Alnylam Pharmaceuticals (ALNY) 10-Q6 May 202020 Q1 Quarterly reportFinancial data

Company Profile

Cover Page

Cover Page - shares	3 Months Ended
Cover Page - shares	Mar. 31, 2020	Apr. 30, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2020
Document Transition Report	false
Entity File Number	001-36407
Entity Registrant Name	ALNYLAM PHARMACEUTICALS, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	77-0602661
Entity Address, Address Line One	675 West Kendall Street,
Entity Address, Address Line Two	Henri A. Termeer Square
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02142
City Area Code	617
Local Phone Number	551-8200
Title of 12(b) Security	Common Stock, $0.01 par value per share
Trading Symbol	ALNY
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		114,819,151
Entity Central Index Key	0001178670
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Amendment Flag	false

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 467,779	$ 547,178
Marketable debt securities	836,346	975,017
Marketable equity securities	38,078	13,967
Accounts receivable, net	75,572	43,011
Inventory	68,300	56,348
Prepaid expenses and other current assets	98,698	80,343
Total current assets	1,584,773	1,715,864
Property, plant and equipment, net	429,814	425,179
Operating lease right-of-use assets	221,280	221,197
Restricted investments	24,725	14,825
Other assets	19,032	18,069
Total assets	2,279,624	2,395,134
Current liabilities:
Accounts payable	40,484	49,884
Accrued expenses	183,221	197,201
Operating lease liability	29,043	27,688
Deferred revenue	86,043	77,821
Total current liabilities	338,791	352,594
Operating lease liability, net of current portion	275,782	276,135
Deferred revenue, net of current portion	306,124	318,383
Other liabilities	9,198	9,330
Total liabilities	929,895	956,442
Commitments and contingencies (Note 14)
Stockholders’ equity:
Preferred stock, $0.01 par value per share, 5,000 shares authorized and no shares issued and outstanding as of March 31, 2020 and December 31, 2019	0	0
Common stock, $0.01 par value per share, 250,000 shares authorized; 113,168 shares issued and outstanding as of March 31, 2020; 112,188 shares issued and outstanding as of December 31, 2019	1,131	1,122
Additional paid-in capital	5,289,966	5,201,176
Accumulated other comprehensive loss	(32,059)	(36,518)
Accumulated deficit	(3,909,309)	(3,727,088)
Total stockholders’ equity	1,349,729	1,438,692
Total liabilities and stockholders’ equity	$ 2,279,624	$ 2,395,134
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, shares outstanding (in shares)	113,168,000	112,188,000

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Mar. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	250,000,000	250,000,000
Common stock, shares issued (in shares)	113,168,000	112,188,000
Common stock, shares outstanding (in shares)	113,168,000	112,188,000

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Revenues:
Total revenues	$ 99,476	$ 33,294
Operating costs and expenses:
Cost of goods sold	13,302	3,347
Research and development	169,571	129,127
Selling, general and administrative	126,761	89,608
Total operating costs and expenses	309,634	222,082
Loss from operations	(210,158)	(188,788)
Other income:
Interest income	5,480	7,525
Other income	23,032	43
Total other income	28,512	7,568
Loss before income taxes	(181,646)	(181,220)
Provision for income taxes	(575)	(695)
Net loss	$ (182,221)	$ (181,915)
Net loss per common share - basic and diluted (in dollars per share)	$ (1.62)	$ (1.73)
Weighted-average common shares used to compute basic and diluted net loss per common share (in shares)	112,748	105,400
Statements of Comprehensive Loss
Net loss	$ (182,221)	$ (181,915)
Unrealized gain on marketable debt securities	4,045	360
Foreign currency translation	340	0
Defined benefit pension plans, net of tax	74	0
Comprehensive loss	(177,762)	(181,555)
Net revenues from collaborations
Revenues:
Total revenues	27,538	7,003
Net product revenues
Revenues:
Total revenues	$ 71,938	$ 26,291

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning balance at Dec. 31, 2018	$ 1,301,965	$ 1,011	$ 4,175,139	$ (33,213)	$ (2,840,972)
Balance (in shares) at Dec. 31, 2018		101,177
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options, net of tax withholdings	11,409	$ 3	11,406
Exercise of common stock options, net of tax withholdings (in shares)		207
Issuance of common stock under equity plans	(58)		(58)
Issuance of common stock under equity plans (in shares)		4
Issuance of common stock under benefit plans	784		784
Issuance of common stock under benefit plans (in shares)		12
Issuance of common stock, net of offering costs	381,900	$ 50	381,850
Issuance of common stock, net of offering costs (in shares)		5,000
Stock-based compensation expense related to equity-classified awards	32,541		32,541
Other comprehensive income	360			360
Net loss	(181,915)				(181,915)
Ending balance at Mar. 31, 2019	1,546,986	$ 1,064	4,601,662	(32,853)	(3,022,887)
Balance (in shares) at Mar. 31, 2019		106,400
Beginning balance at Dec. 31, 2019	$ 1,438,692	$ 1,122	5,201,176	(36,518)	(3,727,088)
Balance (in shares) at Dec. 31, 2019	112,188	112,188
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options, net of tax withholdings	$ 54,221	$ 9	54,212
Exercise of common stock options, net of tax withholdings (in shares)		976
Issuance of common stock under equity plans	0		0
Issuance of common stock under equity plans (in shares)		4
Stock-based compensation expense related to equity-classified awards	34,578		34,578
Other comprehensive income	4,459			4,459
Net loss	(182,221)				(182,221)
Ending balance at Mar. 31, 2020	$ 1,349,729	$ 1,131	$ 5,289,966	$ (32,059)	$ (3,909,309)
Balance (in shares) at Mar. 31, 2020	113,168	113,168

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities:
Net loss	$ (182,221)	$ (181,915)
Non-cash adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	7,613	3,838
Amortization and interest accretion related to operating leases	9,393	10,255
Stock-based compensation	34,578	32,032
Unrealized gain on marketable equity securities	(24,111)	0
Other	660	(1,075)
Changes in operating assets and liabilities:
Accounts receivable, net	(32,882)	(15,041)
Proceeds from landlord lease incentive for tenant improvements	0	12,386
Inventory	(11,952)	(7,134)
Prepaid expenses and other assets	(19,958)	(8,988)
Accounts payable, accrued expenses and other liabilities	(14,215)	(24,332)
Deferred revenue	(4,030)	(834)
Operating lease liability	(9,036)	(7,702)
Net cash used in operating activities	(246,161)	(188,510)
Cash flows from investing activities:
Purchases of property, plant and equipment	(19,617)	(44,049)
Purchases of marketable debt securities	(396,409)	(256,996)
Sales and maturities of marketable securities	539,614	403,697
Purchases of restricted investments	(9,900)	0
Net cash provided by investing activities	113,688	102,652
Cash flows from financing activities:
Proceeds from exercise of stock options and other types of equity, net	53,869	9,031
Offering proceeds, net of costs	0	381,900
Net cash provided by financing activities	53,869	390,931
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(631)	0
Net (decrease) increase in cash, cash equivalents and restricted cash	(79,235)	305,073
Cash, cash equivalents and restricted cash, beginning of period	549,628	422,631
Cash, cash equivalents and restricted cash, end of period	470,393	727,704
Supplemental disclosure of noncash investing and financing activities:
Capital expenditures included in accounts payable and accrued expenses	6,619	13,033
Lease liabilities arising from obtaining right-of-use assets	$ 2,939	$ 0

NATURE OF BUSINESS

NATURE OF BUSINESS	3 Months Ended
NATURE OF BUSINESS	Mar. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
NATURE OF BUSINESS	NATURE OF BUSINESS Alnylam Pharmaceuticals, Inc. (also referred to as Alnylam, we, our or us) commenced operations on June 14, 2002 as a biopharmaceutical company seeking to develop and commercialize novel therapeutics based on RNA interference, or RNAi. We are committed to the advancement of our company strategy of building a multi-product, global, commercial biopharmaceutical company with a deep and sustainable clinical pipeline of RNAi therapeutics for future growth and a robust, organic research engine for sustainable innovation and great potential for patient impact. Since inception, we have focused on discovering, developing and commercializing RNAi therapeutics by establishing and maintaining a strong intellectual property position in the RNAi field, establishing strategic alliances with leading pharmaceutical and life sciences companies, generating revenues through licensing agreements, and ultimately developing and commercializing RNAi therapeutics globally, either independently or with our strategic partners. We have devoted substantially all of our efforts to business planning, research, development, manufacturing and early commercial efforts, acquiring, filing and expanding intellectual property rights, recruiting management and technical staff, and raising capital. In August 2018, we received approval for ONPATTRO from the United States Food and Drug Administration, or FDA, and began commercializing and generating product revenues in the U.S., and also received marketing authorization for ONPATTRO from the European Commission, or EC. As of March 31, 2020, we have launched ONPATTRO in the U.S., Europe, Japan and in several additional countries. In November 2019, we received approval for GIVLAARI from the FDA and began commercializing and generating product revenues in the U.S. in December 2019. In March 2020, we received marketing authorization for GIVLAARI from the EC, and in April 2020, we launched GIVLAARI in Germany. Regulatory filings in additional markets are pending or planned for 2020 and beyond for both products.

BASIS OF PRESENTATION AND PRINC

BASIS OF PRESENTATION AND PRINCIPLES OF CONSOLIDATION	3 Months Ended
BASIS OF PRESENTATION AND PRINCIPLES OF CONSOLIDATION	Mar. 31, 2020
Accounting Policies [Abstract]
BASIS OF PRESENTATION AND PRINCIPLES OF CONSOLIDATION	BASIS OF PRESENTATION AND PRINCIPLES OF CONSOLIDATION The accompanying condensed consolidated financial statements of Alnylam are unaudited and have been prepared in accordance with accounting principles generally accepted in the United States of America, or GAAP, applicable to interim periods and, in the opinion of management, include all normal and recurring adjustments that are necessary to state fairly the results of operations for the reported periods. Our condensed consolidated financial statements have also been prepared on a basis substantially consistent with, and should be read in conjunction with, our audited consolidated financial statements for the year ended December 31, 2019, which were included in our Annual Report on Form 10-K that was filed with the Securities and Exchange Commission on February 13, 2020. The year-end condensed consolidated balance sheet data was derived from our audited financial statements but does not include all disclosures required by GAAP. The results of our operations for any interim period are not necessarily indicative of the results of our operations for any other interim period or for a full fiscal year. The accompanying condensed consolidated financial statements reflect the operations of Alnylam and our wholly-owned subsidiaries. All intercompany accounts and transactions have been eliminated. Our significant accounting policies are described in Note 2 of the Notes to Consolidated Financial Statements included in our Annual Report on Form 10-K for the year ended December 31, 2019. Reclassification Certain prior period amounts in the condensed consolidated financial statements have been reclassified to conform to the current period presentation. Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America, or GAAP, requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. The full extent to which the COVID-19 pandemic will directly or indirectly impact our business, results of operations and financial condition, including sales, expenses, reserves and allowances, clinical trials and research and development costs, will depend on future developments that are highly uncertain, including as a result of new information that may emerge concerning COVID-19 and the actions taken to contain it or treat COVID-19, as well as the economic impact on local, regional, national and international customers and markets. We have made estimates of the impact of COVID-19 within our financial statements and there may be changes to those estimates in future periods. Actual results may differ from these estimates. Liquidity Based on our current operating plan, we believe that our cash, cash equivalents and marketable debt and equity securities as of March 31, 2020, together with the cash we expect to generate from product sales and under our alliances and strategic financing collaboration, will be sufficient to enable us to advance our long-term strategic goals for multiple years from the filing of this Quarterly Report on Form 10-Q. Recently Adopted Accounting Pronouncements In June 2016, the Financial Accounting Standards Board, or FASB, issued new accounting guidance which requires entities to record expected credit losses for certain financial instruments, including trade receivables, as an allowance that reflects the entity's current estimate of credit losses expected to be incurred. For available-for-sale debt securities in unrealized loss positions, the new standard requires allowances to be recorded instead of reducing the amortized cost of the investment. The new standard became effective for us on January 1, 2020 and did not have a significant impact on our condensed consolidated financial statements and related disclosures. In August 2018, the FASB issued amendments to accounting guidance that eliminate, add and modify certain disclosure requirements on fair value measurements. The new standard became effective for us on January 1, 2020 and did not have a significant impact on our condensed consolidated financial statements and related disclosures. In August 2018, the FASB issued new accounting guidance to clarify the accounting for implementation costs in cloud computing arrangements (hosting arrangements). The new standard requires a customer in a cloud computing arrangement to determine which implementation costs to capitalize as assets or expense as incurred. Capitalized implementation costs related to a hosting arrangement that is a service contract will be amortized over the term of the hosting arrangement, beginning when the module or component of the hosting arrangement is ready for its intended use. The new standard became effective for us on January 1, 2020 and did not have a significant impact on our condensed consolidated financial statements and related disclosures. In November 2018, the FASB issued new accounting guidance to clarify the interaction between the accounting guidance for collaborative arrangements and revenue from contracts with customers. The new standard became effective for us on January 1, 2020 using a retrospective transition method. This standard did not have a significant impact on our condensed consolidated financial statements and related disclosures. In December 2019, the FASB issued amendments to accounting guidance that simplify the accounting for income taxes, as part of its initiative to reduce complexity in the accounting standards. The amendments eliminate certain exceptions related to the approach for intraperiod tax allocation, the methodology for calculating income taxes in an interim period and the recognition of deferred tax liabilities for outside basis differences. The amendments also clarify and simplify other aspects of the accounting for income taxes. We early adopted the amendments as of January 1, 2020, on a prospective basis. The amendments did not have a significant impact on our condensed consolidated financial statements and related disclosures.

NET PRODUCT REVENUES

NET PRODUCT REVENUES	3 Months Ended
NET PRODUCT REVENUES	Mar. 31, 2020
Revenue from Contract with Customer [Abstract]
NET PRODUCT REVENUES	NET PRODUCT REVENUES Net product revenues consist of the following: Three Months Ended March 31, (In thousands) 2020 2019 United States $ 42,470 $ 18,760 Europe 21,166 7,531 Rest of World (primarily Japan) 8,302 — Total $ 71,938 $ 26,291 Three Months Ended March 31, (In thousands) 2020 2019 ONPATTRO $ 66,664 $ 26,291 GIVLAARI 5,274 — Total $ 71,938 $ 26,291 The following table presents the balance of our receivables related to our net product revenues: (In thousands) As of March 31, As of December 31, Receivables included in “Accounts receivable, net” $ 49,601 $ 28,082

NET REVENUES FROM COLLABORATION

NET REVENUES FROM COLLABORATIONS	3 Months Ended
NET REVENUES FROM COLLABORATIONS	Mar. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
NET REVENUES FROM COLLABORATIONS	COLLABORATIONS Net revenues from collaborations consist of the following: Three Months Ended March 31, (In thousands) 2020 2019 Regeneron Pharmaceuticals (Regeneron) $ 19,503 $ — Vir Biotechnology (Vir) 6,516 928 The Medicines Company (MDCO) 1,060 1,745 Sanofi Genzyme (Sanofi) — 4,117 Other 459 213 Total $ 27,538 $ 7,003 The following table presents the balance of our receivables and contract liabilities related to our collaboration agreements: (In thousands) As of March 31, As of December 31, Receivables included in “Accounts receivable, net” $ 25,970 $ 14,929 Contract liabilities included in “Deferred revenue” 152,829 153,117 The following table presents revenue recognized as a result of changes in contract liability related to our collaboration agreements: Three Months Ended March 31, (In thousands) 2020 2019 Amounts included in contract liability at the beginning of the period $ 14,678 $ 928 In order to determine revenue recognized in the period from contract liabilities, we first allocate revenue to the individual contract liability balance outstanding at the beginning of the period until the revenue exceeds that balance. If additional consideration is received on those contracts in subsequent periods, we assume all revenue recognized in the reporting period first applies to the beginning contract liability as opposed to a portion applying to the new consideration for the period. The following table provides research and development expenses incurred by type, for which we recognize net revenue, that are directly attributable to our collaboration agreements, by collaboration partner: Three Months Ended March 31, 2020 2019 (In thousands) Clinical Trial and Manufacturing External Services Other Clinical Trial and Manufacturing External Services Other Regeneron $ 4,612 $ — $ 11,491 $ — $ — $ — Vir 339 52 1,693 294 236 129 MDCO 998 — 266 1,612 10 50 Sanofi — 17 231 4,826 135 59 Total $ 5,949 $ 69 $ 13,681 $ 6,732 $ 381 $ 238 The research and development expenses incurred for each agreement listed in the table above consist of costs incurred for (i) clinical and manufacturing expenses, (ii) external services including consulting services and lab supplies and services, and (iii) other expenses, including professional services, facilities and overhead allocations, and a reasonable estimate of compensation and related costs as billed to our counterparties, for which we recognize net revenue from collaborations. For the three months ended March 31, 2020 and 2019, we did not incur material selling, general and administrative expenses related to our collaboration agreements. Product Alliances Vir Biotechnology, Inc. In October 2017, we and Vir Biotechnology, Inc., or Vir, entered into a collaboration and license agreement, or the Vir Agreement, for the development and commercialization of RNAi therapeutics for infectious diseases, including chronic hepatitis B virus, or HBV, infection. Pursuant to the Vir Agreement, we granted to Vir an exclusive license to develop, manufacture and commercialize ALN-HBV02 (VIR-2218), for all uses and purposes other than certain excluded fields, as set forth in the Vir Agreement. In addition, we granted Vir an exclusive option for up to four additional RNAi therapeutic programs for the treatment of infectious diseases. Under the terms of the Vir Agreement, for each product arising from the HBV program, including ALN-HBV02, we retain the right to opt into a profit-sharing arrangement prior to the start of a Phase 3 clinical trial. In addition, we have the right on a product-by-product basis with respect to each additional infectious disease program that Vir elects to pursue, to opt into a profit-sharing arrangement for each such product at any time during a specified period prior to the achievement of clinical proof of concept for each such product. Pursuant to the Vir Agreement, Vir paid us an upfront fee of $10.0 million and issued to us 1,111,111 shares of its common stock. Under the Vir Agreement, we may also receive milestone payments upon the achievement of certain development, regulatory and commercial milestones, as well as royalties on the net sales of licensed products ranging from high-single-digit to sub-teen double-digit percentages. In March 2020, we achieved a development milestone relating to ALN-HBV02 and earned 1,111,111 shares of Vir's common stock and a $15.0 million cash payment. Due to the uncertainty of pharmaceutical development and the high historical failure rates generally associated with drug development, we may not receive any additional milestone payments or any royalty payments under the Vir Agreement. In March 2020, we entered into an amendment to the Vir Agreement to expand our collaboration to include the development and commercialization of RNAi therapeutics targeting SARS-CoV-2, the virus that causes the disease COVID-19. Under the Vir amendments, we and Vir will each be responsible for pre-clinical development costs incurred by each such party in performing its allocated responsibilities under an agreed-upon initial pre-clinical development plan. We and Vir will equally share costs incurred in connection with the manufacture of non-GMP drug product required for pre-clinical development prior to filing an IND for the first product in the coronavirus program. Vir will lead all development and commercialization of any selected development candidates. At clinical proof of concept, we will have an option to share equally in the profits and losses associated with the development and commercialization of the coronavirus program. Alternatively, we may elect to earn development and commercialization milestones and royalties on net sales of products resulting from the collaboration in amounts agreed upon for the coronavirus program. Unless terminated earlier in accordance with the terms of the agreement, the Vir Agreement expires on a licensed product-by-product and country-by-country basis upon expiration of all royalty payment obligations under the agreement. If Vir does not exercise its option for an infectious disease program, the Vir Agreement will expire upon the expiration of the applicable option period with respect to such program. However, if we exercise our profit-sharing option for any product, the term of the agreement will continue until the expiration of the profit-sharing arrangement for such product. Either party may terminate the agreement in the event the other party fails to cure a material breach, or upon patent-related challenges by the other party. In addition, Vir has the right to terminate the agreement on a program-by-program basis or in its entirety for any reason on 90 days’ written notice. We identified one performance obligation under the Vir Agreement, as amended comprised of: i) the exclusive license to develop, manufacture and commercialize RNAi therapeutics (including ALN-HBV02 and other infectious diseases), ii) the obligation to deliver four additional development candidates and supply product for each of the RNAi therapeutic programs for the treatment of infectious diseases, and iii) the obligation to deliver a development candidate and supply product for SARS-CoV-2. The license is not distinct from the services, including the obligation to deliver development candidates and supply product, as Vir cannot benefit on its own from the value of the license without receipt of such services and supply. As of March 31, 2020, the total transaction price was determined to be $105.2 million, comprised of the upfront payment, fair value of non-cash equity consideration at contract inception, the development milestone and variable consideration related to development, manufacture and supply activities. The total transaction price is allocated entirely to the single performance obligation. We utilized the expected value method to determine the amount of reimbursement for these activities. We determined any variable consideration related to sales-based royalties and milestones related to the exclusive license to be constrained and therefore excluded such consideration from the transaction price. As of March 31, 2020, the aggregate amount of the transaction price allocated to the performance obligation that was unsatisfied was $71.8 million, which is expected to be recognized through the term of the Vir Agreement as the services are performed. In April 2020, we further amended the Vir Agreement to include up to three additional targets focused on host factors for SARS-CoV-2, including angiotensin converting enzyme-2, or ACE2, and transmembrane protease, serine 2, or TMPRSS2, and potentially a third host target to emerge from Vir’s functional genomics work. Regeneron Collaboration On April 8, 2019, we entered into a global, strategic collaboration with Regeneron Pharmaceuticals, Inc., or Regeneron, to discover, develop and commercialize RNAi therapeutics for a broad range of diseases by addressing therapeutic targets expressed in the eye and central nervous system, or CNS, in addition to a select number of targets expressed in the liver, which we refer to as the Regeneron Collaboration. The Regeneron Collaboration is governed by a Master Agreement, referred to as the Regeneron Master Agreement, which became effective on May 21, 2019, or the Effective Date. In connection with the Regeneron Master Agreement, we and Regeneron entered into (i) a binding co-co collaboration term sheet covering the continued development of cemdisiran, our C5 small interfering RNA, or siRNA, currently in Phase 2 development for C5 complement-mediated diseases, as a monotherapy and (ii) a binding license term sheet to evaluate anti-C5 antibody-siRNA combinations for C5 complement-mediated diseases including evaluating the combination of Regeneron’s pozelimab (REGN3918), currently in Phase 1 development, and cemdisiran. The C5 co-co collaboration and license agreements were executed in August 2019. Under the terms of the Regeneron Collaboration, we are working exclusively with Regeneron to discover RNAi therapeutics for eye and CNS diseases for an initial five Regeneron will lead development and commercialization for all programs targeting eye diseases (subject to limited exceptions), entitling us to certain potential milestone and royalty payments pursuant to the terms of a license agreement, the form of which has been agreed upon by the parties. We and Regeneron will alternate leadership on CNS and liver programs, with the lead party retaining global development and commercial responsibility. For CNS and liver programs, both we and Regeneron will have the option at lead candidate selection to enter into a co-co collaboration agreement, the form of which has been agreed upon by the parties, whereby both companies will share equally all costs of, and profits from, all development and commercialization activities under the program. If the non-lead party elects to not enter into a co-co collaboration agreement with respect to a given CNS or liver program, we and Regeneron will enter into a license agreement with respect to such program and the lead party will be the “Licensee” for the purposes of the license agreement. If the lead party for a CNS or liver program elects to not enter into the co-co collaboration agreement, then we and Regeneron will enter into a license agreement with respect to such program and leadership of the program will transfer to the other party and the former non-lead party will be the “Licensee” for the purposes of the license agreement. With respect to the programs directed to C5 complement-mediated diseases, we retain control of cemdisiran monotherapy development, and Regeneron is leading combination product development. Under the C5 co-co collaboration agreement, we and Regeneron equally share costs and potential future profits on any monotherapy program. Under the C5 license agreement, for cemdisiran to be used as part of a combination product, Regeneron is solely responsible for all development and commercialization costs and we will receive low double-digit royalties and commercial milestones of up to $325.0 million on any potential combination product sales. The C5 co-co collaboration agreement, the C5 license agreement, and the Master Agreement have been combined for accounting purposes and treated as a single agreement. In connection with the Regeneron Master Agreement, Regeneron made an upfront payment of $400.0 million. We are also eligible to receive up to an additional $200.0 million in milestone payments upon achievement of certain criteria during early clinical development for eye and CNS programs. We and Regeneron plan to advance programs directed to up to 30 targets under the Regeneron Collaboration during the Initial Research Term. For each program, Regeneron will provide us with $2.5 million in funding at program initiation and an additional $2.5 million at lead candidate identification, with the potential for approximately $30.0 million in annual discovery funding to us as the Regeneron Collaboration reaches steady state. Regeneron has the right to terminate the Regeneron Master Agreement for convenience upon ninety days’ notice. The termination of the Regeneron Master Agreement does not affect the term of any license agreement or co-co collaboration agreement then in effect. In addition, either party may terminate the Regeneron Master Agreement for a material breach by, or insolvency of, the other party. Unless earlier terminated pursuant to its terms, the Regeneron Master Agreement will remain in effect with respect to each program until (a) such program becomes a terminated program or (b) the parties enter into a license agreement or co-co collaboration agreement with respect to such program. The Regeneron Master Agreement includes various representations, warranties, covenants, dispute escalation and resolution mechanisms, indemnities and other provisions customary for transactions of this nature. For any license agreement subsequently entered into, the licensee will generally be responsible for its own costs and expenses incurred in connection with the development and commercialization of the collaboration products. The licensee will pay to the licensor certain development and/or commercialization milestone payments totaling up to $150.0 million for each collaboration product. In addition, following the first commercial sale of the applicable collaboration product under a license agreement, the licensee is required to make certain tiered royalty payments, ranging from low double-digits up to 20%, to the licensor based on the aggregate annual net sales of the collaboration product, subject to customary reductions. For any co-co collaboration agreement subsequently entered into, we and Regeneron will share equally all costs of, and profits from, development and commercialization activities. In the event that a party exercises its opt-out right, the lead party will be responsible for all costs and expenses incurred in connection with the development and commercialization of the collaboration products under the applicable co-co collaboration agreement, subject to continued sharing of costs through defined points. If a party exercises its opt-out right, following the first commercial sale of the applicable collaboration product under a co-co collaboration agreement, the lead party is required to make certain tiered royalty payments, ranging from low double-digits up to 20%, to the other party based on the aggregate annual net sales of the collaboration product and the timing of the exercise of the opt-out right, subject to customary reductions and a reduction for opt-out transition costs. Due to the uncertainty of pharmaceutical development and the high historical failure rates generally associated with drug development, we may not receive any milestone or royalty payments from Regeneron under the Regeneron Master Agreement, the C5 license agreement, or any future license agreement, or under any co-co collaboration agreement in the event we exercise our opt-out right. Our obligations under the Regeneron Collaboration include: (i) a research license and research services, collectively referred to as the Research Services Obligation; (ii) a worldwide license to cemdisiran for combination therapies, and manufacturing and supply, and development service obligations, collectively referred to as the C5 License Obligation; and (iii) development, manufacturing and commercialization activities for cemdisiran monotherapies, referred to as the C5 Co-Co Obligation. The research license is not distinct from the research services primarily as a result of Regeneron being unable to benefit on its own or with other resources reasonably available, as the license is providing access to specialized expertise, particularly as it relates to RNAi technology that is not available in the marketplace. Similarly, the worldwide license to cemdisiran for combination therapies is not distinct from the manufacturing and supply, and development service obligations, as Regeneron cannot benefit on its own from the value of the license without receipt of supply. Separately, the cemdisiran monotherapy co-co collaboration agreement is under the scope of ASC 808 as we and Regeneron are both active participants in the development and manufacturing activities and are exposed to significant risks and rewards that are dependent on commercial success of the activities of the arrangement. The development and manufacturing activities are a combined unit of account under the scope of ASC 808 and are not deliverables under ASC 606. The total transaction price is comprised of the $400.0 million upfront payment and additional variable consideration related to research, development, manufacturing and supply activities related to the Research Services Obligation and the C5 License Obligation. We utilized the expected value method to determine the amount of reimbursement for these activities. We determined that any variable consideration related to sales-based royalties and milestones related to the worldwide license to cemdisiran for combination therapies is deemed to be constrained and therefore has been excluded from the transaction price. In addition, we are eligible to receive future milestones upon the achievement of certain criteria during early clinical development for the eye and CNS programs. We are also eligible to receive royalties on future commercial sales for certain eye, CNS or liver targets, if any; however, these amounts are excluded from variable consideration under the Regeneron Collaboration as we are only eligible to receive such amounts if, after a drug candidate is identified, the form of license agreement is subsequently executed resulting in a license that is granted to Regeneron. Any such subsequently granted license would represent a separate transaction under ASC 606. We allocated the initial transaction price to each unit of account based on the applicable accounting guidance as follows, in thousands: Performance Obligations Standalone Selling Price Transaction Price Allocated Accounting Guidance Research Services Obligation $ 130,700 $ 183,100 ASC 606 C5 License Obligation 97,600 92,500 ASC 606 C5 Co-Co Obligation 364,600 246,000 ASC 808 $ 521,600 The transaction price was allocated to the obligations based on the relative estimated standalone selling prices of each obligation, over which management has applied significant judgment. We developed the estimated standalone selling price for the licenses included in the Research Services Obligation and the C5 License Obligation primarily based on the probability-weighted present value of expected future cash flows associated with each license related to each specific program. In developing such estimate, we applied judgment in the determination of the forecasted revenues, taking into consideration the applicable market conditions and relevant entity-specific factors, the expected number of targets or indications expected to be pursued under each license, the probability of success, the time needed to develop a product candidate pursuant to the associated license and the discount rate. We developed the estimated standalone selling price for the services and/or manufacturing and supply included in each of the obligations, as applicable, primarily based on the nature of the services to be performed and/or goods to be manufactured and estimates of the associated costs. The estimated standalone selling price of the C5 Co-Co Obligation was developed by estimating the present value of expected future cash flows that Regeneron is entitled to receive. In developing such estimate, we applied judgment in determining the indications that will be pursued, the forecasted revenues for such indications, the probability of success and the discount rate. For the Research Services Obligation and the C5 License Obligation accounted for under ASC 606, we measure proportional performance over time using an input method based on cost incurred relative to the total estimated costs for each of the identified obligations, on a quarterly basis, by determining the proportion of effort incurred as a percentage of total effort we expect to expend. This ratio is applied to the transaction price allocated to each obligation. Management has applied significant judgment in the process of developing our estimates. Any changes to these estimates will be recognized in the period in which they change as a cumulative catch up. We re-evaluate the transaction price as of the end of each reporting period and during the quarter ended March 31, 2020, there was no change to the transaction price calculated at December 31, 2019. For the C5 Co-Co Obligation accounted for under ASC 808, the transaction price allocated to this obligation is recognized using a proportional performance method. Revenue recognized under this agreement, inclusive of the amount allocated to the C5 Co-Co Obligation and future cost reimbursements, is accounted for as collaboration revenue. The following table provides a summary of the transaction price allocated to each unit of account based on the applicable accounting guidance, in addition to revenue activity during the period, in thousands: Transaction Price Allocated Revenue Recognized During Deferred Revenue Performance Obligations As of March 31, Three Months Ended March 31, 2020 Three Months Ended March 31, 2019 As of March 31, As of December 31, Accounting Guidance Research Services Obligation $ 200,600 $ 12,300 $ — $ 72,300 $ 84,800 ASC 606 C5 License Obligation 108,500 — — 65,800 65,800 ASC 606 C5 Co-Co Obligation 246,000 4,200 — 239,000 243,000 ASC 808 $ 555,100 $ 16,500 $ — $ 377,100 $ 393,600 As of March 31, 2020, the aggregate amount of the transaction price allocated to the remaining Research Services Obligation and C5 License Obligation that was unsatisfied is $296.8 million, which is expected to be recognized through the term of the Regeneron Collaboration as the services are performed. This amount excludes the transaction price allocated to the C5 Co-Co Obligation accounted for under ASC 808. Deferred revenue related to the Regeneron Collaboration is classified as either current or non-current in the condensed consolidated balance sheets based on the period the revenue is expected to be recognized. Sanofi Genzyme Collaboration Collaboration Amendment On April 8, 2019, we and Sanofi Genzyme entered into an amendment to our 2014 Sanofi Genzyme collaboration, which we refer to as the Collaboration Amendment. Under the Collaboration Amendment, we and Sanofi Genzyme agreed to conclude the research and option phase under our collaboration agreement. In connection and simultaneously with entering into the Collaboration Amendment, we and Sanofi Genzyme also entered into the Amended and Restated ALN-AT3 Global License Terms with respect to ALN-AT3 (fitusiran) and certain back-up products, which we refer to as the A&R AT3 License Terms. The A&R AT3 License Terms amend and restate the ALN-AT3 Global License Terms entered into by us and Sanofi Genzyme in January 2018 to modify certain of the business terms. The material collaboration terms for fitusiran, as previously announced, will continue unchanged. In connection with entering into the Collaboration Amendment and the A&R AT3 License Terms, we agreed to advance, at our cost, a selected investigational asset in an undisclosed rare genetic disease through the end of IND-enabling studies. Following completion of such studies, we will transition, at our cost, such asset to Sanofi Genzyme. Thereafter, Sanofi Genzyme will fund all potential future development and commercialization costs for such asset. If this asset is developed and approved, we will be eligible to receive tiered double-digit royalties on global net sales. No changes were made to our Exclusive License Agreement with Sanofi Genzyme, referred to as the Exclusive TTR License, pursuant to which we have global rights for the development and commercialization of ONPATTRO, together with vutrisiran and all back-up products, which remains in full force and effect.

INVENTORY

INVENTORY	3 Months Ended
INVENTORY	Mar. 31, 2020
Inventory Disclosure [Abstract]
INVENTORY	INVENTORY The components of inventory are summarized as follows: (In thousands) As of March 31, 2020 As of December 31, 2019 Raw materials $ 30,662 $ 15,418 Work in progress 33,412 38,275 Finished goods 4,226 2,655 Total $ 68,300 $ 56,348

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	3 Months Ended
FAIR VALUE MEASUREMENTS	Mar. 31, 2020
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTS The following tables present information about our assets that are measured at fair value on a recurring basis and indicate the fair value hierarchy of the valuation techniques we utilized to determine such fair value: (In thousands) As of March 31, 2020 Quoted Significant Significant Cash equivalents: U.S. treasury securities $ 136,492 $ — $ 136,492 $ — Money market funds 254,627 254,627 — — Marketable debt securities: — — — Certificates of deposit 5,134 — 5,134 — Commercial paper 21,792 — 21,792 — Corporate notes 114,280 — 114,280 — U.S. government-sponsored enterprise securities 105,297 — 105,297 — U.S. treasury securities 589,843 — 589,843 — Marketable equity securities 38,078 38,078 — — Restricted cash (money market funds) 1,483 1,483 — — Total $ 1,267,026 $ 294,188 $ 972,838 $ — (In thousands) As of December 31, 2019 Quoted Significant Significant Cash equivalents: Commercial paper $ 3,439 $ — $ 3,439 $ — U.S. treasury securities 336,693 — 336,693 — Money market funds 119,882 119,882 — — Marketable debt securities: Certificates of deposit 4,301 — 4,301 — Commercial paper 36,474 — 36,474 — Corporate notes 146,040 — 146,040 — U.S. government-sponsored enterprise securities 32,488 — 32,488 — U.S. treasury securities 755,714 — 755,714 — Marketable equity securities 13,967 13,967 — — Restricted cash (money market funds) 1,482 1,482 — — Total $ 1,450,480 $ 135,331 $ 1,315,149 $ — During the three months ended March 31, 2020 and 2019, there were no transfers between Level 1 and Level 2 financial assets. The carrying amounts reflected in our condensed consolidated balance sheets for cash, accounts receivable, net, other current assets, accounts payable and accrued expenses approximate fair value due to their short-term maturities.

MARKETABLE DEBT SECURITIES

MARKETABLE DEBT SECURITIES	3 Months Ended
MARKETABLE DEBT SECURITIES	Mar. 31, 2020
Investments, Debt and Equity Securities [Abstract]
MARKETABLE DEBT SECURITIES	MARKETABLE DEBT SECURITIES We invest our excess cash balances in marketable debt securities and at each balance sheet date presented, we classify all of our investments in debt securities as available-for-sale and as current assets as they represent the investment of funds available for current operations. We did not record any impairment charges related to our marketable debt securities during the three months ended March 31, 2020 or 2019. The following tables summarize our marketable debt securities: As of March 31, 2020 (In thousands) Amortized Gross Gross Fair Value Certificates of deposit $ 5,141 $ — $ (7) $ 5,134 Commercial paper 21,792 — — 21,792 Corporate notes 114,592 9 (321) 114,280 U.S. government-sponsored enterprise securities 105,028 275 (6) 105,297 U.S. treasury securities 722,103 4,232 — 726,335 Total $ 968,656 $ 4,516 $ (334) $ 972,838 As of December 31, 2019 (In thousands) Amortized Gross Gross Fair Value Certificates of deposit $ 4,303 $ — $ (2) $ 4,301 Commercial paper 39,913 — — 39,913 Corporate notes 146,016 58 (34) 146,040 U.S. government-sponsored enterprise securities 32,487 3 (2) 32,488 U.S. treasury securities 1,092,293 185 (71) 1,092,407 Total $ 1,315,012 $ 246 $ (109) $ 1,315,149 The fair values of our marketable debt securities by classification in the condensed consolidated balance sheets were as follows: (In thousands) As of March 31, 2020 As of December 31, 2019 Cash and cash equivalents $ 136,492 $ 340,132 Marketable debt securities 836,346 975,017 Total $ 972,838 $ 1,315,149

RECONCILIATION OF CASH, CASH EQ

RECONCILIATION OF CASH, CASH EQUIVALENTS AND RESTRICTED CASH	3 Months Ended
	Mar. 31, 2020
Cash Cash Equivalents And Restricted Cash [Abstract]
RECONCILIATION OF CASH, CASH EQUIVALENTS AND RESTRICTED CASH	RECONCILIATION OF CASH, CASH EQUIVALENTS AND RESTRICTED CASH The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within our condensed consolidated balance sheets that sum to the total of these amounts shown in the condensed consolidated statements of cash flows: As of March 31, (In thousands) 2020 2019 Cash and cash equivalents $ 467,779 $ 724,959 Restricted cash included in prepaid expenses and other current assets 167 439 Restricted cash included in long-term other assets 2,447 2,306 Total cash, cash equivalents, and restricted cash shown in the condensed consolidated statements of cash flows $ 470,393 $ 727,704

OTHER COMPREHENSIVE INCOME AND

OTHER COMPREHENSIVE INCOME AND ACCUMULATED OTHER COMPREHENSIVE LOSS	3 Months Ended
	Mar. 31, 2020
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
OTHER COMPREHENSIVE INCOME AND ACCUMULATED OTHER COMPREHENSIVE LOSS	OTHER COMPREHENSIVE INCOME AND ACCUMULATED OTHER COMPREHENSIVE LOSS The following tables summarize the changes in accumulated other comprehensive (loss) income, by component, for the three months ended March 31, 2020 and 2019: (In thousands) Loss on Investment in Joint Venture Defined Benefit Pension Unrealized Gains from Debt Securities Foreign Currency Translation Total Accumulated Other Comprehensive Loss Balance as of December 31, 2019 $ (32,792) $ (3,520) $ 137 $ (343) $ (36,518) Other comprehensive income before reclassifications — — 1,317 340 1,657 Amounts reclassified from other comprehensive income — 74 2,728 — 2,802 Net other comprehensive income — 74 4,045 340 4,459 Balance as of March 31, 2020 $ (32,792) $ (3,446) $ 4,182 $ (3) $ (32,059) (In thousands) Loss on Investment in Joint Venture Defined Benefit Pension Unrealized Losses from Debt Foreign Currency Translation Total Accumulated Other Balance as of December 31, 2018 $ (32,792) $ — $ (421) $ — $ (33,213) Other comprehensive income before reclassifications — — 346 — 346 Amounts reclassified from other comprehensive income — — 14 — 14 Net other comprehensive income — — 360 — 360 Balance as of March 31, 2019 $ (32,792) $ — $ (61) $ — $ (32,853)

EQUITY

EQUITY	3 Months Ended
EQUITY	Mar. 31, 2020
Equity [Abstract]
EQUITY	EQUITY Public Offering In January 2019, we sold an aggregate of 5,000,000 shares of our common stock through an underwritten public offering at a price to the public of $77.50 per share. As a result of the offering, we received aggregate net proceeds of $381.9 million after deducting underwriting discounts and commissions and other offering expenses of approximately $5.6 million.

STOCK-BASED COMPENSATION

STOCK-BASED COMPENSATION	3 Months Ended
STOCK-BASED COMPENSATION	Mar. 31, 2020
Share-based Payment Arrangement [Abstract]
STOCK-BASED COMPENSATION	STOCK-BASED COMPENSATION The following table summarizes stock-based compensation expenses included in operating costs and expenses: Three Months Ended March 31, (In thousands) 2020 2019 Research and development $ 16,049 $ 16,125 Selling, general and administrative 18,529 15,907 Total $ 34,578 $ 32,032

NET LOSS PER COMMON SHARE

NET LOSS PER COMMON SHARE	3 Months Ended
NET LOSS PER COMMON SHARE	Mar. 31, 2020
Earnings Per Share [Abstract]
NET LOSS PER COMMON SHARE	NET LOSS PER COMMON SHARE We compute basic net loss per common share by dividing net loss by the weighted-average number of common shares outstanding during the period. We compute diluted net loss per common share by dividing net loss by the weighted-average number of common shares and dilutive potential common share equivalents outstanding during the period. Potential common shares consist of shares issuable upon the exercise of stock options (the proceeds of which are then assumed to have been used to repurchase outstanding shares using the treasury stock method). Because the inclusion of potential common shares would be anti-dilutive for all periods presented, diluted net loss per common share is the same as basic net loss per common share. The following common share equivalents were excluded from the calculation of net loss per common share because their inclusion would be anti-dilutive: As of March 31, (In thousands) 2020 2019 Options to purchase common stock 13,609 13,868 Unvested restricted common stock 1,411 717 Total 15,020 14,585

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	3 Months Ended
COMMITMENTS AND CONTINGENCIES	Mar. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES Litigation From time to time, we are a party to legal proceedings in the course of our business, including the matters described below. The claims and legal proceedings in which we could be involved include challenges to the scope, validity or enforceability of patents relating to our products or product candidates, and challenges by us to the scope, validity or enforceability of the patents held by others. These include claims by third parties that we infringe their patents. The outcome of any such legal proceedings, regardless of the merits, is inherently uncertain. In addition, litigation and related matters are costly and may divert the attention of our management and other resources that would otherwise be engaged in other activities. If we were unable to prevail in any such legal proceedings, our business, results of operations, liquidity and financial condition could be adversely affected. Our accounting policy for accrual of legal costs is to recognize such expenses as incurred. Securities Litigation On September 26, 2018, Caryl Hull Leavitt, individually and on behalf of all others similarly situated, filed a class action complaint for violation of federal securities laws against us, our Chief Executive Officer and our former Chief Financial Officer in the United States District Court for the Southern District of New York. By stipulation of the parties and Order of the Court dated November 20, 2018, the action was transferred to the United States District Court for the District of Massachusetts. On May 8, 2019, the Court entered an order appointing a lead plaintiff, and on July 3, 2019, lead plaintiff filed a consolidated class action complaint, or the Complaint. In addition to the originally named defendants, the Complaint also named as defendants certain of our other executive officers, and purported to be brought on behalf of a class of persons who acquired our securities between September 20, 2017 and September 12, 2018 and sought to recover damages caused by defendants’ alleged violations of the federal securities laws and to pursue remedies under Sections 10(b) and 20(a) of the Securities Exchange Act of 1934, as amended, and Rule 10b-5 promulgated thereunder. The Complaint alleged, among other things, that the defendants made materially false and misleading statements related to the efficacy and safety of our product, ONPATTRO. The plaintiff sought, among other things, the designation of this action as a class action, an award of unspecified compensatory damages, interest, costs and expenses, including counsel fees and expert fees, and other relief as the court deems appropriate. All defendants filed a motion to dismiss the Complaint in its entirety on July 31, 2019. The motion to dismiss was fully briefed on September 30, 2019. On March 23, 2020, the Court allowed our motion and dismissed the Complaint without prejudice. On April 13, 2020, the plaintiff filed a motion seeking to amend the judgment to permit the plaintiff to file a further amended complaint. Defendants filed an opposition to that motion on April 17, 2020. On September 12, 2019, the Chester County Employees Retirement Fund, individually and on behalf of all others similarly situated, filed a purported securities class action complaint for violation of federal securities laws against us, certain of our current and former directors and officers, and the underwriters of our November 14, 2017 public stock offering, in the Supreme Court of the State of New York, New York County. On November 7, 2019, plaintiff filed an amended complaint, or the New York Complaint. The New York Complaint is brought on behalf of an alleged class of those who purchased our securities pursuant and/or traceable to our November 14, 2017 public stock offering. The New York Complaint purports to allege claims arising under Sections 11, 12(a)(2) and 15 of the Securities Act of 1933, as amended, and generally alleges that the defendants violated the federal securities laws by, among other things, making material misstatements or omissions concerning the results of our APOLLO Phase 3 clinical trial of patisiran. The plaintiff seeks, among other things, the designation of the action as a class action, an award of unspecified compensatory damages, rescissory damages, interest, costs and expenses, including counsel fees and expert fees, and other relief as the court deems appropriate. All defendants filed a joint motion to dismiss the New York Complaint in its entirety on December 20, 2019. Plaintiff’s response to that motion was filed on February 3, 2020, and defendants filed a joint reply on March 4, 2020. Defendants' motion remains pending. We believe that the allegations contained in the complaints are without merit and intend to defend the cases vigorously. We cannot predict at this point the length of time that these actions will be ongoing or the liabilities, if any, which may arise therefrom.

DEFINED BENEFIT PLANS

DEFINED BENEFIT PLANS	3 Months Ended
DEFINED BENEFIT PLANS	Mar. 31, 2020
Retirement Benefits [Abstract]
DEFINED BENEFIT PLANS	DEFINED BENEFIT PLANSWe maintain defined benefit plans for employees in certain countries outside the U.S., including retirement benefit plans required by applicable local law. The unfunded benefit obligation corresponds to the projected benefit obligations of which the discounted net present value is calculated based on years of employment, expected salary increases and pension adjustments, offset by the fair value of the assets held by plan. The unfunded benefit obligation was approximately $4.3 million as of March 31, 2020 and December 31, 2019, and is recorded in other liabilities on the condensed consolidated balance sheet. The total net periodic benefit cost for the three months ended March 31, 2020 and 2019 was not material.

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	3 Months Ended
SUBSEQUENT EVENTS	Mar. 31, 2020
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	SUBSEQUENT EVENTSOn April 10, 2020, we entered into a broad strategic financing collaboration with the Blackstone Group Inc., or Blackstone, under which Blackstone will provide up to $2.0 billion to support our advancement of innovative RNAi medicines that have the potential to transform the lives of patients suffering from a range of debilitating diseases. The strategic financing collaboration includes: (1) $1.0 billion in committed payments to acquire 50% of royalties and 75% of commercial milestones payable to us in connection with sales of inclisiran; (2) up to $750.0 million in a first lien senior secured term loan; (3) up to $150.0 million for development of vutrisiran and ALN-AGT, subject to completion of a definitive agreement; and (4) the purchase of $100.0 million of our common stock.

BASIS OF PRESENTATION AND PRI_2

BASIS OF PRESENTATION AND PRINCIPLES OF CONSOLIDATION (Policies)	3 Months Ended
	Mar. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation and Principles of Consolidation	The accompanying condensed consolidated financial statements of Alnylam are unaudited and have been prepared in accordance with accounting principles generally accepted in the United States of America, or GAAP, applicable to interim periods and, in the opinion of management, include all normal and recurring adjustments that are necessary to state fairly the results of operations for the reported periods. Our condensed consolidated financial statements have also been prepared on a basis substantially consistent with, and should be read in conjunction with, our audited consolidated financial statements for the year ended December 31, 2019, which were included in our Annual Report on Form 10-K that was filed with the Securities and Exchange Commission on February 13, 2020. The year-end condensed consolidated balance sheet data was derived from our audited financial statements but does not include all disclosures required by GAAP. The results of our operations for any interim period are not necessarily indicative of the results of our operations for any other interim period or for a full fiscal year. The accompanying condensed consolidated financial statements reflect the operations of Alnylam and our wholly-owned subsidiaries. All intercompany accounts and transactions have been eliminated. Our significant accounting policies are described in Note 2 of the Notes to Consolidated Financial Statements included in our Annual Report on Form 10-K for the year ended December 31, 2019.
Reclassification	Reclassification Certain prior period amounts in the condensed consolidated financial statements have been reclassified to conform to the current period presentation.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America, or GAAP, requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. The full extent to which the COVID-19 pandemic will directly or indirectly impact our business, results of operations and financial condition, including sales, expenses, reserves and allowances, clinical trials and research and development costs, will depend on future developments that are highly uncertain, including as a result of new information that may emerge concerning COVID-19 and the actions taken to contain it or treat COVID-19, as well as the economic impact on local, regional, national and international customers and markets. We have made estimates of the impact of COVID-19 within our financial statements and there may be changes to those estimates in future periods. Actual results may differ from these estimates.
Liquidity	Liquidity Based on our current operating plan, we believe that our cash, cash equivalents and marketable debt and equity securities as of March 31, 2020, together with the cash we expect to generate from product sales and under our alliances and strategic
Recent Accounting Pronouncements	Recently Adopted Accounting Pronouncements In June 2016, the Financial Accounting Standards Board, or FASB, issued new accounting guidance which requires entities to record expected credit losses for certain financial instruments, including trade receivables, as an allowance that reflects the entity's current estimate of credit losses expected to be incurred. For available-for-sale debt securities in unrealized loss positions, the new standard requires allowances to be recorded instead of reducing the amortized cost of the investment. The new standard became effective for us on January 1, 2020 and did not have a significant impact on our condensed consolidated financial statements and related disclosures. In August 2018, the FASB issued amendments to accounting guidance that eliminate, add and modify certain disclosure requirements on fair value measurements. The new standard became effective for us on January 1, 2020 and did not have a significant impact on our condensed consolidated financial statements and related disclosures. In August 2018, the FASB issued new accounting guidance to clarify the accounting for implementation costs in cloud computing arrangements (hosting arrangements). The new standard requires a customer in a cloud computing arrangement to determine which implementation costs to capitalize as assets or expense as incurred. Capitalized implementation costs related to a hosting arrangement that is a service contract will be amortized over the term of the hosting arrangement, beginning when the module or component of the hosting arrangement is ready for its intended use. The new standard became effective for us on January 1, 2020 and did not have a significant impact on our condensed consolidated financial statements and related disclosures. In November 2018, the FASB issued new accounting guidance to clarify the interaction between the accounting guidance for collaborative arrangements and revenue from contracts with customers. The new standard became effective for us on January 1, 2020 using a retrospective transition method. This standard did not have a significant impact on our condensed consolidated financial statements and related disclosures. In December 2019, the FASB issued amendments to accounting guidance that simplify the accounting for income taxes, as part of its initiative to reduce complexity in the accounting standards. The amendments eliminate certain exceptions related to the approach for intraperiod tax allocation, the methodology for calculating income taxes in an interim period and the recognition of deferred tax liabilities for outside basis differences. The amendments also clarify and simplify other aspects of the accounting for income taxes. We early adopted the amendments as of January 1, 2020, on a prospective basis. The amendments did not have a significant impact on our condensed consolidated financial statements and related disclosures.

NET PRODUCT REVENUES (Tables)

NET PRODUCT REVENUES (Tables)	3 Months Ended
NET PRODUCT REVENUES (Tables)	Mar. 31, 2020
Revenue from Contract with Customer [Abstract]
Summary of Net Product Revenues	Net product revenues consist of the following: Three Months Ended March 31, (In thousands) 2020 2019 United States $ 42,470 $ 18,760 Europe 21,166 7,531 Rest of World (primarily Japan) 8,302 — Total $ 71,938 $ 26,291 Three Months Ended March 31, (In thousands) 2020 2019 ONPATTRO $ 66,664 $ 26,291 GIVLAARI 5,274 — Total $ 71,938 $ 26,291

NET REVENUES FROM COLLABORATI_2

NET REVENUES FROM COLLABORATIONS (Tables)	3 Months Ended
NET REVENUES FROM COLLABORATIONS (Tables)	Mar. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Revenue from Collaborators	Net revenues from collaborations consist of the following: Three Months Ended March 31, (In thousands) 2020 2019 Regeneron Pharmaceuticals (Regeneron) $ 19,503 $ — Vir Biotechnology (Vir) 6,516 928 The Medicines Company (MDCO) 1,060 1,745 Sanofi Genzyme (Sanofi) — 4,117 Other 459 213 Total $ 27,538 $ 7,003
Balance and Change in Receivables and Contract Liabilities Related to Collaboration Agreements	The following table presents the balance of our receivables and contract liabilities related to our collaboration agreements: (In thousands) As of March 31, As of December 31, Receivables included in “Accounts receivable, net” $ 25,970 $ 14,929 Contract liabilities included in “Deferred revenue” 152,829 153,117 The following table presents revenue recognized as a result of changes in contract liability related to our collaboration agreements: Three Months Ended March 31, (In thousands) 2020 2019 Amounts included in contract liability at the beginning of the period $ 14,678 $ 928
Schedule of Research and Development Expenses Incurred by Type that are Directly Attributable to Collaboration Agreements	The following table provides research and development expenses incurred by type, for which we recognize net revenue, that are directly attributable to our collaboration agreements, by collaboration partner: Three Months Ended March 31, 2020 2019 (In thousands) Clinical Trial and Manufacturing External Services Other Clinical Trial and Manufacturing External Services Other Regeneron $ 4,612 $ — $ 11,491 $ — $ — $ — Vir 339 52 1,693 294 236 129 MDCO 998 — 266 1,612 10 50 Sanofi — 17 231 4,826 135 59 Total $ 5,949 $ 69 $ 13,681 $ 6,732 $ 381 $ 238
Schedule of Allocated Transaction Price Based on Accounting Guidance	We allocated the initial transaction price to each unit of account based on the applicable accounting guidance as follows, in thousands: Performance Obligations Standalone Selling Price Transaction Price Allocated Accounting Guidance Research Services Obligation $ 130,700 $ 183,100 ASC 606 C5 License Obligation 97,600 92,500 ASC 606 C5 Co-Co Obligation 364,600 246,000 ASC 808 $ 521,600
Schedule of Revenue Recognized Based on Accounting Guidance	The following table provides a summary of the transaction price allocated to each unit of account based on the applicable accounting guidance, in addition to revenue activity during the period, in thousands: Transaction Price Allocated Revenue Recognized During Deferred Revenue Performance Obligations As of March 31, Three Months Ended March 31, 2020 Three Months Ended March 31, 2019 As of March 31, As of December 31, Accounting Guidance Research Services Obligation $ 200,600 $ 12,300 $ — $ 72,300 $ 84,800 ASC 606 C5 License Obligation 108,500 — — 65,800 65,800 ASC 606 C5 Co-Co Obligation 246,000 4,200 — 239,000 243,000 ASC 808 $ 555,100 $ 16,500 $ — $ 377,100 $ 393,600

INVENTORY (Tables)

INVENTORY (Tables)	3 Months Ended
INVENTORY (Tables)	Mar. 31, 2020
Inventory Disclosure [Abstract]
Schedule of Inventory	The components of inventory are summarized as follows: (In thousands) As of March 31, 2020 As of December 31, 2019 Raw materials $ 30,662 $ 15,418 Work in progress 33,412 38,275 Finished goods 4,226 2,655 Total $ 68,300 $ 56,348

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	3 Months Ended
FAIR VALUE MEASUREMENTS (Tables)	Mar. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value of Assets Measured on a Recurring Basis	The following tables present information about our assets that are measured at fair value on a recurring basis and indicate the fair value hierarchy of the valuation techniques we utilized to determine such fair value: (In thousands) As of March 31, 2020 Quoted Significant Significant Cash equivalents: U.S. treasury securities $ 136,492 $ — $ 136,492 $ — Money market funds 254,627 254,627 — — Marketable debt securities: — — — Certificates of deposit 5,134 — 5,134 — Commercial paper 21,792 — 21,792 — Corporate notes 114,280 — 114,280 — U.S. government-sponsored enterprise securities 105,297 — 105,297 — U.S. treasury securities 589,843 — 589,843 — Marketable equity securities 38,078 38,078 — — Restricted cash (money market funds) 1,483 1,483 — — Total $ 1,267,026 $ 294,188 $ 972,838 $ — (In thousands) As of December 31, 2019 Quoted Significant Significant Cash equivalents: Commercial paper $ 3,439 $ — $ 3,439 $ — U.S. treasury securities 336,693 — 336,693 — Money market funds 119,882 119,882 — — Marketable debt securities: Certificates of deposit 4,301 — 4,301 — Commercial paper 36,474 — 36,474 — Corporate notes 146,040 — 146,040 — U.S. government-sponsored enterprise securities 32,488 — 32,488 — U.S. treasury securities 755,714 — 755,714 — Marketable equity securities 13,967 13,967 — — Restricted cash (money market funds) 1,482 1,482 — — Total $ 1,450,480 $ 135,331 $ 1,315,149 $ —

MARKETABLE DEBT SECURITIES (Tab

MARKETABLE DEBT SECURITIES (Tables)	3 Months Ended
MARKETABLE DEBT SECURITIES (Tables)	Mar. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Summary of Company's Marketable Debt Securities	The following tables summarize our marketable debt securities: As of March 31, 2020 (In thousands) Amortized Gross Gross Fair Value Certificates of deposit $ 5,141 $ — $ (7) $ 5,134 Commercial paper 21,792 — — 21,792 Corporate notes 114,592 9 (321) 114,280 U.S. government-sponsored enterprise securities 105,028 275 (6) 105,297 U.S. treasury securities 722,103 4,232 — 726,335 Total $ 968,656 $ 4,516 $ (334) $ 972,838 As of December 31, 2019 (In thousands) Amortized Gross Gross Fair Value Certificates of deposit $ 4,303 $ — $ (2) $ 4,301 Commercial paper 39,913 — — 39,913 Corporate notes 146,016 58 (34) 146,040 U.S. government-sponsored enterprise securities 32,487 3 (2) 32,488 U.S. treasury securities 1,092,293 185 (71) 1,092,407 Total $ 1,315,012 $ 246 $ (109) $ 1,315,149
Summary of Fair Value of Marketable Debt Securities	The fair values of our marketable debt securities by classification in the condensed consolidated balance sheets were as follows: (In thousands) As of March 31, 2020 As of December 31, 2019 Cash and cash equivalents $ 136,492 $ 340,132 Marketable debt securities 836,346 975,017 Total $ 972,838 $ 1,315,149

RECONCILIATION OF CASH, CASH _2

RECONCILIATION OF CASH, CASH EQUIVALENTS AND RESTRICTED CASH (Tables)	3 Months Ended
	Mar. 31, 2020
Cash Cash Equivalents And Restricted Cash [Abstract]
Schedule of Reconciliation of Cash, Cash Equivalents And Restricted Cash	The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within our condensed consolidated balance sheets that sum to the total of these amounts shown in the condensed consolidated statements of cash flows: As of March 31, (In thousands) 2020 2019 Cash and cash equivalents $ 467,779 $ 724,959 Restricted cash included in prepaid expenses and other current assets 167 439 Restricted cash included in long-term other assets 2,447 2,306 Total cash, cash equivalents, and restricted cash shown in the condensed consolidated statements of cash flows $ 470,393 $ 727,704

OTHER COMPREHENSIVE INCOME AN_2

OTHER COMPREHENSIVE INCOME AND ACCUMULATED OTHER COMPREHENSIVE LOSS (Tables)	3 Months Ended
	Mar. 31, 2020
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Summary of Changes in Accumulated Other Comprehensive Income (Loss)	The following tables summarize the changes in accumulated other comprehensive (loss) income, by component, for the three months ended March 31, 2020 and 2019: (In thousands) Loss on Investment in Joint Venture Defined Benefit Pension Unrealized Gains from Debt Securities Foreign Currency Translation Total Accumulated Other Comprehensive Loss Balance as of December 31, 2019 $ (32,792) $ (3,520) $ 137 $ (343) $ (36,518) Other comprehensive income before reclassifications — — 1,317 340 1,657 Amounts reclassified from other comprehensive income — 74 2,728 — 2,802 Net other comprehensive income — 74 4,045 340 4,459 Balance as of March 31, 2020 $ (32,792) $ (3,446) $ 4,182 $ (3) $ (32,059) (In thousands) Loss on Investment in Joint Venture Defined Benefit Pension Unrealized Losses from Debt Foreign Currency Translation Total Accumulated Other Balance as of December 31, 2018 $ (32,792) $ — $ (421) $ — $ (33,213) Other comprehensive income before reclassifications — — 346 — 346 Amounts reclassified from other comprehensive income — — 14 — 14 Net other comprehensive income — — 360 — 360 Balance as of March 31, 2019 $ (32,792) $ — $ (61) $ — $ (32,853)

STOCK-BASED COMPENSATION (Table

STOCK-BASED COMPENSATION (Tables)	3 Months Ended
STOCK-BASED COMPENSATION (Tables)	Mar. 31, 2020
Share-based Payment Arrangement [Abstract]
Schedule of Stock Based Compensation	The following table summarizes stock-based compensation expenses included in operating costs and expenses: Three Months Ended March 31, (In thousands) 2020 2019 Research and development $ 16,049 $ 16,125 Selling, general and administrative 18,529 15,907 Total $ 34,578 $ 32,032

NET LOSS PER COMMON SHARE (Tabl

NET LOSS PER COMMON SHARE (Tables)	3 Months Ended
NET LOSS PER COMMON SHARE (Tables)	Mar. 31, 2020
Earnings Per Share [Abstract]
Common Share Equivalents Excluded from the Calculation of Net Loss Per Common Share	The following common share equivalents were excluded from the calculation of net loss per common share because their inclusion would be anti-dilutive: As of March 31, (In thousands) 2020 2019 Options to purchase common stock 13,609 13,868 Unvested restricted common stock 1,411 717 Total 15,020 14,585

NET PRODUCT REVENUES - Summary

NET PRODUCT REVENUES - Summary of Net Product Revenues Of ONPATTRO (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Total revenues	$ 99,476	$ 33,294
Net product revenues
Disaggregation of Revenue [Line Items]
Total revenues	71,938	26,291
ONPATTRO
Disaggregation of Revenue [Line Items]
Total revenues	66,664	26,291
GIVLAARI
Disaggregation of Revenue [Line Items]
Total revenues	5,274	0
United States \| Net product revenues
Disaggregation of Revenue [Line Items]
Total revenues	42,470	18,760
Europe \| Net product revenues
Disaggregation of Revenue [Line Items]
Total revenues	21,166	7,531
Rest of World (primarily Japan) \| Net product revenues
Disaggregation of Revenue [Line Items]
Total revenues	$ 8,302	$ 0

NET PRODUCT REVENUES - Addition

NET PRODUCT REVENUES - Additional Information (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Receivables included in “Accounts receivable, net”	$ 75,572	$ 43,011
Contract liabilities included in “Deferred revenue”	152,829	153,117
Net product revenues
Disaggregation of Revenue [Line Items]
Receivables included in “Accounts receivable, net”	$ 49,601	$ 28,082

NET REVENUES FROM COLLABORATI_3

NET REVENUES FROM COLLABORATIONS - Revenue from Collaborators (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues	$ 99,476	$ 33,294
Net revenues from collaborations
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues	27,538	7,003
Net revenues from collaborations \| Regeneron
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues	19,503	0
Net revenues from collaborations \| Vir Biotechnology
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues	6,516	928
Net revenues from collaborations \| The Medicines Company
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues	1,060	1,745
Net revenues from collaborations \| Sanofi Genzyme
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues	0	4,117
Net revenues from collaborations \| Other
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues	$ 459	$ 213

NET REVENUES FROM COLLABORATI_4

NET REVENUES FROM COLLABORATIONS - Balance of Receivables and Contract Liabilities Related to Collaboration Agreements (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Receivables included in “Accounts receivable, net”	$ 25,970	$ 14,929
Contract liabilities included in “Deferred revenue”	$ 152,829	$ 153,117

NET REVENUES FROM COLLABORATI_5

NET REVENUES FROM COLLABORATIONS - Change in Contract Liability Balance Related to Collaboration Agreements (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
(In thousands)
Amounts included in contract liability at the beginning of the period	$ 14,678	$ 928

NET REVENUES FROM COLLABORATI_6

NET REVENUES FROM COLLABORATIONS - Schedule of Research and Development Expenses Incurred by Type that are Directly Attributable to Collaboration Agreements (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses	$ 169,571	$ 129,127
Clinical Trial and Manufacturing
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses	5,949	6,732
Clinical Trial and Manufacturing \| Regeneron
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses	4,612	0
Clinical Trial and Manufacturing \| Vir
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses	339	294
Clinical Trial and Manufacturing \| MDCO
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses	998	1,612
Clinical Trial and Manufacturing \| Sanofi
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses	0	4,826
External Services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses	69	381
External Services \| Regeneron
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses	0	0
External Services \| Vir
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses	52	236
External Services \| MDCO
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses	0	10
External Services \| Sanofi
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses	17	135
Other
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses	13,681	238
Other \| Regeneron
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses	11,491	0
Other \| Vir
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses	1,693	129
Other \| MDCO
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses	266	50
Other \| Sanofi
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses	$ 231	$ 59

NET REVENUES FROM COLLABORATI_7

NET REVENUES FROM COLLABORATIONS - Additional Information (Detail)	Mar. 31, 2020USD ($)	Apr. 08, 2019USD ($)program	Mar. 31, 2020USD ($)shares	Jan. 31, 2019$ / sharesshares	Oct. 31, 2017USD ($)shares	Mar. 31, 2020USD ($)	Mar. 31, 2019USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Issuance of common stock, net of offering costs (in shares) \| shares				5,000,000
Offering proceeds, net of costs						$ 0	$ 381,900,000
Common stock at a price per share (in dollars per share) \| $ / shares				$ 77.50
Vir Biotechnology
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fee received					$ 10,000,000
Shares of Vir common stock (in shares) \| shares					1,111,111
Milestone shares earned (in shares) \| shares			1,111,111
Milestone payment earned			$ 15,000,000
Agreement termination period						90 days
Transaction Price Allocated						$ 105,200,000
Transactional price remaining performance obligation	$ 71,800,000		71,800,000			71,800,000
Global Strategic Collaboration \| Regeneron
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fee received		$ 400,000,000
Transaction Price Allocated	555,100,000					521,600,000
Transactional price remaining performance obligation	$ 296,800,000		$ 296,800,000			$ 296,800,000
Discovery period of programs development		5 years
Extended additional discovery period of programs development		2 years
Maximum royalties and commercial milestone payments upon potential product sale		$ 325,000,000
Maximum additional milestone payments to be receive upon achievement of certain criteria		$ 200,000,000
Number of targeted programs \| program		30
Maximum percentage of royalty payments		20.00%
Global Strategic Collaboration \| Regeneron \| Funding At Program Initiation
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential proceeds from collaboration arrangement		$ 2,500,000
Global Strategic Collaboration \| Regeneron \| Funding At Lead Candidate Identification
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential proceeds from collaboration arrangement		2,500,000
Global Strategic Collaboration \| Regeneron \| Funding At Steady State
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential proceeds from collaboration arrangement		30,000,000
Global Strategic Collaboration \| Regeneron \| Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research term extension fee		400,000,000
Collaborative arrangement milestone payments		$ 150,000,000
Royalty rate		20.00%

NET REVENUES FROM COLLABORATI_8

NET REVENUES FROM COLLABORATIONS - Schedule of Transaction Price Allocated (Details) - Global Strategic Collaboration - Regeneron $ in Thousands	Mar. 31, 2020USD ($)	Mar. 31, 2020USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Transaction Price Allocated	$ 555,100	$ 521,600
Research Services Obligation
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Standalone Selling Price	130,700	130,700
Transaction Price Allocated	200,600	183,100
C5 License Obligation
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Standalone Selling Price	97,600	97,600
Transaction Price Allocated	108,500	92,500
C5 Co-Co Obligation
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Standalone Selling Price	364,600	364,600
Transaction Price Allocated	$ 246,000	$ 246,000

NET REVENUES FROM COLLABORATI_9

NET REVENUES FROM COLLABORATIONS - Schedule of Revenue Recognized by Accounting Guidance (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognized under ASC 606		$ 99,476	$ 33,294
Deferred revenue	$ 86,043	86,043		$ 77,821
Global Strategic Collaboration \| Regeneron
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Transaction Price Allocated	555,100	521,600
Revenues		16,500	0
Deferred revenue	377,100	377,100		393,600
Research Services Obligation \| Global Strategic Collaboration \| Regeneron
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Transaction Price Allocated	200,600	183,100
Revenue recognized under ASC 606		12,300	0
Deferred revenue	72,300	72,300		84,800
C5 License Obligation \| Global Strategic Collaboration \| Regeneron
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Transaction Price Allocated	108,500	92,500
Revenue recognized under ASC 606		0	0
Deferred revenue	65,800	65,800		65,800
C5 Co-Co Obligation \| Global Strategic Collaboration \| Regeneron
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Transaction Price Allocated	246,000	246,000
Revenue recognized under ASC 808		4,200	$ 0
Deferred revenue	$ 239,000	$ 239,000		$ 243,000

INVENTORY - Schedule of Invento

INVENTORY - Schedule of Inventory (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Inventory Disclosure [Abstract]
Raw materials	$ 30,662	$ 15,418
Work in progress	33,412	38,275
Finished goods	4,226	2,655
Total	$ 68,300	$ 56,348

FAIR VALUE MEASUREMENTS - Fair

FAIR VALUE MEASUREMENTS - Fair Value of Assets Measured on a Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 136,492	$ 340,132
Marketable debt securities	972,838	1,315,149
Marketable equity securities	38,078	13,967
Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable equity securities	38,078	13,967
Total	1,267,026	1,450,480
Recurring \| Quoted Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable equity securities	38,078	13,967
Total	294,188	135,331
Recurring \| Significant Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable equity securities	0	0
Total	972,838	1,315,149
Recurring \| Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable equity securities	0	0
Total	0	0
Recurring \| Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents		3,439
Marketable debt securities	21,792	36,474
Recurring \| Commercial paper \| Quoted Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents		0
Marketable debt securities	0	0
Recurring \| Commercial paper \| Significant Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents		3,439
Marketable debt securities	21,792	36,474
Recurring \| Commercial paper \| Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents		0
Marketable debt securities	0	0
Recurring \| U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	136,492	336,693
Marketable debt securities	589,843	755,714
Recurring \| U.S. treasury securities \| Quoted Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Marketable debt securities	0	0
Recurring \| U.S. treasury securities \| Significant Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	136,492	336,693
Marketable debt securities	589,843	755,714
Recurring \| U.S. treasury securities \| Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Marketable debt securities	0	0
Recurring \| Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	254,627	119,882
Restricted cash (money market funds)	1,483	1,482
Recurring \| Money market funds \| Quoted Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	254,627	119,882
Restricted cash (money market funds)	1,483	1,482
Recurring \| Money market funds \| Significant Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Restricted cash (money market funds)	0	0
Recurring \| Money market funds \| Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Restricted cash (money market funds)	0	0
Recurring \| Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	5,134	4,301
Recurring \| Certificates of deposit \| Quoted Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	0	0
Recurring \| Certificates of deposit \| Significant Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	5,134	4,301
Recurring \| Certificates of deposit \| Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	0	0
Recurring \| Corporate notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	114,280	146,040
Recurring \| Corporate notes \| Quoted Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	0	0
Recurring \| Corporate notes \| Significant Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	114,280	146,040
Recurring \| Corporate notes \| Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	0	0
Recurring \| U.S. government-sponsored enterprise securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	105,297	32,488
Recurring \| U.S. government-sponsored enterprise securities \| Quoted Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	0	0
Recurring \| U.S. government-sponsored enterprise securities \| Significant Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	105,297	32,488
Recurring \| U.S. government-sponsored enterprise securities \| Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	$ 0	$ 0

FAIR VALUE MEASUREMENTS - Addit

FAIR VALUE MEASUREMENTS - Additional Information (Detail) - USD ($)	Mar. 31, 2020	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Transfers between Level 1 and Level 2 financial assets	$ 0	$ 0

MARKETABLE DEBT SECURITIES - Ad

MARKETABLE DEBT SECURITIES - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2019USD ($)
Marketable Securities [Abstract]
Impairment charges of marketable debt securities	$ 0

MARKETABLE DEBT SECURITIES - Su

MARKETABLE DEBT SECURITIES - Summary of Company's Marketable Debt Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 968,656	$ 1,315,012
Gross Unrealized Gains	4,516	246
Gross Unrealized Losses	(334)	(109)
Fair Value	972,838	1,315,149
Corporate notes
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	114,592	146,016
Gross Unrealized Gains	9	58
Gross Unrealized Losses	(321)	(34)
Fair Value	114,280	146,040
U.S. government-sponsored enterprise securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	105,028	32,487
Gross Unrealized Gains	275	3
Gross Unrealized Losses	(6)	(2)
Fair Value	105,297	32,488
U.S. treasury securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	722,103	1,092,293
Gross Unrealized Gains	4,232	185
Gross Unrealized Losses	0	(71)
Fair Value	726,335	1,092,407
Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,141	4,303
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(7)	(2)
Fair Value	5,134	4,301
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	21,792	39,913
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	$ 21,792	$ 39,913

MARKETABLE DEBT SECURITIES - _2

MARKETABLE DEBT SECURITIES - Summary of Fair Value of Marketable Debt Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Cash and cash equivalents	$ 136,492	$ 340,132
Marketable debt securities	836,346	975,017
Total	$ 972,838	$ 1,315,149

RECONCILIATION OF CASH, CASH _3

RECONCILIATION OF CASH, CASH EQUIVALENTS AND RESTRICTED CASH - Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Cash Cash Equivalents And Restricted Cash [Abstract]
Cash and cash equivalents	$ 467,779	$ 547,178	$ 724,959
Restricted cash included in prepaid expenses and other current assets	167		439
Restricted cash included in long-term other assets	2,447		2,306
Total cash, cash equivalents, and restricted cash shown in the condensed consolidated statements of cash flows	$ 470,393	$ 549,628	$ 727,704	$ 422,631

OTHER COMPREHENSIVE INCOME AN_3

OTHER COMPREHENSIVE INCOME AND ACCUMULATED OTHER COMPREHENSIVE LOSS - Summary of Changes in Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 1,438,692	$ 1,301,965
Other comprehensive income before reclassifications	1,657	346
Amounts reclassified from other comprehensive income	2,802	14
Net other comprehensive income	4,459	360
Ending balance	1,349,729	1,546,986
Loss on Investment in Joint Venture
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(32,792)	(32,792)
Other comprehensive income before reclassifications	0	0
Amounts reclassified from other comprehensive income	0	0
Net other comprehensive income	0	0
Ending balance	(32,792)	(32,792)
Defined Benefit Pension Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(3,520)	0
Other comprehensive income before reclassifications	0	0
Amounts reclassified from other comprehensive income	74	0
Net other comprehensive income	74	0
Ending balance	(3,446)	0
Unrealized Gains (Losses) from Debt Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	137	(421)
Other comprehensive income before reclassifications	1,317	346
Amounts reclassified from other comprehensive income	2,728	14
Net other comprehensive income	4,045	360
Ending balance	4,182	(61)
Foreign Currency Translation Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(343)	0
Other comprehensive income before reclassifications	340	0
Amounts reclassified from other comprehensive income	0	0
Net other comprehensive income	340	0
Ending balance	(3)	0
Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(36,518)	(33,213)
Net other comprehensive income	4,459	360
Ending balance	$ (32,059)	$ (32,853)

EQUITY - Additional Information

EQUITY - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended
	Jan. 31, 2019	Mar. 31, 2019
Equity [Abstract]
Issuance of common stock, net of offering costs (in shares)	5,000,000
Shares issued price per share (in dollars per share)	$ 77.50
Issuance of common stock, net of offering costs	$ 381,900	$ 381,900
Underwriting discounts and commissions and other offering expenses	$ 5,600

STOCK-BASED COMPENSATION - Summ

STOCK-BASED COMPENSATION - Summary of Share-Based Compensation Expenses Included Operating Costs and Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total	$ 34,578	$ 32,032
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total	16,049	16,125
Selling, general and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total	$ 18,529	$ 15,907

NET LOSS PER COMMON SHARE - Com

NET LOSS PER COMMON SHARE - Common Share Equivalents Excluded from Calculation of Net Loss Per Common Share (Detail) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share	15,020	14,585
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share	13,609	13,868
Unvested restricted common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share	1,411	717

DEFINED BENEFIT PLANS - Additio

DEFINED BENEFIT PLANS - Additional Information (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Unfunded Plan \| Other Liabilities
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation	$ 4.3	$ 4.3

SUBSEQUENT EVENTS (Details)

SUBSEQUENT EVENTS (Details) - Blackstone Group Inc. - Subsequent Event - Collaborative Arrangement	Apr. 10, 2020USD ($)
Subsequent Event [Line Items]
Maximum proceeds from collaborators	$ 2,000,000,000
Maximum loan amount	750,000,000
Payments committed by collaborator for purchase of common stock	100,000,000
Inclisiran
Subsequent Event [Line Items]
Payments committed by collaborator	$ 1,000,000,000
Royalties acquired by collaborator, percent	50.00%
Commercial milestones acquired by collaborator, percent	75.00%
Cardiometabolic Programs
Subsequent Event [Line Items]
Payments committed by collaborator	$ 150,000,000