ranging from the life of the lease to 40 years.

Real Estate and Accumulated D_5

Real Estate and Accumulated Depreciation Activity of Real Estate and Accumulated Depreciation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Real Estate, Balance at the beginning of the year	$ 21,605,545	$ 21,058,714	$ 20,114,576
Real Estate, Additions to / improvements of real estate	1,671,898	1,043,379	1,099,286
Real Estate, Assets sold / written off	(432,746)	(496,548)	(155,148)
Real Estate, Balance at the end of the year	22,844,697	21,605,545	21,058,714
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate, Accumulated Depreciation [Roll Forward]
Accumulated depreciation, Balance at beginning of the year	4,871,102	4,566,570	4,201,891
Accumulated depreciation, Depreciation expense	564,938	533,342	497,059
Accumulated depreciation, Assets sold / written off	(196,861)	(228,810)	(132,380)
Accumulated depreciation, Balance at end of the year	$ 5,239,179	$ 4,871,102	$ 4,566,570

Real Estate and Accumulated D_6

Real Estate and Accumulated Depreciation Schedule of Real Estate and Accumulated Depreciation (BPLP) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	[1]	$ 2,922,408
Original Land		5,024,060
Original Building		13,057,336
Costs Capitalized Subsequent to Acquisition		4,763,301
Land and improvements	[2]	5,474,337
Buildings and Improvements	[3]	16,325,796
Land Held for Development	[4]	254,828
Development and Construction in Progress		789,736
Total		22,844,697
Accumulated Depreciation		5,239,179
Furniture, Fixtures and Equipment		44,313		$ 44,351
Real Estate Aggregate Accumulated Depreciation For Tax Purposes		$ 4,000,000
Real Estate and Accumulated Depreciation, Life Used for Depreciation		40 years
Unamortized deferred finance costs		$ (26,700)
Right-of-use assets - finance leases		237,394
Right of use assets - operating leases		$ 148,640	$ 151,800
767 Fifth Avenue (the General Motors Building)
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		767 Fifth Avenue (the General Motors Building)
Type		Office
Location		New York, NY
Encumbrances		$ 2,274,028
Original Land		1,796,252
Original Building		1,532,654
Costs Capitalized Subsequent to Acquisition		202,612
Land and improvements		1,796,252
Buildings and Improvements		1,735,266
Land Held for Development		0
Development and Construction in Progress		0
Total		3,531,518
Accumulated Depreciation		$ 313,158
Year(s) Built / Renovated		1968/2019
Year(s) Acquired		2013
Depreciable Lives (Years)	[5]	(1)
Prudential Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Prudential Center
Type		Office
Location		Boston, MA
Encumbrances		$ 0
Original Land		92,077
Original Building		948,357
Costs Capitalized Subsequent to Acquisition		556,458
Land and improvements		115,638
Buildings and Improvements		1,478,578
Land Held for Development		2,676
Development and Construction in Progress		0
Total		1,596,892
Accumulated Depreciation		$ 596,740
Year(s) Built / Renovated		1965/1993/2002/2016-2017
Year(s) Acquired		1998/1999/2000
Depreciable Lives (Years)	[5]	(1)
Embarcadero Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Embarcadero Center
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		179,697
Original Building		847,410
Costs Capitalized Subsequent to Acquisition		415,228
Land and improvements		195,987
Buildings and Improvements		1,246,348
Land Held for Development		0
Development and Construction in Progress		0
Total		1,442,335
Accumulated Depreciation		$ 633,711
Year(s) Built / Renovated		1970/1989
Year(s) Acquired		1998-1999
Depreciable Lives (Years)	[5]	(1)
399 Park Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		399 Park Avenue
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		339,200
Original Building		700,358
Costs Capitalized Subsequent to Acquisition		300,519
Land and improvements		354,107
Buildings and Improvements		985,970
Land Held for Development		0
Development and Construction in Progress		0
Total		1,340,077
Accumulated Depreciation		$ 358,960
Year(s) Built / Renovated		1961/2018
Year(s) Acquired		2002
Depreciable Lives (Years)	[5]	(1)
601 Lexington Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		601 Lexington Avenue
Type		Office
Location		New York, NY
Encumbrances		$ 644,778
Original Land		241,600
Original Building		494,782
Costs Capitalized Subsequent to Acquisition		454,902
Land and improvements		289,639
Buildings and Improvements		688,550
Land Held for Development		0
Development and Construction in Progress		213,095
Total		1,191,284
Accumulated Depreciation		$ 289,482
Year(s) Built / Renovated		1977/1997
Year(s) Acquired		2001
Depreciable Lives (Years)	[5]	(1)
Salesforce Tower
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Salesforce Tower
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		200,349
Original Building		946,205
Costs Capitalized Subsequent to Acquisition		0
Land and improvements		200,349
Buildings and Improvements		946,205
Land Held for Development		0
Development and Construction in Progress		0
Total		1,146,554
Accumulated Depreciation		$ 38,727
Year(s) Built / Renovated		2018
Year(s) Acquired		2013
Depreciable Lives (Years)	[5]	(1)
200 Clarendon Street and Garage
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		200 Clarendon Street and Garage
Type		Office
Location		Boston, MA
Encumbrances		$ 0
Original Land		219,543
Original Building		667,884
Costs Capitalized Subsequent to Acquisition		210,160
Land and improvements		250,134
Buildings and Improvements		829,529
Land Held for Development		17,924
Development and Construction in Progress		0
Total		1,097,587
Accumulated Depreciation		$ 214,533
Year(s) Built / Renovated		1976
Year(s) Acquired		2010
Depreciable Lives (Years)	[5]	(1)
250 West 55th Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		250 West 55th Street
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		285,263
Original Building		603,167
Costs Capitalized Subsequent to Acquisition		51,928
Land and improvements		285,263
Buildings and Improvements		655,095
Land Held for Development		0
Development and Construction in Progress		0
Total		940,358
Accumulated Depreciation		$ 116,857
Year(s) Built / Renovated		2014
Year(s) Acquired		2007
Depreciable Lives (Years)	[5]	(1)
100 Federal Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		100 Federal Street
Type		Office
Location		Boston, MA
Encumbrances		$ 0
Original Land		131,067
Original Building		435,954
Costs Capitalized Subsequent to Acquisition		102,984
Land and improvements		131,067
Buildings and Improvements		538,938
Land Held for Development		0
Development and Construction in Progress		0
Total		670,005
Accumulated Depreciation		$ 122,799
Year(s) Built / Renovated		1971-1975/2017
Year(s) Acquired		2012
Depreciable Lives (Years)	[5]	(1)
Times Square Tower
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Times Square Tower
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		165,413
Original Building		380,438
Costs Capitalized Subsequent to Acquisition		113,222
Land and improvements		169,193
Buildings and Improvements		489,880
Land Held for Development		0
Development and Construction in Progress		0
Total		659,073
Accumulated Depreciation		$ 217,303
Year(s) Built / Renovated		2004
Year(s) Acquired		2000
Depreciable Lives (Years)	[5]	(1)
Carnegie Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Carnegie Center
Type		Office
Location		Princeton, NJ
Encumbrances		$ 0
Original Land		142,666
Original Building		316,856
Costs Capitalized Subsequent to Acquisition		152,280
Land and improvements		94,240
Buildings and Improvements		462,882
Land Held for Development		54,680
Development and Construction in Progress		0
Total		611,802
Accumulated Depreciation		$ 208,331
Year(s) Built / Renovated		1983-2016
Year(s) Acquired		1998/1999/2000/2007/2014/2017/2019
Depreciable Lives (Years)	[5]	(1)
Atlantic Wharf
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Atlantic Wharf
Type		Office
Location		Boston, MA
Encumbrances		$ 0
Original Land		63,988
Original Building		454,537
Costs Capitalized Subsequent to Acquisition		18,709
Land and improvements		63,988
Buildings and Improvements		473,246
Land Held for Development		0
Development and Construction in Progress		0
Total		537,234
Accumulated Depreciation		$ 131,828
Year(s) Built / Renovated		2011
Year(s) Acquired		2007
Depreciable Lives (Years)	[5]	(1)
510 Madison Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		510 Madison Avenue
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		103,000
Original Building		253,665
Costs Capitalized Subsequent to Acquisition		25,495
Land and improvements		103,000
Buildings and Improvements		279,160
Land Held for Development		0
Development and Construction in Progress		0
Total		382,160
Accumulated Depreciation		$ 72,213
Year(s) Built / Renovated		2012
Year(s) Acquired		2010
Depreciable Lives (Years)	[5]	(1)
Fountain Square
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Fountain Square
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		56,853
Original Building		306,298
Costs Capitalized Subsequent to Acquisition		12,140
Land and improvements		56,853
Buildings and Improvements		318,438
Land Held for Development		0
Development and Construction in Progress		0
Total		375,291
Accumulated Depreciation		$ 78,498
Year(s) Built / Renovated		1986-1990
Year(s) Acquired		2012
Depreciable Lives (Years)	[5]	(1)
599 Lexington Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		599 Lexington Avenue
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		81,040
Original Building		100,507
Costs Capitalized Subsequent to Acquisition		188,572
Land and improvements		87,852
Buildings and Improvements		282,267
Land Held for Development		0
Development and Construction in Progress		0
Total		370,119
Accumulated Depreciation		$ 183,291
Year(s) Built / Renovated		1986
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
680 Folsom Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		680 Folsom Street
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		72,545
Original Building		219,766
Costs Capitalized Subsequent to Acquisition		7,907
Land and improvements		72,545
Buildings and Improvements		227,673
Land Held for Development		0
Development and Construction in Progress		0
Total		300,218
Accumulated Depreciation		$ 46,777
Year(s) Built / Renovated		2014
Year(s) Acquired		2012
Depreciable Lives (Years)	[5]	(1)
2200 Pennsylvania Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		2200 Pennsylvania Avenue
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		0
Original Building		183,541
Costs Capitalized Subsequent to Acquisition		113,627
Land and improvements		109,038
Buildings and Improvements		188,130
Land Held for Development		0
Development and Construction in Progress		0
Total		297,168
Accumulated Depreciation		$ 59,190
Year(s) Built / Renovated		2011
Year(s) Acquired		2008
Depreciable Lives (Years)	[5]	(1)
145 Broadway
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		145 Broadway
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		121
Original Building		273,013
Costs Capitalized Subsequent to Acquisition		23,246
Land and improvements		23,367
Buildings and Improvements		273,013
Land Held for Development		0
Development and Construction in Progress		0
Total		296,380
Accumulated Depreciation		$ 1,511
Year(s) Built / Renovated		2019
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
South of Market and Democracy Tower
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		South of Market and Democracy Tower
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		13,603
Original Building		237,479
Costs Capitalized Subsequent to Acquisition		26,415
Land and improvements		13,687
Buildings and Improvements		263,810
Land Held for Development		0
Development and Construction in Progress		0
Total		277,497
Accumulated Depreciation		$ 99,478
Year(s) Built / Renovated		2008-2009
Year(s) Acquired		2003
Depreciable Lives (Years)	[5]	(1)
601 Massachusetts Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		601 Massachusetts Avenue
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		95,310
Original Building		165,173
Costs Capitalized Subsequent to Acquisition		3,945
Land and improvements		95,322
Buildings and Improvements		169,106
Land Held for Development		0
Development and Construction in Progress		0
Total		264,428
Accumulated Depreciation		$ 24,502
Year(s) Built / Renovated		2016
Year(s) Acquired		2008
Depreciable Lives (Years)	[5]	(1)
Bay Colony Corporate Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Bay Colony Corporate Center
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		18,789
Original Building		148,451
Costs Capitalized Subsequent to Acquisition		80,077
Land and improvements		18,789
Buildings and Improvements		228,528
Land Held for Development		0
Development and Construction in Progress		0
Total		247,317
Accumulated Depreciation		$ 79,824
Year(s) Built / Renovated		1985-1989
Year(s) Acquired		2011
Depreciable Lives (Years)	[5]	(1)
Gateway Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Gateway Center
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		28,255
Original Building		139,245
Costs Capitalized Subsequent to Acquisition		61,791
Land and improvements		30,627
Buildings and Improvements		198,664
Land Held for Development		0
Development and Construction in Progress		0
Total		229,291
Accumulated Depreciation		$ 106,680
Year(s) Built / Renovated		1984/1986/2002
Year(s) Acquired		1999
Depreciable Lives (Years)	[5]	(1)
535 Mission Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		535 Mission Street
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		40,933
Original Building		148,378
Costs Capitalized Subsequent to Acquisition		3,276
Land and improvements		40,933
Buildings and Improvements		151,654
Land Held for Development		0
Development and Construction in Progress		0
Total		192,587
Accumulated Depreciation		$ 26,293
Year(s) Built / Renovated		2015
Year(s) Acquired		2013
Depreciable Lives (Years)	[5]	(1)
Mountain View Research Park
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Mountain View Research Park
Type		Office
Location		Mountain View, CA
Encumbrances		$ 0
Original Land		95,066
Original Building		68,373
Costs Capitalized Subsequent to Acquisition		12,704
Land and improvements		95,066
Buildings and Improvements		81,077
Land Held for Development		0
Development and Construction in Progress		0
Total		176,143
Accumulated Depreciation		$ 19,807
Year(s) Built / Renovated		1977-1981/2007-2013
Year(s) Acquired		2013
Depreciable Lives (Years)	[5]	(1)
Reservoir Place
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reservoir Place
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		18,605
Original Building		104,124
Costs Capitalized Subsequent to Acquisition		53,718
Land and improvements		20,108
Buildings and Improvements		156,339
Land Held for Development		0
Development and Construction in Progress		0
Total		176,447
Accumulated Depreciation		$ 70,870
Year(s) Built / Renovated		1955/1987/2017
Year(s) Acquired		1997/1998
Depreciable Lives (Years)	[5]	(1)
1330 Connecticut Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		1330 Connecticut Avenue
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		25,982
Original Building		82,311
Costs Capitalized Subsequent to Acquisition		36,847
Land and improvements		27,135
Buildings and Improvements		118,005
Land Held for Development		0
Development and Construction in Progress		0
Total		145,140
Accumulated Depreciation		$ 32,775
Year(s) Built / Renovated		1984/2018
Year(s) Acquired		2004
Depreciable Lives (Years)	[5]	(1)
Kingstowne Towne Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kingstowne Towne Center
Type		Office
Location		Alexandria, VA
Encumbrances		$ 0
Original Land		18,021
Original Building		109,038
Costs Capitalized Subsequent to Acquisition		3,376
Land and improvements		18,062
Buildings and Improvements		112,373
Land Held for Development		0
Development and Construction in Progress		0
Total		130,435
Accumulated Depreciation		$ 44,294
Year(s) Built / Renovated		2003-2006
Year(s) Acquired		2007
Depreciable Lives (Years)	[5]	(1)
One Freedom Square
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		One Freedom Square
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		9,929
Original Building		84,504
Costs Capitalized Subsequent to Acquisition		34,372
Land and improvements		11,293
Buildings and Improvements		117,512
Land Held for Development		0
Development and Construction in Progress		0
Total		128,805
Accumulated Depreciation		$ 59,006
Year(s) Built / Renovated		2000
Year(s) Acquired		2003
Depreciable Lives (Years)	[5]	(1)
Weston Corporate Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Weston Corporate Center
Type		Office
Location		Weston, MA
Encumbrances		$ 0
Original Land		25,753
Original Building		92,312
Costs Capitalized Subsequent to Acquisition		(123)
Land and improvements		25,854
Buildings and Improvements		92,088
Land Held for Development		0
Development and Construction in Progress		0
Total		117,942
Accumulated Depreciation		$ 29,227
Year(s) Built / Renovated		2010
Year(s) Acquired		2001
Depreciable Lives (Years)	[5]	(1)
Capital Gallery
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Capital Gallery
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		4,725
Original Building		29,565
Costs Capitalized Subsequent to Acquisition		88,704
Land and improvements		8,662
Buildings and Improvements		114,332
Land Held for Development		0
Development and Construction in Progress		0
Total		122,994
Accumulated Depreciation		$ 71,631
Year(s) Built / Renovated		1981/2006
Year(s) Acquired		2007
Depreciable Lives (Years)	[5]	(1)
Two Freedom Square
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Two Freedom Square
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		13,930
Original Building		77,739
Costs Capitalized Subsequent to Acquisition		23,209
Land and improvements		15,420
Buildings and Improvements		99,458
Land Held for Development		0
Development and Construction in Progress		0
Total		114,878
Accumulated Depreciation		$ 50,668
Year(s) Built / Renovated		2001
Year(s) Acquired		2003
Depreciable Lives (Years)	[5]	(1)
One and Two Reston Overlook
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		One and Two Reston Overlook
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		16,456
Original Building		66,192
Costs Capitalized Subsequent to Acquisition		24,181
Land and improvements		16,179
Buildings and Improvements		90,650
Land Held for Development		0
Development and Construction in Progress		0
Total		106,829
Accumulated Depreciation		$ 51,503
Year(s) Built / Renovated		1999
Year(s) Acquired		2000
Depreciable Lives (Years)	[5]	(1)
355 Main Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		355 Main Street
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		18,863
Original Building		53,346
Costs Capitalized Subsequent to Acquisition		27,582
Land and improvements		21,173
Buildings and Improvements		78,618
Land Held for Development		0
Development and Construction in Progress		0
Total		99,791
Accumulated Depreciation		$ 26,439
Year(s) Built / Renovated		1981/1996/2013
Year(s) Acquired		2006
Depreciable Lives (Years)	[5]	(1)
140 Kendrick Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		140 Kendrick Street
Type		Office
Location		Needham, MA
Encumbrances		$ 0
Original Land		18,095
Original Building		66,905
Costs Capitalized Subsequent to Acquisition		17,574
Land and improvements		19,092
Buildings and Improvements		83,482
Land Held for Development		0
Development and Construction in Progress		0
Total		102,574
Accumulated Depreciation		$ 35,721
Year(s) Built / Renovated		2000
Year(s) Acquired		2004
Depreciable Lives (Years)	[5]	(1)
Discovery Square
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Discovery Square
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		11,198
Original Building		71,782
Costs Capitalized Subsequent to Acquisition		20,905
Land and improvements		12,533
Buildings and Improvements		91,352
Land Held for Development		0
Development and Construction in Progress		0
Total		103,885
Accumulated Depreciation		$ 43,619
Year(s) Built / Renovated		2001
Year(s) Acquired		2003
Depreciable Lives (Years)	[5]	(1)
880 & 890 Winter Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		880 & 890 Winter Street
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		29,510
Original Building		65,812
Costs Capitalized Subsequent to Acquisition		0
Land and improvements		29,510
Buildings and Improvements		65,812
Land Held for Development		0
Development and Construction in Progress		0
Total		95,322
Accumulated Depreciation		$ 1,458
Year(s) Built / Renovated		1998-1999
Year(s) Acquired		2019
Depreciable Lives (Years)	[5]	(1)
10 CityPoint
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		10 CityPoint
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		1,953
Original Building		85,752
Costs Capitalized Subsequent to Acquisition		4,697
Land and improvements		2,290
Buildings and Improvements		90,112
Land Held for Development		0
Development and Construction in Progress		0
Total		92,402
Accumulated Depreciation		$ 10,928
Year(s) Built / Renovated		2016
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
90 Broadway
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		90 Broadway
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		19,104
Original Building		52,078
Costs Capitalized Subsequent to Acquisition		19,857
Land and improvements		20,785
Buildings and Improvements		70,254
Land Held for Development		0
Development and Construction in Progress		0
Total		91,039
Accumulated Depreciation		$ 23,621
Year(s) Built / Renovated		1983/1998/2013
Year(s) Acquired		2006
Depreciable Lives (Years)	[5]	(1)
77 CityPoint
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		77 CityPoint
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		13,847
Original Building		60,383
Costs Capitalized Subsequent to Acquisition		10,556
Land and improvements		14,023
Buildings and Improvements		70,763
Land Held for Development		0
Development and Construction in Progress		0
Total		84,786
Accumulated Depreciation		$ 27,172
Year(s) Built / Renovated		2008
Year(s) Acquired		2001
Depreciable Lives (Years)	[5]	(1)
230 CityPoint
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		230 CityPoint
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		13,189
Original Building		49,823
Costs Capitalized Subsequent to Acquisition		22,057
Land and improvements		13,807
Buildings and Improvements		71,262
Land Held for Development		0
Development and Construction in Progress		0
Total		85,069
Accumulated Depreciation		$ 29,255
Year(s) Built / Renovated		1992
Year(s) Acquired		2005
Depreciable Lives (Years)	[5]	(1)
Waltham Weston Corporate Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Waltham Weston Corporate Center
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		10,385
Original Building		60,694
Costs Capitalized Subsequent to Acquisition		13,165
Land and improvements		11,097
Buildings and Improvements		73,147
Land Held for Development		0
Development and Construction in Progress		0
Total		84,244
Accumulated Depreciation		$ 35,567
Year(s) Built / Renovated		2003
Year(s) Acquired		1999
Depreciable Lives (Years)	[5]	(1)
3625-3635 Peterson Way
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		3625-3635 Peterson Way
Type		Office
Location		Santa Clara, CA
Encumbrances		$ 0
Original Land		63,206
Original Building		14,879
Costs Capitalized Subsequent to Acquisition		752
Land and improvements		63,206
Buildings and Improvements		14,879
Land Held for Development		752
Development and Construction in Progress		0
Total		78,837
Accumulated Depreciation		$ 11,172
Year(s) Built / Renovated		1979
Year(s) Acquired		2016
Depreciable Lives (Years)	[5]	(1)
2440 West El Camino Real
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		2440 West El Camino Real
Type		Office
Location		Mountain View, CA
Encumbrances		$ 0
Original Land		16,741
Original Building		51,285
Costs Capitalized Subsequent to Acquisition		5,454
Land and improvements		16,741
Buildings and Improvements		56,739
Land Held for Development		0
Development and Construction in Progress		0
Total		73,480
Accumulated Depreciation		$ 13,090
Year(s) Built / Renovated		1987/2003
Year(s) Acquired		2011
Depreciable Lives (Years)	[5]	(1)
191 Spring Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		191 Spring Street
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		2,850
Original Building		59,751
Costs Capitalized Subsequent to Acquisition		7,695
Land and improvements		3,151
Buildings and Improvements		67,145
Land Held for Development		0
Development and Construction in Progress		0
Total		70,296
Accumulated Depreciation		$ 21,917
Year(s) Built / Renovated		1971/1995/2018
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
300 Binney Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		300 Binney Street
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		18,080
Original Building		51,262
Costs Capitalized Subsequent to Acquisition		140
Land and improvements		18,080
Buildings and Improvements		51,402
Land Held for Development		0
Development and Construction in Progress		0
Total		69,482
Accumulated Depreciation		$ 11,146
Year(s) Built / Renovated		2013
Year(s) Acquired		2009
Depreciable Lives (Years)	[5]	(1)
Wisconsin Place
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Wisconsin Place
Type		Office
Location		Chevy Chase, MD
Encumbrances		$ 0
Original Land		0
Original Building		53,349
Costs Capitalized Subsequent to Acquisition		14,924
Land and improvements		0
Buildings and Improvements		68,273
Land Held for Development		0
Development and Construction in Progress		0
Total		68,273
Accumulated Depreciation		$ 25,934
Year(s) Built / Renovated		2009
Year(s) Acquired		2004
Depreciable Lives (Years)	[5]	(1)
Reston Corporate Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reston Corporate Center
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		9,135
Original Building		50,857
Costs Capitalized Subsequent to Acquisition		6,236
Land and improvements		10,148
Buildings and Improvements		56,080
Land Held for Development		0
Development and Construction in Progress		0
Total		66,228
Accumulated Depreciation		$ 29,860
Year(s) Built / Renovated		1984
Year(s) Acquired		1998
Depreciable Lives (Years)	[5]	(1)
New Dominion Technology Park, Bldg. Two
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		New Dominion Technology Park, Bldg. Two
Type		Office
Location		Herndon, VA
Encumbrances		$ 0
Original Land		5,584
Original Building		51,868
Costs Capitalized Subsequent to Acquisition		4,157
Land and improvements		6,510
Buildings and Improvements		55,099
Land Held for Development		0
Development and Construction in Progress		0
Total		61,609
Accumulated Depreciation		$ 26,894
Year(s) Built / Renovated		2004
Year(s) Acquired		1998
Depreciable Lives (Years)	[5]	(1)
255 Main Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		255 Main Street
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		134
Original Building		25,110
Costs Capitalized Subsequent to Acquisition		34,124
Land and improvements		548
Buildings and Improvements		58,820
Land Held for Development		0
Development and Construction in Progress		0
Total		59,368
Accumulated Depreciation		$ 33,543
Year(s) Built / Renovated		1987
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
University Place
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		University Place
Type		Office
Location		Cambridge, MA
Encumbrances		$ 3,602
Original Land		0
Original Building		37,091
Costs Capitalized Subsequent to Acquisition		16,001
Land and improvements		7,418
Buildings and Improvements		45,674
Land Held for Development		0
Development and Construction in Progress		0
Total		53,092
Accumulated Depreciation		$ 29,423
Year(s) Built / Renovated		1985
Year(s) Acquired		1998
Depreciable Lives (Years)	[5]	(1)
Sumner Square
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Sumner Square
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		624
Original Building		28,745
Costs Capitalized Subsequent to Acquisition		21,344
Land and improvements		3,535
Buildings and Improvements		47,178
Land Held for Development		0
Development and Construction in Progress		0
Total		50,713
Accumulated Depreciation		$ 27,093
Year(s) Built / Renovated		1985
Year(s) Acquired		1999
Depreciable Lives (Years)	[5]	(1)
New Dominion Technology Park, Bldg. One
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		New Dominion Technology Park, Bldg. One
Type		Office
Location		Herndon, VA
Encumbrances		$ 0
Original Land		3,880
Original Building		43,227
Costs Capitalized Subsequent to Acquisition		3,927
Land and improvements		4,583
Buildings and Improvements		46,451
Land Held for Development		0
Development and Construction in Progress		0
Total		51,034
Accumulated Depreciation		$ 29,141
Year(s) Built / Renovated		2001
Year(s) Acquired		1998
Depreciable Lives (Years)	[5]	(1)
200 West Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		200 West Street
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		16,148
Original Building		24,983
Costs Capitalized Subsequent to Acquisition		8,211
Land and improvements		16,813
Buildings and Improvements		30,425
Land Held for Development		0
Development and Construction in Progress		2,104
Total		49,342
Accumulated Depreciation		$ 17,001
Year(s) Built / Renovated		1999
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
North First Business Park
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		North First Business Park
Type		Office
Location		San Jose, CA
Encumbrances		$ 0
Original Land		23,398
Original Building		13,069
Costs Capitalized Subsequent to Acquisition		4,571
Land and improvements		23,377
Buildings and Improvements		17,661
Land Held for Development		0
Development and Construction in Progress		0
Total		41,038
Accumulated Depreciation		$ 16,411
Year(s) Built / Renovated		1981
Year(s) Acquired		2007
Depreciable Lives (Years)	[5]	(1)
150 Broadway
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		150 Broadway
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		850
Original Building		25,042
Costs Capitalized Subsequent to Acquisition		8,540
Land and improvements		1,323
Buildings and Improvements		33,109
Land Held for Development		0
Development and Construction in Progress		0
Total		34,432
Accumulated Depreciation		$ 19,875
Year(s) Built / Renovated		1999
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
105 Broadway
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		105 Broadway
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		1,299
Original Building		12,943
Costs Capitalized Subsequent to Acquisition		11,406
Land and improvements		2,395
Buildings and Improvements		23,253
Land Held for Development		0
Development and Construction in Progress		0
Total		25,648
Accumulated Depreciation		$ 11,870
Year(s) Built / Renovated		1990
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
Lexington Office Park
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Lexington Office Park
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		998
Original Building		1,426
Costs Capitalized Subsequent to Acquisition		18,547
Land and improvements		1,264
Buildings and Improvements		19,707
Land Held for Development		0
Development and Construction in Progress		0
Total		20,971
Accumulated Depreciation		$ 14,312
Year(s) Built / Renovated		1982
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
201 Spring Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		201 Spring Street
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		2,849
Original Building		15,303
Costs Capitalized Subsequent to Acquisition		1,172
Land and improvements		3,124
Buildings and Improvements		16,200
Land Held for Development		0
Development and Construction in Progress		0
Total		19,324
Accumulated Depreciation		$ 8,587
Year(s) Built / Renovated		1997
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
The Point
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		The Point
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		6,395
Original Building		10,040
Costs Capitalized Subsequent to Acquisition		421
Land and improvements		6,492
Buildings and Improvements		10,364
Land Held for Development		0
Development and Construction in Progress		0
Total		16,856
Accumulated Depreciation		$ 1,349
Year(s) Built / Renovated		2015
Year(s) Acquired		2007
Depreciable Lives (Years)	[5]	(1)
33 Hayden Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		33 Hayden Avenue
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		266
Original Building		3,234
Costs Capitalized Subsequent to Acquisition		12,898
Land and improvements		425
Buildings and Improvements		15,973
Land Held for Development		0
Development and Construction in Progress		0
Total		16,398
Accumulated Depreciation		$ 5,678
Year(s) Built / Renovated		1979
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
690 Folsom Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		690 Folsom Street
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		3,219
Original Building		11,038
Costs Capitalized Subsequent to Acquisition		1,157
Land and improvements		3,219
Buildings and Improvements		12,195
Land Held for Development		0
Development and Construction in Progress		0
Total		15,414
Accumulated Depreciation		$ 2,284
Year(s) Built / Renovated		2015
Year(s) Acquired		2012
Depreciable Lives (Years)	[5]	(1)
92-100 Hayden Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		92-100 Hayden Avenue
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		594
Original Building		6,748
Costs Capitalized Subsequent to Acquisition		7,529
Land and improvements		802
Buildings and Improvements		14,069
Land Held for Development		0
Development and Construction in Progress		0
Total		14,871
Accumulated Depreciation		$ 12,041
Year(s) Built / Renovated		1985
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
181 Spring Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		181 Spring Street
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		1,066
Original Building		9,520
Costs Capitalized Subsequent to Acquisition		2,177
Land and improvements		1,160
Buildings and Improvements		11,603
Land Held for Development		0
Development and Construction in Progress		0
Total		12,763
Accumulated Depreciation		$ 5,597
Year(s) Built / Renovated		1999
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
195 West Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		195 West Street
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		1,611
Original Building		6,652
Costs Capitalized Subsequent to Acquisition		4,218
Land and improvements		1,858
Buildings and Improvements		10,623
Land Held for Development		0
Development and Construction in Progress		0
Total		12,481
Accumulated Depreciation		$ 8,352
Year(s) Built / Renovated		1990
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
7501 Boston Boulevard, Building Seven
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		7501 Boston Boulevard, Building Seven
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		665
Original Building		9,273
Costs Capitalized Subsequent to Acquisition		816
Land and improvements		791
Buildings and Improvements		9,963
Land Held for Development		0
Development and Construction in Progress		0
Total		10,754
Accumulated Depreciation		$ 5,393
Year(s) Built / Renovated		1997
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
7435 Boston Boulevard, Building One
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		7435 Boston Boulevard, Building One
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		392
Original Building		3,822
Costs Capitalized Subsequent to Acquisition		4,983
Land and improvements		659
Buildings and Improvements		8,538
Land Held for Development		0
Development and Construction in Progress		0
Total		9,197
Accumulated Depreciation		$ 6,344
Year(s) Built / Renovated		1982
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
7450 Boston Boulevard, Building Three
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		7450 Boston Boulevard, Building Three
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		1,165
Original Building		4,681
Costs Capitalized Subsequent to Acquisition		2,591
Land and improvements		1,430
Buildings and Improvements		7,007
Land Held for Development		0
Development and Construction in Progress		0
Total		8,437
Accumulated Depreciation		$ 3,575
Year(s) Built / Renovated		1987
Year(s) Acquired		1998
Depreciable Lives (Years)	[5]	(1)
32 Hartwell Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		32 Hartwell Avenue
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		168
Original Building		1,943
Costs Capitalized Subsequent to Acquisition		6,115
Land and improvements		314
Buildings and Improvements		7,912
Land Held for Development		0
Development and Construction in Progress		0
Total		8,226
Accumulated Depreciation		$ 1,975
Year(s) Built / Renovated		1968/1979/1987
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
250 Binney Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		250 Binney Street
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		110
Original Building		4,483
Costs Capitalized Subsequent to Acquisition		3,593
Land and improvements		273
Buildings and Improvements		7,913
Land Held for Development		0
Development and Construction in Progress		0
Total		8,186
Accumulated Depreciation		$ 5,829
Year(s) Built / Renovated		1983
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
8000 Grainger Court, Building Five
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		8000 Grainger Court, Building Five
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		366
Original Building		4,282
Costs Capitalized Subsequent to Acquisition		3,198
Land and improvements		601
Buildings and Improvements		7,245
Land Held for Development		0
Development and Construction in Progress		0
Total		7,846
Accumulated Depreciation		$ 5,752
Year(s) Built / Renovated		1984
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
453 Ravendale Drive
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		453 Ravendale Drive
Type		Office
Location		Mountain View, CA
Encumbrances		$ 0
Original Land		5,477
Original Building		1,090
Costs Capitalized Subsequent to Acquisition		676
Land and improvements		5,477
Buildings and Improvements		1,766
Land Held for Development		0
Development and Construction in Progress		0
Total		7,243
Accumulated Depreciation		$ 690
Year(s) Built / Renovated		1977
Year(s) Acquired		2012
Depreciable Lives (Years)	[5]	(1)
7300 Boston Boulevard, Building Thirteen
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		7300 Boston Boulevard, Building Thirteen
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		608
Original Building		4,773
Costs Capitalized Subsequent to Acquisition		1,007
Land and improvements		661
Buildings and Improvements		5,727
Land Held for Development		0
Development and Construction in Progress		0
Total		6,388
Accumulated Depreciation		$ 1,984
Year(s) Built / Renovated		2002
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
17 Hartwell Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		17 Hartwell Avenue
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		26
Original Building		150
Costs Capitalized Subsequent to Acquisition		6,064
Land and improvements		65
Buildings and Improvements		6,175
Land Held for Development		0
Development and Construction in Progress		0
Total		6,240
Accumulated Depreciation		$ 1,966
Year(s) Built / Renovated		1968
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
7601 Boston Boulevard, Building Eight
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		7601 Boston Boulevard, Building Eight
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		200
Original Building		878
Costs Capitalized Subsequent to Acquisition		5,060
Land and improvements		551
Buildings and Improvements		5,587
Land Held for Development		0
Development and Construction in Progress		0
Total		6,138
Accumulated Depreciation		$ 4,689
Year(s) Built / Renovated		1986
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
7500 Boston Boulevard, Building Six
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		7500 Boston Boulevard, Building Six
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		138
Original Building		3,749
Costs Capitalized Subsequent to Acquisition		1,640
Land and improvements		367
Buildings and Improvements		5,160
Land Held for Development		0
Development and Construction in Progress		0
Total		5,527
Accumulated Depreciation		$ 4,237
Year(s) Built / Renovated		1985
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
8000 Corporate Court, Building Eleven
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		8000 Corporate Court, Building Eleven
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		136
Original Building		3,071
Costs Capitalized Subsequent to Acquisition		1,596
Land and improvements		774
Buildings and Improvements		4,029
Land Held for Development		0
Development and Construction in Progress		0
Total		4,803
Accumulated Depreciation		$ 3,191
Year(s) Built / Renovated		1989
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
7375 Boston Boulevard, Building Ten
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		7375 Boston Boulevard, Building Ten
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		23
Original Building		2,685
Costs Capitalized Subsequent to Acquisition		1,032
Land and improvements		93
Buildings and Improvements		3,647
Land Held for Development		0
Development and Construction in Progress		0
Total		3,740
Accumulated Depreciation		$ 2,606
Year(s) Built / Renovated		1988
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
7374 Boston Boulevard, Building Four
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		7374 Boston Boulevard, Building Four
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		241
Original Building		1,605
Costs Capitalized Subsequent to Acquisition		1,828
Land and improvements		398
Buildings and Improvements		3,276
Land Held for Development		0
Development and Construction in Progress		0
Total		3,674
Accumulated Depreciation		$ 2,779
Year(s) Built / Renovated		1984
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
7451 Boston Boulevard, Building Two
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		7451 Boston Boulevard, Building Two
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		249
Original Building		1,542
Costs Capitalized Subsequent to Acquisition		1,667
Land and improvements		613
Buildings and Improvements		2,845
Land Held for Development		0
Development and Construction in Progress		0
Total		3,458
Accumulated Depreciation		$ 2,610
Year(s) Built / Renovated		1982
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
Signature at Reston
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Signature at Reston
Type		Residential
Location		Reston, VA
Encumbrances		$ 0
Original Land		27,076
Original Building		190,580
Costs Capitalized Subsequent to Acquisition		393
Land and improvements		27,076
Buildings and Improvements		190,973
Land Held for Development		0
Development and Construction in Progress		0
Total		218,049
Accumulated Depreciation		$ 8,773
Year(s) Built / Renovated		2018
Year(s) Acquired		2013
Depreciable Lives (Years)	[5]	(1)
Proto Kendall Square
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Proto Kendall Square
Type		Residential
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		9,243
Original Building		127,248
Costs Capitalized Subsequent to Acquisition		2,939
Land and improvements		9,245
Buildings and Improvements		130,185
Land Held for Development		0
Development and Construction in Progress		0
Total		139,430
Accumulated Depreciation		$ 4,566
Year(s) Built / Renovated		2018
Year(s) Acquired		2015
Depreciable Lives (Years)	[5]	(1)
The Avant at Reston Town Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		The Avant at Reston Town Center
Type		Residential
Location		Reston, VA
Encumbrances		$ 0
Original Land		20,350
Original Building		91,995
Costs Capitalized Subsequent to Acquisition		830
Land and improvements		20,350
Buildings and Improvements		92,825
Land Held for Development		0
Development and Construction in Progress		0
Total		113,175
Accumulated Depreciation		$ 14,728
Year(s) Built / Renovated		2014
Year(s) Acquired		2010
Depreciable Lives (Years)	[5]	(1)
The Lofts at Atlantic Wharf
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		The Lofts at Atlantic Wharf
Type		Residential
Location		Boston, MA
Encumbrances		$ 0
Original Land		3,529
Original Building		54,891
Costs Capitalized Subsequent to Acquisition		1,897
Land and improvements		3,529
Buildings and Improvements		56,788
Land Held for Development		0
Development and Construction in Progress		0
Total		60,317
Accumulated Depreciation		$ 12,639
Year(s) Built / Renovated		2011
Year(s) Acquired		2007
Depreciable Lives (Years)	[5]	(1)
Boston Marriott Cambridge
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Boston Marriott Cambridge
Type		Hotel
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		478
Original Building		37,918
Costs Capitalized Subsequent to Acquisition		35,813
Land and improvements		1,201
Buildings and Improvements		73,008
Land Held for Development		0
Development and Construction in Progress		0
Total		74,209
Accumulated Depreciation		$ 46,605
Year(s) Built / Renovated		1986/2017
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
Kendall Center Green Garage
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kendall Center Green Garage
Type		Garage
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		0
Original Building		35,035
Costs Capitalized Subsequent to Acquisition		7,329
Land and improvements		103
Buildings and Improvements		42,261
Land Held for Development		0
Development and Construction in Progress		0
Total		42,364
Accumulated Depreciation		$ 13,512
Year(s) Built / Renovated		1984
Year(s) Acquired		2006
Depreciable Lives (Years)	[5]	(1)
Kendall Center Yellow Garage
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kendall Center Yellow Garage
Type		Garage
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		1,256
Original Building		15,697
Costs Capitalized Subsequent to Acquisition		1,552
Land and improvements		1,434
Buildings and Improvements		17,071
Land Held for Development		0
Development and Construction in Progress		0
Total		18,505
Accumulated Depreciation		$ 6,031
Year(s) Built / Renovated		2006
Year(s) Acquired		2004
Depreciable Lives (Years)	[5]	(1)
Kendall Center Blue Garage
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kendall Center Blue Garage
Type		Garage
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		1,163
Original Building		11,633
Costs Capitalized Subsequent to Acquisition		2,151
Land and improvements		1,579
Buildings and Improvements		13,368
Land Held for Development		0
Development and Construction in Progress		0
Total		14,947
Accumulated Depreciation		$ 9,728
Year(s) Built / Renovated		1990
Year(s) Acquired		1997
Depreciable Lives (Years)	[5]	(1)
The Skylyne (MacArthur Station Residences)
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		The Skylyne (MacArthur Station Residences)
Type		Development
Location		Oakland, CA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		226,526
Land and improvements		29,807
Buildings and Improvements		0
Land Held for Development		0
Development and Construction in Progress		196,719
Total		226,526
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		N/A
Depreciable Lives (Years)		N/A
2100 Pennsylvania Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		2100 Pennsylvania Avenue
Type		Development
Location		Washington, DC
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		224,380
Land and improvements		185,129
Buildings and Improvements		0
Land Held for Development		0
Development and Construction in Progress		39,251
Total		224,380
Accumulated Depreciation		$ 1,024
Year(s) Built / Renovated		N/A
Year(s) Acquired		N/A
Depreciable Lives (Years)		N/A
Reston Gateway
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reston Gateway
Type		Development
Location		Reston, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		150,632
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		0
Development and Construction in Progress		150,632
Total		150,632
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1998
Depreciable Lives (Years)		N/A
17Fifty Presidents Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		17Fifty Presidents Street
Type		Development
Location		Reston, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		99,816
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		0
Development and Construction in Progress		99,816
Total		99,816
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2013
Depreciable Lives (Years)		N/A
20 CityPoint
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		20 CityPoint
Type		Development
Location		Waltham, MA
Encumbrances		$ 0
Original Land		4,721
Original Building		52,039
Costs Capitalized Subsequent to Acquisition		20,007
Land and improvements		4,721
Buildings and Improvements		52,039
Land Held for Development		0
Development and Construction in Progress		20,007
Total		76,767
Accumulated Depreciation		$ 1,136
Year(s) Built / Renovated		N/A
Year(s) Acquired		2007
Depreciable Lives (Years)		N/A
325 Main Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		325 Main Street
Type		Development
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		174
Original Building		0
Costs Capitalized Subsequent to Acquisition		68,903
Land and improvements		965
Buildings and Improvements		0
Land Held for Development		0
Development and Construction in Progress		68,112
Total		69,077
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1997
Depreciable Lives (Years)		N/A
North First Master Plan
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		North First Master Plan
Type		Land
Location		San Jose, CA
Encumbrances		$ 0
Original Land		35,004
Original Building		0
Costs Capitalized Subsequent to Acquisition		3,932
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		38,936
Development and Construction in Progress		0
Total		38,936
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2007
Depreciable Lives (Years)		N/A
Plaza at Almaden
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Plaza at Almaden
Type		Land
Location		San Jose, CA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		34,889
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		34,889
Development and Construction in Progress		0
Total		34,889
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2006
Depreciable Lives (Years)		N/A
4th and Harrison
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		425 Fourth Street
Type		Land
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		22,074
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		22,074
Development and Construction in Progress		0
Total		22,074
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		N/A
Depreciable Lives (Years)		N/A
Springfield Metro Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Springfield Metro Center
Type		Land
Location		Springfield, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		19,844
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		19,844
Development and Construction in Progress		0
Total		19,844
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2007
Depreciable Lives (Years)		N/A
Reston Gateway Master Plan
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reston Gateway Master Plan
Type		Land
Location		Reston, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		18,292
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		18,292
Development and Construction in Progress		0
Total		18,292
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1998
Depreciable Lives (Years)		N/A
214 Third Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		214 Third Avenue
Type		Land
Location		Waltham, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		17,692
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		17,692
Development and Construction in Progress		0
Total		17,692
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2006
Depreciable Lives (Years)		N/A
103 Fourth Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		103 Fourth Avenue
Type		Land
Location		Waltham, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		12,826
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		12,826
Development and Construction in Progress		0
Total		12,826
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2007
Depreciable Lives (Years)		N/A
Crane Meadow
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Crane Meadow
Type		Land
Location		Marlborough, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		8,866
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		8,866
Development and Construction in Progress		0
Total		8,866
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2000
Depreciable Lives (Years)		N/A
Broad Run Business Park
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Broad Run Business Park
Type		Land
Location		Loudoun County, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		2,396
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		2,396
Development and Construction in Progress		0
Total		2,396
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1998
Depreciable Lives (Years)		N/A
Kendall Center Master Plan
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kendall Center Master Plan
Type		Land
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		1,693
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		1,693
Development and Construction in Progress		0
Total		1,693
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1997
Depreciable Lives (Years)		N/A
Weston Quarry
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Weston Quarry
Type		Land
Location		Weston, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		1,249
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		1,249
Development and Construction in Progress		0
Total		1,249
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2001
Depreciable Lives (Years)		N/A
Reston Overlook Master Plan
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reston Overlook Master Plan
Type		Land
Location		Reston, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		39
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		39
Development and Construction in Progress		0
Total		39
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2000
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	[6]	$ 2,922,408
Original Land		5,024,060
Original Building		13,057,336
Costs Capitalized Subsequent to Acquisition		4,368,080
Land and improvements	[7]	5,373,884
Buildings and Improvements	[8]	16,031,028
Land Held for Development	[9]	254,828
Development and Construction in Progress		789,736
Total		22,449,476
Accumulated Depreciation		5,135,289
Furniture, Fixtures and Equipment		44,313		$ 44,351
Real Estate Aggregate Cost For Tax Purposes		20,700,000
Real Estate Aggregate Accumulated Depreciation For Tax Purposes		$ 4,500,000
Real Estate and Accumulated Depreciation, Life Used for Depreciation		40 years
Unamortized deferred finance costs		$ (26,700)
Right-of-use assets - finance leases		237,394
Right of use assets - operating leases		$ 148,640
Boston Properties Limited Partnership \| 767 Fifth Avenue (the General Motors Building)
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		767 Fifth Avenue (the General Motors Building)
Type		Office
Location		New York, NY
Encumbrances		$ 2,274,028
Original Land		1,796,252
Original Building		1,532,654
Costs Capitalized Subsequent to Acquisition		202,612
Land and improvements		1,796,252
Buildings and Improvements		1,735,266
Land Held for Development		0
Development and Construction in Progress		0
Total		3,531,518
Accumulated Depreciation		$ 313,158
Year(s) Built / Renovated		1968/2019
Year(s) Acquired		2013
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| Prudential Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Prudential Center
Type		Office
Location		Boston, MA
Encumbrances		$ 0
Original Land		92,077
Original Building		948,357
Costs Capitalized Subsequent to Acquisition		496,088
Land and improvements		100,540
Buildings and Improvements		1,433,306
Land Held for Development		2,676
Development and Construction in Progress		0
Total		1,536,522
Accumulated Depreciation		$ 580,797
Year(s) Built / Renovated		1965/1993/2002/2016-2017
Year(s) Acquired		1998/1999/2000
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| Embarcadero Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Embarcadero Center
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		179,697
Original Building		847,410
Costs Capitalized Subsequent to Acquisition		352,847
Land and improvements		180,420
Buildings and Improvements		1,199,534
Land Held for Development		0
Development and Construction in Progress		0
Total		1,379,954
Accumulated Depreciation		$ 617,163
Year(s) Built / Renovated		1970/1989
Year(s) Acquired		1998-1999
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 399 Park Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		399 Park Avenue
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		339,200
Original Building		700,358
Costs Capitalized Subsequent to Acquisition		240,911
Land and improvements		339,200
Buildings and Improvements		941,269
Land Held for Development		0
Development and Construction in Progress		0
Total		1,280,469
Accumulated Depreciation		$ 343,191
Year(s) Built / Renovated		1961/2018
Year(s) Acquired		2002
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 601 Lexington Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		601 Lexington Avenue
Type		Office
Location		New York, NY
Encumbrances		$ 644,778
Original Land		241,600
Original Building		494,782
Costs Capitalized Subsequent to Acquisition		417,816
Land and improvements		279,281
Buildings and Improvements		661,822
Land Held for Development		0
Development and Construction in Progress		213,095
Total		1,154,198
Accumulated Depreciation		$ 280,028
Year(s) Built / Renovated		1977/1997
Year(s) Acquired		2001
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| Salesforce Tower
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Salesforce Tower
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		200,349
Original Building		946,205
Costs Capitalized Subsequent to Acquisition		0
Land and improvements		200,349
Buildings and Improvements		946,205
Land Held for Development		0
Development and Construction in Progress		0
Total		1,146,554
Accumulated Depreciation		$ 38,727
Year(s) Built / Renovated		2018
Year(s) Acquired		2013
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 200 Clarendon Street and Garage
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		200 Clarendon Street and Garage
Type		Office
Location		Boston, MA
Encumbrances		$ 0
Original Land		219,543
Original Building		667,884
Costs Capitalized Subsequent to Acquisition		210,160
Land and improvements		250,134
Buildings and Improvements		829,529
Land Held for Development		17,924
Development and Construction in Progress		0
Total		1,097,587
Accumulated Depreciation		$ 214,533
Year(s) Built / Renovated		1976
Year(s) Acquired		2010
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 250 West 55th Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		250 West 55th Street
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		285,263
Original Building		603,167
Costs Capitalized Subsequent to Acquisition		51,928
Land and improvements		285,263
Buildings and Improvements		655,095
Land Held for Development		0
Development and Construction in Progress		0
Total		940,358
Accumulated Depreciation		$ 116,857
Year(s) Built / Renovated		2014
Year(s) Acquired		2007
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 100 Federal Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		100 Federal Street
Type		Office
Location		Boston, MA
Encumbrances		$ 0
Original Land		131,067
Original Building		435,954
Costs Capitalized Subsequent to Acquisition		102,984
Land and improvements		131,067
Buildings and Improvements		538,938
Land Held for Development		0
Development and Construction in Progress		0
Total		670,005
Accumulated Depreciation		$ 122,799
Year(s) Built / Renovated		1971-1975/2017
Year(s) Acquired		2012
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| Times Square Tower
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Times Square Tower
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		165,413
Original Building		380,438
Costs Capitalized Subsequent to Acquisition		75,243
Land and improvements		159,694
Buildings and Improvements		461,400
Land Held for Development		0
Development and Construction in Progress		0
Total		621,094
Accumulated Depreciation		$ 207,272
Year(s) Built / Renovated		2004
Year(s) Acquired		2000
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| Carnegie Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Carnegie Center
Type		Office
Location		Princeton, NJ
Encumbrances		$ 0
Original Land		142,666
Original Building		316,856
Costs Capitalized Subsequent to Acquisition		137,317
Land and improvements		90,498
Buildings and Improvements		451,661
Land Held for Development		54,680
Development and Construction in Progress		0
Total		596,839
Accumulated Depreciation		$ 204,380
Year(s) Built / Renovated		1983-2016
Year(s) Acquired		1998/1999/2000/2007/2014/2017/2019
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| Atlantic Wharf
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Atlantic Wharf
Type		Office
Location		Boston, MA
Encumbrances		$ 0
Original Land		63,988
Original Building		454,537
Costs Capitalized Subsequent to Acquisition		18,709
Land and improvements		63,988
Buildings and Improvements		473,246
Land Held for Development		0
Development and Construction in Progress		0
Total		537,234
Accumulated Depreciation		$ 131,828
Year(s) Built / Renovated		2011
Year(s) Acquired		2007
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 510 Madison Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		510 Madison Avenue
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		103,000
Original Building		253,665
Costs Capitalized Subsequent to Acquisition		25,495
Land and improvements		103,000
Buildings and Improvements		279,160
Land Held for Development		0
Development and Construction in Progress		0
Total		382,160
Accumulated Depreciation		$ 72,213
Year(s) Built / Renovated		2012
Year(s) Acquired		2010
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| Fountain Square
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Fountain Square
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		56,853
Original Building		306,298
Costs Capitalized Subsequent to Acquisition		12,140
Land and improvements		56,853
Buildings and Improvements		318,438
Land Held for Development		0
Development and Construction in Progress		0
Total		375,291
Accumulated Depreciation		$ 78,498
Year(s) Built / Renovated		1986-1990
Year(s) Acquired		2012
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 599 Lexington Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		599 Lexington Avenue
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		81,040
Original Building		100,507
Costs Capitalized Subsequent to Acquisition		161,330
Land and improvements		81,040
Buildings and Improvements		261,837
Land Held for Development		0
Development and Construction in Progress		0
Total		342,877
Accumulated Depreciation		$ 176,101
Year(s) Built / Renovated		1986
Year(s) Acquired		1997
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 680 Folsom Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		680 Folsom Street
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		72,545
Original Building		219,766
Costs Capitalized Subsequent to Acquisition		7,907
Land and improvements		72,545
Buildings and Improvements		227,673
Land Held for Development		0
Development and Construction in Progress		0
Total		300,218
Accumulated Depreciation		$ 46,777
Year(s) Built / Renovated		2014
Year(s) Acquired		2012
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 2200 Pennsylvania Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		2200 Pennsylvania Avenue
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		0
Original Building		183,541
Costs Capitalized Subsequent to Acquisition		113,627
Land and improvements		109,038
Buildings and Improvements		188,130
Land Held for Development		0
Development and Construction in Progress		0
Total		297,168
Accumulated Depreciation		$ 59,190
Year(s) Built / Renovated		2011
Year(s) Acquired		2008
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 145 Broadway
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		145 Broadway
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		121
Original Building		273,013
Costs Capitalized Subsequent to Acquisition		23,043
Land and improvements		23,164
Buildings and Improvements		273,013
Land Held for Development		0
Development and Construction in Progress		0
Total		296,177
Accumulated Depreciation		$ 1,511
Year(s) Built / Renovated		2019
Year(s) Acquired		1997
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| South of Market and Democracy Tower
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		South of Market and Democracy Tower
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		13,603
Original Building		237,479
Costs Capitalized Subsequent to Acquisition		26,079
Land and improvements		13,603
Buildings and Improvements		263,558
Land Held for Development		0
Development and Construction in Progress		0
Total		277,161
Accumulated Depreciation		$ 99,406
Year(s) Built / Renovated		2008-2009
Year(s) Acquired		2003
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 601 Massachusetts Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		601 Massachusetts Avenue
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		95,310
Original Building		165,173
Costs Capitalized Subsequent to Acquisition		3,933
Land and improvements		95,310
Buildings and Improvements		169,106
Land Held for Development		0
Development and Construction in Progress		0
Total		264,416
Accumulated Depreciation		$ 24,502
Year(s) Built / Renovated		2016
Year(s) Acquired		2008
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| Bay Colony Corporate Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Bay Colony Corporate Center
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		18,789
Original Building		148,451
Costs Capitalized Subsequent to Acquisition		80,077
Land and improvements		18,789
Buildings and Improvements		228,528
Land Held for Development		0
Development and Construction in Progress		0
Total		247,317
Accumulated Depreciation		$ 79,824
Year(s) Built / Renovated		1985-1989
Year(s) Acquired		2011
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| Gateway Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Gateway Center
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		28,255
Original Building		139,245
Costs Capitalized Subsequent to Acquisition		55,402
Land and improvements		29,029
Buildings and Improvements		193,873
Land Held for Development		0
Development and Construction in Progress		0
Total		222,902
Accumulated Depreciation		$ 104,993
Year(s) Built / Renovated		1984/1986/2002
Year(s) Acquired		1999
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 535 Mission Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		535 Mission Street
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		40,933
Original Building		148,378
Costs Capitalized Subsequent to Acquisition		3,276
Land and improvements		40,933
Buildings and Improvements		151,654
Land Held for Development		0
Development and Construction in Progress		0
Total		192,587
Accumulated Depreciation		$ 26,293
Year(s) Built / Renovated		2015
Year(s) Acquired		2013
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| Mountain View Research Park
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Mountain View Research Park
Type		Office
Location		Mountain View, CA
Encumbrances		$ 0
Original Land		95,066
Original Building		68,373
Costs Capitalized Subsequent to Acquisition		12,704
Land and improvements		95,066
Buildings and Improvements		81,077
Land Held for Development		0
Development and Construction in Progress		0
Total		176,143
Accumulated Depreciation		$ 19,807
Year(s) Built / Renovated		1977-1981/2007-2013
Year(s) Acquired		2013
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| Reservoir Place
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reservoir Place
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		18,605
Original Building		104,124
Costs Capitalized Subsequent to Acquisition		49,643
Land and improvements		19,089
Buildings and Improvements		153,283
Land Held for Development		0
Development and Construction in Progress		0
Total		172,372
Accumulated Depreciation		$ 69,794
Year(s) Built / Renovated		1955/1987/2017
Year(s) Acquired		1997/1998
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 1330 Connecticut Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		1330 Connecticut Avenue
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		25,982
Original Building		82,311
Costs Capitalized Subsequent to Acquisition		32,234
Land and improvements		25,982
Buildings and Improvements		114,545
Land Held for Development		0
Development and Construction in Progress		0
Total		140,527
Accumulated Depreciation		$ 31,553
Year(s) Built / Renovated		1984/2018
Year(s) Acquired		2004
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| Kingstowne Towne Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kingstowne Towne Center
Type		Office
Location		Alexandria, VA
Encumbrances		$ 0
Original Land		18,021
Original Building		109,038
Costs Capitalized Subsequent to Acquisition		3,212
Land and improvements		18,021
Buildings and Improvements		112,250
Land Held for Development		0
Development and Construction in Progress		0
Total		130,271
Accumulated Depreciation		$ 44,258
Year(s) Built / Renovated		2003-2006
Year(s) Acquired		2007
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| One Freedom Square
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		One Freedom Square
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		9,929
Original Building		84,504
Costs Capitalized Subsequent to Acquisition		28,735
Land and improvements		9,883
Buildings and Improvements		113,285
Land Held for Development		0
Development and Construction in Progress		0
Total		123,168
Accumulated Depreciation		$ 57,516
Year(s) Built / Renovated		2000
Year(s) Acquired		2003
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| Weston Corporate Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Weston Corporate Center
Type		Office
Location		Weston, MA
Encumbrances		$ 0
Original Land		25,753
Original Building		92,312
Costs Capitalized Subsequent to Acquisition		(123)
Land and improvements		25,854
Buildings and Improvements		92,088
Land Held for Development		0
Development and Construction in Progress		0
Total		117,942
Accumulated Depreciation		$ 29,227
Year(s) Built / Renovated		2010
Year(s) Acquired		2001
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| Capital Gallery
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Capital Gallery
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		4,725
Original Building		29,565
Costs Capitalized Subsequent to Acquisition		78,573
Land and improvements		6,128
Buildings and Improvements		106,735
Land Held for Development		0
Development and Construction in Progress		0
Total		112,863
Accumulated Depreciation		$ 68,953
Year(s) Built / Renovated		1981/2006
Year(s) Acquired		2007
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| Two Freedom Square
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Two Freedom Square
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		13,930
Original Building		77,739
Costs Capitalized Subsequent to Acquisition		16,997
Land and improvements		13,866
Buildings and Improvements		94,800
Land Held for Development		0
Development and Construction in Progress		0
Total		108,666
Accumulated Depreciation		$ 49,028
Year(s) Built / Renovated		2001
Year(s) Acquired		2003
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| One and Two Reston Overlook
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		One and Two Reston Overlook
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		16,456
Original Building		66,192
Costs Capitalized Subsequent to Acquisition		19,763
Land and improvements		15,074
Buildings and Improvements		87,337
Land Held for Development		0
Development and Construction in Progress		0
Total		102,411
Accumulated Depreciation		$ 50,336
Year(s) Built / Renovated		1999
Year(s) Acquired		2000
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 355 Main Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		355 Main Street
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		18,863
Original Building		53,346
Costs Capitalized Subsequent to Acquisition		27,284
Land and improvements		21,098
Buildings and Improvements		78,395
Land Held for Development		0
Development and Construction in Progress		0
Total		99,493
Accumulated Depreciation		$ 26,362
Year(s) Built / Renovated		1981/1996/2013
Year(s) Acquired		2006
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 140 Kendrick Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		140 Kendrick Street
Type		Office
Location		Needham, MA
Encumbrances		$ 0
Original Land		18,095
Original Building		66,905
Costs Capitalized Subsequent to Acquisition		13,584
Land and improvements		18,095
Buildings and Improvements		80,489
Land Held for Development		0
Development and Construction in Progress		0
Total		98,584
Accumulated Depreciation		$ 34,667
Year(s) Built / Renovated		2000
Year(s) Acquired		2004
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| Discovery Square
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Discovery Square
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		11,198
Original Building		71,782
Costs Capitalized Subsequent to Acquisition		15,360
Land and improvements		11,146
Buildings and Improvements		87,194
Land Held for Development		0
Development and Construction in Progress		0
Total		98,340
Accumulated Depreciation		$ 42,152
Year(s) Built / Renovated		2001
Year(s) Acquired		2003
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 880 & 890 Winter Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		880 & 890 Winter Street
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		29,510
Original Building		65,812
Costs Capitalized Subsequent to Acquisition		0
Land and improvements		29,510
Buildings and Improvements		65,812
Land Held for Development		0
Development and Construction in Progress		0
Total		95,322
Accumulated Depreciation		$ 1,458
Year(s) Built / Renovated		1998-1999
Year(s) Acquired		2019
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 10 CityPoint
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		10 CityPoint
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		1,953
Original Building		85,752
Costs Capitalized Subsequent to Acquisition		4,534
Land and improvements		2,127
Buildings and Improvements		90,112
Land Held for Development		0
Development and Construction in Progress		0
Total		92,239
Accumulated Depreciation		$ 10,928
Year(s) Built / Renovated		2016
Year(s) Acquired		1997
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 90 Broadway
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		90 Broadway
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		19,104
Original Building		52,078
Costs Capitalized Subsequent to Acquisition		19,678
Land and improvements		20,741
Buildings and Improvements		70,119
Land Held for Development		0
Development and Construction in Progress		0
Total		90,860
Accumulated Depreciation		$ 23,581
Year(s) Built / Renovated		1983/1998/2013
Year(s) Acquired		2006
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 77 CityPoint
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		77 CityPoint
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		13,847
Original Building		60,383
Costs Capitalized Subsequent to Acquisition		10,451
Land and improvements		13,997
Buildings and Improvements		70,684
Land Held for Development		0
Development and Construction in Progress		0
Total		84,681
Accumulated Depreciation		$ 27,148
Year(s) Built / Renovated		2008
Year(s) Acquired		2001
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 230 CityPoint
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		230 CityPoint
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		13,189
Original Building		49,823
Costs Capitalized Subsequent to Acquisition		20,440
Land and improvements		13,403
Buildings and Improvements		70,049
Land Held for Development		0
Development and Construction in Progress		0
Total		83,452
Accumulated Depreciation		$ 28,831
Year(s) Built / Renovated		1992
Year(s) Acquired		2005
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| Waltham Weston Corporate Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Waltham Weston Corporate Center
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		10,385
Original Building		60,694
Costs Capitalized Subsequent to Acquisition		10,178
Land and improvements		10,350
Buildings and Improvements		70,907
Land Held for Development		0
Development and Construction in Progress		0
Total		81,257
Accumulated Depreciation		$ 34,777
Year(s) Built / Renovated		2003
Year(s) Acquired		1999
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 3625-3635 Peterson Way
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		3625-3635 Peterson Way
Type		Office
Location		Santa Clara, CA
Encumbrances		$ 0
Original Land		63,206
Original Building		14,879
Costs Capitalized Subsequent to Acquisition		752
Land and improvements		63,206
Buildings and Improvements		14,879
Land Held for Development		752
Development and Construction in Progress		0
Total		78,837
Accumulated Depreciation		$ 11,172
Year(s) Built / Renovated		1979
Year(s) Acquired		2016
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 2440 West El Camino Real
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		2440 West El Camino Real
Type		Office
Location		Mountain View, CA
Encumbrances		$ 0
Original Land		16,741
Original Building		51,285
Costs Capitalized Subsequent to Acquisition		5,454
Land and improvements		16,741
Buildings and Improvements		56,739
Land Held for Development		0
Development and Construction in Progress		0
Total		73,480
Accumulated Depreciation		$ 13,090
Year(s) Built / Renovated		1987/2003
Year(s) Acquired		2011
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 191 Spring Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		191 Spring Street
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		2,850
Original Building		59,751
Costs Capitalized Subsequent to Acquisition		7,063
Land and improvements		2,850
Buildings and Improvements		66,814
Land Held for Development		0
Development and Construction in Progress		0
Total		69,664
Accumulated Depreciation		$ 21,801
Year(s) Built / Renovated		1971/1995/2018
Year(s) Acquired		1997
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 300 Binney Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		300 Binney Street
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		18,080
Original Building		51,262
Costs Capitalized Subsequent to Acquisition		140
Land and improvements		18,080
Buildings and Improvements		51,402
Land Held for Development		0
Development and Construction in Progress		0
Total		69,482
Accumulated Depreciation		$ 11,146
Year(s) Built / Renovated		2013
Year(s) Acquired		2009
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| Wisconsin Place
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Wisconsin Place
Type		Office
Location		Chevy Chase, MD
Encumbrances		$ 0
Original Land		0
Original Building		53,349
Costs Capitalized Subsequent to Acquisition		14,924
Land and improvements		0
Buildings and Improvements		68,273
Land Held for Development		0
Development and Construction in Progress		0
Total		68,273
Accumulated Depreciation		$ 25,934
Year(s) Built / Renovated		2009
Year(s) Acquired		2004
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| Reston Corporate Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reston Corporate Center
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		9,135
Original Building		50,857
Costs Capitalized Subsequent to Acquisition		3,625
Land and improvements		9,496
Buildings and Improvements		54,121
Land Held for Development		0
Development and Construction in Progress		0
Total		63,617
Accumulated Depreciation		$ 29,170
Year(s) Built / Renovated		1984
Year(s) Acquired		1998
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| New Dominion Technology Park, Bldg. Two
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		New Dominion Technology Park, Bldg. Two
Type		Office
Location		Herndon, VA
Encumbrances		$ 0
Original Land		5,584
Original Building		51,868
Costs Capitalized Subsequent to Acquisition		412
Land and improvements		5,574
Buildings and Improvements		52,290
Land Held for Development		0
Development and Construction in Progress		0
Total		57,864
Accumulated Depreciation		$ 25,900
Year(s) Built / Renovated		2004
Year(s) Acquired		1998
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 255 Main Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		255 Main Street
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		134
Original Building		25,110
Costs Capitalized Subsequent to Acquisition		32,468
Land and improvements		134
Buildings and Improvements		57,578
Land Held for Development		0
Development and Construction in Progress		0
Total		57,712
Accumulated Depreciation		$ 33,108
Year(s) Built / Renovated		1987
Year(s) Acquired		1997
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| University Place
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		University Place
Type		Office
Location		Cambridge, MA
Encumbrances		$ 3,602
Original Land		0
Original Building		37,091
Costs Capitalized Subsequent to Acquisition		14,551
Land and improvements		7,055
Buildings and Improvements		44,587
Land Held for Development		0
Development and Construction in Progress		0
Total		51,642
Accumulated Depreciation		$ 29,044
Year(s) Built / Renovated		1985
Year(s) Acquired		1998
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| Sumner Square
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Sumner Square
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		624
Original Building		28,745
Costs Capitalized Subsequent to Acquisition		19,264
Land and improvements		3,015
Buildings and Improvements		45,618
Land Held for Development		0
Development and Construction in Progress		0
Total		48,633
Accumulated Depreciation		$ 26,547
Year(s) Built / Renovated		1985
Year(s) Acquired		1999
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| New Dominion Technology Park, Bldg. One
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		New Dominion Technology Park, Bldg. One
Type		Office
Location		Herndon, VA
Encumbrances		$ 0
Original Land		3,880
Original Building		43,227
Costs Capitalized Subsequent to Acquisition		1,117
Land and improvements		3,880
Buildings and Improvements		44,344
Land Held for Development		0
Development and Construction in Progress		0
Total		48,224
Accumulated Depreciation		$ 28,398
Year(s) Built / Renovated		2001
Year(s) Acquired		1998
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 200 West Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		200 West Street
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		16,148
Original Building		24,983
Costs Capitalized Subsequent to Acquisition		5,550
Land and improvements		16,148
Buildings and Improvements		28,429
Land Held for Development		0
Development and Construction in Progress		2,104
Total		46,681
Accumulated Depreciation		$ 16,298
Year(s) Built / Renovated		1999
Year(s) Acquired		1997
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| North First Business Park
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		North First Business Park
Type		Office
Location		San Jose, CA
Encumbrances		$ 0
Original Land		23,398
Original Building		13,069
Costs Capitalized Subsequent to Acquisition		4,548
Land and improvements		23,371
Buildings and Improvements		17,644
Land Held for Development		0
Development and Construction in Progress		0
Total		41,015
Accumulated Depreciation		$ 16,411
Year(s) Built / Renovated		1981
Year(s) Acquired		2007
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 150 Broadway
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		150 Broadway
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		850
Original Building		25,042
Costs Capitalized Subsequent to Acquisition		6,535
Land and improvements		822
Buildings and Improvements		31,605
Land Held for Development		0
Development and Construction in Progress		0
Total		32,427
Accumulated Depreciation		$ 19,342
Year(s) Built / Renovated		1999
Year(s) Acquired		1997
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 105 Broadway
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		105 Broadway
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		1,299
Original Building		12,943
Costs Capitalized Subsequent to Acquisition		9,300
Land and improvements		1,868
Buildings and Improvements		21,674
Land Held for Development		0
Development and Construction in Progress		0
Total		23,542
Accumulated Depreciation		$ 11,312
Year(s) Built / Renovated		1990
Year(s) Acquired		1997
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| Lexington Office Park
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Lexington Office Park
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		998
Original Building		1,426
Costs Capitalized Subsequent to Acquisition		17,783
Land and improvements		1,073
Buildings and Improvements		19,134
Land Held for Development		0
Development and Construction in Progress		0
Total		20,207
Accumulated Depreciation		$ 14,114
Year(s) Built / Renovated		1982
Year(s) Acquired		1997
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 201 Spring Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		201 Spring Street
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		2,849
Original Building		15,303
Costs Capitalized Subsequent to Acquisition		73
Land and improvements		2,849
Buildings and Improvements		15,376
Land Held for Development		0
Development and Construction in Progress		0
Total		18,225
Accumulated Depreciation		$ 8,295
Year(s) Built / Renovated		1997
Year(s) Acquired		1997
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| The Point
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		The Point
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		6,395
Original Building		10,040
Costs Capitalized Subsequent to Acquisition		421
Land and improvements		6,492
Buildings and Improvements		10,364
Land Held for Development		0
Development and Construction in Progress		0
Total		16,856
Accumulated Depreciation		$ 1,349
Year(s) Built / Renovated		2015
Year(s) Acquired		2007
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 33 Hayden Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		33 Hayden Avenue
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		266
Original Building		3,234
Costs Capitalized Subsequent to Acquisition		12,261
Land and improvements		266
Buildings and Improvements		15,495
Land Held for Development		0
Development and Construction in Progress		0
Total		15,761
Accumulated Depreciation		$ 5,510
Year(s) Built / Renovated		1979
Year(s) Acquired		1997
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 690 Folsom Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		690 Folsom Street
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		3,219
Original Building		11,038
Costs Capitalized Subsequent to Acquisition		1,157
Land and improvements		3,219
Buildings and Improvements		12,195
Land Held for Development		0
Development and Construction in Progress		0
Total		15,414
Accumulated Depreciation		$ 2,284
Year(s) Built / Renovated		2015
Year(s) Acquired		2012
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 92-100 Hayden Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		92-100 Hayden Avenue
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		594
Original Building		6,748
Costs Capitalized Subsequent to Acquisition		6,800
Land and improvements		619
Buildings and Improvements		13,523
Land Held for Development		0
Development and Construction in Progress		0
Total		14,142
Accumulated Depreciation		$ 11,847
Year(s) Built / Renovated		1985
Year(s) Acquired		1997
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 181 Spring Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		181 Spring Street
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		1,066
Original Building		9,520
Costs Capitalized Subsequent to Acquisition		1,800
Land and improvements		1,066
Buildings and Improvements		11,320
Land Held for Development		0
Development and Construction in Progress		0
Total		12,386
Accumulated Depreciation		$ 5,498
Year(s) Built / Renovated		1999
Year(s) Acquired		1997
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 195 West Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		195 West Street
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		1,611
Original Building		6,652
Costs Capitalized Subsequent to Acquisition		3,229
Land and improvements		1,611
Buildings and Improvements		9,881
Land Held for Development		0
Development and Construction in Progress		0
Total		11,492
Accumulated Depreciation		$ 8,087
Year(s) Built / Renovated		1990
Year(s) Acquired		1997
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 7501 Boston Boulevard, Building Seven
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		7501 Boston Boulevard, Building Seven
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		665
Original Building		9,273
Costs Capitalized Subsequent to Acquisition		311
Land and improvements		665
Buildings and Improvements		9,584
Land Held for Development		0
Development and Construction in Progress		0
Total		10,249
Accumulated Depreciation		$ 5,257
Year(s) Built / Renovated		1997
Year(s) Acquired		1997
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 7435 Boston Boulevard, Building One
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		7435 Boston Boulevard, Building One
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		392
Original Building		3,822
Costs Capitalized Subsequent to Acquisition		4,290
Land and improvements		486
Buildings and Improvements		8,018
Land Held for Development		0
Development and Construction in Progress		0
Total		8,504
Accumulated Depreciation		$ 6,162
Year(s) Built / Renovated		1982
Year(s) Acquired		1997
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 7450 Boston Boulevard, Building Three
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		7450 Boston Boulevard, Building Three
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		1,165
Original Building		4,681
Costs Capitalized Subsequent to Acquisition		2,177
Land and improvements		1,327
Buildings and Improvements		6,696
Land Held for Development		0
Development and Construction in Progress		0
Total		8,023
Accumulated Depreciation		$ 3,462
Year(s) Built / Renovated		1987
Year(s) Acquired		1998
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 32 Hartwell Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		32 Hartwell Avenue
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		168
Original Building		1,943
Costs Capitalized Subsequent to Acquisition		5,529
Land and improvements		168
Buildings and Improvements		7,472
Land Held for Development		0
Development and Construction in Progress		0
Total		7,640
Accumulated Depreciation		$ 1,819
Year(s) Built / Renovated		1968/1979/1987
Year(s) Acquired		1997
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 250 Binney Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		250 Binney Street
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		110
Original Building		4,483
Costs Capitalized Subsequent to Acquisition		2,939
Land and improvements		110
Buildings and Improvements		7,422
Land Held for Development		0
Development and Construction in Progress		0
Total		7,532
Accumulated Depreciation		$ 5,660
Year(s) Built / Renovated		1983
Year(s) Acquired		1997
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 8000 Grainger Court, Building Five
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		8000 Grainger Court, Building Five
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		366
Original Building		4,282
Costs Capitalized Subsequent to Acquisition		2,604
Land and improvements		453
Buildings and Improvements		6,799
Land Held for Development		0
Development and Construction in Progress		0
Total		7,252
Accumulated Depreciation		$ 5,597
Year(s) Built / Renovated		1984
Year(s) Acquired		1997
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 453 Ravendale Drive
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		453 Ravendale Drive
Type		Office
Location		Mountain View, CA
Encumbrances		$ 0
Original Land		5,477
Original Building		1,090
Costs Capitalized Subsequent to Acquisition		676
Land and improvements		5,477
Buildings and Improvements		1,766
Land Held for Development		0
Development and Construction in Progress		0
Total		7,243
Accumulated Depreciation		$ 690
Year(s) Built / Renovated		1977
Year(s) Acquired		2012
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 7300 Boston Boulevard, Building Thirteen
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		7300 Boston Boulevard, Building Thirteen
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		608
Original Building		4,773
Costs Capitalized Subsequent to Acquisition		795
Land and improvements		608
Buildings and Improvements		5,568
Land Held for Development		0
Development and Construction in Progress		0
Total		6,176
Accumulated Depreciation		$ 1,928
Year(s) Built / Renovated		2002
Year(s) Acquired		1997
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 17 Hartwell Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		17 Hartwell Avenue
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		26
Original Building		150
Costs Capitalized Subsequent to Acquisition		5,907
Land and improvements		26
Buildings and Improvements		6,057
Land Held for Development		0
Development and Construction in Progress		0
Total		6,083
Accumulated Depreciation		$ 1,924
Year(s) Built / Renovated		1968
Year(s) Acquired		1997
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 7601 Boston Boulevard, Building Eight
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		7601 Boston Boulevard, Building Eight
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		200
Original Building		878
Costs Capitalized Subsequent to Acquisition		4,367
Land and improvements		378
Buildings and Improvements		5,067
Land Held for Development		0
Development and Construction in Progress		0
Total		5,445
Accumulated Depreciation		$ 4,507
Year(s) Built / Renovated		1986
Year(s) Acquired		1997
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 7500 Boston Boulevard, Building Six
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		7500 Boston Boulevard, Building Six
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		138
Original Building		3,749
Costs Capitalized Subsequent to Acquisition		1,107
Land and improvements		234
Buildings and Improvements		4,760
Land Held for Development		0
Development and Construction in Progress		0
Total		4,994
Accumulated Depreciation		$ 4,097
Year(s) Built / Renovated		1985
Year(s) Acquired		1997
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 8000 Corporate Court, Building Eleven
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		8000 Corporate Court, Building Eleven
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		136
Original Building		3,071
Costs Capitalized Subsequent to Acquisition		1,245
Land and improvements		686
Buildings and Improvements		3,766
Land Held for Development		0
Development and Construction in Progress		0
Total		4,452
Accumulated Depreciation		$ 3,094
Year(s) Built / Renovated		1989
Year(s) Acquired		1997
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 7375 Boston Boulevard, Building Ten
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		7375 Boston Boulevard, Building Ten
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		23
Original Building		2,685
Costs Capitalized Subsequent to Acquisition		851
Land and improvements		47
Buildings and Improvements		3,512
Land Held for Development		0
Development and Construction in Progress		0
Total		3,559
Accumulated Depreciation		$ 2,562
Year(s) Built / Renovated		1988
Year(s) Acquired		1997
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 7374 Boston Boulevard, Building Four
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		7374 Boston Boulevard, Building Four
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		241
Original Building		1,605
Costs Capitalized Subsequent to Acquisition		1,445
Land and improvements		303
Buildings and Improvements		2,988
Land Held for Development		0
Development and Construction in Progress		0
Total		3,291
Accumulated Depreciation		$ 2,681
Year(s) Built / Renovated		1984
Year(s) Acquired		1997
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| 7451 Boston Boulevard, Building Two
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		7451 Boston Boulevard, Building Two
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		249
Original Building		1,542
Costs Capitalized Subsequent to Acquisition		1,354
Land and improvements		535
Buildings and Improvements		2,610
Land Held for Development		0
Development and Construction in Progress		0
Total		3,145
Accumulated Depreciation		$ 2,526
Year(s) Built / Renovated		1982
Year(s) Acquired		1997
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| Signature at Reston
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Signature at Reston
Type		Residential
Location		Reston, VA
Encumbrances		$ 0
Original Land		27,076
Original Building		190,580
Costs Capitalized Subsequent to Acquisition		393
Land and improvements		27,076
Buildings and Improvements		190,973
Land Held for Development		0
Development and Construction in Progress		0
Total		218,049
Accumulated Depreciation		$ 8,773
Year(s) Built / Renovated		2018
Year(s) Acquired		2013
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| Proto Kendall Square
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Proto Kendall Square
Type		Residential
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		9,243
Original Building		127,248
Costs Capitalized Subsequent to Acquisition		2,939
Land and improvements		9,245
Buildings and Improvements		130,185
Land Held for Development		0
Development and Construction in Progress		0
Total		139,430
Accumulated Depreciation		$ 4,566
Year(s) Built / Renovated		2018
Year(s) Acquired		2015
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| The Avant at Reston Town Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		The Avant at Reston Town Center
Type		Residential
Location		Reston, VA
Encumbrances		$ 0
Original Land		20,350
Original Building		91,995
Costs Capitalized Subsequent to Acquisition		830
Land and improvements		20,350
Buildings and Improvements		92,825
Land Held for Development		0
Development and Construction in Progress		0
Total		113,175
Accumulated Depreciation		$ 14,728
Year(s) Built / Renovated		2014
Year(s) Acquired		2010
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| The Lofts at Atlantic Wharf
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		The Lofts at Atlantic Wharf
Type		Residential
Location		Boston, MA
Encumbrances		$ 0
Original Land		3,529
Original Building		54,891
Costs Capitalized Subsequent to Acquisition		1,897
Land and improvements		3,529
Buildings and Improvements		56,788
Land Held for Development		0
Development and Construction in Progress		0
Total		60,317
Accumulated Depreciation		$ 12,639
Year(s) Built / Renovated		2011
Year(s) Acquired		2007
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| Boston Marriott Cambridge
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Boston Marriott Cambridge
Type		Hotel
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		478
Original Building		37,918
Costs Capitalized Subsequent to Acquisition		32,922
Land and improvements		478
Buildings and Improvements		70,840
Land Held for Development		0
Development and Construction in Progress		0
Total		71,318
Accumulated Depreciation		$ 45,842
Year(s) Built / Renovated		1986/2017
Year(s) Acquired		1997
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| Kendall Center Green Garage
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kendall Center Green Garage
Type		Garage
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		0
Original Building		35,035
Costs Capitalized Subsequent to Acquisition		6,915
Land and improvements		0
Buildings and Improvements		41,950
Land Held for Development		0
Development and Construction in Progress		0
Total		41,950
Accumulated Depreciation		$ 13,404
Year(s) Built / Renovated		1984
Year(s) Acquired		2006
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| Kendall Center Yellow Garage
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kendall Center Yellow Garage
Type		Garage
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		1,256
Original Building		15,697
Costs Capitalized Subsequent to Acquisition		840
Land and improvements		1,256
Buildings and Improvements		16,537
Land Held for Development		0
Development and Construction in Progress		0
Total		17,793
Accumulated Depreciation		$ 5,847
Year(s) Built / Renovated		2006
Year(s) Acquired		2004
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| Kendall Center Blue Garage
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kendall Center Blue Garage
Type		Garage
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		1,163
Original Building		11,633
Costs Capitalized Subsequent to Acquisition		486
Land and improvements		1,163
Buildings and Improvements		12,119
Land Held for Development		0
Development and Construction in Progress		0
Total		13,282
Accumulated Depreciation		$ 9,290
Year(s) Built / Renovated		1990
Year(s) Acquired		1997
Depreciable Lives (Years)	[10]	(1)
Boston Properties Limited Partnership \| The Skylyne (MacArthur Station Residences)
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		The Skylyne (MacArthur Station Residences)
Type		Development
Location		Oakland, CA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		226,526
Land and improvements		29,807
Buildings and Improvements		0
Land Held for Development		0
Development and Construction in Progress		196,719
Total		226,526
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		N/A
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership \| 2100 Pennsylvania Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		2100 Pennsylvania Avenue
Type		Development
Location		Washington, DC
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		224,380
Land and improvements		185,129
Buildings and Improvements		0
Land Held for Development		0
Development and Construction in Progress		39,251
Total		224,380
Accumulated Depreciation		$ 1,024
Year(s) Built / Renovated		N/A
Year(s) Acquired		N/A
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership \| Reston Gateway
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reston Gateway
Type		Development
Location		Reston, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		150,632
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		0
Development and Construction in Progress		150,632
Total		150,632
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1998
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership \| 17Fifty Presidents Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		17Fifty Presidents Street
Type		Development
Location		Reston, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		99,816
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		0
Development and Construction in Progress		99,816
Total		99,816
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2013
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership \| 20 CityPoint
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		20 CityPoint
Type		Development
Location		Waltham, MA
Encumbrances		$ 0
Original Land		4,721
Original Building		52,039
Costs Capitalized Subsequent to Acquisition		20,007
Land and improvements		4,721
Buildings and Improvements		52,039
Land Held for Development		0
Development and Construction in Progress		20,007
Total		76,767
Accumulated Depreciation		$ 1,136
Year(s) Built / Renovated		N/A
Year(s) Acquired		2007
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership \| 325 Main Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		325 Main Street
Type		Development
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		174
Original Building		0
Costs Capitalized Subsequent to Acquisition		68,710
Land and improvements		772
Buildings and Improvements		0
Land Held for Development		0
Development and Construction in Progress		68,112
Total		68,884
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1997
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership \| North First Master Plan
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		North First Master Plan
Type		Land
Location		San Jose, CA
Encumbrances		$ 0
Original Land		35,004
Original Building		0
Costs Capitalized Subsequent to Acquisition		3,932
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		38,936
Development and Construction in Progress		0
Total		38,936
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2007
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership \| Plaza at Almaden
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Plaza at Almaden
Type		Land
Location		San Jose, CA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		34,889
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		34,889
Development and Construction in Progress		0
Total		34,889
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2006
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership \| 4th and Harrison
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		425 Fourth Street
Type		Land
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		22,074
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		22,074
Development and Construction in Progress		0
Total		22,074
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		N/A
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership \| Springfield Metro Center
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Springfield Metro Center
Type		Land
Location		Springfield, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		19,844
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		19,844
Development and Construction in Progress		0
Total		19,844
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2007
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership \| Reston Gateway Master Plan
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reston Gateway Master Plan
Type		Land
Location		Reston, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		18,292
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		18,292
Development and Construction in Progress		0
Total		18,292
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1998
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership \| 214 Third Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		214 Third Avenue
Type		Land
Location		Waltham, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		17,692
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		17,692
Development and Construction in Progress		0
Total		17,692
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2006
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership \| 103 Fourth Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		103 Fourth Avenue
Type		Land
Location		Waltham, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		12,826
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		12,826
Development and Construction in Progress		0
Total		12,826
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2007
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership \| Crane Meadow
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Crane Meadow
Type		Land
Location		Marlborough, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		8,866
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		8,866
Development and Construction in Progress		0
Total		8,866
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2000
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership \| Broad Run Business Park
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Broad Run Business Park
Type		Land
Location		Loudoun County, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		2,396
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		2,396
Development and Construction in Progress		0
Total		2,396
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1998
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership \| Kendall Center Master Plan
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kendall Center Master Plan
Type		Land
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		1,693
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		1,693
Development and Construction in Progress		0
Total		1,693
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1997
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership \| Weston Quarry
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Weston Quarry
Type		Land
Location		Weston, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		1,249
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		1,249
Development and Construction in Progress		0
Total		1,249
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2001
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership \| Reston Overlook Master Plan
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reston Overlook Master Plan
Type		Land
Location		Reston, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		39
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		39
Development and Construction in Progress		0
Total		39
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2000
Depreciable Lives (Years)		N/A
Minimum [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate and Accumulated Depreiation Life used for Depreciation		life of the lease
Minimum [Member] \| Boston Properties Limited Partnership
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate and Accumulated Depreiation Life used for Depreciation		life of the lease
Maximum [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate and Accumulated Depreciation, Life Used for Depreciation		40 years
Maximum [Member] \| Boston Properties Limited Partnership
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate and Accumulated Depreciation, Life Used for Depreciation		40 years
Furniture and Fixtures [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Accumulated Depreciation		$ 27,619
Furniture and Fixtures [Member] \| Boston Properties Limited Partnership
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Accumulated Depreciation		27,619
Land and Land Improvements [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Right-of-use assets - finance leases		214,091
Land and Land Improvements [Member] \| Boston Properties Limited Partnership
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Right-of-use assets - finance leases		214,091
Building and Building Improvements [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Right-of-use assets - finance leases		23,303
Building and Building Improvements [Member] \| Boston Properties Limited Partnership
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Right-of-use assets - finance leases		$ 23,303

[1]	Includes unamortized deferred financing costs totaling approximately $(26.7) million .
[2]	Includes Right of Use Assets - Finance Leases and Right of Use Assets - Operating Leases of approximately $214,091 and $148,640 , respectively.
[3]	Includes Right of Use Assets - Finance Leases of approximately $23,303 .
[4]	Includes pre-development costs.
[5]	Depreciation of the buildings and improvements are calculated over lives ranging from the life of the lease to 40 years.
[6]	Includes unamortized deferred financing costs totaling approximately $(26.7) million .
[7]	Includes Right of Use Assets - Finance Leases and Right of Use Assets - Operating Leases of approximately $214,091 and $148,640 , respectively.
[8]	Includes Right of Use Assets - Finance Leases of approximately $23,303 .
[9]	Includes pre-development costs.
[10]	Depreciation of the buildings and improvements are calculated over lives ranging from the life of the lease to 40 years.

Real Estate and Accumulated D_7

Real Estate and Accumulated Depreciation Activity of Real Estate and Accumulated Depreciation (BPLP) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Real Estate, Balance at the beginning of the year	$ 21,605,545	$ 21,058,714	$ 20,114,576
Real Estate, Additions to / improvements of real estate	1,671,898	1,043,379	1,099,286
Real Estate, Assets sold / written off	(432,746)	(496,548)	(155,148)
Real Estate, Balance at the end of the year	22,844,697	21,605,545	21,058,714
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Accumulated depreciation, Balance at beginning of the year	4,871,102	4,566,570	4,201,891
Accumulated depreciation, Depreciation expense	564,938	533,342	497,059
Accumulated depreciation, Assets sold / written off	(196,861)	(228,810)	(132,380)
Accumulated depreciation, Balance at end of the year	5,239,179	4,871,102	4,566,570
Boston Properties Limited Partnership
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Real Estate, Balance at the beginning of the year	21,207,189	20,647,236	19,701,185
Real Estate, Additions to / improvements of real estate	1,671,898	1,043,379	1,099,286
Real Estate, Assets sold / written off	(429,611)	(483,426)	(153,235)
Real Estate, Balance at the end of the year	22,449,476	21,207,189	20,647,236
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Accumulated depreciation, Balance at beginning of the year	4,773,800	4,473,895	4,116,020
Accumulated depreciation, Depreciation expense	557,130	525,584	488,919
Accumulated depreciation, Assets sold / written off	(195,641)	(225,679)	(131,044)
Accumulated depreciation, Balance at end of the year	$ 5,135,289	$ 4,773,800	$ 4,473,895