Ultragenyx Pharmaceutical (RARE) 10-Q 3 Nov 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Oct. 28, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Trading Symbol	RARE
Entity Registrant Name	ULTRAGENYX PHARMACEUTICAL INC.
Entity Central Index Key	0001515673
Entity Current Reporting Status	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		68,162,225
Entity Shell Company	false
Entity File Number	001-36276
Entity Tax Identification Number	27-2546083
Entity Address, Address Line One	60 Leveroni Court
Entity Address, City or Town	Novato
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94949
City Area Code	415
Local Phone Number	483-8800
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock, $0.001 par value
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Document Quarterly Report	true
Document Transition Report	false

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 197,538	$ 713,526
Marketable debt securities	539,579	488,007
Accounts receivable, net	25,383	23,093
Inventory	15,191	13,048
Prepaid expenses and other current assets	69,193	57,630
Total current assets	846,884	1,295,304
Property, plant, and equipment, net	119,069	73,515
Equity investments	86,215	155,375
Marketable debt securities	204,243	10,506
Right-of-use assets	36,696	40,524
Intangible assets, net	130,869	131,113
Goodwill	44,406	44,406
Other assets	16,419	8,812
Total assets	1,484,801	1,759,555
Current liabilities:
Accounts payable	15,575	12,923
Accrued liabilities	109,660	108,491
Contract liabilities		59,219
Lease liabilities	10,698	8,976
Total current liabilities	135,933	189,609
Lease liabilities	33,344	39,251
Deferred tax liabilities	33,306	33,306
Liability related to the sale of future royalties	348,073	335,665
Other liabilities	471	7,349
Total liabilities	551,127	605,180
Stockholders’ equity:
Preferred stock — 25,000,000 shares authorized; nil outstanding as of June 30, 2021 and December 31, 2020
Common stock - 250,000,000 shares authorized; 67,961,963 and 66,818,520 shares issued and outstanding as of September 30, 2021 and December 31, 2020, respectively	68	67
Additional paid-in capital	2,884,695	2,773,195
Accumulated other comprehensive income	54	689
Accumulated deficit	(1,951,143)	(1,619,576)
Total stockholders’ equity	933,674	1,154,375
Total liabilities and stockholders’ equity	$ 1,484,801	$ 1,759,555

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - shares	Sep. 30, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Preferred stock, shares authorized	25,000,000	25,000,000
Preferred stock, shares outstanding	0	0
Common stock, shares authorized	250,000,000	250,000,000
Common stock, shares issued	67,961,963	66,818,520
Common stock, shares outstanding	67,961,963	66,818,520

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenues:
Total revenues	$ 81,647	$ 81,470	$ 268,017	$ 179,488
Operating expenses:
Cost of sales	4,175	2,348	12,499	648
Research and development	113,417	87,314	374,140	280,984
Selling, general and administrative	53,883	42,123	160,551	131,891
Total operating expenses	171,475	131,785	547,190	413,523
Loss from operations	(89,828)	(50,315)	(279,173)	(234,035)
Interest income	408	1,338	1,488	6,054
Change in fair value of equity investments	25,702	(11,520)	(25,963)	91,348
Non-cash interest expense on liability related to the sale of future royalties	(8,683)	(8,582)	(25,618)	(25,093)
Other income (expense)	(415)	547	(1,277)	308
Loss before income taxes	(72,816)	(68,532)	(330,543)	(161,418)
Provision for income taxes	(182)	(313)	(1,024)	(1,137)
Net loss	$ (72,998)	$ (68,845)	$ (331,567)	$ (162,555)
Net loss per share, basic and diluted	$ (1.08)	$ (1.13)	$ (4.91)	$ (2.73)
Weighted-average shares used in computing net loss per share, basic and diluted	67,875,363	60,687,177	67,533,671	59,564,163
Collaboration and License
Revenues:
Total revenues	$ 55,048	$ 66,924	$ 197,998	$ 144,300
Product Sales
Revenues:
Total revenues	21,950	11,215	56,809	25,760
Non-cash Collaboration Royalty Revenue
Revenues:
Total revenues	$ 4,649	$ 3,331	$ 13,210	$ 9,428

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement of Comprehensive Income [Abstract]
Net loss	$ (72,998)	$ (68,845)	$ (331,567)	$ (162,555)
Other comprehensive income (loss):
Foreign currency translation adjustments	(166)	374	(348)	414
Unrealized gain (loss) on available-for-sale securities	(12)	(645)	(287)	746
Other comprehensive income (loss):	(178)	(271)	(635)	1,160
Total comprehensive loss	$ (73,176)	$ (69,116)	$ (332,202)	$ (161,395)

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance at Dec. 31, 2019	$ 653,764	$ 58	$ 2,086,863	$ (147)	$ (1,433,010)
Beginning balance, shares at Dec. 31, 2019		57,838,220
Issuance of common stock in connection with license agreement, net of issuance costs	55,268	$ 1	55,267
Issuance of common stock in connection with license agreement, net of issuance costs, shares		1,243,913
Issuance of common stock in connection with at-the-market offering, net of issuance costs	20,391		20,391
Issuance of common stock in connection with at-the-market offering, net of issuance costs, shares		283,333
Stock-based compensation	63,112		63,112
Issuance of common stock upon exercise of warrants and under equity plan awards, net of tax	35,051	$ 2	35,049
Issuance of common stock upon exercise of warrants and under equity plan awards, net of tax, shares		1,450,224
Other comprehensive income (loss)	1,160			1,160
Net loss	(162,555)				(162,555)
Ending balance at Sep. 30, 2020	666,191	$ 61	2,260,682	1,013	(1,595,565)
Ending balance, shares at Sep. 30, 2020		60,815,690
Beginning balance at Jun. 30, 2020	695,587	$ 60	2,220,963	1,284	(1,526,720)
Beginning balance, shares at Jun. 30, 2020		60,413,756
Stock-based compensation	20,527		20,527
Issuance of common stock under equity plan awards, net of tax	19,193	$ 1	19,192
Issuance of common stock under equity plan awards, net of tax, shares		401,934
Other comprehensive income (loss)	(271)			(271)
Net loss	(68,845)				(68,845)
Ending balance at Sep. 30, 2020	666,191	$ 61	2,260,682	1,013	(1,595,565)
Ending balance, shares at Sep. 30, 2020		60,815,690
Beginning balance at Dec. 31, 2020	$ 1,154,375	$ 67	2,773,195	689	(1,619,576)
Beginning balance, shares at Dec. 31, 2020	66,818,520	66,818,520
Stock-based compensation	$ 78,324		78,324
Issuance of common stock under equity plan awards, net of tax	33,177	$ 1	33,176
Issuance of common stock under equity plan awards, net of tax, shares		1,143,443
Other comprehensive income (loss)	(635)			(635)
Net loss	(331,567)				(331,567)
Ending balance at Sep. 30, 2021	$ 933,674	$ 68	2,884,695	54	(1,951,143)
Ending balance, shares at Sep. 30, 2021	67,961,963	67,961,963
Beginning balance at Jun. 30, 2021	$ 972,171	$ 68	2,850,016	232	(1,878,145)
Beginning balance, shares at Jun. 30, 2021		67,764,950
Stock-based compensation	27,005		27,005
Issuance of common stock under equity plan awards, net of tax	7,674		7,674
Issuance of common stock under equity plan awards, net of tax, shares		197,013
Other comprehensive income (loss)	(178)			(178)
Net loss	(72,998)				(72,998)
Ending balance at Sep. 30, 2021	$ 933,674	$ 68	$ 2,884,695	$ 54	$ (1,951,143)
Ending balance, shares at Sep. 30, 2021	67,961,963	67,961,963

CONDENSED CONSOLIDATED STATEM_4

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Operating activities:
Net loss	$ (331,567)	$ (162,555)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	78,133	62,897
Amortization of premium on marketable debt securities, net	4,499	217
Depreciation and amortization	9,705	9,128
Change in fair value of equity investments	25,963	(91,348)
Non-cash collaboration royalty revenue	(13,210)	(9,428)
Non-cash interest expense on liability related to the sale of future royalties	25,618	25,093
Other	433	478
Changes in operating assets and liabilities:
Accounts receivable	(2,362)	5,126
Inventory	(2,127)	(2,635)
Prepaid expenses and other assets	(6,979)	(12,461)
Accounts payable, accrued, and other liabilities	1,920	2,822
Contract assets and liabilities, net	(74,377)	102,898
Net cash used in operating activities	(284,351)	(69,768)
Investing activities:
Purchase of property, plant, and equipment	(57,045)	(21,959)
Purchase of marketable debt securities	(917,409)	(648,524)
Purchase of equity investments		(10,220)
Proceeds from sale of marketable debt securities	83,318	40,390
Proceeds from maturities of marketable debt securities	583,997	367,446
Proceeds from sale of equity investment	43,197
Other	(487)	(4,155)
Net cash used in investing activities	(264,429)	(277,022)
Financing activities:
Proceeds from the issuance of common stock in connection with the license agreement, net		55,268
Proceeds from the issuance of common stock in connection with at-the-market offering, net		20,391
Proceeds from the issuance of common stock from exercise of warrants and equity plan awards, net	33,177	35,051
Other	(350)	(149)
Net cash provided by financing activities	32,827	110,561
Effect of exchange rate changes on cash	(802)	239
Net decrease in cash, cash equivalents and restricted cash	(516,755)	(235,990)
Cash, cash equivalents and restricted cash at beginning of period	726,294	436,244
Cash, cash equivalents and restricted cash at end of period	209,539	200,254
Supplemental disclosures of non-cash information:
Acquired lease liabilities arising from obtaining right-of-use assets	$ 2,610	$ 13,195

Organization

Organization	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization	1. Organization Ultragenyx Pharmaceutical Inc. (the Company) is a biopharmaceutical company incorporated in Delaware. The Company is focused on the identification, acquisition, development, and commercialization of novel products for the treatment of serious rare and ultra-rare genetic diseases. The Company operates as one reportable segment. The Company has three commercially approved products. Crysvita® (burosumab) is approved in the United States by the U.S. Food and Drug Administration (FDA) and in Canada for the treatment of X-linked hypophosphatemia (XLH) in adult and pediatric patients one year of age and older, and is approved in the European Union (EU) and the United Kingdom, for the treatment of XLH with radiographic evidence of bone disease in children one year of age and older, adolescents, and adults. In Brazil, Colombia, and Mexico, Crysvita is approved for treatment of XLH in adult and pediatric patients one year of age and older. Crysvita is also approved in the United States by the FDA for the treatment of fibroblast growth factor 23 (FGF23)-related hypophosphatemia in tumor-induced osteomalacia (TIO), associated with phosphaturic mesenchymal tumors that cannot be curatively resected or localized in adults and pediatric patients 2 years of age and older. The Company has also received FDA approval for Mepsevii ® (vestronidase alfa), the first medicine approved for the treatment of children and adults with mucopolysaccharidosis VII (MPS VII), also known as Sly syndrome. In the European Union and the United Kingdom, Mepsevii is approved under exceptional circumstances for patients of all ages for the treatment of non-neurological manifestations of MPS VII. In Brazil, Mepsevii is approved for the treatment of MPS VII for patients of all ages. Dojolvi ® , formerly known as UX007, is approved in the United States, Canada, and Brazil for the treatment of pediatric and adult patients severely affected by long-chain fatty acid oxidation disorders (LC-FAOD). In addition to the approved products, the Company has the following ongoing clinical development programs:  DTX401 is an adeno-associated virus 8 (AAV8) gene therapy product candidate for the treatment of patients with glycogen storage disease type Ia (GSDIa);  DTX301 is an AAV8 gene therapy product candidate in development for the treatment of patients with ornithine transcarbamylase (OTC) deficiency, the most common urea cycle disorder;  UX143 (setrusumab), which is subject to the Company's collaboration agreement with Mereo BioPharma 3 (Mereo), is a fully human monoclonal antibody that inhibits sclerostin, a protein that acts on a key bone-signaling pathway and inhibits the activity of bone-forming cells for the treatment of patients with osteogenesis imperfect (OI);  GTX-102 is an antisense oligonucleotide (ASO), which the Company is collaborating on the development with GeneTx Biotherapeutics LLC (GeneTx) for the treatment of Angelman syndrome, a debilitating and rare neurogenetic disorder caused by loss-of-function of the maternally inherited allele of the UBE3A gene;  UX701 is an AAV type 9 gene therapy designed to deliver stable expression of a truncated version of the ATP7B copper transporter following a single intravenous infusion to improve copper distribution and excretion from the body and reverse pathological findings of Wilson liver disease; and  UX053 is a messenger RNA (mRNA) product candidate designed for the treatment of patients with Glycogen Storage Disease Type III (GSDIII), a disease caused by a glycogen debranching enzyme (AGL) deficiency that results in glycogen accumulation in the liver and muscle. The Company has sustained operating losses and expects such annual losses to continue over the next several years. The Company’s ultimate success depends on the outcome of its research and development and commercialization activities, for which it expects to incur additional losses in the future. Management recognizes that the Company will need to raise additional capital to fully implement its business plans. Through September 30, 2021, the Company has relied primarily on its sale of equity securities, its revenues from commercial products, its sale of future royalties, and strategic collaboration arrangements to finance its operations. The Company will likely raise additional capital through the issuance of equity, borrowings, or strategic alliances with partner companies. However, if such financing is not available at adequate levels, the Company would need to reevaluate its operating plans.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying unaudited Condensed Consolidated Financial Statements include the accounts of the Company and its wholly-owned subsidiaries and have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) for interim financial information and in accordance with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. The unaudited interim Condensed Consolidated Financial Statements have been prepared on the same basis as the annual financial statements. In the opinion of management, the accompanying unaudited Condensed Consolidated Financial Statements reflect all adjustments (consisting only of normal recurring adjustments) considered necessary for a fair presentation. These financial statements should be read in conjunction with the audited financial statements and notes thereto for the preceding fiscal year contained in the Company’s Annual Report on Form 10-K filed on February 12, 2021 with the United States Securities and Exchange Commission (the SEC). The results of operations for the three and nine months ended September 30, 2021 are not necessarily indicative of the results to be expected for the year ending December 31, 2021. The Condensed Consolidated Balance Sheet as of December 31, 2020 has been derived from audited financial statements at that date, but does not include all of the information required by GAAP for complete financial statements. Use of Estimates The accompanying Condensed Consolidated Financial Statements have been prepared in accordance with GAAP. The preparation of the Condensed Consolidated Financial Statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent liabilities and the reported amounts of expenses in the Condensed Consolidated Financial Statements and the accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to clinical trial accruals, fair value of assets and liabilities, income taxes, stock-based compensation, and the liability related to the sale of future royalties. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Actual results could differ from those estimates. Cash, Cash Equivalents and Restricted Cash Restricted cash primarily consists of money market accounts used as collateral for the Company’s obligations under its facility leases and the gene therapy building construction project. The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the Condensed Consolidated Balance Sheets that sum to the total of the same such amounts shown in the Condensed Consolidated Statement of Cash Flows (in thousands): September 30, 2021 2020 Cash and cash equivalents $ 197,538 $ 197,486 Restricted cash included in prepaid expenses and 10,000 847 Restricted cash included in other assets 2,001 1,921 Total cash, cash equivalents, and restricted cash $ 209,539 $ 200,254 Credit Losses The Company is exposed to credit losses primarily through receivables from customers and collaborators and through its available-for-sale debt securities. For trade receivables and other instruments, the Company uses a new forward-looking expected loss model that generally results in the earlier recognition of allowances for losses. For available-for-sale debt securities with unrealized losses, the losses are recognized as allowances rather than as reductions in the amortized cost of the securities. The Company’s expected loss allowance methodology for the receivables is developed using historical collection experience, current and future economic market conditions, a review of the current aging status and financial condition of the entities. Specific allowance amounts are established to record the appropriate allowance for customers that have a higher probability of default. Balances are written off when determined to be uncollectible. The Company’s expected loss allowance methodology for the debt securities is developed by reviewing the extent of the unrealized loss, the size, term, geographical location, and industry of the issuer, the issuers’ credit ratings and any changes in those ratings, as well as reviewing current and future economic market conditions and the issuers’ current status and financial condition. There was no material allowance recorded for losses on receivables and available-for-sale debt securities which were attributable to credit risk for the three and nine months ended September 30, 2021 and 2020. Revenue Recognition Collaboration and license revenue The Company has certain license and collaboration agreements that are within the scope of Accounting Standards Codification (ASC) 808, Collaborative Agreements , which provides guidance on the presentation and disclosure of collaborative arrangements. Generally, the classification of the transactions under the collaborative arrangements is determined based on the nature of contractual terms of the arrangement, along with the nature of the operations of the participants. The Company records its share of collaboration revenue, net of transfer pricing related to net sales in the period in which such sales occur, if the Company is considered as an agent in the arrangement. The Company is considered an agent when the collaboration partner controls the product before transfer to the customers and has the ability to direct the use of and obtain substantially all of the remaining benefits from the product. Funding received related to research and development services and commercialization costs is generally classified as a reduction of research and development expenses and selling, general and administrative expenses, respectively, in the Condensed Consolidated Statement of Operations, because the provision of such services for collaborative partners are not considered to be part of the Company’s ongoing major or central operations. In order to record collaboration revenue, the Company utilizes certain information from its collaboration partners, including revenue from the sale of the product, associated reserves on revenue, and costs incurred for development and sales activities. For the periods covered in the financial statements presented, there have been no material changes to prior period estimates of revenues and expenses. The Company sold the right to receive certain royalty payments from net sales of Crysvita to RPI Finance Trust (RPI), an affiliate of Royalty Pharma, as further described in Note 7. The Company records the royalty revenue from the net sales of Crysvita in the applicable European territories on a prospective basis as non-cash royalty revenue in the Condensed Consolidated Statements of Operations over the term of the arrangement. The terms of the Company’s collaboration and license agreements may contain multiple performance obligations, which may include licenses and research and development activities. The Company evaluates these agreements under ASC 606, Revenue from Contracts with Customers (ASC 606), to determine the distinct performance obligations. The Company analogizes to ASC 606 for the accounting for distinct performance obligations for which there is a customer relationship. Prior to recognizing revenue, the Company makes estimates of the transaction price, including variable consideration that is subject to a constraint. Amounts of variable consideration are included in the transaction price to the extent that it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur and when the uncertainty associated with the variable consideration is subsequently resolved. Total consideration may include nonrefundable upfront license fees, payments for research and development activities, reimbursement of certain third-party costs, payments based upon the achievement of specified milestones, and royalty payments based on product sales derived from the collaboration. If there are multiple distinct performance obligations, the Company allocates the transaction price to each distinct performance obligation based on its relative standalone selling price. The standalone selling price is generally determined based on the prices charged to customers or using expected cost-plus margin. The Company estimates the efforts needed to complete the performance obligations and recognizes revenue by measuring the progress towards complete satisfaction of the performance obligations using input measures. Product sales The Company sells its approved products through a limited number of distributors. Under ASC 606, revenue from product sales is recognized at the point in time when the delivery is made and when title and risk of loss transfers to these distributors. The Company also recognizes revenue from sales of certain products on a “named patient” basis, which are allowed in certain countries prior to the commercial approval of the product. Prior to recognizing revenue, the Company makes estimates of the transaction price, including any variable consideration that is subject to a constraint. Amounts of variable consideration are included in the transaction price to the extent that it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur and when the uncertainty associated with the variable consideration is subsequently resolved. Product sales are recorded net of estimated government-mandated rebates and chargebacks, estimated product returns, and other deductions. Provisions for returns and other adjustments are provided for in the period the related revenue is recorded, as estimated by management. These reserves are based on estimates of the amounts earned or to be claimed on the related sales and are reviewed periodically and adjusted as necessary. The Company’s estimates of government mandated rebates, chargebacks, estimated product returns, and other deductions depends on the identification of key customer contract terms and conditions, as well as estimates of sales volumes to different classes of payors. If actual results vary, the Company may need to adjust these estimates, which could have an effect on earnings in the period of the adjustment.

Financial Instruments

Financial Instruments	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Financial Instruments	3. Financial Instruments Financial assets and liabilities are recorded at fair value. The carrying amount of certain financial instruments, including cash and cash equivalents, accounts receivable, accounts payable and accrued liabilities approximate fair value due to their relatively short maturities. Assets and liabilities recorded at fair value on a recurring basis in the balance sheets are categorized based upon the level of judgment associated with the inputs used to measure their fair values. Fair value is defined as the exchange price that would be received for an asset or an exit price that would be paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The authoritative guidance on fair value measurements establishes a three-tier fair value hierarchy for disclosure of fair value measurements as follows: Level 1 —Inputs are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date; Level 2 —Inputs are observable, unadjusted quoted prices in active markets for similar assets or liabilities, unadjusted quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the related assets or liabilities; and Level 3 —Unobservable inputs that are significant to the measurement of the fair value of the assets or liabilities that are supported by little or no market data. The Company determines the fair value of its equity investments in Arcturus Therapeutics Holdings Inc. (Arcturus) and Solid Biosciences Inc. (Solid) by using the quoted market prices, which are Level 1 fair value measurements. The following tables set forth the fair value of the Company’s financial assets remeasured on a recurring basis based on the three-tier fair value hierarchy (in thousands): September 30, 2021 Level 1 Level 2 Level 3 Total Money market funds $ 133,111 $ — $ — $ 133,111 Certificate of deposits and time deposits — 17,501 — 17,501 Corporate bonds — 324,055 — 324,055 Commercial paper — 308,825 — 308,825 Asset-backed securities — 44,457 — 44,457 U.S. Government Treasury and agency securities 62,003 — 62,003 Debt securities in government-sponsored entities — 28,680 — 28,680 Investments in Arcturus and Solid common stock 85,596 — — 85,596 Other — 487 — 487 Total $ 218,707 $ 786,008 $ — $ 1,004,715 December 31, 2020 Level 1 Level 2 Level 3 Total Money market funds $ 598,392 $ — $ — $ 598,392 Time deposits — 10,000 — 10,000 Corporate bonds — 193,802 — 193,802 Commercial paper — 173,859 — 173,859 Asset-backed securities — 11,225 — 11,225 U.S. Government Treasury and agency securities 167,967 17,661 — 185,628 Investments in Arcturus and Solid common stock 154,756 — — 154,756 Total $ 921,115 $ 406,547 $ — $ 1,327,662 In July 2020, the Company invested $ 2.5 million in a private diagnostic company, in the form of a convertible promissory note that matures in two years , if not converted earlier. The Company was also issued a warrant to purchase up to $ 1.0 million of the entity’s preferred stock. The fair value of the warrant to purchase shares of the entity was based on unobservable inputs that are significant to the measurement of the fair value of the asset and is supported by little or no market data; accordingly, the warrant is considered a Level 3 financial asset and is remeasured on a nonrecurring basis. The Company measured the fair value of the warrant by applying the Black-Scholes option pricing method and utilizing the following inputs: stock price, strike price, volatility, risk-free interest rate, and expected term. The Company recognizes the interest income on the convertible promissory note based on the effective interest rate method over the life of the note. As of September 30, 2021 , the balance of the convertible promissory note was $ 2.3 million, including $ 0.4 million in interest receivable, and was recorded in other assets, and the allocated fair value of the warrant was $ 0.6 million and was recorded in equity investments. In December 2020, the Company invested $ 1.4 million in Mahzi Therapeutics, Inc. (Mahzi), a private pharmaceutical company founded by a former employee of the Company, in the form of a convertible promissory note (Note) that matures in two years , if not converted earlier. As of September 30, 2021 , the balance of the Note was $ 1.5 million. In October 2021, pursuant to a qualified financing event, in accordance with the terms of the Note, the outstanding balance of the Note was fully converted into 606,506 shares of preferred stock of Mahzi.

Balance Sheet Components

Balance Sheet Components	9 Months Ended
	Sep. 30, 2021
Investments, Debt and Equity Securities [Abstract]
Balance Sheet Components	4. Balance Sheet Components Cash Equivalents and Investments The fair values of cash equivalents and investments classified as available-for-sale securities consisted of the following (in thousands): September 30, 2021 Gross Unrealized Amortized Gains Losses Estimated Money market funds $ 133,111 $ — $ — $ 133,111 Certificate of deposits and time deposits 17,501 — — 17,501 Corporate bonds 324,109 55 ( 109 ) 324,055 Commercial paper 308,824 1 — 308,825 Asset-backed securities 44,445 19 ( 7 ) 44,457 U.S. Government Treasury and agency securities 61,987 18 ( 2 ) 62,003 Debt securities in government-sponsored entities 28,682 3 ( 5 ) 28,680 Total $ 918,659 $ 96 $ ( 123 ) $ 918,632 December 31, 2020 Gross Unrealized Amortized Gains Losses Estimated Money market funds $ 598,392 $ — $ — $ 598,392 Time deposits 10,000 — — 10,000 Corporate bonds 193,610 209 ( 17 ) 193,802 Commercial paper 173,859 — — 173,859 Asset-backed securities 11,224 1 — 11,225 U.S. Government Treasury and agency securities 185,561 67 — 185,628 Total $ 1,172,646 $ 277 $ ( 17 ) $ 1,172,906 At September 30, 2021 , the remaining contractual maturities of available-for-sale securities were less than four years . There have been no significant realized gains or losses on available-for-sale securities for the three and nine months ended September 30, 2021 and 2020. All marketable securities with unrealized losses at September 30, 2021 have been in a loss position for less than twelve months and were temporary in nature. We do not intend to sell the investments that are in an unrealized loss position before recovery of their amortized cost basis. Inventory Inventory consists of the following (in thousands): September 30, December 31, 2021 2020 Work-in-process $ 9,546 $ 7,184 Finished goods 5,645 5,864 Total inventory $ 15,191 $ 13,048 Accrued Liabilities Accrued liabilities consist of the following (in thousands): September 30, December 31, 2021 2020 Research, clinical study, and manufacturing expenses $ 22,258 $ 25,875 Payroll and related expenses 55,164 58,176 Other 32,238 24,440 Total accrued liabilities $ 109,660 $ 108,491

Revenue

Revenue	9 Months Ended
	Sep. 30, 2021
Revenue from Contract with Customer [Abstract]
Revenue	5. Revenue The following table disaggregates total revenues from customers (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2021 2020 2021 2020 Collaboration and license revenue: Crysvita collaboration revenue in profit- $ 42,971 $ 34,058 $ 120,987 $ 91,079 Crysvita royalty revenue in European 16 — 244 1,498 Daiichi Sankyo 12,061 32,866 76,767 51,723 Total collaboration and license revenue 55,048 66,924 197,998 144,300 Product sales: Crysvita 7,378 3,277 16,150 7,436 Mepsevii 3,918 4,076 12,924 11,686 Dojolvi 10,654 3,862 27,735 6,638 Total product sales 21,950 11,215 56,809 25,760 Crysvita non-cash collaboration royalty 4,649 3,331 13,210 9,428 Total revenues $ 81,647 $ 81,470 $ 268,017 $ 179,488 The following table disaggregates total revenues based on geographic location (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2021 2020 2021 2020 North America $ 66,911 $ 72,651 $ 230,220 $ 154,939 Europe 7,244 5,002 19,581 15,707 Latin America 7,492 3,817 18,216 8,842 Total revenues $ 81,647 $ 81,470 $ 268,017 $ 179,488 The following table presents changes in the contract assets (liabilities) (in thousands): Nine Months Ended September 30, 2021 2020 Balance of contract liabilities at beginning of period $ ( 66,568 ) $ — Additions ( 2,390 ) ( 154,621 ) Deductions 76,767 51,723 Balance of contract assets (liabilities) at end of period $ 7,809 $ ( 102,898 ) See Note 6 for additional details on contract assets (liabilities) activities. The Company’s largest accounts receivable balance accounted for 57 % and 71 % of the total accounts receivable balance as of September 30, 2021 and December 31, 2020, respectively, and was due from a collaboration partner.

License and Research Agreements

License and Research Agreements	9 Months Ended
	Sep. 30, 2021
Research Grant Agreement [Abstract]
License and Research Agreements	6. License and Research Agreements Kyowa Kirin Collaboration and License Agreement In August 2013, the Company entered into a collaboration and license agreement with Kyowa Kirin Co., Ltd. (KKC, formerly Kyowa Hakko Kirin Co., Ltd. or KHK). Under the terms of this collaboration and license agreement, as amended, the Company and KKC collaborate on the development and commercialization of Crysvita in the field of orphan diseases in the United States and Canada, or the profit-share territory, and in the European Union, United Kingdom, and Switzerland, or the European territory, and the Company has the right to develop and commercialize such products in the field of orphan diseases in Mexico and Central and South America, or Latin America. In May 2017, the Company entered into an agreement with a wholly-owned subsidiary of KKC pursuant to which it was granted the right to commercialize Crysvita in Turkey. Development Activities In the field of orphan diseases, and except for ongoing studies being conducted by KKC, the Company is the lead party for development activities in the profit-share territory and in the European territory until the applicable transition date. The Company shares the costs for development activities in the profit-share territory and the European territory conducted pursuant to the development plan before the applicable transition date equally with KKC. In April 2023, which is the transition date for the profit-share territory, KKC will become the lead party and be responsible for the costs of the development activities. However, the Company will continue to share the costs of the studies commenced prior to the applicable transition date equally with KKC. Crysvita was approved in the European Union and United Kingdom in February 2018 and was approved by the FDA in April 2018. The collaboration and license agreements are within the scope of ASC 808, which provides guidance on the presentation and disclosure of collaborative arrangements. Collaboration revenue related to sales in profit-share territory The Company and KKC share commercial responsibilities and profits in the profit-share territory until April 2023. Under the collaboration agreement, KKC manufactures and supplies Crysvita for commercial use in the profit-share territory and charges the Company the transfer price of 35 % of net sales through December 31, 2022, and 30 % thereafter. The remaining profit or loss after supply costs from commercializing products in the profit-share territory are shared between the Company and KKC on a 50 /50 basis until April 2023. Thereafter, the Company will be entitled to receive a tiered double-digit revenue share in the mid-to-high 20 % range. As KKC is the principal in the sale transaction with the customer, the Company recognizes a pro-rata share of collaboration revenue, net of transfer pricing, in the period the sale occurs. The Company concluded that its portion of KKC’s sales in the profit-share territory is analogous to a royalty and therefore recorded its share as collaboration revenue, similar to a royalty. Royalty revenue related to sales in European territory KKC has the commercial responsibility for Crysvita in the European territory. In December 2019, the Company sold its right to receive royalty payments based on sales in the European territory to Royalty Pharma, effective January 1, 2020, as further described in Note 7. Prior to the Company’s sale of the royalty, the Company received a royalty of up to 10 % on net sales in the European territory, which was recognized as the underlying sales occur. Beginning in 2020, the Company recorded the royalty revenue as non-cash royalty revenues. During the nine months ended September 30, 2021 and 2020, there was a change in the estimate of the revenue reserves related to sales made prior to January 1, 2020, as a result of which, the Company recorded $ 0.2 million and $ 1.5 million, respectively, as royalty revenue in European territory. The Company’s share of collaboration and royalty revenue related to Crysvita was as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Company's share of revenue in profit- $ 42,971 $ 34,058 $ 120,987 $ 91,079 Royalty revenue in European territory 16 — 244 1,498 Non-cash royalty revenue in European 4,649 3,331 13,210 9,428 Total $ 47,636 $ 37,389 $ 134,441 $ 102,005 Product revenue related to sales in other territories The Company is responsible for commercializing Crysvita in Latin America and Turkey. The Company is considered the principal in these territories as the Company controls the product before it is transferred to the customer. Accordingly, the Company records revenue on a gross basis related to the sale of Crysvita once the product is delivered and the risk and title of the product is transferred to the distributor. The Company recorded product sales of $ 7.4 million and $ 16.2 million for the three and nine months ended September 30, 2021 , respectively, and $ 3.3 million and $ 7.4 million for the three and nine months ended September 30, 2020, respectively, net of estimated product returns and other deductions. KKC has the option to assume responsibility for commercialization efforts in Turkey from the Company, after a certain minimum period. Under the collaboration agreement, KKC manufactures and supplies Crysvita, which is purchased by the Company for sales in its territories and is based on 35 % of the net sales through December 31, 2022 and 30 % thereafter. The Company also pays to KKC a low single-digit royalty on net sales in Latin America. Cost sharing payments Under the collaboration agreement, KKC and the Company share certain development and commercialization costs. As a result, the Company was reimbursed for these costs and operating expenses were reduced as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Research and development $ 5,161 $ 5,156 $ 16,517 $ 15,814 Selling, general and administrative 8,005 5,492 23,076 18,509 Total $ 13,166 $ 10,648 $ 39,593 $ 34,323 Collaboration receivable and payable The Company had accounts receivable from KKC in the amount of $ 14.4 million and $ 16.4 million from profit-share revenue and royalties and other receivables recorded in prepaid expenses and other current assets of $ 3.7 million and $ 9.6 million and accrued liabilities of $ 3.1 million and $ 2.4 million from commercial and development activity reimbursements, as of September 30, 2021 and December 31, 2020, respectively. Bayer HealthCare LLC The Company has an agreement with Bayer Healthcare LLC (Bayer) to research, develop and commercialize AAV gene therapy products for the treatment of hemophilia A (DTX 201). Under this agreement, Bayer has been granted an exclusive license to develop and commercialize one or more novel gene therapies for hemophilia A. The agreement requires that Bayer use commercially reasonable efforts to conduct and fund a proof-of-concept (POC) clinical trial and any subsequent clinical trials and commercialization of gene therapy products for treatment of hemophilia A. Bayer has worldwide rights to commercialize the potential future product. Bayer was responsible for funding certain research and development services performed by the Company in the performance of its obligations under the annual research plan and budget. Under the terms of the agreement, the Company is eligible to receive development and commercialization milestone payments of up to $ 232.0 million, as well as, royalty payments ranging in the high single-digit to low double-digit percentages, not exceeding the mid-teens, of net sales of licensed products. The Company achieved the first milestone in December 2017, the second milestone in April 2018, and has received $ 15.0 million for such milestones to date. The Company has no further obligations under the contract. The Company may record future milestone payments as revenue, if it becomes probable that a significant reversal in the amount of revenue recognized will not occur and when the uncertainty associated with the variable consideration is subsequently resolved. Arcturus In October 2015, the Company entered into a Research Collaboration and License Agreement with Arcturus Therapeutics Holdings Inc. (Arcturus) whereby the Company and Arcturus would collaborate on the research and development of therapies for select rare diseases. Arcturus has the primary responsibility for conducting certain research services, funded by the Company, and the Company is responsible for development and commercialization costs. In June 2019, the Company entered into an Equity Purchase Agreement and an amendment to the Research Collaboration and License Agreement to expand the field of use and increase the number of disease targets to include mRNA, DNA and siRNA therapeutics for up to 12 rare diseases. Pursuant to the agreements, the Company paid $ 6.0 million in cash upfront to Arcturus and purchased 2,400,000 shares of Arcturus’ common stock at a stated value of $ 10.00 per share, resulting in a total of $ 30.0 million of consideration paid at the close of the transaction. As a result, the Company received expanded license rights, the Arcturus common stock and an option to purchase an additional 600,000 shares of Arcturus’ common stock at $ 16.00 per share. On a product-by-product basis, the Company may be obligated to make development and regulatory milestone payments of up to $ 24.5 million, and commercial milestone payments of up to $ 45.0 million, if certain milestones are achieved. The Company may also be obligated to pay Arcturus royalties on any net sales of products incorporating the licensed intellectual property that range from a mid single-digit to low double-digit percentage. For the three and nine months ended September 30, 2021 and 2020, there were no research and development expenses incurred as part of the collaboration agreement. In May 2020, the Company exercised its option to purchase 600,000 shares of Arcturus’ common stock at $ 16.00 per share, or a total purchase price of $ 9.6 million. In December 2020, the Company sold 800,000 shares of Arcturus’ common stock at a weighted-average price of $ 100.81 per share and received net proceeds of $ 79.8 million. In August 2021, the Company sold an additional 800,000 shares of Arcturus common stock at a weighted-average price of $ 54.54 per share and received net proceeds of $ 43.2 million. As of September 30, 2021 , the Company held 1,400,000 shares of Arcturus’ common stock. Due to the decrease in ownership and in accordance with the terms of the Equity Purchase Agreement, the Company no longer had the right to have its director nominee included in the annual slate of Arcturus director nominees and as a result, the Company’s director designee resigned from the Arcturus board of directors effective August 25, 2021. The Company will continue to apply the fair value option to account for the equity investment. The changes in the fair value of the Company’s equity investment in Arcturus securities were as follows (in thousands): Arcturus common stock Option to purchase additional shares of Arcturus common stock Total December 31, 2019 $ 26,088 $ 1,664 $ 27,752 Change in fair value 113,978 23,948 137,926 Transfer of value upon option exercise 35,212 ( 25,612 ) 9,600 Sale of shares ( 79,842 ) — ( 79,842 ) December 31, 2020 95,436 — 95,436 Change in fair value 14,653 — 14,653 Sale of shares ( 43,197 ) — ( 43,197 ) September 30, 2021 $ 66,892 $ — $ 66,892 The Company recorded $ 35.6 million and $ 14.7 million in realized and unrealized gains for the three and nine months ended September 30, 2021 , respectively, and $ 11.5 million in unrealized losses and $ 91.3 million in unrealized gains for the three and nine months ended September 30, 2020, respectively, from the fair value adjustments on the equity investment in Arcturus securities. GeneTx In August 2019, the Company entered into a Program Agreement and a Unitholder Option Agreement with GeneTx to collaborate on the development of GeneTx’s GTX-102, an ASO for the treatment of Angelman syndrome. Pursuant to the terms of the Unitholder Option Agreement, the Company made an upfront payment of $ 20.0 million for an exclusive option to acquire GeneTx, which was exercisable any time prior to 30 days following FDA acceptance of the IND for GTX-102. Pursuant to the agreement, upon acceptance of the IND, which occurred in January 2020, the Company elected to extend the option period by paying an option extension payment of $ 25.0 million (option extension premium) during the quarter ended March 31, 2020. The Company has the right to acquire GeneTx for a payment of $ 125.0 million, at any time, until the earlier of 30 months from the first dosing of a patient in a planned Phase 1/2 study (subject to extensions) or 90 days after results are available from that study. This exclusive option to acquire GeneTx can be extended under certain circumstances, by up to four additional three-month periods, by paying an additional extension fee for each three-month period. During the exclusive option period, GeneTx is responsible for conducting the program based on the development plan agreed between the parties and, subject to the terms in the Program Agreement, has the decision-making authority on all matters in connection with the research, development, manufacturing and regulatory activities with respect to the Program. The Company will provide support, at its discretion, including strategic guidance and clinical expertise. The Company and GeneTx will collaborate on the management of the Phase 1/2 study in patients with Angelman syndrome. If the Company acquires GeneTx, the Company would then be responsible for all development and commercialization activities from the date of acquisition. The Company would also be required to make payments upon achievement of certain development and commercial milestones, as well as royalties, depending upon the success of the program. Although GeneTx is a variable interest entity, the Company is not the primary beneficiary as it currently does not have the power to direct the activities that would most significantly impact the economic performance of GeneTx. Prior to product regulatory approval, all consideration paid to GeneTx represents rights to potential future benefits associated with GeneTx’s in-process research and development activities, which have not reached technological feasibility and have no alternative future use. Accordingly, for the three months ended March 31, 2020, the Company recorded the option extension payment of $ 25.0 million as an in-process research and development expense. REGENXBIO, Inc. In March 2020, the Company executed a License Agreement with REGENXBIO, Inc. (REGENEX), for an exclusive, sublicensable, worldwide license to REGENX’s NAV AAV8 and AAV9 Vectors for the development and commercialization of gene therapy treatments for a rare metabolic disorder. In return for these rights, the Company made an upfront payment of $ 7.0 million, which was recorded as an in-process research and development expense during the three months ended March 31, 2020. The Company is required to pay certain annual fees of $ 0.1 million, milestone payments of up to $ 14.0 million, and royalties on any net sales of products incorporating the licensed intellectual property that range from a high single-digit to low double-digit royalty. Daiichi Sankyo In March 2020, the Company executed a License and Technology Access Agreement (the License Agreement) with Daiichi Sankyo Co., Ltd. (Daiichi Sankyo). Pursuant to the License Agreement, the Company granted Daiichi Sankyo a non-exclusive license to intellectual property, including know-how and patent applications, with respect to its Producer Cell Line (PCL), and HEK293 transient transfection manufacturing technology platforms for AAV-based gene therapy products. The Company retains the exclusive right to use the manufacturing technology for its current target indications and additional indications identified now and in the future. The Company will provide certain technical assistance and technology transfer services during the technology transfer period of three years to enable Daiichi Sankyo to use the technologies for its internal gene therapy programs. Daiichi Sankyo has an option to extend the technology transfer period including know-how improvements by two additional one-year periods by paying a fixed amount for each additional year. Daiichi Sankyo will be responsible for the manufacturing, development, and commercialization of products manufactured with the licensed technology; however, the Company has the option to co-develop and co-commercialize rare disease products at the IND stage. The Company may also provide strategic consultation to Daiichi Sankyo on the development of both AAV-based gene therapy products and other products for rare diseases. Under the terms of the License Agreement, Daiichi Sankyo made an upfront payment of $ 125.0 million and will pay an additional $ 25.0 million upon completion of the technology transfer of the PCL and HEK293 platforms, as well as single-digit royalties on net sales of products manufactured in either system. Daiichi Sankyo will reimburse the Company for all costs associated with the transfer of the manufacturing technology. The Company also entered into a Stock Purchase Agreement (SPA) with Daiichi Sankyo, pursuant to which Daiichi Sankyo purchased 1,243,913 shares of the Company’s common stock in exchange for $ 75.0 million in cash during the first quarter of 2020. The fair market value of the common stock issued to Daiichi Sankyo was $ 55.3 million based on the stock price of $ 44.43 per share on the date of issuance, resulting in a $ 19.7 million premium on the SPA. Daiichi Sankyo is also subject to a three-year standstill and restrictions on sale of the shares (subject to customary exceptions or release). In June 2020, the Company executed a subsequent license agreement (the Sublicense Agreement) with Daiichi Sankyo for transfer of certain technology in consideration for an upfront payment of $ 8.0 million and annual maintenance fees, milestone payments, and royalties on any net sales of products incorporating the licensed intellectual property. The License Agreement, the Sublicense Agreement, and the SPA are being accounted for as one arrangement because they were entered into at or near the same time and negotiated in contemplation of one another. The Company evaluated the License Agreement and the Sublicense Agreement under ASC 606 and determined that the performance obligations under the agreements are (i) intellectual property with respect to its PCL and HEK293 transient transfection manufacturing technology platforms together with the initial technical assistance and technology transfer services, which are expected to be substantially completed in the fourth quarter of 2021, and (ii) the transfer of any know-how and improvements after the completion of the initial technology transfer through the end of the three year technology transfer period ending March 2023. As of September 30, 2021 , the Company has determined that the total transaction price of the License Agreement was $ 183.5 million which was comprised of the $ 19.7 million premium from the SPA, the $ 125.0 million upfront payment, the $ 25.0 million in unconstrained milestone payments, $ 8.0 million from the Sublicense Agreement, and the $ 5.7 million estimated reimbursement amount for delivering the license and technology services. Total revenue recognized under the license agreement through September 30, 2021 is $ 166.0 million. The Company allocated the total transaction price to the two performance obligations on a relative stand-alone selling price basis. Revenue allocated to the intellectual property and the technology transfer services will be recognized over an initial period which is estimated to be substantially complete in the fourth quarter of 2021, measuring the progress toward complete satisfaction of the individual performance obligation using an input measure. Revenue for know-how and improvements after the completion of technology transfer will be recognized on a straight-line basis over the remaining technology transfer period, which ends in March 2023, as it is expected that Daiichi Sankyo will receive and consume the benefits consistently throughout the period. The estimated period to complete the technology transfer services and the related milestones payments, if any, are subject to revised estimates which could be impacted by limitations or delays from the COVID-19 pandemic, successful scale-up of the manufacturing, and other changes that may impact timing. Royalties from commercial sales will be accounted for as revenue upon achievement of such sales, assuming all other revenue recognition criteria are met. The Company recognized $ 12.1 million and $ 76.8 million for the three and nine months ended September 30, 2021 , respectively, and $ 32.9 million and $ 51.7 million for the three and nine months ended September 30, 2020 , respectively, in revenue related to this arrangement. Accordingly, the Company had recorded $ 7.8 million as contract assets, net, in prepaid expenses and other current assets, and $ 66.6 million of contract liabilities, net, as of September 30, 2021 and December 31, 2020, respectively. The Company recorded an accounts receivable related to the above agreements of $ 0.4 million and $ 1.2 million as of September 30, 2021 and December 31, 2020, respectively. Solid Biosciences, Inc. In October 2020, the Company entered into a strategic Collaboration and License Agreement with Solid Biosciences Inc. (Solid), and received an exclusive license for any pharmaceutical product that expresses Solid’s proprietary microdystrophin construct from AAV8 and variants thereof in clade E for use in the treatment of Duchenne muscular dystrophy and other diseases resulting from lack of functional dystrophin, including Becker muscular dystrophy. The Company will collaborate to develop products that combine Solid’s differentiated microdystrophin construct, the Company’s PCL manufacturing platform, and the Company’s AAV8 variants. Solid will also provide development support and was granted an exclusive option to co-invest in products the Company develops for profit share participation in certain territories. On a product-by-product basis, the Company may be obligated to make development milestone payments of up to $ 25.0 million, regulatory milestone payments of up to $ 65.0 million, and commercial milestone payments of up to $ 165.0 million, if such milestones are achieved, as well as royalties on any net sales of products incorporating the licensed intellectual property that range from a low to mid-double-digit percentage. The royalty rate changes to mid to high double-digit percentage if Solid decides to co-invest in the product. The Company also entered into a Stock Purchase Agreement and the Investor Agreement with Solid, pursuant to which, the Company purchased 7,825,797 shares of Solid’s common stock for an aggregate purchase price of $ 40.0 million. Subject to the terms of the Investor Agreement, the Company is restricted from selling, transferring or otherwise disposing of the shares without the prior approval of Solid until the earlier of (i) 18 months following the closing of the transaction, (ii) the termination of the Collaboration and License Agreement and (iii) certain other specified events. The Company also agreed to customary standstill restrictions in accordance with the terms of the Investor Agreement until the earlier of (a) 24 months after the closing of the transaction and (b) certain specified events. The Company’s investment in Solid is being accounted at fair value, as the fair value is readily determinable. The Company recorded the common stock investment at $ 26.8 million on the transaction date, which was based on the quoted market price on the closing date. Although Solid is a variable interest entity, the Company is not the primary beneficiary as it does not have the power to direct the activities that would most significantly impact the economic performance of Solid. Prior to the achievement of certain development milestones, all consideration paid to Solid represents rights to potential future benefits associated with Solid’s in-process research and development activities, which have not reached technological feasibility and have no alternative future use. Accordingly, the remaining $ 13.2 million of the total $ 40.0 million paid as consideration was attributed to the license rights obtained and was recorded as in-process research and development expense during the year ended December 31, 2020. The changes in the fair value of the Company’s investment in Solid’s common stock were as follows (in thousands): Solid common stock Acquisition of investment in Solid common $ 26,843 Change in fair value 32,477 December 31, 2020 59,320 Change in fair value ( 40,616 ) September 30, 2021 $ 18,704 The Company recorded $ 9.9 million and $ 40.6 million in unrealized losses for the three and nine months ended September 30, 2021, respectively, from the fair value adjustments on the equity investment in Solid securities. Mereo BioPharma 3 Limited In December 2020, the Company entered into a License and Collaboration Agreement with Mereo BioPharma 3 Limited, or Mereo, to collaborate on the development of setrusumab. Under the terms of the agreement, the Company will lead future global development of setrusumab in both pediatric and adult patients with Osteogenesis Imperfecta, or OI. The Company was granted an exclusive license to develop and commercialize setrusumab in the U.S., Turkey, and the rest of the world, excluding the European Economic Area, United Kingdom, and Switzerland, or the Mereo territory, where Mereo retains commercial rights. Each party will be responsible for post-marketing commitments and commercial supply in their respective territories. Upon the closing of the transaction in January 2021, the Company made a payment of $ 50.0 million to Mereo and will be required to make payments of up to $ 254.0 million upon the achievement of certain clinical, regulatory, and commercial milestones. The Company will pay for all global development costs as well as tiered double-digit percentage royalties to Mereo on net sales in the U.S., Turkey, and the rest of the world (excluding the Mereo Territory), and Mereo will pay the Company a fixed double-digit percentage royalty on net sales in the Mereo Territory. Although Mereo is a variable interest entity, the Company is not the primary beneficiary as it does not have the power to direct the activities that would most significantly impact the economic performance of Mereo. Prior to the achievement of certain development milestones, all consideration paid to Mereo represents rights to potential future benefits associated with Mereo’s in-process research and development activities, which have not reached technological feasibility and have no alternative future use. Accordingly, for the three months ended March 31, 2021, the Company recorded the upfront payment of $ 50.0 million as in-process research and development expense.

Liability Related to the Sale o

Liability Related to the Sale of Future Royalties	9 Months Ended
	Sep. 30, 2021
Deferred Revenue Disclosure [Abstract]
Liability Related to the Sale of Future Royalties	7. Liability Related to the Sale of Future Royalties In December 2019, the Company entered into a Royalty Purchase Agreement with RPI. Pursuant to the agreement, RPI paid $ 320.0 million to the Company in consideration for the right to receive royalty payments effective January 1, 2020, arising from the net sales of Crysvita in the European Union, the United Kingdom, and Switzerland under the terms of the Company’s Collaboration and License Agreement with KKC dated August 29, 2013, as amended. The agreement with RPI will automatically terminate, and the payment of royalties to RPI will cease, in the event aggregate royalty payments received by RPI are equal to or greater than $ 608.0 million prior to December 31, 2030, or in the event aggregate royalty payments received by RPI are less than $ 608.0 million prior to December 31, 2030, when aggregate royalty payments received by RPI are equal to $ 800.0 million. Proceeds from the transaction were recorded as a liability (liability related to sale of future royalties on the Condensed Consolidated Balance Sheets). The Company amortizes $ 320.0 million, net of transaction cost of $ 5.8 million, using the effective interest method over the estimated life of the arrangement. In order to determine the amortization of the liability, the Company is required to estimate the total amount of future royalty payments to be received by the Company and paid to RPI, subject to the capped amount, over the life of the arrangement. The excess of future estimated royalty payments (subject to the capped amount), over the $ 314.2 million of net proceeds, is recorded as non-cash interest expense over the life of the arrangement. Consequently, the Company estimates an imputed interest on the unamortized portion of the liability and records interest expense relating to the transaction. The Company records the royalty revenue arising from the net sales of Crysvita in the applicable European territories as non-cash royalty revenue in the Condensed Consolidated Statements of Operations over the term of the arrangement. The Company periodically assesses the expected royalty payments using a combination of historical results, internal projections and forecasts from external sources. To the extent such payments are greater or less than the Company’s initial estimates or the timing of such payments is materially different than its original estimates, the Company will prospectively adjust the amortization of the liability and the effective interest rate. The Company’s effective annual interest rate was approximately 9.9 % as of September 30, 2021. There are a number of factors that could materially affect the amount and timing of royalty payments from KKC in the applicable European territories, most of which are not within the Company’s control. Such factors include, but are not limited to, the success of KKC’s sales and promotion of Crysvita, changing standards of care, delays or disruptions related to the COVID-19 pandemic, the introduction of competing products, pricing for reimbursement in various European territories, manufacturing or other delays, intellectual property matters, adverse events that result in governmental health authority imposed restrictions on the use of Crysvita, significant changes in foreign exchange rates as the royalty payments are made in U.S. dollars (USD) while significant portions of the underlying European sales of Crysvita are made in currencies other than USD, and other events or circumstances that could result in reduced royalty payments from European sales of Crysvita, all of which would result in a reduction of non-cash royalty revenue and the non-cash interest expense over the life of the arrangement. Conversely, if sales of Crysvita in Europe are more than expected, the non-cash royalty revenue and the non-cash interest expense recorded by the Company would be greater over the term of the arrangement. The following table shows the activity within the liability account (in thousands): Liability related to the sale of future royalties December 31, 2019 $ 315,369 Non-cash collaboration royalty revenue ( 12,995 ) Non-cash interest expense 33,291 December 31, 2020 335,665 Non-cash collaboration royalty revenue ( 13,210 ) Non-cash interest expense 25,618 September 30, 2021 $ 348,073

Stock-Based Awards

Stock-Based Awards	9 Months Ended
	Sep. 30, 2021
Share-based Payment Arrangement [Abstract]
Stock-Based Awards	8. Stock-Based Awards The 2014 Incentive Plan (the 2014 Plan) provides for automatic annual increases in shares available for grant, beginning on January 1, 2015 through January 1, 2024 . As of September 30, 2021 , there were 4,086,908 shares reserved under the 2014 Plan for the future issuance of equity awards, 3,956,907 shares reserved for the 2014 Employee Stock Purchase Plan, and 468,963 shares reserved for the Employment Inducement Plan. The table below sets forth the stock-based compensation expense for the periods presented (in thousands): Three Months Ended Nine Months Ended 2021 2020 2021 2020 Cost of sales $ 160 $ 133 $ 762 $ 313 Research and development 15,366 11,533 43,949 35,318 Selling, general and administrative 11,464 8,675 33,719 27,291 Total stock-based compensation expense $ 26,990 $ 20,341 $ 78,430 $ 62,922

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Net Loss Per Share	9. Net Loss Per Share Basic net loss per share has been computed by dividing the net loss by the weighted-average number of shares of common stock outstanding during the period. Diluted net loss per share is calculated by dividing net loss by the weighted-average number of shares of common stock and potential dilutive securities outstanding during the period. The following weighted-average outstanding common stock equivalents were excluded from the computation of diluted net loss per share for the periods presented because including them would have been antidilutive: Three Months Ended Nine Months Ended 2021 2020 2021 2020 Options to purchase common stock and 8,287,010 8,627,419 8,287,394 8,637,904 Employee stock purchase plan 30,196 35,282 16,923 19,701 Common stock warrants — — — 39,337 8,317,206 8,662,701 8,304,317 8,696,942

Equity Transactions

Equity Transactions	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Equity Transactions	10. Equity Transactions In October 2020, the Company completed an underwritten public offering in which 5,111,110 shares of common stock were sold, which included 666,666 shares purchased by the underwriters pursuant to an option granted to them in connection with the offering, at a public offering price of $ 90.00 per share. For the year ended December 31, 2020, the total proceeds that the Company received from the offering were approximately $ 435.6 million, net of underwriting discounts and commissions. In May 2021, the Company entered into an Open Market Sale Agreement with Jefferies LLC, (Jefferies), pursuant to which the Company may offer and sell shares of the Company’s common stock having an aggregate offering proceeds up to $ 350.0 million, from time to time, in at-the-market (ATM) offerings through Jefferies. As of September 30, 2021 , the Company has no t sold any shares under the arrangement.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income	9 Months Ended
	Sep. 30, 2021
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated Other Comprehensive Income	11. Accumulated Other Comprehensive Income Total accumulated other comprehensive income consisted of the following (in thousands): September 30, December 31, 2021 2020 Foreign currency translation adjustments $ 81 $ 429 Unrealized gain (loss) on available-for-sale securities ( 27 ) 260 Total accumulated other comprehensive income $ 54 $ 689

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited Condensed Consolidated Financial Statements include the accounts of the Company and its wholly-owned subsidiaries and have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) for interim financial information and in accordance with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. The unaudited interim Condensed Consolidated Financial Statements have been prepared on the same basis as the annual financial statements. In the opinion of management, the accompanying unaudited Condensed Consolidated Financial Statements reflect all adjustments (consisting only of normal recurring adjustments) considered necessary for a fair presentation. These financial statements should be read in conjunction with the audited financial statements and notes thereto for the preceding fiscal year contained in the Company’s Annual Report on Form 10-K filed on February 12, 2021 with the United States Securities and Exchange Commission (the SEC). The results of operations for the three and nine months ended September 30, 2021 are not necessarily indicative of the results to be expected for the year ending December 31, 2021. The Condensed Consolidated Balance Sheet as of December 31, 2020 has been derived from audited financial statements at that date, but does not include all of the information required by GAAP for complete financial statements.
Use of Estimates	Use of Estimates The accompanying Condensed Consolidated Financial Statements have been prepared in accordance with GAAP. The preparation of the Condensed Consolidated Financial Statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent liabilities and the reported amounts of expenses in the Condensed Consolidated Financial Statements and the accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to clinical trial accruals, fair value of assets and liabilities, income taxes, stock-based compensation, and the liability related to the sale of future royalties. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Actual results could differ from those estimates.
Cash, Cash Equivalents, and Restricted Cash	Cash, Cash Equivalents and Restricted Cash Restricted cash primarily consists of money market accounts used as collateral for the Company’s obligations under its facility leases and the gene therapy building construction project. The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the Condensed Consolidated Balance Sheets that sum to the total of the same such amounts shown in the Condensed Consolidated Statement of Cash Flows (in thousands): September 30, 2021 2020 Cash and cash equivalents $ 197,538 $ 197,486 Restricted cash included in prepaid expenses and 10,000 847 Restricted cash included in other assets 2,001 1,921 Total cash, cash equivalents, and restricted cash $ 209,539 $ 200,254
Credit Losses	Credit Losses The Company is exposed to credit losses primarily through receivables from customers and collaborators and through its available-for-sale debt securities. For trade receivables and other instruments, the Company uses a new forward-looking expected loss model that generally results in the earlier recognition of allowances for losses. For available-for-sale debt securities with unrealized losses, the losses are recognized as allowances rather than as reductions in the amortized cost of the securities. The Company’s expected loss allowance methodology for the receivables is developed using historical collection experience, current and future economic market conditions, a review of the current aging status and financial condition of the entities. Specific allowance amounts are established to record the appropriate allowance for customers that have a higher probability of default. Balances are written off when determined to be uncollectible. The Company’s expected loss allowance methodology for the debt securities is developed by reviewing the extent of the unrealized loss, the size, term, geographical location, and industry of the issuer, the issuers’ credit ratings and any changes in those ratings, as well as reviewing current and future economic market conditions and the issuers’ current status and financial condition. There was no material allowance recorded for losses on receivables and available-for-sale debt securities which were attributable to credit risk for the three and nine months ended September 30, 2021 and 2020.
Revenue Recognition	Revenue Recognition Collaboration and license revenue The Company has certain license and collaboration agreements that are within the scope of Accounting Standards Codification (ASC) 808, Collaborative Agreements , which provides guidance on the presentation and disclosure of collaborative arrangements. Generally, the classification of the transactions under the collaborative arrangements is determined based on the nature of contractual terms of the arrangement, along with the nature of the operations of the participants. The Company records its share of collaboration revenue, net of transfer pricing related to net sales in the period in which such sales occur, if the Company is considered as an agent in the arrangement. The Company is considered an agent when the collaboration partner controls the product before transfer to the customers and has the ability to direct the use of and obtain substantially all of the remaining benefits from the product. Funding received related to research and development services and commercialization costs is generally classified as a reduction of research and development expenses and selling, general and administrative expenses, respectively, in the Condensed Consolidated Statement of Operations, because the provision of such services for collaborative partners are not considered to be part of the Company’s ongoing major or central operations. In order to record collaboration revenue, the Company utilizes certain information from its collaboration partners, including revenue from the sale of the product, associated reserves on revenue, and costs incurred for development and sales activities. For the periods covered in the financial statements presented, there have been no material changes to prior period estimates of revenues and expenses. The Company sold the right to receive certain royalty payments from net sales of Crysvita to RPI Finance Trust (RPI), an affiliate of Royalty Pharma, as further described in Note 7. The Company records the royalty revenue from the net sales of Crysvita in the applicable European territories on a prospective basis as non-cash royalty revenue in the Condensed Consolidated Statements of Operations over the term of the arrangement. The terms of the Company’s collaboration and license agreements may contain multiple performance obligations, which may include licenses and research and development activities. The Company evaluates these agreements under ASC 606, Revenue from Contracts with Customers (ASC 606), to determine the distinct performance obligations. The Company analogizes to ASC 606 for the accounting for distinct performance obligations for which there is a customer relationship. Prior to recognizing revenue, the Company makes estimates of the transaction price, including variable consideration that is subject to a constraint. Amounts of variable consideration are included in the transaction price to the extent that it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur and when the uncertainty associated with the variable consideration is subsequently resolved. Total consideration may include nonrefundable upfront license fees, payments for research and development activities, reimbursement of certain third-party costs, payments based upon the achievement of specified milestones, and royalty payments based on product sales derived from the collaboration. If there are multiple distinct performance obligations, the Company allocates the transaction price to each distinct performance obligation based on its relative standalone selling price. The standalone selling price is generally determined based on the prices charged to customers or using expected cost-plus margin. The Company estimates the efforts needed to complete the performance obligations and recognizes revenue by measuring the progress towards complete satisfaction of the performance obligations using input measures. Product sales The Company sells its approved products through a limited number of distributors. Under ASC 606, revenue from product sales is recognized at the point in time when the delivery is made and when title and risk of loss transfers to these distributors. The Company also recognizes revenue from sales of certain products on a “named patient” basis, which are allowed in certain countries prior to the commercial approval of the product. Prior to recognizing revenue, the Company makes estimates of the transaction price, including any variable consideration that is subject to a constraint. Amounts of variable consideration are included in the transaction price to the extent that it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur and when the uncertainty associated with the variable consideration is subsequently resolved. Product sales are recorded net of estimated government-mandated rebates and chargebacks, estimated product returns, and other deductions. Provisions for returns and other adjustments are provided for in the period the related revenue is recorded, as estimated by management. These reserves are based on estimates of the amounts earned or to be claimed on the related sales and are reviewed periodically and adjusted as necessary. The Company’s estimates of government mandated rebates, chargebacks, estimated product returns, and other deductions depends on the identification of key customer contract terms and conditions, as well as estimates of sales volumes to different classes of payors. If actual results vary, the Company may need to adjust these estimates, which could have an effect on earnings in the period of the adjustment.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Summary of Reconciliation of Cash, Cash Equivalents and Restricted Cash	The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the Condensed Consolidated Balance Sheets that sum to the total of the same such amounts shown in the Condensed Consolidated Statement of Cash Flows (in thousands): September 30, 2021 2020 Cash and cash equivalents $ 197,538 $ 197,486 Restricted cash included in prepaid expenses and 10,000 847 Restricted cash included in other assets 2,001 1,921 Total cash, cash equivalents, and restricted cash $ 209,539 $ 200,254

Financial Instruments (Tables)

Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Summary of Financial Assets Measured on Recurring Basis	The following tables set forth the fair value of the Company’s financial assets remeasured on a recurring basis based on the three-tier fair value hierarchy (in thousands): September 30, 2021 Level 1 Level 2 Level 3 Total Money market funds $ 133,111 $ — $ — $ 133,111 Certificate of deposits and time deposits — 17,501 — 17,501 Corporate bonds — 324,055 — 324,055 Commercial paper — 308,825 — 308,825 Asset-backed securities — 44,457 — 44,457 U.S. Government Treasury and agency securities 62,003 — 62,003 Debt securities in government-sponsored entities — 28,680 — 28,680 Investments in Arcturus and Solid common stock 85,596 — — 85,596 Other — 487 — 487 Total $ 218,707 $ 786,008 $ — $ 1,004,715 December 31, 2020 Level 1 Level 2 Level 3 Total Money market funds $ 598,392 $ — $ — $ 598,392 Time deposits — 10,000 — 10,000 Corporate bonds — 193,802 — 193,802 Commercial paper — 173,859 — 173,859 Asset-backed securities — 11,225 — 11,225 U.S. Government Treasury and agency securities 167,967 17,661 — 185,628 Investments in Arcturus and Solid common stock 154,756 — — 154,756 Total $ 921,115 $ 406,547 $ — $ 1,327,662

Balance Sheet Components (Table

Balance Sheet Components (Tables)	9 Months Ended
	Sep. 30, 2021
Investments, Debt and Equity Securities [Abstract]
Summary of Cash Equivalents and Investments Classified as Available For Sale Securities	The fair values of cash equivalents and investments classified as available-for-sale securities consisted of the following (in thousands): September 30, 2021 Gross Unrealized Amortized Gains Losses Estimated Money market funds $ 133,111 $ — $ — $ 133,111 Certificate of deposits and time deposits 17,501 — — 17,501 Corporate bonds 324,109 55 ( 109 ) 324,055 Commercial paper 308,824 1 — 308,825 Asset-backed securities 44,445 19 ( 7 ) 44,457 U.S. Government Treasury and agency securities 61,987 18 ( 2 ) 62,003 Debt securities in government-sponsored entities 28,682 3 ( 5 ) 28,680 Total $ 918,659 $ 96 $ ( 123 ) $ 918,632 December 31, 2020 Gross Unrealized Amortized Gains Losses Estimated Money market funds $ 598,392 $ — $ — $ 598,392 Time deposits 10,000 — — 10,000 Corporate bonds 193,610 209 ( 17 ) 193,802 Commercial paper 173,859 — — 173,859 Asset-backed securities 11,224 1 — 11,225 U.S. Government Treasury and agency securities 185,561 67 — 185,628 Total $ 1,172,646 $ 277 $ ( 17 ) $ 1,172,906
Summary of Inventory	Inventory consists of the following (in thousands): September 30, December 31, 2021 2020 Work-in-process $ 9,546 $ 7,184 Finished goods 5,645 5,864 Total inventory $ 15,191 $ 13,048
Accrued Liabilities	Accrued liabilities consist of the following (in thousands): September 30, December 31, 2021 2020 Research, clinical study, and manufacturing expenses $ 22,258 $ 25,875 Payroll and related expenses 55,164 58,176 Other 32,238 24,440 Total accrued liabilities $ 109,660 $ 108,491

Revenue (Tables)

Revenue (Tables)	9 Months Ended
	Sep. 30, 2021
Revenue from Contract with Customer [Abstract]
Summary of Disaggregation of Total Revenues	The following table disaggregates total revenues from customers (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2021 2020 2021 2020 Collaboration and license revenue: Crysvita collaboration revenue in profit- $ 42,971 $ 34,058 $ 120,987 $ 91,079 Crysvita royalty revenue in European 16 — 244 1,498 Daiichi Sankyo 12,061 32,866 76,767 51,723 Total collaboration and license revenue 55,048 66,924 197,998 144,300 Product sales: Crysvita 7,378 3,277 16,150 7,436 Mepsevii 3,918 4,076 12,924 11,686 Dojolvi 10,654 3,862 27,735 6,638 Total product sales 21,950 11,215 56,809 25,760 Crysvita non-cash collaboration royalty 4,649 3,331 13,210 9,428 Total revenues $ 81,647 $ 81,470 $ 268,017 $ 179,488 The following table disaggregates total revenues based on geographic location (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2021 2020 2021 2020 North America $ 66,911 $ 72,651 $ 230,220 $ 154,939 Europe 7,244 5,002 19,581 15,707 Latin America 7,492 3,817 18,216 8,842 Total revenues $ 81,647 $ 81,470 $ 268,017 $ 179,488
Summary of Changes in Contract Assets (Liabilities)	The following table presents changes in the contract assets (liabilities) (in thousands): Nine Months Ended September 30, 2021 2020 Balance of contract liabilities at beginning of period $ ( 66,568 ) $ — Additions ( 2,390 ) ( 154,621 ) Deductions 76,767 51,723 Balance of contract assets (liabilities) at end of period $ 7,809 $ ( 102,898 )

License and Research Agreemen_2

License and Research Agreements (Tables)	9 Months Ended
	Sep. 30, 2021
Share of Collaboration and Royalty Revenue Related to Crysvita	The Company’s share of collaboration and royalty revenue related to Crysvita was as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Company's share of revenue in profit- $ 42,971 $ 34,058 $ 120,987 $ 91,079 Royalty revenue in European territory 16 — 244 1,498 Non-cash royalty revenue in European 4,649 3,331 13,210 9,428 Total $ 47,636 $ 37,389 $ 134,441 $ 102,005
Schedule of Cost Sharing Payments	Under the collaboration agreement, KKC and the Company share certain development and commercialization costs. As a result, the Company was reimbursed for these costs and operating expenses were reduced as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Research and development $ 5,161 $ 5,156 $ 16,517 $ 15,814 Selling, general and administrative 8,005 5,492 23,076 18,509 Total $ 13,166 $ 10,648 $ 39,593 $ 34,323
Solid Biosciences, Inc.
Schedule of Changes in Fair Value of Investment in Securities	The changes in the fair value of the Company’s investment in Solid’s common stock were as follows (in thousands): Solid common stock Acquisition of investment in Solid common $ 26,843 Change in fair value 32,477 December 31, 2020 59,320 Change in fair value ( 40,616 ) September 30, 2021 $ 18,704
Arcturus
Schedule of Changes in Fair Value of Equity Investment	The changes in the fair value of the Company’s equity investment in Arcturus securities were as follows (in thousands): Arcturus common stock Option to purchase additional shares of Arcturus common stock Total December 31, 2019 $ 26,088 $ 1,664 $ 27,752 Change in fair value 113,978 23,948 137,926 Transfer of value upon option exercise 35,212 ( 25,612 ) 9,600 Sale of shares ( 79,842 ) — ( 79,842 ) December 31, 2020 95,436 — 95,436 Change in fair value 14,653 — 14,653 Sale of shares ( 43,197 ) — ( 43,197 ) September 30, 2021 $ 66,892 $ — $ 66,892

Liability Related to the Sale_2

Liability Related to the Sale of Future Royalties (Tables)	9 Months Ended
	Sep. 30, 2021
Deferred Revenue Disclosure [Abstract]
Schedule of Activity Within Liability Related to Sale of Future Royalties	The following table shows the activity within the liability account (in thousands): Liability related to the sale of future royalties December 31, 2019 $ 315,369 Non-cash collaboration royalty revenue ( 12,995 ) Non-cash interest expense 33,291 December 31, 2020 335,665 Non-cash collaboration royalty revenue ( 13,210 ) Non-cash interest expense 25,618 September 30, 2021 $ 348,073

Stock-Based Awards (Tables)

Stock-Based Awards (Tables)	9 Months Ended
	Sep. 30, 2021
Share-based Payment Arrangement [Abstract]
Summary of Stock-Based Compensation Expense	The table below sets forth the stock-based compensation expense for the periods presented (in thousands): Three Months Ended Nine Months Ended 2021 2020 2021 2020 Cost of sales $ 160 $ 133 $ 762 $ 313 Research and development 15,366 11,533 43,949 35,318 Selling, general and administrative 11,464 8,675 33,719 27,291 Total stock-based compensation expense $ 26,990 $ 20,341 $ 78,430 $ 62,922

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Outstanding Shares of Common Stock Equivalents Excluded from Computation of Diluted Net Loss per Share	The following weighted-average outstanding common stock equivalents were excluded from the computation of diluted net loss per share for the periods presented because including them would have been antidilutive: Three Months Ended Nine Months Ended 2021 2020 2021 2020 Options to purchase common stock and 8,287,010 8,627,419 8,287,394 8,637,904 Employee stock purchase plan 30,196 35,282 16,923 19,701 Common stock warrants — — — 39,337 8,317,206 8,662,701 8,304,317 8,696,942

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Tables)	9 Months Ended
	Sep. 30, 2021
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Schedule of Total Accumulated Other Comprehensive Income	Total accumulated other comprehensive income consisted of the following (in thousands): September 30, December 31, 2021 2020 Foreign currency translation adjustments $ 81 $ 429 Unrealized gain (loss) on available-for-sale securities ( 27 ) 260 Total accumulated other comprehensive income $ 54 $ 689

Organization - Additional Infor

Organization - Additional Information (Details)	9 Months Ended
	Sep. 30, 2021Segment
United States of America
Organization And Nature Of Business [Line Items]
Number of reportable segments	1

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Summary of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Cash and cash equivalents	$ 197,538	$ 713,526	$ 197,486
Restricted cash included in prepaid expenses and other current assets	$ 10,000		$ 847
Restricted Cash and Cash Equivalents, Current, Asset, Statement of Financial Position [Extensible List]	Prepaid expenses and other current assets		Prepaid expenses and other current assets
Restricted cash included in other assets	$ 2,001		$ 1,921
Restricted Cash and Cash Equivalents, Noncurrent, Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherNoncurrentAssetsMember		us-gaap:OtherNoncurrentAssetsMember
Total cash, cash equivalents, and restricted cash shown in the statements of cash flows	$ 209,539	$ 726,294	$ 200,254	$ 436,244

Financial Instruments - Summary

Financial Instruments - Summary of Financial Assets Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	$ 1,004,715	$ 1,327,662
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	218,707	921,115
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	786,008	406,547
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	133,111	598,392
Money Market Funds | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	133,111	598,392
Asset-backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	44,457	11,225
Asset-backed Securities | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	44,457	11,225
Certificate of Deposits and Time Deposits
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	17,501
Certificate of Deposits and Time Deposits | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	17,501
Corporate Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	324,055	193,802
Corporate Bonds | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	324,055	193,802
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	308,825	173,859
Commercial Paper | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	308,825	173,859
U.S. Government Treasury and Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	62,003	185,628
U.S. Government Treasury and Agency Securities | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value		167,967
U.S. Government Treasury and Agency Securities | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	62,003	17,661
Debt Securities in Government Sponsored Entities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	28,680
Debt Securities in Government Sponsored Entities | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	28,680
Investments in Arcturus and Solid Common Stock
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	85,596	154,756
Investments in Arcturus and Solid Common Stock | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	85,596	154,756
Time Deposits
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value		10,000
Time Deposits | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value		$ 10,000
Other
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	487
Other | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	$ 487

Financial Instruments - Additio

Financial Instruments - Additional Information (Details) - Convertible Promissory Note - USD ($)	1 Months Ended			9 Months Ended
	Oct. 31, 2021	Dec. 31, 2020	Jul. 31, 2020	Sep. 30, 2021
Schedule Of Available For Sale Securities [Line Items]
Investment amount			$ 2,500,000
Debt instrument maturity period			2 years
Debt instrument, face amount				$ 2,300,000
Interest receivable				400,000
Allocated fair value of warrant				600,000
Mahzi Therapeutics, Inc.
Schedule Of Available For Sale Securities [Line Items]
Investment amount		$ 1,400,000
Debt instrument maturity period		2 years
Debt instrument, face amount				$ 1,500,000
Mahzi Therapeutics, Inc. | Preferred Stock | Subsequent Event
Schedule Of Available For Sale Securities [Line Items]
Debt conversion, converted instrument, shares issued	606,506
Maximum | Dia Carta Ltd
Schedule Of Available For Sale Securities [Line Items]
Warrants issued to purchase preferred stock			$ 1,000,000

Balance Sheet Components - Summ

Balance Sheet Components - Summary of Cash Equivalents and Investments Classified as Available For Sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 918,659	$ 1,172,646
Gross Unrealized Gains	96	277
Gross Unrealized Losses	(123)	(17)
Estimated Fair Value	918,632	1,172,906
Money Market Funds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	133,111	598,392
Estimated Fair Value	133,111	598,392
Asset-backed Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	44,445	11,224
Gross Unrealized Gains	19	1
Gross Unrealized Losses	(7)
Estimated Fair Value	44,457	11,225
Certificate of Deposits and Time Deposits
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	17,501
Estimated Fair Value	17,501
Corporate Bonds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	324,109	193,610
Gross Unrealized Gains	55	209
Gross Unrealized Losses	(109)	(17)
Estimated Fair Value	324,055	193,802
Commercial Paper
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	308,824	173,859
Gross Unrealized Gains	1
Estimated Fair Value	308,825	173,859
U.S. Government Treasury and Agency Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	61,987	185,561
Gross Unrealized Gains	18	67
Gross Unrealized Losses	(2)
Estimated Fair Value	62,003	185,628
Debt Securities in Government Sponsored Entities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	28,682
Gross Unrealized Gains	3
Gross Unrealized Losses	(5)
Estimated Fair Value	$ 28,680
Time Deposits
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		10,000
Estimated Fair Value		$ 10,000

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Schedule Of Available For Sale Securities [Line Items]
Significant realized gains or losses on available-for-sale securities	$ 0	$ 0	$ 0	$ 0
Maximum
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale securities remaining contractual maturities			4 years

Balance Sheet Components - Su_2

Balance Sheet Components - Summary of Inventory (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Work-in-process	$ 9,546	$ 7,184
Finished goods	5,645	5,864
Total inventory	$ 15,191	$ 13,048

Balance Sheet Components - Accr

Balance Sheet Components - Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Research, clinical study, and manufacturing expenses	$ 22,258	$ 25,875
Payroll and related expenses	55,164	58,176
Other	32,238	24,440
Total accrued liabilities	$ 109,660	$ 108,491

Revenue - Summary of Disaggrega

Revenue - Summary of Disaggregation of Total Revenues from Customers (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Total revenues
Total revenues	$ 81,647	$ 81,470	$ 268,017	$ 179,488
Collaboration and License
Total revenues
Total revenues	55,048	66,924	197,998	144,300
Collaboration and License | Crysvita
Total revenues
Total revenues	42,971	34,058	120,987	91,079
Collaboration and License | Royalty Revenue in European Territory | Crysvita
Total revenues
Total revenues	16		244	1,498
Collaboration and License | Daiichi Sankyo
Total revenues
Total revenues	12,061	32,866	76,767	51,723
Product Sales
Total revenues
Total revenues	21,950	11,215	56,809	25,760
Product Sales | Crysvita
Total revenues
Total revenues	7,378	3,277	16,150	7,436
Product Sales | Mepsevii
Total revenues
Total revenues	3,918	4,076	12,924	11,686
Product Sales | Dojolvi
Total revenues
Total revenues	10,654	3,862	27,735	6,638
Non-cash Collaboration Royalty Revenue
Total revenues
Total revenues	4,649	3,331	13,210	9,428
Non-cash Collaboration Royalty Revenue | Crysvita
Total revenues
Total revenues	$ 4,649	$ 3,331	$ 13,210	$ 9,428

Revenue - Summary of Disaggre_2

Revenue - Summary of Disaggregation of Total Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation Of Revenue [Line Items]
Total revenues	$ 81,647	$ 81,470	$ 268,017	$ 179,488
North America
Disaggregation Of Revenue [Line Items]
Total revenues	66,911	72,651	230,220	154,939
Europe
Disaggregation Of Revenue [Line Items]
Total revenues	7,244	5,002	19,581	15,707
Latin America
Disaggregation Of Revenue [Line Items]
Total revenues	$ 7,492	$ 3,817	$ 18,216	$ 8,842

Revenue - Summary of Changes in

Revenue - Summary of Changes in Contract Assets (Liabilities) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Abstract]
Balance of contract liabilities at beginning of period	$ (66,568)
Additions	(2,390)	$ (154,621)
Deductions	76,767	51,723
Balance of contract assets (liabilities) at end of period	$ 7,809	$ (102,898)

Revenue - Additional Informatio

Revenue - Additional Information (Details)	Sep. 30, 2021	Dec. 31, 2020
Disaggregation of Revenue [Abstract]
Percentage of gross accounts receivable balance	57.00%	71.00%

License and Research Agreemen_3

License and Research Agreements - Additional Information (Details)	Jan. 01, 2023	Aug. 31, 2021USD ($)$ / sharesshares	Jan. 31, 2021USD ($)	Dec. 31, 2020USD ($)$ / sharesshares	Oct. 31, 2020USD ($)shares	May 31, 2020USD ($)$ / sharesshares	Mar. 31, 2020USD ($)	Aug. 31, 2019USD ($)	Jun. 30, 2019USD ($)DiseaseTarget$ / sharesshares	Oct. 31, 2015USD ($)	Sep. 30, 2021USD ($)$ / sharesshares	Mar. 31, 2021USD ($)	Sep. 30, 2020USD ($)	Mar. 31, 2020USD ($)shares	Sep. 30, 2021USD ($)qtr$ / sharesshares	Sep. 30, 2020USD ($)shares	Dec. 31, 2020USD ($)$ / sharesshares	Dec. 31, 2022
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue											$ 81,647,000		$ 81,470,000		$ 268,017,000	$ 179,488,000
Research and development											$ 113,417,000		87,314,000		$ 374,140,000	280,984,000
Common stock, shares issued | shares				66,818,520							67,961,963				67,961,963		66,818,520
Proceeds from issuance of common stock in connection with license agreement																55,268,000
Issuance of common stock in connection with license agreement, net of issuance costs																55,268,000
Common stock investment value				$ 67,000							$ 68,000				$ 68,000		$ 67,000
Daiichi Sankyo
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue				66,600,000							66,600,000				66,600,000		66,600,000
Revenue recognized											12,100,000		32,900,000		76,800,000	$ 51,700,000
Receivable related to Daiichi Sankyo license agreement				1,200,000							400,000				400,000		1,200,000
Solid Biosciences, Inc.
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Business acquisition, consideration transferred																	40,000,000
Common stock investment value					$ 26,800,000
Remaining consideration paid																	13,200,000
Common Stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Issuance of common stock in connection with license agreement, net of issuance costs, shares | shares																1,243,913
Issuance of common stock in connection with license agreement, net of issuance costs																$ 1,000
Common Stock | Solid Biosciences, Inc.
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Unrealized gain (loss)											(9,900,000)				(40,600,000)
Prepaid Expenses and Other Current Assets | Daiichi Sankyo
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract assets											7,800,000				7,800,000
Product Sales
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue											21,950,000		11,215,000		56,809,000	25,760,000
License and Collaboration Agreement | Mereo
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment for in-process research and development expense												$ 50,000,000
Payments made under agreement			$ 50,000,000
License and Collaboration Agreement | Maximum | Mereo
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future contingent milestone payments			$ 254,000,000
Kyowa Kirin Collaboration | License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue															200,000	1,500,000
Kyowa Kirin Collaboration | License Agreement | Prepaid Expenses and Other Current Assets
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License agreement other receivables				9,600,000							3,700,000				3,700,000		9,600,000
Kyowa Kirin Collaboration | License Agreement | Product Sales
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue											7,400,000		3,300,000		16,200,000	7,400,000
Kyowa Kirin Collaboration | License Agreement | Profit Share Revenue
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License agreement accounts receivable				16,400,000							14,400,000				14,400,000		16,400,000
Kyowa Kirin Collaboration | License Agreement | Commercial and Development Activity Reimbursements
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License agreement accrued liabilities				$ 2,400,000							3,100,000				$ 3,100,000		$ 2,400,000
Kyowa Kirin Collaboration | License Agreement | Scenario Forecast
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Profit loss sharing percentage on net sales	30.00%																	35.00%
Kyowa Kirin Collaboration | License Agreement | Profit Share Territory
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Remaining profit or loss share percentage on commercializing products															50.00%
Tiered double-digit revenue share percentage entitled to receive															20.00%
Kyowa Kirin Collaboration | License Agreement | Royalty Revenue in European Territory
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of royalty on net sales receives															10.00%
Research, Develop and Commercialize AAV Gene Therapy Products | Bayer HealthCare LLC
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments received															$ 15,000,000
Research, Develop and Commercialize AAV Gene Therapy Products | Bayer HealthCare LLC | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future contingent milestone payments											232,000,000				232,000,000
Arcturus
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development									$ 6,000,000		$ 0		0		$ 0	0
Additional option to purchase common stock | shares									600,000
Additional option to purchase common stock value per share | $ / shares									$ 16
Number of shares purchased on exercise of common stock option | shares						600,000
Option exercise price | $ / shares						$ 16
Purchase price of shares purchased on exercise of common stock option						$ 9,600,000
Common stock shares sold | shares		800,000		800,000
Common stock. per share | $ / shares		$ 54.54		$ 100.81					$ 10								$ 100.81
Net proceeds from sale of common stock		$ 43,200,000		$ 79,800,000
Common stock, shares issued | shares									2,400,000
Number of common stock held | shares											1,400,000				1,400,000
Business acquisition, consideration transferred									$ 30,000,000
Arcturus | Common Stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Unrealized gain (loss)											$ 35,600,000		$ (11,500,000)		$ 14,700,000	$ 91,300,000
Realized gain (loss)											35,600,000				$ 14,700,000
Arcturus | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of disease targets | DiseaseTarget									12
Development milestone payment										$ 24,500,000
Regulatory milestone payment										24,500,000
Commercial milestone payment										$ 45,000,000
Program Agreement and Unitholder Option Agreement | GeneTx Biotherapeutics LLC
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development														$ 25,000,000
Upfront payment for exclusive option to acquisition								$ 20,000,000
Business acquisition option exercise period, description															the Company made an upfront payment of $20.0 million for an exclusive option to acquire GeneTx, which was exercisable any time prior to 30 days following FDA acceptance of the IND for GTX-102.
Option extension Premium								25,000,000
Business acquisition, consideration transferred								$ 125,000,000
Exercise of option extension, right to acquire condition															The Company has the right to acquire GeneTx for a payment of $125.0 million, at any time, until the earlier of 30 months from the first dosing of a patient in a planned Phase 1/2 study (subject to extensions) or 90 days after results are available from that study.
Program Agreement and Unitholder Option Agreement | GeneTx Biotherapeutics LLC | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Extension period available for right to acquisition | qtr															4
License Agreement | REGENXBIO, Inc.
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment for in-process research and development expense							$ 7,000,000
Annual fees payable														100,000
License Agreement | REGENXBIO, Inc. | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future contingent milestone payments							$ 14,000,000							$ 14,000,000
License and Technology Access Agreement | Daiichi Sankyo
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received															$ 125,000,000
Deferred revenue											25,000,000				25,000,000
Premium from stock purchase agreement															19,700,000
Transaction price of license agreement															183,500,000
Estimated reimbursement of delivering license and technology services															5,700,000
License and Technology Access Agreement | PCL and HEK293 Platform | Daiichi Sankyo
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue											$ 25,000,000				25,000,000
License and Technology Access Agreement | License Agreement | Daiichi Sankyo
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized															166,000,000
Stock Purchase Agreement | Daiichi Sankyo
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Issuance of common stock in connection with license agreement, net of issuance costs, shares | shares														1,243,913
Proceeds from issuance of common stock in connection with license agreement														$ 75,000,000
Issuance of common stock in connection with license agreement, net of issuance costs															$ 55,300,000
Stock price | $ / shares											$ 44.43				$ 44.43
Premium from stock purchase agreement															$ 19,700,000
Sublicense Agreement | Daiichi Sankyo
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received															$ 8,000,000
Collaboration and License Agreement | Maximum | Solid Biosciences, Inc.
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development milestone payment					25,000,000
Regulatory milestone payment					65,000,000
Commercial milestone payment					$ 165,000,000
Collaboration Agreement | Solid Biosciences, Inc.
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of common stock purchased | shares					7,825,797
Aggregate purchase price					$ 40,000,000

License and Research Agreemen_4

License and Research Agreements - Share of Collaboration and Royalty Revenue Related to Crysvita (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	$ 81,647	$ 81,470	$ 268,017	$ 179,488
Collaboration and Royalty | Kyowa Kirin Collaboration
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	47,636	37,389	134,441	102,005
Collaboration and Royalty | Kyowa Kirin Collaboration | Profit Share Territory
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	42,971	34,058	120,987	91,079
Collaboration and Royalty | Kyowa Kirin Collaboration | Royalty Revenue in European Territory
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	16		244	1,498
Non-cash Collaboration Royalty Revenue
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	4,649	3,331	13,210	9,428
Non-cash Collaboration Royalty Revenue | Kyowa Kirin Collaboration | Royalty Revenue in European Territory
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	$ 4,649	$ 3,331	$ 13,210	$ 9,428

License and Research Agreemen_5

License and Research Agreements - Schedule of Cost Sharing Payments (Details) - Kyowa Kirin Collaboration - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Cost Sharing Payments [Line Items]
Research and development	$ 5,161	$ 5,156	$ 16,517	$ 15,814
Selling, general and administrative	8,005	5,492	23,076	18,509
Total	$ 13,166	$ 10,648	$ 39,593	$ 34,323

License and Research Agreemen_6

License and Research Agreements - Schedule of Changes in Fair Value of Equity Investment (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock, Beginning balance	$ 1,327,662
Common stock, Ending balance	1,004,715	$ 1,327,662
Arcturus
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Fair value of option to purchase additional shares of common stock, Beginning balance		1,664
Fair value of option to purchase additional shares of common stock, Change in fair value		23,948
Fair value of option to purchase additional shares of common stock, Transfer of value upon option exercise		(25,612)
Common stock, Beginning balance	95,436	27,752
Common stock, Change in fair value	14,653	137,926
Common stock, Transfer of value upon option exercise		9,600
Common stock, Sale of shares	(43,197)	(79,842)
Common stock, Ending balance	66,892	95,436
Arcturus | Common Stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock, Beginning balance	95,436	26,088
Common stock, Change in fair value	14,653	113,978
Common stock, Transfer of value upon option exercise		35,212
Common stock, Sale of shares	(43,197)	(79,842)
Common stock, Ending balance	$ 66,892	$ 95,436

License and Research Agreemen_7

License and Research Agreements - Schedule of Changes in Fair Value of Investment in Securities (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Dec. 31, 2020	Sep. 30, 2021
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock, Beginning balance		$ 1,327,662
Common stock, Ending balance	$ 1,327,662	1,004,715
Common Stock | Solid Biosciences, Inc.
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock, Beginning balance		59,320
Common stock, Acquisition of investment in securities	26,843
Common stock, Change in fair value	32,477	(40,616)
Common stock, Ending balance	$ 59,320	$ 18,704

Liability Related to the Sale_3

Liability Related to the Sale of Future Royalties - Additional Information (Details) - Royalty Purchase Agreement - RPI Finance Trust (RPI) - USD ($)	1 Months Ended	9 Months Ended
	Dec. 31, 2019	Sep. 30, 2021
Liability Related To Sale Of Future Royalties [Line Items]
Proceeds from sale of future royalties	$ 320,000,000
Royalty payment termination description		The agreement with RPI will automatically terminate, and the payment of royalties to RPI will cease, in the event aggregate royalty payments received by RPI are equal to or greater than $608.0 million prior to December 31, 2030, or in the event aggregate royalty payments received by RPI are less than $608.0 million prior to December 31, 2030, when aggregate royalty payments received by RPI are equal to $800.0 million.
Royalties transaction costs net	5,800,000
Proceeds from the sale of future royalties, net	314,200,000
Effective annual interest rate		9.90%
Minimum
Liability Related To Sale Of Future Royalties [Line Items]
Royalty agreement termination threshold amount	608,000,000
Maximum
Liability Related To Sale Of Future Royalties [Line Items]
Royalty agreement termination threshold amount	$ 800,000,000

Liability Related to the Sale_4

Liability Related to the Sale of Future Royalties - Schedule of Activity Within Liability Related to Sale of Future Royalties (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Deferred Revenue Disclosure [Abstract]
Liability related to the sale of future royalties at beginning of year			$ 335,665	$ 315,369	$ 315,369
Non-cash collaboration royalty revenue			(13,210)	(9,428)	(12,995)
Non-cash interest expense	$ 8,683	$ 8,582	25,618	$ 25,093	33,291
Liability related to the sale of future royalties at end of year	$ 348,073		$ 348,073		$ 335,665

Stock-Based Awards - Additional

Stock-Based Awards - Additional Information (Details)	9 Months Ended
	Sep. 30, 2021shares
2014 Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share reserved for future issuance	4,086,908
Automatic increases in shares available for grant effective date	Jan. 1, 2015
Shares available for grant, ending date	Jan. 1, 2024
2014 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share reserved for future issuance	3,956,907
Employment Inducement Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share reserved for future issuance	468,963

Stock-Based Awards - Summary of

Stock-Based Awards - Summary of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 26,990	$ 20,341	$ 78,430	$ 62,922
Cost of sales
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	160	133	762	313
Research and development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	15,366	11,533	43,949	35,318
Selling, general and administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 11,464	$ 8,675	$ 33,719	$ 27,291

Net Loss Per Share - Outstandin

Net Loss Per Share - Outstanding Shares of Common Stock Equivalents Excluded from Computation of Diluted Net Loss per Share (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	8,317,206	8,662,701	8,304,317	8,696,942
Options to Purchase Common Stock and Restricted Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	8,287,010	8,627,419	8,287,394	8,637,904
Common Stock Warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share				39,337
Employee Stock Purchase Plan
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	30,196	35,282	16,923	19,701

Equity Transactions - Additiona

Equity Transactions - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		9 Months Ended	12 Months Ended
	May 31, 2021	Oct. 31, 2020	Sep. 30, 2021	Dec. 31, 2020
Underwritten Public Offering
Stockholders Equity [Line Items]
Common stock shares sold		5,111,110
Shares purchased by underwriters		666,666
Public offering price		$ 90
Net proceeds from sale of common stock				$ 435.6
Open Market Sale
Stockholders Equity [Line Items]
Common stock shares sold			0
Option to sell common stock aggregate offering price	$ 350

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income - Schedule of Total Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Foreign currency translation adjustments	$ 81	$ 429
Unrealized gain (loss) on available-for-sale securities	(27)	260
Total accumulated other comprehensive income	$ 54	$ 689