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Alnylam Pharmaceuticals (ALNY)

Cover Page

Cover Page - shares3 Months Ended
Mar. 31, 2021Apr. 23, 2021
Cover [Abstract]
Document Type10-Q
Document Quarterly Reporttrue
Document Period End DateMar. 31,
2021
Document Transition Reportfalse
Entity File Number001-36407
Entity Registrant NameALNYLAM PHARMACEUTICALS, INC.
Entity Incorporation, State or Country CodeDE
Entity Tax Identification Number77-0602661
Entity Address, Address Line One675 West Kendall Street,
Entity Address, Address Line TwoHenri A. Termeer Square
Entity Address, City or TownCambridge
Entity Address, State or ProvinceMA
Entity Address, Postal Zip Code02142
City Area Code617
Local Phone Number551-8200
Title of 12(b) SecurityCommon Stock, $0.01 par value per share
Trading SymbolALNY
Security Exchange NameNASDAQ
Entity Current Reporting StatusYes
Entity Interactive Data CurrentYes
Entity Filer CategoryLarge Accelerated Filer
Entity Small Businessfalse
Entity Emerging Growth Companyfalse
Entity Shell Companyfalse
Entity Common Stock, Shares Outstanding117,545,040
Amendment Flagfalse
Document Fiscal Year Focus2021
Current Fiscal Year End Date--12-31
Document Fiscal Period FocusQ1
Entity Central Index Key0001178670

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in ThousandsMar. 31, 2021Dec. 31, 2020
Current assets:
Cash and cash equivalents $ 379,543 $ 496,580
Marketable debt securities1,273,027 1,333,182
Marketable equity securities56,967 44,633
Accounts receivable, net110,626 102,413
Inventory73,940 75,202
Prepaid expenses and other current assets75,980 62,767
Receivable related to the sale of future royalties500,000 500,000
Total current assets2,470,083 2,614,777
Property, plant and equipment, net464,572 465,029
Operating lease right-of-use assets237,213 241,485
Restricted investments40,725 40,725
Other assets42,676 45,045
Total assets3,255,269 3,407,061
Current liabilities:
Accounts payable45,381 51,966
Accrued expenses280,527 355,909
Operating lease liability38,917 36,872
Deferred revenue116,340 127,207
Liability related to the sale of future royalties13,660 13,316
Total current liabilities494,825 585,270
Operating lease liability, net of current portion288,015 293,039
Deferred revenue, net of current portion208,123 225,094
Long-term debt191,590 191,278
Liability related to the sale of future royalties, net of current portion1,086,065 1,058,225
Other liabilities60,461 37,908
Total liabilities2,329,079 2,390,814
Commitments and contingencies
Stockholders’ equity:
Preferred stock, $0.01 par value per share, 5,000 shares authorized and no shares issued and outstanding as of March 31, 2021 and December 31, 20200 0
Common stock, $0.01 par value per share, 250,000 shares authorized; 117,321 shares issued and outstanding as of March 31, 2021; 116,427 shares issued and outstanding as of December 31, 20201,173 1,164
Additional paid-in capital5,747,394 5,644,074
Accumulated other comprehensive loss(36,717)(43,622)
Accumulated deficit(4,785,660)(4,585,369)
Total stockholders’ equity926,190 1,016,247
Total liabilities and stockholders’ equity $ 3,255,269 $ 3,407,061

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / sharesMar. 31, 2021Dec. 31, 2020
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)117,321,000 116,427,000
Common stock, shares outstanding (in shares)117,321,000 116,427,000

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands3 Months Ended
Mar. 31, 2021Mar. 31, 2020
Revenues:
Total revenues $ 177,566 $ 99,476
Operating costs and expenses:
Cost of goods sold23,023 13,302
Cost of collaborations8,039 0
Research and development185,899 169,571
Selling, general and administrative146,859 126,761
Total operating costs and expenses363,820 309,634
Loss from operations(186,254)(210,158)
Other (expense) income:
Interest expense(32,515)0
Interest income450 5,480
Other income, net19,044 23,032
Total other (expense) income(13,021)28,512
Loss before income taxes(199,275)(181,646)
Provision for income taxes(1,016)(575)
Net loss $ (200,291) $ (182,221)
Net loss per common share - basic and diluted (in dollars per share) $ (1.71) $ (1.62)
Weighted-average common shares used to compute basic and diluted net loss per common share (in shares)117,080 112,748
Statements of Comprehensive Loss
Net loss $ (200,291) $ (182,221)
Other comprehensive (loss) income:
Unrealized (loss) gain on marketable securities(1)4,045
Foreign currency translation gains6,848 340
Defined benefit pension plans, net of tax58 74
Total other comprehensive income6,905 4,459
Comprehensive loss(193,386)(177,762)
Net revenues from collaborations
Revenues:
Total revenues41,797 27,538
Net product revenues
Revenues:
Total revenues $ 135,769 $ 71,938

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in ThousandsTotalCommon StockAdditional Paid-in CapitalAccumulated Other Comprehensive LossAccumulated Deficit
Balance (in shares) at Dec. 31, 2019112,188,000
Beginning balance at Dec. 31, 2019 $ 1,438,692 $ 1,122 $ 5,201,176 $ (36,518) $ (3,727,088)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options, net of tax withholdings (in shares)976,000
Exercise of common stock options, net of tax withholdings54,221 $ 9 54,212
Issuance of common stock under equity plans (in shares)4,000
Stock-based compensation expense related to equity-classified awards34,578 34,578
Other comprehensive income (loss), net of tax4,459 4,459
Net loss(182,221)(182,221)
Balance (in shares) at Mar. 31, 2020113,168,000
Ending balance at Mar. 31, 2020 $ 1,349,729 $ 1,131 5,289,966 (32,059)(3,909,309)
Balance (in shares) at Dec. 31, 2020116,427,000 116,427,000
Beginning balance at Dec. 31, 2020 $ 1,016,247 $ 1,164 5,644,074 (43,622)(4,585,369)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options, net of tax withholdings (in shares)614,000
Exercise of common stock options, net of tax withholdings47,034 $ 6 47,028
Issuance of common stock under equity plans (in shares)280,000
Issuance of common stock under equity plans0 $ 3 (3)
Stock-based compensation expense related to equity-classified awards56,295 56,295
Other comprehensive income (loss), net of tax6,905 6,905
Net loss $ (200,291)(200,291)
Balance (in shares) at Mar. 31, 2021117,321,000 117,321,000
Ending balance at Mar. 31, 2021 $ 926,190 $ 1,173 $ 5,747,394 $ (36,717) $ (4,785,660)

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands3 Months Ended
Mar. 31, 2021Mar. 31, 2020
Cash flows from operating activities:
Net loss $ (200,291) $ (182,221)
Non-cash adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization12,601 7,613
Amortization and interest accretion related to operating leases10,261 9,393
Non-cash interest expense on liability related to the sale of future royalties28,184 0
Stock-based compensation55,690 34,578
Realized and unrealized gain on marketable equity securities(47,016)(24,111)
Other30,777 660
Changes in operating assets and liabilities:
Accounts receivable, net(10,709)(32,882)
Inventory1,934 (11,952)
Prepaid expenses and other assets(13,654)(19,958)
Accounts payable, accrued expenses and other liabilities(66,573)(14,215)
Deferred revenue(27,804)(4,030)
Operating lease liability(9,060)(9,036)
Net cash used in operating activities(235,660)(246,161)
Cash flows from investing activities:
Purchases of property, plant and equipment(17,178)(19,617)
Purchases of marketable securities(345,954)(396,409)
Sales and maturities of marketable securities438,682 539,614
Purchases of restricted investments(10,650)(9,900)
Proceeds from maturity of restricted investments10,650 0
Other investing activities(4,198)0
Net cash provided by investing activities71,352 113,688
Cash flows from financing activities:
Proceeds from exercise of stock options and other types of equity, net46,977 53,869
Proceeds from development derivative4,200 0
Net cash provided by financing activities51,177 53,869
Effect of exchange rate changes on cash, cash equivalents and restricted cash(3,910)(631)
Net decrease in cash, cash equivalents and restricted cash(117,041)(79,235)
Cash, cash equivalents and restricted cash, beginning of period499,046 549,628
Cash, cash equivalents and restricted cash, end of period382,005 470,393
Supplemental disclosure of noncash investing and financing activities:
Capital expenditures included in accounts payable and accrued expenses $ 7,289 $ 6,619

NATURE OF BUSINESS

NATURE OF BUSINESS3 Months Ended
Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
NATURE OF BUSINESSNATURE 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 early 2021, we launched our Alnylam P 5 x25 strategy, which focuses on our planned transition to a top five biotech company, as measured by market capitalization, by the end of 2025. With Alnylam P 5 x25 , we aim to deliver transformative rare and prevalent disease medicines for patients around the world through sustainable innovation, delivering exceptional financial performance and driving profitability. As of March 31, 2021, we have four products that have received marketing approval, including one partnered product, and six late-stage investigational programs advancing towards potential commercialization. We currently generate product revenues from ONPATTRO in the U.S., Europe, Japan and in several additional countries as well as from GIVLAARI and OXLUMO in the U.S. and several countries in Europe.

BASIS OF PRESENTATION AND PRINC

BASIS OF PRESENTATION AND PRINCIPLES OF CONSOLIDATION3 Months Ended
Mar. 31, 2021
Accounting Policies [Abstract]
BASIS OF PRESENTATION AND PRINCIPLES OF CONSOLIDATIONBASIS 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, 2020, which were included in our Annual Report on Form 10-K that was filed with the Securities and Exchange Commission on February 11, 2021. 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, 2020. Use of Estimates The preparation of financial statements in conformity with 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. In our condensed consolidated financial statements, we use estimates and assumptions related to our inventory valuation and related reserves, liability related to the sale of future royalties, development derivative liability, income taxes, revenue recognition, research and development expenses, and stock-based compensation. We base our estimates on historical experience and on various other assumptions that we believe to be reasonable. Actual results could differ from those estimates. 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, the supply of our products and product candidates, 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 variants thereof, and the actions taken to contain or treat it or vaccinate against it, 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 securities as of March 31, 2021, together with the cash we expect to generate from product sales and under our current alliances, in addition to our strategic financing collaboration with The Blackstone Group Inc. and certain of its affiliates, will be sufficient to enable us to advance our Alnylam P 5 x25 strategy for at least the next 12 months from the filing of this Quarterly Report on Form 10-Q.

NET PRODUCT REVENUES

NET PRODUCT REVENUES3 Months Ended
Mar. 31, 2021
Revenue from Contract with Customer [Abstract]
NET PRODUCT REVENUESNET PRODUCT REVENUES Net product revenues consist of the following: Three Months Ended (In thousands) 2021 2020 ONPATTRO United States $ 49,471 $ 37,196 Europe 40,653 21,166 Rest of World (primarily Japan) 11,827 8,302 Total $ 101,951 $ 66,664 GIVLAARI United States $ 17,762 $ 5,274 Europe 6,873 — Rest of World 38 — Total $ 24,673 $ 5,274 OXLUMO United States $ 1,408 $ — Europe 7,737 — Total $ 9,145 $ — Total net product revenues $ 135,769 $ 71,938 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” $ 91,516 $ 68,871

NET REVENUES FROM COLLABORATION

NET REVENUES FROM COLLABORATIONS3 Months Ended
Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
NET REVENUES FROM COLLABORATIONSNET REVENUES FROM COLLABORATIONS Net revenues from collaborations consist of the following: Three Months Ended March 31, (In thousands) 2021 2020 Regeneron Pharmaceuticals $ 30,343 $ 19,503 Novartis AG 8,111 1,060 Vir Biotechnology 2,822 6,516 Other 521 459 Total $ 41,797 $ 27,538 The following table presents the balance of our receivables and contract liabilities related to our collaboration agreements: (In thousands) As of March 31, 2021 As of December 31, 2020 Receivables included in “Accounts receivable, net” $ 19,111 $ 33,542 Contract liabilities included in “Deferred revenue” $ 94,759 $ 120,021 We recognized revenue of $25.3 million and $14.7 million in the three months ended March 31, 2021 and 2020, respectively, that was included in the contract liability balance at the beginning of the respective period. 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, 2021 2020 (In thousands) Clinical Trial and Manufacturing External Services Other Clinical Trial and Manufacturing External Services Other Regeneron Pharmaceuticals $ 4,799 $ 94 $ 12,235 $ 4,612 $ — $ 11,491 Vir Biotechnology 1,029 159 1,355 339 52 1,693 Novartis AG — — 3 998 — 266 Other 11 52 859 — 17 231 Total $ 5,839 $ 305 $ 14,452 $ 5,949 $ 69 $ 13,681 The research and development expenses incurred for each agreement listed in the table above consist of costs incurred for (i) clinical expenses, including manufacturing of clinical product, (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, 2021 and 2020, we did not incur material selling, general and administrative expenses related to our collaboration agreements. Product Alliances Regeneron Pharmaceuticals, Inc. In April 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 2 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-year research period, which we refer to as the Initial Research Term. Regeneron has an option to extend the Initial Research Term (referred to as the Research Term Extension Period, and together with the Initial Research Term, the Research Term) for up to an additional five years, for a research term extension fee of up to $400.0 million. The Regeneron Collaboration also covers a select number of RNAi therapeutic programs designed to target genes expressed in the liver, including our previously announced collaboration with Regeneron to identify RNAi therapeutics for the chronic liver disease nonalcoholic steatohepatitis. We retain broad global rights to all of our other unpartnered liver- directed clinical and pre-clinical pipeline programs. The Regeneron Collaboration is governed by a joint steering committee that is comprised of an equal number of representatives from each party. 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. Reimbursement of our share of costs will be recognized as a reduction to research and development expense in the condensed consolidated statements of operations and comprehensive loss. 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, as of March 31, 2021, the total transaction price was $530.5 million. As of March 31, 2021, the transaction price is comprised of the upfront payment and variable consideration related to development, manufacture and supply activities. 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, is accounted for as collaboration revenue. The following tables provide 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 Deferred Revenue Performance Obligations As of March 31, As of March 31, As of December 31, Accounting Guidance Research Services Obligation $ 200,600 $ 45,100 $ 54,900 ASC 606 C5 License Obligation 83,900 45,200 58,700 ASC 606 C5 Co-Co Obligation 246,000 228,900 231,400 ASC 808 $ 530,500 $ 319,200 $ 345,000 Revenue Recognized During Performance Obligations Three Months Ended Three Months Ended Accounting Guidance Research Services Obligation $ 9,800 $ 12,300 ASC 606 C5 License Obligation 13,500 — ASC 606 C5 Co-Co Obligation 2,500 4,200 ASC 808 $ 25,800 $ 16,500 As of March 31, 2021, the aggregate amount of the transaction price allocated to the remaining Research Services Obligation and C5 License Obligation that was unsatisfied was $188.3 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. Novartis AG In February 2013, we and The Medicines Company, or MDCO, entered into a license and collaboration agreement pursuant to which we granted to MDCO an exclusive, worldwide license to develop, manufacture and commercialize RNAi therapeutics targeting proprotein convertase subtilisin/kexin type 9, or PCSK9, for the treatment of hypercholesterolemia and other human diseases, including inclisiran. We refer to this agreement, as amended through the date hereof, as the MDCO License Agreement. On January 6, 2020, Novartis completed its acquisition of MDCO, and assumed all rights and obligations under the MDCO License Agreement. As of March 31, 2021, we have earned $45.0 million of milestones and upon achievement of certain events, we will be entitled to receive additional milestones, up to an aggregate of $135.0 million, including $25.0 million associated with the U.S. regulatory approval milestone, $10.0 million in other specified regulatory milestones and $100.0 million in specified commercialization milestones. In addition, we will be entitled to royalties ranging from 10% up to 20% based on annual worldwide net sales of licensed products by Novartis, its affiliates and sublicensees, subject to reduction under specified circumstances. 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 under the MDCO License Agreement. Unless terminated earlier in accordance with the terms of the agreement, the MDCO License Agreement expires on a licensed product-by-licensed product and country-by-country basis upon expiration of the last royalty term for any licensed product in any country, where a royalty term is defined as the latest to occur of (1) the expiration of the last valid claim of patent rights covering a licensed product, (2) the expiration of the Regulatory Exclusivity, as defined in the MDCO License Agreement, and (3) the twelfth anniversary of the first commercial sale of the licensed product in such country. We estimate that our fundamental RNAi patents covering licensed products under the MDCO License Agreement will expire both in and outside of the U.S. generally between 2016 and 2028. We also estimate that our inclisiran product-specific patents covering licensed products under the MDCO License Agreement will expire in the U.S., Europe, China and Japan in 2036 and elsewhere at the end of 2033. These patent rights are subject to potential patent term extensions and/or supplemental protection certificates extending such terms in countries where such extensions may become available due to regulatory delay. In addition, more patent filings relating to the collaboration may be made in the future. Either party may terminate the MDCO License Agreement in the event the other party fails to cure a material breach or upon patent-related challenges by the other party. In addition, Novartis has the right to terminate the agreement without cause at any time upon four months’ prior written notice. During the term of the MDCO License Agreement, neither party will, alone or with an affiliate or third party, research, develop or commercialize, or grant a license to any third party to research, develop or commercialize, in any country, any siRNA product directed to the PCSK9 gene, other than a licensed product, without the prior written agreement of the other party, subject to the terms of the MDCO License Agreement. We evaluated the MDCO License Agreement and concluded that Novartis meets the definition of a customer and that the MDCO License Agreement is a contract. During 2018, we completed the performance obligations identified in the MDCO License Agreement. However, we continue to receive additional orders for supply of certain material. Given Novartis now has the ability to manufacture on its own through its own vendors, such orders will be treated as separate agreements and any associated revenue will be recognized upon transfer of control. 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 retained 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 initiation of a Phase 3 clinical trial 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 a $15.0 million cash milestone and 1,111,111 shares of Vir's common stock, which were received in the second quarter of 2020. In June 2020, we earned and received a $10.0 million payment from Vir related to Vir's sublicense for ALN-HBV02 in China. 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 and April 2020, we entered into amendments 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, along with three additional targets focused on human host factors for SARS-CoV-2, including angiotensin converting enzyme-2 and transmembrane protease, serine 2 and potentially a third mutually selected host factor target. Under the Vir amendments, we and Vir were each responsible for our own pre-clinical development costs incurred in performing our allocated responsibilities under an agreed-upon initial pre-clinical development plan. Under the original agreements, we and Vir agreed to equally share certain 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. We also agreed that Vir would lead all development and commercialization of any selected development candidates. In December 2020, we signed a letter agreement to amend the Vir Agreement such that we are solely responsible for conducting pre-clinical research activities under the pre-clinical development plan, related to the COVID-19 activities in the March and April 2020 amendments, at our discretion and sole expense, and effective as of July 1, 2020, we are responsible for all pre-clinical development costs incurred under such plan for such COVID-19 related activities. 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); ii) the obligation to deliver four additional development candidates and supply product for each such RNAi therapeutic program; and iii) the obligation to deliver up to four development candidates and supply product for RNAi therapeutic programs targeting 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. We measure proportional performance over time using an input method based on cost incurred relative to the total estimated costs for the identified performance obligation, 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 total transaction price. 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. As of March 31, 2021, the total transaction price was determined to be $110.1 million, and is comprised of the upfront payment, fair value of non-cash equity consideration at contract inception, milestones achieved and variable consideration related to development, manufacture and supply activities. We utilized the expected value method to determine the amount of reimbursement for these activities. The total transaction price is allocated entirely to the single performance obligation. 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, 2021, the aggregate amount of the transaction price allocated to the performance obligation that was unsatisfied was $48.8 million, which is expected to be recognized through the term of the Vir Agreement as the services are performed.

LIABILITY RELATED TO THE SALE O

LIABILITY RELATED TO THE SALE OF FUTURE ROYALTIES3 Months Ended
Mar. 31, 2021
Related Party Transactions [Abstract]
LIABILITY RELATED TO SALE OF FUTURE ROYALTIESLIABILITY RELATED TO THE SALE OF FUTURE ROYALTIES In April 2020, we entered into a purchase and sale agreement, or Purchase Agreement, with BX Bodyguard Royalties L.P. (an affiliate of The Blackstone Group Inc.), or Blackstone Royalties, under which Blackstone Royalties acquired 50% of royalties payable, or Royalty Interest, with respect to net sales by MDCO, its affiliates or sublicensees of inclisiran and any other licensed products under the MDCO License Agreement, and 75% of the commercial milestone payments payable under the MDCO License Agreement, together with the Royalty Interest, the Purchased Interest. If Blackstone Royalties does not receive payments in respect of the Royalty Interest by December 31, 2029, equaling at least $1.00 billion, Blackstone Royalties will receive 55% of the Royalty Interest beginning on January 1, 2030. In consideration for the sale of the Purchased Interest, Blackstone Royalties paid us $500.0 million in April 2020 and has an unconditional obligation to pay us an additional $500.0 million on September 30, 2021, which was recorded as a receivable upon execution of the Purchase Agreement. We continue to own or control all inclisiran intellectual property rights and are responsible for certain ongoing manufacturing and supply obligations related to the generation of the Purchased Interest. Due to our continuing involvement, we will continue to account for any royalties and commercial milestones due to us under the MDCO License Agreement as revenue on our condensed consolidated statement of operations and comprehensive loss and record the proceeds from this transaction as a liability, net of closing costs, on our condensed consolidated balance sheet. In order to determine the amortization of the liability related to the sale of future royalties, we are required to estimate the total amount of future payments to Blackstone Royalties over the life of the Purchase Agreement. The $1.00 billion liability, recorded at execution of the agreement, will be accreted to the total of these royalty and commercial milestone payments as interest expense over the life of the Purchase Agreement. At execution, our estimate of this total interest expense resulted in an effective annual interest rate of 11%. This estimate contains assumptions that impact both the amount recorded at execution and the interest expense that will be recognized in future periods. As payments are made to Blackstone Royalties, the balance of the liability will be effectively repaid over the life of the Purchase Agreement. The exact timing and amount of repayment is likely to change each reporting period. A significant increase or decrease in net sales of inclisiran will materially impact the liability related to the sale of future royalties, interest expense and the time period for repayment. We will periodically assess the expected payments to Blackstone Royalties and to the extent the amount or timing of such payments is materially different than our initial estimates, we will prospectively adjust the amortization of the liability related to the sale of future royalties and the related interest expense. As of March 31, 2021, the carrying value of the liability related to the sale of future royalties was $1.10 billion, net of closing costs of $13.0 million. The carrying value of the liability related to the sale of future royalties approximates fair value as of March 31, 2021 and is based on our current estimates of future royalties and commercial milestones expected to be paid to Blackstone Royalties over the life of the arrangement, which are considered Level 3 inputs. The following table shows the activity with respect to the liability related to the sale of future royalties, in thousands: Carrying value of liability related to sale of future royalties as of December 31, 2020 $ 1,071,541 Interest expense recognized 28,184 Carrying value of liability related to sale of future royalties as of March 31, 2021 $ 1,099,725

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS3 Months Ended
Mar. 31, 2021
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTSFAIR VALUE MEASUREMENTS The following tables present information about our financial assets and liabilities 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, 2021 Quoted Significant Significant Financial assets Cash equivalents: Money market funds $ 177,470 $ 177,470 $ — $ — Marketable debt securities: U.S. government-sponsored enterprise securities 215,200 — 215,200 — U.S. treasury securities 1,057,827 — 1,057,827 — Marketable equity securities 56,967 56,967 — — Restricted cash (money market funds) 1,483 1,483 — — Total financial assets $ 1,508,947 $ 235,920 $ 1,273,027 $ — Financial liabilities Development derivative liability (Note 10) $ 48,038 $ — $ — $ 48,038 (In thousands) As of December 31, 2020 Quoted Significant Significant Financial assets Cash equivalents: U.S. treasury securities $ 20,000 $ — $ 20,000 $ — Money market funds 75,726 75,726 — — Marketable debt securities: U.S. government-sponsored enterprise securities 245,214 — 245,214 — U.S. treasury securities 1,087,968 — 1,087,968 — Marketable equity securities 44,633 44,633 — — Restricted cash (money market funds) 1,483 1,483 — — Total financial assets $ 1,475,024 $ 121,842 $ 1,353,182 $ — Financial liabilities Development derivative liability (Note 10) $ 25,585 $ — $ — $ 25,585 The carrying amounts reflected on 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. The carrying

MARKETABLE DEBT SECURITIES

MARKETABLE DEBT SECURITIES3 Months Ended
Mar. 31, 2021
Investments, Debt and Equity Securities [Abstract]
MARKETABLE DEBT SECURITIESMARKETABLE 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, 2021 or 2020. The following tables summarize our marketable debt securities: As of March 31, 2021 (In thousands) Amortized Gross Gross Fair Value U.S. government-sponsored enterprise securities $ 215,171 $ 87 $ (58) $ 215,200 U.S. treasury securities 1,057,509 335 (17) 1,057,827 Total $ 1,272,680 $ 422 $ (75) $ 1,273,027 As of December 31, 2020 (In thousands) Amortized Gross Gross Fair Value U.S. government-sponsored enterprise securities $ 245,113 $ 135 $ (34) $ 245,214 U.S. treasury securities 1,107,721 328 (81) 1,107,968 Total $ 1,352,834 $ 463 $ (115) $ 1,353,182 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, 2021 As of December 31, 2020 Cash and cash equivalents $ — $ 20,000 Marketable debt securities 1,273,027 1,333,182 Total $ 1,273,027 $ 1,353,182

OTHER BALANCE SHEET DETAILS

OTHER BALANCE SHEET DETAILS3 Months Ended
Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
OTHER BALANCE SHEET DETAILSOTHER BALANCE SHEET DETAILS Inventory The components of inventory are summarized as follows: (In thousands) As of March 31, 2021 As of December 31, 2020 Raw materials $ 53,694 $ 63,460 Work in progress 23,593 16,149 Finished goods 13,753 12,693 Total $ 91,040 $ 92,302 As of March 31, 2021 and December 31, 2020, we held $17.1 million of long- term inventory included within other assets in our condensed consolidated balance sheet as we anticipate it being consumed beyond our normal operating cycle. 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) 2021 2020 Cash and cash equivalents $ 379,543 $ 467,779 Total restricted cash included in prepaid expenses, other current assets and long-term other assets 2,462 2,614 Total cash, cash equivalents, and restricted cash shown in the condensed consolidated statements of cash flows $ 382,005 $ 470,393 Accumulated Other Comprehensive (Loss) Income The following tables summarize the changes in accumulated other comprehensive loss, by component: (In thousands) Loss on Investment in Joint Venture Defined Benefit Pension Unrealized Gains (Losses) from Debt Securities Foreign Currency Translation Total Accumulated Other Comprehensive Loss Balance as of December 31, 2020 $ (32,792) $ (3,754) $ 348 $ (7,424) $ (43,622) Other comprehensive (loss) income before reclassifications — — (1) 6,848 6,847 Amounts reclassified from other comprehensive income — 58 — — 58 Net other comprehensive income (loss) — 58 (1) 6,848 6,905 Balance as of March 31, 2021 $ (32,792) $ (3,696) $ 347 $ (576) $ (36,717) (In thousands) Loss on Investment in Joint Venture Defined Benefit Pension Unrealized Gains from Debt Foreign Currency Translation Total Accumulated Other 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) Amounts reclassified out of accumulated other comprehensive loss relate to settlements of marketable debt securities and amortization of our pension obligation which are recorded as interest income and other income, respectively, in the condensed consolidated statements of operations and comprehensive loss.

CREDIT AGREEMENT

CREDIT AGREEMENT3 Months Ended
Mar. 31, 2021
Line of Credit Facility [Abstract]
CREDIT AGREEMENTCREDIT AGREEMENT In April 2020, we entered into a credit agreement, or Credit Agreement, among us, certain of our subsidiaries (such subsidiaries, together with us, the Loan Parties), funds or accounts managed or advised by GSO Capital Partners LP (now Blackstone Alternative Credit Advisors LP) and certain other affiliates of T he Blackstone Group Inc. , and the other lenders from time to time parties thereto, collectively, the Lenders, and Wilmington Trust, National Association, as the administrative agent for the Lenders. The Credit Agreement provides for a senior secured delayed draw term loan facility, referred to as the Term Loans, which consists of three tranches providing funding up to $700.0 million . The Tranche 1 Loan of $200.0 million was drawn as of December 31, 2020 and is included in long-term debt in the condensed consolidated balance sheets. The remaining two tranches will provide funds as follows: Tranche Requested No Later Than Aggregate Principal Amount, up to (in thousands) Tranche 2 Loan June 30, 2021 $ 250,000 Tranche 3 Loan December 31, 2021 $ 250,000 In addition, we may request an increase in respect of the unfunded commitments in an amount not to exceed $50.0 million on terms to be agreed and subject to the consent of the Lenders providing such increase. The Tranche 2 Loan will be requested no later than June 30, 2021 and the Tranche 3 Loan will be requested no later than December 31, 2021, in each case, subject to customary terms and conditions, including, in the case of the Tranche 2 Loan and Tranche 3 Loan, either (a) the first sale of inclisiran in the U.S. for end use or consumption after FDA regulatory approval thereof or (b) revenue attributable to ONPATTRO and GIVLAARI equal to or greater than $300.0 million as of the last day of the most recently ended twelve month period, referred to as the Subsequent Borrowing Conditions. In the event the Subsequent Borrowing Conditions are not satisfied as of the dates set forth in the table above, the Tranche 2 Loan and Tranche 3 Loan will be funded if such Subsequent Borrowing Conditions are satisfied on or prior to December 31, 2022. The Term Loans mature in December 2027. We can elect an interest rate of either LIBOR plus 7% subject to a floor of 1%, referred to as the LIBOR Rate, or a base rate plus 6%, subject to a floor of 2%. We may, at our option, pay interest in kind on interest due through 2023 at a rate that is 1% higher than the interest rate otherwise applicable to such Term Loan . In December 2020, we drew the Tranche 1 Loan, elected a LIBOR Rate plus 7%, and paid a $5.0 million funding fee. On the date the Tranche 2 Loan or Tranche 3 Loan is funded, we will pay a funding fee equal to 2.5% of the principal amount of the Term Loans funded on such date. In addition, we will pay an exit fee equal to 1% of the commitments in respect of the Term Loans, payable upon any repayment of the Term Loans or termination of the unfunded Term Loan commitments. Our interest rate was 8% as of March 31, 2021 and December 31, 2020. We are obligated to pay interest due on the Term Loans from 2021 through 2022 which will be calculated without regard to the Term Loans being prepaid or an unfunded tranche being terminated during this period (in whole or in part). Any prepayments of Term Loans or terminations of unfunded tranches that occur between 2023 and 2025 are subject to a fee of up to 5% of the loan principal that is prepaid or the amount of the unfunded tranche that is terminated. All obligations under the Credit Agreement are secured, subject to certain exceptions, by security interests in the following assets: (i) intellectual property owned by us relating to ONPATTRO, GIVLAARI and vutrisiran, (ii) the equity interests held by the Loan Parties in their subsidiaries, (iii) all of our ownership of the inclisiran royalty remaining after the royalty purchase under the Purchase Agreement, and (iv) material real property, and certain personal property, including, without limitation, cash held in certain deposit accounts of the Loan Parties and equipment. The Credit Agreement contains negative covenants that, among other things and subject to certain exceptions, could restrict our ability to, incur additional liens, incur additional indebtedness, make investments, including acquisitions, engage in fundamental changes, sell or dispose of assets that constitute collateral, including certain intellectual property, pay dividends or make any distribution or payment on or redeem, retire or purchase any equity interests, amend, modify or waive certain material agreements or organizational documents and make payments of certain subordinated indebtedness. Additionally, the Credit Agreement contains certain customary representations and warranties, affirmative covenants and provisions relating to events of default, including nonpayment of principal, interest and other amounts; failure to comply with covenants; the rendering of judgments or orders or default by us in respect of other material indebtedness; and certain insolvency and ERISA events. The Credit Agreement also requires us to have consolidated liquidity of at least $100.0 million as of the last day of each fiscal quarter. As of March 31, 2021, we were in compliance with the applicable terms and conditions of the covenants under the Credit Agreement.

DEVELOPMENT DERIVATIVE LIABILIT

DEVELOPMENT DERIVATIVE LIABILITY3 Months Ended
Mar. 31, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
DEVELOPMENT DERIVATIVE LIABILITYDEVELOPMENT DERIVATIVE LIABILITYIn August 2020, we entered into a co-development agreement, referred to as the Funding Agreement, with BXLS V Bodyguard – PCP L.P. and BXLS Family Investment Partnership V – ESC L.P., collectively referred to as Blackstone Life Sciences, pursuant to which Blackstone Life Sciences will provide up to $150.0 million in funding for the clinical development of vutrisiran and ALN-AGT, two of our cardiometabolic programs. With respect to vutrisiran, Blackstone Life Sciences has committed to provide up to $70.0 million to fund development costs related to the HELIOS-B Phase 3 clinical trial. In addition, Blackstone Life Sciences has the right, but is not obligated, to fund up to $26.0 million for development costs related to a Phase 2 clinical trial of ALN-AGT and up to $54.0 million for development costs related to a Phase 3 clinical trial of ALN-AGT. The amount of funding ultimately provided by Blackstone Life Sciences is dependent on us achieving specified development milestones with respect to each clinical trial. We retain sole responsibility for the development and commercialization of both vutrisiran and ALN-AGT. As consideration for Blackstone Life Sciences’ funding for vutrisiran clinical development costs, we have agreed to pay Blackstone Life Sciences a 1% royalty on net sales of vutrisiran for a 10-year term beginning upon the first commercial sale following regulatory approval of vutrisiran for ATTR-cardiomyopathy, as well as fixed payments of up to 2.5 times their investment over a two-year period upon regulatory approval of vutrisiran for ATTR-cardiomyopathy in specified countries, unless it is later withdrawn from the market following a mandatory recall. As consideration for Blackstone Life Sciences’ funding for Phase 2 clinical development costs of ALN-AGT, we have agreed to pay Blackstone Life Sciences fixed payments of up to 3.25 times their Phase 2 investment over a four-year period upon the successful completion of the ALN-AGT Phase 2 clinical trial, unless certain regulatory events affecting the continued development of ALN-AGT occur. As consideration for Blackstone Life Sciences’ funding for Phase 3 clinical development costs of ALN-AGT, we have agreed to pay Blackstone Life Sciences fixed payments of up to 4.5 times their Phase 3 investment over a four-year period upon regulatory approval of ALN-AGT in specified countries, unless it is later withdrawn from the market following a mandatory recall. Our payment obligations under the Funding Agreement will be secured, subject to certain exceptions, by security interests in intellectual property owned by us relating to vutrisiran and ALN-AGT, as well as in our bank account in which the funding deposits will be made. We and Blackstone Life Sciences each have the right to terminate the Funding Agreement in its entirety in the event of the other party’s bankruptcy or similar proceedings. We and Blackstone Life Sciences may each terminate the Funding Agreement in its entirety or with respect to either product in the event of an uncured material breach by the other party, or with respect to a product for certain patient health and safety reasons, or if regulatory approval in specified major market countries is not obtained for the product following the completion of clinical trials for the product. In addition, Blackstone Life Sciences has the right to terminate the Funding Agreement in its entirety upon the occurrence of certain events affecting our ability to make payments under the agreement or to develop or commercialize the products, or upon a change of control of us. Blackstone Life Sciences may also terminate the Funding Agreement with respect to a product if the joint steering committee elects to terminate the development program for that product in its entirety, if certain clinical endpoints are not achieved for that product or, with respect to vutrisiran only, if our right to develop or commercialize vutrisiran is enjoined in a specified major market as a result of an alleged patent infringement. In certain termination circumstances, we will be obligated to pay Blackstone Life Sciences an amount that is equal to, or a multiplier of, the development funding received from Blackstone Life Sciences, and we may remain obligated under certain circumstances to make the payments to Blackstone Life Sciences described above, or the royalty described above in the case of vutrisiran, should we obtain regulatory approval for vutrisiran or ALN-AGT following termination. We account for the Funding Agreement under ASC 815 as a derivative liability, measured at fair value, within other liabilities on our condensed consolidated balance sheets. The change in fair value due to the remeasurement of the development derivative liability is recorded as other expense on our condensed consolidated statements of operations and comprehensive loss. As of March 31, 2021, the derivative liability is classified as a Level 3 financial liability in the fair value hierarchy. The valuation method incorporates certain unobservable Level 3 key inputs including (i) the probability and timing of achieving stated development milestones to receive payments from Blackstone Life Sciences, (ii) the probability and timing of achieving regulatory approval and payments to Blackstone Life Sciences, (iii) an estimate of the amount and timing of the royalty payable on net sales of vutrisiran, assuming regulatory approval, (iv) our cost of borrowing (15%), and (v) Blackstone Life Sciences' cost of borrowing (4%). The following table presents the activity with respect to the development derivative liability, in thousands: Development derivative liability as of December 31, 2020 $ 25,585 Amount received under the Funding Agreement 4,200 Loss recorded from remeasurement of development derivative liability 18,253 Development derivative liability as of March 31, 2021 $ 48,038

STOCK-BASED COMPENSATION

STOCK-BASED COMPENSATION3 Months Ended
Mar. 31, 2021
Share-based Payment Arrangement [Abstract]
STOCK-BASED COMPENSATIONSTOCK-BASED COMPENSATION The following table summarizes stock-based compensation expenses included in operating costs and expenses: Three Months Ended March 31, (In thousands) 2021 2020 Research and development $ 24,375 $ 16,049 Selling, general and administrative 31,315 18,529 Total $ 55,690 $ 34,578

NET LOSS PER COMMON SHARE

NET LOSS PER COMMON SHARE3 Months Ended
Mar. 31, 2021
Earnings Per Share [Abstract]
NET LOSS PER COMMON SHARENET 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) 2021 2020 Options to purchase common stock 13,859 13,609 Unvested restricted common stock 1,538 1,411 Total 15,397 15,020

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES3 Months Ended
Mar. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIESCOMMITMENTS AND CONTINGENCIES Legal Matters From time to time, we may be a party to litigation, arbitration or other 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 or breach our license or other agreements with such third parties. 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. On March 23, 2020, the Court granted our motion and dismissed the Complaint without prejudice. Pursuant to a prior Order of the Court, on June 1, 2020, plaintiff filed a motion seeking leave to file a further amended complaint. That motion was fully briefed on June 22, 2020. By Memorandum & Order dated March 12, 2021, the Court denied plaintiffs’ motion. 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. On November 2, 2020, the Court entered a Decision and Order denying defendants’ motion to dismiss. In November 2020, defendants filed a notice of appeal of the Court’s decision to the Appellate Division of the Supreme Court of the State of New York for the First Department. Defendants’ appeal was fully briefed in March 2021, and the Appellate Division heard oral argument on April 7, 2021. Defendants’ appeal remains pending. We believe that the allegations contained in the New York Complaint are without merit and intend to defend the case vigorously. We cannot predict at this point the length of time that this action will be ongoing or the liabilities, if any, which may arise therefrom. Government Investigation On or about April 9, 2021, we received a subpoena from the U.S. Department of Justice, U.S. Attorney’s Office for the District of Massachusetts, requiring production of documents pertaining to our marketing and promotion of ONPATTRO (patisiran) in the United States. We are preparing a response to the subpoena and cooperating with the government. Experienced outside legal counsel has been retained to assist with this matter. Since learning of this federal government investigation, and consistent with its charter, our nominating and corporate governance committee is directing our review of and response to the matter. Given the early stage and ongoing nature of the investigation, no determination has been made that a loss, if any, arising from this matter is probable or that the amount of any such loss, or range of loss, is reasonably estimable.

BASIS OF PRESENTATION AND PRI_2

BASIS OF PRESENTATION AND PRINCIPLES OF CONSOLIDATION (Policies)3 Months Ended
Mar. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation and Principles of ConsolidationThe 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, 2020, which were included in our Annual Report on Form 10-K that was filed with the Securities and Exchange Commission on February 11, 2021. 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, 2020.
Use of EstimatesUse of Estimates The preparation of financial statements in conformity with 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. In our condensed consolidated financial statements, we use estimates and assumptions related to our inventory valuation and related reserves, liability related to the sale of future royalties, development derivative liability, income taxes, revenue recognition, research and development expenses, and stock-based compensation. We base our estimates on historical experience and on various other assumptions that we believe to be reasonable. Actual results could differ from those estimates. 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, the supply of our products and product candidates, 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 variants thereof, and the actions taken to contain or treat it or vaccinate against it, 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.
LiquidityLiquidity Based on our current operating plan, we believe that our cash, cash equivalents and marketable securities as of March 31, 2021, together with the cash we expect to generate from product sales and under our current alliances, in addition to our strategic financing collaboration with The Blackstone Group Inc. and certain of its affiliates, will be sufficient to enable us to advance our Alnylam P 5 x25 strategy for at least the next 12 months from the filing of this Quarterly Report on Form 10-Q.

NET PRODUCT REVENUES (Tables)

NET PRODUCT REVENUES (Tables)3 Months Ended
Mar. 31, 2021
Revenue from Contract with Customer [Abstract]
Summary of Net Product RevenuesNet product revenues consist of the following: Three Months Ended (In thousands) 2021 2020 ONPATTRO United States $ 49,471 $ 37,196 Europe 40,653 21,166 Rest of World (primarily Japan) 11,827 8,302 Total $ 101,951 $ 66,664 GIVLAARI United States $ 17,762 $ 5,274 Europe 6,873 — Rest of World 38 — Total $ 24,673 $ 5,274 OXLUMO United States $ 1,408 $ — Europe 7,737 — Total $ 9,145 $ — Total net product revenues $ 135,769 $ 71,938
Schedule of Receivables Related to Net Product RevenuesThe 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” $ 91,516 $ 68,871

NET REVENUES FROM COLLABORATI_2

NET REVENUES FROM COLLABORATIONS (Tables)3 Months Ended
Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Revenue from CollaboratorsNet revenues from collaborations consist of the following: Three Months Ended March 31, (In thousands) 2021 2020 Regeneron Pharmaceuticals $ 30,343 $ 19,503 Novartis AG 8,111 1,060 Vir Biotechnology 2,822 6,516 Other 521 459 Total $ 41,797 $ 27,538
Balance and Change in Receivables and Contract Liabilities Related to Collaboration AgreementsThe following table presents the balance of our receivables and contract liabilities related to our collaboration agreements: (In thousands) As of March 31, 2021 As of December 31, 2020 Receivables included in “Accounts receivable, net” $ 19,111 $ 33,542 Contract liabilities included in “Deferred revenue” $ 94,759 $ 120,021
Schedule of Research and Development Expenses Incurred by Type that are Directly Attributable to Collaboration AgreementsThe 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, 2021 2020 (In thousands) Clinical Trial and Manufacturing External Services Other Clinical Trial and Manufacturing External Services Other Regeneron Pharmaceuticals $ 4,799 $ 94 $ 12,235 $ 4,612 $ — $ 11,491 Vir Biotechnology 1,029 159 1,355 339 52 1,693 Novartis AG — — 3 998 — 266 Other 11 52 859 — 17 231 Total $ 5,839 $ 305 $ 14,452 $ 5,949 $ 69 $ 13,681
Schedule of Allocated Transaction Price Based on Accounting GuidanceWe 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 following tables provide 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 Deferred Revenue Performance Obligations As of March 31, As of March 31, As of December 31, Accounting Guidance Research Services Obligation $ 200,600 $ 45,100 $ 54,900 ASC 606 C5 License Obligation 83,900 45,200 58,700 ASC 606 C5 Co-Co Obligation 246,000 228,900 231,400 ASC 808 $ 530,500 $ 319,200 $ 345,000
Schedule of Revenue Recognized Based on Accounting GuidanceRevenue Recognized During Performance Obligations Three Months Ended Three Months Ended Accounting Guidance Research Services Obligation $ 9,800 $ 12,300 ASC 606 C5 License Obligation 13,500 — ASC 606 C5 Co-Co Obligation 2,500 4,200 ASC 808 $ 25,800 $ 16,500

LIABILITY RELATED TO THE SALE_2

LIABILITY RELATED TO THE SALE OF FUTURE ROYALTIES (Tables)3 Months Ended
Mar. 31, 2021
Related Party Transactions [Abstract]
Schedule of Royalty LiabilityThe following table shows the activity with respect to the liability related to the sale of future royalties, in thousands: Carrying value of liability related to sale of future royalties as of December 31, 2020 $ 1,071,541 Interest expense recognized 28,184 Carrying value of liability related to sale of future royalties as of March 31, 2021 $ 1,099,725

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)3 Months Ended
Mar. 31, 2021
Fair Value Disclosures [Abstract]
Schedule of Fair Value of Assets Measured on a Recurring BasisThe following tables present information about our financial assets and liabilities 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, 2021 Quoted Significant Significant Financial assets Cash equivalents: Money market funds $ 177,470 $ 177,470 $ — $ — Marketable debt securities: U.S. government-sponsored enterprise securities 215,200 — 215,200 — U.S. treasury securities 1,057,827 — 1,057,827 — Marketable equity securities 56,967 56,967 — — Restricted cash (money market funds) 1,483 1,483 — — Total financial assets $ 1,508,947 $ 235,920 $ 1,273,027 $ — Financial liabilities Development derivative liability (Note 10) $ 48,038 $ — $ — $ 48,038 (In thousands) As of December 31, 2020 Quoted Significant Significant Financial assets Cash equivalents: U.S. treasury securities $ 20,000 $ — $ 20,000 $ — Money market funds 75,726 75,726 — — Marketable debt securities: U.S. government-sponsored enterprise securities 245,214 — 245,214 — U.S. treasury securities 1,087,968 — 1,087,968 — Marketable equity securities 44,633 44,633 — — Restricted cash (money market funds) 1,483 1,483 — — Total financial assets $ 1,475,024 $ 121,842 $ 1,353,182 $ — Financial liabilities Development derivative liability (Note 10) $ 25,585 $ — $ — $ 25,585

MARKETABLE DEBT SECURITIES (Tab

MARKETABLE DEBT SECURITIES (Tables)3 Months Ended
Mar. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Summary of Marketable Debt SecuritiesThe following tables summarize our marketable debt securities: As of March 31, 2021 (In thousands) Amortized Gross Gross Fair Value U.S. government-sponsored enterprise securities $ 215,171 $ 87 $ (58) $ 215,200 U.S. treasury securities 1,057,509 335 (17) 1,057,827 Total $ 1,272,680 $ 422 $ (75) $ 1,273,027 As of December 31, 2020 (In thousands) Amortized Gross Gross Fair Value U.S. government-sponsored enterprise securities $ 245,113 $ 135 $ (34) $ 245,214 U.S. treasury securities 1,107,721 328 (81) 1,107,968 Total $ 1,352,834 $ 463 $ (115) $ 1,353,182
Summary of Fair Value of Marketable Debt SecuritiesThe fair values of our marketable debt securities by classification in the condensed consolidated balance sheets were as follows: (In thousands) As of March 31, 2021 As of December 31, 2020 Cash and cash equivalents $ — $ 20,000 Marketable debt securities 1,273,027 1,333,182 Total $ 1,273,027 $ 1,353,182

OTHER BALANCE SHEET DETAILS (Ta

OTHER BALANCE SHEET DETAILS (Tables)3 Months Ended
Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of InventoryThe components of inventory are summarized as follows: (In thousands) As of March 31, 2021 As of December 31, 2020 Raw materials $ 53,694 $ 63,460 Work in progress 23,593 16,149 Finished goods 13,753 12,693 Total $ 91,040 $ 92,302
Schedule of Reconciliation of Cash, Cash Equivalents And Restricted CashThe 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) 2021 2020 Cash and cash equivalents $ 379,543 $ 467,779 Total restricted cash included in prepaid expenses, other current assets and long-term other assets 2,462 2,614 Total cash, cash equivalents, and restricted cash shown in the condensed consolidated statements of cash flows $ 382,005 $ 470,393
Summary of Changes in Accumulated Other Comprehensive Income (Loss)The following tables summarize the changes in accumulated other comprehensive loss, by component: (In thousands) Loss on Investment in Joint Venture Defined Benefit Pension Unrealized Gains (Losses) from Debt Securities Foreign Currency Translation Total Accumulated Other Comprehensive Loss Balance as of December 31, 2020 $ (32,792) $ (3,754) $ 348 $ (7,424) $ (43,622) Other comprehensive (loss) income before reclassifications — — (1) 6,848 6,847 Amounts reclassified from other comprehensive income — 58 — — 58 Net other comprehensive income (loss) — 58 (1) 6,848 6,905 Balance as of March 31, 2021 $ (32,792) $ (3,696) $ 347 $ (576) $ (36,717) (In thousands) Loss on Investment in Joint Venture Defined Benefit Pension Unrealized Gains from Debt Foreign Currency Translation Total Accumulated Other 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)

CREDIT AGREEMENT (Tables)

CREDIT AGREEMENT (Tables)3 Months Ended
Mar. 31, 2021
Line of Credit Facility [Abstract]
Schedule of Term LoanTranche Requested No Later Than Aggregate Principal Amount, up to (in thousands) Tranche 2 Loan June 30, 2021 $ 250,000 Tranche 3 Loan December 31, 2021 $ 250,000

DEVELOPMENT DERIVATIVE LIABIL_2

DEVELOPMENT DERIVATIVE LIABILITY (Tables)3 Months Ended
Mar. 31, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Development Derivative Liability ActivityThe following table presents the activity with respect to the development derivative liability, in thousands: Development derivative liability as of December 31, 2020 $ 25,585 Amount received under the Funding Agreement 4,200 Loss recorded from remeasurement of development derivative liability 18,253 Development derivative liability as of March 31, 2021 $ 48,038

STOCK-BASED COMPENSATION (Table

STOCK-BASED COMPENSATION (Tables)3 Months Ended
Mar. 31, 2021
Share-based Payment Arrangement [Abstract]
Schedule of Stock Based CompensationThe following table summarizes stock-based compensation expenses included in operating costs and expenses: Three Months Ended March 31, (In thousands) 2021 2020 Research and development $ 24,375 $ 16,049 Selling, general and administrative 31,315 18,529 Total $ 55,690 $ 34,578

NET LOSS PER COMMON SHARE (Tabl

NET LOSS PER COMMON SHARE (Tables)3 Months Ended
Mar. 31, 2021
Earnings Per Share [Abstract]
Schedule of Common Share Equivalents Excluded from the Calculation of Net Loss Per Common ShareThe 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) 2021 2020 Options to purchase common stock 13,859 13,609 Unvested restricted common stock 1,538 1,411 Total 15,397 15,020

NATURE OF BUSINESS (Details)

NATURE OF BUSINESS (Details)Mar. 31, 2021productprogram
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of marketed products4
Number of partnered products1
Number of clinical programs in late stages | program6

NET PRODUCT REVENUES - Summary

NET PRODUCT REVENUES - Summary of Net Product Revenues (Detail) - USD ($) $ in Thousands3 Months Ended
Mar. 31, 2021Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Total revenues $ 177,566 $ 99,476
Net product revenues
Disaggregation of Revenue [Line Items]
Total revenues135,769 71,938
ONPATTRO
Disaggregation of Revenue [Line Items]
Total revenues101,951 66,664
GIVLAARI
Disaggregation of Revenue [Line Items]
Total revenues24,673 5,274
OXLUMO
Disaggregation of Revenue [Line Items]
Total revenues9,145 0
United States | ONPATTRO
Disaggregation of Revenue [Line Items]
Total revenues49,471 37,196
United States | GIVLAARI
Disaggregation of Revenue [Line Items]
Total revenues17,762 5,274
United States | OXLUMO
Disaggregation of Revenue [Line Items]
Total revenues1,408 0
Europe | ONPATTRO
Disaggregation of Revenue [Line Items]
Total revenues40,653 21,166
Europe | GIVLAARI
Disaggregation of Revenue [Line Items]
Total revenues6,873 0
Europe | OXLUMO
Disaggregation of Revenue [Line Items]
Total revenues7,737 0
Rest of World | ONPATTRO
Disaggregation of Revenue [Line Items]
Total revenues11,827 8,302
Rest of World | GIVLAARI
Disaggregation of Revenue [Line Items]
Total revenues $ 38 $ 0

NET PRODUCT REVENUES - Receivab

NET PRODUCT REVENUES - Receivables (Detail) - USD ($) $ in ThousandsMar. 31, 2021Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Receivables included in “Accounts receivable, net” $ 110,626 $ 102,413
Net product revenues
Disaggregation of Revenue [Line Items]
Receivables included in “Accounts receivable, net” $ 91,516 $ 68,871

NET REVENUES FROM COLLABORATI_3

NET REVENUES FROM COLLABORATIONS - Revenue from Collaborators (Detail) - USD ($) $ in Thousands3 Months Ended
Mar. 31, 2021Mar. 31, 2020
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues $ 177,566 $ 99,476
Net revenues from collaborations
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues41,797 27,538
Net revenues from collaborations | Regeneron Pharmaceuticals
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues30,343 19,503
Net revenues from collaborations | Novartis AG
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues8,111 1,060
Net revenues from collaborations | Vir Biotechnology
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues2,822 6,516
Net revenues from collaborations | Other
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues $ 521 $ 459

NET REVENUES FROM COLLABORATI_4

NET REVENUES FROM COLLABORATIONS - Balance of Receivables and Contract Liabilities Related to Collaboration Agreements (Detail) - USD ($) $ in ThousandsMar. 31, 2021Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Receivables included in “Accounts receivable, net” $ 19,111 $ 33,542
Contract liabilities included in “Deferred revenue” $ 94,759 $ 120,021

NET REVENUES FROM COLLABORATI_5

NET REVENUES FROM COLLABORATIONS - Additional Information (Detail)Mar. 31, 2021USD ($)candidateApr. 08, 2019USD ($)programJun. 30, 2020USD ($)Mar. 31, 2020USD ($)sharesOct. 31, 2017USD ($)sharesFeb. 28, 2013USD ($)Mar. 31, 2021USD ($)candidateMar. 31, 2020USD ($)Mar. 31, 2021USD ($)candidate
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract with customer liability revenue recognized $ 25,300,000 $ 14,700,000
Vir Biotechnology
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fee received $ 10,000,000
Agreement termination period90 days
Transaction price $ 110,100,000
Transactional price remaining performance obligation $ 48,800,000 $ 48,800,000 $ 48,800,000
Milestone payment earned $ 10,000,000 $ 15,000,000
Shares of Vir common stock (in shares) | shares1,111,111
Milestone shares earned (in shares) | shares1,111,111
Additional development candidates to be delivered | candidate4 4 4
Global Strategic Collaboration | Regeneron Pharmaceuticals
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Discovery period of programs development5 years
Extended additional discovery period of programs development5 years
Maximum royalties and commercial milestone payments upon potential product sale $ 325,000,000
Upfront fee received400,000,000
Maximum additional milestone payments to be receive upon achievement of certain criteria $ 200,000,000
Number of targeted programs | program30
Agreement termination period90 days
Maximum percentage of royalty payments20.00%
Transaction price $ 530,500,000 $ 521,600,000
Transactional price remaining performance obligation $ 188,300,000 $ 188,300,000 $ 188,300,000
Global Strategic Collaboration | Funding At Program Initiation | Regeneron Pharmaceuticals
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential proceeds from collaboration arrangement $ 2,500,000
Global Strategic Collaboration | Funding At Lead Candidate Identification | Regeneron Pharmaceuticals
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential proceeds from collaboration arrangement2,500,000
Global Strategic Collaboration | Funding At Steady State | Regeneron Pharmaceuticals
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential proceeds from collaboration arrangement30,000,000
Global Strategic Collaboration | Maximum | Regeneron Pharmaceuticals
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research term extension fee400,000,000
Collaborative arrangement milestone payments $ 150,000,000
Royalty rate20.00%
Product Alliances | Novartis AG
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payment earned $ 45,000,000
Maximum amount of potential future milestones $ 135,000,000
Future payments on achievement of specified regulatory milestones25,000,000
Future payments on achievement of other specified regulatory milestones10,000,000
Future payments on achievement of specified commercialization milestones $ 100,000,000
Product Alliances | Minimum | Novartis AG
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty rate10.00%10.00%10.00%
Product Alliances | Maximum | Novartis AG
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty rate20.00%20.00%20.00%

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 Thousands3 Months Ended
Mar. 31, 2021Mar. 31, 2020
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses $ 185,899 $ 169,571
Clinical Trial and Manufacturing
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses5,839 5,949
Clinical Trial and Manufacturing | Regeneron Pharmaceuticals
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses4,799 4,612
Clinical Trial and Manufacturing | Vir Biotechnology
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses1,029 339
Clinical Trial and Manufacturing | Novartis AG
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses0 998
Clinical Trial and Manufacturing | Other
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses11 0
External Services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses305 69
External Services | Regeneron Pharmaceuticals
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses94 0
External Services | Vir Biotechnology
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses159 52
External Services | Novartis AG
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses0 0
External Services | Other
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses52 17
Other
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses14,452 13,681
Other | Regeneron Pharmaceuticals
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses12,235 11,491
Other | Vir Biotechnology
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses1,355 1,693
Other | Novartis AG
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses3 266
Other | Other
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research and development expenses $ 859 $ 231

NET REVENUES FROM COLLABORATI_7

NET REVENUES FROM COLLABORATIONS - Schedule of Transaction Price Allocated (Details) - Global Strategic Collaboration - Regeneron Pharmaceuticals $ in ThousandsMar. 31, 2021USD ($)Mar. 31, 2021USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Transaction Price Allocated $ 530,500 $ 521,600
Research Services Obligation
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Standalone Selling Price130,700 130,700
Transaction Price Allocated200,600 183,100
C5 License Obligation
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Standalone Selling Price97,600 97,600
Transaction Price Allocated83,900 92,500
C5 Co-Co Obligation
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Standalone Selling Price364,600 364,600
Transaction Price Allocated $ 246,000 $ 246,000

NET REVENUES FROM COLLABORATI_8

NET REVENUES FROM COLLABORATIONS - Schedule of Deferred Revenue (Details) - USD ($) $ in ThousandsMar. 31, 2021Mar. 31, 2021Dec. 31, 2020
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue $ 116,340 $ 116,340 $ 127,207
Global Strategic Collaboration | Regeneron Pharmaceuticals
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Transaction Price Allocated530,500 521,600
Deferred revenue319,200 319,200 345,000
Research Services Obligation | Global Strategic Collaboration | Regeneron Pharmaceuticals
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Transaction Price Allocated200,600 183,100
Deferred revenue45,100 45,100 54,900
C5 License Obligation | Global Strategic Collaboration | Regeneron Pharmaceuticals
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Transaction Price Allocated83,900 92,500
Deferred revenue45,200 45,200 58,700
C5 Co-Co Obligation | Global Strategic Collaboration | Regeneron Pharmaceuticals
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Transaction Price Allocated246,000 246,000
Deferred revenue $ 228,900 $ 228,900 $ 231,400

NET REVENUES FROM COLLABORATI_9

NET REVENUES FROM COLLABORATIONS - Schedule of Revenue Recognized by Accounting Guidance (Details) - USD ($) $ in Thousands3 Months Ended
Mar. 31, 2021Mar. 31, 2020
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognized under ASC 606 $ 177,566 $ 99,476
Regeneron Pharmaceuticals | Global Strategic Collaboration
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues25,800 16,500
Regeneron Pharmaceuticals | Research Services Obligation | Global Strategic Collaboration
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognized under ASC 6069,800 12,300
Regeneron Pharmaceuticals | C5 License Obligation | Global Strategic Collaboration
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognized under ASC 60613,500 0
Regeneron Pharmaceuticals | C5 Co-Co Obligation | Global Strategic Collaboration
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognized under ASC 808 $ 2,500 $ 4,200

LIABILITY RELATED TO THE SALE_3

LIABILITY RELATED TO THE SALE OF FUTURE ROYALTIES (Details) - USD ($)1 Months Ended3 Months Ended
Apr. 30, 2020Mar. 31, 2021Jan. 01, 2030Dec. 31, 2020Apr. 10, 2020
Liability Related To The Sale Of Future Royalties Line Items [Line Items]
Receivable related to the sale of future royalties $ 500,000,000 $ 500,000,000
Liability related to the sale of future royalties, net of current portion1,086,065,000 1,058,225,000
Blackstone Group Inc. | Collaborative Arrangement
Liability Related To The Sale Of Future Royalties Line Items [Line Items]
Collaborative arrangement, royalties and commercial milestones acquired by collaborator, percent50.00%
Commercial milestones acquired by collaborator, percent75.00%
Expected royalty interest payments1,000,000,000
Consideration received $ 500,000,000
Receivable related to the sale of future royalties500,000,000
Liability related to the sale of future royalties, net of current portion1,099,725,000 $ 1,071,541,000 $ 1,000,000,000
Interest rate11.00%
Closing costs(13,000,000)
Interest expense including amortization of closing costs $ 28,184,000
Forecast | Blackstone Group Inc. | Collaborative Arrangement
Liability Related To The Sale Of Future Royalties Line Items [Line Items]
Collaborative arrangement, royalties and commercial milestones acquired by collaborator, percent55.00%

FAIR VALUE MEASUREMENTS - Fair

FAIR VALUE MEASUREMENTS - Fair Value of Assets Measured on a Recurring Basis (Detail) - USD ($) $ in ThousandsMar. 31, 2021Dec. 31, 2020
Financial assets
Cash equivalents $ 0 $ 20,000
Marketable debt securities1,273,027 1,353,182
Marketable equity securities56,967 44,633
Recurring
Financial assets
Marketable equity securities56,967 44,633
Total financial assets1,508,947 1,475,024
Financial liabilities
Development derivative liability (Note 10)48,038 25,585
Recurring | Quoted Prices in Active Markets (Level 1)
Financial assets
Marketable equity securities56,967 44,633
Total financial assets235,920 121,842
Financial liabilities
Development derivative liability (Note 10)0 0
Recurring | Significant Observable Inputs (Level 2)
Financial assets
Marketable equity securities0 0
Total financial assets1,273,027 1,353,182
Financial liabilities
Development derivative liability (Note 10)0 0
Recurring | Significant Unobservable Inputs (Level 3)
Financial assets
Marketable equity securities0 0
Total financial assets0 0
Financial liabilities
Development derivative liability (Note 10)48,038 25,585
Recurring | U.S. treasury securities
Financial assets
Cash equivalents20,000
Marketable debt securities1,057,827 1,087,968
Recurring | U.S. treasury securities | Quoted Prices in Active Markets (Level 1)
Financial assets
Cash equivalents0
Marketable debt securities0 0
Recurring | U.S. treasury securities | Significant Observable Inputs (Level 2)
Financial assets
Cash equivalents20,000
Marketable debt securities1,057,827 1,087,968
Recurring | U.S. treasury securities | Significant Unobservable Inputs (Level 3)
Financial assets
Cash equivalents0
Marketable debt securities0 0
Recurring | Money market funds
Financial assets
Cash equivalents177,470 75,726
Restricted cash (money market funds)1,483 1,483
Recurring | Money market funds | Quoted Prices in Active Markets (Level 1)
Financial assets
Cash equivalents177,470 75,726
Restricted cash (money market funds)1,483 1,483
Recurring | Money market funds | Significant Observable Inputs (Level 2)
Financial assets
Cash equivalents0 0
Restricted cash (money market funds)0 0
Recurring | Money market funds | Significant Unobservable Inputs (Level 3)
Financial assets
Cash equivalents0 0
Restricted cash (money market funds)0 0
Recurring | U.S. government-sponsored enterprise securities
Financial assets
Marketable debt securities215,200 245,214
Recurring | U.S. government-sponsored enterprise securities | Quoted Prices in Active Markets (Level 1)
Financial assets
Marketable debt securities0 0
Recurring | U.S. government-sponsored enterprise securities | Significant Observable Inputs (Level 2)
Financial assets
Marketable debt securities215,200 245,214
Recurring | U.S. government-sponsored enterprise securities | Significant Unobservable Inputs (Level 3)
Financial assets
Marketable debt securities $ 0 $ 0

MARKETABLE DEBT SECURITIES - Ad

MARKETABLE DEBT SECURITIES - Additional Information (Detail) - USD ($)3 Months Ended
Mar. 31, 2021Mar. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Impairment charges of marketable debt securities $ 0 $ 0

MARKETABLE DEBT SECURITIES - Su

MARKETABLE DEBT SECURITIES - Summary of Marketable Debt Securities (Detail) - USD ($) $ in ThousandsMar. 31, 2021Dec. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost $ 1,272,680 $ 1,352,834
Gross Unrealized Gains422 463
Gross Unrealized Losses(75)(115)
Fair Value1,273,027 1,353,182
U.S. government-sponsored enterprise securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost215,171 245,113
Gross Unrealized Gains87 135
Gross Unrealized Losses(58)(34)
Fair Value215,200 245,214
U.S. treasury securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost1,057,509 1,107,721
Gross Unrealized Gains335 328
Gross Unrealized Losses(17)(81)
Fair Value $ 1,057,827 $ 1,107,968

MARKETABLE DEBT SECURITIES - _2

MARKETABLE DEBT SECURITIES - Summary of Fair Value of Marketable Debt Securities (Detail) - USD ($) $ in ThousandsMar. 31, 2021Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Cash and cash equivalents $ 0 $ 20,000
Marketable debt securities1,273,027 1,333,182
Total $ 1,273,027 $ 1,353,182

OTHER BALANCE SHEET DETAILS - S

OTHER BALANCE SHEET DETAILS - Schedule of Inventory (Detail) - USD ($) $ in ThousandsMar. 31, 2021Dec. 31, 2020
Inventory [Line Items]
Raw materials $ 53,694 $ 63,460
Work in progress23,593 16,149
Finished goods13,753 12,693
Total91,040 92,302
Other Assets
Inventory [Line Items]
Long-term inventory $ 17,100 $ 17,100

OTHER BALANCE SHEET DETAILS -_2

OTHER BALANCE SHEET DETAILS - Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in ThousandsMar. 31, 2021Dec. 31, 2020Mar. 31, 2020Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash and cash equivalents $ 379,543 $ 496,580 $ 467,779
Total restricted cash included in prepaid expenses, other current assets and long-term other assets2,462 2,614
Total cash, cash equivalents, and restricted cash shown in the condensed consolidated statements of cash flows $ 382,005 $ 499,046 $ 470,393 $ 549,628

OTHER BALANCE SHEET DETAILS -_3

OTHER BALANCE SHEET DETAILS - Summary of Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands3 Months Ended
Mar. 31, 2021Mar. 31, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance $ 1,016,247 $ 1,438,692
Other comprehensive (loss) income before reclassifications6,847 1,657
Amounts reclassified from other comprehensive income58 2,802
Total other comprehensive income6,905 4,459
Ending balance926,190 1,349,729
Loss on Investment in Joint Venture
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance(32,792)(32,792)
Other comprehensive (loss) income before reclassifications0 0
Amounts reclassified from other comprehensive income0 0
Total other comprehensive income0 0
Ending balance(32,792)(32,792)
Defined Benefit Pension Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance(3,754)(3,520)
Other comprehensive (loss) income before reclassifications0 0
Amounts reclassified from other comprehensive income58 74
Total other comprehensive income58 74
Ending balance(3,696)(3,446)
Unrealized Gains from Debt Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance348 137
Other comprehensive (loss) income before reclassifications(1)1,317
Amounts reclassified from other comprehensive income0 2,728
Total other comprehensive income(1)4,045
Ending balance347 4,182
Foreign Currency Translation Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance(7,424)(343)
Other comprehensive (loss) income before reclassifications6,848 340
Amounts reclassified from other comprehensive income0 0
Total other comprehensive income6,848 340
Ending balance(576)(3)
Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance(43,622)(36,518)
Total other comprehensive income6,905 4,459
Ending balance $ (36,717) $ (32,059)

CREDIT AGREEMENT - Additional I

CREDIT AGREEMENT - Additional Information (Details) - Line of Credit - Secured DebtDec. 31, 2020USD ($)Apr. 10, 2020USD ($)trancheDec. 31, 2020USD ($)Mar. 31, 2021USD ($)
Financing Receivable, Impaired [Line Items]
Number Of tranches | tranche3
Loan facility $ 700,000,000
Proceeds from lines of credit $ 200,000,000
Maximum borrowing capacity, accordion feature $ 50,000,000
Interest rate floor8.00%8.00%8.00%
Interest in kind, interest rate increase1.00%
Commitment fee amount $ 5,000,000
Commitment fee percentage2.50%
Exit fee percent1.00%
Prepayment and termination fee percentage5.00%
Minimum consolidated liquidity $ 100,000,000
LIBOR
Financing Receivable, Impaired [Line Items]
Debt instrument, basis spread on variable rate7.00%7.00%
LIBOR | Minimum
Financing Receivable, Impaired [Line Items]
Interest rate floor1.00%
Base Rate
Financing Receivable, Impaired [Line Items]
Debt instrument, basis spread on variable rate6.00%
Base Rate | Minimum
Financing Receivable, Impaired [Line Items]
Interest rate floor2.00%
Tranche 2 Loan
Financing Receivable, Impaired [Line Items]
Aggregate Principal Amount $ 250,000,000
Tranche 3 Loan
Financing Receivable, Impaired [Line Items]
Aggregate Principal Amount $ 250,000,000
Tranche 2 Loan And Tranche 3 Loan | ONPATTRO And GIVLAARI
Financing Receivable, Impaired [Line Items]
Minimum product revenue $ 300,000,000

DEVELOPMENT DERIVATIVE LIABIL_3

DEVELOPMENT DERIVATIVE LIABILITY - Narrative (Details) - USD ($)1 Months Ended
Aug. 31, 2020Mar. 31, 2021
Derivative [Line Items]
Cost of borrowing15.00%
Blackstone Life Sciences
Derivative [Line Items]
Cost of borrowing4.00%
Collaborative Arrangement | Blackstone Life Sciences | Vutrisiran and ALN-AGT
Derivative [Line Items]
Maximum funding $ 150,000,000
Collaborative Arrangement | Blackstone Life Sciences | HELIOS-B Phase 3 Clinical Trial
Derivative [Line Items]
Maximum funding70,000,000
Collaborative Arrangement | Blackstone Life Sciences | ALN-AGT Phase 2 Clinical Trial
Derivative [Line Items]
Maximum funding $ 26,000,000
Fixed payment multiplier3.25
Fixed payment, term4 years
Collaborative Arrangement | Blackstone Life Sciences | ALN-AGT Phase 3 Clinical Trial
Derivative [Line Items]
Maximum funding $ 54,000,000
Fixed payment multiplier4.5
Fixed payment, term4 years
Collaborative Arrangement | Blackstone Life Sciences | Vutrisiran
Derivative [Line Items]
Royalties payable, percent1.00%
Royalties payable, term10 years
Fixed payment multiplier2.5
Fixed payment, term2 years

DEVELOPMENT DERIVATIVE LIABIL_4

DEVELOPMENT DERIVATIVE LIABILITY - Development Derivative Liability Activity (Details) - Derivative $ in Thousands3 Months Ended
Mar. 31, 2021USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Development derivative liability, beginning balance $ 25,585
Amount received under the Funding Agreement4,200
Loss recorded from remeasurement of development derivative liability18,253
Development derivative liability, ending balance $ 48,038

STOCK-BASED COMPENSATION - Summ

STOCK-BASED COMPENSATION - Summary of Share-Based Compensation Expenses Included Operating Costs and Expense (Detail) - USD ($) $ in Thousands3 Months Ended
Mar. 31, 2021Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense $ 55,690 $ 34,578
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense24,375 16,049
Selling, general and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense $ 31,315 $ 18,529

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 Thousands3 Months Ended
Mar. 31, 2021Mar. 31, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share (in shares)15,397 15,020
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 (in shares)13,859 13,609
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 (in shares)1,538 1,411