Boston Properties LTD Partnership 10-K26 Feb 212020 FY Annual reportFinancial data

Company Profile

Cover

Cover - USD ($)	12 Months Ended
Cover - USD ($)	Dec. 31, 2020	Feb. 22, 2021	Jun. 30, 2020
Entity Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
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	2020
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
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 14,037,034,481
Entity Common Stock, Shares Outstanding		155,805,646
Documents Incorporated by Reference	Certain information contained in Boston Properties Inc.’s Proxy Statement relating to its Annual Meeting of Stockholders to be held M ay 20, 2021 is incorporated by reference in Items 10, 11, 12, 13 and 14 of Part III. Boston Properties, Inc. intends to file such Proxy Stat
Boston Properties Limited Partnership
Entity Information [Line Items]
Document Type	10-K
Document Period End Date	Dec. 31, 2020
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	2020
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
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
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, 2020	Dec. 31, 2019
ASSETS
Real estate, at cost (amounts related to variable interest entities (“VIEs”) of $6,592,019 and $6,497,031 at December 31, 2020 and December 31, 2019, respectively)	$ 22,969,110	$ 22,502,976
Right of use assets - finance leases (amounts related to VIEs of $21,000 and $21,000 at December 31, 2020 and December 31, 2019, respectively)	237,393	237,394
Right of use assets - operating leases	146,406	148,640
Less: accumulated depreciation (amounts related to VIEs of $(1,158,548) and $(1,058,495) at December 31, 2020 and December 31, 2019, respectively)	(5,534,102)	(5,266,798)
Total real estate	17,818,807	17,622,212
Cash and cash equivalents (amounts related to VIEs of $340,642 and $280,033 at December 31, 2020 and December 31, 2019, respectively)	1,668,742	644,950
Cash held in escrows	50,587	46,936
Investments in securities	39,457	36,747
Tenant and other receivables, net (amounts related to VIEs of $10,911 and $28,918 at December 31, 2020 and December 31, 2019, respectively)	77,411	112,807
Related party note receivable, net	77,552	80,000
Notes receivable, net	18,729	15,920
Accrued rental income, net (amounts related to VIEs of $336,594 and $298,318 at December 31, 2020 and December 31, 2019, respectively)	1,122,502	1,038,788
Deferred charges, net (amounts related to VIEs of $183,306 and $214,769 at December 31, 2020 and December 31, 2019, respectively)	640,085	689,213
Prepaid expenses and other assets (amounts related to VIEs of $13,137 and $20,931 at December 31, 2020 and December 31, 2019, respectively)	33,840	41,685
Investments in unconsolidated joint ventures	1,310,478	955,647
Total assets	22,858,190	21,284,905
Liabilities:
Mortgage notes payable, net (amounts related to VIEs of $2,907,590 and $2,918,806 at December 31, 2020 and December 31, 2019, respectively)	2,909,081	2,922,408
Unsecured senior notes, net	9,639,287	8,390,459
Unsecured line of credit	0	0
Unsecured term loan, net	499,390	498,939
Lease liabilities - finance leases (amounts related to VIEs of $20,306 and $20,189 at December 31, 2020 and December 31, 2019, respectively)	236,492	224,042
Lease liabilities - operating leases	201,713	200,180
Accounts payable and accrued expenses (amounts related to VIEs of $23,128 and $45,777 at December 31, 2020 and December 31, 2019, respectively)	336,264	377,553
Dividends and distributions payable	171,082	170,713
Accrued interest payable	106,288	90,016
Other liabilities (amounts related to VIEs of $158,805 and $140,110 at December 31, 2020 and December 31, 2019, respectively)	412,084	387,994
Total liabilities	14,511,681	13,262,304
Redeemable deferred stock units— 72,966 and 60,676 units outstanding at redemption value at December 31, 2020 and December 31, 2019, respectively	6,897	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, 2020 and December 31, 2019, respectively	200,000	200,000
Common stock, $0.01 par value, 250,000,000 shares authorized, 155,797,725 and 154,869,198 issued and 155,718,825 and 154,790,298 outstanding at December 31, 2020 and December 31, 2019, respectively	1,557	1,548
Additional paid-in capital	6,356,791	6,294,719
Dividends in excess of earnings	(509,653)	(760,523)
Treasury common stock at cost, 78,900 shares at December 31, 2020 and December 31, 2019	(2,722)	(2,722)
Accumulated other comprehensive loss	(49,890)	(48,335)
Total stockholders' equity attributable to Boston Properties, Inc.	5,996,083	5,684,687
Noncontrolling interests:
Common units of the Operating Partnership	616,596	600,860
Property partnerships	1,726,933	1,728,689
Total equity / capital	8,339,612	8,014,236
Total liabilities and equity / capital	22,858,190	21,284,905
Boston Properties Limited Partnership
ASSETS
Real estate, at cost (amounts related to variable interest entities (“VIEs”) of $6,592,019 and $6,497,031 at December 31, 2020 and December 31, 2019, respectively)	22,592,301	22,107,755
Right of use assets - finance leases (amounts related to VIEs of $21,000 and $21,000 at December 31, 2020 and December 31, 2019, respectively)	237,393	237,394
Right of use assets - operating leases	146,406	148,640
Less: accumulated depreciation (amounts related to VIEs of $(1,158,548) and $(1,058,495) at December 31, 2020 and December 31, 2019, respectively)	(5,428,576)	(5,162,908)
Total real estate	17,547,524	17,330,881
Cash and cash equivalents (amounts related to VIEs of $340,642 and $280,033 at December 31, 2020 and December 31, 2019, respectively)	1,668,742	644,950
Cash held in escrows	50,587	46,936
Investments in securities	39,457	36,747
Tenant and other receivables, net (amounts related to VIEs of $10,911 and $28,918 at December 31, 2020 and December 31, 2019, respectively)	77,411	112,807
Related party note receivable, net	77,552	80,000
Notes receivable, net	18,729	15,920
Accrued rental income, net (amounts related to VIEs of $336,594 and $298,318 at December 31, 2020 and December 31, 2019, respectively)	1,122,502	1,038,788
Deferred charges, net (amounts related to VIEs of $183,306 and $214,769 at December 31, 2020 and December 31, 2019, respectively)	640,085	689,213
Prepaid expenses and other assets (amounts related to VIEs of $13,137 and $20,931 at December 31, 2020 and December 31, 2019, respectively)	33,840	41,685
Investments in unconsolidated joint ventures	1,310,478	955,647
Total assets	22,586,907	20,993,574
Liabilities:
Mortgage notes payable, net (amounts related to VIEs of $2,907,590 and $2,918,806 at December 31, 2020 and December 31, 2019, respectively)	2,909,081	2,922,408
Unsecured senior notes, net	9,639,287	8,390,459
Unsecured line of credit	0	0
Unsecured term loan, net	499,390	498,939
Lease liabilities - finance leases (amounts related to VIEs of $20,306 and $20,189 at December 31, 2020 and December 31, 2019, respectively)	236,492	224,042
Lease liabilities - operating leases	201,713	200,180
Accounts payable and accrued expenses (amounts related to VIEs of $23,128 and $45,777 at December 31, 2020 and December 31, 2019, respectively)	336,264	377,553
Dividends and distributions payable	171,082	170,713
Accrued interest payable	106,288	90,016
Other liabilities (amounts related to VIEs of $158,805 and $140,110 at December 31, 2020 and December 31, 2019, respectively)	412,084	387,994
Total liabilities	14,511,681	13,262,304
Redeemable deferred stock units— 72,966 and 60,676 units outstanding at redemption value at December 31, 2020 and December 31, 2019, respectively	6,897	8,365
Redeemable partnership units— 16,037,121 and 16,764,466 common units and 1,336,115 and 1,143,215 long term incentive units outstanding at redemption value at December 31, 2020 and December 31, 2019, respectively	1,643,024	2,468,753
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, 2020 and December 31, 2019, respectively	193,623	193,623
Boston Properties Limited Partnership partners’ capital— 1,730,921 and 1,726,980 general partner units and 153,987,904 and 153,063,318 limited partner units outstanding at December 31, 2020 and December 31, 2019, respectively	4,554,639	3,380,175
Accumulated other comprehensive loss	(49,890)	(48,335)
Total partners’ capital	4,698,372	3,525,463
Noncontrolling interests in property partnerships	1,726,933	1,728,689
Noncontrolling interests:
Total equity / capital	6,425,305	5,254,152
Total liabilities and equity / capital	$ 22,586,907	$ 20,993,574

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Real estate, at cost (amounts related to variable interest entities (“VIEs”) of $6,592,019 and $6,497,031 at December 31, 2020 and December 31, 2019, respectively)	$ 22,969,110	$ 22,502,976
Right of use assets - finance leases (amounts related to VIEs of $21,000 and $21,000 at December 31, 2020 and December 31, 2019, respectively)	237,393	237,394
Less: accumulated depreciation (amounts related to VIEs of $(1,158,548) and $(1,058,495) at December 31, 2020 and December 31, 2019, respectively)	(5,534,102)	(5,266,798)
Cash and cash equivalents (amounts related to VIEs of $340,642 and $280,033 at December 31, 2020 and December 31, 2019, respectively)	1,668,742	644,950
Tenant and other receivables, net (amounts related to VIEs of $10,911 and $28,918 at December 31, 2020 and December 31, 2019, respectively)	77,411	112,807
Accrued rental income, net (amounts related to VIEs of $336,594 and $298,318 at December 31, 2020 and December 31, 2019, respectively)	1,122,502	1,038,788
Deferred charges, net (amounts related to VIEs of $183,306 and $214,769 at December 31, 2020 and December 31, 2019, respectively)	640,085	689,213
Prepaid expenses and other assets (amounts related to VIEs of $13,137 and $20,931 at December 31, 2020 and December 31, 2019, respectively)	33,840	41,685
Mortgage notes payable, net (amounts related to VIEs of $2,907,590 and $2,918,806 at December 31, 2020 and December 31, 2019, respectively)	2,909,081	2,922,408
Lease liabilities - finance leases (amounts related to VIEs of $20,306 and $20,189 at December 31, 2020 and December 31, 2019, respectively)	236,492	224,042
Accounts payable and accrued expenses (amounts related to VIEs of $23,128 and $45,777 at December 31, 2020 and December 31, 2019, respectively)	336,264	377,553
Other liabilities (amounts related to VIEs of $158,805 and $140,110 at December 31, 2020 and December 31, 2019, respectively)	$ 412,084	$ 387,994
Reddemable deferred stock units, units	72,966	60,676
Limited Partners' Capital Account, Units Outstanding (in units)	153,987,904
General Partners' Capital Account, Units Outstanding (in units)	1,730,921
Excess stock, par value	$ 0.01	$ 0.01
Excess stock, shares authorized	150,000,000	150,000,000
Excess stock, shares outstanding	0	0
Excess stock, shares issued	0	0
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	50,000,000	50,000,000
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Common stock, shares authorized	250,000,000	250,000,000
Common stock, shares issued	155,797,725	154,869,198
Common Stock, Shares, Outstanding	155,718,825	154,790,298
Treasury common stock at cost, shares	78,900	78,900
Boston Properties Limited Partnership
Real estate, at cost (amounts related to variable interest entities (“VIEs”) of $6,592,019 and $6,497,031 at December 31, 2020 and December 31, 2019, respectively)	$ 22,592,301	$ 22,107,755
Right of use assets - finance leases (amounts related to VIEs of $21,000 and $21,000 at December 31, 2020 and December 31, 2019, respectively)	237,393	237,394
Less: accumulated depreciation (amounts related to VIEs of $(1,158,548) and $(1,058,495) at December 31, 2020 and December 31, 2019, respectively)	(5,428,576)	(5,162,908)
Cash and cash equivalents (amounts related to VIEs of $340,642 and $280,033 at December 31, 2020 and December 31, 2019, respectively)	1,668,742	644,950
Tenant and other receivables, net (amounts related to VIEs of $10,911 and $28,918 at December 31, 2020 and December 31, 2019, respectively)	77,411	112,807
Accrued rental income, net (amounts related to VIEs of $336,594 and $298,318 at December 31, 2020 and December 31, 2019, respectively)	1,122,502	1,038,788
Deferred charges, net (amounts related to VIEs of $183,306 and $214,769 at December 31, 2020 and December 31, 2019, respectively)	640,085	689,213
Prepaid expenses and other assets (amounts related to VIEs of $13,137 and $20,931 at December 31, 2020 and December 31, 2019, respectively)	33,840	41,685
Mortgage notes payable, net (amounts related to VIEs of $2,907,590 and $2,918,806 at December 31, 2020 and December 31, 2019, respectively)	2,909,081	2,922,408
Lease liabilities - finance leases (amounts related to VIEs of $20,306 and $20,189 at December 31, 2020 and December 31, 2019, respectively)	236,492	224,042
Accounts payable and accrued expenses (amounts related to VIEs of $23,128 and $45,777 at December 31, 2020 and December 31, 2019, respectively)	336,264	377,553
Other liabilities (amounts related to VIEs of $158,805 and $140,110 at December 31, 2020 and December 31, 2019, respectively)	$ 412,084	$ 387,994
Reddemable deferred stock units, units	72,966	60,676
NonControlling Interest Redeemable Partnership Units Common Units Shares Outstanding	16,037,121	16,764,466
NonControlling Interest Redeemable Partnership Units Common Units Long Term Incentive Units At Redemption Value Shares Outstanding	1,336,115	1,143,215
Limited Partners' Capital Account, Units Outstanding (in units)	153,987,904	153,063,318
General Partners' Capital Account, Units Outstanding (in units)	1,730,921	1,726,980
Series B Cumulative Redeemable Preferred Stock / Unit [Member]
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	92,000	92,000
Preferred stock / units, shares / units issued (in shares / units)	80,000	80,000
Preferred stock / units, shares / units outstanding (in shares / units)	80,000	80,000
Series B Dividend Rate Percentage	5.25%	5.25%
Series B Liquidation Preference Per Share/ Unit	$ 2,500	$ 2,500
Series B Cumulative Redeemable Preferred Stock / Unit [Member] \| Boston Properties Limited Partnership
Preferred stock / units, shares / units issued (in shares / units)	80,000	80,000
Preferred stock / units, shares / units outstanding (in shares / units)	80,000	80,000
Series B Dividend Rate Percentage	5.25%	5.25%
Series B Liquidation Preference Per Share/ Unit	$ 2,500	$ 2,500
Variable Interest Entity, Primary Beneficiary [Member]
Real estate, at cost (amounts related to variable interest entities (“VIEs”) of $6,592,019 and $6,497,031 at December 31, 2020 and December 31, 2019, respectively)	$ 6,592,019	$ 6,497,031
Right of use assets - finance leases (amounts related to VIEs of $21,000 and $21,000 at December 31, 2020 and December 31, 2019, respectively)	21,000	21,000
Less: accumulated depreciation (amounts related to VIEs of $(1,158,548) and $(1,058,495) at December 31, 2020 and December 31, 2019, respectively)	(1,158,548)	(1,058,495)
Cash and cash equivalents (amounts related to VIEs of $340,642 and $280,033 at December 31, 2020 and December 31, 2019, respectively)	340,642	280,033
Tenant and other receivables, net (amounts related to VIEs of $10,911 and $28,918 at December 31, 2020 and December 31, 2019, respectively)	10,911	28,918
Accrued rental income, net (amounts related to VIEs of $336,594 and $298,318 at December 31, 2020 and December 31, 2019, respectively)	336,594	298,318
Deferred charges, net (amounts related to VIEs of $183,306 and $214,769 at December 31, 2020 and December 31, 2019, respectively)	183,306	214,769
Prepaid expenses and other assets (amounts related to VIEs of $13,137 and $20,931 at December 31, 2020 and December 31, 2019, respectively)	13,137	20,931
Mortgage notes payable, net (amounts related to VIEs of $2,907,590 and $2,918,806 at December 31, 2020 and December 31, 2019, respectively)	2,907,590	2,918,806
Lease liabilities - finance leases (amounts related to VIEs of $20,306 and $20,189 at December 31, 2020 and December 31, 2019, respectively)	20,306	20,189
Accounts payable and accrued expenses (amounts related to VIEs of $23,128 and $45,777 at December 31, 2020 and December 31, 2019, respectively)	23,128	45,777
Other liabilities (amounts related to VIEs of $158,805 and $140,110 at December 31, 2020 and December 31, 2019, respectively)	158,805	140,110
Variable Interest Entity, Primary Beneficiary [Member] \| Boston Properties Limited Partnership
Real estate, at cost (amounts related to variable interest entities (“VIEs”) of $6,592,019 and $6,497,031 at December 31, 2020 and December 31, 2019, respectively)	6,592,019	6,497,031
Right of use assets - finance leases (amounts related to VIEs of $21,000 and $21,000 at December 31, 2020 and December 31, 2019, respectively)	21,000	21,000
Less: accumulated depreciation (amounts related to VIEs of $(1,158,548) and $(1,058,495) at December 31, 2020 and December 31, 2019, respectively)	(1,158,548)	(1,058,495)
Cash and cash equivalents (amounts related to VIEs of $340,642 and $280,033 at December 31, 2020 and December 31, 2019, respectively)	340,642	280,033
Tenant and other receivables, net (amounts related to VIEs of $10,911 and $28,918 at December 31, 2020 and December 31, 2019, respectively)	10,911	28,918
Accrued rental income, net (amounts related to VIEs of $336,594 and $298,318 at December 31, 2020 and December 31, 2019, respectively)	336,594	298,318
Deferred charges, net (amounts related to VIEs of $183,306 and $214,769 at December 31, 2020 and December 31, 2019, respectively)	183,306	214,769
Prepaid expenses and other assets (amounts related to VIEs of $13,137 and $20,931 at December 31, 2020 and December 31, 2019, respectively)	13,137	20,931
Mortgage notes payable, net (amounts related to VIEs of $2,907,590 and $2,918,806 at December 31, 2020 and December 31, 2019, respectively)	2,907,590	2,918,806
Lease liabilities - finance leases (amounts related to VIEs of $20,306 and $20,189 at December 31, 2020 and December 31, 2019, respectively)	20,306	20,189
Accounts payable and accrued expenses (amounts related to VIEs of $23,128 and $45,777 at December 31, 2020 and December 31, 2019, respectively)	23,128	45,777
Other liabilities (amounts related to VIEs of $158,805 and $140,110 at December 31, 2020 and December 31, 2019, respectively)	$ 158,805	$ 140,110

Consolidated Statements Of Oper

Consolidated Statements Of Operations - USD ($) shares in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue
Lease		$ 2,646,261,000	$ 2,758,014,000
Base rent				$ 2,103,723,000
Recoveries from tenants				402,066,000
Total revenue		2,765,686,000	2,960,562,000	2,717,076,000
Expenses
Rental		1,017,208,000	1,050,010,000	979,151,000
General and administrative		133,112,000	140,777,000	121,722,000
Transaction costs		1,531,000	1,984,000	1,604,000
Depreciation, Depletion and Amortization		683,751,000	677,764,000	645,649,000
Depreciation and amortization		683,751,000	677,764,000	645,649,000
Total expenses		1,860,364,000	1,914,925,000	1,791,579,000
Other income (expense)
Income (Loss) from Unconsolidated Joint Ventures		(85,110,000)	46,592,000	2,222,000
Gains (losses) on sales of real estate		618,982,000	709,000	182,356,000
Interest and other income (loss)		5,953,000	18,939,000	10,823,000
Gains (losses) from investments in securities		5,261,000	6,417,000	(1,865,000)
Impairment loss		0	(24,038,000)	(11,812,000)
Loss from early extinguishment of debt		0	(29,540,000)	(16,490,000)
Interest expense		(431,717,000)	(412,717,000)	(378,168,000)
Net income		1,018,691,000	651,999,000	712,563,000
Net (income) loss attributable to noncontrolling interests
Noncontrolling interests in property partnerships		(48,260,000)	(71,120,000)	(62,909,000)
Noncontrolling interest - common units of the Operating Partnership		(97,704,000)	(59,345,000)	(66,807,000)
Net income attributable to the Company		872,727,000	521,534,000	582,847,000
Preferred dividends / distributions		(10,500,000)	(10,500,000)	(10,500,000)
Net income attributable to the company's common shareholders / unitholders		$ 862,227,000	$ 511,034,000	$ 572,347,000
Basic earnings per common share / unit attributable to the Company
Earnings Per Share After Allccation of Undistributed Earnings to Particiapting Securities Basic (dollars per share)		$ 5.54		$ 3.71
Net income (in dollars per share / unit)		$ 5.55	$ 3.31	$ 3.71
Weighted average number of common shares / units outstanding (in shares / units)		155,432	154,582	154,427
Diluted earnings per common share / unit attributable to the Company
Diluted Earnings: Net income, Per Share Amount (in dollars per share / unit)		$ 5.54	$ 3.30	$ 3.70
Weighted average number of common and common equivalent shares / units outstanding (in shares / units)		155,517	154,883	154,682
Boston Properties Limited Partnership
Revenue
Lease		$ 2,646,261,000	$ 2,758,014,000
Base rent				$ 2,103,723,000
Recoveries from tenants				402,066,000
Total revenue		2,765,686,000	2,960,562,000	2,717,076,000
Expenses
Rental		1,017,208,000	1,050,010,000	979,151,000
General and administrative		133,112,000	140,777,000	121,722,000
Transaction costs		1,531,000	1,984,000	1,604,000
Depreciation, Depletion and Amortization		676,666,000	669,956,000	637,891,000
Depreciation and amortization		676,666,000	669,956,000
Total expenses		1,853,279,000	1,907,117,000	1,783,821,000
Other income (expense)
Income (Loss) from Unconsolidated Joint Ventures		(85,110,000)	46,592,000	2,222,000
Gains (losses) on sales of real estate		631,945,000	858,000	190,716,000
Interest and other income (loss)		5,953,000	18,939,000	10,823,000
Gains (losses) from investments in securities		5,261,000	6,417,000	(1,865,000)
Impairment loss		0	(22,272,000)	(10,181,000)
Loss from early extinguishment of debt		0	(29,540,000)	(16,490,000)
Interest expense		(431,717,000)	(412,717,000)	(378,168,000)
Net income		1,038,739,000	661,722,000	730,312,000
Net (income) loss attributable to noncontrolling interests
Noncontrolling interests in property partnerships		(48,260,000)	(71,120,000)	(62,909,000)
Net income attributable to the Company		990,479,000	590,602,000	667,403,000
Preferred dividends / distributions		(10,500,000)	(10,500,000)	(10,500,000)
Net income attributable to the company's common shareholders / unitholders		$ 979,979,000	$ 580,102,000	$ 656,903,000
Basic earnings per common share / unit attributable to the Company
Earnings Per Share After Allccation of Undistributed Earnings to Particiapting Securities Basic (dollars per share)		$ 5.67		$ 3.82
Net income (in dollars per share / unit)		$ 5.68	$ 3.37	$ 3.82
Weighted average number of common shares / units outstanding (in shares / units)		172,643	172,200	171,912
Diluted earnings per common share / unit attributable to the Company
Diluted Earnings: Net income, Per Share Amount (in dollars per share / unit)		$ 5.67	$ 3.36	$ 3.81
Weighted average number of common and common equivalent shares / units outstanding (in shares / units)		172,728	172,501	172,167
Parking and Other [Member]
Revenue
Other revenue		$ 70,680,000	$ 103,534,000	$ 107,421,000
Parking and Other [Member] \| Boston Properties Limited Partnership
Revenue
Other revenue		70,680,000	103,534,000	107,421,000
Hotel [Member]
Revenue
Other revenue	[1]	7,478,000	48,589,000	49,118,000
Expenses
Operating expense		13,136,000	34,004,000	33,863,000
Hotel [Member] \| Boston Properties Limited Partnership
Revenue
Other revenue		7,478,000	48,589,000	49,118,000
Expenses
Operating expense		13,136,000	34,004,000	33,863,000
Real Estate, Other [Member]
Revenue
Other revenue		11,626,000	10,386,000	9,590,000
Expenses
Operating expense		11,626,000	10,386,000	9,590,000
Real Estate, Other [Member] \| Boston Properties Limited Partnership
Revenue
Other revenue		11,626,000	10,386,000	9,590,000
Expenses
Operating expense		11,626,000	10,386,000	9,590,000
Management Service [Member]
Revenue
Other revenue		29,641,000	40,039,000	45,158,000
Management Service [Member] \| Boston Properties Limited Partnership
Revenue
Other revenue		$ 29,641,000	$ 40,039,000	$ 45,158,000

[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, 2020	Dec. 31, 2019	Dec. 31, 2018
Net income		$ 1,018,691	$ 651,999	$ 712,563
Other comprehensive income (loss):
Effective portion of interest rate contracts		(7,848)	(6,751)	(3,096)
Amortization of interest rate contracts	[1]	6,697	6,664	6,664
Other comprehensive income (loss)		(1,151)	(87)	3,568
Comprehensive Income		1,017,540	651,912	716,131
Comprehensive income attributable to noncontrolling interests		(145,964)	(130,465)	(129,716)
Other comprehensive income attributable to noncontrolling interests		(404)	(507)	(880)
Comprehensive income attributable to the Company		871,172	520,940	585,535
Boston Properties Limited Partnership
Net income		1,038,739	661,722	730,312
Other comprehensive income (loss):
Effective portion of interest rate contracts		(7,848)	(6,751)	(3,096)
Amortization of interest rate contracts	[2]	6,697	6,664	6,664
Other comprehensive income (loss)		(1,151)	(87)	3,568
Comprehensive Income		1,037,588	661,635	733,880
Comprehensive income attributable to noncontrolling interests		(48,836)	(71,696)	(63,485)
Comprehensive income attributable to the Company		$ 988,752	$ 589,939	$ 670,395

[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 Equi

Consolidated Statements Of Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock [Member]	Preferred Stock [Member]	Additional Paid-In Capital [Member]	Dividends In Excess Of Earnings [Member]	Dividends In Excess Of Earnings [Member]Cumulative Effect, Period of Adoption, Adjustment	Treasury Stock, at cost [Member]	Accumulated Other Comprehensive Loss [Member]	Noncontrolling Interests [Member]	Noncontrolling Interests [Member]Cumulative Effect, Period of Adoption, Adjustment	Noncontrolling interest - property partnerships [Member]	Noncontrolling interest - property partnerships [Member]Cumulative Effect, Period of Adoption, Adjustment
Equity, shares at Dec. 31, 2017			154,325,000
Equity, value at Dec. 31, 2017	$ 8,102,456	$ 5,496	$ 1,543	$ 200,000	$ 6,377,908	$ (712,343)	$ 4,933	$ (2,722)	$ (50,429)	$ 604,739	$ 563	$ 1,683,760
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Redemption of operating partnership units to common stock, shares			83,000
Redemption of operating partnership units to common stock, value	0		$ 2		2,878					(2,880)
Allocated net income for the year	712,563					582,847				66,807		62,909
Dividends/distributions declared	(613,702)					(550,971)				(62,731)
Shares issued pursuant to stock purchase plan, shares			6,000
Shares issued pursuant to stock purchase plan, value	797				797
Net activity from stock option and incentive plan, shares			44,000
Net activity from stock option and incentive plan, value	38,590		$ 0		1,729					36,861
Contributions from noncontrolling interests in property partnerships	46,701											46,701
Distributions to noncontrolling interests in property partnerships	(82,501)											(82,501)
Effective portion of interest rate contracts	(3,096)								(2,781)	(315)		0
Amortization of interest rate contracts	6,664								5,469	619		576
Reallocation of noncontrolling interest	0				24,311					(24,311)
Equity, shares at Dec. 31, 2018			154,458,000
Equity, value at Dec. 31, 2018	$ 8,213,968	(4,379)	$ 1,545	200,000	6,407,623	(675,534)	(3,864)	(2,722)	(47,741)	619,352	(445)	1,711,445	$ (70)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible List] \| Accounting Standards Update 2014-09	us-gaap:AccountingStandardsUpdate201409Member
Redemption of operating partnership units to common stock, shares			145,000
Redemption of operating partnership units to common stock, value	$ 0		$ 2		4,883					(4,885)
Allocated net income for the year	651,999					521,534				59,345		71,120
Dividends/distributions declared	(671,893)					(602,659)				(69,234)
Shares issued pursuant to stock purchase plan, shares			6,000
Shares issued pursuant to stock purchase plan, value	688				688
Net activity from stock option and incentive plan, shares			181,000
Net activity from stock option and incentive plan, value	45,000		$ 1		8,771					36,228
Sale of an interest in property partnerships	0				(4,216)							4,216
Acquisition of noncontrolling interest in property partnership	(186,963)				(162,462)							(24,501)
Contributions from noncontrolling interests in property partnerships	35,816											35,816
Distributions to noncontrolling interests in property partnerships	(69,913)											(69,913)
Effective portion of interest rate contracts	(6,751)								(6,060)	(691)		0
Amortization of interest rate contracts	6,664								5,466	622		576
Reallocation of noncontrolling interest	$ 0				39,432					(39,432)
Equity, shares at Dec. 31, 2019	154,790,298		154,790,000
Equity, value at Dec. 31, 2019	$ 8,014,236	$ (1,679)	$ 1,548	200,000	6,294,719	(760,523)	$ (1,505)	(2,722)	(48,335)	600,860	$ (174)	1,728,689
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible List] \| Accounting Standards Update 2016-02	us-gaap:AccountingStandardsUpdate201602Member
Redemption of operating partnership units to common stock, shares			857,000
Redemption of operating partnership units to common stock, value	$ 0		$ 9		29,689					(29,698)
Allocated net income for the year	1,018,691					872,727				97,704		48,260
Dividends/distributions declared	(689,273)					(620,352)				(68,921)
Shares issued pursuant to stock purchase plan, shares			7,000
Shares issued pursuant to stock purchase plan, value	759				759
Net activity from stock option and incentive plan, shares			65,000
Net activity from stock option and incentive plan, value	48,621		$ 0		9,303					39,318
Contributions from noncontrolling interests in property partnerships	8,219											8,219
Distributions to noncontrolling interests in property partnerships	(58,811)											(58,811)
Effective portion of interest rate contracts	(7,848)								(7,066)	(782)		0
Amortization of interest rate contracts	6,697								5,511	610		576
Reallocation of noncontrolling interest	$ 0				22,321					(22,321)
Equity, shares at Dec. 31, 2020	155,718,825		155,719,000
Equity, value at Dec. 31, 2020	$ 8,339,612		$ 1,557	$ 200,000	$ 6,356,791	$ (509,653)		$ (2,722)	$ (49,890)	$ 616,596		$ 1,726,933
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible List] \| Accounting Standards Update 2018-09	us-gaap:AccountingStandardsUpdate201809Member

Consolidated Statement of Capit

Consolidated Statement of Capital and Noncontrolling Interests - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Common Stock, Shares, Outstanding	155,718,825	154,790,298
Beginning Balance
Effective portion of interest rate contracts	$ (7,848)	$ (6,751)	$ (3,096)
Amortization of interest rate contracts	6,697	6,664	6,664
Acquisition of noncontrolling interest in property partnership		(186,963)
Sale of an interest in property partnerships		0
Contributions from noncontrolling interests in property partnerships	8,219	35,816	46,701
Distributions to noncontrolling interests in property partnerships	$ (58,811)	$ (69,913)	$ (82,501)
Accounting Standards Update 2014-09
Accounting Standards Update [Extensible List]			us-gaap:AccountingStandardsUpdate201409Member
Accounting Standards Update 2016-02
Accounting Standards Update [Extensible List]		us-gaap:AccountingStandardsUpdate201602Member
Accounting Standards Update 2018-09
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201809Member
General Partner [Member]
Common Stock, Shares, Outstanding	1,731,000	1,727,000	1,722,000	1,720,000
Contributions, units	1,000	3,000	1,000
Conversion of redeemable partnership units	3,000	2,000	1,000
Limited Partner [Member]
Common Stock, Shares, Outstanding	153,988,000	153,063,000	152,736,000	152,606,000
Contributions, units	72,000	185,000	49,000
Conversion of redeemable partnership units	853,000	142,000	81,000
Partners' Capital (General and Limited Partners)[Member]
Beginning Balance	$ 4,554,639	$ 3,380,175	$ 4,054,996	$ 3,664,436
Contributions, value	7,529	17,115	1,642
Allocated net income for the period	882,275	520,757	590,096
Distributions	(609,852)	(592,159)	(540,471)
Unearned compensation	2,533	(7,655)	884
Conversion of redeemable partnership units, value	29,689	4,885	2,880
Adjustment to reflect redeemable partnership units at redemption value	863,795	(447,222)	330,596
Acquisition of noncontrolling interest in property partnership		(162,462)
Sale of an interest in property partnerships		(4,216)
Partners' Capital (General and Limited Partners)[Member] \| Cumulative Effect, Period of Adoption, Adjustment
Beginning Balance		(1,505)	(3,864)	4,933
Preferred Units [Member]
Beginning Balance	193,623	193,623	193,623	193,623
Allocated net income for the period	10,500	10,500	10,500
Distributions	(10,500)	(10,500)	(10,500)
Accumulated Other Comprehensive Loss [Member]
Beginning Balance	(49,890)	(48,335)	(47,741)	(50,429)
Effective portion of interest rate contracts	(7,066)	(6,060)	(2,781)
Amortization of interest rate contracts	5,511	5,466	5,469
Noncontrolling interest - property partnerships [Member]
Beginning Balance	1,726,933	1,728,689	1,711,445	1,683,760
Allocated net income for the period	48,260	71,120	62,909
Effective portion of interest rate contracts	0	0	0
Amortization of interest rate contracts	576	576	576
Acquisition of noncontrolling interest in property partnership		(24,501)
Sale of an interest in property partnerships		4,216
Contributions from noncontrolling interests in property partnerships	8,219	35,816	46,701
Distributions to noncontrolling interests in property partnerships	(58,811)	(69,913)	(82,501)
Noncontrolling interest - property partnerships [Member] \| Cumulative Effect, Period of Adoption, Adjustment
Beginning Balance			(70)
Total Capital [Member]
Beginning Balance	6,425,305	5,254,152	5,912,323	5,491,390
Contributions, value	7,529	17,115	1,642
Allocated net income for the period	941,035	602,377	663,505
Distributions	(620,352)	(602,659)	(550,971)
Unearned compensation	2,533	(7,655)	884
Conversion of redeemable partnership units, value	29,689	4,885	2,880
Adjustment to reflect redeemable partnership units at redemption value	863,795	(447,222)	330,596
Effective portion of interest rate contracts	(7,066)	(6,060)	(2,781)
Amortization of interest rate contracts	6,087	6,042	6,045
Acquisition of noncontrolling interest in property partnership		(186,963)
Contributions from noncontrolling interests in property partnerships	8,219	35,816	46,701
Distributions to noncontrolling interests in property partnerships	(58,811)	(69,913)	(82,501)
Total Capital [Member] \| Cumulative Effect, Period of Adoption, Adjustment
Beginning Balance		(1,505)	(3,934)	4,933
Noncontrolling interest - Redeemable partnership units [Member]
Redeemable Noncontrolling Interest, Equity, Preferred, Carrying Amount	1,643,024	2,468,753	2,000,591	2,292,263
Contributions, value	38,841	34,217	34,680
Allocated net income for the period	97,704	59,345	66,807
Distributions	(68,921)	(69,234)	(62,731)
Unearned compensation	477	2,011	2,181
Conversion of redeemable partnership units, value	(29,689)	(4,885)	(2,880)
Adjustment to reflect redeemable partnership units at redemption value	(863,795)	447,222	(330,596)
Effective portion of interest rate contracts	(782)	(691)	(315)
Amortization of interest rate contracts	$ 610	622	619
Noncontrolling interest - Redeemable partnership units [Member] \| Cumulative Effect, Period of Adoption, Adjustment
Redeemable Noncontrolling Interest, Equity, Preferred, Carrying Amount		$ (174)	$ (445)	$ 563

Consolidated Statements Of Cash

Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net income	$ 1,018,691	$ 651,999	$ 712,563
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	683,751	677,764	645,649
Amortization of right of use assets - operating leases	2,234	2,412	0
Impairment losses	0	24,038	11,812
Non-cash compensation expense	44,142	40,958	40,117
(Income) Loss from unconsolidated joint ventures	85,110	(46,592)	(2,222)
Distributions of net cash flow from operations of unconsolidated joint ventures	31,892	17,155	6,703
(Gains) losses from investments in securities	(5,261)	(6,417)	1,865
Allowance for current expected credit losses	1,849	0	0
Non-cash portion of interest expense	23,384	22,254	21,303
Settlement of accreted debt discount on redemption of unsecured senior notes	0	(763)	(483)
Loss from early extinguishment of debt	0	29,540	16,490
Gains on sales of real estate	(618,982)	(709)	(182,356)
Change in assets and liabilities:
Tenant and other receivables, net	22,550	(24,876)	29,204
Notes receivable, net	(19)	4	(13)
Accrued rental income, net	(97,099)	(56,817)	(43,662)
Prepaid expenses and other assets	12,488	2,965	12,472
Lease liabilities - finance leases	568	0	0
Lease liabilities - operating leases	1,533	1,616	0
Accounts payable and accrued expenses	(4,059)	12,627	1,353
Accrued interest payable	16,211	858	5,237
Other liabilities	17,629	(49,569)	4,955
Tenant leasing costs	(79,772)	(117,282)	(130,742)
Total adjustments	138,149	529,166	437,682
Net cash provided by operating activities	1,156,840	1,181,165	1,150,245
Cash flows from investing activities:
Acquisitions of real estate	(137,976)	(149,031)	0
Construction in progress	(482,507)	(546,060)	(694,791)
Building and other capital improvements	(160,126)	(180,556)	(189,771)
Tenant improvements	(234,423)	(251,831)	(210,034)
Right of use assets - finance leases	0	(5,152)	0
Proceeds from sales of real estate	519,303	90,824	455,409
Capital contributions to unconsolidated joint ventures	(172,436)	(87,392)	(345,717)
Capital distributions from unconsolidated joint ventures	55,298	136,807	0
Cash and cash equivalents deconsolidated	0	(24,112)	0
Deposit on capital lease	0	0	(13,615)
Issuance of related party note receivable	0	0	(80,000)
Issuance of notes receivable, net	(9,800)	0	(19,455)
Proceeds from note receivable	6,397	3,544	0
Investments in securities, net	2,551	(2,132)	(902)
Net cash used in investing activities	(613,719)	(1,015,091)	(1,098,876)
Cash flows from financing activities:
Repayments of mortgage notes payable	(17,168)	(46,173)	(18,634)
Proceeds from unsecured senior notes	1,248,125	1,548,106	996,410
Redemption of unsecured senior notes	0	(699,237)	(699,517)
Borrowings on unsecured line of credit	265,000	380,000	745,000
Repayments of unsecured line of credit	(265,000)	(380,000)	(790,000)
Proceeds from unsecured term loan	0	0	500,000
Payments on finance lease obligations	0	(502)	0
Payments on capital lease obligations	0	0	(1,353)
Payments on real estate transaction	0	0	(960)
Deferred financing costs	(10,416)	(13,213)	(8,362)
Debt prepayment and extinguishment costs	0	(28,716)	(15,973)
Net proceeds from equity transactions	3,277	13,710	(730)
Dividends and distributions	(688,904)	(666,294)	(587,628)
Contributions from noncontrolling interests in property partnerships	8,219	35,816	46,701
Distributions to noncontrolling interests in property partnerships	(58,811)	(69,913)	(82,501)
Acquisition of noncontrolling interest in property partnership	0	(186,963)	0
Net cash provided by (used in) financing activities	484,322	(113,379)	82,453
Net increase (decrease) in cash and cash equivalents and cash held in escrows	1,027,443	52,695	133,822
Cash and cash equivalents and cash held in escrows, beginning of period	691,886	639,191	505,369
Cash and cash equivalents and cash held in escrows, end of period	1,719,329	691,886	639,191
Reconciliation of cash and cash equivalents and cash held in escrow
Cash and cash equivalents, beginning of period	644,950	543,359	434,767
Cash held in escrows, beginning of period	46,936	95,832	70,602
Cash and cash equivalents, end of period	1,668,742	644,950	543,359
Cash held in escrows,end of period	50,587	46,936	95,832
Supplemental disclosures:
Cash paid for interest	433,492	439,059	416,019
Interest capitalized	53,881	54,911	65,766
Non-cash investing and financing activities:
Write-off of fully depreciated real estate	(99,494)	(129,831)	(135,431)
Change in real estate included in accounts payable and accrued expenses	(19,848)	89,245	(44,866)
Real estate acquired through capital lease	0	0	12,397
Right of use assets obtained in exchange for lease liabilities	0	287,540	0
Prepaid rent reclassified to right of use asset	0	15,000	0
Accrued rental income, net deconsolidated	(4,558)	0	0
Tenant leasing costs, net deconsolidated	(3,462)	0	0
Building and other capital improvements, net deconsolidated	(111,889)	(12,767)	0
Tenant improvements, net deconsolidated	(12,331)	0	0
Right of use asset - finance lease deconsolidated	0	(135,004)	0
Lease liability - finance lease deconsolidated	0	119,534	0
Investment in unconsolidated joint venture recorded upon deconsolidation	347,898	29,246	0
Dividends and distributions declared but not paid	171,082	170,713	165,114
Conversions of noncontrolling interests to stockholders’ equity	29,698	4,885	2,880
Issuance of restricted securities to employees and non-employee directors	42,607	37,622	37,052
Boston Properties Limited Partnership
Net income	1,038,739	661,722	730,312
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	676,666	669,956	637,891
Amortization of right of use assets - operating leases	2,234	2,412	0
Impairment losses	0	22,272	10,181
Non-cash compensation expense	44,142	40,958	40,117
(Income) Loss from unconsolidated joint ventures	85,110	(46,592)	(2,222)
Distributions of net cash flow from operations of unconsolidated joint ventures	31,892	17,155	6,703
(Gains) losses from investments in securities	(5,261)	(6,417)	1,865
Allowance for current expected credit losses	1,849	0	0
Non-cash portion of interest expense	23,384	22,254	21,303
Settlement of accreted debt discount on redemption of unsecured senior notes	0	(763)	(483)
Loss from early extinguishment of debt	0	29,540	16,490
Gains on sales of real estate	(631,945)	(858)	(190,716)
Change in assets and liabilities:
Tenant and other receivables, net	22,550	(24,876)	29,204
Notes receivable, net	(19)	4	(13)
Accrued rental income, net	(97,099)	(56,817)	(43,662)
Prepaid expenses and other assets	12,488	2,965	12,472
Lease liabilities - finance leases	568	0	0
Lease liabilities - operating leases	1,533	1,616	0
Accounts payable and accrued expenses	(4,059)	12,627	1,353
Accrued interest payable	16,211	858	5,237
Other liabilities	17,629	(49,569)	4,955
Tenant leasing costs	(79,772)	(117,282)	(130,742)
Total adjustments	118,101	519,443	419,933
Net cash provided by operating activities	1,156,840	1,181,165	1,150,245
Cash flows from investing activities:
Acquisitions of real estate	(137,976)	(149,031)	0
Construction in progress	(482,507)	(546,060)	(694,791)
Building and other capital improvements	(160,126)	(180,556)	(189,771)
Tenant improvements	(234,423)	(251,831)	(210,034)
Right of use assets - finance leases	0	(5,152)	0
Proceeds from sales of real estate	519,303	90,824	455,409
Capital contributions to unconsolidated joint ventures	(172,436)	(87,392)	(345,717)
Capital distributions from unconsolidated joint ventures	55,298	136,807	0
Cash and cash equivalents deconsolidated	0	(24,112)	0
Deposit on capital lease	0	0	(13,615)
Issuance of related party note receivable	0	0	(80,000)
Issuance of notes receivable, net	(9,800)	0	(19,455)
Proceeds from note receivable	6,397	3,544	0
Investments in securities, net	2,551	(2,132)	(902)
Net cash used in investing activities	(613,719)	(1,015,091)	(1,098,876)
Cash flows from financing activities:
Repayments of mortgage notes payable	(17,168)	(46,173)	(18,634)
Proceeds from unsecured senior notes	1,248,125	1,548,106	996,410
Redemption of unsecured senior notes	0	(699,237)	(699,517)
Borrowings on unsecured line of credit	265,000	380,000	745,000
Repayments of unsecured line of credit	(265,000)	(380,000)	(790,000)
Proceeds from unsecured term loan	0	0	500,000
Payments on finance lease obligations	0	(502)
Payments on capital lease obligations			(1,353)
Payments on real estate transaction	0	0	(960)
Deferred financing costs	(10,416)	(13,213)	(8,362)
Debt prepayment and extinguishment costs	0	(28,716)	(15,973)
Net proceeds from equity transactions	3,277	13,710	(730)
Dividends and distributions	(688,904)	(666,294)	(587,628)
Contributions from noncontrolling interests in property partnerships	8,219	35,816	46,701
Distributions to noncontrolling interests in property partnerships	(58,811)	(69,913)	(82,501)
Acquisition of noncontrolling interest in property partnership	0	(186,963)	0
Net cash provided by (used in) financing activities	484,322	(113,379)	82,453
Net increase (decrease) in cash and cash equivalents and cash held in escrows	1,027,443	52,695	133,822
Cash and cash equivalents and cash held in escrows, beginning of period	691,886	639,191	505,369
Cash and cash equivalents and cash held in escrows, end of period	1,719,329	691,886	639,191
Reconciliation of cash and cash equivalents and cash held in escrow
Cash and cash equivalents, beginning of period	644,950	543,359	434,767
Cash held in escrows, beginning of period	46,936	95,832	70,602
Cash and cash equivalents, end of period	1,668,742	644,950	543,359
Cash held in escrows,end of period	50,587	46,936	95,832
Supplemental disclosures:
Cash paid for interest	433,492	439,059	416,019
Interest capitalized	53,881	54,911	65,766
Non-cash investing and financing activities:
Write-off of fully depreciated real estate	(99,494)	(129,253)	(135,431)
Change in real estate included in accounts payable and accrued expenses	(19,848)	89,245	(44,866)
Real estate acquired through capital lease	0	0	12,397
Right of use assets obtained in exchange for lease liabilities	0	287,540	0
Prepaid rent reclassified to right of use asset	0	15,000	0
Accrued rental income, net deconsolidated	(4,558)	0	0
Tenant leasing costs, net deconsolidated	(3,462)	0	0
Building and other capital improvements, net deconsolidated	(111,889)	(12,767)	0
Tenant improvements, net deconsolidated	(12,331)	0	0
Right of use asset - finance lease deconsolidated	0	(135,004)	0
Lease liability - finance lease deconsolidated	0	119,534	0
Investment in unconsolidated joint venture recorded upon deconsolidation	347,898	29,246	0
Dividends and distributions declared but not paid	171,082	170,713	165,114
Conversions of noncontrolling interests to stockholders’ equity	29,698	4,885	2,880
Issuance of restricted securities to employees and non-employee directors	$ 42,607	$ 37,622	$ 37,052

Organization

Organization	12 Months Ended
Organization	Dec. 31, 2020
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, 2020 owned an approximate 90.0% (89.6% at December 31, 2019) 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 - 2020 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 and the 2013 - 2017 MYLTIP Units have ended 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 2018 - 2020 MYLTIP Units differ from other LTIP Units granted to employees (including the 2012 OPP Units and the 2013 - 2017 MYLTIP Units, which have been earned). Therefore, unless specifically noted otherwise, all references to LTIP Units exclude the 2018 - 2020 MYLTIP Units. LTIP Units (including the earned 2012 OPP Units and the earned 2013 - 2017 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 11, 16 and 18). At December 31, 2020 and 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 12). Properties At December 31, 2020, the Company owned or had joint venture interests in a portfolio of 196 commercial real estate properties (the “Properties”) aggregating approximately 51.2 million net rentable square feet (unaudited) of primarily Class A office properties, including six properties under construction/redevelopment totaling approximately 3.7 million net rentable square feet (unaudited). At December 31, 2020, the Properties consisted of: • 177 office properties (including six properties under construction/redevelopment); • 12 retail properties; • six residential properties; and • one hotel. The Company considers Class A office properties to be well-located buildings that are modern structures or have been modernized to compete with newer buildings and professionally managed and maintained. As such, these properties attract high-quality tenants and command upper-tier rental rates. 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 seven entities that are VIEs as of December 31, 2020. Consolidated Variable Interest Entities As of December 31, 2020, 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), Times 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 (excluding Boston Properties Limited Partnership’s interest) are reflected as noncontrolling interests in property partnerships in the accompanying consolidated financial statements (See Note 11). 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 As of December 31, 2020, the Company has determined that the Platform 16 Holdings LP joint venture is a VIE. The Company does not consolidate this entity 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, 2020
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 indicators of imp airment following the end of each quarter and when events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. This evaluation of long-lived assets is dependent on a number of factors, including when there is an event or adverse change in the operating performance of the long-lived asset or a current expectation that, more likely than not, a long-lived asset will be sold or otherwise disposed of significantly before the end of its previously estimated useful life or hold period. 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 may be 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 hold 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” 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, 2020, 2019 and 2018 were approximately $53.9 million, $54.9 million and $65.8 million, respectively. Salaries and related costs capitalized for the years ended December 31, 2020, 2019 and 2018 were approximately $12.9 million, $10.4 million and $12.5 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, 2020 and 2019, the Company had maintained approximately $39.5 million and $36.7 million, respectively, in separate accounts, which are not restricted as to their use. The Company recognized gains (losses) of approximately $5.3 million, $6.4 million and $(1.9) million on its investments in the accounts associated with the Company’s deferred compensation plans during the years ended December 31, 2020, 2019 and 2018, 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 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 years ended December 31, 2020 and 2019 (see “ Leases ”) . Internal leasing salaries and related costs capitalized for the year ended December 31, 2018 were approximately $5.4 million. 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 indicators of impairment on a quarterly basis 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. This evaluation of the investments 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. The fair value is calculated using discounted cash flows which is subjective and considers 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. 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 6. 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 $104.9 million, $58.4 million and $51.9 million for the years ended December 31, 2020, 2019 and 2018, 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 must make estimates as to the collectability of its accrued rent and accounts receivable related to lease revenue. Management analyzes accrued rent and accounts receivable by considering tenant creditworthiness, current economic trends, including the impact of the novel coronavirus (“COVID-19”) pandemic on tenants’ businesses, and changes in tenants’ payment patterns when evaluating the collectability of the tenant’s receivable balance, including the accrued rent receivable, on a lease-by-lease basis. The Company writes-off the tenant’s receivable balance, including the accrued rent receivable, if the Company considers the balances no longer probable of collection. 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 the balances are considered no longer probable of collection and therefore written off, the Company will cease to recognize lease income, including straight-line rent, unless cash is received (See Note 4). 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. 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. 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 $6.5 million, $20.9 million and $23.8 million for the years ended December 31, 2020, 2019 and 2018, 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 2021 $ 3,019 $ 6,193 2022 354 5,437 2023 183 5,296 2024 135 3,780 2025 135 3,775 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 “ Leases” ). The Company 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. Leases Lessee For leases in which the Company is the lessee (generally ground leases), in accordance with ASC 842 the Company recognizes a right-of-use asset and a lease liability. The Company made the policy election to not apply the revenue recognition requirements of ASC 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. The lease liability is equal to the present value of the minimum lease payments in accordance with ASC 842. The Company will use its 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 exceeding 31 years, • 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. Lessor The Company leases primarily Class A office, life sciences, 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. Per ASC 842, lessors do not need to separate nonlease components from the associated lease component if certain criteria stated above are met for each class of underlying assets. The guidance in ASC 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, the 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, life sciences, 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 January 1, 2019 adoption of ASC 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. 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 . The Company recognizes these reimburseme

Real Estate

Real Estate	12 Months Ended
Real Estate	Dec. 31, 2020
Real Estate [Abstract]
Real Estate	3. Real Estate Boston Properties, Inc. Real estate consisted of the following at December 31, 2020 and December 31, 2019 (in thousands): December 31, 2020 December 31, 2019 Land $ 5,069,206 $ 5,111,606 Right of use assets - finance leases 237,393 237,394 Right of use assets - operating leases 146,406 148,640 Land held for future development (1) 450,954 254,828 Buildings and improvements 13,777,691 13,646,054 Tenant improvements 2,752,880 2,656,439 Furniture, fixtures and equipment 49,606 44,313 Construction in progress 868,773 789,736 Total 23,352,909 22,889,010 Less: Accumulated depreciation (5,534,102) (5,266,798) $ 17,818,807 $ 17,622,212 _______________ (1) Includes pre-development costs. Boston Properties Limited Partnership Real estate consisted of the following at December 31, 2020 and December 31, 2019 (in thousands): December 31, 2020 December 31, 2019 Land $ 4,971,990 $ 5,011,153 Right of use assets - finance leases 237,393 237,394 Right of use assets - operating leases 146,406 148,640 Land held for future development (1) 450,954 254,828 Buildings and improvements 13,498,098 13,351,286 Tenant improvements 2,752,880 2,656,439 Furniture, fixtures and equipment 49,606 44,313 Construction in progress 868,773 789,736 Total 22,976,100 22,493,789 Less: Accumulated depreciation (5,428,576) (5,162,908) $ 17,547,524 $ 17,330,881 _______________ (1) Includes pre-development costs. Developments On March 26, 2020, the Company completed and fully placed in-service 17Fifty Presidents Street located in Reston, Virginia. 17Fifty Presidents Street is a build-to-suit project with approximately 276,000 net rentable square feet of Class A office space that is 100% leased. On June 1, 2020, the Company completed and fully placed in-service 20 CityPoint, a Class A office project with approximately 211,000 net rentable square feet located in Waltham, Massachusetts. The office portion of the property is 100% leased, including a lease with a future commencement. On June 26, 2020, the Company completed the acquisition of real property at 777 Harrison Street (known as Fourth + Harrison and formerly known as 425 Fourth Street) located in San Francisco, California for a gross purchase price, including entitlements, totaling approximately $140.1 million. On July 31, 2020 and December 16, 2020, the Company acquired real property at 759 Harrison Street located in San Francisco, California, which is expected to be included in the Fourth + Harrison development project, for an aggregate purchase price totaling approximately $4.5 million. 759 Harrison Street and Fourth + Harrison are expected to support the development of approximately 850,000 square feet of primarily commercial office space. On August 15, 2020, the Company completed and fully placed in-service The Skylyne, an approximately 331,000 square foot project comprised of 402 residential units and retail space located in Oakland, California. On November 3, 2020, the Company signed an approximately 138,000 square-foot, 10-year lease with a new tenant at 200 West Street in Waltham, Massachusetts. The Company is currently redeveloping a portion of 200 West Street into life sciences space with expected completion in 2021. With this lease, the property is 100% leased. Dispositions 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. As a result of the partner’s deferred contribution, the Company had an initial approximately 55% interest in the joint venture. Future development projects will be owned 49% by the Company and 51% by its partner. Upon the partner’s 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 in the joint venture entity and no longer has a controlling financial or operating interest in the joint venture entity (See Note 6). The Company recognized a gain on the retained and sold interest in the real estate contributed to the joint venture totaling approximately $217.7 million for Boston Properties, Inc. and $222.4 million for Boston Properties Limited Partnership during the year ended December 31, 2020 within Gains on Sales of Real Estate on the respective Consolidated Statements of Operations, as the fair value of the real estate exceeded its carrying value. 601, 611 and 651 Gateway contributed approximately $0.2 million of net income to the Company for the period from January 1, 2020 through January 27, 2020 and contributed approximately $10.4 million and $8.6 million of net income to the Company for the years ended December 31, 2019 and 2018, respectively. On February 20, 2020, the Company completed the sale of New Dominion Technology Park located in Herndon, Virginia for a gross sale price of $256.0 million. Net cash proceeds totaled approximately $254.0 million, resulting in a gain on sale of real estate totaling approximately $192.3 million for Boston Properties, Inc. and approximately $197.1 million for Boston Properties Limited Partnership. New Dominion Technology Park is comprised of two Class A office properties aggregating approximately 493,000 net rentable square feet. New Dominion Technology Park contributed approximately $1.6 million of net income to the Company for the period from January 1, 2020 through February 19, 2020 and contributed approximately $6.8 million and $8.2 million of net income to the Company for the years ended December 31, 2019 and 2018, respectively. On June 25, 2020, the Company completed the sale of a portion of its Capital Gallery property located in Washington, DC for a gross sale price of approximately $253.7 million. Net cash proceeds totaled approximately $246.6 million, resulting in a gain on sale of real estate totaling approximately $203.5 million for Boston Properties, Inc. and approximately $207.0 million for Boston Properties Limited Partnership. Capital Gallery is an approximately 631,000 net rentable square foot Class A office property. The portion sold was comprised of approximately 455,000 net rentable square feet of commercial office space. The Company continues to own the land, underground parking garage and remaining commercial office and retail space containing approximately 176,000 net rentable square feet at the property. The sold portion of Capital Gallery contributed approximately $6.3 million of net income to the Company for the period from January 1, 2020 through June 24, 2020 and contributed approximately $15.0 million and $14.5 million of net income to the Company for the years ended December 31, 2019 and 2018, respectively.

Leases

Leases	12 Months Ended
Leases	Dec. 31, 2020
Leases [Abstract]
Leases of Lessor Disclosure [Text Block]	4. Leases The Company must make estimates as to the collectability of its accrued rent and accounts receivable related to lease revenue. Management analyzes accrued rent and accounts receivable by considering tenant creditworthiness, current economic trends, including the impact of COVID-19 on tenants’ businesses, and changes in tenants’ payment patterns when evaluating the collectability of the tenant’s receivable balance, including the accrued rent receivable, on a lease-by-lease basis. As a result of this analysis, during the year ended December 31, 2020, the Company wrote off approximately $67.7 million, related to accrued rent balances and approximately $22.6 million, related to accounts receivable balances. The write-offs were for tenants, primarily in the retail, entertainment and co-working sectors, that either terminated their leases or that the Company considered their accrued rent and/or accounts receivable balances no longer probable of collection. In April 2020, the FASB staff issued a question and answer document (“Lease Modification Q & A”) related to the application of lease accounting guidance for lease concessions, in accordance with ASC 842, as a result of COVID-19. Under existing lease guidance, the Company would have to determine, on a lease-by-lease basis, if a lease concession was the result of a new arrangement reached with the tenant (treated within the lease modification accounting framework) or if a lease concession was under the enforceable rights and obligations within the existing lease agreement (precluded from applying the lease modification accounting framework). The Lease Modification Q & A allows the Company, if certain criteria have been met, to assume that a lease concession was included within the enforceable rights and obligations of the existing lease agreement and instead elect to either apply the lease modification accounting framework or not, with such election applied consistently to leases with similar characteristics and similar circumstances. The Company did not utilize the guidance provided in the Lease Modification Q & A and instead elected to continue to account for the COVID-19 lease concessions on a lease-by-lease basis in accordance with the existing lease modification accounting framework. Lessee The Company has four non-cancelable ground lease obligations, as lessee, 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 the extension option, 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. The following table provides lease cost information for the Company’s operating and finance leases for the year ended (in thousands): Lease costs December 31, 2020 December 31, 2019 Operating lease costs $ 13,948 $ 14,573 Finance lease costs Amortization of right of use asset (1) $ 56 $ 29 Interest on lease liabilities (2) $ 583 $ 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 for all or a portion of the years ended December 31, 2020 and December 31, 2019, respectively, and as such, a portion of the interest amount was capitalized. The following table provides other quantitative information for the Company’s operating and finance leases as of December 31, 2020 and December 31, 2019: December 31, 2020 December 31, 2019 Other information Weighted-average remaining lease term (in years) Operating leases 51 51 Finance leases 70 71 Weighted-average discount rate Operating leases 5.7 % 5.7 % Finance leases 6.2 % 6.2 % The following table provides a maturity analysis for the Company’s lease liabilities related to its operating and finance leases as of December 31, 2020 (in thousands): Operating Finance 2021 $ 25,092 $ 5,896 2022 18,020 10,206 2023 10,262 9,701 2024 (1) 9,277 48,518 2025 9,476 9,971 Thereafter 548,478 1,373,177 Total lease payments 620,605 1,457,469 Less: Interest portion (418,892) (1,220,977) Present value of lease payments $ 201,713 $ 236,492 _______________ (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 following table summarizes the components of lease revenue recognized during the years ended December 31, 2020 and 2019 included within the Company's Consolidated Statements of Operations (in thousands): Year ended December 31, Lease Revenue 2020 2019 Fixed contractual payments $ 2,211,915 $ 2,261,260 Variable lease payments 434,346 496,754 $ 2,646,261 $ 2,758,014

Deferred Charges

Deferred Charges	12 Months Ended
Deferred Charges	Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Deferred Charges	5. Deferred Charges Deferred charges consisted of the following at December 31, 2020 and 2019 (in thousands): 2020 2019 Leasing costs, including lease related intangibles $ 1,023,058 $ 1,155,958 Financing costs 12,728 12,728 1,035,786 1,168,686 Less: Accumulated amortization (395,701) (479,473) $ 640,085 $ 689,213 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 2021 $ 10,352 2022 5,464 2023 3,854 2024 2,220 2025 2,174

Investments in Unconsolidated J

Investments in Unconsolidated Joint Ventures	12 Months Ended
Investments in Unconsolidated Joint Ventures	Dec. 31, 2020
Investments In Unconsolidated Joint Ventures [Abstract]
Investments In Unconsolidated Joint Ventures	6. Investments in Unconsolidated Joint Ventures The investments in unconsolidated joint ventures consist of the following at December 31, 2020 and December 31, 2019: Carrying Value of Investment (1) Entity Properties Nominal % December 31, December 31, (in thousands) Square 407 Limited Partnership Market Square North 50.0 % $ (3,766) $ (4,872) BP/CRF Metropolitan Square, LLC Metropolitan Square 20.0 % (13,584) 9,134 901 New York, LLC 901 New York Avenue 25.0 % (2) (12,264) (12,113) WP Project Developer LLC Wisconsin Place Land and Infrastructure 33.3 % (3) 35,297 36,789 Annapolis Junction NFM LLC Annapolis Junction 50.0 % (4) 13,463 25,391 540 Madison Venture LLC 540 Madison Avenue 60.0 % (5) 122 2,953 500 North Capitol Venture LLC 500 North Capitol Street, NW 30.0 % (6,945) (5,439) 501 K Street LLC 1001 6th Street 50.0 % (6) 42,499 42,496 Podium Developer LLC The Hub on Causeway - Podium 50.0 % 48,818 49,466 Residential Tower Developer LLC Hub50House 50.0 % 50,943 55,092 Hotel Tower Developer LLC The Hub on Causeway - Hotel Air Rights 50.0 % 10,754 9,883 Office Tower Developer LLC 100 Causeway Street 50.0 % 56,312 56,606 1265 Main Office JV LLC 1265 Main Street 50.0 % 3,787 3,780 BNY Tower Holdings LLC Dock 72 50.0 % 29,536 94,804 BNYTA Amenity Operator LLC Dock 72 50.0 % 1,846 N/A CA-Colorado Center Limited Partnership Colorado Center 50.0 % 227,671 252,069 7750 Wisconsin Avenue LLC 7750 Wisconsin Avenue 50.0 % 58,112 56,247 BP-M 3HB Venture LLC 3 Hudson Boulevard 25.0 % 113,774 67,499 SMBP Venture LP Santa Monica Business Park 55.0 % 145,761 163,937 Platform 16 Holdings LP Platform 16 55.0 % (7) 108,393 29,501 Gateway Portfolio Holdings LLC Gateway Commons 50.0 % (8) 336,206 N/A Rosecrans-Sepulveda Partners 4, LLC Beach Cities Media Campus 50.0 % 27,184 N/A $ 1,273,919 $ 933,223 _______________ (1) Investments with deficit balances aggregating approximately $36.6 million and $22.4 million at December 31, 2020 and 2019, 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. At December 31, 2020 and 2019, the Company’s economic ownership was approximately 50%. (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 two in-service buildings. (5) T he property was sold on June 27, 2019. As of December 31, 2020 and 2019, the investment consisted of undistributed cash. (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). (8) As a result of the partner’s deferred contribution, the Company owns an approximately 55% interest in the joint venture at December 31, 2020. Future development projects will be owned 49% by the Company and 51% by its partner. 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) $ 4,708,571 $ 3,904,400 Other assets 531,071 502,706 Total assets $ 5,239,642 $ 4,407,106 LIABILITIES AND MEMBERS’/PARTNERS’ EQUITY Mortgage and notes payable, net $ 2,637,911 $ 2,218,853 Other liabilities (2) 650,433 749,675 Members’/Partners’ equity 1,951,298 1,438,578 Total liabilities and members’/partners’ equity $ 5,239,642 $ 4,407,106 Company’s share of equity $ 936,087 $ 591,905 Basis differentials (3) 337,832 341,318 Carrying value of the Company’s investments in unconsolidated joint ventures (4) $ 1,273,919 $ 933,223 _______________ (1) At December 31, 2020 and 2019, this amount included right of use assets - finance leases totaling approximately $248.9 million and $383.9 million, respectively, and right of use assets - operating leases totaling approximately $22.5 million and $12.1 million, respectively. (2) At December 31, 2020 and 2019, this amount included lease liabilities - finance leases totaling approximately $388.7 million and $510.8 million, respectively, and lease liabilities - operating leases totaling approximately $29.0 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, 2020 and 2019, there was an aggregate basis differential of approximately $307.3 million and $311.3 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. At December 31, 2020, there was an aggregate basis differential of approximately $51.9 million between the carrying value of the Company’s investment in the joint venture that owns Gateway Commons and the joint venture’s basis in the assets and liabilities. At December 31, 2020, there was an aggregate basis differential of approximately $(52.2) million between the carrying value of the Company’s investment in the joint venture that owns Dock 72 and the joint venture’s basis in the assets and liabilities. These basis differentials (excluding land) will be amortized over the remaining lives of the related assets and liabilities. (4) Investments with deficit balances aggregating approximately $36.6 million and $22.4 million at December 31, 2020 and 2019, respectively, are 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: Year ended December 31, 2020 2019 2018 (in thousands) Total revenue (1) $ 319,560 $ 322,817 $ 271,951 Expenses Operating 144,347 122,992 106,610 Transaction costs 1,027 1,000 — Depreciation and amortization (2) 141,853 102,296 103,079 Total expenses 287,227 226,288 209,689 Other income (expense) Interest expense (98,051) (84,409) (71,308) Gains on sales of real estate (3) 11,737 32,706 16,951 Net income (loss) $ (53,981) $ 44,826 $ 7,905 Company’s share of net income (loss) $ (16,256) $ 24,423 $ 8,084 Impairment loss on investment (4) (60,524) — — Basis differential (3)(4)(5) (8,330) 22,169 (5,862) (Loss) income from unconsolidated joint ventures $ (85,110) $ 46,592 $ 2,222 _______________ (1) Includes straight-line rent adjustments of approximately $(10.1) million, $32.4 million and $15.9 million for the years ended December 31, 2020, 2019 and 2018, respectively. Due primarily to the impact of COVID-19, for the year ended December 31, 2020, write-offs of accounts receivable and accrued rent balances totaled approximately $51.7 million. (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. 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) During the year ended December 31, 2020, the Company recognized an other-than-temporary impairment loss on its investment in the unconsolidated joint venture that owns Dock 72 in Brooklyn, New York totaling approximately $60.5 million. (5) Includes straight-line rent adjustments of approximately $1.8 million, $2.1 million and $2.4 million for the years ended December 31, 2020, 2019 and 2018, respectively. Also includes net above-/below-market rent adjustments of approximately $0.9 million, $1.7 million and $1.6 million for the years ended December 31, 2020, 2019 and 2018, respectively. 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 (See Note 3). 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. As a result of the partner’s deferred contribution, the Company had an initial approximately 55% interest in the joint venture. Future development projects will be owned 49% by the Company and 51% by its partner. On February 20, 2020, a joint venture in which the Company has a 55% interest acquired the land underlying the ground lease at its Platform 16 property located in San Jose, California for a purchase price totaling approximately $134.8 million. The joint venture had previously made a deposit totaling $15.0 million, which was credited against the purchase price. Platform 16 consists of a parcel of land totaling approximately 5.6 acres that is expected to support the development of approximately 1.1 million square feet of commercial office space. On June 9, 2020, a joint venture in which the Company has a 20% interest refinanced with a new lender the mortgage loan collateralized by its Metropolitan Square property located in Washington, DC. The outstanding balance of the loan totaled approximately $155.9 million, bore interest at a fixed rate of 5.75% per annum and was scheduled to mature on August 5, 2020. The new mortgage loan totaling $325.0 million, of which $288.0 million was advanced at closing, bears interest at a variable rate equal to (1) the greater of (x) LIBOR or (y) 0.65%, plus (2) 4.75% per annum, and matures on July 7, 2022, with two, one-year extension options, subject to certain conditions. The joint venture entered into an interest rate cap agreement with a financial institution to limit its exposure to increases in the LIBOR at a cap of 3.00% per annum on a notional amount of $325.0 million through July 7, 2022. The joint venture distributed excess loan proceeds from the new mortgage loan totaling approximately $112.7 million, of which the Company’s share totaled approximately $22.5 million. Metropolitan Square is a Class A office property with approximately 654,000 net rentable square feet. On Jun e 25, 2020, a joint venture in which the Company has a 50% interest completed the sale of Annapolis Junction Building Eight and two land parcels located in Annapolis, Maryland for a gross sale price of $47.0 million. Net cash proceeds totaled approximately $45.8 million after the payment of transaction costs. The Company recognized a gain on sale of real estate totaling approximately $5.8 million, which is included in Income (Loss) from Unconsolidated Joint Ventures in the accompanying Consolidated Statements of Operations. The joint venture distributed approximately $36.8 million of available cash and the net proceeds from the sale after the pay down of the mortgage loan, of which the Company’s share totaled approximately $18.4 million. Annapolis Junction Building Eight is an approximately 126,000 net rentable square foot Class A office property, which is vacant. The two land parcels will support the development of approximately 300,000 square feet of commercial office space with one parcel currently containing surface parking for approximately 511 vehicles. On June 25, 2020, in conjunction with the joint venture’s sale of Annapolis Junction Building Eight, the joint venture in which the Company has a 50% interest modified the mortgage loan collateralized by Annapolis Junction Building Seven and Building Eight with the release of Annapolis Junction Building Eight as collateral under the loan in exchange for a principal pay down of approximately $16.1 million using a portion of the net proceeds from the sale of the property. At the time of the modification, the outstanding balance of the loan totaled approximately $34.5 million, bore interest at a variable rate equal to LIBOR plus 2.35% per annum and was scheduled to mature on June 30, 2020. The modified mortgage loan totaling approximately $18.4 million is collateralized by Annapolis Junction Building Seven, continues to bear interest at a variable rate equal to LIBOR plus 2.35% per annum and matures on March 25, 2021. Annapolis Junction Building Seven is a Class A office property with approximately 127,000 net rentable square feet located in Annapolis, Maryland. On July 23, 2020, the Company acquired a 50% interest in a joint venture entity that owns Beach Cities Media Campus, a 6.4-acre parcel of land located in El Segundo, California, for a purchase price of approximately $21.2 million. Beach Cities Media Campus is expected to support the development of approximately 275,000 square feet of Class A office space. On July 24, 2020, a joint venture in which the Company has a 50% interest completed and fully placed in-service Hub50House, an approximately 320,000 square foot project comprised of 440 residential units located in Boston, Massachusetts. On September 1, 2020, the Company entered into an agreement with its partner in the joint venture that owns 1265 Main Street located in Waltham, Massachusetts to (1) form additional joint ventures to own and develop a mixed-use property containing approximately 1,200,000 square feet to be developed in phases on an approximately 41-acre site adjacent to 1265 Main Street and (2) share the costs of certain offsite infrastructure improvements with its joint venture partner and other third-party abutting land owners. The Company will serve as the development manager and expects to own a 50% interest in each of the joint ventures. On September 30, 2020, a joint venture in which the Company has a 50% interest extended the mortgage loan collateralized by its Market Square North property. At the time of the extension, the outstanding balance of the loan totaled approximately $114.2 million, bore interest at a fixed rate of 4.85% per annum and was scheduled to mature on October 1, 2020. The extended loan was scheduled to mature on November 1, 2020. On October 30, 2020, the joint venture refinanced the mortgage loan. The new mortgage loan totals $125.0 million, bears interest at a variable rate equal to (1) the greater of (x) LIBOR or (y) 0.50%, plus (2) 2.30% per annum, and matures on November 10, 2025, with one, one-year extension option, subject to certain conditions. Market Square North is a Class A office property with approximately 418,000 net rentable square feet. On October 1, 2020, a joint venture in which the Company has a 50% interest completed and fully placed in-service Dock 72, a Class A office project with approximately 669,000 net rentable square feet located in Brooklyn, New York that is 33% leased. During December 2020, the Company recognized a non-cash impairment charge totaling approximately $60.5 million, which represented the other-than temporary decline in the fair value below the carrying value of the Company’s investment in the unconsolidated joint venture that owns Dock 72. The non-cash impairment charge was the result of an increase in costs, an extension of the projected period to fully lease the property and lower projected rental rates due to the COVID-19 pandemic, resulting in a current fair value that was less than the carrying value of the Company’s investment. The Company assessed the impairment and concluded that it was other than temporary. The Company determined that its valuation of the investment was categorized within Level 3 of the fair value hierarchy, as it utilized significant unobservable inputs in its assessment including an exit capitalization rate of 5.25%, a discount rate on the Company’s equity investment (the property is encumbered by mortgage debt) of 8.0% and an average lease commencement on currently vacant space of mid-2023. In addition, on December 14, 2020, the joint venture extended the mortgage loan collateralized by the property. At the time of the extension, the outstanding balance of the loan totaled approximately $198.6 million, bore interest at a variable rate equal to LIBOR plus 2.25% per annum and was scheduled to mature on December 18, 2020. The extended mortgage loan has a total commitment amount of $250.0 million, bears interest at an initial variable rate equal to (1) the greater of (x) LIBOR or (y) 0.25%, plus (2) 2.85% per annum and matures on December 18, 2023. On November 13, 2020, a joint venture in which the Company has a 50% interest extended the mortgage loan collateralized by its Annapolis Junction Building Six property located in Annapolis, Maryland. At the time of the extension, the outstanding balance of the loan totaled approximately $12.0 million, bore interest at a variable rate equal to LIBOR plus 2.00% per annum and was scheduled to mature on November 17, 2020. The extended mortgage loan has a total commitment amount of approximately $13.2 million, bears interest at a variable rate equal to (1) the greater of (x) LIBOR or (y) 0.50%, plus (2) 2.50% per annum and matures on November 16, 2021. Annapolis Junction Building Six is a Class A office property with approximately 119,000 net rentable square feet.

Mortgage Notes Payable, Net

Mortgage Notes Payable, Net	12 Months Ended
Mortgage Notes Payable, Net	Dec. 31, 2020
Debt Disclosure [Abstract]
Mortgage Notes Payable Disclosure	7. Mortgage Notes Payable, Net The Company had outstanding mortgage notes payable totaling approximately $2.9 billion as of December 31, 2020 and 2019, 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 at December 31, 2020 and 2019, with contractual interest rates ranging from 3.43% to 6.94% per annum at December 31, 2020 and 2019 (with a weighted-average interest rate of 3.72% and 3.73% per annum at December 31, 2020 and 2019, respectively). There were no variable rate mortgage loans at December 31, 2020 and 2019. Contractual aggregate principal payments of mortgage notes payable at December 31, 2020 are as follows (in thousands): Principal Payments 2021 $ 17,276 2022 614,710 2023 — 2024 — 2025 — Thereafter 2,300,000 Total aggregate principal payments 2,931,986 Deferred financing costs, net (22,905) Total carrying value of mortgage notes payable, net $ 2,909,081

Unsecured Senior Notes

Unsecured Senior Notes	12 Months Ended
Unsecured Senior Notes	Dec. 31, 2020
Debt Disclosure [Abstract]
Unsecured Senior Notes	8. Unsecured Senior Notes The following summarizes the unsecured senior notes outstanding as of December 31, 2020 (dollars in thousands): Coupon/ Effective Principal Maturity Date(2) 10 Year Unsecured Senior Notes 4.125 % 4.289 % $ 850,000 May 15, 2021 (3) 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 10.75 Year Unsecured Senior Notes 3.250 % 3.343 % 1,250,000 January 30, 2031 Total principal 9,700,000 Net unamortized discount (16,034) Deferred financing costs, net (44,679) Total $ 9,639,287 _______________ (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. (3) See Note 18. On May 5, 2020, Boston Properties Limited Partnership completed a public offering of $1.25 billion in aggregate principal amount of its 3.250% unsecured senior notes due 2031. The notes were priced at 99.850% of the principal amount to yield an effective rate (including financing fees) of approximately 3.343% per annum to maturity. The notes will mature on January 30, 2031, unless earlier redeemed. The aggregate net proceeds from the offering were approximately $1.24 billion, after deducting underwriting discounts and transaction expenses.

Unsecured Credit Facility

Unsecured Credit Facility	12 Months Ended
Unsecured Credit Facility	Dec. 31, 2020
Line of Credit Facility [Abstract]
Unsecured line of Credit	9. 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 0.95% 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, 2020 credit rating, (1) the applicable Eurocurrency margins for the Revolving Facility and Delayed Draw Facility are 0.875% and 0.95% per annum, 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 0.15% per annum. At December 31, 2020 and 2019, Boston Properties Limited Partnership had $500.0 million of borrowings outstanding under its Delayed Draw Facility and no amounts outstanding under its Revolving Facility.

Commitments And Contingencies

Commitments And Contingencies	12 Months Ended
Commitments And Contingencies	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments And Contingencies	10. 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 $20.0 million at December 31, 2020. 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. 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, 2020, the maximum funding obligation under the guarantee was approximately $30.6 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, 2020, 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 provided a financing guaranty as required with respect to the 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 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. An affiliate of The Bernstein Companies exercised its option to borrow $10.0 million from the Company under such agreements, which financing was provided by the Company on June 1, 2020. The financing bears interest at a fixed rate of 8.00% per annum, compounded monthly, and matures on the fifth anniversary of the date on which the base building of the affiliate of The Bernstein Companies’ hotel property is substantially completed. The financing is collateralized by a pledge of the partner’s equity interest in the joint venture that owns and is developing 7750 Wisconsin Avenue . 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, 2020, 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, 2020, no amounts related to the contingent aspect of the guarantee are recorded as a liability in the Company’s consolidated financial statements. 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, which is expected to occur during the third quarter of 2022. 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. 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 2020, the Company received a distribution totaling approximately $0.1 million. During the years 2014 through 2018, the Company received distributions aggregating approximately $18.0 million, leaving a remaining claim of approximately $27.1 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, 2020. 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.” The program trigger is $200 million, the coinsurance is 20% and the deductible is 20% of the premiums earned by the insurer for the year prior to a claim. 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. Due to the current COVID-19 pandemic, the Company anticipates the possibility of business interruption, loss of lease revenue and/or other associated expenses related to the Company’s operations across its portfolio. Because this is an ongoing situation it is not yet possible to quantify the Company’s losses and expenses, which continue to develop. Because of the complexity of the Company’s insurance policies and limited precedent for claims being made related to pandemics, it is not yet possible to determine if such losses and expenses will be covered by the Company’s insurance policies. Therefore, at this time, the Company is providing notice to the applicable insurers of the potential for claims in order to protect the Company’s rights under its policies. The Company continues to monitor the state of the insurance market in general, and the scope and costs of coverage for acts of terrorism, California earthquake risk and pandemics, 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. For example, 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 contractual limitations, including time limits, 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 vapor intrusion concerns and/or potential contaminant migration to or from the subject property in groundwater, assess potential liability risks and estimate the costs of required response actions and special handling procedures 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, 2020
Noncontrolling Interest [Abstract]
Noncontrolling Interests	11. 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, 2020, the noncontrolling interests in Boston Properties Limited Partnership consisted of 16,037,121 OP Units, 1,336,115 LTIP Units (including 105,080 2012 OPP Units, 64,468 2013 MYLTIP Units, 23,100 2014 MYLTIP Units, 24,966 2015 MYLTIP Units, 89,791 2016 MYLTIP Units and 116,078 2017 MYLTIP Units), 336,195 2018 MYLTIP Units, 219,916 2019 MYLTIP Units and 203,278 2020 MYLTIP Units held by parties other than Boston Properties, Inc. Noncontrolling Interest—Common Units During the years ended December 31, 2020 and 2019, 856,811 and 144,481 OP Units, respectively, were presented by the holders for redemption (including 88,168 and 92,678 OP Units, respectively, issued upon conversion of LTIP Units, 2012 OPP Units and 2013 - 2017 MYLTIP Units) and were redeemed by Boston Properties, Inc. in exchange for an equal number of shares of Common Stock. At December 31, 2020, Boston Properties Limited Partnership had outstanding 336,195 2018 MYLTIP Units, 219,916 2019 MYLTIP Units and 203,278 2020 MYLTIP Units. Prior to the applicable measurement date (February 5, 2021 for 2018 MYLTIP Units (See Note 18), February 4, 2022 for 2019 MYLTIP Units and February 3, 2023 for 2020 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 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. 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. The following table presents Boston Properties Limited Partnership’s distributions on the OP Units and LTIP Units (including the 2012 OPP Units, 2013 - 2016 MYLTIP Units and, after the February 6, 2020 measurement date, the 2017 MYLTIP Units) and its distributions on the 2017 MYLTIP Units (prior to the February 6, 2020 measurement date) and 2018 - 2020 MYLTIP Units (after the February 4, 2020 issuance date) that occurred during the year ended December 31, 2020: Record Date Payment Date Distributions per OP Unit and LTIP Unit Distributions per MYLTIP Unit December 31, 2020 January 28, 2021 $0.98 $0.098 September 30, 2020 October 30, 2020 $0.98 $0.098 June 30, 2020 July 31, 2020 $0.98 $0.098 March 31, 2020 April 30, 2020 $0.98 $0.098 December 31, 2019 January 30, 2020 $0.98 $0.098 The following table presents Boston Properties Limited Partnership’s distributions on the OP Units and LTIP Units (including the 2012 OPP Units, 2013 - 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) and 2017 - 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 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 and 2013 - 2017 MYLTIP Units) assuming that all conditions had been met for the conversion thereof) had all of such units been redeemed at December 31, 2020 was approximately $1.6 billion based on the last reported price of a share of Common Stock on the New York Stock Exchange of $94.53 per share on December 31, 2020. 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, 2020 and 2019, are included in Noncontrolling Interests—Property Partnerships on the accompanying Consolidated Balance Sheets. On April 1, 2019, the Company completed the acquisition of its partner’s 5% ownership interest and promoted profits interest in the consolidated entity that owns Salesforce Tower located in San Francisco, California 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. 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.

Stockholders' Equity _ Partners

Stockholders' Equity / Partners' Capital	12 Months Ended
Stockholders' Equity / Partners' Capital	Dec. 31, 2020
Equity [Abstract]
Stockholders' Equity / Partners' Capital	12. Stockholders’ Equity / Partners’ Capital Boston Properties, Inc. As of December 31, 2020, Boston Properties, Inc. had 155,718,825 shares of Common Stock outstanding. As of December 31, 2020, Boston Properties, Inc. owned 1,730,921 general partnership units and 153,987,904 limited partnership units in Boston Properties Limited Partnership. On May 22, 2020, 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. Under the ATM stock offering program, Boston Properties, Inc. may also engage in forward sale transactions with affiliates of certain sales agents for the sale of its Common Stock on a forward basis. This program replaced Boston Properties, Inc.’s prior $600.0 million ATM stock offering program that was scheduled to expire on June 2, 2020. Boston Properties, Inc. 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 years ended December 31, 2020 and 2019, Boston Properties, Inc. issued 43,792 and 145,088 shares of Common Stock, respectively, upon the exercise of options to purchase Common Stock. During the years ended December 31, 2020 and 2019, Boston Properties, Inc. issued 856,811 and 144,481 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 declared in 2020 and during the year ended December 31, 2019: Record Date Payment Date Dividend (Per Share) Distribution (Per Unit) December 31, 2020 January 28, 2021 $0.98 $0.98 September 30, 2020 October 30, 2020 $0.98 $0.98 June 30, 2020 July 31, 2020 $0.98 $0.98 March 31, 2020 April 30, 2020 $0.98 $0.98 December 31, 2019 January 30, 2020 $0.98 $0.98 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 Preferred Stock As of December 31, 2020, 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 have the right to 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 declared during 2020 and during the year ended December 31, 2019: Record Date Payment Date Dividend (Per Share) February 5, 2021 February 16, 2021 $32.8125 November 4, 2020 November 16, 2020 $32.8125 August 3, 2020 August 17, 2020 $32.8125 May 1, 2020 May 15, 2020 $32.8125 February 4, 2020 February 18, 2020 $32.8125 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

Segment Information

Segment Information	12 Months Ended
Segment Information	Dec. 31, 2020
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, 2020, 2019 and 2018. Boston Properties, Inc. Year ended December 31, 2020 2019 2018 (in thousands) Net income attributable to Boston Properties, Inc. common shareholders $ 862,227 $ 511,034 $ 572,347 Add: Preferred dividends 10,500 10,500 10,500 Noncontrolling interest—common units of the Operating Partnership 97,704 59,345 66,807 Noncontrolling interests in property partnerships 48,260 71,120 62,909 Interest expense 431,717 412,717 378,168 Loss from early extinguishment of debt — 29,540 16,490 Impairment loss — 24,038 11,812 Net operating income from unconsolidated joint ventures 94,943 97,716 79,893 Depreciation and amortization expense 683,751 677,764 645,649 Transaction costs 1,531 1,984 1,604 Payroll and related costs from management services contracts 11,626 10,386 9,590 General and administrative expense 133,112 140,777 121,722 Less: Net operating income attributable to noncontrolling interests in property partnerships 162,887 183,989 177,365 Gains (losses) from investments in securities 5,261 6,417 (1,865) Interest and other income (loss) 5,953 18,939 10,823 Gains on sales of real estate 618,982 709 182,356 Income (loss) from unconsolidated joint ventures (85,110) 46,592 2,222 Direct reimbursements of payroll and related costs from management services contracts 11,626 10,386 9,590 Development and management services revenue 29,641 40,039 45,158 Company’s share of Net Operating Income $ 1,626,131 $ 1,739,850 $ 1,551,842 Boston Properties Limited Partnership Year ended December 31, 2020 2019 2018 (in thousands) Net income attributable to Boston Properties Limited Partnership common unitholders $ 979,979 $ 580,102 $ 656,903 Add: Preferred distributions 10,500 10,500 10,500 Noncontrolling interests in property partnerships 48,260 71,120 62,909 Interest expense 431,717 412,717 378,168 Loss from early extinguishment of debt — 29,540 16,490 Impairment loss — 22,272 10,181 Net operating income from unconsolidated joint ventures 94,943 97,716 79,893 Depreciation and amortization expense 676,666 669,956 637,891 Transaction costs 1,531 1,984 1,604 Payroll and related costs from management services contracts 11,626 10,386 9,590 General and administrative expense 133,112 140,777 121,722 Less: Net operating income attributable to noncontrolling interests in property partnerships 162,887 183,989 177,365 Gains (losses) from investments in securities 5,261 6,417 (1,865) Interest and other income (loss) 5,953 18,939 10,823 Gains on sales of real estate 631,945 858 190,716 Income (loss) from unconsolidated joint ventures (85,110) 46,592 2,222 Direct reimbursements of payroll and related costs from management services contracts 11,626 10,386 9,590 Development and management services revenue 29,641 40,039 45,158 Company’s share of Net Operating Income $ 1,626,131 $ 1,739,850 $ 1,551,842 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, loss from early extinguishment of debt, impairment loss, 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 (loss), gains on sales of real estate, income (loss) 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. The Company’s internal reporting utilizes its share of NOI, which includes its share of NOI from consolidated and unconsolidated joint ventures, which is a non-GAAP financial measure that is calculated as the consolidated amount, plus the Company’s share of the amount from the Company’s unconsolidated joint ventures (calculated based upon the Company’s economic percentage ownership interest and, in some cases, after priority allocations), minus the Company’s partners’ share of the amount from the Company’s consolidated joint ventures (calculated based upon the partners’ economic percentage ownership interests and, in some cases, after priority allocations, income allocation to private REIT shareholders and their share of fees due to the Company). The Company’s share of NOI from unconsolidated joint ventures does not include impairment losses on its investments in unconsolidated joint ventures or its share of gains on sales of real estate from unconsolidated joint ventures, both of which are included within Income From Unconsolidated Joint Ventures in the Company’s Consolidated Statements of Operations. Management utilizes its share of NOI in assessing its performance as the Company has several significant joint ventures and, in some cases, the Company exercises significant influence over, but does not control, the joint venture, in which case GAAP requires that the Company account for the joint venture entity using the equity method of accounting and the Company does not consolidate it for financial reporting purposes. In other cases, GAAP requires that the Company consolidate the venture even though the Company’s partner(s) owns a significant percentage interest. As a result, the presentations of the Company’s share of NOI should not be considered a substitute for, and should only be considered together with and as a supplement to, the Company’s financial information presented in accordance with GAAP. 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, loss from early extinguishment of debt, impairment loss, 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 (loss), gains on sales of real estate, income (loss) from unconsolidated joint ventures, 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. Included within the Office property type are commercial office and retail leases, as well as parking revenue. Upon the adoption of ASC 842, any write-off for bad debt, including accrued rent, will be recorded as a reduction to lease revenue. As a result of COVID-19, during the year ended December 31, 2020, the Company wrote off approximately $67.7 million related to accrued rent balances and approximately $22.6 million related to accounts receivable balances. The write-offs were for tenants, primarily in the retail, entertainment and co-working sectors, that either terminated their leases or that the Company considered their accrued rent and/or accounts receivable balances no longer probable of collection. In addition, parking and other revenue for the year ended December 31, 2020 decreased by approximately $32.9 million compared to 2019. These decreases were primarily in transient and monthly parking revenue. The degree to which the Company’s commercial and retail tenants’ and parking operators’ businesses are, or will continue to be, negatively impacted by COVID-19, including by measures intended to reduce its spread, such as mandatory business closures and “stay-at-home” orders, could result in a reduction in the Company’s cash flows or require that the Company write off additional accrued rent and/or accounts receivable balances, and this could have a material adverse effect on lease revenue and thus the results of the Company’s Office property type. The Boston Marriott Cambridge closed in March 2020 due to COVID-19. The hotel re-opened on October 2, 2020 and has been operating at a diminished occupancy due to the continued impacts that COVID-19 has had on business and leisure travel. The closing of the hotel for more than two fiscal quarters, weak demand and low occupancy since its re-opening, have had, and are expected to continue to have, a material adverse effect on the hotel’s operations and thus the results of the Company’s Hotel property type. Information by geographic area and property type (dollars in thousands): For the year ended December 31, 2020: Boston Los Angeles New York San Francisco Washington, DC Total Rental Revenue: (1) Office $ 897,915 $ — $ 935,966 $ 508,327 $ 336,587 $ 2,678,795 Residential 13,616 — — 155 24,375 38,146 Hotel 7,478 — — — — 7,478 Total 919,009 — 935,966 508,482 360,962 2,724,419 % of Grand Totals 33.73 % — % 34.36 % 18.66 % 13.25 % 100.00 % Rental Expenses: Office 318,509 — 384,753 163,156 132,051 998,469 Residential 5,378 — — 2,261 11,100 18,739 Hotel 13,136 — — — — 13,136 Total 337,023 — 384,753 165,417 143,151 1,030,344 % of Grand Totals 32.71 % — % 37.35 % 16.05 % 13.89 % 100.00 % Net operating income $ 581,986 $ — $ 551,213 $ 343,065 $ 217,811 $ 1,694,075 % of Grand Totals 34.35 % — % 32.54 % 20.25 % 12.86 % 100.00 % Less: Net operating income attributable to noncontrolling interests in property partnerships (41,849) — (121,038) — — (162,887) Add: Company’s share of net operating income from unconsolidated joint ventures 10,765 57,907 (5,326) 14,928 16,669 94,943 Company’s share of net operating income $ 550,902 $ 57,907 $ 424,849 $ 357,993 $ 234,480 $ 1,626,131 % of Grand Totals 33.88 % 3.56 % 26.12 % 22.02 % 14.42 % 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, 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.

Earnings Per Share _ Common Uni

Earnings Per Share / Common Unit	12 Months Ended
Earnings Per Share / Common Unit	Dec. 31, 2020
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 and 2013 - 2017 MYLTIP Units required, and the 2018 - 2020 MYLTIP Units require, Boston Properties, Inc. to outperform absolute and/or 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. Year ended December 31, 2020 Income Shares Per Share (in thousands, except for per share amounts) Basic Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 862,227 155,432 $ 5.55 Allocation of undistributed earnings to participating securities (748) — (0.01) Net income attributable to Boston Properties, Inc. common shareholders $ 861,479 155,432 $ 5.54 Effect of Dilutive Securities: Stock Based Compensation — 85 — Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 861,479 155,517 $ 5.54 Year ended December 31, 2019 Income Shares Per Share (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 Year ended December 31, 2018 Income Shares Per Share (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 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 and 2013 - 2017 MYLTIP Units required, and the 2018 - 2020 MYLTIP Units require, Boston Properties, Inc. to outperform absolute and/or 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 17,211,000 and 17,618,000 and 17,485,000 redeemable common units for the years ended December 31, 2020, 2019 and 2018, respectively. Year ended December 31, 2020 Income Units Per Unit (in thousands, except for per unit amounts) Basic Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 979,979 172,643 $ 5.68 Allocation of undistributed earnings to participating securities (830) — (0.01) Net income attributable to Boston Properties Limited Partnership common unitholders $ 979,149 172,643 $ 5.67 Effect of Dilutive Securities: Stock Based Compensation — 85 — Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 979,149 172,728 $ 5.67 Year ended December 31, 2019 Income Units Per Unit (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 Year ended December 31, 2018 Income Units Per Unit (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

Employee Benefits Plan

Employee Benefits Plan	12 Months Ended
Employee Benefits Plan	Dec. 31, 2020
Disclosure Text Block Supplement [Abstract]
Employee Benefit Plans	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 ($285,000, $280,000 and $275,000 in 2020, 2019 and 2018, respectively), indexed for inflation) with no vesting requirement. The Company’s aggregate matching contribution for the years ended December 31, 2020, 2019 and 2018 was approximately $4.0 million, $4.2 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, 2020 and 2019, the Company had maintained approximately $38.6 million and $36.0 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, 2020 and 2019 was approximately $38.6 million and $36.0 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, 2020
Share-based Payment Arrangement [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 4, 2020, Boston Properties, Inc.’s Compensation Committee granted the 2020 MYLTIP awards under the Boston Properties, Inc.’s 2012 Stock Option and Incentive Plan (the “2012 Plan”) to certain officers and employees of Boston Properties, Inc. The 2020 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 range from zero to a maximum of 203,278 LTIP Units depending on Boston Properties, Inc.’s TSR relative to the FTSE Russell 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. Earned awards (if any) will vest 50% on February 3, 2023 and 50% on February 3, 2024, 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 3, 2023, earned awards will be calculated based on TSR performance up to the date of the change of control. The 2020 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, the 2020 MYLTIP awards have an aggregate value of approximately $13.7 million, which amount will generally be amortized into earnings under the graded vesting method. 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 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. Boston Properties, Inc. issued 29,630, 26,503 and 20,320 shares of restricted common stock and Boston Properties Limited Partnership issued 207,181, 181,919 and 205,838 LTIP Units to employees and non-employee directors under the 2012 Plan during the years ended December 31, 2020, 2019 and 2018, respectively. Boston Properties, Inc. did not issue any non-qualified stock options under the 2012 Plan during the years ended December 31, 2020, 2019 and 2018. Boston Properties Limited Partnership issued 203,278 2020 MYLTIP Units, 220,734 2019 MYLTIP Units and 342,659 2018 MYLTIP Units to employees under the 2012 Plan during the years ended December 31, 2020, 2019 and 2018, respectively. Employees and non-employee directors paid $0.01 per share of restricted common stock and $0.25 per LTIP 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 of Boston Properties, Inc. and Boston Properties Limited Partnership. A majority of the grants of restricted common stock and LTIP Units to employees vest in 4 equal annual installments. Restricted common 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. Because the 2012 OPP Units and 2013 - 2020 MYLTIP Units are subject to both a service condition and a market condition, the Company recognizes the related compensation expense 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, LTIP Units and 2015 - 2020 MYLTIP Units was approximately $43.0 million, $39.8 million and $38.0 million for the years ended December 31, 2020, 2019 and 2018, respectively. At December 31, 2020, there was (1) an aggregate of approximately $25.4 million of unrecognized compensation expense related to unvested restricted stock and LTIP Units and (2) an aggregate of approximately $10.3 million of unrecognized compensation expense related to unvested 2018 - 2020 MYLTIP Units that is expected to be recognized over a weighted-average period of approximately 2.1 years. The shares of restricted stock were valued at approximately $4.0 million ($133.81 per share weighted-average), $3.5 million ($131.27 per share weighted-average) and $2.4 million ($119.27 per share weighted-average) for the years ended December 31, 2020, 2019 and 2018, 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, 2020, 2019 and 2018 were valued at approximately $26.3 million, $22.1 million and $22.7 million, respectively. The weighted-average per unit fair value of LTIP Unit grants in 2020, 2019 and 2018 was $127.14, $121.50 and $110.29, respectively. The per unit fair value of each LTIP Unit granted in 2020, 2019 and 2018 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 1.47%, 2.68% and 2.63% and an expected price volatility of 18.0%, 27.0% and 27.0%, respectively. There were no non-qualified stock options granted during the years ended December 31, 2020, 2019 and 2018. A summary of the status of Boston Properties, Inc.’s stock options as of December 31, 2020, 2019 and 2018 and changes during the years then ended are presented below: Shares Weighted-Average 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 Exercised (43,792) $ 91.60 Outstanding at December 31, 2020 351,561 $ 96.97 The following table summarizes information about Boston Properties, Inc.’s stock options outstanding at December 31, 2020: Options Outstanding Options Exercisable Number Outstanding at 12/31/20 Weighted-Average Remaining Number Exercisable at 12/31/20 Exercise Price 54,003 0.1 years $ 86.86 54,003 $ 86.86 54,282 2.3 years $ 95.69 54,282 $ 95.69 133,834 2.1 years $ 98.46 133,834 $ 98.46 109,442 1.1 years $ 100.77 109,442 $ 100.77 The total intrinsic value of the outstanding and exercisable stock options as of December 31, 2020 was approximately $0.4 million. In addition, Boston Properties, Inc. had 395,353 and 540,441 options exercisable at a weighted-average exercise price of $96.37 and $96.35 at December 31, 2019 and 2018, respectively. 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 7,195, 5,862 and 6,268 shares with the weighted-average purchase price equal to $90.53 per share, $104.11 per share and $107.20 per share under the Stock Purchase Plan during the years ended December 31, 2020, 2019 and 2018, respectively.

Related Party Disclosures

Related Party Disclosures	12 Months Ended
Related Party Disclosures	Dec. 31, 2020
Related Party Transactions [Abstract]
Related Party Transactions Disclosure	17. Related Party Transactions A fir m controlled by Mr. Raymond A. Ritchey’s brother was paid aggregate leasing commissions of approximately $914,000, $21,000 and $921,000 during the years ended December 31, 2020, 2019 and 2018, respectively, related to certain exclusive leasing arrangements for certain Northern Virginia properties. In addition, Mr. Ritchey’s brother is employed by a real estate brokerage firm and participated in brokerage activities for which the Company paid the firm approximately $3.4 million and $2.6 million for the years ended December 31, 2020 and 2019, respectively. Mr. Ritchey’s brother did not participate in brokerage activities related to such arrangement during the year ended December 31, 2018. 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 2020. 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 non-employee director compensation program provides, 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, 2020 and 2019, the Company had maintained approximately $0.8 million and $0.7 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 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, 2020 and 2019 was approximately $0.8 million and $0.7 million, respectively, which is included in the accompanying Consolidated Balance Sheets. The terms of the non-employee director compensation program require the classification of these deferred stock units as temporary equity on the Consolidated Balance Sheets of Boston Properties, Inc. and Boston Properties Limited Partnership within Redeemable Deferred Stock Units. 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. At December 31, 2020 and 2019, Boston Properties, Inc. had outstanding 72,966 and 60,676 deferred stock units, respectively.

Subsequent Events

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2020
Subsequent Events [Abstract]
Subsequent Events	18. Subsequent Events On January 29, 2021 and February 2, 2021, Boston Properties, Inc. issued an aggregate of 33,449 shares of restricted Common Stock and Boston Properties Limited Partnership issued an aggregate of 263,527 LTIP Units under the 2012 Plan to certain employees of Boston Properties, Inc. On February 2, 2021, Boston Properties, Inc.’s Compensation Committee approved the 2021 Multi-Year Long-Term Incentive Program (the “2021 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 352,021 LTIP Units depending on Boston Properties, Inc.’s relative and absolute TSR performance with a target of approximately 176,009 LTIP Units. Under ASC 718, the 2021 MYLTIP awards have an aggregate value of approximately $15.3 million. On February 5, 2021, the measurement period for the Company’s 2018 MYLTIP awards ended and, based on Boston Properties, Inc.’s relative TSR performance, the final awards were determined to be 29.2% of target, or an aggregate of approximately $4.6 million (after giving effect to employee separations). As a result, an aggregate of 285,925 2018 MYLTIP Units that had been previously granted were automatically forfeited.

SEC Schedule, Article 12-28, Re

SEC Schedule, Article 12-28, Real Estate and Accumulated Depreciation	12 Months Ended
	Dec. 31, 2020
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, 2020 (dollars in thousands) Property Name Type Location Encumbrances Original Costs Land and Improvements Building and Land Development Total Accumulated Year(s) Built/ Year(s) Acquired Depreciable Land Building 767 Fifth Avenue (the General Motors Building) Office New York, NY $ 2,277,522 $ 1,796,252 $ 1,532,654 $ 227,450 $ 1,796,252 $ 1,760,104 $ — $ — $ 3,556,356 $ 364,145 1968/2019 2013 (1) Prudential Center Office Boston, MA — 92,077 948,357 573,187 115,638 1,480,302 17,681 — 1,613,621 634,402 1965/1993/2002/2016-2017 1998/1999/2000 (1) Embarcadero Center Office San Francisco, CA — 179,697 847,410 469,860 195,987 1,300,980 — — 1,496,967 680,507 1970/1989 1998-1999 (1) 399 Park Avenue Office New York, NY — 339,200 700,358 340,960 354,107 1,026,411 — — 1,380,518 387,217 1961/2018 2002 (1) 601 Lexington Avenue Office New York, NY 630,068 241,600 494,782 446,950 289,639 663,694 — 229,999 1,183,332 284,477 1977/1997 2001 (1) Salesforce Tower Office San Francisco, CA — 200,349 946,205 5,355 200,349 951,560 — — 1,151,909 68,918 2018 2013 (1) 200 Clarendon Street and Garage Office Boston, MA — 219,543 667,884 218,821 251,374 854,874 — — 1,106,248 244,882 1976 2010 (1) 250 West 55th Street Office New York, NY — 285,263 603,167 51,860 285,263 655,027 — — 940,290 138,004 2014 2007 (1) 100 Federal Street Office Boston, MA — 131,067 435,954 111,196 131,067 547,150 — — 678,217 141,629 1971-1975/2017 2012 (1) Times Square Tower Office New York, NY — 165,413 380,438 108,206 169,193 484,864 — — 654,057 217,845 2004 2000 (1) Carnegie Center Office Princeton, NJ — 142,666 316,856 153,797 94,240 463,959 55,120 — 613,319 221,323 1983-2016 1998/1999/2000/2007/2014/2017/2019 (1) Atlantic Wharf Office Boston, MA — 63,988 454,537 18,538 63,988 473,075 — — 537,063 146,860 2011 2007 (1) 599 Lexington Avenue Office New York, NY — 81,040 100,507 214,275 87,852 307,970 — — 395,822 193,058 1986 1997 (1) 510 Madison Avenue Office New York, NY — 103,000 253,665 28,446 103,000 282,111 — — 385,111 81,517 2012 2010 (1) Fountain Square Office Reston, VA — 56,853 306,298 21,030 56,853 327,328 — — 384,181 90,047 1986-1990 2012 (1) 680 Folsom Street Office San Francisco, CA — 72,545 219,766 7,917 72,545 227,683 — — 300,228 55,319 2014 2012 (1) 145 Broadway Office Cambridge, MA — 121 273,013 25,712 23,367 275,479 — — 298,846 9,941 2019 1997 (1) 2200 Pennsylvania Avenue Office Washington, DC — — 183,541 112,436 107,356 188,621 — — 295,977 66,072 2011 2008 (1) South of Market and Democracy Tower Office Reston, VA — 13,603 237,479 41,163 13,687 278,558 — — 292,245 107,358 2008-2009 2003 (1) 601 Massachusetts Avenue Office Washington, DC — 95,310 165,173 3,945 95,322 169,106 — — 264,428 30,743 2016 2008 (1) Bay Colony Corporate Center Office Waltham, MA — 18,789 148,451 81,302 18,789 229,753 — — 248,542 89,232 1985-1989 2011 (1) 535 Mission Street Office San Francisco, CA — 40,933 148,378 3,287 40,933 151,665 — — 192,598 31,953 2015 2013 (1) Mountain View Research Park Office Mountain View, CA — 95,066 68,373 18,479 95,066 86,852 — — 181,918 21,725 1977-1981/2007-2013 2013 (1) Reservoir Place Office Waltham, MA — 18,605 104,124 57,154 20,108 159,775 — — 179,883 76,993 1955/1987/2017 1997/1998 (1) 1330 Connecticut Avenue Office Washington, DC — 25,982 82,311 37,049 27,135 118,207 — — 145,342 38,000 1984/2018 2004 (1) One Freedom Square Office Reston, VA — 9,929 84,504 39,884 11,293 123,024 — — 134,317 62,808 2000 2003 (1) Kingstowne Towne Center Office Alexandria, VA — 18,021 109,038 3,299 18,062 112,296 — — 130,358 46,469 2003-2006 2007 (1) Boston Properties, Inc. Schedule 3—Real Estate and Accumulated Depreciation December 31, 2020 (dollars in thousands) Property Name Type Location Encumbrances Original Costs Land and Improvements Building and Land Development Total Accumulated Year(s) Built/ Year(s) Acquired Depreciable Land Building One and Two Reston Overlook Office Reston, VA — 16,456 66,192 46,762 16,179 113,231 — — 129,410 57,441 1999 2000 (1) Weston Corporate Center Office Weston, MA — 25,753 92,312 (5) 25,854 92,206 — — 118,060 32,278 2010 2001 (1) Two Freedom Square Office Reston, VA — 13,930 77,739 25,510 15,420 101,759 — — 117,179 53,885 2001 2003 (1) 17Fifty Presidents Street Office Reston, VA — — 113,362 — — 113,362 — — 113,362 3,466 2020 2013 (1) 140 Kendrick Street Office Needham, MA — 18,095 66,905 26,458 19,092 92,366 — — 111,458 35,918 2000 2004 (1) Discovery Square Office Reston, VA — 11,198 71,782 20,742 12,533 91,189 — — 103,722 45,920 2001 2003 (1) 355 Main Street Office Cambridge, MA — 18,863 53,346 27,593 21,173 78,629 — — 99,802 29,479 1981/1996/2013 2006 (1) 880 & 890 Winter Street Office Waltham, MA — 29,510 65,812 1,367 29,510 66,561 618 — 96,689 5,706 1998-1999 2019 (1) 10 CityPoint Office Waltham, MA — 1,953 85,752 4,744 2,290 90,159 — — 92,449 14,073 2016 1997 (1) 90 Broadway Office Cambridge, MA — 19,104 52,078 18,077 20,785 68,474 — — 89,259 24,200 1983/1998/2013 2006 (1) 230 CityPoint Office Waltham, MA — 13,189 49,823 23,958 13,807 73,163 — — 86,970 32,678 1992 2005 (1) 77 CityPoint Office Waltham, MA — 13,847 60,383 11,937 14,023 72,144 — — 86,167 29,691 2008 2001 (1) Waltham Weston Corporate Center Office Waltham, MA — 10,385 60,694 13,151 11,097 73,133 — — 84,230 38,118 2003 1999 (1) 3625-3635 Peterson Way Office Santa Clara, CA — 63,206 14,879 907 63,206 14,879 907 — 78,992 14,198 1979 2016 (1) 20 CityPoint Office Waltham, MA — 4,887 72,764 — 4,887 72,764 — — 77,651 3,325 2020 2007 (1) 2440 West El Camino Real Office Mountain View, CA — 16,741 51,285 5,518 16,741 56,803 — — 73,544 15,215 1987/2003 2011 (1) 191 Spring Street Office Lexington, MA — 2,850 59,751 7,543 3,151 66,993 — — 70,144 24,275 1971/1995/2018 1997 (1) 300 Binney Street Office Cambridge, MA — 18,080 51,262 140 18,080 51,402 — — 69,482 12,842 2013 2009 (1) Wisconsin Place Office Chevy Chase, MD — — 53,349 14,771 — 68,120 — — 68,120 28,305 2009 2004 (1) Reston Corporate Center Office Reston, VA — 9,135 50,857 6,236 10,148 56,080 — — 66,228 31,405 1984 1998 (1) 200 West Street Office Waltham, MA — 16,148 24,983 21,102 16,813 30,496 317 14,607 62,233 18,585 1999 1997 (1) 255 Main Street Office Cambridge, MA — 134 25,110 34,107 548 58,803 — — 59,351 37,353 1987 1997 (1) University Place Office Cambridge, MA 1,491 — 37,091 16,745 6,909 46,927 — — 53,836 30,983 1985 1998 (1) Sumner Square Office Washington, DC — 624 28,745 20,396 2,251 47,514 — — 49,765 28,329 1985 1999 (1) Capital Gallery Office Washington, DC — 4,725 29,565 8,679 8,662 34,307 — — 42,969 21,150 1981/2006 2007 (1) North First Business Park Office San Jose, CA — 23,398 13,069 4,580 23,377 17,670 — — 41,047 16,749 1981 2007 (1) 150 Broadway Office Cambridge, MA — 850 25,042 2,253 1,323 26,822 — — 28,145 14,154 1999 1997 (1) 105 Broadway Office Cambridge, MA — 1,299 12,943 12,723 2,395 24,570 — — 26,965 13,041 1990 1997 (1) Lexington Office Park Office Lexington, MA — 998 1,426 18,567 1,264 19,727 — — 20,991 15,289 1982 1997 (1) 201 Spring Street Office Lexington, MA — 2,849 15,303 1,124 3,124 16,152 — — 19,276 8,985 1997 1997 (1) The Point Office Waltham, MA — 6,395 10,040 421 6,492 10,364 — — 16,856 1,667 2015 2007 (1) 690 Folsom Street Office San Francisco, CA — 3,219 11,038 1,157 3,219 12,195 — — 15,414 2,778 2015 2012 (1) 33 Hayden Avenue Office Lexington, MA — 266 3,234 11,566 425 14,641 — — 15,066 5,674 1979 1997 (1) 92-100 Hayden Avenue Office Lexington, MA — 594 6,748 7,669 802 14,209 — — 15,011 12,507 1985 1997 (1) 181 Spring Street Office Lexington, MA — 1,066 9,520 2,177 1,160 11,603 — — 12,763 5,908 1999 1997 (1) 195 West Street Office Waltham, MA — 1,611 6,652 4,221 1,858 10,626 — — 12,484 8,589 1990 1997 (1) Boston Properties, Inc. Schedule 3—Real Estate and Accumulated Depreciation December 31, 2020 (dollars in thousands) Property Name Type Location Encumbrances Original Costs Land and Improvements Building and Land Development Total Accumulated Year(s) Built/ Year(s) Acquired Depreciable Land Building 7501 Boston Boulevard, Building Seven Office Springfield, VA — 665 9,273 819 791 9,966 — — 10,757 5,665 1997 1997 (1) 7435 Boston Boulevard, Building One Office Springfield, VA — 392 3,822 5,016 659 8,571 — — 9,230 6,756 1982 1997 (1) 32 Hartwell Avenue Office Lexington, MA — 168 1,943 6,944 314 8,741 — — 9,055 2,365 1968/1979/1987 1997 (1) 7450 Boston Boulevard, Building Three Office Springfield, VA — 1,165 4,681 2,591 1,430 7,007 — — 8,437 4,103 1987 1998 (1) 250 Binney Street Office Cambridge, MA — 110 4,483 3,593 273 7,913 — — 8,186 6,211 1983 1997 (1) 8000 Grainger Court, Building Five Office Springfield, VA — 366 4,282 3,198 601 7,245 — — 7,846 5,923 1984 1997 (1) 453 Ravendale Drive Office Mountain View, CA — 5,477 1,090 676 5,477 1,766 — — 7,243 819 1977 2012 (1) 7300 Boston Boulevard, Building Thirteen Office Springfield, VA — 608 4,773 1,075 661 5,795 — — 6,456 2,269 2002 1997 (1) 17 Hartwell Avenue Office Lexington, MA — 26 150 6,064 65 6,175 — — 6,240 2,487 1968 1997 (1) 7601 Boston Boulevard, Building Eight Office Springfield, VA — 200 878 5,035 551 5,562 — — 6,113 4,838 1986 1997 (1) 7500 Boston Boulevard, Building Six Office Springfield, VA — 138 3,749 1,640 367 5,160 — — 5,527 4,399 1985 1997 (1) 8000 Corporate Court, Building Eleven Office Springfield, VA — 136 3,071 1,649 774 4,082 — — 4,856 3,320 1989 1997 (1) 7375 Boston Boulevard, Building Ten Office Springfield, VA — 23 2,685 1,035 93 3,650 — — 3,743 2,724 1988 1997 (1) 7374 Boston Boulevard, Building Four Office Springfield, VA — 241 1,605 1,821 398 3,269 — — 3,667 2,870 1984 1997 (1) 7451 Boston Boulevard, Building Two Office Springfield, VA — 249 1,542 1,658 613 2,836 — — 3,449 2,699 1982 1997 (1) The Skylyne Residential Oakland, CA — 28,962 239,077 — 28,962 239,077 — — 268,039 2,128 2020 N/A (1) Signature at Reston Residential Reston, VA — 27,076 190,580 659 27,076 191,239 — — 218,315 13,650 2018 2013 (1) Proto Kendall Square Residential Cambridge, MA — 9,243 127,248 3,336 9,245 130,582 — — 139,827 7,883 2018 2015 (1) The Avant at Reston Town Center Residential Reston, VA — 20,350 91,995 846 20,350 92,841 — — 113,191 17,204 2014 2010 (1) The Lofts at Atlantic Wharf Residential Boston, MA — 3,529 54,891 2,129 3,529 57,020 — — 60,549 14,166 2011 2007 (1) Boston Marriott Cambridge Hotel Cambridge, MA — 478 37,918 35,486 1,201 72,681 — — 73,882 49,103 1986/2017 1997 (1) Kendall Center Green Garage Garage Cambridge, MA — — 35,035 6,846 103 41,778 — — 41,881 14,442 1984 2006 (1) Kendall Center Yellow Garage Garage Cambridge, MA — 1,256 15,697 1,552 1,434 17,071 — — 18,505 6,485 2006 2004 (1) Kendall Center Blue Garage Garage Cambridge, MA — 1,163 11,633 2,111 1,579 13,328 — — 14,907 10,044 1990 1997 (1) Reston Next (formerly Reston Gateway) Development Reston, VA — — — 354,174 — — — 354,174 354,174 — N/A 1998 N/A 2100 Pennsylvania Avenue Development Washington, DC — — — 294,445 185,129 — — 109,316 294,445 3,481 N/A N/A N/A 325 Main Street Development Cambridge, MA — 174 — 161,468 965 — — 160,677 161,642 — N/A 1997 N/A 777 Harrison Street (formerly 425 Fourth Street) Land San Francisco, CA — 144,647 — 25,930 — 47 170,530 — 170,577 — N/A 2020 N/A North First Master Plan Land San Jose, CA — 35,004 — 3,937 — — 38,941 — 38,941 — N/A 2007 N/A Boston Properties, Inc. Schedule 3—Real Estate and Accumulated Depreciation December 31, 2020 (dollars in thousands) Property Name Type Location Encumbrances Original Costs Land and Improvements Building and Land Development Total Accumulated Year(s) Built/ Year(s) Acquired Depreciable Land Building Plaza at Almaden Land San Jose, CA — — — 36,431 — — 36,431 — 36,431 — N/A 2006 N/A Back Bay Station Master Plan Land Boston, MA — — — 30,643 — — 30,643 — 30,643 — N/A N/A N/A Reston Gateway Master Plan Land Reston, VA — — — 28,610 — — 28,610 — 28,610 — N/A 1998 N/A Springfield Metro Center Land Springfield, VA — — — 19,871 — — 19,871 — 19,871 — N/A 2007 N/A 214 Third Avenue Land Waltham, MA — — — 19,206 — — 19,206 — 19,206 — N/A 2006 N/A CityPoint South Master Plan Land Waltham, MA — — — 13,363 — — 13,363 — 13,363 — N/A N/A N/A 103 Fourth Avenue Land Waltham, MA — — — 12,888 — — 12,888 — 12,888 — N/A 2007 N/A Broad Run Business Park Land Loudoun County, VA — — — 2,392 — — 2,392 — 2,392 — N/A 1998 N/A Kendall Center Master Plan Land Cambridge, MA — — — 2,145 — — 2,145 — 2,145 — 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 — — — 42 — — 42 — 42 — N/A 2000 N/A $ 2,909,081 (2) $ 5,160,116 $ 13,196,160 $ 4,947,027 $ 5,429,703 (3) $ 16,553,873 (4) $ 450,954 (5) $ 868,773 $ 23,303,303 $ 5,501,637 Note: Total Real Estate does not include Furniture, Fixtures and Equipment totaling approximately $49,606. Accumulated Depreciation does not include approximately $32,465 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 $(22.9) million. (3) Includes Right of Use Assets - Finance Leases and Right of Use Assets - Operating Leases of approximately $214,091 and $146,406, respectively. (4) Includes Right of Use Assets - Finance Leases of approximately $23,302. (5) Includes pre-development costs. Boston Properties, Inc. Real Estate and Accumulated Depreciation December 31, 2020, 2019 and 2018 (dollars in thousands) A summary of activity for real estate and accumulated depreciation is as follows: 2020 2019 2018 Real Estate: Balance at the beginning of the year $ 22,844,697 $ 21,605,545 $ 21,058,714 Additions to/improvements of real estate 996,989 1,671,898 1,043,379 Assets sold/written-off (538,383) (432,746) (496,548) Balance at the end of the year $ 23,303,303 $ 22,844,697 $ 21,605,545 Accumulated Depreciation: Balance at the beginning of the year $ 5,239,179 $ 4,871,102 $ 4,566,570 Depreciation expense 573,898 564,938 533,342 Assets sold/written-off (311,440) (196,861) (228,810) Balance at the end of the year $ 5,501,637 $ 5,239,179 $ 4,871,102 Note: Real Estate and Accumulated Depreciation amounts do not include Furniture, Fixtures and Equipment. Boston Properties Limited Partnership Schedule 3—Real Estate and Accumulated Depreciation December 31, 2020 (dollars in thousands) Original Costs Land and Building Land Held Development Total Accumulated Year(s) Built/ Year(s) Acquired Depreciable Property Name Type Location Encumbrances Land Building 767 Fifth Avenue (the General Motors Building) Office New York, NY $ 2,277,522 $ 1,796,252 $ 1,532,654 $ 227,450 $ 1,796,252 $ 1,760,104 $ — $ — $ 3,556,356 $ 364,145 1968/2019 2013 (1) Prudential Center Office Boston, MA — 92,077 948,357 512,816 100,540 1,435,029 17,681 — 1,553,250 617,331 1965/1993/2002/2016-2017 1998/1999/2000 (1) Embarcadero Center Office San Francisco, CA — 179,697 847,410 407,480 180,420 1,254,167 — — 1,434,587 662,756 1970/1989 1998-1999 (1) 399 Park Avenue Office New York, NY — 339,200 700,358 281,352 339,200 981,710 — — 1,320,910 370,361 1961/2018 2002 (1) Salesforce Tower Office San Francisco, CA — 200,349 946,205 5,355 200,349 951,560 — — 1,151,909 68,918 2018 2013 (1) 601 Lexington Avenue Office New York, NY 630,068 241,600 494,782 409,864 279,281 636,966 — 229,999 1,146,246 274,343 1977/1997 2001 (1) 200 Clarendon Street and Garage Office Boston, MA — 219,543 667,884 218,821 251,374 854,874 — — 1,106,248 244,882 1976 2010 (1) 250 West 55th Street Office New York, NY — 285,263 603,167 51,860 285,263 655,027 — — 940,290 138,004 2014 2007 (1) 100 Federal Street Office Boston, MA — 131,067 435,954 111,196 131,067 547,150 — — 678,217 141,629 1971-1975/2017 2012 (1) Times Square Tower Office New York, NY — 165,413 380,438 70,227 159,694 456,384 — — 616,078 207,106 2004 2000 (1) Carnegie Center Office Princeton, NJ — 142,666 316,856 138,834 90,498 452,738 55,120 — 598,356 217,092 1983-2016 1998/1999/2000/2007/2014/2017/2019 (1) Atlantic Wharf Office Boston, MA — 63,988 454,537 18,538 63,988 473,075 — — 537,063 146,860 2011 2007 (1) 510 Madison Avenue Office New York, NY — 103,000 253,665 28,446 103,000 282,111 — — 385,111 81,517 2012 2010 (1) Fountain Square Office Reston, VA — 56,853 306,298 21,030 56,853 327,328 — — 384,181 90,047 1986-1990 2012 (1) 599 Lexington Avenue Office New York, NY — 81,040 100,507 187,033 81,040 287,540 — — 368,580 185,354 1986 1997 (1) 680 Folsom Street Office San Francisco, CA — 72,545 219,766 7,917 72,545 227,683 — — 300,228 55,319 2014 2012 (1) 145 Broadway Office Cambridge, MA — 121 273,013 25,509 23,164 275,479 — — 298,643 9,941 2019 1997 (1) 2200 Pennsylvania Avenue Office Washington, DC — — 183,541 112,436 107,356 188,621 — — 295,977 66,072 2011 2008 (1) South of Market and Democracy Tower Office Reston, VA — 13,603 237,479 40,827 13,603 278,306 — — 291,909 107,279 2008-2009 2003 (1) 601 Massachusetts Avenue Office Washington, DC — 95,310 165,173 3,933 95,310 169,106 — — 264,416 30,743 2016 2008 (1) Bay Colony Corporate Center Office Waltham, MA — 18,789 148,451 81,302 18,789 229,753 — — 248,542 89,232 1985-1989 2011 (1) 535 Mission Street Office San Francisco, CA — 40,933 148,378 3,287 40,933 151,665 — — 192,598 31,953 2015 2013 (1) Mountain View Research Park Office Mountain View, CA — 95,066 68,373 18,479 95,066 86,852 — — 181,918 21,725 1977-1981/2007-2013 2013 (1) Reservoir Place Office Waltham, MA — 18,605 104,124 53,079 19,089 156,719 — — 175,808 75,841 1955/1987/2017 1997/1998 (1) 1330 Connecticut Avenue Office Washington, DC — 25,982 82,311 32,436 25,982 114,747 — — 140,729 36,695 1984/2018 2004 (1) Kingstowne Towne Center Office Alexandria, VA — 18,021 109,038 3,135 18,021 112,173 — — 130,194 46,430 2003-2006 2007 (1) One Freedom Square Office Reston, VA — 9,929 84,504 34,247 9,883 118,797 — — 128,680 61,215 2000 2003 (1) One and Two Reston Overlook Office Reston, VA — 16,456 66,192 42,344 15,074 109,918 — — 124,992 56,191 1999 2000 (1) Weston Corporate Center Office Weston, MA — 25,753 92,312 (5) 25,854 92,206 — — 118,060 32,278 2010 2001 (1) 17Fifty Presidents Street Office Reston, VA — — 113,362 — — 113,362 — — 113,362 3,466 2020 2013 (1) Two Freedom Square Office Reston, VA — 13,930 77,739 19,298 13,866 97,101 — — 110,967 52,128 2001 2003 (1) 140 Kendrick Street Office Needham, MA — 18,095 66,905 22,468 18,095 89,373 — — 107,468 34,790 2000 2004 (1) Boston Properties Limited Partnership Schedule 3—Real Estate and Accumulated Depreciation December 31, 2020 (dollars in thousands) Original Costs Land and Building Land Held Development Total Accumulated Year(s) Built/ Year(s) Acquired Depreciable Property Name Type Location Encumbrances Land Building 355 Main Street Office Cambridge, MA — 18,863 53,346 27,295 21,098 78,406 — — 99,504 29,397 1981/1996/2013 2006 (1) Discovery Square Office Reston, VA — 11,198 71,782 15,197 11,146 87,031 — — 98,177 44,352 2001 2003 (1) 880 & 890 Winter Street Office Waltham, MA — 29,510 65,812 1,367 29,510 66,561 618 — 96,689 5,706 1998-1999 2019 (1) 10 CityPoint Office Waltham, MA — 1,953 85,752 4,581 2,127 90,159 — — 92,286 14,073 2016 1997 (1) 90 Broadway Office Cambridge, MA — 19,104 52,078 17,898 20,741 68,339 — — 89,080 24,156 1983/1998/2013 2006 (1) 77 CityPoint Office Waltham, MA — 13,847 60,383 11,832 13,997 72,065 — — 86,062 29,665 2008 2001 (1) 230 CityPoint Office Waltham, MA — 13,189 49,823 22,341 13,403 71,950 — — 85,353 32,224 1992 2005 (1) Waltham Weston Corporate Center Office Waltham, MA — 10,385 60,694 10,164 10,350 70,893 — — 81,243 37,273 2003 1999 (1) 3625-3635 Peterson Way Office Santa Clara, CA — 63,206 14,879 907 63,206 14,879 907 — 78,992 14,198 1979 2016 (1) 20 CityPoint Office Waltham, MA — 4,887 72,764 — 4,887 72,764 — — 77,651 3,325 2020 2007 (1) 2440 West El Camino Real Office Mountain View, CA — 16,741 51,285 5,518 16,741 56,803 — — 73,544 15,215 1987/2003 2011 (1) 191 Spring Street Office Lexington, MA — 2,850 59,751 6,911 2,850 66,662 — — 69,512 24,150 1971/1995/2018 1997 (1) 300 Binney Street Office Cambridge, MA — 18,080 51,262 140 18,080 51,402 — — 69,482 12,842 2013 2009 (1) Wisconsin Place Office Chevy Chase, MD — — 53,349 14,771 — 68,120 — — 68,120 28,305 2009 2004 (1) Reston Corporate Center Office Reston, VA — 9,135 50,857 3,625 9,496 54,121 — — 63,617 30,666 1984 1998 (1) 200 West Street Office Waltham, MA — 16,148 24,983 18,441 16,148 28,500 317 14,607 59,572 17,832 1999 1997 (1) 255 Main Street Office Cambridge, MA — 134 25,110 32,451 134 57,561 — — 57,695 36,887 1987 1997 (1) University Place Office Cambridge, MA 1,491 — 37,091 15,295 6,546 45,840 — — 52,386 30,577 1985 1998 (1) Sumner Square Office Washington, DC — 624 28,745 18,316 1,731 45,954 — — 47,685 27,744 1985 1999 (1) North First Business Park Office San Jose, CA — 23,398 13,069 4,557 23,371 17,653 — — 41,024 16,743 1981 2007 (1) Capital Gallery Office Washington, DC — 4,725 29,565 4,016 6,128 32,178 — — 38,306 20,348 1981/2006 2007 (1) 150 Broadway Office Cambridge, MA — 850 25,042 248 822 25,318 — — 26,140 13,584 1999 1997 (1) 105 Broadway Office Cambridge, MA — 1,299 12,943 10,617 1,868 22,991 — — 24,859 12,445 1990 1997 (1) Lexington Office Park Office Lexington, MA — 998 1,426 17,803 1,073 19,154 — — 20,227 15,076 1982 1997 (1) 201 Spring Street Office Lexington, MA — 2,849 15,303 25 2,849 15,328 — — 18,177 8,672 1997 1997 (1) The Point Office Waltham, MA — 6,395 10,040 421 6,492 10,364 — — 16,856 1,667 2015 2007 (1) 690 Folsom Street Office San Francisco, CA — 3,219 11,038 1,157 3,219 12,195 — — 15,414 2,778 2015 2012 (1) 33 Hayden Avenue Office Lexington, MA — 266 3,234 10,929 266 14,163 — — 14,429 5,494 1979 1997 (1) 92-100 Hayden Avenue Office Lexington, MA — 594 6,748 6,940 619 13,663 — — 14,282 12,300 1985 1997 (1) 181 Spring Street Office Lexington, MA — 1,066 9,520 1,800 1,066 11,320 — — 12,386 5,802 1999 1997 (1) 195 West Street Office Waltham, MA — 1,611 6,652 3,232 1,611 9,884 — — 11,495 8,306 1990 1997 (1) 7501 Boston Boulevard, Building Seven Office Springfield, VA — 665 9,273 314 665 9,587 — — 10,252 5,520 1997 1997 (1) 7435 Boston Boulevard, Building One Office Springfield, VA — 392 3,822 4,323 486 8,051 — — 8,537 6,561 1982 1997 (1) 32 Hartwell Avenue Office Lexington, MA — 168 1,943 6,358 168 8,301 — — 8,469 2,199 1968/1979/1987 1997 (1) 7450 Boston Boulevard, Building Three Office Springfield, VA — 1,165 4,681 2,177 1,327 6,696 — — 8,023 3,983 1987 1998 (1) Boston Properties Limited Partnership Schedule 3—Real Estate and Accumulated Depreciation December 31, 2020 (dollars in thousands) Original Costs Land and Building Land Held Development Total Accumulated Year(s) Built/ Year(s) Acquired Depreciable Property Name Type Location Encumbrances Land Building 250 Binney Street Office Cambridge, MA — 110 4,483 2,939 110 7,422 — — 7,532 6,030 1983 1997 (1) 8000 Grainger Court, Building Five Office Springfield, VA — 366 4,282 2,604 453 6,799 — — 7,252 5,756 1984 1997 (1) 453 Ravendale Drive Office Mountain View, CA — 5,477 1,090 676 5,477 1,766 — — 7,243 819 1977 2012 (1) 7300 Boston Boulevard, Building Thirteen Office Springfield, VA — 608 4,773 863 608 5,636 — — 6,244 2,209 2002 1997 (1) 17 Hartwell Avenue Office Lexington, MA — 26 150 5,907 26 6,057 — — 6,083 2,442 1968 1997 (1) 7601 Boston Boulevard, Building Eight Office Springfield, VA — 200 878 4,342 378 5,042 — — 5,420 4,643 1986 1997 (1) 7500 Boston Boulevard, Building Six Office Springfield, VA — 138 3,749 1,107 234 4,760 — — 4,994 4,249 1985 1997 (1) 8000 Corporate Court, Building Eleven Office Springfield, VA — 136 3,071 1,298 686 3,819 — — 4,505 3,217 1989 1997 (1) 7375 Boston Boulevard, Building Ten Office Springfield, VA — 23 2,685 854 47 3,515 — — 3,562 2,676 1988 1997 (1) 7374 Boston Boulevard, Building Four Office Springfield, VA — 241 1,605 1,438 303 2,981 — — 3,284 2,765 1984 1997 (1) 7451 Boston Boulevard, Building Two Office Springfield, VA — 249 1,542 1,345 535 2,601 — — 3,136 2,609 1982 1997 (1) The Skylyne Residential Oakland, CA — 28,962 239,077 — 28,962 239,077 — — 268,039 2,128 2020 N/A (1) Signature at Reston Residential Reston, VA — 27,076 190,580 659 27,076 191,239 — — 218,315 13,650 2018 2013 (1) Proto Kendall Square Residential Cambridge, MA — 9,243 127,248 3,336 9,245 130,582 — — 139,827 7,883 2018 2015 (1) The Avant at Reston Town Center Residential Reston, VA — 20,350 91,995 846 20,350 92,841 — — 113,191 17,204 2014 2010 (1) The Lofts at Atlantic Wharf Residential Boston, MA — 3,529 54,891 2,129 3,529 57,020 — — 60,549 14,166 2011 2007 (1) Boston Marriott Cambridge Hotel Cambridge, MA — 478 37,918 32,595 478 70,513 — — 70,991 48,286 1986/2017 1997 (1) Kendall Center Green Garage Garage Cambridge, MA — — 35,035 6,432 — 41,467 — — 41,467 14,327 1984 2006 (1) Kendall Center Yellow Garage Garage Cambridge, MA — 1,256 15,697 840 1,256 16,537 — — 17,793 6,287 2006 2004 (1) Kendall Center Blue Garage Garage Cambridge, MA — 1,163 11,633 446 1,163 12,079 — — 13,242 9,576 1990 1997 (1) Reston Next (formerly Reston Gateway) Development Reston, VA — — — 354,174 — — — 354,174 354,174 — N/A 1998 N/A 2100 Pennsylvania Avenue Development Washington, DC — — — 294,445 185,129 — — 109,316 294,445 3,481 N/A N/A N/A 325 Main Street Development Cambridge, MA — 174 — 161,275 772 — — 160,677 161,449 — N/A 1997 N/A 777 Harrison Street (formerly 425 Fourth Street) Land San Francisco, CA — 144,647 — 25,930 — 47 170,530 — 170,577 — N/A 2020 N/A North First Master Plan Land San Jose, CA — 35,004 — 3,937 — — 38,941 — 38,941 — N/A 2007 N/A Plaza at Almaden Land San Jose, CA — — — 36,431 — — 36,431 — 36,431 — N/A 2006 N/A Back Bay Station Master Plan Land Boston, MA — — — 30,643 — — 30,643 — 30,643 — N/A N/A N/A Reston Gateway Master Plan Land Reston, VA — — — 28,610 — — 28,610 — 28,610 — N/A 1998 N/A Springfield Metro Center Land Springfield, VA — — — 19,871 — — 19,871 — 19,871 — N/A 2007 N/A 214 Third Avenue Land Waltham, MA — — — 19,206 — — 19,206 — 19,206 — N/A 2006 N/A Boston Properties Limited Partnership Schedule 3—Real Estate and Accumulated Depreciation December 31, 2020 (dollars in thousands) Original Costs Land and Building Land Held Development Total Accumulated Year(s) Built/ Year(s) Acquired Depreciable Property Name Type Location Encumbrances Land Building CityPoint South Master Plan Land Waltham, MA — — — 13,363 — — 13,363 — 13,363 — N/A N/A N/A 103 Fourth Avenue Land Waltham, MA — — — 12,888 — — 12,888 — 12,888 — N/A 2007 N/A Broad Run Business Park Land Loudoun County, VA — — — 2,392 — — 2,392 — 2,392 — N/A 1998 N/A Kendall Center Master Plan Land Cambridge, MA — — — 2,145 — — 2,145 — 2,145 — 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 — — — 42 — — 42 — 42 — N/A 2000 N/A $ 2,909,081 (2) $ 5,160,116 $ 13,196,160 $ 4,570,218 $ 5,332,487 (3) $ 16,274,280 (4) $ 450,954 (5) $ 868,773 $ 22,926,494 $ 5,396,111 Note: Total Real Estate does not include Furniture, Fixtures and Equipment totaling approximately $49,606. Accumulated Depreciation does not include approximately $32,465 of accumulated depreciation related to Furniture, Fixtures and Equipment. The aggregate cost and accumulated depreciation for tax purposes was approximately $23.0 billion and $5.0 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 $(22.9) 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 $23,302. (5) Includes pre-development costs. Boston Properties Limited Partnership Real Estate and Accumulated Depreciation December 31, 2020, 2019 and 2018 (dollars in thousands) A summary of activity for real estate and accumulated depreciation is as follows: 2020 2019 2018 Real Estate: Balance at the beginning of the year $ 22,449,476 $ 21,207,189 $ 20,647,236 Additions to/improvements of real estate 996,989 1,671,898 1,043,379 Assets sold/written-off (519,971) (429,611) (483,426) Balance at the end of the year $ 22,926,494 $ 22,449,476 $ 21,207,189 Accumulated Depreciation: Balance at the beginning of the year $ 5,135,289 $ 4,773,800 $ 4,473,895 Depreciation expense 566,813 557,130 525,584 Assets sold/written-off (305,991) (195,641) (225,679) Balance at the end of the year $ 5,396,111 $ 5,135,289 $ 4,773,800 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, 2020
Text Block [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.
Consolidation, Policy	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.

Summary Of Significant Accoun_2

Summary Of Significant Accounting Policies (Policies)	12 Months Ended
Summary Of Significant Accounting Policies (Policies)	Dec. 31, 2020
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.
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 indicators of imp airment following the end of each quarter and when events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. This evaluation of long-lived assets is dependent on a number of factors, including when there is an event or adverse change in the operating performance of the long-lived asset or a current expectation that, more likely than not, a long-lived asset will be sold or otherwise disposed of significantly before the end of its previously estimated useful life or hold period. 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 may be 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 hold 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” 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, 2020, 2019 and 2018 were approximately $53.9 million, $54.9 million and $65.8 million, respectively. Salaries and related costs capitalized for the years ended December 31, 2020, 2019 and 2018 were approximately $12.9 million, $10.4 million and $12.5 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 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
Investment in Securities	Investments in Securities
Tenant and Other Receivables and Notes Receivable	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 Adopted—Financial Instruments - Credit Losses”
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 years ended December 31, 2020 and 2019 (see “ Leases ”) . Internal leasing salaries and related costs capitalized for the year ended December 31, 2018 were approximately $5.4 million. 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.
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 indicators of impairment on a quarterly basis 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. This evaluation of the investments 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. The fair value is calculated using discounted cash flows which is subjective and considers 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. 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 $104.9 million, $58.4 million and $51.9 million for the years ended December 31, 2020, 2019 and 2018, 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 must make estimates as to the collectability of its accrued rent and accounts receivable related to lease revenue. Management analyzes accrued rent and accounts receivable by considering tenant creditworthiness, current economic trends, including the impact of the novel coronavirus (“COVID-19”) pandemic on tenants’ businesses, and changes in tenants’ payment patterns when evaluating the collectability of the tenant’s receivable balance, including the accrued rent receivable, on a lease-by-lease basis. The Company writes-off the tenant’s receivable balance, including the accrued rent receivable, if the Company considers the balances no longer probable of collection. 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 the balances are considered no longer probable of collection and therefore written off, the Company will cease to recognize lease income, including straight-line rent, unless cash is received (See Note 4). 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. 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. 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 $6.5 million, $20.9 million and $23.8 million for the years ended December 31, 2020, 2019 and 2018, 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 2021 $ 3,019 $ 6,193 2022 354 5,437 2023 183 5,296 2024 135 3,780 2025 135 3,775 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 “ Leases” ). The Company 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.
Lessee, Leases	Lessee For leases in which the Company is the lessee (generally ground leases), in accordance with ASC 842 the Company recognizes a right-of-use asset and a lease liability. The Company made the policy election to not apply the revenue recognition requirements of ASC 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. The lease liability is equal to the present value of the minimum lease payments in accordance with ASC 842. The Company will use its 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 exceeding 31 years, • observable mortgage rates spread over U.S. Treasury issuances, and • unlevered property yields and discount rates.
Lessor, Leases	Lessor The Company leases primarily Class A office, life sciences, 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. Per ASC 842, lessors do not need to separate nonlease components from the associated lease component if certain criteria stated above are met for each class of underlying assets. The guidance in ASC 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, the 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, life sciences, 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 January 1, 2019 adoption of ASC 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. 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 . 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.
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 Company follows the authoritative guidance for fair value measurements when valuing its financial instruments for disclosure purposes. The table below presents the financial instruments that are being valued for disclosure purposes as well as the Level at which they are categorized as defined in ASC 820 “Fair Value Measurements and Disclosures” (“ASC 820”) (see “ New Accounting Pronouncements Adopted— Fair Value Measurement” ). Financial Instrument Level Unsecured senior notes (1) Level 1 Related party note receivable Level 3 Notes receivable Level 3 Mortgage notes payable Level 3 Unsecured term loan / line of credit Level 3 _______________ (1) If trading volume for the period is low, the valuation could be categorized as Level 2. Because the Company’s valuations of its financial instruments are based on the above Levels and involve the use of estimates, the actual fair values of its financial instruments may differ materially from those estimates. The following table identifies the range and weighted average discount rate for the significant unobservable inputs for the Company’s Level 3 fair value measured instruments as of December 31, 2020. Financial Instrument Level Range Weighted Average Related party note receivable Level 3 3.64% 3.64% Notes receivable Level 3 3.60% - 8.00% 5.87% Mortgage notes payable Level 3 2.00% - 3.04% 2.21% Unsecured term loan / line of credit Level 3 1.04% 1.04% In addition, the Company’s estimated fair values for these instruments as of the end of the applicable reporting period are not projections of, nor 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, net, notes receivable, net, 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, 2020 and December 31, 2019 (in thousands): December 31, 2020 December 31, 2019 Carrying Estimated Carrying Estimated Related party note receivable, net $ 77,552 $ 84,579 $ 80,000 $ 81,931 Note receivable, net 18,729 19,372 15,920 14,978 Total $ 96,281 $ 103,951 $ 95,920 $ 96,909 Mortgage notes payable, net $ 2,909,081 $ 3,144,150 $ 2,922,408 $ 2,984,956 Unsecured senior notes, net 9,639,287 10,620,527 8,390,459 8,826,375 Unsecured line of credit — — — — Unsecured term loan, net 499,390 500,326 498,939 500,561 Total $ 13,047,758 $ 14,265,003 $ 11,811,806 $ 12,311,892 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 operatio ns (see “ New Accounting Pronouncements Adopted—Derivatives and Hedging”
Stock-Based Employee Compensation Plans	Stock-Based Employee Compensation PlansAt December 31, 2020, the Company had a stock-based employee compensation plan. The Company accounts for the plan under the guidance in ASC 718 “Compensation – Stock Compensation” (“ASC 718”), which revised the fair value based method of accounting for share-based payment liabilities, forfeitures and modifications of stock-based awards and clarified previous guidance in several areas, including measuring fair value, classifying an award as equity or as a liability and attributing compensation cost to reporting periods.
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. The Company bases its estimates on historical experience and on various other assumptions that it considers to be reasonable under the circumstances, including the impact of extraordinary events such as COVID-19, the results of which form the basis for making significant judgments about the carrying values of assets and liabilities, assessments of future collectability, and other areas of the financial statements that are impacted by the use of estimates. Actual results may differ from these estimates under different assumptions or conditions.
New Accounting Pronouncements	New Accounting Pronouncements Adopted Financial Instruments - Credit Losses In June 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“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 - “Leases” (“ASC 842”). ASU 2016-13 and ASU 2018-19 were 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 notes 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 resulted in the Company recognizing an allowance for current expected credit losses associated with (1) its related party note receivable, (2) its notes receivable and (3) an off-balance sheet loan commitment arrangement. As a result, the modified retrospective approach resulted in the Company recognizing on January 1, 2020, the cumulative effect of adopting ASU 2016-13 and ASU 2018-19 aggregating approximately $1.5 million to Dividends in Excess of Earnings of Boston Properties, Inc. and Partners’ Capital of Boston Properties Limited Partnership and approximately $0.2 million to Noncontrolling Interests - Common Units of Boston Properties, Inc. and Noncontrolling Interests - Redeemable Partnership Units of Boston Properties Limited Partnership on the corresponding Consolidated Balance Sheets. 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 was effective for the Company for reporting periods beginning after December 15, 2019, with early adoption permitted. The Company adopted ASU 2018-13 on January 1, 2020 and the adoption did 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, “Derivatives and Hedging (Topic 815).” ASU 2018-16 was effective for the Company, which has already adopted ASU 2017-12, “Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities” for reporting periods beginning after December 15, 2018 and was 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 Company adopted ASU 2018-16 on January 1, 2019 and the adoption did not have a material impact on the Company’s consolidated financial statements. In March 2020, the FASB issued ASU 2020-04, “Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting” (“ASU 2020-04”). ASU 2020-04 contains practical expedients for reference rate reform related activities that impact debt, leases, derivatives and other contracts. The guidance in ASU 2020-04 is optional and may be elected over time as reference rate reform activities occur. During the year ended December 31, 2020, the Company elected to apply the hedge accounting expedients related to probability and the assessments of effectiveness for future LIBOR-indexed cash flows to assume that the index upon which future hedged transactions will be based matches the index on the corresponding derivatives. Application of these expedients preserves the presentation of derivatives consistent with past presentation. The Company continues to evaluate the impact of the guidance and may apply other elections as applicable as additional changes in the market occur. In January 2021, the FASB issued ASU 2021-01, “Reference Rate Reform (Topic 848): Scope” (“ASU 2021-01”). ASU 2021-01 amends the scope of the recent reference rate reform guidance (Topic 848). ASU 2021-01 permits entities to elect certain optional expedients when accounting for derivative instruments impacted by changes in the interest rate used for margining, discounting, or contract price alignment (i.e., discount transition). The new optional expedients for contract modifications and hedge accounting are expected to benefit companies, including those with certain centrally cleared derivatives affected by a discount rate transition in 2020. ASU 2021-01 is effective immediately and can be applied retrospectively to any interim period beginning January 1, 2020 or prospectively to any new modifications in any period including or subsequent to the issuance date. ASU 2021-01 did not have a material impact on the Company’s consolidated financial statements. Consolidation
Equity Offering Costs	Equity Offering Costs
Treasury Stock	Treasury Stock
Dividends	Dividends
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, 2020 and 2019. At December 31, 2020, Boston Properties, Inc.’s tax returns for the years 2017 forward remain subject to examination by the major tax jurisdictions under the statute of limitations. 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, 2020, 2019 and 2018. 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, 2020 and 2019. At December 31, 2020, Boston Properties Limited Partnership’s tax returns for the years 2017 forward remain subject to examination by the major tax jurisdictions under the statute of limitations. 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, 2020, 2019 and 2018. 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, 2020
Summary Of Significant Accounting Policies [Line Items]
Fair Value Measurement Inputs and Valuation Techniques [Table Text Block]	Fair Value of Financial Instruments The Company follows the authoritative guidance for fair value measurements when valuing its financial instruments for disclosure purposes. The table below presents the financial instruments that are being valued for disclosure purposes as well as the Level at which they are categorized as defined in ASC 820 “Fair Value Measurements and Disclosures” (“ASC 820”) (see “ New Accounting Pronouncements Adopted— Fair Value Measurement” ). Financial Instrument Level Unsecured senior notes (1) Level 1 Related party note receivable Level 3 Notes receivable Level 3 Mortgage notes payable Level 3 Unsecured term loan / line of credit Level 3 _______________ (1) If trading volume for the period is low, the valuation could be categorized as Level 2. Because the Company’s valuations of its financial instruments are based on the above Levels and involve the use of estimates, the actual fair values of its financial instruments may differ materially from those estimates. The following table identifies the range and weighted average discount rate for the significant unobservable inputs for the Company’s Level 3 fair value measured instruments as of December 31, 2020. Financial Instrument Level Range Weighted Average Related party note receivable Level 3 3.64% 3.64% Notes receivable Level 3 3.60% - 8.00% 5.87% Mortgage notes payable Level 3 2.00% - 3.04% 2.21% Unsecured term loan / line of credit Level 3 1.04% 1.04%
Property, Plant and Equipment	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	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 2021 $ 3,019 $ 6,193 2022 354 5,437 2023 183 5,296 2024 135 3,780 2025 135 3,775 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 “ Leases”
Fair Value, by Balance Sheet Grouping [Table Text Block]	December 31, 2020 December 31, 2019 Carrying Estimated Carrying Estimated Related party note receivable, net $ 77,552 $ 84,579 $ 80,000 $ 81,931 Note receivable, net 18,729 19,372 15,920 14,978 Total $ 96,281 $ 103,951 $ 95,920 $ 96,909 Mortgage notes payable, net $ 2,909,081 $ 3,144,150 $ 2,922,408 $ 2,984,956 Unsecured senior notes, net 9,639,287 10,620,527 8,390,459 8,826,375 Unsecured line of credit — — — — Unsecured term loan, net 499,390 500,326 498,939 500,561 Total $ 13,047,758 $ 14,265,003 $ 11,811,806 $ 12,311,892
Dividends Declared	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 declared in 2020 and during the year ended December 31, 2019: Record Date Payment Date Dividend (Per Share) Distribution (Per Unit) December 31, 2020 January 28, 2021 $0.98 $0.98 September 30, 2020 October 30, 2020 $0.98 $0.98 June 30, 2020 July 31, 2020 $0.98 $0.98 March 31, 2020 April 30, 2020 $0.98 $0.98 December 31, 2019 January 30, 2020 $0.98 $0.98 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
Dividend Paid [Member]
Summary Of Significant Accounting Policies [Line Items]
Dividends Declared	The tax treatment of common dividends per share for federal income tax purposes is as follows: For the year ended December 31, 2020 2019 2018 Per Share % Per Share % Per Share % Ordinary income $ 2.52 64.91 % $ 2.99 94.84 % $ 2.79 78.17 % Capital gain income 0.99 25.49 % 0.16 5.16 % 0.78 21.83 % Return of capital 0.37 9.60 % — — % — — % Total $ 3.88 (1) 100.00 % $ 3.15 (2) 100.00 % $ 3.57 (3) 100.00 % _____________ (1) The fourth quarter 2020 regular quarterly dividend was $0.98 per common share, all of which was allocable to 2021. (2) 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 was allocable to 2020. (3) 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 was allocable to 2019.

Real Estate (Tables)

Real Estate (Tables)	12 Months Ended
Real Estate (Tables)	Dec. 31, 2020
Real Estate Properties [Line Items]
Schedule of Real Estate Properties	Boston Properties, Inc. Real estate consisted of the following at December 31, 2020 and December 31, 2019 (in thousands): December 31, 2020 December 31, 2019 Land $ 5,069,206 $ 5,111,606 Right of use assets - finance leases 237,393 237,394 Right of use assets - operating leases 146,406 148,640 Land held for future development (1) 450,954 254,828 Buildings and improvements 13,777,691 13,646,054 Tenant improvements 2,752,880 2,656,439 Furniture, fixtures and equipment 49,606 44,313 Construction in progress 868,773 789,736 Total 23,352,909 22,889,010 Less: Accumulated depreciation (5,534,102) (5,266,798) $ 17,818,807 $ 17,622,212 _______________ (1) Includes pre-development costs.
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, 2020 and December 31, 2019 (in thousands): December 31, 2020 December 31, 2019 Land $ 4,971,990 $ 5,011,153 Right of use assets - finance leases 237,393 237,394 Right of use assets - operating leases 146,406 148,640 Land held for future development (1) 450,954 254,828 Buildings and improvements 13,498,098 13,351,286 Tenant improvements 2,752,880 2,656,439 Furniture, fixtures and equipment 49,606 44,313 Construction in progress 868,773 789,736 Total 22,976,100 22,493,789 Less: Accumulated depreciation (5,428,576) (5,162,908) $ 17,547,524 $ 17,330,881 _______________ (1) Includes pre-development costs.

Leases (Tables)

Leases (Tables)	12 Months Ended
Leases (Tables)	Dec. 31, 2020
Leases [Abstract]
Lease, Cost	The following table provides lease cost information for the Company’s operating and finance leases for the year ended (in thousands): Lease costs December 31, 2020 December 31, 2019 Operating lease costs $ 13,948 $ 14,573 Finance lease costs Amortization of right of use asset (1) $ 56 $ 29 Interest on lease liabilities (2) $ 583 $ 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 for all or a portion of the years ended December 31, 2020 and December 31, 2019, respectively, and as such, a portion of the interest amount was capitalized. The following table provides other quantitative information for the Company’s operating and finance leases as of December 31, 2020 and December 31, 2019: December 31, 2020 December 31, 2019 Other information Weighted-average remaining lease term (in years) Operating leases 51 51 Finance leases 70 71 Weighted-average discount rate Operating leases 5.7 % 5.7 % Finance leases 6.2 % 6.2 %
Finance Lease, Liability, Maturity	The following table provides a maturity analysis for the Company’s lease liabilities related to its operating and finance leases as of December 31, 2020 (in thousands): Operating Finance 2021 $ 25,092 $ 5,896 2022 18,020 10,206 2023 10,262 9,701 2024 (1) 9,277 48,518 2025 9,476 9,971 Thereafter 548,478 1,373,177 Total lease payments 620,605 1,457,469 Less: Interest portion (418,892) (1,220,977) Present value of lease payments $ 201,713 $ 236,492
Operating Lease, Lease Income [Table Text Block]	The following table summarizes the components of lease revenue recognized during the years ended December 31, 2020 and 2019 included within the Company's Consolidated Statements of Operations (in thousands): Year ended December 31, Lease Revenue 2020 2019 Fixed contractual payments $ 2,211,915 $ 2,261,260 Variable lease payments 434,346 496,754 $ 2,646,261 $ 2,758,014
Lessor, Operating Lease, Payments to be Received, Maturity	The future contractual lease payments to be received (excluding operating expense reimbursements and percentage rent) by the Company as of December 31, 2020, under non-cancelable operating leases which expire on various dates through 2049 (in thousands): Years Ending December 31, 2021 $ 2,177,848 2022 2,188,846 2023 2,144,213 2024 2,043,264 2025 1,901,624 Thereafter 12,577,660

Deferred Charges (Tables)

Deferred Charges (Tables)	12 Months Ended
Deferred Charges (Tables)	Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Deferred Costs	Deferred charges consisted of the following at December 31, 2020 and 2019 (in thousands): 2020 2019 Leasing costs, including lease related intangibles $ 1,023,058 $ 1,155,958 Financing costs 12,728 12,728 1,035,786 1,168,686 Less: Accumulated amortization (395,701) (479,473) $ 640,085 $ 689,213
Finite-lived Intangible Assets Amortization Expense	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 2021 $ 10,352 2022 5,464 2023 3,854 2024 2,220 2025 2,174

Investments in Unconsolidated_2

Investments in Unconsolidated Joint Ventures (Tables)	12 Months Ended
Investments in Unconsolidated Joint Ventures (Tables)	Dec. 31, 2020
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, 2020 and December 31, 2019: Carrying Value of Investment (1) Entity Properties Nominal % December 31, December 31, (in thousands) Square 407 Limited Partnership Market Square North 50.0 % $ (3,766) $ (4,872) BP/CRF Metropolitan Square, LLC Metropolitan Square 20.0 % (13,584) 9,134 901 New York, LLC 901 New York Avenue 25.0 % (2) (12,264) (12,113) WP Project Developer LLC Wisconsin Place Land and Infrastructure 33.3 % (3) 35,297 36,789 Annapolis Junction NFM LLC Annapolis Junction 50.0 % (4) 13,463 25,391 540 Madison Venture LLC 540 Madison Avenue 60.0 % (5) 122 2,953 500 North Capitol Venture LLC 500 North Capitol Street, NW 30.0 % (6,945) (5,439) 501 K Street LLC 1001 6th Street 50.0 % (6) 42,499 42,496 Podium Developer LLC The Hub on Causeway - Podium 50.0 % 48,818 49,466 Residential Tower Developer LLC Hub50House 50.0 % 50,943 55,092 Hotel Tower Developer LLC The Hub on Causeway - Hotel Air Rights 50.0 % 10,754 9,883 Office Tower Developer LLC 100 Causeway Street 50.0 % 56,312 56,606 1265 Main Office JV LLC 1265 Main Street 50.0 % 3,787 3,780 BNY Tower Holdings LLC Dock 72 50.0 % 29,536 94,804 BNYTA Amenity Operator LLC Dock 72 50.0 % 1,846 N/A CA-Colorado Center Limited Partnership Colorado Center 50.0 % 227,671 252,069 7750 Wisconsin Avenue LLC 7750 Wisconsin Avenue 50.0 % 58,112 56,247 BP-M 3HB Venture LLC 3 Hudson Boulevard 25.0 % 113,774 67,499 SMBP Venture LP Santa Monica Business Park 55.0 % 145,761 163,937 Platform 16 Holdings LP Platform 16 55.0 % (7) 108,393 29,501 Gateway Portfolio Holdings LLC Gateway Commons 50.0 % (8) 336,206 N/A Rosecrans-Sepulveda Partners 4, LLC Beach Cities Media Campus 50.0 % 27,184 N/A $ 1,273,919 $ 933,223 _______________ (1) Investments with deficit balances aggregating approximately $36.6 million and $22.4 million at December 31, 2020 and 2019, 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. At December 31, 2020 and 2019, the Company’s economic ownership was approximately 50%. (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 two in-service buildings. (5) T he property was sold on June 27, 2019. As of December 31, 2020 and 2019, the investment consisted of undistributed cash. (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). (8) As a result of the partner’s deferred contribution, the Company owns an approximately 55% interest in the joint venture at December 31, 2020. Future development projects will be owned 49% by the Company and 51% by its partner.
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) $ 4,708,571 $ 3,904,400 Other assets 531,071 502,706 Total assets $ 5,239,642 $ 4,407,106 LIABILITIES AND MEMBERS’/PARTNERS’ EQUITY Mortgage and notes payable, net $ 2,637,911 $ 2,218,853 Other liabilities (2) 650,433 749,675 Members’/Partners’ equity 1,951,298 1,438,578 Total liabilities and members’/partners’ equity $ 5,239,642 $ 4,407,106 Company’s share of equity $ 936,087 $ 591,905 Basis differentials (3) 337,832 341,318 Carrying value of the Company’s investments in unconsolidated joint ventures (4) $ 1,273,919 $ 933,223 _______________ (1) At December 31, 2020 and 2019, this amount included right of use assets - finance leases totaling approximately $248.9 million and $383.9 million, respectively, and right of use assets - operating leases totaling approximately $22.5 million and $12.1 million, respectively. (2) At December 31, 2020 and 2019, this amount included lease liabilities - finance leases totaling approximately $388.7 million and $510.8 million, respectively, and lease liabilities - operating leases totaling approximately $29.0 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, 2020 and 2019, there was an aggregate basis differential of approximately $307.3 million and $311.3 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. At December 31, 2020, there was an aggregate basis differential of approximately $51.9 million between the carrying value of the Company’s investment in the joint venture that owns Gateway Commons and the joint venture’s basis in the assets and liabilities. At December 31, 2020, there was an aggregate basis differential of approximately $(52.2) million between the carrying value of the Company’s investment in the joint venture that owns Dock 72 and the joint venture’s basis in the assets and liabilities. These basis differentials (excluding land) will be amortized over the remaining lives of the related assets and liabilities. (4) Investments with deficit balances aggregating approximately $36.6 million and $22.4 million at December 31, 2020 and 2019, respectively, are 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: Year ended December 31, 2020 2019 2018 (in thousands) Total revenue (1) $ 319,560 $ 322,817 $ 271,951 Expenses Operating 144,347 122,992 106,610 Transaction costs 1,027 1,000 — Depreciation and amortization (2) 141,853 102,296 103,079 Total expenses 287,227 226,288 209,689 Other income (expense) Interest expense (98,051) (84,409) (71,308) Gains on sales of real estate (3) 11,737 32,706 16,951 Net income (loss) $ (53,981) $ 44,826 $ 7,905 Company’s share of net income (loss) $ (16,256) $ 24,423 $ 8,084 Impairment loss on investment (4) (60,524) — — Basis differential (3)(4)(5) (8,330) 22,169 (5,862) (Loss) income from unconsolidated joint ventures $ (85,110) $ 46,592 $ 2,222 _______________ (1) Includes straight-line rent adjustments of approximately $(10.1) million, $32.4 million and $15.9 million for the years ended December 31, 2020, 2019 and 2018, respectively. Due primarily to the impact of COVID-19, for the year ended December 31, 2020, write-offs of accounts receivable and accrued rent balances totaled approximately $51.7 million. (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. 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) During the year ended December 31, 2020, the Company recognized an other-than-temporary impairment loss on its investment in the unconsolidated joint venture that owns Dock 72 in Brooklyn, New York totaling approximately $60.5 million.

Mortgage Notes Payable, Net (Ta

Mortgage Notes Payable, Net (Tables)	12 Months Ended
Mortgage Notes Payable, Net (Tables)	Dec. 31, 2020
Mortgage Notes Payable [Abstract]
Schedule Of Aggregate Principal Payments On Mortgage Notes	Contractual aggregate principal payments of mortgage notes payable at December 31, 2020 are as follows (in thousands): Principal Payments 2021 $ 17,276 2022 614,710 2023 — 2024 — 2025 — Thereafter 2,300,000 Total aggregate principal payments 2,931,986 Deferred financing costs, net (22,905) Total carrying value of mortgage notes payable, net $ 2,909,081

Unsecured Senior Notes (Tables)

Unsecured Senior Notes (Tables)	12 Months Ended
Unsecured Senior Notes (Tables)	Dec. 31, 2020
Debt Disclosure [Abstract]
Schedule of Long-term Debt Instruments	The following summarizes the unsecured senior notes outstanding as of December 31, 2020 (dollars in thousands): Coupon/ Effective Principal Maturity Date(2) 10 Year Unsecured Senior Notes 4.125 % 4.289 % $ 850,000 May 15, 2021 (3) 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 10.75 Year Unsecured Senior Notes 3.250 % 3.343 % 1,250,000 January 30, 2031 Total principal 9,700,000 Net unamortized discount (16,034) Deferred financing costs, net (44,679) Total $ 9,639,287 _______________ (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. (3) See Note 18.

Noncontrolling Interests (Table

Noncontrolling Interests (Tables)	12 Months Ended
Noncontrolling Interests (Tables)	Dec. 31, 2020
Noncontrolling Interest [Line Items]
Distribution Declared to OP, LTIP, OPP and MYLTIP Units [Table Text Block]	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 declared in 2020 and during the year ended December 31, 2019: Record Date Payment Date Dividend (Per Share) Distribution (Per Unit) December 31, 2020 January 28, 2021 $0.98 $0.98 September 30, 2020 October 30, 2020 $0.98 $0.98 June 30, 2020 July 31, 2020 $0.98 $0.98 March 31, 2020 April 30, 2020 $0.98 $0.98 December 31, 2019 January 30, 2020 $0.98 $0.98 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
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 - 2016 MYLTIP Units and, after the February 6, 2020 measurement date, the 2017 MYLTIP Units) and its distributions on the 2017 MYLTIP Units (prior to the February 6, 2020 measurement date) and 2018 - 2020 MYLTIP Units (after the February 4, 2020 issuance date) that occurred during the year ended December 31, 2020: Record Date Payment Date Distributions per OP Unit and LTIP Unit Distributions per MYLTIP Unit December 31, 2020 January 28, 2021 $0.98 $0.098 September 30, 2020 October 30, 2020 $0.98 $0.098 June 30, 2020 July 31, 2020 $0.98 $0.098 March 31, 2020 April 30, 2020 $0.98 $0.098 December 31, 2019 January 30, 2020 $0.98 $0.098 The following table presents Boston Properties Limited Partnership’s distributions on the OP Units and LTIP Units (including the 2012 OPP Units, 2013 - 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) and 2017 - 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

Stockholders' Equity _ Partne_2

Stockholders' Equity / Partners' Capital (Tables)	12 Months Ended
Stockholders' Equity / Partners' Capital (Tables)	Dec. 31, 2020
Class of Stock [Line Items]
Dividends Declared [Table Text Block]	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 declared in 2020 and during the year ended December 31, 2019: Record Date Payment Date Dividend (Per Share) Distribution (Per Unit) December 31, 2020 January 28, 2021 $0.98 $0.98 September 30, 2020 October 30, 2020 $0.98 $0.98 June 30, 2020 July 31, 2020 $0.98 $0.98 March 31, 2020 April 30, 2020 $0.98 $0.98 December 31, 2019 January 30, 2020 $0.98 $0.98 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
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 declared during 2020 and during the year ended December 31, 2019: Record Date Payment Date Dividend (Per Share) February 5, 2021 February 16, 2021 $32.8125 November 4, 2020 November 16, 2020 $32.8125 August 3, 2020 August 17, 2020 $32.8125 May 1, 2020 May 15, 2020 $32.8125 February 4, 2020 February 18, 2020 $32.8125 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

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
Segment Information (Tables)	Dec. 31, 2020
Segment Reporting [Abstract]
Schedule Of Reconciliation Of Net Operating Income To Net Income	Boston Properties, Inc. Year ended December 31, 2020 2019 2018 (in thousands) Net income attributable to Boston Properties, Inc. common shareholders $ 862,227 $ 511,034 $ 572,347 Add: Preferred dividends 10,500 10,500 10,500 Noncontrolling interest—common units of the Operating Partnership 97,704 59,345 66,807 Noncontrolling interests in property partnerships 48,260 71,120 62,909 Interest expense 431,717 412,717 378,168 Loss from early extinguishment of debt — 29,540 16,490 Impairment loss — 24,038 11,812 Net operating income from unconsolidated joint ventures 94,943 97,716 79,893 Depreciation and amortization expense 683,751 677,764 645,649 Transaction costs 1,531 1,984 1,604 Payroll and related costs from management services contracts 11,626 10,386 9,590 General and administrative expense 133,112 140,777 121,722 Less: Net operating income attributable to noncontrolling interests in property partnerships 162,887 183,989 177,365 Gains (losses) from investments in securities 5,261 6,417 (1,865) Interest and other income (loss) 5,953 18,939 10,823 Gains on sales of real estate 618,982 709 182,356 Income (loss) from unconsolidated joint ventures (85,110) 46,592 2,222 Direct reimbursements of payroll and related costs from management services contracts 11,626 10,386 9,590 Development and management services revenue 29,641 40,039 45,158 Company’s share of Net Operating Income $ 1,626,131 $ 1,739,850 $ 1,551,842 Boston Properties Limited Partnership Year ended December 31, 2020 2019 2018 (in thousands) Net income attributable to Boston Properties Limited Partnership common unitholders $ 979,979 $ 580,102 $ 656,903 Add: Preferred distributions 10,500 10,500 10,500 Noncontrolling interests in property partnerships 48,260 71,120 62,909 Interest expense 431,717 412,717 378,168 Loss from early extinguishment of debt — 29,540 16,490 Impairment loss — 22,272 10,181 Net operating income from unconsolidated joint ventures 94,943 97,716 79,893 Depreciation and amortization expense 676,666 669,956 637,891 Transaction costs 1,531 1,984 1,604 Payroll and related costs from management services contracts 11,626 10,386 9,590 General and administrative expense 133,112 140,777 121,722 Less: Net operating income attributable to noncontrolling interests in property partnerships 162,887 183,989 177,365 Gains (losses) from investments in securities 5,261 6,417 (1,865) Interest and other income (loss) 5,953 18,939 10,823 Gains on sales of real estate 631,945 858 190,716 Income (loss) from unconsolidated joint ventures (85,110) 46,592 2,222 Direct reimbursements of payroll and related costs from management services contracts 11,626 10,386 9,590 Development and management services revenue 29,641 40,039 45,158 Company’s share of Net Operating Income $ 1,626,131 $ 1,739,850 $ 1,551,842
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, 2020: Boston Los Angeles New York San Francisco Washington, DC Total Rental Revenue: (1) Office $ 897,915 $ — $ 935,966 $ 508,327 $ 336,587 $ 2,678,795 Residential 13,616 — — 155 24,375 38,146 Hotel 7,478 — — — — 7,478 Total 919,009 — 935,966 508,482 360,962 2,724,419 % of Grand Totals 33.73 % — % 34.36 % 18.66 % 13.25 % 100.00 % Rental Expenses: Office 318,509 — 384,753 163,156 132,051 998,469 Residential 5,378 — — 2,261 11,100 18,739 Hotel 13,136 — — — — 13,136 Total 337,023 — 384,753 165,417 143,151 1,030,344 % of Grand Totals 32.71 % — % 37.35 % 16.05 % 13.89 % 100.00 % Net operating income $ 581,986 $ — $ 551,213 $ 343,065 $ 217,811 $ 1,694,075 % of Grand Totals 34.35 % — % 32.54 % 20.25 % 12.86 % 100.00 % Less: Net operating income attributable to noncontrolling interests in property partnerships (41,849) — (121,038) — — (162,887) Add: Company’s share of net operating income from unconsolidated joint ventures 10,765 57,907 (5,326) 14,928 16,669 94,943 Company’s share of net operating income $ 550,902 $ 57,907 $ 424,849 $ 357,993 $ 234,480 $ 1,626,131 % of Grand Totals 33.88 % 3.56 % 26.12 % 22.02 % 14.42 % 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, 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.

Earnings Per Share _ Common U_2

Earnings Per Share / Common Unit (Tables)	12 Months Ended
Earnings Per Share / Common Unit (Tables)	Dec. 31, 2020
Entity Information [Line Items]
Computation Of Basic And Diluted Earnings Per Share / Unit	Year ended December 31, 2020 Income Shares Per Share (in thousands, except for per share amounts) Basic Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 862,227 155,432 $ 5.55 Allocation of undistributed earnings to participating securities (748) — (0.01) Net income attributable to Boston Properties, Inc. common shareholders $ 861,479 155,432 $ 5.54 Effect of Dilutive Securities: Stock Based Compensation — 85 — Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 861,479 155,517 $ 5.54 Year ended December 31, 2019 Income Shares Per Share (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 Year ended December 31, 2018 Income Shares Per Share (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
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 17,211,000 and 17,618,000 and 17,485,000 redeemable common units for the years ended December 31, 2020, 2019 and 2018, respectively. Year ended December 31, 2020 Income Units Per Unit (in thousands, except for per unit amounts) Basic Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 979,979 172,643 $ 5.68 Allocation of undistributed earnings to participating securities (830) — (0.01) Net income attributable to Boston Properties Limited Partnership common unitholders $ 979,149 172,643 $ 5.67 Effect of Dilutive Securities: Stock Based Compensation — 85 — Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 979,149 172,728 $ 5.67 Year ended December 31, 2019 Income Units Per Unit (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 Year ended December 31, 2018 Income Units Per Unit (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

Stock Option and Incentive Pl_2

Stock Option and Incentive Plan (Tables)	12 Months Ended
Stock Option and Incentive Plan (Tables)	Dec. 31, 2020
Text Block [Abstract]
Share-based Payment Arrangement, Option, Activity	A summary of the status of Boston Properties, Inc.’s stock options as of December 31, 2020, 2019 and 2018 and changes during the years then ended are presented below: Shares Weighted-Average 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 Exercised (43,792) $ 91.60 Outstanding at December 31, 2020 351,561 $ 96.97
Schedule of Stock Options Outstanding	The following table summarizes information about Boston Properties, Inc.’s stock options outstanding at December 31, 2020: Options Outstanding Options Exercisable Number Outstanding at 12/31/20 Weighted-Average Remaining Number Exercisable at 12/31/20 Exercise Price 54,003 0.1 years $ 86.86 54,003 $ 86.86 54,282 2.3 years $ 95.69 54,282 $ 95.69 133,834 2.1 years $ 98.46 133,834 $ 98.46 109,442 1.1 years $ 100.77 109,442 $ 100.77

Organization (Details)

Organization (Details) ft² in Millions	12 Months Ended
Organization (Details) ft² in Millions	Dec. 31, 2020ft²Real_Estate_Propertiesyrshares	Dec. 31, 2019shares
Real Estate Properties [Line Items]
General and limited partnership interest in the operating partnership (percent)		89.60%
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	1
Number of VIEs	6
Number of VIEs - Total	7
Commercial Real Estate Properties [Member]
Real Estate Properties [Line Items]
Number of real estate properties	196
Net Rentable Area (in sf) \| ft²	51.2
Number of VIEs	5
Total Properties Under Construction [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	6
Net Rentable Area (in sf) \| ft²	3.7
Total Office Properties [Member]
Real Estate Properties [Line Items]
Number of real estate properties	177
Office Properties Under Construction [Member]
Real Estate Properties [Line Items]
Number of real estate properties	6
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
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%	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	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	80,000

Summary Of Significant Accoun_4

Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 15, 2020
Summary Of Significant Accounting Policies [Line Items]
Interest capitalized	$ 53,881,000	$ 54,911,000	$ 65,766,000
Salaries And Related Costs Capitalized	12,900,000	10,400,000	12,500,000
Cash FDIC Insured Limit	250,000
Gains (losses) from investments in securities	5,261,000	6,417,000	(1,865,000)
Internal Leasing Salaries And Related Costs Capitalized			5,400,000
Straight Line Rent Adjustments	104,900,000	58,400,000	51,900,000
Above and below market rent adjustments, net	6,500,000	20,900,000	23,800,000
Separate Unrestricted Cash For Deferred Compensation Plan.	39,500,000	36,700,000
Adoption of ASU 2016-13 and 2018-19	(509,653,000)	(760,523,000)
Adoption of ASU 2016-13 and 2018-19	616,596,000	600,860,000
Distributions Payable, Amount Per Unit				$ 0.98
Boston Properties Limited Partnership
Summary Of Significant Accounting Policies [Line Items]
Interest capitalized	53,881,000	54,911,000	65,766,000
Gains (losses) from investments in securities	5,261,000	6,417,000	$ (1,865,000)
Adoption of ASU 2016-13 and 2018-19	4,554,639,000	3,380,175,000
Adoption of ASU 2016-13 and 2018-19	1,643,024,000	$ 2,468,753,000
Distributions Payable, Amount Per Unit				$ 0.98
Boston Properties Limited Partnership \| Cumulative Effect, Period of Adoption, Adjustment
Summary Of Significant Accounting Policies [Line Items]
Adoption of ASU 2016-13 and 2018-19	1,500,000
Dividends In Excess Of Earnings [Member] \| Cumulative Effect, Period of Adoption, Adjustment
Summary Of Significant Accounting Policies [Line Items]
Adoption of ASU 2016-13 and 2018-19	1,500,000
Noncontrolling Interests [Member] \| Cumulative Effect, Period of Adoption, Adjustment
Summary Of Significant Accounting Policies [Line Items]
Adoption of ASU 2016-13 and 2018-19	200,000
Noncontrolling Interests [Member] \| Boston Properties Limited Partnership \| Cumulative Effect, Period of Adoption, Adjustment
Summary Of Significant Accounting Policies [Line Items]
Adoption of ASU 2016-13 and 2018-19	$ 200,000

Summary Of Significant Accoun_5

Summary Of Significant Accounting Policies Schedule of Estimated Useful Lives (Details)	12 Months Ended
	Dec. 31, 2020
Land Improvements \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	25 to 40 years
Land Improvements \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	25 to 40 years
Buildings and improvements \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	10 to 40 years
Buildings and improvements \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	10 to 40 years
Tenant improvements
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	Shorter of useful life or terms of related lease
Furniture, fixtures, and equipment \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	3 to 7 years
Furniture, fixtures, and equipment \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	3 to 7 years

Summary Of Significant Accoun_6

Summary Of Significant Accounting Policies Fair Value of Debt (Level 3) (Details) - Measurement Input, Discount Rate [Member]	Dec. 31, 2020
Mortgage Notes [Member] \| Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt Instrument, Measurement Input	0.0200
Mortgage Notes [Member] \| Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt Instrument, Measurement Input	0.0304
Mortgage Notes [Member] \| Weighted Average [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt Instrument, Measurement Input	0.0221
Unsecured Term Loan / Line of Credit[Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt Instrument, Measurement Input	0.0104
Unsecured Term Loan / Line of Credit[Member] \| Weighted Average [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt Instrument, Measurement Input	0.0104
Related Party Note Receivable [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt Instrument, Measurement Input	0.0364
Related Party Note Receivable [Member] \| Weighted Average [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt Instrument, Measurement Input	0.0364
Notes Receivables [Member] \| Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt Instrument, Measurement Input	0.0360
Notes Receivables [Member] \| Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt Instrument, Measurement Input	0.0800
Notes Receivables [Member] \| Weighted Average [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt Instrument, Measurement Input	0.0587

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, 2020	Dec. 31, 2019
Summary Of Significant Accounting Policies [Line Items]
Related party note receivable, net	$ 77,552	$ 80,000
Notes receivable, net	18,729	15,920
Mortgage notes payable, net	2,909,081	2,922,408
Unsecured senior notes, net	9,639,287	8,390,459
Unsecured line of credit	0	0
Unsecured term loan, net	499,390	498,939
Total	2,931,986
Carrying Amount [Member]
Summary Of Significant Accounting Policies [Line Items]
Related party note receivable, net	77,552	80,000
Notes receivable, net	18,729	15,920
Total	96,281	95,920
Mortgage notes payable, net	2,909,081	2,922,408
Unsecured senior notes, net	9,639,287	8,390,459
Unsecured line of credit	0	0
Unsecured term loan, net	499,390	498,939
Total	13,047,758	11,811,806
Estimated Fair Value [Member]
Summary Of Significant Accounting Policies [Line Items]
Related party note receivable, net	84,579	81,931
Notes receivable, net	19,372	14,978
Total	103,951	96,909
Mortgage notes payable, net	3,144,150	2,984,956
Unsecured senior notes, net	10,620,527	8,826,375
Unsecured line of credit	0	0
Unsecured term loan, net	500,326	500,561
Total	$ 14,265,003	$ 12,311,892

Schedule of Finite Lived Intagi

Schedule of Finite Lived Intagible Assets Future Amortization Expense (Details) $ in Thousands	Dec. 31, 2020USD ($)
Acquired Finite-Lived Intangible Assets [Line Items]
2022	$ 5,464
2023	3,854
2024	2,220
2025	2,174
Above Market Leases [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
2021	3,019
2022	354
2023	183
2024	135
2025	135
Below Market Lease [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
2021	6,193
2022	5,437
2023	5,296
2024	3,780
2025	$ 3,775

Summary Of Significant Accoun_8

Summary Of Significant Accounting Policies of Tax Treatment of Common Dividends Per Share for Federal Tax Purposes (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018		Dec. 15, 2020
Summary Of Significant Accounting Policies [Line Items]
Dividends Treatment For Federal Tax Purposes, Percentage	100.00%		100.00%		100.00%
Dividends treatment for federal tax purposes.	$ 3.88	[1]	$ 3.15	[2]	$ 3.57	[3]
Distributions Payable, Amount Per Unit							$ 0.98
Ordinary income
Summary Of Significant Accounting Policies [Line Items]
Dividends Treatment For Federal Tax Purposes, Percentage	64.91%		94.84%		78.17%
Dividends treatment for federal tax purposes.	$ 2.52		$ 2.99		$ 2.79
Capital Gain Income
Summary Of Significant Accounting Policies [Line Items]
Dividends Treatment For Federal Tax Purposes, Percentage	25.49%		5.16%		21.83%
Dividends treatment for federal tax purposes.	$ 0.99		$ 0.16		$ 0.78
Return of Capital
Summary Of Significant Accounting Policies [Line Items]
Dividends Treatment For Federal Tax Purposes, Percentage	9.60%		0.00%		0.00%
Dividends treatment for federal tax purposes.	$ 0.37		$ 0		$ 0
Dividend Declared
Summary Of Significant Accounting Policies [Line Items]
Distributions Payable, Amount Per Unit	$ 0.98		0.98		0.95
Allocated to 2019
Summary Of Significant Accounting Policies [Line Items]
Distributions Payable, Amount Per Unit			0.04		0.26
Allocated to 2020
Summary Of Significant Accounting Policies [Line Items]
Distributions Payable, Amount Per Unit			$ 0.94
Allocated to 2018
Summary Of Significant Accounting Policies [Line Items]
Distributions Payable, Amount Per Unit					$ 0.69

[1]	The fourth quarter 2020 regular quarterly dividend was $0.98 per common share, all of which was allocable to 2021.
[2]	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 was allocable to 2020.
[3]	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 was allocable to 2019.

Real Estate Schedule of Real Es

Real Estate Schedule of Real Estate Properties (Details) - USD ($) $ in Thousands		Dec. 31, 2020	Dec. 31, 2019
Real Estate Properties [Line Items]
Land		$ 5,069,206	$ 5,111,606
Right-of-use assets - finance leases		237,393	237,394
Right of use assets - operating leases		146,406	148,640
Land held for future development	[1]	450,954	254,828
Buildings and improvements		13,777,691	13,646,054
Tenant improvements		2,752,880	2,656,439
Furniture, Fixtures and Equipment		49,606	44,313
Construction in progress		868,773	789,736
Total		23,352,909	22,889,010
Less: accumulated depreciation		(5,534,102)	(5,266,798)
Total real estate		17,818,807	17,622,212
Boston Properties Limited Partnership
Real Estate Properties [Line Items]
Land		4,971,990	5,011,153
Right-of-use assets - finance leases		237,393	237,394
Right of use assets - operating leases		146,406	148,640
Land held for future development	[1]	450,954	254,828
Buildings and improvements		13,498,098	13,351,286
Tenant improvements		2,752,880	2,656,439
Furniture, Fixtures and Equipment		49,606	44,313
Construction in progress		868,773	789,736
Total		22,976,100	22,493,789
Less: accumulated depreciation		(5,428,576)	(5,162,908)
Total real estate		$ 17,547,524	$ 17,330,881

[1]	Includes pre-development costs.

Real Estate (Narrative) (Detail

Real Estate (Narrative) (Details) $ in Thousands

Dec. 16, 2020USD ($)

Nov. 03, 2020ft²

Jun. 25, 2020USD ($)ft²

Feb. 20, 2020USD ($)ft²Buildings

Jan. 28, 2020USD ($)ft²Buildings

Jan. 27, 2020USD ($)

Feb. 19, 2020USD ($)

Jun. 24, 2020USD ($)

Dec. 31, 2020USD ($)

Dec. 31, 2019USD ($)

Dec. 31, 2018USD ($)

Aug. 15, 2020ft²apartments

Jul. 31, 2020USD ($)

Jun. 26, 2020USD ($)ft²

Jun. 01, 2020ft²

Mar. 26, 2020ft²

Real Estate Properties [Line Items]

Proceeds from sales of real estate

$ 519,303

$ 90,824

$ 455,409

Gains on sales of real estate

618,982

709

182,356

Payments to Acquire Equity Method Investments

172,436

87,392

345,717

Revenues

$ 2,765,686

2,960,562

2,717,076

Capital Gallery [Member]

Real Estate Properties [Line Items]

Net Rentable Area (in sf) | ft²

455,000

Contractual Sales Price

$ 253,700

Proceeds from sales of real estate

246,600

Gains on sales of real estate

$ 203,500

Operating Income (Loss)

$ 6,300

15,000

14,500

Crane Meadow

Real Estate Properties [Line Items]

Contractual Sales Price

$ 14,300

Proceeds from sales of real estate

14,200

Gains on sales of real estate

$ 5,200

New Dominion Technology Park [Member]

Real Estate Properties [Line Items]

Net Rentable Area (in sf) | ft²

493,000

Contractual Sales Price

$ 256,000

Proceeds from sales of real estate

254,000

Gains on sales of real estate

$ 192,300

Operating Income (Loss)

$ 1,600

6,800

8,200

Number of buildings | Buildings

Gateway Center [Member]

Real Estate Properties [Line Items]

Gains on sales of real estate

$ 217,700

Operating Income (Loss)

$ 200

10,400

8,600

425 Fourth Street [Member]

Real Estate Properties [Line Items]

Aggregate purchase price

$ 140,100

Net Rentable Area (in sf) | ft²

850,000

17Fifty Presidents Street

Real Estate Properties [Line Items]

Net Rentable Area (in sf) | ft²

276,000

Leased percentage

100.00%

20 Citypoint

Real Estate Properties [Line Items]

Net Rentable Area (in sf) | ft²

211,000

Leased percentage

100.00%

Capital Gallery [Member]

Real Estate Properties [Line Items]

Net Rentable Area (in sf) | ft²

631,000

176,000

759 Harrison Street [Member]

Real Estate Properties [Line Items]

Aggregate purchase price

$ 4,500

200 West Street

Real Estate Properties [Line Items]

Leased percentage

100.00%

Lessor, Operating Lease, Lease Not yet Commenced, Description

10-year

Lessor Operating Lease Lease Not Yet Commenced Leased SF | ft²

138,000

Residential Building | The Skylyne

Real Estate Properties [Line Items]

Net Rentable Area (in sf) | ft²

331,000

Number of Units in Real Estate Property | apartments

402

Gateway Commons Complex [Member]

Real Estate Properties [Line Items]

Net Rentable Area (in sf) | ft²

768,000

Payments to Acquire Equity Method Investments

$ 350,000

Ownership Percentage

50.00%

[1]

Number of buildings | Buildings

Gateway Commons Complex prior to deferred contribution [Member] [Member]

Real Estate Properties [Line Items]

Ownership Percentage

55.00%

Gateway Commons Complex Future Development[Member] [Member]

Real Estate Properties [Line Items]

Ownership Percentage

49.00%

Joint Venture Partner [Member] | Gateway Commons Complex [Member]

Real Estate Properties [Line Items]

Payments to Acquire Equity Method Investments

$ 280,800

Future payment to acquire interest in equity method investment

$ 69,200

Ownership Percentage

50.00%

Number of buildings | Buildings

Joint Venture Partner [Member] | Gateway Commons Complex Future Development[Member] [Member]

Real Estate Properties [Line Items]

Ownership Percentage

51.00%

Boston Properties Limited Partnership

Real Estate Properties [Line Items]

Proceeds from sales of real estate

$ 519,303

90,824

455,409

Gains on sales of real estate

631,945

858

190,716

Payments to Acquire Equity Method Investments

172,436

87,392

345,717

Revenues

$ 2,765,686

$ 2,960,562

$ 2,717,076

Boston Properties Limited Partnership | Capital Gallery [Member]

Real Estate Properties [Line Items]

Gains on sales of real estate

$ 207,000

Boston Properties Limited Partnership | New Dominion Technology Park [Member]

Real Estate Properties [Line Items]

Gains on sales of real estate

$ 197,100

Boston Properties Limited Partnership | Gateway Center [Member]

Real Estate Properties [Line Items]

Gains on sales of real estate

$ 222,400

[1]

As a result of the partner’s deferred contribution, the Company owns an approximately 55% interest in the joint venture at December 31, 2020. Future development projects will be owned 49% by the Company and 51% by its partner.

Leases (Details)

Leases (Details) - USD ($) $ in Thousands	12 Months Ended
Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Fixed contractual payments	$ 2,211,915	$ 2,261,260
Variable lease payments	434,346	496,754
Lease	$ 2,646,261	$ 2,758,014

Leases Narrative (Details)

Leases Narrative (Details) - USD ($) $ in Thousands	Oct. 21, 2020	Dec. 31, 2020
Lessor, Lease, Description [Line Items]
Write-off for accounts receivable		$ 22,600
Write-off for accrued rent		$ 67,700
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description		The Company has four non-cancelable ground lease obligations, as lessee, which were classified as operating leases, with various initial term expiration dates through 2114.
Hotel Ground Lease
Lessor, Lease, Description [Line Items]
Lessor, Operating Lease, Option to Terminate	On July 29, 2020, the Company entered into a 99-year ground lease with a third-party hotel developer for land at its Reston Next property located in Reston Virginia, which will support the development of a 270-room, approximately 241,000 square foot hotel property. The lease commenced on October 21, 2020 and upon commencement, the Company performed classification testing. The ground lease is subject to termination rights with respect to the hotel developer’s ability to obtain construction financing for the property and as of the lease commencement date, the Company was not reasonably certain that those termination rights would not be exercised and as such it has accounted for this as an operating lease that will expire on August 28, 2022.

Lessee, Lease Cost and Other In

Lessee, Lease Cost and Other Information (Details) $ in Thousands		12 Months Ended
		Dec. 31, 2020USD ($)Vehicles	Dec. 31, 2019USD ($)Vehicles
Lessee, Lease, Description [Line Items]
Operating lease costs		$ 13,948	$ 14,573
Amortization of right-of-use asset	[1]	56	29
Interest on lease liabilities	[2]	$ 583	$ 47
Operating leases, Weighted-average remaining lease term		51 years	51 years
Finance leases, Weighted-average remaining lease term		70 years	71 years
Operating leases, Weighted-average discount rate		5.70%	5.70%
Finance leases, Weighted-average discount rate		6.20%	6.20%
Finance leases under development \| Vehicles		3	3

[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 for all or a portion of the years ended December 31, 2020 and December 31, 2019, respectively, and as such, a portion of the interest amount was capitalized.

Future Minimum Lease Payments f

Future Minimum Lease Payments for Capital Leases (Details) $ in Thousands	Dec. 31, 2020USD ($)
Leases [Abstract]
Lessee purchase option reasonably certain of exercising	$ 38,700

Lease Liability Maturity Schedu

Lease Liability Maturity Schedule (Details) - USD ($) $ in Thousands		Dec. 31, 2020	Dec. 31, 2019
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2021		$ 25,092
2022		18,020
2023		10,262
2024		9,277
2025		9,476
Thereafter		548,478
Total lease payments		620,605
Less: Interest Portion		(418,892)
Present value of lease payments		201,713	$ 200,180
Finance Lease, Liability, Payment, Due [Abstract]
2021		5,896
2022		10,206
2023		9,701
2024	[1]	48,518
2025		9,971
Thereafter		1,373,177
Total lease payments		1,457,469
Less: Interest Portion		(1,220,977)
Present value of lease payments		$ 236,492	$ 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

Future Minimum Rent (Details)

Future Minimum Rent (Details) $ in Thousands	12 Months Ended
Future Minimum Rent (Details) $ in Thousands	Dec. 31, 2020USD ($)
Leases [Abstract]
2021	$ 2,177,848
2022	2,188,846
2023	2,144,213
2024	2,043,264
2025	1,901,624
Thereafter	$ 12,577,660
Schedule of Future Minimum Lease Payments
Concentration Risk, Percentage	10.00%
Number Of Tenants Above Concentration Amount.	0

Deferred Charges (Details)

Deferred Charges (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Leasing costs, including lease related intangibles	$ 1,023,058	$ 1,155,958
Financing costs	12,728	12,728
Deferred Costs Gross	1,035,786	1,168,686
Less: Accumulated amortization	(395,701)	(479,473)
Deferred Costs, total	$ 640,085	$ 689,213

Deferred Charges Schedule of Ac

Deferred Charges Schedule of Acquired In-Place Lease Intangibles (Details) $ in Thousands	Dec. 31, 2020USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2021	$ 10,352
2022	5,464
2023	3,854
2024	2,220
2025	$ 2,174

Investments in Unconsolidated_3

Investments in Unconsolidated Joint Ventures (Investments in Unconsolidated Joint Ventures) (Details) $ in Thousands		12 Months Ended
		Dec. 31, 2020USD ($)ft²paymentsBuildings		Jun. 25, 2020Land_Parcels	Jan. 28, 2020	Dec. 31, 2019USD ($)
Schedule of Equity Method Investments [Line Items]
Other Liabilities		$ (412,084)				$ (387,994)
Investments in unconsolidated joint ventures		1,310,478				955,647
Investments In Affiliates Subsidiaries Associates And Joint Ventures net	[1]	1,273,919				933,223
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Other Liabilities		$ (36,600)				(22,400)
Square 407 Limited Partnership [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Market Square North
Ownership Percentage		50.00%
Other Liabilities	[1]	$ (3,766)				(4,872)
BP/CRF Metropolitan Square LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Metropolitan Square
Ownership Percentage		20.00%
Other Liabilities	[1]	$ (13,584)
Investments in unconsolidated joint ventures	[1]					9,134
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]	$ (12,264)				(12,113)
901 New York Avenue LLC (economic ownership) [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		50.00%
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]	$ 35,297				36,789
Annapolis Junction NFM, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Annapolis Junction
Ownership Percentage		50.00%	[4]	50.00%
Investments in unconsolidated joint ventures	[1]	$ 13,463				25,391
Number of real estate properties \| Buildings		2
Parcels of undeveloped land \| Land_Parcels				2
540 Madison Venture
Schedule of Equity Method Investments [Line Items]
Properties		540 Madison Avenue
Ownership Percentage	[5]	60.00%
Investments in unconsolidated joint ventures	[1]	$ 122				2,953
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]	$ (6,945)				(5,439)
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]	$ 42,499				42,496
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]	$ 48,818				49,466
Residential Tower Developer LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Hub50House
Ownership Percentage		50.00%
Investments in unconsolidated joint ventures	[1]	$ 50,943				55,092
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]	$ 10,754				9,883
Office Tower Developer LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		100 Causeway Street
Ownership Percentage		50.00%
Investments in unconsolidated joint ventures	[1]	$ 56,312				56,606
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]	$ 3,787				3,780
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]	$ 29,536				94,804
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]	$ 1,846
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]	$ 227,671				252,069
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]	$ 58,112				56,247
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]	$ 113,774				67,499
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]	$ 145,761				163,937
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]	$ 108,393				$ 29,501
Gateway Portfolio Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Gateway Commons
Ownership Percentage		50.00%	[8]		50.00%
Investments in unconsolidated joint ventures	[1]	$ 336,206
Rosecrans-Sepulveda Partners 4, LLC
Schedule of Equity Method Investments [Line Items]
Properties		Beach Cities Media Campus
Ownership Percentage		50.00%
Investments in unconsolidated joint ventures	[1]	$ 27,184
Entity Owning Land And Infrastructure Of Project [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		33.30%
Gateway Commons Complex prior to deferred contribution [Member] [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage					55.00%
Gateway Commons Complex Future Development[Member] [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage					49.00%
Joint Venture Partner [Member] \| Gateway Portfolio Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage					50.00%
Joint Venture Partner [Member] \| Gateway Commons Complex Future Development[Member] [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage					51.00%

[1]	Investments with deficit balances aggregating approximately $36.6 million and $22.4 million at December 31, 2020 and 2019, 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. At December 31, 2020 and 2019, the Company’s economic ownership was approximately 50%.
[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 two in-service buildings.
[5]	T he property was sold on June 27, 2019. As of December 31, 2020 and 2019, the investment consisted of undistributed cash.
[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).
[8]	As a result of the partner’s deferred contribution, the Company owns an approximately 55% interest in the joint venture at December 31, 2020. Future development projects will be owned 49% by the Company and 51% by its partner.

Investments in Unconsolidated_4

Investments in Unconsolidated Joint Ventures (Balance Sheets of the Unconsolidated Joint Ventures) (Details) - USD ($) $ in Thousands		Dec. 31, 2020	Dec. 13, 2020	Dec. 31, 2019
ASSETS
Real estate and development in process, net		$ 17,818,807		$ 17,622,212
Total assets		22,858,190		21,284,905
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Mortgage and notes payable, net		2,909,081		2,922,408
Other Liabilities		412,084		387,994
Members’/Partners’ equity		5,996,083		5,684,687
Total liabilities and equity / capital		22,858,190		21,284,905
Carying value of the Company's investment in unconsolidated joint ventures		1,310,478		955,647
Right-of-use assets - finance leases		237,393		237,394
Right of use assets - operating leases		146,406		148,640
Present value of lease payments		236,492		224,042
Lease liabilities - operating leases		201,713		200,180
Unconsolidated Joint Ventures [Member]
ASSETS
Real estate and development in process, net	[1]	4,708,571		3,904,400
Other assets		531,071		502,706
Total assets		5,239,642		4,407,106
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Mortgage and notes payable, net				2,218,853
Other Liabilities	[2]	650,433		749,675
Members’/Partners’ equity		1,951,298		1,438,578
Total liabilities and equity / capital		5,239,642		4,407,106
Company's share of equity		936,087		591,905
Basis differentials	[3]	337,832		341,318
Carying value of the Company's investment in unconsolidated joint ventures	[4]	1,273,919		933,223
Right-of-use assets - finance leases		248,900		383,900
Right of use assets - operating leases		22,500		12,100
Present value of lease payments		388,700		510,800
Lease liabilities - operating leases		29,000		17,300
Colorado Center [Member]
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Basis differentials		307,300		311,300
Unconsolidated Joint Ventures [Member]
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Other Liabilities		36,600		$ 22,400
Gateway Commons Complex [Member]
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Basis differentials		51,900
Carying value of the Company's investment in unconsolidated joint ventures	[5]	336,206
Dock 72 [Member]
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Mortgage and notes payable, net			$ 198,600
Basis differentials		$ (52,200)

[1]	At December 31, 2020 and 2019, this amount included right of use assets - finance leases totaling approximately $248.9 million and $383.9 million, respectively, and right of use assets - operating leases totaling approximately $22.5 million and $12.1 million, respectively.
[2]	At December 31, 2020 and 2019, this amount included lease liabilities - finance leases totaling approximately $388.7 million and $510.8 million, respectively, and lease liabilities - operating leases totaling approximately $29.0 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, 2020 and 2019, there was an aggregate basis differential of approximately $307.3 million and $311.3 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. At December 31, 2020, there was an aggregate basis differential of approximately $51.9 million between the carrying value of the Company’s investment in the joint venture that owns Gateway Commons and the joint venture’s basis in the assets and liabilities. At December 31, 2020, there was an aggregate basis differential of approximately $(52.2) million between the carrying value of the Company’s investment in the joint venture that owns Dock 72 and the joint venture’s basis in the assets and liabilities. These basis differentials (excluding land) will be amortized over the remaining lives of the related assets and liabilities.
[4]	Investments with deficit balances aggregating approximately $36.6 million and $22.4 million at December 31, 2020 and 2019, respectively, are reflected within Other Liabilities in the Company’s Consolidated Balance Sheets.
[5]	Investments with deficit balances aggregating approximately $36.6 million and $22.4 million at December 31, 2020 and 2019, respectively, are included 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		12 Months Ended
		Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Total revenue		$ 2,765,686		$ 2,960,562		$ 2,717,076
Expenses
Transaction costs		1,531		1,984		1,604
Depreciation and amortization		683,751		677,764		645,649
Total expenses		1,860,364		1,914,925		1,791,579
Other income (expense)
Interest expense		(431,717)		(412,717)		(378,168)
Gains on sales of real estate		618,982		709		182,356
Net income		1,018,691		651,999		712,563
Income (Loss) from Equity Method Investments		(85,110)		46,592		2,222
Straight-line rent adjustments		(104,900)		(58,400)		(51,900)
Above and below market rent adjustments, net		6,500		20,900		23,800
Write-off for accrued rent		67,700
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Total revenue	[1]	319,560		322,817		271,951
Expenses
Operating		144,347		122,992		106,610
Transaction costs		1,027		1,000		0
Depreciation and amortization		141,853		102,296		103,079	[2]
Total expenses		287,227		226,288		209,689
Other income (expense)
Interest expense		(98,051)		(84,409)		(71,308)
Gains on sales of real estate		11,737		32,706	[3]	16,951
Net income		(53,981)		44,826		7,905
Company's share of net income		(16,256)		24,423		8,084
Impairment loss on investment		(60,524)	[4]	0		0
Basis differential	[5]	(8,330)	[4]	22,169	[3]	(5,862)
Income (Loss) from Equity Method Investments		(85,110)		46,592		2,222
Straight-line rent adjustments		(10,100)		32,400		15,900
Write-off for accrued rent		51,700
Colorado Center [Member]
Other income (expense)
Straight-line rent adjustments		1,800		2,100		2,400
Above and below market rent adjustments, net		900		1,700		1,600
Dock 72 [Member]
Other income (expense)
Impairment loss on investment		$ (60,500)
540 Madison Avenue [Member]
Other income (expense)
Gains on sales of real estate				$ 47,200
Metropolitan Square
Expenses
Depreciation and amortization						22,400
Metropolitan Square \| Company's Share [Member]
Expenses
Depreciation and amortization						$ 4,500

[1]	Includes straight-line rent adjustments of approximately $(10.1) million, $32.4 million and $15.9 million for the years ended December 31, 2020, 2019 and 2018, respectively. Due primarily to the impact of COVID-19, for the year ended December 31, 2020, write-offs of accounts receivable and accrued rent balances totaled approximately $51.7 million.
[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. 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]	During the year ended December 31, 2020, the Company recognized an other-than-temporary impairment loss on its investment in the unconsolidated joint venture that owns Dock 72 in Brooklyn, New York totaling approximately $60.5 million.
[5]	Includes straight-line rent adjustments of approximately $1.8 million, $2.1 million and $2.4 million for the years ended December 31, 2020, 2019 and 2018, respectively. Also includes net above-/below-market rent adjustments of approximately $0.9 million, $1.7 million and $1.6 million for the years ended December 31, 2020, 2019 and 2018, respectively.

Investment in Unconsolidated Jo

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

Dec. 14, 2020USD ($)

Dec. 13, 2020USD ($)

Nov. 13, 2020USD ($)ft²

Nov. 12, 2020USD ($)

Oct. 30, 2020USD ($)ft²yr

Jul. 23, 2020USD ($)aft²

Jun. 25, 2020USD ($)ft²Land_ParcelsVehicles

Jun. 09, 2020USD ($)ft²yr

Jan. 28, 2020USD ($)ft²Buildings

Dec. 31, 2020USD ($)

Dec. 31, 2019USD ($)

Dec. 31, 2018USD ($)

Oct. 01, 2020ft²

Sep. 30, 2020USD ($)

Sep. 01, 2020ft²a

Jul. 24, 2020ft²apartments

Jun. 08, 2020USD ($)

Feb. 20, 2020USD ($)aft²

Schedule of Equity Method Investments [Line Items]

Mortgage notes payable, net

$ 2,909,081

$ 2,922,408

Payments to Acquire Equity Method Investments

172,436

87,392

$ 345,717

Income (Loss) from Equity Method Investments

(85,110)

46,592

2,222

Capital distributions from unconsolidated joint ventures

55,298

136,807

Proceeds from sales of real estate

$ 519,303

$ 90,824

$ 455,409

Significant unobservable inputs used in other than temporary impairment analysis

The Company determined that its valuation of the investment was categorized within Level 3 of the fair value hierarchy, as it utilized significant unobservable inputs in its assessment including an exit capitalization rate of 5.25%, a discount rate on the Company’s equity investment (the property is encumbered by mortgage debt) of 8.0% and an average lease commencement on currently vacant space of mid-2023.

Gateway Commons Complex [Member]

Schedule of Equity Method Investments [Line Items]

Ownership Percentage

50.00%

[1]

50.00%

[1]

Number of buildings | Buildings

Net Rentable Area (in sf) | ft²

768,000

Payments to Acquire Equity Method Investments

$ 350,000

Annapolis Junction Building Six [Member]

Schedule of Equity Method Investments [Line Items]

Ownership Percentage

50.00%

Mortgage notes payable, net

$ 13,200

$ 12,000

Debt Instrument, Basis Spread on Variable Rate

2.50%

2.00%

Net Rentable Area (in sf) | ft²

119,000

Debt Instrument, Description of Variable Rate Basis

bears interest at a variable rate equal to (1) the greater of (x) LIBOR or (y) 0.50%, plus (2) 2.50% per annum

Gateway Commons Complex prior to deferred contribution [Member] [Member]

Schedule of Equity Method Investments [Line Items]

Ownership Percentage

55.00%

Gateway Commons Complex Future Development[Member] [Member]

Schedule of Equity Method Investments [Line Items]

Ownership Percentage

49.00%

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

Finance Lease fixed purchase price

$ 134,800

Prepaid purchase price

$ 15,000

Area of Land | a

5.6

Metropolitan Square

Schedule of Equity Method Investments [Line Items]

Ownership Percentage

20.00%

Number of extensions

Extension Option (in years) | yr

Debt instrument, borrowing capacity

$ 325,000

Debt Instrument, Basis Spread on Variable Rate

4.75%

Net Rentable Area (in sf) | ft²

654,000

Debt

$ 288,000

$ 155,900

Debt Instrument, Interest Rate, Stated Percentage

5.75%

Capital distributions from unconsolidated joint ventures

$ 112,700

Derivative, Cap Interest Rate

3.00%

Derivative, Notional Amount

$ 325,000

Annapolis Junction NFM, LLC [Member]

Schedule of Equity Method Investments [Line Items]

Ownership Percentage

50.00%

[3]

50.00%

[3]

Net Rentable Area (in sf) | ft²

300,000

Contractual Sales Price

$ 47,000

Number of Vehicles | Vehicles

511

Parcels of undeveloped land | Land_Parcels

land parcel | Land_Parcels

Income (Loss) from Equity Method Investments

$ 5,800

Capital distributions from unconsolidated joint ventures

36,800

Proceeds from sales of real estate

$ 45,800

Annapolis Junction Building Eight [Member]

Schedule of Equity Method Investments [Line Items]

Ownership Percentage

50.00%

Mortgage notes payable, net

$ 34,500

Debt Instrument, Basis Spread on Variable Rate

2.35%

Net Rentable Area (in sf) | ft²

126,000

Repayments of Debt

$ 16,100

Annapolis Junction Building Seven [Member]

Schedule of Equity Method Investments [Line Items]

Mortgage notes payable, net

$ 18,400

Debt Instrument, Basis Spread on Variable Rate

2.35%

Net Rentable Area (in sf) | ft²

127,000

Beach Cities Media Center [Member]

Schedule of Equity Method Investments [Line Items]

Ownership Percentage

50.00%

Net Rentable Area (in sf) | ft²

275,000

Area of Land | a

6.4

Payments to Acquire Equity Method Investments

$ 21,200

1265 Main Office JV LLC [Member]

Schedule of Equity Method Investments [Line Items]

Ownership Percentage

50.00%

Market Square North [Member]

Schedule of Equity Method Investments [Line Items]

Ownership Percentage

50.00%

Mortgage notes payable, net

$ 114,200

Number of extensions

Extension Option (in years) | yr

Debt Instrument, Basis Spread on Variable Rate

2.30%

Net Rentable Area (in sf) | ft²

418,000

Debt

$ 125,000

Debt Instrument, Interest Rate, Stated Percentage

4.85%

Debt Instrument, Description of Variable Rate Basis

variable rate equal to (1) the greater of (x) LIBOR or (y) 0.50%, plus (2) 2.30% per annum

Agreement with 1265 Main Office JV LLC partner [Member]

Schedule of Equity Method Investments [Line Items]

Ownership Percentage

50.00%

Net Rentable Area (in sf) | ft²

1,200,000

Area of Land | a

Dock 72 [Member]

Schedule of Equity Method Investments [Line Items]

Ownership Percentage

50.00%

Mortgage notes payable, net

$ 198,600

Debt Instrument, Basis Spread on Variable Rate

2.85%

2.25%

Net Rentable Area (in sf) | ft²

669,000

Debt Instrument, Description of Variable Rate Basis

initial variable rate equal to (1) the greater of (x) LIBOR or (y) 0.25%, plus (2) 2.85% per annum

Leased percentage

33.00%

Debt instrument, total commitment

$ 250,000

Impairment loss on investment

$ 60,500

Joint Venture Partner [Member] | Gateway Commons Complex [Member]

Schedule of Equity Method Investments [Line Items]

Ownership Percentage

50.00%

Number of buildings | Buildings

Payments to Acquire Equity Method Investments

$ 280,800

Future payment to acquire interest in equity method investment

$ 69,200

Joint Venture Partner [Member] | Gateway Commons Complex Future Development[Member] [Member]

Schedule of Equity Method Investments [Line Items]

Ownership Percentage

51.00%

Residential Building | 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] | Metropolitan Square

Schedule of Equity Method Investments [Line Items]

Capital distributions from unconsolidated joint ventures

$ 22,500

Company's Share [Member] | Annapolis Junction NFM, LLC [Member]

Schedule of Equity Method Investments [Line Items]

Parcels of undeveloped land | Land_Parcels

Capital distributions from unconsolidated joint ventures

$ 18,400

Base Rate [Member] | Metropolitan Square

Schedule of Equity Method Investments [Line Items]

Debt Instrument, Description of Variable Rate Basis

the greater of (x) LIBOR or (y) 0.65%

[1]

[2]

This entity is a VIE (See Note 1).

[3]

The joint venture owns two in-service buildings.

Mortgage Notes Payable, Net (De

Mortgage Notes Payable, Net (Details) $ in Thousands	12 Months Ended
Mortgage Notes Payable, Net (Details) $ in Thousands	Dec. 31, 2020USD ($)Vehicles	Dec. 31, 2019USD ($)Vehicles
Debt Instrument [Line Items]
Mortgage and notes payable, net	$ 2,909,081	$ 2,922,408
Debt Instrument, Collateral	each collateralized by one or more buildings and related land included in real estate assets	each collateralized by one or more buildings and related land included in real estate assets
Number Of Variable Mortgage Loans \| Vehicles	0	0
Fixed Rate Mortgage [Member]
Debt Instrument [Line Items]
Mortgage and notes payable, net	$ 2,909,081	$ 2,922,408
Debt, Weighted Average Interest Rate	3.72%	3.73%
Fixed Rate Mortgage [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.43%	3.43%
Fixed Rate Mortgage [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.94%	6.94%

Schedule of Aggregate Principal

Schedule of Aggregate Principal Payments on Mortgage Notes (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Disclosure [Abstract]
2021	$ 17,276
2022	614,710
2023	0
2024	0
2025	0
Thereafter	2,300,000
Total	2,931,986
Deferred financing costs, net	(22,905)
Mortgage notes payable, net (amounts related to VIEs of $2,907,590 and $2,918,806 at December 31, 2020 and December 31, 2019, respectively)	$ 2,909,081	$ 2,922,408

Schedule of Unsecured Senior No

Schedule of Unsecured Senior Notes (Details) - USD ($) $ in Thousands		Dec. 31, 2020		May 05, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Debt Issuance Costs, Net		$ (22,905)
Senior Notes		9,639,287			$ 8,390,459
Boston Properties Limited Partnership
Debt Instrument [Line Items]
Debt Issuance Costs, Net		(22,900)
Senior Notes		9,639,287			$ 8,390,459
Boston Properties Limited Partnership \| Senior Notes
Debt Instrument [Line Items]
Debt		9,700,000
Debt Instrument, Unamortized Discount		(16,034)
Debt Issuance Costs, Net		(44,679)
Senior Notes		$ 9,639,287
Boston Properties Limited Partnership \| Senior Notes \| 4.289% unsecured senior notes
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		4.125%
Debt Instrument, Interest Rate, Effective Percentage	[1]	4.289%
Debt		$ 850,000
Long-term Debt, Maturity Date	[2],[3]	May 15, 2021
Boston Properties Limited Partnership \| Senior Notes \| 3.954% unsecured senior notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		3.85%
Debt Instrument, Interest Rate, Effective Percentage	[1]	3.954%
Debt		$ 1,000,000
Long-term Debt, Maturity Date	[2]	Feb. 1, 2023
Boston Properties Limited Partnership \| Senior Notes \| 3.279% unsecured senior notes
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		3.125%
Debt Instrument, Interest Rate, Effective Percentage	[1]	3.279%
Debt		$ 500,000
Long-term Debt, Maturity Date	[2]	Sep. 1, 2023
Boston Properties Limited Partnership \| Senior Notes \| 3.916% unsecured senior notes
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		3.80%
Debt Instrument, Interest Rate, Effective Percentage	[1]	3.916%
Debt		$ 700,000
Long-term Debt, Maturity Date	[2]	Feb. 1, 2024
Boston Properties Limited Partnership \| Senior Notes \| 3.350% unsecured senior notes
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		3.20%
Debt Instrument, Interest Rate, Effective Percentage	[1]	3.35%
Debt		$ 850,000
Long-term Debt, Maturity Date	[2]	Jan. 15, 2025
Boston Properties Limited Partnership \| Senior Notes \| 3.766% unsecured senior notes
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		3.65%
Debt Instrument, Interest Rate, Effective Percentage	[1]	3.766%
Debt		$ 1,000,000
Long-term Debt, Maturity Date	[2]	Feb. 1, 2026
Boston Properties Limited Partnership \| Senior Notes \| 3.495% unsecured senior notes
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		2.75%
Debt Instrument, Interest Rate, Effective Percentage	[1]	3.495%
Debt		$ 1,000,000
Long-term Debt, Maturity Date	[2]	Oct. 1, 2026
Boston Properties Limited Partnership \| Senior Notes \| 4.628% unsecured senior notes
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		4.50%
Debt Instrument, Interest Rate, Effective Percentage	[1]	4.628%
Debt		$ 1,000,000
Long-term Debt, Maturity Date	[2]	Dec. 1, 2028
Boston Properties Limited Partnership \| Senior Notes \| 3.505% unsecured senior notes
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		3.40%
Debt Instrument, Interest Rate, Effective Percentage	[1]	3.505%
Debt		$ 850,000
Long-term Debt, Maturity Date	[2]	Jun. 21, 2029
Boston Properties Limited Partnership \| Senior Notes \| 2.984% unsecured senior notes
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		2.90%
Debt Instrument, Interest Rate, Effective Percentage	[1]	2.984%
Debt		$ 700,000
Long-term Debt, Maturity Date	[2]	Mar. 15, 2030
Boston Properties Limited Partnership \| Senior Notes \| 3.343 % unsecured senior notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		3.25%		3.25%
Debt Instrument, Interest Rate, Effective Percentage		3.343%	[1]	3.343%
Debt		$ 1,250,000		$ 1,250,000
Long-term Debt, Maturity Date	[2]	Jan. 30, 2031

[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.
[3]	See Note 18

Unsecured Senior Notes (Narrati

Unsecured Senior Notes (Narrative) (Details) - USD ($) $ in Thousands	May 05, 2020	Dec. 31, 2020		Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Proceeds from unsecured senior notes		$ 1,248,125		$ 1,548,106	$ 996,410
Boston Properties Limited Partnership
Debt Instrument [Line Items]
Proceeds from unsecured senior notes		$ 1,248,125		$ 1,548,106	$ 996,410
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, 2020, Boston Properties Limited Partnership was in compliance with each of these financial restrictions and requirements.
Senior Notes \| Boston Properties Limited Partnership
Debt Instrument [Line Items]
Debt		$ 9,700,000
3.343 % unsecured senior notes [Member] \| Senior Notes \| Boston Properties Limited Partnership
Debt Instrument [Line Items]
Debt	$ 1,250,000	$ 1,250,000
Debt Instrument, Interest Rate, Stated Percentage	3.25%	3.25%
Senior Notes Pricing	99.85%
Debt Instrument, Interest Rate, Effective Percentage	3.343%	3.343%	[1]
Proceeds from unsecured senior notes	$ 1,240,000

[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 Line of Credit (Detai

Unsecured Line of Credit (Details) - USD ($) $ in Thousands	Apr. 24, 2017	Dec. 31, 2020	Dec. 31, 2019	Apr. 24, 2018	Apr. 23, 2017
Line of Credit Facility [Line Items]
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.
Unsecured term loan, net		$ 499,390	$ 498,939
Long-term Line of Credit		$ 0	0
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
Debt Instrument, Basis Spread on Variable Rate		0.875%
Competitive bid quote	65.00%
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage		0.15%
Long-term Line of Credit		$ 0	0
Revolving Credit Facility [Member] \| Maximum [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.30%
Revolving Credit Facility [Member] \| Minimum [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.10%
Delayed Draw Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 500,000			$ 500,000
Debt Instrument, Basis Spread on Variable Rate		0.95%
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.15%
Unsecured term loan, net		$ 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.

Commitments And Contingencies (

Commitments And Contingencies (Details)	12 Months Ended
Commitments And Contingencies (Details)	Dec. 31, 2020USD ($)ft²	Dec. 31, 2009USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Jan. 10, 2014USD ($)
Commitments And Contingencies [Line Items]
Letter of credit and performance obligations	$ 20,000,000
Notes Receivable, Related Parties	77,552,000		$ 80,000,000
Property insurance program per occurrence limits	1,000,000,000
Per occurrence limit for NBCR Coverage	1,000,000,000
Value of program trigger	$ 200,000,000
Coinsurance of program trigger	20.00%
Program trigger deductible	20.00%
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
Notes receivable, net	18,729,000		15,920,000
Affiliate of Bernstein Companies [Member]
Commitments And Contingencies [Line Items]
Notes receivable, net	$ 10,000,000
Note receivable fixed interest rate	8.00%
Boston Properties Limited Partnership
Commitments And Contingencies [Line Items]
Notes Receivable, Related Parties	$ 77,552,000		80,000,000
Operating partnership guarantee to cover liabilities of IXP	20,000,000
Notes receivable, net	18,729,000		$ 15,920,000
767 Venture, LLC [Member]
Commitments And Contingencies [Line Items]
Maximum funding obligation	30,600,000
Property insurance program per occurrence limits	1,625,000,000
7750 Wisconsin Avenue [Member]
Commitments And Contingencies [Line Items]
Liabilities for Contingent Guarantees	0
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	100,000			$ 18,000,000
Bankruptcy remaining claim amount allowed by court to creditor	27,100,000
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
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
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
Future Retail Building [Member] \| 325 Main Street
Commitments And Contingencies [Line Items]
Net Rentable Area (in sf) \| ft²	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, 2020shares
OP Units [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Noncontrolling Interest, Outstanding	16,037,121
LTIP Units [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Noncontrolling Interest, Outstanding	1,336,115
OPP Units 2012 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Noncontrolling Interest, Outstanding	105,080
MYLTIP 2013
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Noncontrolling Interest, Outstanding	64,468
MYLTIP 2014
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Noncontrolling Interest, Outstanding	23,100
MYLTIP 2015 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Noncontrolling Interest, Outstanding	24,966
MYLTIP 2016 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Noncontrolling Interest, Outstanding	89,791
MYLTIP 2017 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Noncontrolling Interest, Outstanding	116,078
MYLTIP 2018
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Noncontrolling Interest, Outstanding	336,195
MYLTIP 2019 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Noncontrolling Interest, Outstanding	219,916
MYLTIP 2020 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Noncontrolling Interest, Outstanding	203,278

(Common Units) (Narrative) (Det

(Common Units) (Narrative) (Details) $ / shares in Units, $ in Thousands	Feb. 06, 2020USD ($)shares	Sep. 03, 2019shares	Feb. 09, 2019USD ($)shares	Feb. 04, 2018USD ($)shares	Dec. 31, 2020USD ($)yr$ / sharesshares	Dec. 31, 2019USD ($)shares
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
OP Units for redemption (in shares)		4,917
Boston Properties Limited Partnership
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Redeemable Noncontrolling Interest, Equity, Preferred, Carrying Amount \| $					$ 1,643,024	$ 2,468,753
Unvested MYLTIP Units [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
unvested MYLTIP distributions as compared to total distributions (percentage)					10.00%
MYLTIP 2017 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Final awards percentage of target	83.80%
Value of MYLTIP Awards \| $	$ 17,600
Forfeitures, in units	270,942
MYLTIP 2017 [Member] \| Boston Properties Limited Partnership
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Noncontrolling Interest, Outstanding					116,078
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
Forfeitures, in units			364,980
MYLTIP 2016 [Member] \| Boston Properties Limited Partnership
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Noncontrolling Interest, Outstanding					89,791
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
Forfeitures, in units				337,847
MYLTIP 2015 [Member] \| Boston Properties Limited Partnership
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Noncontrolling Interest, Outstanding					24,966
OP Units [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
OP Units for redemption (in shares)					856,811	144,481
Restriction on redemption of OP Unit to Common Stock (in years) \| yr					1
Redemption of OP Unit equivalent to Common Stock (in shares)					1
Redeemable Noncontrolling Interest, Equity, Preferred, Carrying Amount \| $					$ 1,600,000
Closing price of common stock (in dollars per share) \| $ / shares					$ 94.53
Vested 2012 OPP units and MYLTIPS
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
OP Units for redemption (in shares)					88,168	92,678

Noncontrolling Interests Common

Noncontrolling Interests Common Units Distributions (Details) - $ / shares	Oct. 30, 2020	Jul. 31, 2020	Apr. 30, 2020	Jan. 30, 2020	Oct. 31, 2019	Jul. 31, 2019	Apr. 30, 2019	Jan. 30, 2019	Dec. 15, 2020
Dividends Payable [Line Items]
Distributions Payable, Amount Per Unit									$ 0.98
Dividends, Per Unit, Cash Paid	$ 0.98	$ 0.98	$ 0.98	$ 0.98	$ 0.95	$ 0.95	$ 0.95	$ 0.95
Op units and LTIP units
Dividends Payable [Line Items]
Distributions Payable, Amount Per Unit									0.98
Unvested MYLTIP Units [Member]
Dividends Payable [Line Items]
Distributions Payable, Amount Per Unit									0.098
Boston Properties Limited Partnership
Dividends Payable [Line Items]
Distributions Payable, Amount Per Unit									$ 0.98
Dividends, Per Unit, Cash Paid	0.98	0.98	0.98	0.98	0.95	0.95	0.95	0.95
Boston Properties Limited Partnership \| Op units and LTIP units
Dividends Payable [Line Items]
Dividends, Per Unit, Cash Paid	0.98	0.98	0.98	0.98	0.95	0.95	0.95	0.95
Boston Properties Limited Partnership \| Unvested MYLTIP Units [Member]
Dividends Payable [Line Items]
Dividends, Per Unit, Cash Paid	$ 0.098	$ 0.098	$ 0.098	$ 0.098	$ 0.095	$ 0.095	$ 0.095	$ 0.095

Noncontrolling Interests (Prope

Noncontrolling Interests (Property Partnerships) (Narrative) (Details) - USD ($) $ in Thousands	Apr. 01, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Noncontrolling Interest [Line Items]
Noncontrolling Interest in Limited Partnerships		$ 1,726,933	$ 1,728,689
Payments to Noncontrolling Interests		$ 58,811	69,913	$ 82,501
Acquisition of noncontrolling interest in property partnership			$ (186,963)
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 Shareholder	186,800
Acquisition of noncontrolling interest in property partnership	$ 162,500

Stockholders' Equity _ Partne_3

Stockholders' Equity / Partners' Capital Narrative (Details) $ / shares in Units, $ in Millions	May 22, 2020USD ($)yr	Dec. 31, 2020$ / sharesshares	Dec. 31, 2019$ / sharesshares	Mar. 27, 2018$ / shares	Jun. 02, 2017USD ($)
Class of Stock [Line Items]
Common Stock, Shares, Outstanding		155,718,825	154,790,298
General Partners' Capital Account, Units Outstanding (in units)		1,730,921
Limited Partners' Capital Account, Units Outstanding (in units)		153,987,904
Options exercised		43,792	145,088
Shares of Common Stock issued in connection with redemption of an equal number of OP Units (in shares)		856,811	144,481
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%	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	8,000,000
Series B, Liquidation Preference Per Share (dollars per share) \| $ / shares		$ 25		$ 25

Stockholders' Equity _ Partne_4

Stockholders' Equity / Partners' Capital Dividends / Distributions (Details) - $ / shares	Nov. 16, 2020	Oct. 30, 2020	Aug. 17, 2020	Jul. 31, 2020	May 15, 2020	Apr. 30, 2020	Feb. 18, 2020	Jan. 30, 2020	Nov. 15, 2019	Oct. 31, 2019	Aug. 15, 2019	Jul. 31, 2019	May 15, 2019	Apr. 30, 2019	Feb. 15, 2019	Jan. 30, 2019	Dec. 15, 2020
Dividends / Distributions [Line Items]
Dividends Payable, Amount Per Share / Unit																	$ 0.98
Common Stock / Unit, Dividends / Distributions, Per Share / Unit, Cash Paid		$ 0.98		$ 0.98		$ 0.98		$ 0.98		$ 0.95		$ 0.95		$ 0.95		$ 0.95
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		$ 0.98		$ 0.98		$ 0.98		$ 0.98		$ 0.95		$ 0.95		$ 0.95		$ 0.95
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

Segment Information Narrative (

Segment Information Narrative (Details) $ in Thousands	12 Months Ended
Segment Information Narrative (Details) $ in Thousands	Dec. 31, 2020USD ($)
Segment Reporting Information [Line Items]
Write-off for accrued rent	$ 67,700
Write-off for accounts receivable	22,600
Parking and Other [Member]
Segment Reporting Information [Line Items]
Increase (decrease) in parking and other revenue primarily related to COVID-19	$ 32,900

Segment Information (Schedule O

Segment Information (Schedule Of Reconciliation Of Net Operating Income To Net Income) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019		Dec. 31, 2018
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net income attributable to the Company's common shareholders / unitholders	$ 862,227,000	$ 511,034,000		$ 572,347,000
Preferred dividends / distributions	(10,500,000)	(10,500,000)		(10,500,000)
Noncontrolling interest-common units of the Operating Partnership	(97,704,000)	(59,345,000)		(66,807,000)
Noncontrolling interest in property partnerships	(48,260,000)	(71,120,000)		(62,909,000)
Interest expense	(431,717,000)	(412,717,000)		(378,168,000)
Loss from early extinguishment of debt	0	29,540,000		16,490,000
Company's share of net operating income from joint ventures	(1,694,075,000)	(1,826,123,000)		(1,649,314,000)
Depreciation and amortization expense	(683,751,000)	(677,764,000)		(645,649,000)
Transaction costs	(1,531,000)	(1,984,000)		(1,604,000)
General and administrative expense	(133,112,000)	(140,777,000)		(121,722,000)
Gains (losses) from investments in securities	(5,261,000)	(6,417,000)		1,865,000
Interest and other income (loss)	(5,953,000)	(18,939,000)		(10,823,000)
Gains on sales of real estate	(618,982,000)	(709,000)		(182,356,000)
Income (loss) from unconsolidated joint ventures	85,110,000	(46,592,000)		(2,222,000)
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	862,227,000	511,034,000		572,347,000
Preferred dividends / distributions	10,500,000	10,500,000		10,500,000
Noncontrolling interest-common units of the Operating Partnership	97,704,000	59,345,000		66,807,000
Noncontrolling interest in property partnerships	48,260,000	71,120,000		62,909,000
Interest expense	431,717,000	412,717,000		378,168,000
Loss from early extinguishment of debt	0	29,540,000		16,490,000
Impairment loss	0	24,038,000		11,812,000
Depreciation and amortization expense	683,751,000	677,764,000		645,649,000
Transaction costs	1,531,000	1,984,000		1,604,000
Operating expense	11,626,000	10,386,000		9,590,000
General and administrative expense	133,112,000	140,777,000		121,722,000
Gains (losses) from investments in securities	5,261,000	6,417,000		(1,865,000)
Interest and other income (loss)	5,953,000	18,939,000		10,823,000
Gains on sales of real estate	618,982,000	709,000		182,356,000
Income (loss) from unconsolidated joint ventures	(85,110,000)	46,592,000		2,222,000
Other revenue	11,626,000	10,386,000		9,590,000
Company's share of Net Operating Income	1,626,131,000	1,739,850,000		1,551,842,000
Unconsolidated Joint Ventures [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Interest expense	(98,051,000)	(84,409,000)		(71,308,000)
Company's share of net operating income from joint ventures	(94,943,000)	(97,716,000)		(79,893,000)
Depreciation and amortization expense	(141,853,000)	(102,296,000)		(103,079,000)	[1]
Transaction costs	(1,027,000)	(1,000,000)		0
Gains on sales of real estate	(11,737,000)	(32,706,000)	[2]	(16,951,000)
Income (loss) from unconsolidated joint ventures	85,110,000	(46,592,000)		(2,222,000)
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	94,943,000	97,716,000		79,893,000
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	979,979,000	580,102,000		656,903,000
Preferred dividends / distributions	(10,500,000)	(10,500,000)		(10,500,000)
Noncontrolling interest in property partnerships	(48,260,000)	(71,120,000)		(62,909,000)
Interest expense	(431,717,000)	(412,717,000)		(378,168,000)
Loss from early extinguishment of debt	0	29,540,000		16,490,000
Depreciation and amortization expense	(676,666,000)	(669,956,000)
Transaction costs	(1,531,000)	(1,984,000)		(1,604,000)
General and administrative expense	(133,112,000)	(140,777,000)		(121,722,000)
Gains (losses) from investments in securities	(5,261,000)	(6,417,000)		1,865,000
Interest and other income (loss)	(5,953,000)	(18,939,000)		(10,823,000)
Gains on sales of real estate	(631,945,000)	(858,000)		(190,716,000)
Income (loss) from unconsolidated joint ventures	85,110,000	(46,592,000)		(2,222,000)
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	979,979,000	580,102,000		656,903,000
Preferred dividends / distributions	10,500,000	10,500,000		10,500,000
Noncontrolling interest in property partnerships	48,260,000	71,120,000		62,909,000
Interest expense	431,717,000	412,717,000		378,168,000
Loss from early extinguishment of debt	0	29,540,000		16,490,000
Impairment loss	0	22,272,000		10,181,000
Depreciation and amortization expense	676,666,000	669,956,000		637,891,000
Transaction costs	1,531,000	1,984,000		1,604,000
Operating expense	11,626,000	10,386,000		9,590,000
General and administrative expense	133,112,000	140,777,000		121,722,000
Gains (losses) from investments in securities	5,261,000	6,417,000		(1,865,000)
Interest and other income (loss)	5,953,000	18,939,000		10,823,000
Gains on sales of real estate	631,945,000	858,000		190,716,000
Income (loss) from unconsolidated joint ventures	(85,110,000)	46,592,000		2,222,000
Other revenue	11,626,000	10,386,000		9,590,000
Company's share of Net Operating Income	1,626,131,000	1,739,850,000		1,551,842,000
Management Service [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Other revenue	(29,641,000)	(40,039,000)		(45,158,000)
Management Service [Member] \| Business Intersegment, Eliminations [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Other revenue	29,641,000	40,039,000		45,158,000
Management Service [Member] \| Boston Properties Limited Partnership
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Other revenue	(29,641,000)	(40,039,000)		(45,158,000)
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	29,641,000	40,039,000		45,158,000
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	162,887,000	183,989,000		177,365,000
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	162,887,000	183,989,000		177,365,000
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	$ 162,887,000	$ 183,989,000		$ 177,365,000

[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.
[2]	For the year ended December 31, 2019, represents the gain on sale of 540 Madison Avenue recognized by the joint venture. 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.

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, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	[1]	$ 2,678,795	$ 2,824,634	$ 2,590,659
Rental Revenue: Residential	[1]	38,146	36,914	22,551
Rental Revenue Total	[1]	$ 2,724,419	$ 2,910,137	$ 2,662,328
Rental Revenue: % of Grand Totals	[1]	100.00%	100.00%	100.00%
Rental Expenses: Class A Office		$ 998,469	$ 1,034,025	$ 966,547
Rental Expenses: Residential		18,739	15,985	12,604
Rental Expenses: Total		$ 1,030,344	$ 1,084,014	$ 1,013,014
Rental Expenses: % Of Grand Totals		100.00%	100.00%	100.00%
Net Operating Income		$ 1,694,075	$ 1,826,123	$ 1,649,314
Net Operating Income: % of Grand Totals		100.00%	100.00%	100.00%
Company's Share of Net Operating Income: % of Grand Totals		100.00%	100.00%	100.00%
Total revenue		$ 2,765,686	$ 2,960,562	$ 2,717,076
Boston [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	[1]	897,915	895,098	838,341
Rental Revenue: Residential	[1]	13,616	13,786	6,694
Rental Revenue Total	[1]	$ 919,009	$ 957,473	$ 894,153
Rental Revenue: % of Grand Totals	[1]	33.73%	32.90%	33.59%
Rental Expenses: Class A Office		$ 318,509	$ 322,282	$ 315,653
Rental Expenses: Residential		5,378	5,071	3,632
Rental Expenses: Total		$ 337,023	$ 361,357	$ 353,148
Rental Expenses: % Of Grand Totals		32.71%	33.34%	34.86%
Net Operating Income		$ 581,986	$ 596,116	$ 541,005
Net Operating Income: % of Grand Totals		34.35%	32.64%	32.80%
Company's Share of Net Operating Income: % of Grand Totals		33.88%	32.27%	32.86%
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		$ 0	$ 0	$ 0
Net Operating Income: % of Grand Totals		0.00%	0.00%	0.00%
Company's Share of Net Operating Income: % of Grand Totals		3.56%	3.53%	2.75%
New York [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	[1]	$ 935,966	$ 1,011,912	$ 959,050
Rental Revenue: Residential	[1]	0	0	0
Rental Revenue Total	[1]	$ 935,966	$ 1,011,912	$ 959,050
Rental Revenue: % of Grand Totals	[1]	34.36%	34.78%	36.02%
Rental Expenses: Class A Office		$ 384,753	$ 389,532	$ 377,992
Rental Expenses: Residential		0	0	0
Rental Expenses: Total		$ 384,753	$ 389,532	$ 377,992
Rental Expenses: % Of Grand Totals		37.35%	35.93%	37.32%
Net Operating Income		$ 551,213	$ 622,380	$ 581,058
Net Operating Income: % of Grand Totals		32.54%	34.09%	35.23%
Company's Share of Net Operating Income: % of Grand Totals		26.12%	27.77%	28.63%
San Francisco [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	[1]	$ 508,327	$ 533,189	$ 397,180
Rental Revenue: Residential	[1]	155	0	0
Rental Revenue Total	[1]	$ 508,482	$ 533,189	$ 397,180
Rental Revenue: % of Grand Totals	[1]	18.66%	18.32%	14.92%
Rental Expenses: Class A Office		$ 163,156	$ 177,994	$ 130,016
Rental Expenses: Residential		2,261	0	0
Rental Expenses: Total		$ 165,417	$ 177,994	$ 130,016
Rental Expenses: % Of Grand Totals		16.05%	16.42%	12.83%
Net Operating Income		$ 343,065	$ 355,195	$ 267,164
Net Operating Income: % of Grand Totals		20.25%	19.45%	16.20%
Company's Share of Net Operating Income: % of Grand Totals		22.02%	20.39%	17.22%
Washington, DC [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	[1]	$ 336,587	$ 384,435	$ 396,088
Rental Revenue: Residential	[1]	24,375	23,128	15,857
Rental Revenue Total	[1]	$ 360,962	$ 407,563	$ 411,945
Rental Revenue: % of Grand Totals	[1]	13.25%	14.00%	15.47%
Rental Expenses: Class A Office		$ 132,051	$ 144,217	$ 142,886
Rental Expenses: Residential		11,100	10,914	8,972
Rental Expenses: Total		$ 143,151	$ 155,131	$ 151,858
Rental Expenses: % Of Grand Totals		13.89%	14.31%	14.99%
Net Operating Income		$ 217,811	$ 252,432	$ 260,087
Net Operating Income: % of Grand Totals		12.86%	13.82%	15.77%
Company's Share of Net Operating Income: % of Grand Totals		14.42%	16.04%	18.54%
Hotel [Member]
Segment Reporting Information [Line Items]
Other revenue	[1]	$ 7,478	$ 48,589	$ 49,118
Operating expense		13,136	34,004	33,863
Hotel [Member] \| Boston [Member]
Segment Reporting Information [Line Items]
Other revenue	[1]	7,478	48,589	49,118
Operating expense		13,136	34,004	33,863
Hotel [Member] \| Los Angeles [Member]
Segment Reporting Information [Line Items]
Other revenue	[1]	0	0	0
Operating expense		0	0	0
Hotel [Member] \| New York [Member]
Segment Reporting Information [Line Items]
Other revenue	[1]	0	0	0
Operating expense		0	0	0
Hotel [Member] \| San Francisco [Member]
Segment Reporting Information [Line Items]
Other revenue	[1]	0	0	0
Operating expense		0	0	0
Hotel [Member] \| Washington, DC [Member]
Segment Reporting Information [Line Items]
Other revenue	[1]	0	0	0
Operating expense		0	0	0
Noncontrolling interest - property partnerships [Member]
Segment Reporting Information [Line Items]
Net Operating Income		(162,887)	(183,989)	(177,365)
Noncontrolling interest - property partnerships [Member] \| Boston [Member]
Segment Reporting Information [Line Items]
Net Operating Income		(41,849)	(40,109)	(33,862)
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		(121,038)	(143,432)	(143,562)
Noncontrolling interest - property partnerships [Member] \| San Francisco [Member]
Segment Reporting Information [Line Items]
Net Operating Income		0	(448)	59
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		94,943	97,716	79,893
Total revenue	[2]	319,560	322,817	271,951
Unconsolidated Joint Ventures [Member] \| Boston [Member]
Segment Reporting Information [Line Items]
Net Operating Income		10,765	5,494	2,866
Unconsolidated Joint Ventures [Member] \| Los Angeles [Member]
Segment Reporting Information [Line Items]
Net Operating Income		57,907	61,338	42,750
Unconsolidated Joint Ventures [Member] \| New York [Member]
Segment Reporting Information [Line Items]
Net Operating Income		(5,326)	4,174	6,590
Unconsolidated Joint Ventures [Member] \| San Francisco [Member]
Segment Reporting Information [Line Items]
Net Operating Income		14,928	0	0
Unconsolidated Joint Ventures [Member] \| Washington, DC [Member]
Segment Reporting Information [Line Items]
Net Operating Income		16,669	26,710	27,687
Company's Share [Member]
Segment Reporting Information [Line Items]
Net Operating Income		1,626,131	1,739,850	1,551,842
Company's Share [Member] \| Boston [Member]
Segment Reporting Information [Line Items]
Net Operating Income		550,902	561,501	510,009
Company's Share [Member] \| Los Angeles [Member]
Segment Reporting Information [Line Items]
Net Operating Income		57,907	61,338	42,750
Company's Share [Member] \| New York [Member]
Segment Reporting Information [Line Items]
Net Operating Income		424,849	483,122	444,086
Company's Share [Member] \| San Francisco [Member]
Segment Reporting Information [Line Items]
Net Operating Income		357,993	354,747	267,223
Company's Share [Member] \| Washington, DC [Member]
Segment Reporting Information [Line Items]
Net Operating Income		$ 234,480	$ 279,142	$ 287,774

[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.
[2]	Includes straight-line rent adjustments of approximately $(10.1) million, $32.4 million and $15.9 million for the years ended December 31, 2020, 2019 and 2018, respectively. Due primarily to the impact of COVID-19, for the year ended December 31, 2020, write-offs of accounts receivable and accrued rent balances totaled approximately $51.7 million.

Earnings Per Share _ Common U_3

Earnings Per Share / Common Unit (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Basic Earnings:
Net income attributable to the company's common shareholders / unitholders	$ 862,227	$ 511,034	$ 572,347
Net income attributable to the company's common shareholders / unitholders (in shares / units)	155,432,000	154,582,000	154,427,000
Net income attributable to the company's common shareholders / unitholders (in dollars per share / unit)	$ 5.55	$ 3.31	$ 3.71
Allocation of undistributed earnings to participating securities	$ (748)		$ (101)
Allocation of undistributed earnings to participating securities (in shares / units)	0		0
Allocation of undistributed earnings to participating securities (in dollars per share / unit)	$ (0.01)		$ 0
Net Income Available To Common Stockholders After Allocation of Undistributed Earnings to Participating Securities Basic	$ 861,479		$ 572,246
Weighted Average Number Of Shares Outstanding After Allocation of Undistributed Earnings to Participating Securities Basic (in shares)	155,432,000		154,427,000
Earnings Per Share After Allccation of Undistributed Earnings to Particiapting Securities Basic (dollars per share)	$ 5.54		$ 3.71
Effect of Dilutive Securities:
Stock Based Compensation	$ 0	$ 0	$ 0
Stock Based Compensation (in shares / units)	85,000	301,000	255,000
Weighted Average Number Diluted Shares Outstanding Adjustment (per share)	$ 0	$ (0.01)	$ (0.01)
Diluted Earnings:
Diluted Earnings: Net income attributable to the Company's common shareholders / unitholders	$ 861,479	$ 511,034	$ 572,246
Diluted Earnings: Net income attributable to the Company's common shareholders / unitholders (in shares / units)	155,517,000	154,883,000	154,682,000
Diluted Earnings: Net income, Per Share Amount (in dollars per share / unit)	$ 5.54	$ 3.30	$ 3.70
Boston Properties Limited Partnership
Redeemable Common Units	17,211,000	17,618,000	17,485,000
Basic Earnings:
Net income attributable to the company's common shareholders / unitholders	$ 979,979	$ 580,102	$ 656,903
Net income attributable to the company's common shareholders / unitholders (in shares / units)	172,643,000	172,200,000	171,912,000
Net income attributable to the company's common shareholders / unitholders (in dollars per share / unit)	$ 5.68	$ 3.37	$ 3.82
Allocation of undistributed earnings to participating securities	$ (830)		$ (113)
Allocation of undistributed earnings to participating securities (in shares / units)	0		0
Allocation of undistributed earnings to participating securities (in dollars per share / unit)	$ (0.01)		$ 0
Net Income Available To Common Stockholders After Allocation of Undistributed Earnings to Participating Securities Basic	$ 979,149		$ 656,790
Weighted Average Number Of Shares Outstanding After Allocation of Undistributed Earnings to Participating Securities Basic (in shares)	172,643,000		171,912,000
Earnings Per Share After Allccation of Undistributed Earnings to Particiapting Securities Basic (dollars per share)	$ 5.67		$ 3.82
Effect of Dilutive Securities:
Stock Based Compensation	$ 0	$ 0	$ 0
Stock Based Compensation (in shares / units)	85,000	301,000	255,000
Weighted Average Number Diluted Shares Outstanding Adjustment (per share)	$ 0	$ (0.01)	$ (0.01)
Diluted Earnings:
Diluted Earnings: Net income attributable to the Company's common shareholders / unitholders	$ 979,149	$ 580,102	$ 656,790
Diluted Earnings: Net income attributable to the Company's common shareholders / unitholders (in shares / units)	172,728,000	172,501,000	172,167,000
Diluted Earnings: Net income, Per Share Amount (in dollars per share / unit)	$ 5.67	$ 3.36	$ 3.81

Employee Benefits Plan (Details

Employee Benefits Plan (Details) - USD ($) $ in Thousands	12 Months Ended
Employee Benefits Plan (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Contribution Plan Disclosure [Line Items]
Defined Contribution Plan, Employer Matching Contribution, Percent of Match	200.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	3.00%
Defined Contribution Plan, Employer Matching Contribution, Eligible Earnings Limit by IRS Amount	$ 285	$ 280	$ 275
Defined Contribution Plan, Employer Discretionary Contribution Amount	4,000	4,200	$ 4,100
Deferred Compensation Liability, Current and Noncurrent	38,600	36,000
Separate Unrestricted Cash For Deferred Compensation Plan.	39,500	36,700
Officer [Member]
Defined Contribution Plan Disclosure [Line Items]
Separate Unrestricted Cash For Deferred Compensation Plan.	$ 38,600	$ 36,000

Stock Option and Incentive Pl_3

Stock Option and Incentive Plan (Narrative) (Details) - USD ($) $ in Millions	Feb. 06, 2020	Feb. 04, 2020	Feb. 09, 2019	Feb. 04, 2018	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting Period					4 years
MYLTIP 2017 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value of MYLTIP Awards	$ 17.6
Final awards percentage of target	83.80%
Forfeitures, in units	270,942
MYLTIP 2016 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value of MYLTIP Awards			$ 13.6
Final awards percentage of target			69.50%
Forfeitures, in units			364,980
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%
Forfeitures, in units				337,847
2012 Stock Option and Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Description					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.
MYLTIP 2020 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting Period		4 years
TSR measurement (in years)		three-year
Minimum earned awards		0
Maximum Earned Awards		203,278
Earned awards - Target		101,638
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights		Earned awards (if any) will vest 50% on February 3, 2023 and 50% on February 3, 2024, 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 3, 2023, earned awards will be calculated based on TSR performance up to the date of the change of control. The 2020 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		$ 13.7

Stock Option and Incentive Pl_4

Stock Option and Incentive Plan Stock and Units (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	Feb. 04, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued		155,797,725	154,869,198
Stock based compensation expense		$ 43,000	$ 39,800	$ 38,000
Common Stock, Value, Issued		1,557	$ 1,548
Intrinsic Value of stock options		$ 400
Vesting Period		4 years
Beginning outstanding, shares		351,561	395,353	540,441	540,441
Weighted Average Exercise Price		$ 96.97	$ 96.37	$ 96.35	$ 96.35
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued		29,630	26,503	20,320
LTIP Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value Of LTIP Units Issued		$ 26,300	$ 22,100	$ 22,700
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		1.47%	2.68%	2.63%
Expected price volatility		18.00%	27.00%	27.00%
Weighted average price (per unit)		$ 127.14	$ 121.50	$ 110.29
Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock available for issuance		250,000
Number of shares issued		7,195	5,862	6,268
Employee discount		85.00%
Weighted Average Price of Shares Purchased		$ 90.53	$ 104.11	$ 107.20
stock option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic Value of stock options		$ 0	$ 0	$ 0
Boston Properties Limited Partnership \| LTIP Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued		207,181	181,919	205,838
Boston Properties Limited Partnership \| MYLTIP 2020 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued		203,278
Boston Properties Limited Partnership \| MYLTIP 2019 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued			220,734
Boston Properties Limited Partnership \| MYLTIP 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued				342,659
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee and director payment per share (in dollars per share)		$ 0.01
Common Stock, Value, Issued		$ 4,000	$ 3,500	$ 2,400
Common Stock Weighted Average Price (in dollars per share)		$ 133.81	$ 131.27	$ 119.27
MYLTIP 2020 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting Period	4 years
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)		$ 0.25
Ltips (including vested MYLTIPS) And Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expenses		$ 25,400
Unvested MYLTIP Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expenses		$ 10,300
Weighted-average period (years)		2 years 1 month 6 days

Stock Option Rollforward Table

Stock Option Rollforward Table (Details) - $ / shares	12 Months Ended
Stock Option Rollforward Table (Details) - $ / shares	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Text Block [Abstract]
Beginning outstanding, shares	395,353	540,441	540,441
Ending outstanding, shares	351,561	395,353	540,441
Exercised	(43,792)	(145,088)	0
Beginning outstanding, Weighted-average Exercise Price	$ 96.37	$ 96.35	$ 96.35
Weighted Average Exercise Price	91.60	96.27	0
Ending outstanding, Weighted-average Exercise Price	$ 96.97	$ 96.37	$ 96.35

Stock Options Outstanding Table

Stock Options Outstanding Table (Details) - $ / shares	12 Months Ended
Stock Options Outstanding Table (Details) - $ / shares	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Text Block [Abstract]
Beginning outstanding, shares	351,561	395,353	540,441	540,441
Weighted Average Exercise Price	$ 96.97	$ 96.37	$ 96.35	$ 96.35
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning outstanding, shares	351,561	395,353	540,441	540,441
Weighted Average Exercise Price	$ 96.97	$ 96.37	$ 96.35	$ 96.35
Exercise price of $86.86
Text Block [Abstract]
Beginning outstanding, shares	54,003
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	1 month 6 days
Weighted Average Exercise Price	$ 86.86
Number Exercisable	54,003
Exercisable, Weighted Average Exercise Price	$ 86.86
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning outstanding, shares	54,003
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	1 month 6 days
Weighted Average Exercise Price	$ 86.86
Number Exercisable	54,003
Exercisable, Weighted Average Exercise Price	$ 86.86
Exercise price $95.69
Text Block [Abstract]
Beginning outstanding, shares	54,282
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	2 years 3 months 18 days
Weighted Average Exercise Price	$ 95.69
Number Exercisable	54,282
Exercisable, Weighted Average Exercise Price	$ 95.69
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning outstanding, shares	54,282
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	2 years 3 months 18 days
Weighted Average Exercise Price	$ 95.69
Number Exercisable	54,282
Exercisable, Weighted Average Exercise Price	$ 95.69
Exercise Price $98.46
Text Block [Abstract]
Beginning outstanding, shares	133,834
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	2 years 1 month 6 days
Weighted Average Exercise Price	$ 98.46
Number Exercisable	133,834
Exercisable, Weighted Average Exercise Price	$ 98.46
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning outstanding, shares	133,834
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	2 years 1 month 6 days
Weighted Average Exercise Price	$ 98.46
Number Exercisable	133,834
Exercisable, Weighted Average Exercise Price	$ 98.46
Exercise price $100.77
Text Block [Abstract]
Beginning outstanding, shares	109,442
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	1 year 1 month 6 days
Weighted Average Exercise Price	$ 100.77
Number Exercisable	109,442
Exercisable, Weighted Average Exercise Price	$ 100.77
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning outstanding, shares	109,442
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	1 year 1 month 6 days
Weighted Average Exercise Price	$ 100.77
Number Exercisable	109,442
Exercisable, Weighted Average Exercise Price	$ 100.77

Related Party Transactions (Det

Related Party Transactions (Details) $ in Thousands	Sep. 03, 2019shares	Dec. 31, 2020USD ($)Vehiclesshares	Dec. 31, 2019USD ($)Vehiclesshares	Dec. 31, 2018USD ($)	May 21, 2019shares
Related Party Transaction [Line Items]
Number Of Non Employee Directors Electing To Receive Deferred Stock Units \| Vehicles		7
Separate Unrestricted Cash For Deferred Compensation Plan.		$ 39,500	$ 36,700
Liability for directors		$ 336,264	$ 377,553
Common stock, shares issued \| shares		155,797,725	154,869,198
OP Units for redemption (in shares) \| shares	4,917
Deferred stock units outstanding \| Vehicles		72,966	60,676
Director Cessation Member [Member]
Related Party Transaction [Line Items]
Common stock, shares issued \| shares					17,949
Director
Related Party Transaction [Line Items]
Separate Unrestricted Cash For Deferred Compensation Plan.		$ 800	$ 700
Liability for directors		800	700
Immediate Family Member of Management or Principal Owner
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party		914	21	$ 921
Real Estate Brokerage Firm
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party		$ 3,400	$ 2,600

Subsequent Events (Details)

Subsequent Events (Details) - USD ($) $ in Thousands	Feb. 14, 2021	Feb. 05, 2021	Feb. 02, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jan. 29, 2021
Subsequent Event [Line Items]
Common stock, shares issued				155,797,725	154,869,198
Repayments of Unsecured Debt				$ 0	$ 699,237	$ 699,517
Boston Properties Limited Partnership
Subsequent Event [Line Items]
Repayments of Unsecured Debt				0	$ 699,237	$ 699,517
Boston Properties Limited Partnership \| Senior Notes
Subsequent Event [Line Items]
Debt				9,700,000
Boston Properties Limited Partnership \| 4.289% unsecured senior notes \| Senior Notes
Subsequent Event [Line Items]
Debt				$ 850,000
Debt Instrument, Interest Rate, Stated Percentage				4.125%
Restricted Stock [Member]
Subsequent Event [Line Items]
Common stock, shares issued				29,630	26,503	20,320
LTIP Units [Member] \| Boston Properties Limited Partnership
Subsequent Event [Line Items]
Number of shares issued				207,181	181,919	205,838
Subsequent Event [Member] \| Boston Properties Limited Partnership \| 4.289% unsecured senior notes \| Senior Notes
Subsequent Event [Line Items]
Debt	$ 850,000
Debt Instrument, Interest Rate, Stated Percentage	4.125%
Repayments of Unsecured Debt	$ 858,700
Debt Instrument, Increase, Accrued Interest	$ 8,700
Subsequent Event [Member] \| Restricted Stock [Member]
Subsequent Event [Line Items]
Common stock, shares issued							33,449
Subsequent Event [Member] \| LTIP Units [Member] \| Boston Properties Limited Partnership
Subsequent Event [Line Items]
Number of shares issued			263,527
Subsequent Event [Member] \| MYLTIP 2021
Subsequent Event [Line Items]
Value of MYLTIP Awards			$ 15,300
Minimum earned awards			0
Maximum Earned Awards			352,021
Earned awards - Target			176,009
Subsequent Event [Member] \| MYLTIP 2018
Subsequent Event [Line Items]
Value of MYLTIP Awards		$ 4,600
Forfeitures, in units		285,925
Final awards percentage of target		29.20%

SEC Schedule, Article 12-28, _2

SEC Schedule, Article 12-28, Real Estate and Accumulated Depreciation (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances		$ 2,909,081
Original Cost
Original Land		5,160,116
Original Building		13,196,160
Costs Capitalized Subsequent to Acquisition		4,947,027
Land and Improvements		5,429,703
Building and Improvements		16,553,873
Land held for development	[1]	450,954	$ 254,828
Development and Construction in Progress		868,773	789,736
Total		23,303,303	22,844,697	$ 21,605,545	$ 21,058,714
Accumulated Depreciation		5,501,637	5,239,179	4,871,102	4,566,570
Furniture, Fixtures and Equipment		49,606	44,313
Aggregate cost for tax purpose		20,700,000
Real Estate Aggregate Accumulated Depreciation For Tax Purposes		4,500,000
Debt Issuance Costs, Net		(22,905)
Right-of-use assets - finance leases		237,393	237,394
Right of use assets - operating leases		$ 146,406	148,640
Maximum [Member]
Original Cost
Real Estate and Accumulated Depreciation, Life Used for Depreciation		40 years
Furniture, fixtures, and equipment
Original Cost
Accumulated Depreciation Related to Furniture, Fixtures and Equipment		$ 32,465
Land and Land Improvements [Member]
Original Cost
Right-of-use assets - finance leases		214,091
Right of use assets - operating leases		146,406
Buildings and improvements
Original Cost
Right-of-use assets - finance leases		23,302
Boston Properties Limited Partnership
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	[2]	2,909,081
Original Cost
Original Land		5,160,116
Original Building		13,196,160
Costs Capitalized Subsequent to Acquisition		4,570,218
Land and Improvements	[3]	5,332,487
Building and Improvements	[4]	16,274,280
Land held for development	[1]	450,954	254,828
Development and Construction in Progress		868,773	789,736
Total		22,926,494	22,449,476	21,207,189	20,647,236
Accumulated Depreciation		5,396,111	5,135,289	$ 4,773,800	$ 4,473,895
Furniture, Fixtures and Equipment		49,606	44,313
Aggregate cost for tax purpose		23,000,000
Real Estate Aggregate Accumulated Depreciation For Tax Purposes		5,000,000
Debt Issuance Costs, Net		(22,900)
Right-of-use assets - finance leases		237,393	237,394
Right of use assets - operating leases		$ 146,406	$ 148,640
Boston Properties Limited Partnership \| Maximum [Member]
Original Cost
Real Estate and Accumulated Depreciation, Life Used for Depreciation		40 years
Boston Properties Limited Partnership \| Furniture, fixtures, and equipment
Original Cost
Accumulated Depreciation Related to Furniture, Fixtures and Equipment		$ 32,465
Boston Properties Limited Partnership \| Land and Land Improvements [Member]
Original Cost
Right-of-use assets - finance leases		214,091
Right of use assets - operating leases		148,640
Boston Properties Limited Partnership \| Buildings and improvements
Original Cost
Right-of-use assets - finance leases		23,302
767Fifth Avenue (the General Motors Building) \| Office Building [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances		2,277,522
Original Cost
Original Land		1,796,252
Original Building		1,532,654
Costs Capitalized Subsequent to Acquisition		227,450
Land and Improvements		1,796,252
Building and Improvements		1,760,104
Total		3,556,356
Accumulated Depreciation		$ 364,145
Depreciable Lives (Years)	[5]	(1)
767Fifth Avenue (the General Motors Building) \| Boston Properties Limited Partnership \| Office Building [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances		$ 2,277,522
Original Cost
Original Land		1,796,252
Original Building		1,532,654
Costs Capitalized Subsequent to Acquisition		227,450
Land and Improvements		1,796,252
Building and Improvements		1,760,104
Total		3,556,356
Accumulated Depreciation		$ 364,145
Depreciable Lives (Years)	[6]	(1)
Prudential Center \| Office Building [Member]
Original Cost
Original Land		$ 92,077
Original Building		948,357
Costs Capitalized Subsequent to Acquisition		573,187
Land and Improvements		115,638
Building and Improvements		1,480,302
Land held for development		17,681
Total		1,613,621
Accumulated Depreciation		$ 634,402
Depreciable Lives (Years)		(1)
Prudential Center \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 92,077
Original Building		948,357
Costs Capitalized Subsequent to Acquisition		512,816
Land and Improvements		100,540
Building and Improvements		1,435,029
Land held for development		17,681
Total		1,553,250
Accumulated Depreciation		$ 617,331
Depreciable Lives (Years)	[6]	(1)
Embarcadero Center \| Office Building [Member]
Original Cost
Original Land		$ 179,697
Original Building		847,410
Costs Capitalized Subsequent to Acquisition		469,860
Land and Improvements		195,987
Building and Improvements		1,300,980
Total		1,496,967
Accumulated Depreciation		$ 680,507
Depreciable Lives (Years)	[5]	(1)
Embarcadero Center \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 179,697
Original Building		847,410
Costs Capitalized Subsequent to Acquisition		407,480
Land and Improvements		180,420
Building and Improvements		1,254,167
Total		1,434,587
Accumulated Depreciation		$ 662,756
Depreciable Lives (Years)	[6]	(1)
399 Park Avenue \| Office Building [Member]
Original Cost
Original Land		$ 339,200
Original Building		700,358
Costs Capitalized Subsequent to Acquisition		340,960
Land and Improvements		354,107
Building and Improvements		1,026,411
Total		1,380,518
Accumulated Depreciation		$ 387,217
Depreciable Lives (Years)	[5]	(1)
399 Park Avenue \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 339,200
Original Building		700,358
Costs Capitalized Subsequent to Acquisition		281,352
Land and Improvements		339,200
Building and Improvements		981,710
Total		1,320,910
Accumulated Depreciation		$ 370,361
Depreciable Lives (Years)	[6]	(1)
Salesforce Tower \| Office Building [Member]
Original Cost
Original Land		$ 200,349
Original Building		946,205
Costs Capitalized Subsequent to Acquisition		5,355
Land and Improvements		200,349
Building and Improvements		951,560
Total		1,151,909
Accumulated Depreciation		$ 68,918
Depreciable Lives (Years)	[5]	(1)
Salesforce Tower \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 200,349
Original Building		946,205
Costs Capitalized Subsequent to Acquisition		5,355
Land and Improvements		200,349
Building and Improvements		951,560
Total		1,151,909
Accumulated Depreciation		$ 68,918
Depreciable Lives (Years)	[6]	(1)
601 Lexington Avenue \| Office Building [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances		$ 630,068
Original Cost
Original Land		241,600
Original Building		494,782
Costs Capitalized Subsequent to Acquisition		446,950
Land and Improvements		289,639
Building and Improvements		663,694
Development and Construction in Progress		229,999
Total		1,183,332
Accumulated Depreciation		$ 284,477
Depreciable Lives (Years)	[5]	(1)
601 Lexington Avenue \| Boston Properties Limited Partnership \| Office Building [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances		$ 630,068
Original Cost
Original Land		241,600
Original Building		494,782
Costs Capitalized Subsequent to Acquisition		409,864
Land and Improvements		279,281
Building and Improvements		636,966
Development and Construction in Progress		229,999
Total		1,146,246
Accumulated Depreciation		$ 274,343
Depreciable Lives (Years)	[6]	(1)
200 Clarendon Street and Garage \| Office Building [Member]
Original Cost
Original Land		$ 219,543
Original Building		667,884
Costs Capitalized Subsequent to Acquisition		218,821
Land and Improvements		251,374
Building and Improvements		854,874
Total		1,106,248
Accumulated Depreciation		$ 244,882
Depreciable Lives (Years)	[5]	(1)
200 Clarendon Street and Garage \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 219,543
Original Building		667,884
Costs Capitalized Subsequent to Acquisition		218,821
Land and Improvements		251,374
Building and Improvements		854,874
Total		1,106,248
Accumulated Depreciation		$ 244,882
Depreciable Lives (Years)	[6]	(1)
250 West 55th Street \| Office Building [Member]
Original Cost
Original Land		$ 285,263
Original Building		603,167
Costs Capitalized Subsequent to Acquisition		51,860
Land and Improvements		285,263
Building and Improvements		655,027
Total		940,290
Accumulated Depreciation		$ 138,004
Depreciable Lives (Years)	[5]	(1)
250 West 55th Street \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 285,263
Original Building		603,167
Costs Capitalized Subsequent to Acquisition		51,860
Land and Improvements		285,263
Building and Improvements		655,027
Total		940,290
Accumulated Depreciation		$ 138,004
Depreciable Lives (Years)	[6]	(1)
100 Federal Street \| Office Building [Member]
Original Cost
Original Land		$ 131,067
Original Building		435,954
Costs Capitalized Subsequent to Acquisition		111,196
Land and Improvements		131,067
Building and Improvements		547,150
Total		678,217
Accumulated Depreciation		$ 141,629
Depreciable Lives (Years)	[5]	(1)
100 Federal Street \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 131,067
Original Building		435,954
Costs Capitalized Subsequent to Acquisition		111,196
Land and Improvements		131,067
Building and Improvements		547,150
Total		678,217
Accumulated Depreciation		$ 141,629
Depreciable Lives (Years)	[6]	(1)
Times Square Tower \| Office Building [Member]
Original Cost
Original Land		$ 165,413
Original Building		380,438
Costs Capitalized Subsequent to Acquisition		108,206
Land and Improvements		169,193
Building and Improvements		484,864
Total		654,057
Accumulated Depreciation		$ 217,845
Depreciable Lives (Years)	[5]	(1)
Times Square Tower \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 165,413
Original Building		380,438
Costs Capitalized Subsequent to Acquisition		70,227
Land and Improvements		159,694
Building and Improvements		456,384
Total		616,078
Accumulated Depreciation		$ 207,106
Depreciable Lives (Years)	[6]	(1)
Carnegie Center \| Office Building [Member]
Original Cost
Original Land		$ 142,666
Original Building		316,856
Costs Capitalized Subsequent to Acquisition		153,797
Land and Improvements		94,240
Building and Improvements		463,959
Land held for development		55,120
Total		613,319
Accumulated Depreciation		$ 221,323
Depreciable Lives (Years)	[5]	(1)
Carnegie Center \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 142,666
Original Building		316,856
Costs Capitalized Subsequent to Acquisition		138,834
Land and Improvements		90,498
Building and Improvements		452,738
Land held for development		55,120
Total		598,356
Accumulated Depreciation		$ 217,092
Depreciable Lives (Years)	[6]	(1)
Atlantic Wharf \| Office Building [Member]
Original Cost
Original Land		$ 63,988
Original Building		454,537
Costs Capitalized Subsequent to Acquisition		18,538
Land and Improvements		63,988
Building and Improvements		473,075
Total		537,063
Accumulated Depreciation		$ 146,860
Depreciable Lives (Years)	[5]	(1)
Atlantic Wharf \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 63,988
Original Building		454,537
Costs Capitalized Subsequent to Acquisition		18,538
Land and Improvements		63,988
Building and Improvements		473,075
Total		537,063
Accumulated Depreciation		$ 146,860
Depreciable Lives (Years)	[6]	(1)
510 Madison Avenue \| Office Building [Member]
Original Cost
Original Land		$ 103,000
Original Building		253,665
Costs Capitalized Subsequent to Acquisition		28,446
Land and Improvements		103,000
Building and Improvements		282,111
Total		385,111
Accumulated Depreciation		$ 81,517
Depreciable Lives (Years)	[5]	(1)
510 Madison Avenue \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 103,000
Original Building		253,665
Costs Capitalized Subsequent to Acquisition		28,446
Land and Improvements		103,000
Building and Improvements		282,111
Total		385,111
Accumulated Depreciation		$ 81,517
Depreciable Lives (Years)	[6]	(1)
Fountain Square \| Office Building [Member]
Original Cost
Original Land		$ 56,853
Original Building		306,298
Costs Capitalized Subsequent to Acquisition		21,030
Land and Improvements		56,853
Building and Improvements		327,328
Total		384,181
Accumulated Depreciation		$ 90,047
Depreciable Lives (Years)	[5]	(1)
Fountain Square \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 56,853
Original Building		306,298
Costs Capitalized Subsequent to Acquisition		21,030
Land and Improvements		56,853
Building and Improvements		327,328
Total		384,181
Accumulated Depreciation		$ 90,047
Depreciable Lives (Years)	[6]	(1)
599 Lexington Avenue \| Office Building [Member]
Original Cost
Original Land		$ 81,040
Original Building		100,507
Costs Capitalized Subsequent to Acquisition		214,275
Land and Improvements		87,852
Building and Improvements		307,970
Total		395,822
Accumulated Depreciation		$ 193,058
Depreciable Lives (Years)	[5]	(1)
599 Lexington Avenue \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 81,040
Original Building		100,507
Costs Capitalized Subsequent to Acquisition		187,033
Land and Improvements		81,040
Building and Improvements		287,540
Total		368,580
Accumulated Depreciation		$ 185,354
Depreciable Lives (Years)	[6]	(1)
680 Folsom Street \| Office Building [Member]
Original Cost
Original Land		$ 72,545
Original Building		219,766
Costs Capitalized Subsequent to Acquisition		7,917
Land and Improvements		72,545
Building and Improvements		227,683
Total		300,228
Accumulated Depreciation		$ 55,319
Depreciable Lives (Years)	[5]	(1)
680 Folsom Street \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 72,545
Original Building		219,766
Costs Capitalized Subsequent to Acquisition		7,917
Land and Improvements		72,545
Building and Improvements		227,683
Total		300,228
Accumulated Depreciation		$ 55,319
Depreciable Lives (Years)	[6]	(1)
145 Broadway \| Office Building [Member]
Original Cost
Original Land		$ 121
Original Building		273,013
Costs Capitalized Subsequent to Acquisition		25,712
Land and Improvements		23,367
Building and Improvements		275,479
Total		298,846
Accumulated Depreciation		$ 9,941
Depreciable Lives (Years)	[5]	(1)
145 Broadway \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 121
Original Building		273,013
Costs Capitalized Subsequent to Acquisition		25,509
Land and Improvements		23,164
Building and Improvements		275,479
Total		298,643
Accumulated Depreciation		$ 9,941
Depreciable Lives (Years)	[6]	(1)
2200 Pennsylvania Avenue \| Office Building [Member]
Original Cost
Original Land		$ 0
Original Building		183,541
Costs Capitalized Subsequent to Acquisition		112,436
Land and Improvements		107,356
Building and Improvements		188,621
Total		295,977
Accumulated Depreciation		$ 66,072
Depreciable Lives (Years)	[5]	(1)
2200 Pennsylvania Avenue \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 0
Original Building		183,541
Costs Capitalized Subsequent to Acquisition		112,436
Land and Improvements		107,356
Building and Improvements		188,621
Total		295,977
Accumulated Depreciation		$ 66,072
Depreciable Lives (Years)	[6]	(1)
South of Market and Democracy Tower \| Office Building [Member]
Original Cost
Original Land		$ 13,603
Original Building		237,479
Costs Capitalized Subsequent to Acquisition		41,163
Land and Improvements		13,687
Building and Improvements		278,558
Total		292,245
Accumulated Depreciation		$ 107,358
Depreciable Lives (Years)	[5]	(1)
South of Market and Democracy Tower \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 13,603
Original Building		237,479
Costs Capitalized Subsequent to Acquisition		40,827
Land and Improvements		13,603
Building and Improvements		278,306
Total		291,909
Accumulated Depreciation		$ 107,279
Depreciable Lives (Years)	[6]	(1)
601 Massachusetts Avenue \| Office Building [Member]
Original Cost
Original Land		$ 95,310
Original Building		165,173
Costs Capitalized Subsequent to Acquisition		3,945
Land and Improvements		95,322
Building and Improvements		169,106
Total		264,428
Accumulated Depreciation		$ 30,743
Depreciable Lives (Years)	[5]	(1)
601 Massachusetts Avenue \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 95,310
Original Building		165,173
Costs Capitalized Subsequent to Acquisition		3,933
Land and Improvements		95,310
Building and Improvements		169,106
Total		264,416
Accumulated Depreciation		$ 30,743
Depreciable Lives (Years)	[6]	(1)
Bay Colony Corporate Center \| Office Building [Member]
Original Cost
Original Land		$ 18,789
Original Building		148,451
Costs Capitalized Subsequent to Acquisition		81,302
Land and Improvements		18,789
Building and Improvements		229,753
Total		248,542
Accumulated Depreciation		$ 89,232
Depreciable Lives (Years)	[5]	(1)
Bay Colony Corporate Center \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 18,789
Original Building		148,451
Costs Capitalized Subsequent to Acquisition		81,302
Land and Improvements		18,789
Building and Improvements		229,753
Total		248,542
Accumulated Depreciation		$ 89,232
Depreciable Lives (Years)	[6]	(1)
535 Mission Street \| Office Building [Member]
Original Cost
Original Land		$ 40,933
Original Building		148,378
Costs Capitalized Subsequent to Acquisition		3,287
Land and Improvements		40,933
Building and Improvements		151,665
Total		192,598
Accumulated Depreciation		$ 31,953
Depreciable Lives (Years)	[5]	(1)
535 Mission Street \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 40,933
Original Building		148,378
Costs Capitalized Subsequent to Acquisition		3,287
Land and Improvements		40,933
Building and Improvements		151,665
Total		192,598
Accumulated Depreciation		$ 31,953
Depreciable Lives (Years)	[6]	(1)
Mountain View Research Park \| Office Building [Member]
Original Cost
Original Land		$ 95,066
Original Building		68,373
Costs Capitalized Subsequent to Acquisition		18,479
Land and Improvements		95,066
Building and Improvements		86,852
Total		181,918
Accumulated Depreciation		$ 21,725
Depreciable Lives (Years)	[5]	(1)
Mountain View Research Park \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 95,066
Original Building		68,373
Costs Capitalized Subsequent to Acquisition		18,479
Land and Improvements		95,066
Building and Improvements		86,852
Total		181,918
Accumulated Depreciation		$ 21,725
Depreciable Lives (Years)	[6]	(1)
Reservoir Place \| Office Building [Member]
Original Cost
Original Land		$ 18,605
Original Building		104,124
Costs Capitalized Subsequent to Acquisition		57,154
Land and Improvements		20,108
Building and Improvements		159,775
Total		179,883
Accumulated Depreciation		$ 76,993
Depreciable Lives (Years)	[5]	(1)
Reservoir Place \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 18,605
Original Building		104,124
Costs Capitalized Subsequent to Acquisition		53,079
Land and Improvements		19,089
Building and Improvements		156,719
Total		175,808
Accumulated Depreciation		$ 75,841
Depreciable Lives (Years)	[6]	(1)
1330 Connecticut Avenue \| Office Building [Member]
Original Cost
Original Land		$ 25,982
Original Building		82,311
Costs Capitalized Subsequent to Acquisition		37,049
Land and Improvements		27,135
Building and Improvements		118,207
Total		145,342
Accumulated Depreciation		$ 38,000
Depreciable Lives (Years)	[5]	(1)
1330 Connecticut Avenue \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 25,982
Original Building		82,311
Costs Capitalized Subsequent to Acquisition		32,436
Land and Improvements		25,982
Building and Improvements		114,747
Total		140,729
Accumulated Depreciation		$ 36,695
Depreciable Lives (Years)	[6]	(1)
Kingstowne Towne Center \| Office Building [Member]
Original Cost
Original Land		$ 18,021
Original Building		109,038
Costs Capitalized Subsequent to Acquisition		3,299
Land and Improvements		18,062
Building and Improvements		112,296
Total		130,358
Accumulated Depreciation		$ 46,469
Depreciable Lives (Years)	[5]	(1)
Kingstowne Towne Center \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 18,021
Original Building		109,038
Costs Capitalized Subsequent to Acquisition		3,135
Land and Improvements		18,021
Building and Improvements		112,173
Total		130,194
Accumulated Depreciation		$ 46,430
Depreciable Lives (Years)	[6]	(1)
One Freedom Square \| Office Building [Member]
Original Cost
Original Land		$ 9,929
Original Building		84,504
Costs Capitalized Subsequent to Acquisition		39,884
Land and Improvements		11,293
Building and Improvements		123,024
Total		134,317
Accumulated Depreciation		$ 62,808
Depreciable Lives (Years)	[5]	(1)
One Freedom Square \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 9,929
Original Building		84,504
Costs Capitalized Subsequent to Acquisition		34,247
Land and Improvements		9,883
Building and Improvements		118,797
Total		128,680
Accumulated Depreciation		$ 61,215
Depreciable Lives (Years)	[6]	(1)
One and Two Reston Overlook \| Office Building [Member]
Original Cost
Original Land		$ 16,456
Original Building		66,192
Costs Capitalized Subsequent to Acquisition		46,762
Land and Improvements		16,179
Building and Improvements		113,231
Total		129,410
Accumulated Depreciation		$ 57,441
Depreciable Lives (Years)	[5]	(1)
One and Two Reston Overlook \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 16,456
Original Building		66,192
Costs Capitalized Subsequent to Acquisition		42,344
Land and Improvements		15,074
Building and Improvements		109,918
Total		124,992
Accumulated Depreciation		$ 56,191
Depreciable Lives (Years)	[6]	(1)
Weston Corporate Center \| Office Building [Member]
Original Cost
Original Land		$ 25,753
Original Building		92,312
Costs Capitalized Subsequent to Acquisition		(5)
Land and Improvements		25,854
Building and Improvements		92,206
Total		118,060
Accumulated Depreciation		$ 32,278
Depreciable Lives (Years)	[5]	(1)
Weston Corporate Center \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 25,753
Original Building		92,312
Costs Capitalized Subsequent to Acquisition		(5)
Land and Improvements		25,854
Building and Improvements		92,206
Total		118,060
Accumulated Depreciation		$ 32,278
Depreciable Lives (Years)	[6]	(1)
17Fifty Presidents Street \| Office Building [Member]
Original Cost
Original Land		$ 0
Original Building		113,362
Costs Capitalized Subsequent to Acquisition		0
Land and Improvements		0
Building and Improvements		113,362
Total		113,362
Accumulated Depreciation		$ 3,466
Depreciable Lives (Years)	[5]	(1)
17Fifty Presidents Street \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 0
Original Building		113,362
Costs Capitalized Subsequent to Acquisition		0
Land and Improvements		0
Building and Improvements		113,362
Total		113,362
Accumulated Depreciation		$ 3,466
Depreciable Lives (Years)	[6]	(1)
Two Freedom Square \| Office Building [Member]
Original Cost
Original Land		$ 13,930
Original Building		77,739
Costs Capitalized Subsequent to Acquisition		25,510
Land and Improvements		15,420
Building and Improvements		101,759
Total		117,179
Accumulated Depreciation		$ 53,885
Depreciable Lives (Years)	[5]	(1)
Two Freedom Square \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 13,930
Original Building		77,739
Costs Capitalized Subsequent to Acquisition		19,298
Land and Improvements		13,866
Building and Improvements		97,101
Total		110,967
Accumulated Depreciation		$ 52,128
Depreciable Lives (Years)	[6]	(1)
140 Kendrick Street \| Office Building [Member]
Original Cost
Original Land		$ 18,095
Original Building		66,905
Costs Capitalized Subsequent to Acquisition		26,458
Land and Improvements		19,092
Building and Improvements		92,366
Total		111,458
Accumulated Depreciation		$ 35,918
Depreciable Lives (Years)	[5]	(1)
140 Kendrick Street \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 18,095
Original Building		66,905
Costs Capitalized Subsequent to Acquisition		22,468
Land and Improvements		18,095
Building and Improvements		89,373
Total		107,468
Accumulated Depreciation		$ 34,790
Depreciable Lives (Years)	[6]	(1)
355 Main Street \| Office Building [Member]
Original Cost
Original Land		$ 18,863
Original Building		53,346
Costs Capitalized Subsequent to Acquisition		27,593
Land and Improvements		21,173
Building and Improvements		78,629
Total		99,802
Accumulated Depreciation		$ 29,479
Depreciable Lives (Years)	[5]	(1)
355 Main Street \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 18,863
Original Building		53,346
Costs Capitalized Subsequent to Acquisition		27,295
Land and Improvements		21,098
Building and Improvements		78,406
Total		99,504
Accumulated Depreciation		$ 29,397
Depreciable Lives (Years)	[6]	(1)
Discovery Square \| Office Building [Member]
Original Cost
Original Land		$ 11,198
Original Building		71,782
Costs Capitalized Subsequent to Acquisition		20,742
Land and Improvements		12,533
Building and Improvements		91,189
Total		103,722
Accumulated Depreciation		$ 45,920
Depreciable Lives (Years)	[5]	(1)
Discovery Square \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 11,198
Original Building		71,782
Costs Capitalized Subsequent to Acquisition		15,197
Land and Improvements		11,146
Building and Improvements		87,031
Total		98,177
Accumulated Depreciation		$ 44,352
Depreciable Lives (Years)	[6]	(1)
880 & 890 Winter Street \| Office Building [Member]
Original Cost
Original Land		$ 29,510
Original Building		65,812
Costs Capitalized Subsequent to Acquisition		1,367
Land and Improvements		29,510
Building and Improvements		66,561
Land held for development		618
Total		96,689
Accumulated Depreciation		$ 5,706
Depreciable Lives (Years)	[5]	(1)
880 & 890 Winter Street \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 29,510
Original Building		65,812
Costs Capitalized Subsequent to Acquisition		1,367
Land and Improvements		29,510
Building and Improvements		66,561
Land held for development		618
Total		96,689
Accumulated Depreciation		$ 5,706
Depreciable Lives (Years)	[6]	(1)
10 CityPoint \| Office Building [Member]
Original Cost
Original Land		$ 1,953
Original Building		85,752
Costs Capitalized Subsequent to Acquisition		4,744
Land and Improvements		2,290
Building and Improvements		90,159
Total		92,449
Accumulated Depreciation		$ 14,073
Depreciable Lives (Years)	[5]	(1)
10 CityPoint \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 1,953
Original Building		85,752
Costs Capitalized Subsequent to Acquisition		4,581
Land and Improvements		2,127
Building and Improvements		90,159
Total		92,286
Accumulated Depreciation		$ 14,073
Depreciable Lives (Years)	[6]	(1)
90 Broadway \| Office Building [Member]
Original Cost
Original Land		$ 19,104
Original Building		52,078
Costs Capitalized Subsequent to Acquisition		18,077
Land and Improvements		20,785
Building and Improvements		68,474
Total		89,259
Accumulated Depreciation		$ 24,200
Depreciable Lives (Years)	[5]	(1)
90 Broadway \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 19,104
Original Building		52,078
Costs Capitalized Subsequent to Acquisition		17,898
Land and Improvements		20,741
Building and Improvements		68,339
Total		89,080
Accumulated Depreciation		$ 24,156
Depreciable Lives (Years)	[6]	(1)
77 CityPoint \| Office Building [Member]
Original Cost
Original Land		$ 13,847
Original Building		60,383
Costs Capitalized Subsequent to Acquisition		11,937
Land and Improvements		14,023
Building and Improvements		72,144
Total		86,167
Accumulated Depreciation		$ 29,691
Depreciable Lives (Years)	[5]	(1)
77 CityPoint \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 13,847
Original Building		60,383
Costs Capitalized Subsequent to Acquisition		11,832
Land and Improvements		13,997
Building and Improvements		72,065
Total		86,062
Accumulated Depreciation		$ 29,665
Depreciable Lives (Years)	[6]	(1)
230 CityPoint \| Office Building [Member]
Original Cost
Original Land		$ 13,189
Original Building		49,823
Costs Capitalized Subsequent to Acquisition		23,958
Land and Improvements		13,807
Building and Improvements		73,163
Total		86,970
Accumulated Depreciation		$ 32,678
Depreciable Lives (Years)	[5]	(1)
230 CityPoint \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 13,189
Original Building		49,823
Costs Capitalized Subsequent to Acquisition		22,341
Land and Improvements		13,403
Building and Improvements		71,950
Total		85,353
Accumulated Depreciation		$ 32,224
Depreciable Lives (Years)	[6]	(1)
Waltham Weston Corporate Center \| Office Building [Member]
Original Cost
Original Land		$ 10,385
Original Building		60,694
Costs Capitalized Subsequent to Acquisition		13,151
Land and Improvements		11,097
Building and Improvements		73,133
Total		84,230
Accumulated Depreciation		$ 38,118
Depreciable Lives (Years)	[5]	(1)
Waltham Weston Corporate Center \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 10,385
Original Building		60,694
Costs Capitalized Subsequent to Acquisition		10,164
Land and Improvements		10,350
Building and Improvements		70,893
Total		81,243
Accumulated Depreciation		$ 37,273
Depreciable Lives (Years)	[6]	(1)
3625 - 3635 Peterson Way \| Office Building [Member]
Original Cost
Original Land		$ 63,206
Original Building		14,879
Costs Capitalized Subsequent to Acquisition		907
Land and Improvements		63,206
Building and Improvements		14,879
Land held for development		907
Total		78,992
Accumulated Depreciation		$ 14,198
Depreciable Lives (Years)	[5]	(1)
3625 - 3635 Peterson Way \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 63,206
Original Building		14,879
Costs Capitalized Subsequent to Acquisition		907
Land and Improvements		63,206
Building and Improvements		14,879
Land held for development		907
Total		78,992
Accumulated Depreciation		$ 14,198
Depreciable Lives (Years)	[6]	(1)
20 Citypoint \| Office Building [Member]
Original Cost
Original Land		$ 4,887
Original Building		72,764
Costs Capitalized Subsequent to Acquisition		0
Land and Improvements		4,887
Building and Improvements		72,764
Total		77,651
Accumulated Depreciation		$ 3,325
Depreciable Lives (Years)	[5]	(1)
20 Citypoint \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 4,887
Original Building		72,764
Costs Capitalized Subsequent to Acquisition		0
Land and Improvements		4,887
Building and Improvements		72,764
Total		77,651
Accumulated Depreciation		$ 3,325
Depreciable Lives (Years)	[6]	(1)
2440 West El Camino Real \| Office Building [Member]
Original Cost
Original Land		$ 16,741
Original Building		51,285
Costs Capitalized Subsequent to Acquisition		5,518
Land and Improvements		16,741
Building and Improvements		56,803
Total		73,544
Accumulated Depreciation		$ 15,215
Depreciable Lives (Years)	[5]	(1)
2440 West El Camino Real \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 16,741
Original Building		51,285
Costs Capitalized Subsequent to Acquisition		5,518
Land and Improvements		16,741
Building and Improvements		56,803
Total		73,544
Accumulated Depreciation		$ 15,215
Depreciable Lives (Years)	[6]	(1)
191 Spring Street \| Office Building [Member]
Original Cost
Original Land		$ 2,850
Original Building		59,751
Costs Capitalized Subsequent to Acquisition		7,543
Land and Improvements		3,151
Building and Improvements		66,993
Total		70,144
Accumulated Depreciation		$ 24,275
Depreciable Lives (Years)	[5]	(1)
191 Spring Street \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 2,850
Original Building		59,751
Costs Capitalized Subsequent to Acquisition		6,911
Land and Improvements		2,850
Building and Improvements		66,662
Total		69,512
Accumulated Depreciation		$ 24,150
Depreciable Lives (Years)	[6]	(1)
300 Binney Street \| Office Building [Member]
Original Cost
Original Land		$ 18,080
Original Building		51,262
Costs Capitalized Subsequent to Acquisition		140
Land and Improvements		18,080
Building and Improvements		51,402
Total		69,482
Accumulated Depreciation		$ 12,842
Depreciable Lives (Years)	[5]	(1)
300 Binney Street \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 18,080
Original Building		51,262
Costs Capitalized Subsequent to Acquisition		140
Land and Improvements		18,080
Building and Improvements		51,402
Total		69,482
Accumulated Depreciation		$ 12,842
Depreciable Lives (Years)	[6]	(1)
Wisconsin Place \| Office Building [Member]
Original Cost
Original Land		$ 0
Original Building		53,349
Costs Capitalized Subsequent to Acquisition		14,771
Land and Improvements		0
Building and Improvements		68,120
Total		68,120
Accumulated Depreciation		$ 28,305
Depreciable Lives (Years)	[5]	(1)
Wisconsin Place \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 0
Original Building		53,349
Costs Capitalized Subsequent to Acquisition		14,771
Land and Improvements		0
Building and Improvements		68,120
Total		68,120
Accumulated Depreciation		$ 28,305
Depreciable Lives (Years)	[6]	(1)
Reston Corporate Center \| Office Building [Member]
Original Cost
Original Land		$ 9,135
Original Building		50,857
Costs Capitalized Subsequent to Acquisition		6,236
Land and Improvements		10,148
Building and Improvements		56,080
Total		66,228
Accumulated Depreciation		$ 31,405
Depreciable Lives (Years)	[5]	(1)
Reston Corporate Center \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 9,135
Original Building		50,857
Costs Capitalized Subsequent to Acquisition		3,625
Land and Improvements		9,496
Building and Improvements		54,121
Total		63,617
Accumulated Depreciation		$ 30,666
Depreciable Lives (Years)	[6]	(1)
200 West Street \| Office Building [Member]
Original Cost
Original Land		$ 16,148
Original Building		24,983
Costs Capitalized Subsequent to Acquisition		21,102
Land and Improvements		16,813
Building and Improvements		30,496
Land held for development		317
Development and Construction in Progress		14,607
Total		62,233
Accumulated Depreciation		$ 18,585
Depreciable Lives (Years)	[5]	(1)
200 West Street \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 16,148
Original Building		24,983
Costs Capitalized Subsequent to Acquisition		18,441
Land and Improvements		16,148
Building and Improvements		28,500
Land held for development		317
Development and Construction in Progress		14,607
Total		59,572
Accumulated Depreciation		$ 17,832
Depreciable Lives (Years)	[6]	(1)
255 Main Street \| Office Building [Member]
Original Cost
Original Land		$ 134
Original Building		25,110
Costs Capitalized Subsequent to Acquisition		34,107
Land and Improvements		548
Building and Improvements		58,803
Total		59,351
Accumulated Depreciation		$ 37,353
Depreciable Lives (Years)	[5]	(1)
255 Main Street \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 134
Original Building		25,110
Costs Capitalized Subsequent to Acquisition		32,451
Land and Improvements		134
Building and Improvements		57,561
Total		57,695
Accumulated Depreciation		$ 36,887
Depreciable Lives (Years)	[6]	(1)
University Place \| Office Building [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances		$ 1,491
Original Cost
Original Land		0
Original Building		37,091
Costs Capitalized Subsequent to Acquisition		16,745
Land and Improvements		6,909
Building and Improvements		46,927
Total		53,836
Accumulated Depreciation		$ 30,983
Depreciable Lives (Years)	[5]	(1)
University Place \| Boston Properties Limited Partnership \| Office Building [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances		$ 1,491
Original Cost
Original Land		0
Original Building		37,091
Costs Capitalized Subsequent to Acquisition		15,295
Land and Improvements		6,546
Building and Improvements		45,840
Total		52,386
Accumulated Depreciation		$ 30,577
Depreciable Lives (Years)	[6]	(1)
Sumner Square \| Office Building [Member]
Original Cost
Original Land		$ 624
Original Building		28,745
Costs Capitalized Subsequent to Acquisition		20,396
Land and Improvements		2,251
Building and Improvements		47,514
Total		49,765
Accumulated Depreciation		$ 28,329
Depreciable Lives (Years)	[5]	(1)
Sumner Square \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 624
Original Building		28,745
Costs Capitalized Subsequent to Acquisition		18,316
Land and Improvements		1,731
Building and Improvements		45,954
Total		47,685
Accumulated Depreciation		$ 27,744
Depreciable Lives (Years)	[6]	(1)
North First Business Park \| Office Building [Member]
Original Cost
Original Land		$ 23,398
Original Building		13,069
Costs Capitalized Subsequent to Acquisition		4,580
Land and Improvements		23,377
Building and Improvements		17,670
Total		41,047
Accumulated Depreciation		$ 16,749
Depreciable Lives (Years)	[5]	(1)
North First Business Park \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 23,398
Original Building		13,069
Costs Capitalized Subsequent to Acquisition		4,557
Land and Improvements		23,371
Building and Improvements		17,653
Total		41,024
Accumulated Depreciation		$ 16,743
Depreciable Lives (Years)	[6]	(1)
Capital Gallery \| Office Building [Member]
Original Cost
Original Land		$ 4,725
Original Building		29,565
Costs Capitalized Subsequent to Acquisition		8,679
Land and Improvements		8,662
Building and Improvements		34,307
Total		42,969
Accumulated Depreciation		$ 21,150
Depreciable Lives (Years)	[5]	(1)
Capital Gallery \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 4,725
Original Building		29,565
Costs Capitalized Subsequent to Acquisition		4,016
Land and Improvements		6,128
Building and Improvements		32,178
Total		38,306
Accumulated Depreciation		$ 20,348
Depreciable Lives (Years)	[6]	(1)
150 Broadway \| Office Building [Member]
Original Cost
Original Land		$ 850
Original Building		25,042
Costs Capitalized Subsequent to Acquisition		2,253
Land and Improvements		1,323
Building and Improvements		26,822
Total		28,145
Accumulated Depreciation		$ 14,154
Depreciable Lives (Years)	[5]	(1)
150 Broadway \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 850
Original Building		25,042
Costs Capitalized Subsequent to Acquisition		248
Land and Improvements		822
Building and Improvements		25,318
Total		26,140
Accumulated Depreciation		$ 13,584
Depreciable Lives (Years)	[6]	(1)
105 Broadway \| Office Building [Member]
Original Cost
Original Land		$ 1,299
Original Building		12,943
Costs Capitalized Subsequent to Acquisition		12,723
Land and Improvements		2,395
Building and Improvements		24,570
Total		26,965
Accumulated Depreciation		$ 13,041
Depreciable Lives (Years)	[5]	(1)
105 Broadway \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 1,299
Original Building		12,943
Costs Capitalized Subsequent to Acquisition		10,617
Land and Improvements		1,868
Building and Improvements		22,991
Total		24,859
Accumulated Depreciation		$ 12,445
Depreciable Lives (Years)	[6]	(1)
Lexington Office Park \| Office Building [Member]
Original Cost
Original Land		$ 998
Original Building		1,426
Costs Capitalized Subsequent to Acquisition		18,567
Land and Improvements		1,264
Building and Improvements		19,727
Total		20,991
Accumulated Depreciation		$ 15,289
Depreciable Lives (Years)	[5]	(1)
Lexington Office Park \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 998
Original Building		1,426
Costs Capitalized Subsequent to Acquisition		17,803
Land and Improvements		1,073
Building and Improvements		19,154
Total		20,227
Accumulated Depreciation		$ 15,076
Depreciable Lives (Years)	[6]	(1)
201 Spring Street \| Office Building [Member]
Original Cost
Original Land		$ 2,849
Original Building		15,303
Costs Capitalized Subsequent to Acquisition		1,124
Land and Improvements		3,124
Building and Improvements		16,152
Total		19,276
Accumulated Depreciation		$ 8,985
Depreciable Lives (Years)	[5]	(1)
201 Spring Street \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 2,849
Original Building		15,303
Costs Capitalized Subsequent to Acquisition		25
Land and Improvements		2,849
Building and Improvements		15,328
Total		18,177
Accumulated Depreciation		$ 8,672
Depreciable Lives (Years)	[6]	(1)
The Point \| Office Building [Member]
Original Cost
Original Land		$ 6,395
Original Building		10,040
Costs Capitalized Subsequent to Acquisition		421
Land and Improvements		6,492
Building and Improvements		10,364
Total		16,856
Accumulated Depreciation		$ 1,667
Depreciable Lives (Years)	[5]	(1)
The Point \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 6,395
Original Building		10,040
Costs Capitalized Subsequent to Acquisition		421
Land and Improvements		6,492
Building and Improvements		10,364
Total		16,856
Accumulated Depreciation		$ 1,667
Depreciable Lives (Years)	[6]	(1)
690 Folsom Street \| Office Building [Member]
Original Cost
Original Land		$ 3,219
Original Building		11,038
Costs Capitalized Subsequent to Acquisition		1,157
Land and Improvements		3,219
Building and Improvements		12,195
Total		15,414
Accumulated Depreciation		$ 2,778
Depreciable Lives (Years)	[5]	(1)
690 Folsom Street \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 3,219
Original Building		11,038
Costs Capitalized Subsequent to Acquisition		1,157
Land and Improvements		3,219
Building and Improvements		12,195
Total		15,414
Accumulated Depreciation		$ 2,778
Depreciable Lives (Years)	[6]	(1)
33 Hayden Avenue \| Office Building [Member]
Original Cost
Original Land		$ 266
Original Building		3,234
Costs Capitalized Subsequent to Acquisition		11,566
Land and Improvements		425
Building and Improvements		14,641
Total		15,066
Accumulated Depreciation		$ 5,674
Depreciable Lives (Years)	[5]	(1)
33 Hayden Avenue \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 266
Original Building		3,234
Costs Capitalized Subsequent to Acquisition		10,929
Land and Improvements		266
Building and Improvements		14,163
Total		14,429
Accumulated Depreciation		$ 5,494
Depreciable Lives (Years)	[6]	(1)
92-100 Hayden Avenue \| Office Building [Member]
Original Cost
Original Land		$ 594
Original Building		6,748
Costs Capitalized Subsequent to Acquisition		7,669
Land and Improvements		802
Building and Improvements		14,209
Total		15,011
Accumulated Depreciation		$ 12,507
Depreciable Lives (Years)	[5]	(1)
92-100 Hayden Avenue \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 594
Original Building		6,748
Costs Capitalized Subsequent to Acquisition		6,940
Land and Improvements		619
Building and Improvements		13,663
Total		14,282
Accumulated Depreciation		$ 12,300
Depreciable Lives (Years)	[6]	(1)
181 Spring Street \| Office Building [Member]
Original Cost
Original Land		$ 1,066
Original Building		9,520
Costs Capitalized Subsequent to Acquisition		2,177
Land and Improvements		1,160
Building and Improvements		11,603
Total		12,763
Accumulated Depreciation		$ 5,908
Depreciable Lives (Years)	[5]	(1)
181 Spring Street \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 1,066
Original Building		9,520
Costs Capitalized Subsequent to Acquisition		1,800
Land and Improvements		1,066
Building and Improvements		11,320
Total		12,386
Accumulated Depreciation		$ 5,802
Depreciable Lives (Years)	[6]	(1)
195 West Street \| Office Building [Member]
Original Cost
Original Land		$ 1,611
Original Building		6,652
Costs Capitalized Subsequent to Acquisition		4,221
Land and Improvements		1,858
Building and Improvements		10,626
Total		12,484
Accumulated Depreciation		$ 8,589
Depreciable Lives (Years)	[5]	(1)
195 West Street \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 1,611
Original Building		6,652
Costs Capitalized Subsequent to Acquisition		3,232
Land and Improvements		1,611
Building and Improvements		9,884
Total		11,495
Accumulated Depreciation		$ 8,306
Depreciable Lives (Years)	[6]	(1)
7501 Boston Boulevard, Building Seven \| Office Building [Member]
Original Cost
Original Land		$ 665
Original Building		9,273
Costs Capitalized Subsequent to Acquisition		819
Land and Improvements		791
Building and Improvements		9,966
Total		10,757
Accumulated Depreciation		$ 5,665
Depreciable Lives (Years)	[5]	(1)
7501 Boston Boulevard, Building Seven \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 665
Original Building		9,273
Costs Capitalized Subsequent to Acquisition		314
Land and Improvements		665
Building and Improvements		9,587
Total		10,252
Accumulated Depreciation		$ 5,520
Depreciable Lives (Years)	[6]	(1)
7435 Boston Boulevard, Building One \| Office Building [Member]
Original Cost
Original Land		$ 392
Original Building		3,822
Costs Capitalized Subsequent to Acquisition		5,016
Land and Improvements		659
Building and Improvements		8,571
Total		9,230
Accumulated Depreciation		$ 6,756
Depreciable Lives (Years)	[5]	(1)
7435 Boston Boulevard, Building One \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 392
Original Building		3,822
Costs Capitalized Subsequent to Acquisition		4,323
Land and Improvements		486
Building and Improvements		8,051
Total		8,537
Accumulated Depreciation		$ 6,561
Depreciable Lives (Years)	[6]	(1)
32 Hartwell Avenue \| Office Building [Member]
Original Cost
Original Land		$ 168
Original Building		1,943
Costs Capitalized Subsequent to Acquisition		6,944
Land and Improvements		314
Building and Improvements		8,741
Total		9,055
Accumulated Depreciation		$ 2,365
Depreciable Lives (Years)	[5]	(1)
32 Hartwell Avenue \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 168
Original Building		1,943
Costs Capitalized Subsequent to Acquisition		6,358
Land and Improvements		168
Building and Improvements		8,301
Total		8,469
Accumulated Depreciation		$ 2,199
Depreciable Lives (Years)	[6]	(1)
7450 Boston Boulevard, Building Three \| Office Building [Member]
Original Cost
Original Land		$ 1,165
Original Building		4,681
Costs Capitalized Subsequent to Acquisition		2,591
Land and Improvements		1,430
Building and Improvements		7,007
Total		8,437
Accumulated Depreciation		$ 4,103
Depreciable Lives (Years)	[5]	(1)
7450 Boston Boulevard, Building Three \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 1,165
Original Building		4,681
Costs Capitalized Subsequent to Acquisition		2,177
Land and Improvements		1,327
Building and Improvements		6,696
Total		8,023
Accumulated Depreciation		$ 3,983
Depreciable Lives (Years)	[6]	(1)
250 Binney Street \| Office Building [Member]
Original Cost
Original Land		$ 110
Original Building		4,483
Costs Capitalized Subsequent to Acquisition		3,593
Land and Improvements		273
Building and Improvements		7,913
Total		8,186
Accumulated Depreciation		$ 6,211
Depreciable Lives (Years)	[5]	(1)
250 Binney Street \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 110
Original Building		4,483
Costs Capitalized Subsequent to Acquisition		2,939
Land and Improvements		110
Building and Improvements		7,422
Total		7,532
Accumulated Depreciation		$ 6,030
Depreciable Lives (Years)	[6]	(1)
8000 Grainger Court Building Five \| Office Building [Member]
Original Cost
Original Land		$ 366
Original Building		4,282
Costs Capitalized Subsequent to Acquisition		3,198
Land and Improvements		601
Building and Improvements		7,245
Total		7,846
Accumulated Depreciation		$ 5,923
Depreciable Lives (Years)	[5]	(1)
8000 Grainger Court Building Five \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 366
Original Building		4,282
Costs Capitalized Subsequent to Acquisition		2,604
Land and Improvements		453
Building and Improvements		6,799
Total		7,252
Accumulated Depreciation		$ 5,756
Depreciable Lives (Years)	[6]	(1)
453 Ravendale Drive \| Office Building [Member]
Original Cost
Original Land		$ 5,477
Original Building		1,090
Costs Capitalized Subsequent to Acquisition		676
Land and Improvements		5,477
Building and Improvements		1,766
Total		7,243
Accumulated Depreciation		$ 819
Depreciable Lives (Years)	[5]	(1)
453 Ravendale Drive \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 5,477
Original Building		1,090
Costs Capitalized Subsequent to Acquisition		676
Land and Improvements		5,477
Building and Improvements		1,766
Total		7,243
Accumulated Depreciation		$ 819
Depreciable Lives (Years)	[6]	(1)
7300 Boston Boulevard Building Thirteen \| Office Building [Member]
Original Cost
Original Land		$ 608
Original Building		4,773
Costs Capitalized Subsequent to Acquisition		1,075
Land and Improvements		661
Building and Improvements		5,795
Total		6,456
Accumulated Depreciation		$ 2,269
Depreciable Lives (Years)	[5]	(1)
7300 Boston Boulevard Building Thirteen \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 608
Original Building		4,773
Costs Capitalized Subsequent to Acquisition		863
Land and Improvements		608
Building and Improvements		5,636
Total		6,244
Accumulated Depreciation		$ 2,209
Depreciable Lives (Years)	[6]	(1)
17 Hartwell Avenue \| Office Building [Member]
Original Cost
Original Land		$ 26
Original Building		150
Costs Capitalized Subsequent to Acquisition		6,064
Land and Improvements		65
Building and Improvements		6,175
Total		6,240
Accumulated Depreciation		$ 2,487
Depreciable Lives (Years)	[5]	(1)
17 Hartwell Avenue \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 26
Original Building		150
Costs Capitalized Subsequent to Acquisition		5,907
Land and Improvements		26
Building and Improvements		6,057
Total		6,083
Accumulated Depreciation		$ 2,442
Depreciable Lives (Years)	[6]	(1)
7601 Boston Boulevard Building Eight \| Office Building [Member]
Original Cost
Original Land		$ 200
Original Building		878
Costs Capitalized Subsequent to Acquisition		5,035
Land and Improvements		551
Building and Improvements		5,562
Total		6,113
Accumulated Depreciation		$ 4,838
Depreciable Lives (Years)	[5]	(1)
7601 Boston Boulevard Building Eight \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 200
Original Building		878
Costs Capitalized Subsequent to Acquisition		4,342
Land and Improvements		378
Building and Improvements		5,042
Total		5,420
Accumulated Depreciation		$ 4,643
Depreciable Lives (Years)	[6]	(1)
7500 Boston Boulevard Building Six \| Office Building [Member]
Original Cost
Original Land		$ 138
Original Building		3,749
Costs Capitalized Subsequent to Acquisition		1,640
Land and Improvements		367
Building and Improvements		5,160
Total		5,527
Accumulated Depreciation		$ 4,399
Depreciable Lives (Years)	[5]	(1)
7500 Boston Boulevard Building Six \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 138
Original Building		3,749
Costs Capitalized Subsequent to Acquisition		1,107
Land and Improvements		234
Building and Improvements		4,760
Total		4,994
Accumulated Depreciation		$ 4,249
Depreciable Lives (Years)	[6]	(1)
8000 Corporate Court Building Eleven \| Office Building [Member]
Original Cost
Original Land		$ 136
Original Building		3,071
Costs Capitalized Subsequent to Acquisition		1,649
Land and Improvements		774
Building and Improvements		4,082
Total		4,856
Accumulated Depreciation		$ 3,320
Depreciable Lives (Years)	[5]	(1)
8000 Corporate Court Building Eleven \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 136
Original Building		3,071
Costs Capitalized Subsequent to Acquisition		1,298
Land and Improvements		686
Building and Improvements		3,819
Total		4,505
Accumulated Depreciation		$ 3,217
Depreciable Lives (Years)	[6]	(1)
7375 Boston Boulevard Building Ten \| Office Building [Member]
Original Cost
Original Land		$ 23
Original Building		2,685
Costs Capitalized Subsequent to Acquisition		1,035
Land and Improvements		93
Building and Improvements		3,650
Total		3,743
Accumulated Depreciation		$ 2,724
Depreciable Lives (Years)	[5]	(1)
7375 Boston Boulevard Building Ten \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 23
Original Building		2,685
Costs Capitalized Subsequent to Acquisition		854
Land and Improvements		47
Building and Improvements		3,515
Total		3,562
Accumulated Depreciation		$ 2,676
Depreciable Lives (Years)	[6]	(1)
7374 Boston Boulevard Building Four \| Office Building [Member]
Original Cost
Original Land		$ 241
Original Building		1,605
Costs Capitalized Subsequent to Acquisition		1,821
Land and Improvements		398
Building and Improvements		3,269
Total		3,667
Accumulated Depreciation		$ 2,870
Depreciable Lives (Years)	[5]	(1)
7374 Boston Boulevard Building Four \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 241
Original Building		1,605
Costs Capitalized Subsequent to Acquisition		1,438
Land and Improvements		303
Building and Improvements		2,981
Total		3,284
Accumulated Depreciation		$ 2,765
Depreciable Lives (Years)	[6]	(1)
7451 Boston Boulevard Building Two \| Office Building [Member]
Original Cost
Original Land		$ 249
Original Building		1,542
Costs Capitalized Subsequent to Acquisition		1,658
Land and Improvements		613
Building and Improvements		2,836
Total		3,449
Accumulated Depreciation		$ 2,699
Depreciable Lives (Years)	[5]	(1)
7451 Boston Boulevard Building Two \| Boston Properties Limited Partnership \| Office Building [Member]
Original Cost
Original Land		$ 249
Original Building		1,542
Costs Capitalized Subsequent to Acquisition		1,345
Land and Improvements		535
Building and Improvements		2,601
Total		3,136
Accumulated Depreciation		$ 2,609
Depreciable Lives (Years)	[6]	(1)
The Skylyne \| Residential Building
Original Cost
Original Land		$ 28,962
Original Building		239,077
Costs Capitalized Subsequent to Acquisition		0
Land and Improvements		28,962
Building and Improvements		239,077
Total		268,039
Accumulated Depreciation		$ 2,128
Depreciable Lives (Years)	[5]	(1)
The Skylyne \| Boston Properties Limited Partnership \| Residential Building
Original Cost
Original Land		$ 28,962
Original Building		239,077
Costs Capitalized Subsequent to Acquisition		0
Land and Improvements		28,962
Building and Improvements		239,077
Total		268,039
Accumulated Depreciation		$ 2,128
Depreciable Lives (Years)	[6]	(1)
Signature at Reston \| Residential Building
Original Cost
Original Land		$ 27,076
Original Building		190,580
Costs Capitalized Subsequent to Acquisition		659
Land and Improvements		27,076
Building and Improvements		191,239
Total		218,315
Accumulated Depreciation		$ 13,650
Depreciable Lives (Years)	[5]	(1)
Signature at Reston \| Boston Properties Limited Partnership \| Residential Building
Original Cost
Original Land		$ 27,076
Original Building		190,580
Costs Capitalized Subsequent to Acquisition		659
Land and Improvements		27,076
Building and Improvements		191,239
Total		218,315
Accumulated Depreciation		$ 13,650
Depreciable Lives (Years)	[6]	(1)
Proto Kendall Square \| Residential Building
Original Cost
Original Land		$ 9,243
Original Building		127,248
Costs Capitalized Subsequent to Acquisition		3,336
Land and Improvements		9,245
Building and Improvements		130,582
Total		139,827
Accumulated Depreciation		$ 7,883
Depreciable Lives (Years)	[5]	(1)
Proto Kendall Square \| Boston Properties Limited Partnership \| Residential Building
Original Cost
Original Land		$ 9,243
Original Building		127,248
Costs Capitalized Subsequent to Acquisition		3,336
Land and Improvements		9,245
Building and Improvements		130,582
Total		139,827
Accumulated Depreciation		$ 7,883
Depreciable Lives (Years)	[6]	(1)
The Avant at Reston Town Center \| Residential Building
Original Cost
Original Land		$ 20,350
Original Building		91,995
Costs Capitalized Subsequent to Acquisition		846
Land and Improvements		20,350
Building and Improvements		92,841
Total		113,191
Accumulated Depreciation		$ 17,204
Depreciable Lives (Years)	[5]	(1)
The Avant at Reston Town Center \| Boston Properties Limited Partnership \| Residential Building
Original Cost
Original Land		$ 20,350
Original Building		91,995
Costs Capitalized Subsequent to Acquisition		846
Land and Improvements		20,350
Building and Improvements		92,841
Total		113,191
Accumulated Depreciation		$ 17,204
Depreciable Lives (Years)	[6]	(1)
The Lofts at Atlantic Wharf \| Residential Building
Original Cost
Original Land		$ 3,529
Original Building		54,891
Costs Capitalized Subsequent to Acquisition		2,129
Land and Improvements		3,529
Building and Improvements		57,020
Total		60,549
Accumulated Depreciation		$ 14,166
Depreciable Lives (Years)	[5]	(1)
The Lofts at Atlantic Wharf \| Boston Properties Limited Partnership \| Residential Building
Original Cost
Original Land		$ 3,529
Original Building		54,891
Costs Capitalized Subsequent to Acquisition		2,129
Land and Improvements		3,529
Building and Improvements		57,020
Total		60,549
Accumulated Depreciation		$ 14,166
Depreciable Lives (Years)	[6]	(1)
Boston Cambridge Marriott \| Hotel [Member]
Original Cost
Original Land		$ 478
Original Building		37,918
Costs Capitalized Subsequent to Acquisition		35,486
Land and Improvements		1,201
Building and Improvements		72,681
Total		73,882
Accumulated Depreciation		$ 49,103
Depreciable Lives (Years)	[5]	(1)
Boston Cambridge Marriott \| Boston Properties Limited Partnership \| Hotel [Member]
Original Cost
Original Land		$ 478
Original Building		37,918
Costs Capitalized Subsequent to Acquisition		32,595
Land and Improvements		478
Building and Improvements		70,513
Total		70,991
Accumulated Depreciation		$ 48,286
Depreciable Lives (Years)	[6]	(1)
Kendall Center Green Garage \| Garage
Original Cost
Original Land		$ 0
Original Building		35,035
Costs Capitalized Subsequent to Acquisition		6,846
Land and Improvements		103
Building and Improvements		41,778
Total		41,881
Accumulated Depreciation		$ 14,442
Depreciable Lives (Years)	[5]	(1)
Kendall Center Green Garage \| Boston Properties Limited Partnership \| Garage
Original Cost
Original Land		$ 0
Original Building		35,035
Costs Capitalized Subsequent to Acquisition		6,432
Land and Improvements		0
Building and Improvements		41,467
Total		41,467
Accumulated Depreciation		$ 14,327
Depreciable Lives (Years)	[6]	(1)
Kendall Center Yellow Garage \| Garage
Original Cost
Original Land		$ 1,256
Original Building		15,697
Costs Capitalized Subsequent to Acquisition		1,552
Land and Improvements		1,434
Building and Improvements		17,071
Total		18,505
Accumulated Depreciation		$ 6,485
Depreciable Lives (Years)	[5]	(1)
Kendall Center Yellow Garage \| Boston Properties Limited Partnership \| Garage
Original Cost
Original Land		$ 1,256
Original Building		15,697
Costs Capitalized Subsequent to Acquisition		840
Land and Improvements		1,256
Building and Improvements		16,537
Total		17,793
Accumulated Depreciation		$ 6,287
Depreciable Lives (Years)	[6]	(1)
Kendall Center Blue Garage \| Garage
Original Cost
Original Land		$ 1,163
Original Building		11,633
Costs Capitalized Subsequent to Acquisition		2,111
Land and Improvements		1,579
Building and Improvements		13,328
Total		14,907
Accumulated Depreciation		$ 10,044
Depreciable Lives (Years)	[5]	(1)
Kendall Center Blue Garage \| Boston Properties Limited Partnership \| Garage
Original Cost
Original Land		$ 1,163
Original Building		11,633
Costs Capitalized Subsequent to Acquisition		446
Land and Improvements		1,163
Building and Improvements		12,079
Total		13,242
Accumulated Depreciation		$ 9,576
Depreciable Lives (Years)	[6]	(1)
Reston Next \| Development
Original Cost
Original Land		$ 0
Original Building		0
Costs Capitalized Subsequent to Acquisition		354,174
Land and Improvements		0
Building and Improvements		0
Development and Construction in Progress		354,174
Total		354,174
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A
Reston Next \| Boston Properties Limited Partnership \| Development
Original Cost
Original Land		$ 0
Original Building		0
Costs Capitalized Subsequent to Acquisition		354,174
Land and Improvements		0
Building and Improvements		0
Development and Construction in Progress		354,174
Total		354,174
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A
2100 Pennsylvania Avenue \| Development
Original Cost
Original Land		$ 0
Original Building		0
Costs Capitalized Subsequent to Acquisition		294,445
Land and Improvements		185,129
Building and Improvements		0
Development and Construction in Progress		109,316
Total		294,445
Accumulated Depreciation		$ 3,481
Depreciable Lives (Years)		N/A
2100 Pennsylvania Avenue \| Boston Properties Limited Partnership \| Development
Original Cost
Original Land		$ 0
Original Building		0
Costs Capitalized Subsequent to Acquisition		294,445
Land and Improvements		185,129
Building and Improvements		0
Development and Construction in Progress		109,316
Total		294,445
Accumulated Depreciation		$ 3,481
Depreciable Lives (Years)		N/A
325 Main Street \| Development
Original Cost
Original Land		$ 174
Original Building		0
Costs Capitalized Subsequent to Acquisition		161,468
Land and Improvements		965
Building and Improvements		0
Development and Construction in Progress		160,677
Total		161,642
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A
325 Main Street \| Boston Properties Limited Partnership \| Development
Original Cost
Original Land		$ 174
Original Building		0
Costs Capitalized Subsequent to Acquisition		161,275
Land and Improvements		772
Building and Improvements		0
Development and Construction in Progress		160,677
Total		161,449
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A
777 Harrison Street \| Land
Original Cost
Original Land		$ 144,647
Original Building		0
Costs Capitalized Subsequent to Acquisition		25,930
Land and Improvements		0
Building and Improvements		47
Land held for development		170,530
Total		170,577
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A
777 Harrison Street \| Boston Properties Limited Partnership \| Land
Original Cost
Original Land		$ 144,647
Original Building		0
Costs Capitalized Subsequent to Acquisition		25,930
Land and Improvements		0
Building and Improvements		47
Land held for development		170,530
Total		170,577
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A
North First Master Plan \| Land
Original Cost
Original Land		$ 35,004
Original Building		0
Costs Capitalized Subsequent to Acquisition		3,937
Land and Improvements		0
Building and Improvements		0
Land held for development		38,941
Total		38,941
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A
North First Master Plan \| Boston Properties Limited Partnership \| Land
Original Cost
Original Land		$ 35,004
Original Building		0
Costs Capitalized Subsequent to Acquisition		3,937
Land and Improvements		0
Building and Improvements		0
Land held for development		38,941
Total		38,941
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A
Plaza at Almaden \| Land
Original Cost
Original Land		$ 0
Original Building		0
Costs Capitalized Subsequent to Acquisition		36,431
Land and Improvements		0
Building and Improvements		0
Land held for development		36,431
Total		36,431
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A
Plaza at Almaden \| Boston Properties Limited Partnership \| Land
Original Cost
Original Land		$ 0
Original Building		0
Costs Capitalized Subsequent to Acquisition		36,431
Land and Improvements		0
Building and Improvements		0
Land held for development		36,431
Total		36,431
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A
Back Bay Station Master Plan \| Land
Original Cost
Original Land		$ 0
Original Building		0
Costs Capitalized Subsequent to Acquisition		30,643
Land and Improvements		0
Building and Improvements		0
Land held for development		30,643
Total		30,643
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A
Back Bay Station Master Plan \| Boston Properties Limited Partnership \| Land
Original Cost
Original Land		$ 0
Original Building		0
Costs Capitalized Subsequent to Acquisition		30,643
Land and Improvements		0
Building and Improvements		0
Land held for development		30,643
Total		30,643
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A
Reston Gateway Master Plan \| Land
Original Cost
Original Land		$ 0
Original Building		0
Costs Capitalized Subsequent to Acquisition		28,610
Land and Improvements		0
Building and Improvements		0
Land held for development		28,610
Total		28,610
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A
Reston Gateway Master Plan \| Boston Properties Limited Partnership \| Land
Original Cost
Original Land		$ 0
Original Building		0
Costs Capitalized Subsequent to Acquisition		28,610
Land and Improvements		0
Building and Improvements		0
Land held for development		28,610
Total		28,610
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A
Springfield Metro Center \| Land
Original Cost
Original Land		$ 0
Original Building		0
Costs Capitalized Subsequent to Acquisition		19,871
Land and Improvements		0
Building and Improvements		0
Land held for development		19,871
Total		19,871
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A
Springfield Metro Center \| Boston Properties Limited Partnership \| Land
Original Cost
Original Land		$ 0
Original Building		0
Costs Capitalized Subsequent to Acquisition		19,871
Land and Improvements		0
Building and Improvements		0
Land held for development		19,871
Total		19,871
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A
214 Third Avenue \| Land
Original Cost
Original Land		$ 0
Original Building		0
Costs Capitalized Subsequent to Acquisition		19,206
Land and Improvements		0
Building and Improvements		0
Land held for development		19,206
Total		19,206
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A
214 Third Avenue \| Boston Properties Limited Partnership \| Land
Original Cost
Original Land		$ 0
Original Building		0
Costs Capitalized Subsequent to Acquisition		19,206
Land and Improvements		0
Building and Improvements		0
Land held for development		19,206
Total		19,206
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A
CityPoint South Master Plan \| Land
Original Cost
Original Land		$ 0
Original Building		0
Costs Capitalized Subsequent to Acquisition		13,363
Land and Improvements		0
Building and Improvements		0
Land held for development		13,363
Total		13,363
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A
CityPoint South Master Plan \| Boston Properties Limited Partnership \| Land
Original Cost
Original Land		$ 0
Original Building		0
Costs Capitalized Subsequent to Acquisition		13,363
Land and Improvements		0
Building and Improvements		0
Land held for development		13,363
Total		13,363
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A
103 Fourth Avenue \| Land
Original Cost
Original Land		$ 0
Original Building		0
Costs Capitalized Subsequent to Acquisition		12,888
Land and Improvements		0
Building and Improvements		0
Land held for development		12,888
Total		12,888
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A
103 Fourth Avenue \| Boston Properties Limited Partnership \| Land
Original Cost
Original Land		$ 0
Original Building		0
Costs Capitalized Subsequent to Acquisition		12,888
Land and Improvements		0
Building and Improvements		0
Land held for development		12,888
Total		12,888
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A
Broad Run Business Park \| Land
Original Cost
Original Land		$ 0
Original Building		0
Costs Capitalized Subsequent to Acquisition		2,392
Land and Improvements		0
Building and Improvements		0
Land held for development		2,392
Total		2,392
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A
Broad Run Business Park \| Boston Properties Limited Partnership \| Land
Original Cost
Original Land		$ 0
Original Building		0
Costs Capitalized Subsequent to Acquisition		2,392
Land and Improvements		0
Building and Improvements		0
Land held for development		2,392
Total		2,392
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A
Kendall Center Master Plan \| Land
Original Cost
Original Land		$ 0
Original Building		0
Costs Capitalized Subsequent to Acquisition		2,145
Land and Improvements		0
Building and Improvements		0
Land held for development		2,145
Total		2,145
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A
Kendall Center Master Plan \| Boston Properties Limited Partnership \| Land
Original Cost
Original Land		$ 0
Original Building		0
Costs Capitalized Subsequent to Acquisition		2,145
Land and Improvements		0
Building and Improvements		0
Land held for development		2,145
Total		2,145
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A
Weston Quarry \| Land
Original Cost
Original Land		$ 0
Original Building		0
Costs Capitalized Subsequent to Acquisition		1,249
Land and Improvements		0
Building and Improvements		0
Land held for development		1,249
Total		1,249
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A
Weston Quarry \| Boston Properties Limited Partnership \| Land
Original Cost
Original Land		$ 0
Original Building		0
Costs Capitalized Subsequent to Acquisition		1,249
Land and Improvements		0
Building and Improvements		0
Land held for development		1,249
Total		1,249
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A
Reston Overlook Master Plan \| Land
Original Cost
Original Land		$ 0
Original Building		0
Costs Capitalized Subsequent to Acquisition		42
Land and Improvements		0
Building and Improvements		0
Land held for development		42
Total		42
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A
Reston Overlook Master Plan \| Boston Properties Limited Partnership \| Land
Original Cost
Original Land		$ 0
Original Building		0
Costs Capitalized Subsequent to Acquisition		42
Land and Improvements		0
Building and Improvements		0
Land held for development		42
Total		42
Accumulated Depreciation		$ 0
Depreciable Lives (Years)		N/A

[1]	Includes pre-development costs.
[2]	Includes unamortized deferred financing costs totaling approximately $(22.9) 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 $23,302.
[5]	Depreciation of the buildings and improvements are calculated over lives ranging from the life of the lease to 40 years.
[6]	Depreciation of the buildings and improvements are calculated over lives ranging from the life of the lease to 40 years.

SEC Schedule, Article 12-28, _3

SEC Schedule, Article 12-28, Real Estate and Accumulated Depreciation Roll Forward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate [Roll Forward]
Balance at the beginning of the year	$ 22,844,697	$ 21,605,545	$ 21,058,714
Additions to / improvements of real estate	996,989	1,671,898	1,043,379
Assets sold/written-off	(538,383)	(432,746)	(496,548)
Balance at the end of the year	23,303,303	22,844,697	21,605,545
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate, Accumulated Depreciation [Roll Forward]
Balance at the beginning of the year	5,239,179	4,871,102	4,566,570
Depreciation expense	573,898	564,938	533,342
Assets sold/written-off	(311,440)	(196,861)	(228,810)
Balance at the end of the year	5,501,637	5,239,179	4,871,102
Boston Properties Limited Partnership
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate [Roll Forward]
Balance at the beginning of the year	22,449,476	21,207,189	20,647,236
Additions to / improvements of real estate	996,989	1,671,898	1,043,379
Assets sold/written-off	(519,971)	(429,611)	(483,426)
Balance at the end of the year	22,926,494	22,449,476	21,207,189
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate, Accumulated Depreciation [Roll Forward]
Balance at the beginning of the year	5,135,289	4,773,800	4,473,895
Depreciation expense	566,813	557,130	525,584
Assets sold/written-off	(305,991)	(195,641)	(225,679)
Balance at the end of the year	$ 5,396,111	$ 5,135,289	$ 4,773,800