Ultragenyx Pharmaceutical (RARE) 10-K 21 Feb 24 2023 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2023	Feb. 15, 2024	Jun. 30, 2023
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2023
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Trading Symbol	RARE
Entity Registrant Name	Ultragenyx Pharmaceutical Inc.
Entity Central Index Key	0001515673
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Document Financial Statement Error Correction [Flag]	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		82,335,687
Entity Public Float			$ 3.1
Security Exchange Name	NASDAQ
Title of 12(b) Security	Common Stock, $0.001 par value
Entity File Number	001-36276
Entity Incorporation, State or Country Code	DE
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
Document Annual Report	true
Document Transition Report	false
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the registrant’s definitive proxy statement relating to its 2024 Annual Meeting of Stockholders, to be held on or about June 18, 2024, are incorporated by reference into Part III of this Annual Report on Form 10-K where indicated. Such proxy statement will be filed with the U.S. Securities and Exchange Commission within 120 days after the end of the fiscal year to which this report relates.
Auditor Firm ID	42
Auditor Name	Ernst & Young LLP
Auditor Location	San Mateo, California

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 213,584	$ 132,944
Marketable debt securities	363,625	614,818
Accounts receivable, net	73,390	40,445
Inventory	33,969	26,766
Other assets	47,616	68,926
Total current assets	732,184	883,899
Property, plant, and equipment, net	290,566	259,726
Marketable debt securities	199,901	148,970
Intangible assets, net	166,271	160,105
Goodwill	44,406	44,406
Other assets	57,685	48,338
Total assets	1,491,013	1,545,444
Current liabilities:
Accounts payable	42,114	43,274
Accrued liabilities	196,486	204,678
Contract liabilities	0	1,479
Lease liabilities	12,595	11,779
Liabilities for sales of future royalties	29,242	0
Total current liabilities	280,437	261,210
Lease liabilities	30,574	19,814
Deferred tax liabilities	30,058	31,667
Liabilities for sales of future royalties	862,325	875,439
Other liabilities	12,205	4,820
Total liabilities	1,215,599	1,192,950
Commitments and contingencies (Notes 9 and 15)
Stockholders’ equity:
Preferred stock, par value of $0.001 per share - 25,000,000 shares authorized; nil outstanding in 2023 and in 2022	0	0
Common stock, par value of $0.001 per share - 250,000,000 shares authorized;outstanding - 82,315,590 in 2023 and 70,197,297 in 2022	82	70
Treasury stock, at cost, 9,559 in 2023 and nil in 2022	(432)	0
Deferred compensation obligation	432	0
Additional paid-in capital	3,662,346	3,140,019
Accumulated other comprehensive income (loss)	647	(6,573)
Accumulated deficit	(3,387,661)	(2,781,022)
Total stockholders’ equity	275,414	352,494
Total liabilities and stockholders’ equity	$ 1,491,013	$ 1,545,444

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	25,000,000	25,000,000
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	250,000,000	250,000,000
Common stock, shares outstanding	82,315,590	70,197,297
Treasury stock , shares	9,559	0

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Revenues:
Total revenues	$ 434,249	$ 363,329	$ 351,406
Operating expenses:
Cost of sales	45,209	28,320	16,008
Research and development	648,449	705,789	497,153
Selling, general and administrative	309,799	278,139	219,982
Total operating expenses	1,003,457	1,012,248	733,143
Loss from operations	(569,208)	(648,919)	(381,737)
Interest income	26,688	11,074	1,928
Change in fair value of equity investments	397	(19,299)	(42,063)
Non-cash interest expense on liabilities for sales of future royalties	(66,004)	(43,015)	(29,422)
Other expense	(337)	(1,566)	(1,687)
Loss before income taxes	(608,464)	(701,725)	(452,981)
Benefit from (provision for) income taxes	1,825	(5,696)	(1,044)
Net loss	$ (606,639)	$ (707,421)	$ (454,025)
Net loss per share, basic	$ (8.25)	$ (10.12)	$ (6.7)
Net loss per share, diluted	$ (8.25)	$ (10.12)	$ (6.7)
Shares used in computing net loss per share, Basic	73,543,862	69,914,225	67,795,540
Shares used in computing net loss per share, Diluted	73,543,862	69,914,225	67,795,540
Product sales
Revenues:
Total revenues	$ 180,413	$ 118,927	$ 77,017
Royalty revenue
Revenues:
Total revenues	182,652	21,692	17,951
Collaboration and license
Revenues:
Total revenues	$ 71,184	$ 222,710	$ 256,438

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Statement of Comprehensive Income [Abstract]
Net loss	$ (606,639)	$ (707,421)	$ (454,025)
Other comprehensive income (loss):
Foreign currency translation adjustments	239	(724)	(550)
Unrealized gain (loss) on available-for-sale securities	6,981	(4,445)	(1,543)
Other comprehensive income (loss):	7,220	(5,169)	(2,093)
Total comprehensive loss	$ (599,419)	$ (712,590)	$ (456,118)

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Treasury Stock	Deferred Compensation Obligation
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
Issuance of common stock in connection with at-the-market offering, net of issuance costs	78,943	$ 1	78,942
Issuance of common stock in connection with at-the-market offering, net of issuance costs, shares		1,050,372
Stock-based compensation	105,260		105,260
Issuance of common stock under equity plan awards, net of tax	40,101	$ 1	40,100
Issuance of common stock under equity plan awards, net of tax, shares		1,476,106
Other comprehensive income (loss)	(2,093)			(2,093)
Net loss	(454,025)				(454,025)
Ending balance at Dec. 31, 2021	922,561	$ 69	2,997,497	(1,404)	(2,073,601)
Ending balance, shares at Dec. 31, 2021		69,344,998
Stock-based compensation	131,710		131,710
Issuance of common stock under equity plan awards, net of tax	10,813	$ 1	10,812
Issuance of common stock under equity plan awards, net of tax, shares		852,299
Other comprehensive income (loss)	(5,169)			(5,169)
Net loss	(707,421)				(707,421)
Ending balance at Dec. 31, 2022	$ 352,494	$ 70	3,140,019	(6,573)	(2,781,022)
Ending balance, shares at Dec. 31, 2022	70,197,297	70,197,297
Issuance of common stock and pre-funded warrants in connection with underwritten public offering, net of issuance costs	$ 326,456	$ 10	326,446
Issuance of common stock in connection with at-the-market offering, net of issuance costs	$ 53,299	$ 1	53,298
Issuance of common stock and pre-funded warrants in connection with underwritten public offering, net of issuance costs,shares		9,833,334
Issuance of common stock in connection with at-the-market offering, net of issuance costs, shares	1,175,584	1,175,584
Stock-based compensation	$ 134,169		134,169
Issuance of common stock upon exercise of warrants and under equity plan awards, net of tax	8,415	$ 1	8,414
Issuance of common stock upon exercise of warrants and under equity plan awards, net of tax, shares		1,109,375
Deferred compensation						$ (432)	$ 432
Other comprehensive income (loss)	7,220			7,220
Net loss	(606,639)				(606,639)
Ending balance at Dec. 31, 2023	$ 275,414	$ 82	$ 3,662,346	$ 647	$ (3,387,661)	$ (432)	$ 432
Ending balance, shares at Dec. 31, 2023	82,315,590	82,315,590

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating activities:
Net loss	$ (606,639)	$ (707,421)	$ (454,025)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	135,227	130,377	104,952
Acquired in-process research and development	0	75,033	0
Amortization of premium (discount) on marketable debt securities, net	(12,842)	2,699	6,606
Depreciation and amortization	26,006	18,220	13,239
Change in fair value of equity investments	(397)	19,299	42,063
Non-cash collaboration royalty revenue	(69,364)	(21,692)	(17,951)
Non-cash interest expense on liabilities for sales of future royalties	66,004	43,015	29,422
Other	2,300	(230)	235
Changes in operating assets and liabilities:
Accounts receivable	(22,778)	(12,068)	(5,432)
Inventory	(6,930)	(9,701)	(3,117)
Other assets	15,325	3,798	(29,508)
Accounts payable, accrued, and other liabilities	2,380	87,442	32,313
Contract liabilities, net	(1,479)	(7,597)	(57,492)
Deferred tax liabilities	(1,619)	(1,639)	0
Net cash used in operating activities	(474,806)	(380,465)	(338,695)
Investing activities:
Purchase of property, plant, and equipment	(44,267)	(116,123)	(73,093)
Acquisition, net of cash acquired	0	(75,025)	0
Purchase of marketable debt securities	(526,382)	(614,735)	(1,012,187)
Proceeds from sale of marketable debt securities	50,672	84,275	92,896
Proceeds from sale of equity investments	0	10,094	79,843
Proceeds from maturities of marketable debt securities	695,525	450,706	718,111
Payment for intangible asset	(2,500)	(30,000)	0
Other	(5,048)	(844)	(942)
Net cash provided by (used in) investing activities	168,000	(291,652)	(195,372)
Financing activities:
Proceeds from the sale of future royalties, net	0	490,950	0
Proceeds from the issuance of common stock and pre-funded warrants in connection with underwritten public offerings, net of issuance costs	326,456	0	0
Proceeds from the issuance of common stock in connection with at-the-market offering, net of issuances costs	53,299	0	78,943
Proceeds from the issuance of common stock from exercise of warrants and equity plan awards, net	8,415	10,813	40,101
Other	(28)	(555)	(492)
Net cash provided by financing activities	388,142	501,208	118,552
Effect of exchange rate changes on cash	462	(1,075)	(1,194)
Net increase (decrease) in cash, cash equivalents, and restricted cash	81,798	(171,984)	(416,709)
Cash, cash equivalents, and restricted cash at beginning of year	137,601	309,585	726,294
Cash, cash equivalents, and restricted cash at end of year	219,399	137,601	309,585
Supplemental disclosures of non-cash investing and financing information:
Acquired lease liabilities arising from obtaining right-of-use assets and property, plant, and equipment	22,162	1,168	3,142
Costs of property and equipment included in accounts payable, accrued, and other liabilities	1,577	17,963	18,993
Non-cash interest expense on liabilities for sales of future royalties capitalized during the year into ending property, plant and equipment	$ 9,431	$ 11,380	$ 4,650

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pay vs Performance Disclosure
Net Income (Loss)	$ (606,639)	$ (707,421)	$ (454,025)

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Dec. 31, 2023 shares
Trading Arrangements, by Individual
Material Terms of Trading Arrangement	On November 10, 2023 , Corsee Sanders , Ph.D., a member of the Company’s Board of Directors , adopted a trading arrangement intended to satisfy the affirmative defense of Rule 10b5-1(c), to sell up to 2,322 shares of the Company’s common stock through July 12, 2024, subject to certain conditions. On December 7, 2023 , Matthew Fust , a member of the Company’s Board of Directors , adopted a trading arrangement intended to satisfy the affirmative defense of Rule 10b5-1(c), to sell up to 12,195 shares of the Company’s common stock through December 6, 2024, subject to certain conditions.
Corsee Sanders [Member]
Trading Arrangements, by Individual
Name	Corsee Sanders
Title	member of the Company’s Board of Directors
Rule 10b5-1 Arrangement Adopted	true
Adoption Date	November 10, 2023
Aggregate Available	2,322
Matthew Fust [Member]
Trading Arrangements, by Individual
Name	Matthew Fust
Title	member of the Company’s Board of Directors
Rule 10b5-1 Arrangement Adopted	true
Adoption Date	December 7, 2023
Aggregate Available	12,195

Organization and Basis of Prese

Organization and Basis of Presentation	12 Months Ended
	Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Basis of Presentation	1. Organizat ion and Basis of Presentation Ultragenyx Pharmaceutical Inc., or 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 ultrarare genetic diseases. The Company operates as one reportable segment and has four commercially approved products. Crysvita® (burosumab) is approved in the United States, or U.S., the European Union, or EU, and certain other regions for the treatment of X-linked hypophosphatemia, or XLH, in adult and pediatric patients one year of age and older. Crysvita is also approved in the U.S. and certain other regions for the treatment of fibroblast growth factor 23, or FGF23-related hypophosphatemia in tumor-induced osteomalacia, or TIO, associated with phosphaturic mesenchymal tumors that cannot be curatively resected or localized in adults and pediatric patients 2 years of age and older. Mepsevii® (vestronidase alfa) is approved in the U.S., the EU and certain other regions, as the first medicine for the treatment of children and adults with mucopolysaccharidosis VII, or MPS VII, also known as Sly syndrome. Dojolvi® (triheptanoin) is approved in the U.S. and certain other regions for the treatment of pediatric and adult patients severely affected by long-chain fatty acid oxidation disorders, or LC-FAOD. Evkeeza® (evinacumab) is approved in the U.S. and the European Economic Area, or EEA, for the treatment of homozygous familial hypercholesterolemia, or HoFH. The Company has exclusive rights to commercialize Evkeeza® (evinacumab) outside of the U.S. In addition to the approved products, the Company has the following ongoing clinical development programs: • UX111 (formerly ABO-102) is an AAV9 gene therapy product candidate for the treatment of patients with Sanfilippo syndrome type A, or MPS IIIA, a rare lysosomal storage disease; • DTX401 is an adeno-associated virus 8, or AAV8, gene therapy product candidate for the treatment of patients with glycogen storage disease type Ia, or GSDIa; • DTX301 is an AAV8 gene therapy product candidate in development for the treatment of patients with ornithine transcarbamylase, or OTC deficiency, the most common urea cycle disorder; • UX143 (setrusumab), which is subject to the Company ’ s collaboration agreement with Mereo BioPharma 3, or 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, or OI; • GTX-102 is an antisense oligonucleotide, or ASO 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.; and • UX701 is an adeno-associated virus 9, or AAV9, 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; 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. Through December 31, 2023 , 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 may need to raise additional capital to fully implement its business plans 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	12 Months Ended
	Dec. 31, 2023
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Consolidation The Consolidated Financial Statements include the accounts of Ultragenyx Pharmaceutical Inc. and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated. Use of Estimates The accompanying Consolidated Financial Statements have been prepared in accordance with U.S. generally accepted accounting principles, or GAAP. The preparation of the 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 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, revenue recognition, and the liabilities for sales 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 The Company considers all highly liquid investments with original maturities of three months or less from the date of purchase to be cash equivalents. Cash equivalents consist primarily of amounts invested in money market accounts. 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 Consolidated Balance Sheets that sum to the total of the same such amounts shown in the Consolidated Statements of Cash Flows (in thousands): December 31, 2023 2022 2021 Cash and cash equivalents $ 213,584 $ 132,944 $ 307,584 Restricted cash included in other current assets 2,008 862 — Restricted cash included in other non-current assets 3,807 3,795 2,001 Total cash, cash equivalents, and restricted cash $ 219,399 $ 137,601 $ 309,585 Marketable Debt Securities All marketable debt securities have been classified as “available-for-sale” and are carried at estimated fair value as determined based upon quoted market prices or pricing models for similar securities. Management determines the appropriate classification of its investments at the time of purchase and reevaluates such designation as of each balance sheet date. Investments with a maturity of one year or less from the balance sheet date are reported as current marketable debt securities and investments with a maturity of greater than one year from the balance sheet date are reported as non-current marketable debt securities. Unrealized gains and losses are excluded from earnings and are reported as a component of comprehensive loss. Realized gains and losses and declines in fair value judged to be other than temporary, if any, on available-for-sale securities are included in other income (expense). The cost of securities sold is based on the specific-identification method. Interest on investments is included in interest income. Equity Investments The Company records investments in equity securities, other than equity method investments, at fair market value, if the fair value is readily determinable. Equity securities with no readily determinable fair values are recorded using the measurement alternative of cost adjusted for observable price changes in orderly transactions for identical or similar investments of the same issuer less impairment, if any. Investments in equity securities are recorded in Equity investments on the Company's Consolidated Balance Sheets. Unrealized gains and losses are reported in Change in fair value of equity investments on the Company’s Consolidated Statements of Operations. The Company regularly reviews its non-marketable equity securities for indicators of impairment. Concentration of Credit Risk, Credit Losses, and Other Risks and Uncertainties Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash, cash equivalents, and investments. The Company’s cash, cash equivalents, and investments are held by financial institutions that management believes are of high credit quality. The Company’s investment policy limits investments to fixed income securities denominated and payable in U.S. dollars such as U.S. government obligations, money market instruments and funds, corporate bonds, commercial paper, and asset-backed securities and places restrictions on maturities and concentrations by type and issuer. Such deposits may, at times, exceed federally insured limits. The Company has not experienced any losses on its deposits of cash and cash equivalents and its accounts are monitored by management to mitigate risk. The Company is exposed to credit risk in the event of default by the financial institutions holding its cash and cash equivalents, corporate issuers, and other financial instruments, to the extent recorded in the Consolidated Balance Sheets. 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 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 allowance for losses on available-for-sale debt securities which were attributable to credit risk for the years ended December 31, 2023 and 2022. The Company is dependent on third-party manufacturers to supply products for research and development activities in its programs. In particular, the Company relies and expects to continue to rely on a small number of manufacturers to supply it with its requirements for the active pharmaceutical ingredients and formulated drugs related to these programs. These programs could be adversely affected by a significant interruption in the supply of active pharmaceutical ingredients and formulated drugs. Inventory The Company values inventory at the lower of cost and net realizable value and determines the cost of inventory using the average-cost method. The Company expenses costs associated with the manufacture of product candidates prior to regulatory approval. Inventories consist of currently approved products. The Company periodically reviews its inventories for excess amounts or obsolescence and writes down obsolete or otherwise unmarketable inventory to its estimated net realizable value. Management determines excess inventory based on expected future demand. Estimates related to future demand are sensitive to significant inputs and assumptions such as acceptance by patients and physicians and the availability of formulary coverage and adequate reimbursement from private third-party payers for the product. Property, Plant, and Equipment Property, plant, and equipment are stated at cost, less accumulated depreciation and amortization. Depreciation and amortization is computed using the straight-line method over the estimated useful lives of the respective assets. Depreciation and amortization begins when the asset is placed in service. Interest costs incurred during the construction of major capital projects are capitalized until the underlying asset is ready to be placed in service. Maintenance and repairs are charged to operations as incurred. Upon sale or retirement of assets, the cost and related accumulated depreciation or amortization are removed from the balance sheet and the resulting gain or loss, if any, is reflected in operations. See “Note 4. Balance Sheet Components” for further disclosure on the useful lives of property, plant, and equipment. Intangible Assets Finite-lived intangibles consist of contractual payments made for certain milestones achieved with collaboration partners. The contractual payments are recorded as intangible assets and are amortized over their estimated useful lives. The Company reviews its definite-lived intangible assets when events or circumstances may indicate that the carrying value of these assets is not recoverable and exceeds their fair value. The Company measures fair value based on the estimated future undiscounted cash flows associated with these assets in addition to other assumptions and projections that the Company deems to be reasonable and supportable. Indefinite-lived intangibles consist of acquired in-process research and development, or IPR&D. IPR&D assets represent capitalized incomplete research projects that the Company acquired through business combinations. Such assets are initially measured at their acquisition date fair values and are tested for impairment annually and whenever events or changes in circumstances indicate that the carrying amount may not be recoverable. When development of the project is complete, which generally occurs when regulatory approval to market a product is obtained, the associated assets will be deemed finite-lived and will be amortized over a period that best reflects the economic benefits provided by these assets. If it is determined that an intangible asset becomes impaired, the carrying value is written down to its fair value with the related impairment charge recognized in Consolidated Statements of Operations in the period in which the impairment occurs. The Company has not recorded any impairments of intangible assets to date. Goodwill Goodwill represents the excess of purchase price over fair value of net assets acquired in a business combination and is not amortized. Goodwill is subject to impairment testing at least annually during the fourth quarter or when a triggering event occurs that could indicate a potential impairment. If it is determined that the goodwill becomes impaired, the carrying value is written down to its fair value with the related impairment charge recognized in Consolidated Statements of Operations in the period in which the impairment occurs. The Company has not recorded any impairments of goodwill. Impairment of Long-Lived Assets The Company evaluates its long-lived assets, including property and equipment, for impairment whenever events or changes in circumstances indicate that the carrying value of these assets may not be recoverable. Recoverability of these assets is measured by comparison of the carrying amount of each asset to the future undiscounted cash flows expected to result from the use of the asset and its eventual disposition. If the asset is considered to be impaired, the amount of any impairment is measured as the difference between the carrying value and the fair value of the impaired asset. The Company has not recorded material impairment of any long-lived assets. Accruals of Research and Development Costs The Company records accruals for estimated costs of research, preclinical and clinical studies and manufacturing development. These costs are a significant component of the Company’s research and development expenses. A substantial portion of the Company’s ongoing research and development activities are conducted by third-party service providers, including contract research organizations. The Company accrues the costs incurred under its agreements with these third parties based on actual work completed in accordance with agreements established with these third parties. The Company determines the actual costs through obtaining information from external service providers as to the progress or stage of completion of the services and the agreed-upon fee to be paid for such services. Revenue Recognition 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 control is transferred 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 a material effect on earnings in the period of the adjustment. Collaboration, License, and Royalty Revenue The Company has certain license and collaboration agreements that are within the scope of Accounting Standards Codification, or 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 Consolidated Statements 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. The Company utilizes certain information from its collaboration partners to record collaboration revenue, 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 also records royalty revenues under certain of the Company’s license or collaboration agreements in exchange for license of intellectual property. The Company sold the right to receive certain royalty payments from net sales of Crysvita in certain territories to RPI Finance Trust, or RPI, an affiliate of Royalty Pharma, and to OCM LS23 Holdings LP, an investment vehicle for Ontario Municipal Employees Retirement System, or OMERS, as further described in “Note 10. Liabilities for Sales of Future Royalties.” The Company records the royalty revenue from the net sales of Crysvita in the applicable territories on a prospective basis as non-cash royalty revenue in the Consolidated Statements of Operations over the term of the applicable 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, or 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. Deferred Compensation Plan The Company maintains a nonqualified deferred compensation plan whereby certain employees and members of the board of directors are able to defer certain equity awards and other compensation. Amounts deferred are invested into shares of the Company's common stock, mutual funds, and other investment options. The plan complies with the provisions of Section 409A of the Internal Revenue Code. All of the various mutual funds held in the plan are classified as trading securities and recorded at fair value in other non-current assets in the Consolidated Balance Sheets with changes in fair value recognized as earnings in the period they occur. The short-term portion of the corresponding liability for the plan is included in accrued expenses. The long-term portion of the liability is included in other non-current liabilities in the Consolidated Balance Sheets. Certain equity awards deferred under the plan are required to be settled through the issuance of Company stock. These awards are recorded as treasury stock and deferred compensation obligation within stockholders’ equity. Leases Lease agreements are evaluated to determine whether an arrangement is or contains a lease in accordance with ASC 842, Leases . The Company determines if an arrangement includes a lease at inception. Right-of-use lease assets and lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term at the commencement date. The right-of-use lease asset includes any lease payments made and excludes lease incentives. Incremental borrowing rate is used in determining the present value of future payments. The Company applies a portfolio approach to the property leases to apply an incremental borrowing rate to leases with similar lease terms. The lease terms may include options to extend or terminate the lease. The Company recognizes the options to extend the lease as part of the right-of-use lease assets and lease liabilities only if it is reasonably certain that the option would be exercised. Lease expense for minimum lease payments is recognized on a straight-line basis over the non-cancelable lease term. The Company has elected to not separate lease and non-lease components. See “Note 9. Leases” for further disclosure. Comprehensive Loss Comprehensive loss is the change in stockholders’ equity from transactions and other events and circumstances other than those resulting from investments by stockholders and distributions to stockholders. The Company’s other comprehensive loss is comprised of unrealized gains and losses on investments in available-for-sale securities and foreign currency translation adjustments. Research and Development Research and development costs are expensed as incurred and consist of salaries and benefits, stock-based compensation expense, lab supplies and facility costs, as well as fees paid to other nonemployees and entities that conduct certain research and development activities on the Company’s behalf. Amounts incurred in connection with license agreements are also included in research and development expense. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are deferred. The deferred amounts are expensed as the related goods are delivered or the services are performed. Stock-Based Compensation Stock-based awards issued to employees, including stock options, performance stock options, or PSOs, restricted stock units, or RSUs, and performance stock units, or PSUs are recorded at fair value as of the grant date and recognized as expense on a straight-line basis over the employee’s requisite service period (generally the vesting period). PSOs and PSUs vest only if certain specified criteria are achieved and the employees’ continued service requirements are met; therefore, the expense recognition occurs when the likelihood of the PSOs and PSUs being earned is deemed probable. Stock compensation expense on awards expected to vest is recognized net of estimated forfeitures. Income Taxes The Company uses the liability method of accounting for income taxes. Under this method, deferred tax assets and liabilities are determined based on the differences between the financial reporting and the tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. The Company must then assess the likelihood that the resulting deferred tax assets will be realized. A valuation allowance is provided when it is more likely than not that some portion or all of a deferred tax asset will not be realized. Due to the Company’s lack of earnings history, the net deferred tax assets have been fully offset by a valuation allowance. In conjunction with the acquisition of Dimension Therapeutics, Inc., or Dimension, a deferred tax liability was recorded reflecting the tax impact of the difference between the book basis and tax basis of acquired IPR&D. Such deferred income tax liability is not used to offset deferred tax assets when analyzing the Company’s valuation allowance as the acquired IPR&D is considered to have an indefinite life until the Company completes or abandons development of the acquired IPR&D. The Company recognizes benefits of uncertain tax positions if it is more likely than not that such positions will be sustained upon examination based solely on their technical merits, as the largest amount of benefit that is more likely than not to be realized upon the ultimate settlement. The Company’s policy is to recognize interest and penalties related to the underpayment of income taxes as a component of income tax expense or benefit. To date, there have been no interest or penalties charged in relation to the unrecognized tax benefits. Foreign Currency Assets and liabilities of non-U.S. subsidiaries that operate in a local currency environment, where the local currency is the functional currency, are translated to U.S. dollars at exchange rates in effect at the balance sheet date, with the resulting translation adjustments directly recorded to a separate component of accumulated other comprehensive loss. Income and expense accounts are translated at average exchange rates for the period. Transactions which are not in the functional currency of the entity are remeasured into the functional currency and gains or losses resulting from the remeasurement recorded in other income (expense). Net Loss per Share Basic net loss per share is calculated by dividing the net loss by the weighted-average number of shares of common stock outstanding during the period, without consideration for common stock equivalents. Shares of common stock into which pre-funded warrants may be exercised are considered outstanding for the purposes of computing basic net loss per share because the shares may be issued for little or no consideration, are fully vested and are exercisable after the original issuance date. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive. In periods when we have incurred a net loss, options and warrants to purchase common stock are considered common stock equivalents, but have been excluded from the calculation of diluted net loss per share, as their effect is antidilutive.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2023
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements 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’s financial instruments consist of Level 1, Level 2, and Level 3 assets. Where quoted prices are available in an active market, securities are classified as Level 1. Money market funds and U.S. Government treasury bills are classified as Level 1. Level 2 assets consist primarily of corporate bonds, asset backed securities, commercial paper, U.S. Government Treasury and agency securities, and debt securities in government-sponsored entities based upon quoted market prices for similar movements in active markets, quoted prices for identical or similar instruments in markets that are not active and model-based valuation techniques for which all significant inputs are observable in the market or can be corroborated by observable market data for substantially the full term of the assets. Where applicable these models project future cash flows and discount the future amounts to a present value using market-based observable inputs obtained from various third-party data providers, including but not limited to, benchmark yields, interest rate curves, reported trades, broker/dealer quotes and reference data. The Company determines the fair value of its equity investments in Solid Biosciences, Inc., or 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): December 31, 2023 Level 1 Level 2 Level 3 Total Financial Assets: Money market funds $ 162,289 $ — $ — $ 162,289 Certificates of deposit and time deposits — 17,986 — 17,986 Corporate bonds — 215,166 — 215,166 Commercial paper — 20,620 — 20,620 Asset-backed securities — 2,712 — 2,712 U.S. Government Treasury and agency securities 57,437 259,605 — 317,042 Investment in Solid common stock 3,204 — — 3,204 Deferred compensation assets — 10,220 — 10,220 Total financial assets $ 222,930 $ 526,309 $ — $ 749,239 Financial Liabilities: Deferred compensation liabilities $ — $ 10,365 $ — $ 10,365 December 31, 2022 Level 1 Level 2 Level 3 Total Financial Assets: Money market funds $ 102,847 $ — $ — $ 102,847 Certificates of deposit and time deposits — 25,972 — 25,972 Corporate bonds — 427,598 — 427,598 Commercial paper — 135,393 — 135,393 Asset-backed securities — 11,980 — 11,980 U.S. Government Treasury and agency securities 27,645 129,345 — 156,990 Debt securities in government-sponsored entities — 15,855 — 15,855 Investment in Solid common stock 2,807 — — 2,807 Deferred compensation assets — 4,575 — 4,575 Total financial assets $ 133,299 $ 750,718 $ — $ 884,017 Financial Liabilities: Deferred compensation liabilities $ — $ 4,657 $ — $ 4,657 Deferred compensation assets are recorded at fair value in other non-current assets in the Consolidated Balance Sheets. There have been no significant gains or losses on deferred compensation assets for the periods presented. Deferred compensation liabilities consist of short-term liabilities of $ 0.2 million and nil as of December 31, 2023 and 2022 , respectively, included in accrued liabilities on the Consolidated Balance Sheets, and long-term liabilities of $ 10.1 million and $ 4.7 million as of December 31, 2023 and 2022 , respectively, included in other non-current liabilities on the Consolidated Balance Sheets.

Balance Sheet Components

Balance Sheet Components	12 Months Ended
	Dec. 31, 2023
Investments, Debt and Equity Securities [Abstract]
Balance Sheet Components	4. Balance Sheet Components Cash Equivalents and Marketable Debt Securities The fair values of cash equivalents and marketable debt securities classified as available-for-sale securities consisted of the following (in thousands): December 31, 2023 Gross Unrealized Amortized Gains Losses Estimated Money market funds $ 162,289 $ — $ — $ 162,289 Certificates of deposit and time deposits 17,986 — — 17,986 Corporate bonds 214,792 711 ( 337 ) 215,166 Commercial paper 20,620 — — 20,620 Asset-backed securities 2,715 — ( 3 ) 2,712 U.S. Government Treasury and agency securities 316,160 982 ( 100 ) 317,042 Total $ 734,562 $ 1,693 $ ( 440 ) $ 735,815 December 31, 2022 Gross Unrealized Amortized Cost Gains Losses Estimated Money market funds $ 102,847 $ — $ — $ 102,847 Certificates of deposit and time deposits 25,972 — — 25,972 Corporate bonds 432,211 87 ( 4,700 ) 427,598 Commercial paper 135,393 — — 135,393 Asset-backed securities 12,002 — ( 22 ) 11,980 U.S. Government Treasury and agency securities 157,933 320 ( 1,263 ) 156,990 Debt securities in government-sponsored entities 16,005 — ( 150 ) 15,855 Total $ 882,363 $ 407 $ ( 6,135 ) $ 876,635 At December 31, 2023 , the remaining contractual maturities of available-for-sale securities were less than three years . There have been no significant realized gains or losses on available-for-sale securities for the periods presented. Inventory Inventory consists of the following (in thousands): December 31, 2023 2022 Work-in-process $ 18,859 $ 17,486 Finished goods 15,110 9,280 Total inventory $ 33,969 $ 26,766 Property, Plant, and Equipment, net Property, plant, and equipment, net consists of the following (in thousands): December 31, Useful life (years) 2023 2022 Building 20 - 30 $ 181,356 $ 2,798 Leasehold improvements Shorter of lease term or 58,683 43,941 Research and development equipment 5 56,347 50,291 Furniture and office equipment 5 6,419 5,540 Computer equipment and software 3 - 5 16,196 13,876 Manufacturing equipment 5 - 15 37,297 570 Land Not applicable 16,619 16,619 Construction-in-progress Not applicable 867 189,448 Other Varies by asset 183 24 Property, plant, and equipment, gross 373,967 323,107 Less: accumulated depreciation ( 83,401 ) ( 63,381 ) Property, plant, and equipment, net $ 290,566 $ 259,726 Depreciation expense for the years ended December 31, 2023, 2022, and 2021 was $ 22.2 million, $ 15.0 million and $ 12.9 million, respectively. Amortization of leasehold improvements and software is included in depreciation expense. Construction in progress reflects amounts incurred for construction or improvements of property or costs for equipment that has not been placed in service. The construction-in-progress balance as of December 31, 2022 is primarily the construction costs for the gene therapy manufacturing facility in Bedford, Massachusetts. Accrued Liabilities Accrued liabilities consists of the following (in thousands): December 31, 2023 2022 Research, clinical study, and manufacturing expenses $ 65,326 $ 73,558 Payroll and related expenses 82,936 78,938 Other 48,224 52,182 Total accrued liabilities $ 196,486 $ 204,678

Intangible Assets, Net

Intangible Assets, Net	12 Months Ended
	Dec. 31, 2023
Intangible Assets, Net (Excluding Goodwill) [Abstract]
Intangible Assets, Net	5. Intangible Assets, net Indefinite-lived Intangibles The Company has IPR&D assets of $ 129.0 million as of December 31, 2023 and 2022. IPR&D assets represent the fair value of acquired programs to develop an AAV gene therapy for OTC deficiency and to develop an AAV gene therapy for glycogen storage disease type Ia. The fair value of IPR&D assets acquired was determined based on the discounted present value of each research project’s projected cash flows using an income approach, including the application of probability factors related to the likelihood of success of the program reaching final development and commercialization. Additionally, the projections consider the relevant market sizes and growth factors, estimated future cash flows from product sales resulting from completed products and in-process projects and timing and costs to complete the in-process projects. The rates utilized to discount the net cash flows to their present value are commensurate with the stage of development of the projects and uncertainties in the economic estimates used in the projections. IPR&D assets are considered to be indefinite-life until the completion or abandonment of the associated research and development efforts. Finite-lived Intangibles Subsequent to the FDA approval of Dojolvi for the treatment of LC-FAOD in 2020, the Company recorded $ 4.8 million for the attainment of various development and commercial milestones as finite-lived intangible assets which are amortized over a weighted-average useful life of 5.7 years. In January 2022, the Company announced a collaboration with Regeneron to commercialize Evkeeza for HoFH outside of the U.S. Upon closing of the transaction in January 2022, the Company paid Regeneron a $ 30.0 million upfront payment. During the year ended December 31, 2023, a $ 10.0 million regulatory milestone was achieved. As both the upfront payment and the regulatory milestone are related to the Company’s use of intellectual property for Evkeeza for HoFH, these amounts were recorded as intangible assets, which are amortized over a weighted-average useful life of ten years . The Company's intangible assets were as follows: December 31, 2023 Gross Carrying Amount Weighted-Average Life (Years) Accumulated Amortization Net Carrying Amount Indefinite-lived intangibles $ 129,000 — $ — $ 129,000 Finite-lived intangibles 44,775 9.6 ( 7,504 ) 37,271 Total intangible assets $ 173,775 — $ ( 7,504 ) $ 166,271 December 31, 2022 Gross Carrying Amount Weighted-Average Life (Years) Accumulated Amortization Net Carrying Amount Indefinite-lived intangibles $ 129,000 — $ — $ 129,000 Finite-lived intangibles 34,775 9.9 ( 3,670 ) 31,105 Total intangible assets $ 163,775 — $ ( 3,670 ) $ 160,105 The Company recorded costs of sales of $ 3.8 million, $ 3.2 million and $ 0.3 million for the years ended December 31, 2023, 2022, and 2021, respectively, related to the amortization of the intangible assets. The expected amortization of the intangible assets, as of December 31, 2023, for each of the next five years and thereafter is as follows: 2024 $ 4,903 2025 4,903 2026 4,903 2027 4,462 2028 4,022 Thereafter 14,078 Total $ 37,271

Revenue

Revenue	12 Months Ended
	Dec. 31, 2023
Revenue from Contract with Customer [Abstract]
Revenue	6. Revenue The following table disaggregates total revenues from external customers by product sales, royalty revenue, and collaboration and license revenue (in thousands): Year Ended December 31, 2023 2022 2021 Product sales: Crysvita $ 75,697 $ 42,678 $ 21,422 Mepsevii 30,441 20,637 16,035 Dojolvi 70,633 55,612 39,560 Evkeeza 3,642 — — Total product sales 180,413 118,927 77,017 Crysvita royalty revenue 182,652 21,692 17,951 Collaboration and license revenue: Crysvita collaboration revenue in Profit-Share Territory 69,705 215,024 171,198 Crysvita royalty revenue in European Territory — — 244 Daiichi Sankyo 1,479 7,686 84,996 Total collaboration and license revenue 71,184 222,710 256,438 Total revenues $ 434,249 $ 363,329 $ 351,406 The following table disaggregates total revenues based on geographic location (in thousands): Year Ended December 31, 2023 2022 2021 North America $ 307,149 $ 281,088 $ 301,110 Latin America 77,342 44,711 23,636 Europe 47,534 36,369 26,660 Japan 2,224 1,161 — Total revenues $ 434,249 $ 363,329 $ 351,406 The following table presents the activity and ending balances for sales-related accruals and allowances (in thousands): Year Ended December 31, 2023 2022 2021 Balance of product sales reserve at beginning of year $ 11,487 $ 7,181 $ 3,913 Provisions 18,761 13,525 9,586 Payments ( 12,746 ) ( 9,613 ) ( 6,120 ) Adjustments ( 473 ) 394 ( 198 ) Balance of product sales reserve at end of year $ 17,029 $ 11,487 $ 7,181 The following table presents changes in the contract liabilities for the years ended December 31, 2023 and 2022 (in thousands): Year Ended December 31, 2023 2022 Balance of contract liabilities at beginning of period $ 1,479 $ 9,076 Additions — 89 Deductions ( 1,479 ) ( 7,686 ) Balance of contract liabilities at end of period, net $ — $ 1,479 See Note 8 for additional details on contract liabilities activities. The Company’s largest accounts receivable balance was from a collaboration partner and was 53 % and 68 % of the total accounts receivable balance as of December 31, 2023 and 2022 , respectively.

GeneTx Acquisition

GeneTx Acquisition	12 Months Ended
	Dec. 31, 2023
Business Combinations [Abstract]
Acquisition	7. GeneTx Acquisition In August 2019, the Company entered into a Program Agreement and a Unitholder Option Agreement with GeneTx Biotherapeutics LLC, or GeneTx, to collaborate on the development of GeneTx’s GTX-102, an ASO for the treatment of Angelman syndrome. In July 2022, pursuant to the terms of the Unitholder Option Agreement, as amended, the Company exercised the option to acquire GeneTx and entered into a Unit Purchase Agreement, or the Purchase Agreement, pursuant to which the Company purchased all the outstanding units of GeneTx. In accordance with the terms of the Purchase Agreement, the Company paid the option exercise price of $ 75.0 million and an additional $ 15.6 million to acquire the outstanding cash of GeneTx, and adjustments for working capital and transaction expenses of $ 0.6 million, for a total purchase consideration of $ 91.2 million. The Company may be required to make payments of up to $ 190.0 million upon the achievement of certain milestones, including up to $ 30.0 million in milestone payments upon achievement of the earlier of initiation of a Phase 3 clinical study or product approvals in Canada and the U.K., up to $ 85.0 million in additional regulatory approval milestones for the achievement of U.S. and EU product approvals, and up to $ 75.0 million in commercial milestone payments based on annual worldwide net product sales. The Company will also pay tiered mid- to high single-digit percentage royalties based on licensed product annual net sales. If the Company receives and resells an FDA priority review voucher, or PRV, in connection with a new drug application approval, GeneTx is entitled to receive a portion of proceeds from the sale or a cash payment from the Company if the Company choses to retain the PRV. As part of the Company's acquisition of GeneTx, the Company assumed a License Agreement with Texas A&M University, or TAMU. Under this agreement, TAMU is eligible to receive from the Company up to $ 23.5 million upon the achievement of various future milestones, a nominal annual license fee that may increase up to a maximum of $ 2.0 million, as well as royalties in the mid-single-digits of net sales. The transaction was accounted as an asset acquisition, as substantially all of the fair value of the gross assets acquired was concentrated in a single identifiable in-process research and development intangible asset. Prior to the achievement of certain development and regulatory milestones, the acquired in-process research and development intangible asset has not yet reached technological feasibility and has no alternative future use. Accordingly, the Company recorded the acquisition price of $ 75.0 million, net of cash and working capital acquired, as in-process research and development expense during the year ended December 31, 2022.

License and Research Agreements

License and Research Agreements	12 Months Ended
	Dec. 31, 2023
Research Grant Agreement [Abstract]
License and Research Agreements	8. License and Research Agreements Kyowa Kirin Co., Ltd. In August 2013, the Company entered into a collaboration and license agreement with Kyowa Kirin Co., Ltd., or KKC. 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 U.S. 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. Development Activities In the field of orphan diseases, except for ongoing studies being conducted by KKC, the Company was the lead party for development activities in the Profit-Share Territory and in the European Territory until the applicable transition date. The Company shared 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 was the transition date for the Profit-Share Territory, KKC became the lead party and became responsible for the costs of the subsequent development activities. However, the Company will continue to equally share in the costs of the studies with KKC that commenced prior to the applicable transition date. The collaboration and license agreements are within the scope of ASC 808, which provides guidance on the presentation and disclosure of collaborative arrangements. Collaboration and Royalty Revenue for Sales in the Profit-Share Territory The Company and KKC shared commercial responsibilities and profits in the Profit-Share Territory until April 2023. Under the collaboration agreement, KKC manufactured and supplied Crysvita for commercial use in the Profit-Share Territory and charged the Company a transfer price of 30 % of net sales in 2023, and 35 % prior to December 31, 2022. The remaining profit or loss after supply costs from commercializing products in the Profit-Share Territory was shared between the Company and KKC on a 50 / 50 basis until April 2023. In April 2023, commercialization responsibilities for Crysvita in the Profit-Share Territory transitioned to KKC. Thereafter, the Company is entitled to receive a tiered double-digit revenue share from the mid- 20 % range up to a maximum rate of 30 %. In 2022, the Company entered into an amendment to the collaboration agreement which granted the Company the right to continue to support KKC in commercial field activities in the U.S. through April 2024, subject to the limitations and conditions set forth in the amendment. The parties subsequently mutually agreed to extend the Company's right to continue to support KKC in commercial field activities in the U.S. through December 31, 2024, and as a result, the Company will continue to support commercial field efforts in the U.S. through a cost share arrangement through December 2024. After December 31, 2024, the Company’s rights to promote Crysvita in the U.S. will be limited to medical geneticists and the Company will solely bear its expenses for the promotion of Crysvita in the Profit-Share Territory. As KKC was the principal in the sale transaction with the customer during the profit-share period, the Company recognized 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 prior to April 2023 was analogous to a royalty and therefore recorded its share as collaboration revenue, similar to a royalty. Starting in April 2023, the Company began to record the royalty revenue as the underlying sales occur. In July 2022, the Company sold to OMERS its right to receive 30 % of the future royalty payments due to the Company based on net sales of Crysvita in the U.S. and Canada, subject to a cap, beginning in April 2023, as further described in Note 10. The Company records this revenue as royalty revenue. Product Sales Revenue for 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 for the sale of Crysvita once the product is delivered and the risk and title of the product is transferred to the distributor. 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 Latin American territories and charges the Company a transfer price of 30 % of net sales. The transfer price on these sales was 35 % prior to December 31, 2022. The Company also pays to KKC a low single-digit royalty on net sales in Latin America. Total Crysvita revenue was as follows (in thousands): Year Ended December 31, 2023 2022 2021 Revenue in profit-share territory: Collaboration revenue $ 69,705 $ 215,024 $ 171,198 Royalty revenue 113,288 — — Non-cash royalty revenue 48,581 — — Total revenue in Profit-Share Territory 231,574 215,024 171,198 Product sales 75,697 42,678 21,422 Royalty revenue in European Territory — — 244 Non-cash royalty revenue in European Territories 20,783 21,692 17,951 Total Crysvita revenue $ 328,054 $ 279,394 $ 210,815 Royalty Revenue for Sales in the 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 10. 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 records the royalty revenue as non-cash royalty revenues. The Company records this revenue as royalty revenue. Collaboration Cost Sharing and Payments Under the collaboration agreement, KKC and the Company share certain development and commercialization costs and as a result, the Company was reimbursed for these costs and operating expenses were reduced. Additionally, KKC is owed a transfer price fee and royalties on certain revenues and the Company recorded amounts owed to KKC in cost of sales. These amounts were recognized in the Company’s Statements of Operations in connection with the collaboration agreement with KKC as follows (in thousands): Year Ended December 31, 2023 2022 2021 Research and development $ ( 6,510 ) $ ( 15,974 ) $ ( 21,657 ) Selling, general and administrative $ ( 17,199 ) $ ( 37,217 ) $ ( 32,629 ) Cost of sales $ 18,476 $ 13,250 $ 6,701 Collaboration Receivable and Payable The Company had accounts receivable from KKC in the amount of $ 39.2 million and $ 27.5 million from profit-share revenue and royalties and other receivables recorded in other current assets of $ 1.1 million and $ 6.4 million and accrued liabilities of $ 5.3 million and $ 3.1 million from commercial and development activity reimbursements, as of December 31, 2023 and 2022, respectively. Saint Louis University In November 2010, the Company entered into a license agreement with Saint Louis University, or SLU. Under the terms of this license agreement, SLU granted the Company an exclusive worldwide license to make, have made, use, import, offer for sale, and sell therapeutics related to SLU’s beta-glucuronidase product for use in the treatment of human diseases. The Company made a milestone payment of $ 0.1 million upon approval of Mepsevii for treatment of MPS 7. The Company is required to pay to SLU a low single-digit royalty on net sales of the licensed products in any country or region, upon reaching a certain level of cumulative worldwide sales of the product. Baylor Research Institute In September 2012, the Company entered into a license agreement with Baylor Research Institute, or BRI. Under the terms of this license agreement, as amended, BRI exclusively licensed to the Company its territories for certain intellectual property related to Dojolvi (triheptanoin) for the treatment of LC-FAOD. For the years ended December 31, 2023 and 2022 , the Company recorded nil and $ 2.5 million, respectively, for the attainment of various development and commercial milestones as finite-lived intangible assets. The Company is obligated to make additional future payments of up to $ 7.5 million contingent upon attainment of various development and commercial milestones. Additionally, the Company is paying BRI a mid- single-digit royalty on net sales of the licensed product in the licensed territories. REGENXBIO, Inc. The Company has a license agreement with REGENXBIO, Inc., or REGENX, for an exclusive, sublicensable, worldwide commercial license under certain intellectual property for preclinical and clinical research and development, and commercialization of drug therapies using REGENX's licensed patents for the treatment of hemophilia A, OTC deficiency, and GSD1a. The Company will pay an annual fee and certain milestone fees per disease indication, low to mid- single-digit royalty percentages on net sales of licensed products, and milestone and sublicense fees owed by REGENX to its licensors, contingent upon the attainment of certain development activities as outlined in the agreement. The Company also has an option and license agreement with REGENX under which the Company has an exclusive, sublicensable, worldwide license to make, have made, use, import, sell, and offer for sale licensed products to treat Wilson disease and CDKL5 deficiency. For each disease indication, the Company is obligated to pay an annual maintenance fee of $ 0.1 million and up to $ 9.0 million upon achievement of various milestones, as well as mid- to high single-digit royalties on net sales of licensed products and mid- single-digit to low double-digit percentage sublicenses fees, if any. In March 2020, the Company entered into a license agreement with REGENX, 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. The Company will 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. Bayer HealthCare LLC The Company previously had a collaboration and license agreement with Bayer Healthcare LLC, or Bayer, to research, develop and commercialize AAV gene therapy products for the treatment of hemophilia A, or DTX 201. Under this agreement, Bayer had been granted an exclusive license to develop and commercialize one or more novel gene therapies for hemophilia A. In October 2022, the Collaboration and License Agreement for DTX201 with Bayer was terminated and all licensed rights to DTX201 have reverted back to the Company. The Company also obtained rights to all necessary data and information to further develop DTX201 or another hemophilia A program through a royalty-free, worldwide, sublicensable, perpetual license. University of Pennsylvania The Company has a research, collaboration, and license agreement with University of Pennsylvania School of Medicine, or Penn, which provides the terms for the Company and Penn to collaborate with respect to the pre-clinical development of gene therapy products for the treatment of certain indications. Under the agreement, Penn granted the Company an exclusive, worldwide license to certain patent rights arising out of the research program, subject to certain retained rights, and a non-exclusive, worldwide license to certain Penn intellectual property, in each case to research, develop, make, have made, use, sell, offer for sale, commercialize and import licensed products in each indication for the term of the agreement. The Company will fund the cost of the research program in accordance with a mutually agreed-upon research budget and will be responsible for clinical development, manufacturing and commercialization of each indication. The Company may be obligated to make milestone payments of up to $ 5.0 million for each indication, if certain development milestones are achieved over time. The Company is also obligated to make milestone payments of up to $ 25.0 million per approved product if certain commercial milestones are achieved, as well as low to mid- single-digit royalties on net sales of each licensed product. Arcturus Therapeutics Holdings Inc. In October 2015, the Company entered into a Research Collaboration and License Agreement with Arcturus Therapeutics Holdings Inc., or Arcturus, to collaborate on the research and development of therapies for select rare diseases. Arcturus was responsible for conducting certain research services, funded by the Company, and the Company was responsible for development and commercialization costs. On a product-by-product basis, the Company is 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. For the year ended December 31, 2021, the Company achieved a $ 1.0 million development milestone, which was paid with a corresponding credit received from Arcturus for prior research and collaboration activities. The Company is also obligated to pay Arcturus royalties on any net sales of products incorporating the licensed intellectual property that may range from a mid- single-digit to low double-digit percentage. There were no material expenses for this arrangement during the years ended December 31, 2023, 2022, and 2021. In June 2019, the Company entered into an Equity Purchase Agreement and an amendment to the Research Collaboration and License Agreement, or 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 under the License Agreement, Arcturus common stock, and an option to purchase an additional 600,000 shares of Arcturus’ common stock at $ 16.00 per share. In May 2020, the Company exercised its option to purchase 600,000 shares of Arcturus common stock for a total purchase price of $ 9.6 million. The Company’s investment in Arcturus was accounted at fair value, as the fair value was readily determinable. During the year ended December 31, 2022, the Company sold 500,000 shares of Arcturus common stock, at a weighted-average price of $ 20.39 per share. As of December 31, 2022, the Company held no shares of Arcturus common stock. The changes in the fair value of the Company’s equity investment in Arcturus were as follows (in thousands): Arcturus Common Stock December 31, 2021 $ 18,505 Change in fair value ( 8,411 ) Sale of shares ( 10,094 ) December 31, 2022 $ — Daiichi Sankyo In March 2020, the Company executed a License and Technology Access Agreement, or the License Agreement, with Daiichi Sankyo Co., Ltd., or 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 Pinnacle PCL TM producer cell line platform, or Pinnacle PCL Platform, and HEK293 transient transfection manufacturing technology platforms for AAV-based gene therapy products. Under the terms of the License Agreement, Daiichi Sankyo made an upfront payment of $ 125.0 million and an additional $ 25.0 million upon completion of the technology transfer of the Pinnacle PCL Platform and HEK293 platform. Daiichi Sankyo reimbursed the Company for all costs associated with the transfer of the manufacturing technology. The Company also entered into a Stock Purchase Agreement, or 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. In June 2020, the Company executed a subsequent license agreement, or 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 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 Pinnacle PCL Platform and HEK293 transient transfection manufacturing technology platform together with the initial technical assistance and technology transfer services, 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. 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 was recognized over an initial period which was completed during the first quarter of 2022, 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 was recognized on a straight-line basis over the remaining technology transfer period, which ended in March 2023, as it was expected that Daiichi Sankyo would receive and consume the benefits consistently throughout the period. The Company’s current obligations under the License Agreement and the Sublicense Agreement were completed following the conclusion of the technology transfer period. Total revenue recognized under the arrangement through December 31, 2023 was $ 183.3 million. The Company recognized $ 1.5 million, $ 7.7 million, and $ 85.0 million for the years ended December 31, 2023, 2022, and 2021 , respectively, in revenue related to this arrangement. Accordingly, the Company recorded contract liabilities of nil and $ 1.5 million, net, for this arrangement as of December 31, 2023 and 2022, respectively. Mereo In December 2020, the Company entered into a License and Collaboration Agreement with 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 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. For the years ended December 31, 2023, 2022, and 2021 , the Company recorded research and development expense of $ 9.0 million for the achievement of a clinical milestone, nil , and $ 50.0 million for the upfront payment, respectively. Regeneron In January 2022, the Company announced a collaboration with Regeneron Pharmaceuticals, or Regeneron, to commercialize Evkeeza for HoFH outside of the U.S. Evkeeza is approved in the U.S., where it is marketed by Regeneron, and in the EU and U.K. as a first-in-class therapy for use together with diet and other low-density lipoprotein-cholesterol-lowering therapies to treat adults and adolescents aged 12 years and older with HoFH. Pursuant to the terms of the agreement, the Company received the rights to develop, commercialize and distribute the product for HoFH in countries outside of the U.S. The Company is obligated to pay up to $ 63.0 million in future milestone payments, contingent upon the achievement of certain regulatory and sales milestones. The Company may share in certain costs for global trials led by Regeneron and also received the right to opt into other potential indications. The collaboration agreement is within the scope of ASC 808 which provides guidance on the presentation and disclosure of collaborative arrangements. As the Company would be the principal in future sale transactions with the customer, the Company will recognize product sales and cost of sales in the period the related sales occur and the related revenue recognition criteria are met. Under the collaboration agreement, Regeneron supplies the product and charges the Company a transfer price from the low 20 % range up to 40 % on net sales, which is recognized as cost of sales in the Company’s Statement of Operations. The Company paid Regeneron a $ 30.0 million upfront payment upon the closing of the transaction in January 2022, and d uring the year ended December 31, 2023, a $ 10.0 million regulatory milestone was achieved. As these payments are for the Company’s use of intellectual property for Evkeeza for HoFH, they were recorded as intangible assets. See Note 5 for additional details. Under the collaboration agreement, the Company reimbursed Regeneron for development costs of $ 7.6 million, $ 7.3 million, and nil for the years ended December 31, 2023, 2022, and 2021, respectively, which were recorded as research and development expense on the Consolidated Statements of Operations. The Company had collaboration payables for this arrangement included in accrued liabilities on the Consolidated Balance Sheets of $ 10.6 million and $ 6.8 million as of December 31, 2023 and December 31, 2022, respectively. A dditionally, Regeneron is owed a transfer price fee and royalties on certain revenues and the Company recorded amounts owed to Regeneron of $ 0.7 million in cost of sales on the Consolidated Statements of Operations for the year ended December 31, 2023. Abeona In May 2022, the Company announced an exclusive License Agreement for the AAV gene therapy for UX111 with Abeona for the treatment of MPS IIIA. Under the terms of the agreement, the Company assumed responsibility for the UX111 program and in return, Abeona is eligible to receive tiered royalties of up to 10 % on net sales and commercial milestone payments of up to $ 30.0 million following regulatory approval of the product. Additionally, the Company entered into an Assignment and Assumption Agreement with Abeona to transfer and assign to the Company the exclusive license agreement between Nationwide Children’s Hospital, or NCH, and Abeona for certain rights related to UX111. Under this agreement, NCH is eligible to receive from the Company up to $ 1.0 million in development and regulatory milestones as well as royalties in the low single-digits of net sales. The Company is obligated to pay Abeona certain prior development costs and other transition costs related to UX111. Prior to product regulatory approval, all consideration paid to Abeona represents rights to potential future benefits associated with Abeona’s in-process research and development activities, which have not reached technological feasibility and have no alternative future use. Accordingly, the value of the acquired intellectual property rights and clinical inventory as well as prior development costs and transition costs of $ 3.1 million, were recorded as research and development expense for the year ended December 31, 2022. The Company did no t incur any other material costs related to this agreement in the years presented. Solid Biosciences, Inc. In October 2020, the Company entered into a strategic Collaboration and License Agreement with Solid Biosciences Inc., or 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 is collaborating to develop products that combine Solid’s differentiated microdystrophin construct, the Company’s Pinnacle PCL Platform, and the Company’s AAV8 variants. Solid is providing 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 is 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. In October 2022, Solid announced a 1 for 15 reverse stock split. After the split, the Company held 521,719 shares of Solid's common stock. 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 December 31, 2021 $ 13,695 Change in fair value ( 10,888 ) December 31, 2022 2,807 Change in fair value 397 December 31, 2023 $ 3,204

Leases

Leases	12 Months Ended
	Dec. 31, 2023
Lessee Disclosure [Abstract]
Leases	9. Leases The Company leases office space and research, testing and manufacturing laboratory space in various facilities in Novato and Brisbane, California, in Somerville, and Woburn, Massachusetts, and in certain foreign countries, under operating agreements expiring at various dates through 2029 . Certain lease agreements include options for the Company to extend the lease for multiple renewal periods and provide for annual minimum increases in rent, usually based on a consumer price index or annual minimum increases. None of these optional periods have been considered in the determination of the right-of-use lease asset or the lease liability for the leases as the Company did not consider it reasonably certain that it would exercise any such options. The Company recognizes lease expense on a straight-line basis over the non-cancelable term of its operating leases. The variable lease expense primarily consists of common area maintenance and other operating costs. The components of lease expense were as follows (in thousands): Year Ended December 31, 2023 2022 2021 Operating lease expense $ 12,883 $ 11,775 $ 11,209 Variable lease expense 5,272 4,785 4,142 Financing: Amortization 203 343 310 Interest expense — 37 58 Total $ 18,358 $ 16,940 $ 15,719 Cash paid for amounts included in the measurement of operating lease liabilities for the years ended December 31, 2023, 2022, and 2021 was $ 13.4 million, $ 13.1 million, and $ 11.8 million, respectively, and was included in net cash used in operating activities in the Consolidated Statements of Cash Flows. Right-of-use lease assets were $ 23.9 million and $ 26.0 million as of December 31, 2023 and 2022, respectively, and were included in other non-current assets on the Consolidated Balance Sheets. The following table summarizes maturities of lease liabilities and the reconciliation of lease liabilities as of December 31, 2023: Year Ending December 31, Operating 2024 $ 16,234 2025 11,932 2026 8,430 2027 5,867 2028 5,887 Thereafter 6,009 Total future lease payments 54,359 Less: Amount representing interest ( 11,190 ) Present value of future lease payments 43,169 Less: Lease liabilities, current ( 12,595 ) Lease liabilities , non-curre nt $ 30,574 Lease liabilities are based on the net present value of the remaining lease payments over the remaining lease term. For the years ended December 31, 2023 and 2022 , the weighted-average remaining operating lease terms were 4.5 years and 3.0 years, the weighted-average remaining financing lease terms were nil and 2.8 years, the weighted-average discount rates used to determine the lease liability for operating leases were 9.6 % and 6.7 %, and the weighted-average discount rates used to determine the lease liability for finance leases were nil and 5.1 % respectively.

Liabilities for Sales of Future

Liabilities for Sales of Future Royalties	12 Months Ended
	Dec. 31, 2023
Deferred Revenue Disclosure [Abstract]
Liabilities for Sales of Future Royalties	10. Liabilities for Sales 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 EU, the U.K., and Switzerland under the terms of the Company’s Collaboration and License Agreement with KKC dated August 29, 2013, as amended, or the KKC Collaboration Agreement. 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, or when aggregate royalty payments received by RPI are equal to $ 800.0 million. In July 2022, the Company entered into a Royalty Purchase Agreement with OMERS. Pursuant to the agreement, OMERS paid $ 500.0 million to the Company in consideration for the right to receive 30 % of the future royalty payments due to the Company from KKC based on net sales of Crysvita in the U.S. and Canada under the terms of the KKC Collaboration Agreement. The calculation of royalty payments to OMERS is based on net sales of Crysvita beginning in April 2023 and will expire upon the earlier of the date on which aggregate payments received by OMERS equals $ 725.0 million or the date the final royalty payment is made to the Company under the KKC Collaboration Agreement. Proceeds from these transactions were recorded as liabilities for sales of future royalties on the Consolidated Balance Sheets. Upon inception of the respective arrangements, the Company recorded $ 320.0 million and $ 500.0 million, net of transaction costs of $ 5.8 million and $ 9.1 million for RPI and OMERS, respectively, using the effective interest method over the estimated life of the applicable arrangement. In order to determine the amortization of the liabilities, the Company is required to estimate the total amount of future royalty payments to be received by the Company and paid to RPI and OMERS, subject to the capped amount, over the life of the arrangements. The excess of future estimated royalty payments (subject to the capped amount) to RPI and OMERS, over the $ 314.2 million and $ 491.0 million, respectively, of net proceeds, is recorded as non-cash interest expense over the life of the arrangements. Consequently, the Company estimates an imputed interest on the unamortized portion of the liabilities and records interest expense relating to the transactions. The Company records the royalty revenue arising from the net sales of Crysvita in the applicable territories as royalty revenue in the Consolidated Statements of Operations over the term of the arrangements. Royalties earned under the RPI and OMERS arrangements from inception to December 31, 2023 have been $ 73.4 million and $4 8.6 million, respectively. 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 liabilities and the effective interest rate. The Company’s effective annual interest rates were 6.2 % and 7.8 %, for RPI and OMERS, respectively, as of December 31, 2023. There are a number of factors that could materially affect the amount and timing of royalty payments from KKC in the applicable 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, macroeconomic and inflationary pressures, the introduction of competing products, pricing for reimbursement in various 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, or USD, while significant portions of the underlying sales of Crysvita are made in currencies other than USD, and other events or circumstances that could result in reduced royalty payments from sales of Crysvita, all of which would result in a reduction of royalty revenue and the non-cash interest expense over the life of the arrangement. Conversely, if sales of Crysvita in the relevant territories are more than expected, the royalty revenue and the non-cash interest expense recorded by the Company would be greater over the term of the arrangements. The following table shows the activity within the liability account (in thousands): Liabilities for Sales of Future Royalties RPI OMERS Total December 31, 2021 $ 351,786 $ — $ 351,786 Net proceeds from sale of future — 490,950 490,950 Royalty revenue ( 21,692 ) — ( 21,692 ) Non-cash interest expense 35,095 19,300 54,395 December 31, 2022 365,189 510,250 875,439 Royalty revenue ( 20,783 ) ( 38,524 ) ( 59,307 ) Non-cash interest expense 32,235 43,200 75,435 December 31, 2023 $ 376,641 $ 514,926 $ 891,567

Equity

Equity	12 Months Ended
	Dec. 31, 2023
Equity [Abstract]
Equity	11. Equity At-the-Market Offerings In May 2021, the Company entered into an Open Market Sale Agreement with Jefferies LLC, or 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, or ATM, offerings through Jefferies. During the year ended December 31, 2023, there were 1,175,584 shares sold under the ATM resulting in net proceeds of $ 53.3 million. There were no shares sold under the ATM for year ended December 31, 2022. As of December 31, 2023 , the Company has sold a total of 2,225,956 shares under the ATM, resulting in net proceeds of $ 132.2 million. Underwritten Public Offering In October 2023, the Company completed an underwritten public offering in which 9,833,334 shares of common stock were sold, including the exercise in full by the underwriters of their option to purchase an additional 1,500,000 shares, at a public offering price of $ 30.00 per share. In connection with the offering, the Company sold to certain investors pre-funded warrants, in lieu of common stock, to purchase 1,666,722 shares of common stock at a purchase price of $ 29.999 per pre-funded warrant, which equals the public offering price per share of common stock less the $ 0.001 exercise price per share of each pre-funded warrant. The total proceeds that the Company received from the offering were $ 326.5 million, net of underwriting discounts and commissions. As of December 31, 2023 , no ne of the pre-funded warrants had been exercised. The pre-funded warrants were classified as a component of permanent equity in the Company's Consolidated Balance Sheets as they are freestanding financial instruments that are immediately exercisable, do not embody an obligation for the Company to repurchase its own shares and permit the holders to receive a fixed number of shares of common stock upon exercise. All of the shares underlying the pre-funded warrants have been included in the weighted-average number of shares of common stock used to calculate net loss per share, basic and diluted, attributable to common stockholders because the shares may be issued for little or no consideration, are fully vested, and are exercisable after the original issuance date of the pre-funded warrants.

Stock-Based Awards

Stock-Based Awards	12 Months Ended
	Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]
Stock-Based Awards	12. Stock-Based Awards Equity Plan Awards In 2014, the Company adopted the 2014 Incentive Plan, or the 2014 Plan, for the granting of stock-based awards to employees, directors, and consultants under terms and provisions established by the board of directors. The 2014 Plan had 2,250,000 shares of common stock available for future issuance at the time of its inception. The 2014 Plan provided for automatic annual increases in shares available for grant, beginning on January 1, 2015 through June 7, 2023 . In June 2023, the Company adopted the 2023 Incentive Plan which had 4,500,000 shares of common stock available for future issuance at the time of its inception, plus the number of shares subject to the 2014 Plan cancelled after June 7, 2023. No further shares were granted under the 2014 Plan after June 7, 2023.In February 2021, the Company adopted the Employment Inducement Plan, or the Inducement Plan, which was subsequently amended in June 2023 to provide for a maximum of 850,000 shares available for grant under the plan. In 2014, the Company adopted the 2014 Incentive Plan, or the 2014 Plan, for the granting of stock-based awards to employees, directors, and consultants under terms and provisions established by the board of directors. Under the terms of the 2023 Plan and Inducement Plan, awards may be granted at an exercise price not less than fair market value. The exercise price of an option may not be less than the fair market value. The term of an award granted under the 2023 Plan and Inducement Plan may not exceed ten years . Typically, the vesting schedule for option grants to the employees provides that ¼ of the grant vests upon the first anniversary of the date of grant, with the remainder of the shares vesting monthly thereafter at a rate of 1/48 of the total shares subject to the option. Typically, the vesting schedule for RSU grants provides that ¼ of the grant vests upon the annual anniversary of the date of grant over the period of four years . As of December 31, 2023 , an aggregate of 19,610,125 shares of common stock have been authorized for issuance under the 2014 Plan, the 2023 Plan, and the Inducement Plan. Stock Option Activity The following table summarizes activity under the Company’s stock option plans and related information: Options Outstanding Number of Options Weighted- Average Exercise Price Weighted-Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (In thousands) Outstanding — December 31, 2022 7,773,367 $ 72.56 6.60 $ 8,476 Options granted 2,123,256 45.05 Options exercised ( 209,793 ) 13.07 Options cancelled ( 899,118 ) 71.56 Outstanding — December 31, 2023 8,787,712 67.43 6.39 7,558 Vested and exercisable — December 31, 2023 5,415,110 73.28 4.96 1,214 Vested and expected to vest — December 31, 2023 8,461,973 67.96 6.29 6,794 The aggregate intrinsic values of options outstanding, vested and exercisable, and vested and expected to vest were calculated as the difference between the exercise price of the options and the fair value of the Company’s common stock. The total intrinsic value of options exercised during the years ended December 31, 2023, 2022, and 2021 was $ 4.9 million, $ 2.6 million, and $ 38.8 million, respectively. Cash received from the exercise of options was $ 2.7 million, $ 6.2 million, and $ 36.6 million for the years ended December 31, 2023, 2022, and 2021, respectively. The weighted-average estimated fair value of stock options granted was $ 25.53 , $ 34.77 , and $ 70.84 per share of the Company’s common stock during the years ended December 31, 2023, 2022, and 2021, respectively. The total estimated grant date fair value of options vested during the years ended December 31, 2023, 2022, and 2021 was $ 59.7 million, $ 58.7 million, and $ 48.1 million, respectively. Performance Stock Options The following table summarizes activity under the Company’s Performance Stock Option, or PSO, plans and related information: PSOs Outstanding Number of Options Weighted- Average Exercise Price Weighted-Average Remaining Contractual Term (Years) Aggregate Intrinsic Value Outstanding — December 31, 2022 1,624,599 $ 67.37 4.14 $ — PSOs cancelled ( 243,601 ) 67.37 Outstanding — December 31, 2023 1,380,998 67.37 3.15 — Vested and exercisable — December 31, 2023 117,865 67.37 3.09 — Vested and expected to vest — December 31, 2023 983,173 67.37 3.14 — During the year ended December 31, 2022, PSOs were granted to certain nonexecutive employees. PSOs are subject to vest only if specified operational milestones are achieved and the employees’ continued service with the Company. The Company uses the Black-Scholes method to calculate the fair value at the grant date and is recognizing stock-based compensation expense for the PSOs that are expected to vest. Stock-based compensation for PSOs is recognized over the service period, beginning in the period the Company determines it is probable that a milestone will be achieved. Forfeitures of PSOs are recognized as they occur. The Company reassesses the probability of the performance condition at each reporting period and adjusts the compensation cost based on the probability assessment. As of December 31, 2023, certain operational milestones were deemed probable of achievement. The aggregate intrinsic values of PSOs outstanding, vested and exercisable, and vested and expected to vest were calculated as the difference between the exercise price of the PSOs and the fair value of the Company’s common stock. The total estimated grant date fair value of PSOs vested during the year ended December 31, 2023 , was $ 3.4 million. No PSOs were granted or were exercised during the year ended December 31, 2023. The weighted-average estimated fair value of PSOs granted was $ 28.76 during the year ended December 31, 2022. Restricted Stock Units The following table summarizes activity under the Company’s Restricted Stock Units, or RSU, plans and related information: RSUs Outstanding Number Weighted- Average Grant Date Fair Value Unvested — December 31, 2022 2,129,153 $ 75.11 RSUs granted 2,447,170 44.52 RSUs vested ( 738,130 ) 73.99 RSUs cancelled ( 394,081 ) 61.22 Unvested — December 31, 2023 3,444,112 55.21 The fair value of the RSUs is determined on the grant date based on the fair value of the Company’s common stock. The fair value of the RSUs is recognized as expense ratably over the vesting period of one to four years . The total grant date fair value of the RSUs vested during the years ended December 31, 2023, 2022, and 2021 was $ 54.6 million, $ 47.1 million, and $ 35.5 million, respectively. The aggregate intrinsic value of the shares of the RSUs vested during the years ended December 31, 2023, 2022, and 2021 was $ 33.0 million, $ 37.8 million, and $ 69.9 million, respectively. Performance Stock Units The following table summarizes activity under the Company’s Performance Stock Units, or PSUs and related information: PSUs Outstanding Number Weighted- Average Grant Date Fair Value Unvested — December 31, 2022 209,230 $ 98.09 PSUs granted 362,470 50.29 PSUs vested ( 27,581 ) 141.86 PSUs cancelled ( 38,013 ) 106.80 Unvested — December 31, 2023 506,106 60.82 The fair value of the PSUs is determined on the grant date based on the fair value of the Company’s common stock, except for certain PSUs with a market vesting condition, for which fair value is estimated using a Monte Carlo simulation model. PSUs are subject to vest only if certain specified criteria are achieved and the employees’ continued service with the Company. For certain PSUs, the number of PSUs that may vest are also subject to the achievement of certain specified criteria, including both performance conditions and market conditions. As of December 31, 2023, certain specified criteria were deemed probable of achievement or already achieved. Stock-based compensation for PSUs is recognized over the service period beginning in the period the Company determines it is probable that the performance criteria will be achieved. The total grant date fair value of the PSUs vested during the years ended December 31, 2023, 2022, and 2021 was $ 3.9 million, $ 1.6 million, and $ 9.2 million, respectively, with an aggregate intrinsic value of the shares of $ 1.3 million, $ 2.0 million and $ 18.9 million, respectively. Employee Stock Purchase Plan In January 2014, the Company adopted the 2014 Employee Stock Purchase Plan, or ESPP, which was amended and restated in June 2023. Under the ESPP, eligible employees may purchase common stock at 85 % of the lesser of the fair market value of common stock on the offering date or the purchase date with a six-month look-back feature. ESPP purchases are settled with common stock from the ESPP’s previously authorized and available pool of shares. During the year ended December 31, 2023 , the Company issued 195,462 shares of common stock under the ESPP. As of December 31, 2023 , an aggregate of 6,609,795 shares of common stock have been authorized for future issuance on the ESPP. Stock-Based Compensation Expense Total stock-based compensation recognized was as follows (in thousands): Year Ended December 31, 2023 2022 2021 Cost of sales $ 1,166 $ 902 $ 871 Research and development 74,531 74,464 59,097 Selling, general and administrative 59,516 55,002 45,011 Total stock-based compensation expense $ 135,213 $ 130,368 $ 104,979 Stock-based compensation of $ 1.9 million, $ 2.2 million, and $ 1.7 million was capitalized into inventory for the years ended December 31, 2023, 2022, and 2021, respectively. Capitalized stock-based compensation is recognized as cost of sales when the related product is sold. As of December 31, 2023 , the total unrecognized compensation expense related to unvested equity awards, net of estimated forfeitures, was $ 219.8 million, which the Company expects to recognize over an estimated weighted-average period of 2.2 years. In determining the estimated fair value of the stock options, PSOs and ESPP, the Company uses the Black-Scholes option-pricing model and assumptions discussed below. Each of these inputs is subjective and generally requires significant judgment to determine. Expected Term —The Company’s expected term represents the period that the Company’s stock-based awards are expected to be outstanding and is determined using the simplified method (based on the mid-point between the vesting date and the end of the contractual term). Expected Volatility —The Company’s expected volatility is based on historical volatility over the look-back period corresponding to the expected term. Risk-Free Interest Rate —The risk-free interest rate is based on the U.S. Treasury zero coupon issues in effect at the time of grant for periods corresponding with the expected term of option. Expected Dividend —The Company has never paid dividends on its common stock and has no plans to pay dividends on its common stock. Therefore, the Company used an expected dividend yield of zero. Strike price for options awards and PSOs is equal to the closing market value of our common stock on the date of grant. The fair value of stock option awards granted was estimated at the date of grant using a Black-Scholes option-pricing model with the following weighted-average assumptions: Year Ended December 31, 2023 2022 2021 Expected term (years) 6.07 6.07 6.06 Expected volatility 55 % 56 % 60 % Risk-free interest rate 4.2 % 2.0 % 1.0 % Expected dividend rate 0.0 % 0.0 % 0.0 % The fair value of PSOs granted was estimated at the date of grant using a Black-Scholes option-pricing model with the following weighted-average assumptions: Year Ended December 31, 2022 Expected term in years 3.60 Expected volatility 57 % Risk-free interest rate 1.5 % Expected dividend rate 0.0 %

Defined Contribution Plan

Defined Contribution Plan	12 Months Ended
	Dec. 31, 2023
Defined Contribution Pension And Other Post Retirement Plan Disclosure [Abstract]
Defined Contribution Plan	13. Defined Contribution Plan The Company sponsors a retirement plan in which substantially all of its full-time employees in the U.S. and certain other foreign countries are eligible to participate. Eligible participants may contribute a percentage of their annual compensation to this plan, subject to statutory limitations. The Company recorded $ 9.7 million, $ 9.0 million, and $ 5.5 million as expense related to the plan for the years ended December 31, 2023, 2022, and 2021 , respectively.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Income Taxes	14. Income Taxes The components of the Company’s loss before income taxes were as follows (in thousands): Year Ended December 31, 2023 2022 2021 Domestic $ 608,166 $ 703,411 $ 455,314 Foreign 298 ( 1,686 ) ( 2,333 ) Total loss before income taxes $ 608,464 $ 701,725 $ 452,981 The components of the Company’s income tax provision were as follows (in thousands): Year Ended December 31, 2023 2022 2021 Current provision for income taxes: Federal $ — $ — $ — State ( 3,187 ) 6,062 ( 14 ) International 3,127 1,274 1,058 Total current tax provision ( 60 ) 7,336 1,044 Deferred tax provision: Federal — — — State ( 1,608 ) ( 1,640 ) — International ( 157 ) — — Total deferred tax provision ( 1,765 ) ( 1,640 ) — Total (benefit from) provision for income taxes $ ( 1,825 ) $ 5,696 $ 1,044 The Company has incurred net operating losses since inception. The Company has not reflected any benefit of such net operating loss carryforwards in the accompanying financial statements. The Company has established a full valuation allowance against its deferred tax assets due to the uncertainty surrounding the realization of such assets. Beginning in 2022, the Tax Cuts and Jobs Act of 2017 eliminated the right to deduct research and development expenditures for tax purposes in the period the expenses were incurred and instead requires all U.S. and foreign research and development expenditures to be amortized over five and fifteen tax years, respectively. Due to this required capitalization of research and development expenditures and the significant taxable income generated as a result of our sale of royalties in July 2022, the Company has recorded current state income tax expense of $ 6.1 million for the year ended December 31, 2022. For the year ended December 31, 2023, the Company recognized an income tax benefit of $ 4.8 million attributable to modifications in its state apportionment methodology. The Company realized no benefit for current year losses due to a full valuation allowance against the U.S. net deferred tax assets. The benefit was offset by an income tax expense of $ 3.0 million from foreign jurisdictions. The effective tax rate of our provision for income taxes differs from the federal statutory rate as follows: Year Ended December 31, 2023 2022 2021 Federal statutory income tax rate 21.0 % 21.0 % 21.0 % State income taxes, net of federal benefit 0.8 ( 0.4 ) — Federal tax credits 7.3 5.9 7.2 Other ( 0.7 ) ( 0.1 ) 0.5 Nondeductible permanent items ( 0.3 ) ( 0.6 ) ( 0.8 ) Stock-based compensation ( 1.8 ) ( 1.2 ) 1.3 Uncertain tax positions ( 1.4 ) ( 1.2 ) ( 1.4 ) Change in valuation allowance ( 24.1 ) ( 24.0 ) ( 27.9 ) Foreign rate differential ( 0.5 ) ( 0.2 ) ( 0.1 ) Provision for income taxes 0.3 % ( 0.8 ) % ( 0.2 ) % The tax effect of temporary differences that give rise to significant portions of the deferred tax assets is presented below (in thousands): Year Ended December 31, 2023 2022 Deferred tax assets: Loss carryforwards $ 266,253 $ 231,835 Tax credits 305,198 260,546 Stock options 44,795 39,784 Accruals and reserves 27,694 27,029 Fixed assets and intangibles 33,853 39,233 Liabilities for sales of future royalties 205,400 214,900 Basis difference in equity investments 8,423 8,971 Capitalized research and development costs 149,898 75,335 Other 281 3,028 Gross deferred tax assets 1,041,795 900,661 Valuation allowance ( 1,035,836 ) ( 894,518 ) Total deferred tax assets 5,959 6,143 Deferred tax liabilities: In-process research and development ( 30,688 ) ( 31,667 ) Right-of-use lease assets ( 5,329 ) ( 6,143 ) Gross deferred tax liabilities ( 36,017 ) ( 37,810 ) Net deferred tax liabilities $ ( 30,058 ) $ ( 31,667 ) As of December 31, 2023 and 2022 , the Company had approximately $ 1,004.8 million and $ 756.6 million, respectively, of federal net operating loss carryforwards available to reduce future taxable income that will begin to expire in 2031 . As of December 31, 2023 and 2022 , the Company had approximately $ 659.9 million and $ 710.0 million, respectively, of state net operating loss carryforwards available to reduce future taxable income that will begin to expire in 2031 . As of December 31, 2023 and 2022 , the Company had federal research tax credit carryforwards of approximately $ 46.9 million and $ 32.6 million, respectively, available to reduce future tax liabilities that will begin to expire in 2030 . As of December 31, 2023 and 2022 , the Company had state research credit carryforwards of $ 74.4 million and $ 59.9 million, respectively, available to reduce future tax liabilities that will be carried forward indefinitely. As of December 31, 2023 and 2022 , the Company had federal Orphan Drug Credits of $ 269.6 million and $ 239.3 million, respectively, available to reduce future tax liabilities that will begin to expire in 2031 . The Company’s ability to use net operating loss and tax credit carryforwards to reduce future taxable income and liabilities may be subject to annual limitations pursuant to Internal Revenue Code Sections 382 and 383 as a result of ownership changes in the past and future. As a result of ownership changes in 2012 and 2011, $ 3.6 million of federal net operating loss carryforwards, $ 3.6 million of state net operating loss carryforwards, and $ 0.2 million of federal tax credits are permanently limited. Deferred tax assets for net operating losses and tax credits have been reduced and a corresponding adjustment to the valuation allowance has been recorded. The valuation allowance increased by $ 141.3 million and $ 193.8 million during the years ended December 31, 2023 and 2022, respectively. Due to a change in the state tax rates, the Company recorded a net decrease to the deferred tax liability of $ 1.6 million with a corresponding deferred income tax benefit of $ 1.6 million for the year ended December 31, 2023. The Company recorded unrecognized tax benefits for uncertainties in income taxes. A reconciliation of the Company’s unrecognized tax benefits follows (in thousands): December 31, 2023 2022 2021 Balance at beginning of year $ 66,794 $ 55,360 $ 46,662 Additions based on tax positions related to current 12,562 11,316 8,542 Additions for tax positions of prior years 642 377 356 Reductions for tax positions of prior years — ( 259 ) ( 200 ) Balance at end of year $ 79,998 $ 66,794 $ 55,360 Approximately $ 1.3 million in unrecognized tax benefits would impact the Company’s effective tax rate if recognized. The Company has elected to include interest and penalties as a component of tax expense. For the year ended December 31, 2023, the Company recognized accrued interest and penalties of $ 0.2 million as a component of income tax expense. No accrued interest and penalties were recognized as a component of income tax expense during the years ended December 31, 2022 and 2021. The Company does not anticipate that the amount of existing unrecognized tax benefits will significantly increase or decrease during the next year. It is the Company’s intention to reinvest the earnings of its non-U.S. subsidiaries in their operations. As of December 31, 2023 , the Company had not made a provision for any incremental foreign withholding taxes on approximately $ 10.8 million of the excess of the amount of net income for financial reporting over the tax basis of investments in foreign subsidiaries that are essentially permanent in duration. If these earnings were repatriated to the U.S., the deferred tax liability associated with these temporary differences would result in a nominal amount of withholding taxes. The Company files income tax returns in the U.S. federal, 40 state tax jurisdictions, and ten foreign countries. The federal and state income tax returns from inception to December 31, 2023 remain subject to examination.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	15. Commitments and Contingencies The Company has various manufacturing, construction, clinical, research, and other contracts with vendors in the conduct of the normal course of its business. Other than as noted below, contracts are terminable, with varying provisions regarding termination. If a contract with a specific vendor were to be terminated, the Company would only be obligated for the products or services that the Company had received at the time the termination became effective. Manufacturing and service contract obligations primarily relate to the manufacture of inventory for our approved products, the majority of which are due in the next 12 months . As of December 31, 2023, the aggregate payments under contractually-binding manufacturing and service agreements are as follows (in thousands): Year Ended December 31, 2024 2025 Total Manufacturing and Services $ 27,899 $ 5,718 $ 33,617 The terms of certain of the Company’s licenses, royalties, development and collaboration agreements, as well as other research and development activities, require the Company to pay potential future milestone payments based on product development success. The amount and timing of such obligations are unknown or uncertain. These potential obligations are further described in “Note 8. License and Research Agreements.” See “Note 9. Leases” for lease commitments. Contingencies While there are no material legal proceedings the Company is aware of, the Company may become party to various claims and complaints arising in the ordinary course of business. Management does not believe that any ultimate liability resulting from any of these potential claims will have a material adverse effect on its results of operations, financial position, or liquidity. However, management cannot give any assurance regarding the ultimate outcome of these claims, and their resolution could be material to operating results for any particular period, depending upon the level of income for the period. Guarantees and Indemnifications The Company indemnifies each of its directors and officers for certain events or occurrences, subject to certain limits, while the director or officer is or was serving at the Company’s request in such capacity, as permitted under Delaware law and in accordance with its certificate of incorporation and bylaws. The term of the indemnification period lasts as long as a director or officer may be subject to any proceeding arising out of acts or omissions of such director and officer in such capacity. The maximum amount of potential future indemnification is unlimited; however, the Company currently holds director liability insurance. This insurance allows the transfer of risk associated with the Company’s exposure and may enable it to recover a portion of any future amounts paid. The Company believes that the fair value of these indemnification obligations is minimal. Accordingly, it has not recognized any liabilities relating to these obligations for any period presented.

Related Party Transaction

Related Party Transaction	12 Months Ended
	Dec. 31, 2023
Related Party Transactions [Abstract]
Related Party Transaction	16. Related Party Transaction In July 2022, the Company entered into an agreement with a non-profit foundation in which two members of the Company’s board of directors, including the Company’s Chief Executive Officer, also serve as board members of the foundation, whereby an aggregate $ 1.0 million contribution is being paid to the foundation over a four-year period, beginning in the third quarter of 2022, to support rare disease education and awareness. As a result, the Company recorded $ 0.3 million and $ 0.3 million as research and development expense for this agreement for the years ended December 31, 2023 and 2022 , respectively.

Net Loss per Share

Net Loss per Share	12 Months Ended
	Dec. 31, 2023
Earnings Per Share [Abstract]
Net Loss per Share	17. Net Loss per Share The following table sets forth the computation of the basic and diluted net loss per share during the years ended December 31, 2023, 2022, and 2021 (in thousands, except share and per share data): Year Ended December 31, 2023 2022 2021 Numerator: Net loss $ ( 606,639 ) $ ( 707,421 ) $ ( 454,025 ) Denominator: Weighted-average shares used to compute net loss per 73,543,862 69,914,225 67,795,540 Net loss per share, basic and diluted $ ( 8.25 ) $ ( 10.12 ) $ ( 6.70 ) 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: Year Ended December 31, 2023 2022 2021 Options to purchase common stock, 14,152,286 11,290,935 8,214,063 Employee stock purchase plan 8,450 7,581 3,511 14,160,736 11,298,516 8,217,574

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2023
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss)	18. Accumulated Other Comprehensive Income (Loss) Total accumulated other comprehensive income (loss) consisted of the following (in thousands): Year Ended December 31, 2023 2022 Cumulative foreign currency translation adjustment $ ( 606 ) $ ( 845 ) Unrealized gain (loss) on securities available-for-sale 1,253 ( 5,728 ) Total accumulated other comprehensive income (loss) $ 647 $ ( 6,573 )

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2023
Accounting Policies [Abstract]
Basis of Consolidation	Basis of Consolidation The Consolidated Financial Statements include the accounts of Ultragenyx Pharmaceutical Inc. and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated.
Use of Estimates	Use of Estimates The accompanying Consolidated Financial Statements have been prepared in accordance with U.S. generally accepted accounting principles, or GAAP. The preparation of the 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 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, revenue recognition, and the liabilities for sales 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 The Company considers all highly liquid investments with original maturities of three months or less from the date of purchase to be cash equivalents. Cash equivalents consist primarily of amounts invested in money market accounts. 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 Consolidated Balance Sheets that sum to the total of the same such amounts shown in the Consolidated Statements of Cash Flows (in thousands): December 31, 2023 2022 2021 Cash and cash equivalents $ 213,584 $ 132,944 $ 307,584 Restricted cash included in other current assets 2,008 862 — Restricted cash included in other non-current assets 3,807 3,795 2,001 Total cash, cash equivalents, and restricted cash $ 219,399 $ 137,601 $ 309,585
Marketable Debt Securities	Marketable Debt Securities All marketable debt securities have been classified as “available-for-sale” and are carried at estimated fair value as determined based upon quoted market prices or pricing models for similar securities. Management determines the appropriate classification of its investments at the time of purchase and reevaluates such designation as of each balance sheet date. Investments with a maturity of one year or less from the balance sheet date are reported as current marketable debt securities and investments with a maturity of greater than one year from the balance sheet date are reported as non-current marketable debt securities. Unrealized gains and losses are excluded from earnings and are reported as a component of comprehensive loss. Realized gains and losses and declines in fair value judged to be other than temporary, if any, on available-for-sale securities are included in other income (expense). The cost of securities sold is based on the specific-identification method. Interest on investments is included in interest income.
Equity Investments	Equity Investments The Company records investments in equity securities, other than equity method investments, at fair market value, if the fair value is readily determinable. Equity securities with no readily determinable fair values are recorded using the measurement alternative of cost adjusted for observable price changes in orderly transactions for identical or similar investments of the same issuer less impairment, if any. Investments in equity securities are recorded in Equity investments on the Company's Consolidated Balance Sheets. Unrealized gains and losses are reported in Change in fair value of equity investments on the Company’s Consolidated Statements of Operations. The Company regularly reviews its non-marketable equity securities for indicators of impairment.
Concentration of Credit Risk, Credit Losses, and Other Risks and Uncertainties	Concentration of Credit Risk, Credit Losses, and Other Risks and Uncertainties Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash, cash equivalents, and investments. The Company’s cash, cash equivalents, and investments are held by financial institutions that management believes are of high credit quality. The Company’s investment policy limits investments to fixed income securities denominated and payable in U.S. dollars such as U.S. government obligations, money market instruments and funds, corporate bonds, commercial paper, and asset-backed securities and places restrictions on maturities and concentrations by type and issuer. Such deposits may, at times, exceed federally insured limits. The Company has not experienced any losses on its deposits of cash and cash equivalents and its accounts are monitored by management to mitigate risk. The Company is exposed to credit risk in the event of default by the financial institutions holding its cash and cash equivalents, corporate issuers, and other financial instruments, to the extent recorded in the Consolidated Balance Sheets. 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 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 allowance for losses on available-for-sale debt securities which were attributable to credit risk for the years ended December 31, 2023 and 2022. The Company is dependent on third-party manufacturers to supply products for research and development activities in its programs. In particular, the Company relies and expects to continue to rely on a small number of manufacturers to supply it with its requirements for the active pharmaceutical ingredients and formulated drugs related to these programs. These programs could be adversely affected by a significant interruption in the supply of active pharmaceutical ingredients and formulated drugs.
Inventory	Inventory The Company values inventory at the lower of cost and net realizable value and determines the cost of inventory using the average-cost method. The Company expenses costs associated with the manufacture of product candidates prior to regulatory approval. Inventories consist of currently approved products. The Company periodically reviews its inventories for excess amounts or obsolescence and writes down obsolete or otherwise unmarketable inventory to its estimated net realizable value. Management determines excess inventory based on expected future demand. Estimates related to future demand are sensitive to significant inputs and assumptions such as acceptance by patients and physicians and the availability of formulary coverage and adequate reimbursement from private third-party payers for the product.
Property, Plant, and Equipment	Property, Plant, and Equipment Property, plant, and equipment are stated at cost, less accumulated depreciation and amortization. Depreciation and amortization is computed using the straight-line method over the estimated useful lives of the respective assets. Depreciation and amortization begins when the asset is placed in service. Interest costs incurred during the construction of major capital projects are capitalized until the underlying asset is ready to be placed in service. Maintenance and repairs are charged to operations as incurred. Upon sale or retirement of assets, the cost and related accumulated depreciation or amortization are removed from the balance sheet and the resulting gain or loss, if any, is reflected in operations. See “Note 4. Balance Sheet Components” for further disclosure on the useful lives of property, plant, and equipment.
Intangible Assets	Intangible Assets Finite-lived intangibles consist of contractual payments made for certain milestones achieved with collaboration partners. The contractual payments are recorded as intangible assets and are amortized over their estimated useful lives. The Company reviews its definite-lived intangible assets when events or circumstances may indicate that the carrying value of these assets is not recoverable and exceeds their fair value. The Company measures fair value based on the estimated future undiscounted cash flows associated with these assets in addition to other assumptions and projections that the Company deems to be reasonable and supportable. Indefinite-lived intangibles consist of acquired in-process research and development, or IPR&D. IPR&D assets represent capitalized incomplete research projects that the Company acquired through business combinations. Such assets are initially measured at their acquisition date fair values and are tested for impairment annually and whenever events or changes in circumstances indicate that the carrying amount may not be recoverable. When development of the project is complete, which generally occurs when regulatory approval to market a product is obtained, the associated assets will be deemed finite-lived and will be amortized over a period that best reflects the economic benefits provided by these assets. If it is determined that an intangible asset becomes impaired, the carrying value is written down to its fair value with the related impairment charge recognized in Consolidated Statements of Operations in the period in which the impairment occurs. The Company has not recorded any impairments of intangible assets to date.
Goodwill	Goodwill Goodwill represents the excess of purchase price over fair value of net assets acquired in a business combination and is not amortized. Goodwill is subject to impairment testing at least annually during the fourth quarter or when a triggering event occurs that could indicate a potential impairment. If it is determined that the goodwill becomes impaired, the carrying value is written down to its fair value with the related impairment charge recognized in Consolidated Statements of Operations in the period in which the impairment occurs. The Company has not recorded any impairments of goodwill.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company evaluates its long-lived assets, including property and equipment, for impairment whenever events or changes in circumstances indicate that the carrying value of these assets may not be recoverable. Recoverability of these assets is measured by comparison of the carrying amount of each asset to the future undiscounted cash flows expected to result from the use of the asset and its eventual disposition. If the asset is considered to be impaired, the amount of any impairment is measured as the difference between the carrying value and the fair value of the impaired asset. The Company has not recorded material impairment of any long-lived assets.
Accruals of Research and Development Costs	Accruals of Research and Development Costs The Company records accruals for estimated costs of research, preclinical and clinical studies and manufacturing development. These costs are a significant component of the Company’s research and development expenses. A substantial portion of the Company’s ongoing research and development activities are conducted by third-party service providers, including contract research organizations. The Company accrues the costs incurred under its agreements with these third parties based on actual work completed in accordance with agreements established with these third parties. The Company determines the actual costs through obtaining information from external service providers as to the progress or stage of completion of the services and the agreed-upon fee to be paid for such services.
Revenue Recognition	Revenue Recognition 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 control is transferred 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 a material effect on earnings in the period of the adjustment. Collaboration, License, and Royalty Revenue The Company has certain license and collaboration agreements that are within the scope of Accounting Standards Codification, or 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 Consolidated Statements 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. The Company utilizes certain information from its collaboration partners to record collaboration revenue, 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 also records royalty revenues under certain of the Company’s license or collaboration agreements in exchange for license of intellectual property. The Company sold the right to receive certain royalty payments from net sales of Crysvita in certain territories to RPI Finance Trust, or RPI, an affiliate of Royalty Pharma, and to OCM LS23 Holdings LP, an investment vehicle for Ontario Municipal Employees Retirement System, or OMERS, as further described in “Note 10. Liabilities for Sales of Future Royalties.” The Company records the royalty revenue from the net sales of Crysvita in the applicable territories on a prospective basis as non-cash royalty revenue in the Consolidated Statements of Operations over the term of the applicable 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, or 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.
Deferred Compensation Plan	Deferred Compensation Plan The Company maintains a nonqualified deferred compensation plan whereby certain employees and members of the board of directors are able to defer certain equity awards and other compensation. Amounts deferred are invested into shares of the Company's common stock, mutual funds, and other investment options. The plan complies with the provisions of Section 409A of the Internal Revenue Code. All of the various mutual funds held in the plan are classified as trading securities and recorded at fair value in other non-current assets in the Consolidated Balance Sheets with changes in fair value recognized as earnings in the period they occur. The short-term portion of the corresponding liability for the plan is included in accrued expenses. The long-term portion of the liability is included in other non-current liabilities in the Consolidated Balance Sheets. Certain equity awards deferred under the plan are required to be settled through the issuance of Company stock. These awards are recorded as treasury stock and deferred compensation obligation within stockholders’ equity.
Leases	Leases Lease agreements are evaluated to determine whether an arrangement is or contains a lease in accordance with ASC 842, Leases . The Company determines if an arrangement includes a lease at inception. Right-of-use lease assets and lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term at the commencement date. The right-of-use lease asset includes any lease payments made and excludes lease incentives. Incremental borrowing rate is used in determining the present value of future payments. The Company applies a portfolio approach to the property leases to apply an incremental borrowing rate to leases with similar lease terms. The lease terms may include options to extend or terminate the lease. The Company recognizes the options to extend the lease as part of the right-of-use lease assets and lease liabilities only if it is reasonably certain that the option would be exercised. Lease expense for minimum lease payments is recognized on a straight-line basis over the non-cancelable lease term. The Company has elected to not separate lease and non-lease components. See “Note 9. Leases” for further disclosure.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is the change in stockholders’ equity from transactions and other events and circumstances other than those resulting from investments by stockholders and distributions to stockholders. The Company’s other comprehensive loss is comprised of unrealized gains and losses on investments in available-for-sale securities and foreign currency translation adjustments.
Research and Development	Research and Development Research and development costs are expensed as incurred and consist of salaries and benefits, stock-based compensation expense, lab supplies and facility costs, as well as fees paid to other nonemployees and entities that conduct certain research and development activities on the Company’s behalf. Amounts incurred in connection with license agreements are also included in research and development expense. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are deferred. The deferred amounts are expensed as the related goods are delivered or the services are performed.
Stock-Based Compensation	Stock-Based Compensation Stock-based awards issued to employees, including stock options, performance stock options, or PSOs, restricted stock units, or RSUs, and performance stock units, or PSUs are recorded at fair value as of the grant date and recognized as expense on a straight-line basis over the employee’s requisite service period (generally the vesting period). PSOs and PSUs vest only if certain specified criteria are achieved and the employees’ continued service requirements are met; therefore, the expense recognition occurs when the likelihood of the PSOs and PSUs being earned is deemed probable. Stock compensation expense on awards expected to vest is recognized net of estimated forfeitures.
Income Taxes	Income Taxes The Company uses the liability method of accounting for income taxes. Under this method, deferred tax assets and liabilities are determined based on the differences between the financial reporting and the tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. The Company must then assess the likelihood that the resulting deferred tax assets will be realized. A valuation allowance is provided when it is more likely than not that some portion or all of a deferred tax asset will not be realized. Due to the Company’s lack of earnings history, the net deferred tax assets have been fully offset by a valuation allowance. In conjunction with the acquisition of Dimension Therapeutics, Inc., or Dimension, a deferred tax liability was recorded reflecting the tax impact of the difference between the book basis and tax basis of acquired IPR&D. Such deferred income tax liability is not used to offset deferred tax assets when analyzing the Company’s valuation allowance as the acquired IPR&D is considered to have an indefinite life until the Company completes or abandons development of the acquired IPR&D. The Company recognizes benefits of uncertain tax positions if it is more likely than not that such positions will be sustained upon examination based solely on their technical merits, as the largest amount of benefit that is more likely than not to be realized upon the ultimate settlement. The Company’s policy is to recognize interest and penalties related to the underpayment of income taxes as a component of income tax expense or benefit. To date, there have been no interest or penalties charged in relation to the unrecognized tax benefits.
Foreign Currency	Foreign Currency Assets and liabilities of non-U.S. subsidiaries that operate in a local currency environment, where the local currency is the functional currency, are translated to U.S. dollars at exchange rates in effect at the balance sheet date, with the resulting translation adjustments directly recorded to a separate component of accumulated other comprehensive loss. Income and expense accounts are translated at average exchange rates for the period. Transactions which are not in the functional currency of the entity are remeasured into the functional currency and gains or losses resulting from the remeasurement recorded in other income (expense).
Net Loss per Share	Net Loss per Share Basic net loss per share is calculated by dividing the net loss by the weighted-average number of shares of common stock outstanding during the period, without consideration for common stock equivalents. Shares of common stock into which pre-funded warrants may be exercised are considered outstanding for the purposes of computing basic net loss per share because the shares may be issued for little or no consideration, are fully vested and are exercisable after the original issuance date. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive. In periods when we have incurred a net loss, options and warrants to purchase common stock are considered common stock equivalents, but have been excluded from the calculation of diluted net loss per share, as their effect is antidilutive.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2023
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 Consolidated Balance Sheets that sum to the total of the same such amounts shown in the Consolidated Statements of Cash Flows (in thousands): December 31, 2023 2022 2021 Cash and cash equivalents $ 213,584 $ 132,944 $ 307,584 Restricted cash included in other current assets 2,008 862 — Restricted cash included in other non-current assets 3,807 3,795 2,001 Total cash, cash equivalents, and restricted cash $ 219,399 $ 137,601 $ 309,585

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2023
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): December 31, 2023 Level 1 Level 2 Level 3 Total Financial Assets: Money market funds $ 162,289 $ — $ — $ 162,289 Certificates of deposit and time deposits — 17,986 — 17,986 Corporate bonds — 215,166 — 215,166 Commercial paper — 20,620 — 20,620 Asset-backed securities — 2,712 — 2,712 U.S. Government Treasury and agency securities 57,437 259,605 — 317,042 Investment in Solid common stock 3,204 — — 3,204 Deferred compensation assets — 10,220 — 10,220 Total financial assets $ 222,930 $ 526,309 $ — $ 749,239 Financial Liabilities: Deferred compensation liabilities $ — $ 10,365 $ — $ 10,365 December 31, 2022 Level 1 Level 2 Level 3 Total Financial Assets: Money market funds $ 102,847 $ — $ — $ 102,847 Certificates of deposit and time deposits — 25,972 — 25,972 Corporate bonds — 427,598 — 427,598 Commercial paper — 135,393 — 135,393 Asset-backed securities — 11,980 — 11,980 U.S. Government Treasury and agency securities 27,645 129,345 — 156,990 Debt securities in government-sponsored entities — 15,855 — 15,855 Investment in Solid common stock 2,807 — — 2,807 Deferred compensation assets — 4,575 — 4,575 Total financial assets $ 133,299 $ 750,718 $ — $ 884,017 Financial Liabilities: Deferred compensation liabilities $ — $ 4,657 $ — $ 4,657

Balance Sheet Components (Table

Balance Sheet Components (Tables)	12 Months Ended
	Dec. 31, 2023
Investments, Debt and Equity Securities [Abstract]
Summary of Cash Equivalents and Marketable Debt Securities Classified as Available For Sale Securities	The fair values of cash equivalents and marketable debt securities classified as available-for-sale securities consisted of the following (in thousands): December 31, 2023 Gross Unrealized Amortized Gains Losses Estimated Money market funds $ 162,289 $ — $ — $ 162,289 Certificates of deposit and time deposits 17,986 — — 17,986 Corporate bonds 214,792 711 ( 337 ) 215,166 Commercial paper 20,620 — — 20,620 Asset-backed securities 2,715 — ( 3 ) 2,712 U.S. Government Treasury and agency securities 316,160 982 ( 100 ) 317,042 Total $ 734,562 $ 1,693 $ ( 440 ) $ 735,815 December 31, 2022 Gross Unrealized Amortized Cost Gains Losses Estimated Money market funds $ 102,847 $ — $ — $ 102,847 Certificates of deposit and time deposits 25,972 — — 25,972 Corporate bonds 432,211 87 ( 4,700 ) 427,598 Commercial paper 135,393 — — 135,393 Asset-backed securities 12,002 — ( 22 ) 11,980 U.S. Government Treasury and agency securities 157,933 320 ( 1,263 ) 156,990 Debt securities in government-sponsored entities 16,005 — ( 150 ) 15,855 Total $ 882,363 $ 407 $ ( 6,135 ) $ 876,635
Summary of Inventory	Inventory consists of the following (in thousands): December 31, 2023 2022 Work-in-process $ 18,859 $ 17,486 Finished goods 15,110 9,280 Total inventory $ 33,969 $ 26,766
Summary of Property, Plant and Equipment, Net	Property, plant, and equipment, net consists of the following (in thousands): December 31, Useful life (years) 2023 2022 Building 20 - 30 $ 181,356 $ 2,798 Leasehold improvements Shorter of lease term or 58,683 43,941 Research and development equipment 5 56,347 50,291 Furniture and office equipment 5 6,419 5,540 Computer equipment and software 3 - 5 16,196 13,876 Manufacturing equipment 5 - 15 37,297 570 Land Not applicable 16,619 16,619 Construction-in-progress Not applicable 867 189,448 Other Varies by asset 183 24 Property, plant, and equipment, gross 373,967 323,107 Less: accumulated depreciation ( 83,401 ) ( 63,381 ) Property, plant, and equipment, net $ 290,566 $ 259,726
Summary of Accrued Liabilities	Accrued liabilities consists of the following (in thousands): December 31, 2023 2022 Research, clinical study, and manufacturing expenses $ 65,326 $ 73,558 Payroll and related expenses 82,936 78,938 Other 48,224 52,182 Total accrued liabilities $ 196,486 $ 204,678

Intangible Assets, net (Table)

Intangible Assets, net (Table)	12 Months Ended
	Dec. 31, 2023
Intangible Assets, Net (Excluding Goodwill) [Abstract]
Summary of Company's Intangible Assets	The Company's intangible assets were as follows: December 31, 2023 Gross Carrying Amount Weighted-Average Life (Years) Accumulated Amortization Net Carrying Amount Indefinite-lived intangibles $ 129,000 — $ — $ 129,000 Finite-lived intangibles 44,775 9.6 ( 7,504 ) 37,271 Total intangible assets $ 173,775 — $ ( 7,504 ) $ 166,271 December 31, 2022 Gross Carrying Amount Weighted-Average Life (Years) Accumulated Amortization Net Carrying Amount Indefinite-lived intangibles $ 129,000 — $ — $ 129,000 Finite-lived intangibles 34,775 9.9 ( 3,670 ) 31,105 Total intangible assets $ 163,775 — $ ( 3,670 ) $ 160,105
Schedule of Expected Amortization of the Intangible Assets	The expected amortization of the intangible assets, as of December 31, 2023, for each of the next five years and thereafter is as follows: 2024 $ 4,903 2025 4,903 2026 4,903 2027 4,462 2028 4,022 Thereafter 14,078 Total $ 37,271

Revenue (Tables)

Revenue (Tables)	12 Months Ended
	Dec. 31, 2023
Revenue from Contract with Customer [Abstract]
Summary of Disaggregation of Total Revenues	The following table disaggregates total revenues from external customers by product sales, royalty revenue, and collaboration and license revenue (in thousands): Year Ended December 31, 2023 2022 2021 Product sales: Crysvita $ 75,697 $ 42,678 $ 21,422 Mepsevii 30,441 20,637 16,035 Dojolvi 70,633 55,612 39,560 Evkeeza 3,642 — — Total product sales 180,413 118,927 77,017 Crysvita royalty revenue 182,652 21,692 17,951 Collaboration and license revenue: Crysvita collaboration revenue in Profit-Share Territory 69,705 215,024 171,198 Crysvita royalty revenue in European Territory — — 244 Daiichi Sankyo 1,479 7,686 84,996 Total collaboration and license revenue 71,184 222,710 256,438 Total revenues $ 434,249 $ 363,329 $ 351,406 The following table disaggregates total revenues based on geographic location (in thousands): Year Ended December 31, 2023 2022 2021 North America $ 307,149 $ 281,088 $ 301,110 Latin America 77,342 44,711 23,636 Europe 47,534 36,369 26,660 Japan 2,224 1,161 — Total revenues $ 434,249 $ 363,329 $ 351,406
Schedule of Sales-Related Accruals and Allowances	The following table presents the activity and ending balances for sales-related accruals and allowances (in thousands): Year Ended December 31, 2023 2022 2021 Balance of product sales reserve at beginning of year $ 11,487 $ 7,181 $ 3,913 Provisions 18,761 13,525 9,586 Payments ( 12,746 ) ( 9,613 ) ( 6,120 ) Adjustments ( 473 ) 394 ( 198 ) Balance of product sales reserve at end of year $ 17,029 $ 11,487 $ 7,181
Summary of Changes in Contract Liabilities	The following table presents changes in the contract liabilities for the years ended December 31, 2023 and 2022 (in thousands): Year Ended December 31, 2023 2022 Balance of contract liabilities at beginning of period $ 1,479 $ 9,076 Additions — 89 Deductions ( 1,479 ) ( 7,686 ) Balance of contract liabilities at end of period, net $ — $ 1,479

License and Research Agreemen_2

License and Research Agreements (Tables)	12 Months Ended
	Dec. 31, 2023
Share of Collaboration and Royalty Revenue Related to Crysvita	Total Crysvita revenue was as follows (in thousands): Year Ended December 31, 2023 2022 2021 Revenue in profit-share territory: Collaboration revenue $ 69,705 $ 215,024 $ 171,198 Royalty revenue 113,288 — — Non-cash royalty revenue 48,581 — — Total revenue in Profit-Share Territory 231,574 215,024 171,198 Product sales 75,697 42,678 21,422 Royalty revenue in European Territory — — 244 Non-cash royalty revenue in European Territories 20,783 21,692 17,951 Total Crysvita revenue $ 328,054 $ 279,394 $ 210,815 Royalty Revenue for Sales in the 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 10. 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 records the royalty revenue as non-cash royalty revenues. The Company records this revenue as royalty revenue.
Schedule Of Collaboration Cost Sharing and Payments	These amounts were recognized in the Company’s Statements of Operations in connection with the collaboration agreement with KKC as follows (in thousands): Year Ended December 31, 2023 2022 2021 Research and development $ ( 6,510 ) $ ( 15,974 ) $ ( 21,657 ) Selling, general and administrative $ ( 17,199 ) $ ( 37,217 ) $ ( 32,629 ) Cost of sales $ 18,476 $ 13,250 $ 6,701
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 December 31, 2021 $ 13,695 Change in fair value ( 10,888 ) December 31, 2022 2,807 Change in fair value 397 December 31, 2023 $ 3,204
Arcturus
Schedule of Changes in Fair Value of Equity Investment	The changes in the fair value of the Company’s equity investment in Arcturus were as follows (in thousands): Arcturus Common Stock December 31, 2021 $ 18,505 Change in fair value ( 8,411 ) Sale of shares ( 10,094 ) December 31, 2022 $ —

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2023
Lessee Disclosure [Abstract]
Summary of Components of Lease Expense	The components of lease expense were as follows (in thousands): Year Ended December 31, 2023 2022 2021 Operating lease expense $ 12,883 $ 11,775 $ 11,209 Variable lease expense 5,272 4,785 4,142 Financing: Amortization 203 343 310 Interest expense — 37 58 Total $ 18,358 $ 16,940 $ 15,719
Schedule of Maturities of Lease Liabilities and the Reconciliation of Lease Liabilities	The following table summarizes maturities of lease liabilities and the reconciliation of lease liabilities as of December 31, 2023: Year Ending December 31, Operating 2024 $ 16,234 2025 11,932 2026 8,430 2027 5,867 2028 5,887 Thereafter 6,009 Total future lease payments 54,359 Less: Amount representing interest ( 11,190 ) Present value of future lease payments 43,169 Less: Lease liabilities, current ( 12,595 ) Lease liabilities , non-curre nt $ 30,574

Liabilities for Sales of Futu_2

Liabilities for Sales of Future Royalties (Tables)	12 Months Ended
	Dec. 31, 2023
Deferred Revenue Disclosure [Abstract]
Schedule of Activity Within Liability for Sale of Future Royalties	The following table shows the activity within the liability account (in thousands): Liabilities for Sales of Future Royalties RPI OMERS Total December 31, 2021 $ 351,786 $ — $ 351,786 Net proceeds from sale of future — 490,950 490,950 Royalty revenue ( 21,692 ) — ( 21,692 ) Non-cash interest expense 35,095 19,300 54,395 December 31, 2022 365,189 510,250 875,439 Royalty revenue ( 20,783 ) ( 38,524 ) ( 59,307 ) Non-cash interest expense 32,235 43,200 75,435 December 31, 2023 $ 376,641 $ 514,926 $ 891,567

Stock-Based Awards (Tables)

Stock-Based Awards (Tables)	12 Months Ended
	Dec. 31, 2023
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Summary of Activity Under Stock Option Plans Including 2011 Plan, 2014 Plan and 2023 Plan	Stock Option Activity The following table summarizes activity under the Company’s stock option plans and related information: Options Outstanding Number of Options Weighted- Average Exercise Price Weighted-Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (In thousands) Outstanding — December 31, 2022 7,773,367 $ 72.56 6.60 $ 8,476 Options granted 2,123,256 45.05 Options exercised ( 209,793 ) 13.07 Options cancelled ( 899,118 ) 71.56 Outstanding — December 31, 2023 8,787,712 67.43 6.39 7,558 Vested and exercisable — December 31, 2023 5,415,110 73.28 4.96 1,214 Vested and expected to vest — December 31, 2023 8,461,973 67.96 6.29 6,794
Summary of Stock-Based Compensation Expense	Total stock-based compensation recognized was as follows (in thousands): Year Ended December 31, 2023 2022 2021 Cost of sales $ 1,166 $ 902 $ 871 Research and development 74,531 74,464 59,097 Selling, general and administrative 59,516 55,002 45,011 Total stock-based compensation expense $ 135,213 $ 130,368 $ 104,979
Fair Value of Stock Option Awards Granted Estimated Using Black-Scholes Option-Pricing Model	The fair value of stock option awards granted was estimated at the date of grant using a Black-Scholes option-pricing model with the following weighted-average assumptions: Year Ended December 31, 2023 2022 2021 Expected term (years) 6.07 6.07 6.06 Expected volatility 55 % 56 % 60 % Risk-free interest rate 4.2 % 2.0 % 1.0 % Expected dividend rate 0.0 % 0.0 % 0.0 % The fair value of PSOs granted was estimated at the date of grant using a Black-Scholes option-pricing model with the following weighted-average assumptions: Year Ended December 31, 2022 Expected term in years 3.60 Expected volatility 57 % Risk-free interest rate 1.5 % Expected dividend rate 0.0 %
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Summary of Activity Under Stock Units from 2014 Plan	The following table summarizes activity under the Company’s Restricted Stock Units, or RSU, plans and related information: RSUs Outstanding Number Weighted- Average Grant Date Fair Value Unvested — December 31, 2022 2,129,153 $ 75.11 RSUs granted 2,447,170 44.52 RSUs vested ( 738,130 ) 73.99 RSUs cancelled ( 394,081 ) 61.22 Unvested — December 31, 2023 3,444,112 55.21
Performance Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Summary of Activity Under Stock Units from 2014 Plan	The following table summarizes activity under the Company’s Performance Stock Units, or PSUs and related information: PSUs Outstanding Number Weighted- Average Grant Date Fair Value Unvested — December 31, 2022 209,230 $ 98.09 PSUs granted 362,470 50.29 PSUs vested ( 27,581 ) 141.86 PSUs cancelled ( 38,013 ) 106.80 Unvested — December 31, 2023 506,106 60.82
Performance Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Summary of Activity Under Stock Option Plans Including 2011 Plan, 2014 Plan and 2023 Plan	The following table summarizes activity under the Company’s Performance Stock Option, or PSO, plans and related information: PSOs Outstanding Number of Options Weighted- Average Exercise Price Weighted-Average Remaining Contractual Term (Years) Aggregate Intrinsic Value Outstanding — December 31, 2022 1,624,599 $ 67.37 4.14 $ — PSOs cancelled ( 243,601 ) 67.37 Outstanding — December 31, 2023 1,380,998 67.37 3.15 — Vested and exercisable — December 31, 2023 117,865 67.37 3.09 — Vested and expected to vest — December 31, 2023 983,173 67.37 3.14 —

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Components of Company's Loss Before Income Taxes	The components of the Company’s loss before income taxes were as follows (in thousands): Year Ended December 31, 2023 2022 2021 Domestic $ 608,166 $ 703,411 $ 455,314 Foreign 298 ( 1,686 ) ( 2,333 ) Total loss before income taxes $ 608,464 $ 701,725 $ 452,981
Components of Company's Income Tax Provision	The components of the Company’s income tax provision were as follows (in thousands): Year Ended December 31, 2023 2022 2021 Current provision for income taxes: Federal $ — $ — $ — State ( 3,187 ) 6,062 ( 14 ) International 3,127 1,274 1,058 Total current tax provision ( 60 ) 7,336 1,044 Deferred tax provision: Federal — — — State ( 1,608 ) ( 1,640 ) — International ( 157 ) — — Total deferred tax provision ( 1,765 ) ( 1,640 ) — Total (benefit from) provision for income taxes $ ( 1,825 ) $ 5,696 $ 1,044
Effective Tax Rate of Provision for Income Taxes from Federal Statutory Rate	The effective tax rate of our provision for income taxes differs from the federal statutory rate as follows: Year Ended December 31, 2023 2022 2021 Federal statutory income tax rate 21.0 % 21.0 % 21.0 % State income taxes, net of federal benefit 0.8 ( 0.4 ) — Federal tax credits 7.3 5.9 7.2 Other ( 0.7 ) ( 0.1 ) 0.5 Nondeductible permanent items ( 0.3 ) ( 0.6 ) ( 0.8 ) Stock-based compensation ( 1.8 ) ( 1.2 ) 1.3 Uncertain tax positions ( 1.4 ) ( 1.2 ) ( 1.4 ) Change in valuation allowance ( 24.1 ) ( 24.0 ) ( 27.9 ) Foreign rate differential ( 0.5 ) ( 0.2 ) ( 0.1 ) Provision for income taxes 0.3 % ( 0.8 ) % ( 0.2 ) %
Schedule of Tax Effect of Temporary Differences to Significant Portions of Deferred Tax Assets	The tax effect of temporary differences that give rise to significant portions of the deferred tax assets is presented below (in thousands): Year Ended December 31, 2023 2022 Deferred tax assets: Loss carryforwards $ 266,253 $ 231,835 Tax credits 305,198 260,546 Stock options 44,795 39,784 Accruals and reserves 27,694 27,029 Fixed assets and intangibles 33,853 39,233 Liabilities for sales of future royalties 205,400 214,900 Basis difference in equity investments 8,423 8,971 Capitalized research and development costs 149,898 75,335 Other 281 3,028 Gross deferred tax assets 1,041,795 900,661 Valuation allowance ( 1,035,836 ) ( 894,518 ) Total deferred tax assets 5,959 6,143 Deferred tax liabilities: In-process research and development ( 30,688 ) ( 31,667 ) Right-of-use lease assets ( 5,329 ) ( 6,143 ) Gross deferred tax liabilities ( 36,017 ) ( 37,810 ) Net deferred tax liabilities $ ( 30,058 ) $ ( 31,667 )
Unrecognized Tax Benefits	A reconciliation of the Company’s unrecognized tax benefits follows (in thousands): December 31, 2023 2022 2021 Balance at beginning of year $ 66,794 $ 55,360 $ 46,662 Additions based on tax positions related to current 12,562 11,316 8,542 Additions for tax positions of prior years 642 377 356 Reductions for tax positions of prior years — ( 259 ) ( 200 ) Balance at end of year $ 79,998 $ 66,794 $ 55,360

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Summary of Aggregate Payments under Contractually Binding Manufacturing and Service Agreements	As of December 31, 2023, the aggregate payments under contractually-binding manufacturing and service agreements are as follows (in thousands): Year Ended December 31, 2024 2025 Total Manufacturing and Services $ 27,899 $ 5,718 $ 33,617

Net Loss per Share (Tables)

Net Loss per Share (Tables)	12 Months Ended
	Dec. 31, 2023
Earnings Per Share [Abstract]
Computation of Basic and Diluted Net Loss per Share	The following table sets forth the computation of the basic and diluted net loss per share during the years ended December 31, 2023, 2022, and 2021 (in thousands, except share and per share data): Year Ended December 31, 2023 2022 2021 Numerator: Net loss $ ( 606,639 ) $ ( 707,421 ) $ ( 454,025 ) Denominator: Weighted-average shares used to compute net loss per 73,543,862 69,914,225 67,795,540 Net loss per share, basic and diluted $ ( 8.25 ) $ ( 10.12 ) $ ( 6.70 )
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: Year Ended December 31, 2023 2022 2021 Options to purchase common stock, 14,152,286 11,290,935 8,214,063 Employee stock purchase plan 8,450 7,581 3,511 14,160,736 11,298,516 8,217,574

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2023
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Schedule of Total Accumulated Other Comprehensive Income (Loss)	Total accumulated other comprehensive income (loss) consisted of the following (in thousands): Year Ended December 31, 2023 2022 Cumulative foreign currency translation adjustment $ ( 606 ) $ ( 845 ) Unrealized gain (loss) on securities available-for-sale 1,253 ( 5,728 ) Total accumulated other comprehensive income (loss) $ 647 $ ( 6,573 )

Organization and Basis of Pre_2

Organization and Basis of Presentation - Additional Information (Details)	12 Months Ended
	Dec. 31, 2023 Segment
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	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Accounting Policies [Abstract]
Cash and cash equivalents	$ 213,584	$ 132,944	$ 307,584
Restricted cash included in other current assets	$ 2,008	$ 862	$ 0
Restricted Cash and Cash Equivalents, Current, Asset, Statement of Financial Position [Extensible List]	Other assets	Other assets	Other assets
Restricted cash included in other non-current assets	$ 3,807	$ 3,795	$ 2,001
Restricted Cash and Cash Equivalents, Noncurrent, Asset, Statement of Financial Position [Extensible List]	Other assets	Other assets	Other assets
Total cash, cash equivalents, and restricted cash shown in the statements of cash flows	$ 219,399	$ 137,601	$ 309,585	$ 726,294

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Accounting Policies [Abstract]
Allowance for doubtful accounts	$ 0	$ 0
Unrecognized tax benefits related to interest or penalties	$ 0

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	$ 749,239	$ 884,017
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	222,930	133,299
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	526,309	750,718
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	162,289	102,847
Money Market Funds | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	162,289	102,847
Asset-backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	2,712	11,980
Asset-backed Securities | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	2,712	11,980
Certificates of Deposit and Time Deposits
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	17,986	25,972
Certificates of Deposit and Time Deposits | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	17,986	25,972
Corporate Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	215,166	427,598
Corporate Bonds | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	215,166	427,598
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	20,620	135,393
Commercial Paper | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	20,620	135,393
U.S. Government Treasury and Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	317,042	156,990
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	57,437	27,645
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	259,605	129,345
Debt Securities in Government Sponsored Entities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value		15,855
Debt Securities in Government Sponsored Entities | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value		15,855
Investments in Solid Common Stock
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	3,204	2,807
Investments in Solid Common Stock | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	3,204	2,807
Deferred compensation assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	10,220	4,575
Deferred compensation assets | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	10,220	4,575
Deferred compensation liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	10,365	4,657
Deferred compensation liabilities | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	$ 10,365	$ 4,657

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Short-Term Debt [Member]
Schedule Of Available For Sale Securities [Line Items]
Deferred compensation liabilities	$ 0.2	$ 0
Long-Term Debt [Member]
Schedule Of Available For Sale Securities [Line Items]
Deferred compensation liabilities	$ 10.1	$ 4.7

Balance Sheet Components - Summ

Balance Sheet Components - Summary of Cash Equivalents and Marketable Debt Securities Classified as Available For Sale Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 734,562	$ 882,363
Gross Unrealized Gains	1,693	407
Gross Unrealized Losses	(440)	(6,135)
Estimated Fair Value	735,815	876,635
Money Market Funds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	162,289	102,847
Estimated Fair Value	162,289	102,847
Asset-backed Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	2,715	12,002
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(3)	(22)
Estimated Fair Value	2,712	11,980
Certificates of Deposit and Time Deposits
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	17,986	25,972
Estimated Fair Value	17,986	25,972
Corporate Bonds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	214,792	432,211
Gross Unrealized Gains	711	87
Gross Unrealized Losses	(337)	(4,700)
Estimated Fair Value	215,166	427,598
Commercial Paper
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	20,620	135,393
Estimated Fair Value	20,620	135,393
U.S. Government Treasury and Agency Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	316,160	157,933
Gross Unrealized Gains	982	320
Gross Unrealized Losses	(100)	(1,263)
Estimated Fair Value	$ 317,042	156,990
Debt Securities in Government Sponsored Entities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		16,005
Gross Unrealized Losses		(150)
Estimated Fair Value		$ 15,855

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Schedule Of Available For Sale Securities [Line Items]
Depreciation expense	$ 22.2	$ 15	$ 12.9
Maximum
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale securities remaining contractual maturities	3 years

Balance Sheet Components - Su_2

Balance Sheet Components - Summary of Inventory (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Inventory, Net [Abstract]
Work-in-process	$ 18,859	$ 17,486
Finished goods	15,110	9,280
Total inventory	$ 33,969	$ 26,766

Balance Sheet Components - Su_3

Balance Sheet Components - Summary of Property, Plant and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 373,967	$ 323,107
Less accumulated depreciation	(83,401)	(63,381)
Property, plant and equipment, net	290,566	259,726
Building
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 181,356	$ 2,798
Building | Minimum
Property Plant And Equipment [Line Items]
Property, plant and equipment, estimated useful lives (years)	20 years	20 years
Building | Maximum
Property Plant And Equipment [Line Items]
Property, plant and equipment, estimated useful lives (years)	30 years	30 years
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 58,683	$ 43,941
Property, plant and equipment, estimated useful lives	us-gaap:UsefulLifeShorterOfTermOfLeaseOrAssetUtilityMember	us-gaap:UsefulLifeShorterOfTermOfLeaseOrAssetUtilityMember
Research and Development Equipment
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 56,347	$ 50,291
Property, plant and equipment, estimated useful lives (years)	5 years	5 years
Furniture and Office Equipment
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 6,419	$ 5,540
Property, plant and equipment, estimated useful lives (years)	5 years	5 years
Computer Equipment and Software
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 16,196	$ 13,876
Computer Equipment and Software | Minimum
Property Plant And Equipment [Line Items]
Property, plant and equipment, estimated useful lives (years)	3 years	3 years
Computer Equipment and Software | Maximum
Property Plant And Equipment [Line Items]
Property, plant and equipment, estimated useful lives (years)	5 years	5 years
Manufacturing Equipment
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 37,297	$ 570
Manufacturing Equipment | Minimum
Property Plant And Equipment [Line Items]
Property, plant and equipment, estimated useful lives (years)	5 years	5 years
Manufacturing Equipment | Maximum
Property Plant And Equipment [Line Items]
Property, plant and equipment, estimated useful lives (years)	15 years	15 years
Land
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 16,619	$ 16,619
Construction-in-progress
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	867	189,448
Other
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 183	$ 24

Balance Sheet Components - Su_4

Balance Sheet Components - Summary of Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Payables and Accruals [Abstract]
Research, clinical study, and manufacturing expenses	$ 65,326	$ 73,558
Payroll and related expenses	82,936	78,938
Other	48,224	52,182
Total accrued liabilities	$ 196,486	$ 204,678

Intangible Assets, Net - Additi

Intangible Assets, Net - Additional Information (Details) 1 - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
IPR&D Assets
Indefinite-Lived Intangible Assets [Line Items]
Business combination recognized intangible assets	$ 129	$ 129

Intangible Assets, Net - Addi_2

Intangible Assets, Net - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jan. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Finite Lived Intangible Assets Line Items
upfront payment	$ 30
Acquired Finite Lived Intangible Assets Weighted Average Useful Life		10 years
Regulatory milestone payments achieved		$ 10
Cost of sales
Finite Lived Intangible Assets Line Items
Costs of sales related to amortization of intangible asset		$ 3.8	$ 3.2	$ 0.3
Dimension
Finite Lived Intangible Assets Line Items
Intangible assets, remaining amortization period		5 years 8 months 12 days
Regulatory milestone payments achieved		$ 4.8

Intangible Assets, Net - Summar

Intangible Assets, Net - Summary of Company's Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Schedule of Finite and Indefinite Lived Intangible Assets [Line Items]
Intangible assets - Gross carrying amount	$ 173,775	$ 163,775
Intangible assets - Accumulated Amortization	(7,504)	(3,670)
Intangible assets - Net Carrying Amount	166,271	160,105
Indefinite-lived Intangible Assets
Schedule of Finite and Indefinite Lived Intangible Assets [Line Items]
Intangible assets - Gross carrying amount	129,000	129,000
Intangible assets - Net Carrying Amount	129,000	129,000
Finite lived intangible assets
Schedule of Finite and Indefinite Lived Intangible Assets [Line Items]
Intangible assets - Gross carrying amount	$ 44,775	$ 34,775
Intangible assets - Weighted Average Life	9 years 7 months 6 days	9 years 10 months 24 days
Intangible assets - Accumulated Amortization	$ (7,504)	$ (3,670)
Intangible assets - Net Carrying Amount	$ 37,271	$ 31,105

Intangible Assets, Net - Schedu

Intangible Assets, Net - Schedule of Expected Amortization of the Intangible Assets (Details) $ in Thousands	Dec. 31, 2023 USD ($)
Intangible Assets, Net (Excluding Goodwill) [Abstract]
2024	$ 4,903
2025	4,903
2026	4,903
2027	4,462
2028	4,022
Thereafter	14,078
Total	$ 37,271

Revenue - Summary of Disaggrega

Revenue - Summary of Disaggregation of Total Revenues from Customers (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disaggregation Of Revenue [Line Items]
Total revenues	$ 434,249	$ 363,329	$ 351,406
Collaboration and license
Disaggregation Of Revenue [Line Items]
Total revenues	71,184	222,710	256,438
Collaboration and license | Crysvita
Disaggregation Of Revenue [Line Items]
Total revenues	69,705	215,024	171,198
Collaboration and license | Crysvita | Royalty Revenue in European Territory
Disaggregation Of Revenue [Line Items]
Total revenues	0	0	244
Collaboration and license | Daiichi Sankyo
Disaggregation Of Revenue [Line Items]
Total revenues	1,479	7,686	84,996
Product Revenue
Disaggregation Of Revenue [Line Items]
Total revenues	180,413	118,927	77,017
Product Revenue | Crysvita
Disaggregation Of Revenue [Line Items]
Total revenues	75,697	42,678	21,422
Product Revenue | Mepsevii
Disaggregation Of Revenue [Line Items]
Total revenues	30,441	20,637	16,035
Product Revenue | Dojolvi
Disaggregation Of Revenue [Line Items]
Total revenues	70,633	55,612	39,560
Product Revenue | Evkeeza
Disaggregation Of Revenue [Line Items]
Total revenues	3,642	0	0
Royalty revenue
Disaggregation Of Revenue [Line Items]
Total revenues	182,652	21,692	17,951
Royalty revenue | Crysvita
Disaggregation Of Revenue [Line Items]
Total revenues	$ 182,652	$ 21,692	$ 17,951

Revenue - Summary of Disaggre_2

Revenue - Summary of Disaggregation of Total Revenues (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disaggregation Of Revenue [Line Items]
Total revenues	$ 434,249	$ 363,329	$ 351,406
North America
Disaggregation Of Revenue [Line Items]
Total revenues	307,149	281,088	301,110
Latin America
Disaggregation Of Revenue [Line Items]
Total revenues	77,342	44,711	23,636
Europe
Disaggregation Of Revenue [Line Items]
Total revenues	47,534	36,369	26,660
Japan
Disaggregation Of Revenue [Line Items]
Total revenues	$ 2,224	$ 1,161	$ 0

Revenue - Schedule of Sales-Rel

Revenue - Schedule of Sales-Related Accruals and Allowances (Details) - Product sales - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disaggregation Of Revenue [Line Items]
Balance of product sales reserve at beginning of year	$ 11,487	$ 7,181	$ 3,913
Provisions	18,761	13,525	9,586
Payments	(12,746)	(9,613)	(6,120)
Adjustments	(473)	394	(198)
Balance of product sales reserve at end of year	$ 17,029	$ 11,487	$ 7,181

Revenue - Summary of Changes in

Revenue - Summary of Changes in Contract Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Disaggregation of Revenue [Abstract]
Balance of contract liabilities at beginning of period	$ 1,479	$ 9,076
Additions	0	89
Deductions	(1,479)	(7,686)
Balance of contract liabilities at end of period, net	$ 0	$ 1,479

Revenue - Additional Informatio

Revenue - Additional Information (Details)	Dec. 31, 2023	Dec. 31, 2022
Customer One
Disaggregation of Revenue [Line Items]
Percentage of gross accounts receivable balance	53%	68%

GeneTx Acquisition - Additional

GeneTx Acquisition - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jul. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Business Acquisition [Line Items]
Acquired in-process research and development		$ 0	$ 75,033	$ 0
GeneTx [Member]
Business Acquisition [Line Items]
Business acquisition, consideration transferred	$ 75,000
Regulatory Approval Milestones	85,000
Outstanding Cash and Cash Equivalents Acquired	15,600
Amount on adjustments for working capital and transaction expenses	600
Payments to Acquire Businesses, Gross	91,200
GeneTx [Member] | Maximum
Business Acquisition [Line Items]
Future contingent milestone payments	190,000
Additional Milestone Payments	30,000
Commercial Milestone Payment	75,000
Texas A&M University [Member] | Maximum
Business Acquisition [Line Items]
Future contingent milestone payments	23,500
Annual License Fee Payment	$ 2,000
In-process Research and Development [Member] | GeneTx [Member]
Business Acquisition [Line Items]
Acquired in-process research and development			$ 75,000

License and Research Agreemen_3

License and Research Agreements - Kyowa Kirin Co., Ltd. - Additional Information (Details) - Kyowa Kirin Collaboration - License Agreement - USD ($) $ in Millions		12 Months Ended	113 Months Ended
	Jul. 01, 2022	Dec. 31, 2023	Dec. 31, 2022
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Profit loss sharing percentage on net sales		30%	35%
Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Tiered double-digit revenue share percentage entitled to receive		20%
Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Tiered double-digit revenue share percentage entitled to receive		30%
Other Current Assets
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
License agreement other receivables		$ 1.1	$ 6.4
Profit Share Revenue
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
License agreement accounts receivable		39.2	27.5
Commercial And Development Activity Reimbursements [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
License agreement accrued liabilities		$ 5.3	$ 3.1
Profit Share Territory
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Remaining profit or loss share percentage on commercializing products		50%
Percentage of right to receive royalty payments on net sales	30%
Royalty Revenue in European Territory
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of royalty on net sales receives		10%

License and Research Agreemen_4

License and Research Agreements - Saint Louis University - Additional Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($)
Saint Louis University
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone payments paid	$ 0.1

License and Research Agreemen_5

License and Research Agreements - Baylor Research Institute - Additional Information (Details) - Baylor Research Institute - Development Milestones - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Future contingent milestone payments	$ 7.5
Research and Development Expense
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Contingent milestone payment	$ 0	$ 2.5

License and Research Agreemen_6

License and Research Agreements - REGENXBIO, Inc. - Additional Information (Details) - REGENXBIO, Inc. - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2023
Option and License Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Future contingent milestone payments		$ 9
Option and license agreement description		The Company also has an option and license agreement with REGENX under which the Company has an exclusive, sublicensable, worldwide license to make, have made, use, import, sell, and offer for sale licensed products to treat Wilson disease and CDKL5 deficiency.
Annual maintenance fee for each option exercised		$ 0.1
License Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Future contingent milestone payments		14
Upfront payment for in-process research and development expense	$ 7
Annual fees payable		$ 0.1

License and Research Agreemen_7

License and Research Agreements - University of Pennsylvania - Additional Information (Details) - University of Pennsylvania School of Medicine (Penn) $ in Millions	Dec. 31, 2023 USD ($)
Research Collaboration and License Agreement Development Milestones
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Future contingent milestone payments	$ 5
Research Collaboration and License Agreement Commercial Milestones
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Future contingent milestone payments	$ 25

License and Research Agreemen_8

License and Research Agreements - Arcturus Therapeutics Holdings Inc. - Additional Information (Details) $ / shares in Units, $ in Millions	1 Months Ended			12 Months Ended
	May 31, 2020 USD ($) shares	Jun. 30, 2019 USD ($) DiseaseTarget $ / shares shares	Oct. 31, 2015 USD ($)	Dec. 31, 2022 $ / shares shares	Dec. 31, 2021 USD ($)	Dec. 31, 2023 $ / shares
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Common stock. per share | $ / shares				$ 0.001		$ 0.001
Arcturus Therapeutics Holdings Inc
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone payments received					$ 1
Upfornt cash payment paid		$ 6
Common stock purchased | shares		2,400,000
Common stock shares sold | shares				500,000
Common stock. per share | $ / shares		$ 10		$ 20.39
Business acquisition, consideration transferred		$ 30
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
Purchase price of shares purchased on exercise of common stock option	$ 9.6
Number of common stock held | shares				0
Arcturus Therapeutics Holdings Inc | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of disease targets | DiseaseTarget		12
Regulatory milestone payments			$ 24.5
Commercial milestone payments			$ 45

License and Research Agreemen_9

License and Research Agreements - Daiichi Sankyo - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		3 Months Ended	12 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Mar. 31, 2020	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaborative Arrangement, Revenue Not from Contract with Customer, Statement of Income or Comprehensive Income [Extensible Enumeration]				Revenue
Daiichi Sankyo
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred Revenue balance				$ 0	$ 1.5
Deferred Revenue Recognized				1.5	$ 7.7	$ 85
License and Technology Access Agreement | Daiichi Sankyo
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred Revenue balance				25
Upfront payment received				125
License and Technology Access Agreement | Daiichi Sankyo | Licenses Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue recognized				$ 183.3
Stock Purchase Agreement | Daiichi Sankyo
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Issuance of common stock in connection with license agreement, net of issuance costs, shares		1,243,913
Proceeds from issuance of common stock in connection with license agreement			$ 75
Issuance of common stock in connection with license agreement, net of issuance costs			$ 55.3
Stock price		$ 44.43	$ 44.43
Premium from stock purchase agreement			$ 19.7
Sublicense Agreement | Daiichi Sankyo
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront payment received	$ 8

License and Research Agreeme_10

License and Research Agreements - Mereo - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2021	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development		$ 648,449	$ 705,789	$ 497,153
License and Collaboration Agreement | Mereo
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development		$ 9,000	$ 0	$ 50,000
Payments made under agreement	$ 50,000
License and Collaboration Agreement | Maximum | Mereo
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Future contingent milestone payments	$ 254,000

License and Research Agreeme_11

License and Research Agreements - Regeneron - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Regulatory milestone payments achieved		$ 10,000
Cost of sales		45,209	$ 28,320	$ 16,008
Regeneron Pharmaceuticals Inc
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront payments of collaboration	$ 30,000
Regulatory milestone payments achieved		10,000
Development costs		7,600	7,300	$ 0
Eligible future milestone payments	$ 63,000
Accrued collaboration payables		10,600	$ 6,800
Cost of sales		$ 700
Maximum | Regeneron Pharmaceuticals Inc
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Profit loss sharing percentage on net sales		40%
Minimum | Regeneron Pharmaceuticals Inc
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Profit loss sharing percentage on net sales	20%

License and Research Agreeme_12

License and Research Agreements - Abeona - Additional Information (Details) - Abeona - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	May 31, 2022	Dec. 31, 2023	Dec. 31, 2022
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Other costs			$ 0
Development and transition costs			$ 3.1
Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Eligible future milestone payments		$ 1
License and Collaboration Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of royalty on net sales receives		10%
Commercial milestone payments	$ 30

License and Research Agreeme_13

License and Research Agreements - Solid Biosciences, Inc. - Additional Information (Details) $ in Thousands	1 Months Ended		12 Months Ended
	Oct. 31, 2022 shares	Oct. 31, 2020 USD ($) shares	Dec. 31, 2020 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Common stock investment value				$ 82	$ 70
Solid Biosciences, Inc.
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Remaining consideration paid			$ 13,200
Business acquisition, consideration transferred			$ 40,000
Common stock investment value		$ 26,800
Description of the stock split	In October 2022, Solid announced a 1 for 15 reverse stock split. After the split, the Company held 521,719 shares of Solid's common stock.
stock split conversion ratio	1
Number of common shares held after split | shares	521,719
Collaboration Agreement | Solid Biosciences, Inc.
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of common stock purchased | shares		7,825,797
Aggregate purchase price		$ 40,000
Maximum | Collaboration and License Agreement | Solid Biosciences, Inc.
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Development milestone payments		25,000
Regulatory milestone payments		65,000
Commercial milestone payments		$ 165,000

License and Research Agreeme_14

License and Research Agreements - Share of Collaboration and Royalty Revenue Related to Crysvita (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	$ 434,249	$ 363,329	$ 351,406
Collaboration and Royalty | Kyowa Kirin Collaboration
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	328,054	279,394	210,815
Collaboration and Royalty | Kyowa Kirin Collaboration | Profit Share Territory
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	231,574	215,024	171,198
Royalty revenue
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	182,652	21,692	17,951
Royalty revenue | Kyowa Kirin Collaboration | Profit Share Territory
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	113,288	0	0
Royalty revenue | Kyowa Kirin Collaboration | Royalty Revenue in European Territory
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	0	0	244
Product sales
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	180,413	118,927	77,017
Product sales | Kyowa Kirin Collaboration
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	75,697	42,678	21,422
Collaboration Revenue | Kyowa Kirin Collaboration | Profit Share Territory
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	69,705	215,024	171,198
Non-cash royalty revenue | Kyowa Kirin Collaboration | Profit Share Territory
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	48,581	0	0
Non-cash royalty revenue | Kyowa Kirin Collaboration | Royalty Revenue in European Territory
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	$ 20,783	$ 21,692	$ 17,951

License and Research Agreeme_15

License and Research Agreements - Schedule of Collaboration Cost Sharing and Payments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cost Sharing Payments [Line Items]
Cost of sales	$ 45,209	$ 28,320	$ 16,008
Kyowa Kirin Collaboration
Cost Sharing Payments [Line Items]
Research and development	(6,510)	(15,974)	(21,657)
Selling, general and administrative	(17,199)	(37,217)	(32,629)
Cost of sales	$ 18,476	$ 13,250	$ 6,701

License and Research Agreeme_16

License and Research Agreements - Schedule of Changes in Fair Value of Equity Investment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock, Beginning balance	$ 884,017
Common stock, Ending balance	749,239	$ 884,017
Arcturus | Common Stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock, Beginning balance	$ 0	18,505
Common stock, Change in fair value		(8,411)
Common stock, Sale of shares		(10,094)
Common stock, Ending balance		$ 0

License and Research Agreeme_17

License and Research Agreements - Schedule of Changes in Fair Value of Investment in Securities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock, Beginning balance	$ 884,017
Common stock, Ending balance	749,239	$ 884,017
Common Stock | Solid Biosciences, Inc.
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock, Beginning balance	2,807	13,695
Common stock, Change in fair value	397	(10,888)
Common stock, Ending balance	$ 3,204	$ 2,807

Leases - Additional Information

Leases - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Lessee Disclosure [Abstract]
Operating lease extension details	multiple renewal periods
Operating lease, existence of option to extend	true
Operating lease expiry term	2029
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Other Assets, Noncurrent	Other Assets, Noncurrent
Right-of-use lease assets	$ 23.9	$ 26
Cash paid for measurement of operating lease liabilities	$ 13.4	$ 13.1	$ 11.8
Operating lease weighted average remaining lease term	4 years 6 months	3 years
Financing lease weighted average remaining lease term		2 years 9 months 18 days
Operating lease weighted average discount rate	9.60%	6.70%
Financing lease weighted average discount rate		5.10%

Leases - Summary of Components

Leases - Summary of Components of Lease Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Lease, Cost [Abstract]
Operating lease expense	$ 12,883	$ 11,775	$ 11,209
Variable lease expense	5,272	4,785	4,142
Financing:
Amortization	203	343	310
Interest expense	0	37	58
Total	$ 18,358	$ 16,940	$ 15,719

Leases - Schedule of Maturities

Leases - Schedule of Maturities of Lease Liabilities and the Reconciliation of Lease Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Operating
2024	$ 16,234
2025	11,932
2026	8,430
2027	5,867
2028	5,887
Thereafter	6,009
Total future lease payments	54,359
Less: Amount representing interest	(11,190)
Present value of future lease payments	43,169
Less: Lease liabilities, current	$ (12,595)
Operating Lease, Liability, Statement of Financial Position [Extensible List]	Less: Lease liabilities, current
Lease liabilities, non-current	$ 30,574
Operating Lease, Liability, Statement of Financial Position [Extensible List]	Non-current lease liability
Future Minimum Lease Payments - Operating and Financing Leases
Less: Lease liabilities, current	$ (12,595)	$ (11,779)
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Less: Lease liabilities, current
Non-current lease liability	$ 30,574	$ 19,814
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Non-current lease liability

Liabilities for Sales of Futu_3

Liabilities for Sales of Future Royalties - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended		12 Months Ended			49 Months Ended
	Jul. 31, 2022	Dec. 31, 2019	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2023
Liability For Sale Of Future Royalties [Line Items]
Proceeds from the sale of future royalties, net			$ 0	$ 490,950	$ 0
Non-cash collaboration royalty revenue			$ 69,364	21,692	$ 17,951
RPI Finance Trust (RPI)
Liability For Sale Of Future Royalties [Line Items]
Proceeds from the sale of future royalties, net				0
OMERS
Liability For Sale Of Future Royalties [Line Items]
Proceeds from the sale of future royalties, net				$ 490,950
Royalty Purchase Agreement
Liability For Sale Of Future Royalties [Line Items]
Profit loss sharing percentage on net sales	30%
Royalty Purchase Agreement | RPI Finance Trust (RPI)
Liability For Sale Of Future Royalties [Line Items]
Proceeds from sale of future royalties		$ 320,000
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, or when aggregate royalty payments received by RPI are equal to $800.0 million.
Royalties transaction costs net		5,800
Proceeds from the sale of future royalties, net		314,200
Effective annual interest rate			6.20%			6.20%
Non-cash collaboration royalty revenue						$ 73,400
Royalty Purchase Agreement | OMERS
Liability For Sale Of Future Royalties [Line Items]
Proceeds from sale of future royalties	$ 500,000
Royalty payment termination description	In July 2022, the Company entered into a Royalty Purchase Agreement with OMERS. Pursuant to the agreement, OMERS paid $500.0 million to the Company in consideration for the right to receive 30% of the future royalty payments due to the Company from KKC based on net sales of Crysvita in the U.S. and Canada under the terms of the KKC Collaboration Agreement. The calculation of royalty payments to OMERS is based on net sales of Crysvita beginning in April 2023 and will expire upon the earlier of the date on which aggregate payments received by OMERS equals $725.0 million or the date the final royalty payment is made to the Company under the KKC Collaboration Agreement.
Royalty agreement termination threshold amount	$ 725,000
Payment from sale of future royalties	500,000
Royalties transaction costs net	$ 9,100
Proceeds from the sale of future royalties, net		$ 491,000
Effective annual interest rate			7.80%			7.80%
Non-cash collaboration royalty revenue						$ 8,600
Royalty Purchase Agreement | Minimum | RPI Finance Trust (RPI)
Liability For Sale Of Future Royalties [Line Items]
Royalty agreement termination threshold amount			$ 608,000			608,000
Royalty Purchase Agreement | Maximum | RPI Finance Trust (RPI)
Liability For Sale Of Future Royalties [Line Items]
Royalty agreement termination threshold amount			$ 800,000			$ 800,000

Liabilities for Sales of Futu_4

Liabilities for Sales of Future Royalties - Schedule of Activity Within Liability Related to Sale of Future Royalties (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Liability For Sale Of Future Royalties [Line Items]
Liability for sale of future royalties at beginning of year	$ 875,439	$ 351,786
Net proceeds from sale of future royalties	0	490,950	$ 0
Royalty revenue	(59,307)	(21,692)
Non-cash interest expense	75,435	54,395
Liability for sale of future royalties at end of year	891,567	875,439	351,786
RPI Finance Trust (RPI)
Liability For Sale Of Future Royalties [Line Items]
Liability for sale of future royalties at beginning of year	365,189	351,786
Net proceeds from sale of future royalties		0
Royalty revenue	(20,783)	(21,692)
Non-cash interest expense	32,235	35,095
Liability for sale of future royalties at end of year	376,641	365,189	351,786
OMERS
Liability For Sale Of Future Royalties [Line Items]
Liability for sale of future royalties at beginning of year	510,250	0
Net proceeds from sale of future royalties		490,950
Royalty revenue	(38,524)	0
Non-cash interest expense	43,200	19,300
Liability for sale of future royalties at end of year	$ 514,926	$ 510,250	$ 0

Equity - Additional Information

Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		12 Months Ended		32 Months Ended
	Oct. 31, 2023	May 31, 2021	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2023
Stockholders Equity Line Items
Stock sold in at-the-market offering			1,175,584
Net proceeds from at-the-market offering			$ 53.3
Pre Funded Warrant
Stockholders Equity Line Items
Number of warrants exercised			0		0
Underwritten Public Offering
Stockholders Equity Line Items
Common stock shares sold	9,833,334
Shares purchased by underwriters	1,500,000
Public offering price	$ 30
Underwritten Public Offering | Pre Funded Warrant
Stockholders Equity Line Items
Net proceeds from sale of common stock	$ 326.5
Underwritten Public Offering Shares	1,666,722
Pre-funded warrant price	$ 29.999
Common stock warrants, exercise price	$ 0.001
Open Market Sale
Stockholders Equity Line Items
Common stock shares sold				0
Stock sold in at-the-market offering					2,225,956
Net proceeds from at-the-market offering					$ 132.2
Option to sell common stock aggregate offering price		$ 350

Stock-Based Awards - Additional

Stock-Based Awards - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Jun. 30, 2023	Feb. 01, 2021	Feb. 05, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total intrinsic value of options exercised	$ 4.9	$ 2.6	$ 38.8
Cash received from exercise of options	$ 2.7	$ 6.2	$ 36.6
weighted-average estimated fair value	$ 25.53	$ 34.77	$ 70.84
Total estimated fair value of options vested	$ 59.7	$ 58.7	$ 48.1
Total unrecognized compensation cost	219.8
Weighted-average period to recognize cost		2 years 2 months 12 days
Stock-based compensation capitalized to inventory	1.9	$ 2.2	1.7
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total fair value of shares vested	54.6	47.1	35.5
Aggregate intrinsic value	33	37.8	69.9
Performance Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total fair value of shares vested	3.9	1.6	9.2
Aggregate intrinsic value	1.3	$ 2	$ 18.9
Performance Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
weighted-average estimated fair value		$ 28.76
Total estimated fair value of options vested	$ 3.4
Maximum | Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock based awards vesting period	4 years
Minimum | Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock based awards vesting period	1 year
2014 Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share of common stock authorized for future issuance						2,250,000
Automatic increases in shares available for grant effective date	Jan. 01, 2015
Shares available for grant, ending date	Jun. 07, 2023
2023 Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share of common stock authorized for future issuance				4,500,000
2023 Plan and Inducement Plan | Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option vesting rights, percentage			25%
Stock based awards vesting period			4 years
2023 Plan and Inducement Plan | Maximum | Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award expiration period			10 years
2023 Plan and Inducement Plan | First Anniversary | Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option vesting rights, percentage			25%
2023 Plan and Inducement Plan | Shares Vesting Monthly After First Anniversary | Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option vesting rights, percentage			2.08%
2014 Equity Incentive, 2023 Incentive and Employment Inducement Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share of common stock authorized for future issuance	19,610,125
2014 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share of common stock authorized for future issuance	6,609,795
Percentage of statutory stock awards	85%
Common stock shares issued	195,462
Employment Inducement Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share of common stock available for grant					850,000

Stock-Based Awards - Summary of

Stock-Based Awards - Summary of Activity Under Stock Option Plans Including 2011 Plan and 2014 Plan and 2023 Plan (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share-Based Payment Arrangement [Abstract]
Number of Options, Outstanding, Beginning Balance	7,773,367
Number of Options, Options granted	2,123,256
Number of Options, Options exercised	(209,793)
Number of Options, Options cancelled	(899,118)
Number of Options, Outstanding, Ending Balance	8,787,712	7,773,367
Vested and exercisable December 31, 2023	5,415,110
Vested and expected to vest December 31, 2023	8,461,973
Weighted Average Exercise Price, Outstanding, Beginning Balance	$ 72.56
Weighted Average Exercise Price, Options granted	45.05
Weighted Average Exercise Price, Options exercised	13.07
Weighted Average Exercise Price, Options cancelled	71.56
Weighted Average Exercise Price, Outstanding, Ending Balance	67.43	$ 72.56
Weighted- Average Exercise Price,Weighted Average Exercise Price	73.28
Weighted Average Exercise Price, Vested and expected to vest December 31, 2023	$ 67.96
Weighted Average Remaining Contractual Term (Years), Outstanding	6 years 4 months 20 days	6 years 7 months 6 days
Weighted Average Remaining Contractual Term (Years), Vested and exercisable - December 31, 2023	4 years 11 months 15 days
Weighted-Average Remaining Contractual Term,Vested and expected to vest December 31, 2023	6 years 3 months 14 days
Aggregate Intrinsic Value, Outstanding	$ 7,558	$ 8,476
Aggregate Intrinsic Value, Vested and exercisable - December 31, 2023	1,214
Aggregate Intrinsic Value, Vested and expected to vest - December 31, 2023	$ 6,794

Stock-Based Awards- Summary Act

Stock-Based Awards- Summary Activity Under the Performance Stock Option (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Vested and exercisable December 31, 2023	5,415,110
Vested and expected to vest December 31, 2023	8,461,973
Weighted- Average Exercise Price,Weighted Average Exercise Price	$ 73.28
Weighted Average Exercise Price, Vested and expected to vest December 31, 2023	$ 67.96
Weighted-Average Remaining Contractual Term,Vested and expected to vest December 31, 2023	6 years 3 months 14 days
Weighted Average Remaining Contractual Term (Years), Vested and exercisable - December 31, 2023	4 years 11 months 15 days
Aggregate Intrinsic Value, Vested and exercisable - December 31, 2023	$ 1,214
Aggregate Intrinsic Value, Vested and expected to vest - December 31, 2023	$ 6,794
Performance Stock Options [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Outstanding, Number of Shares, Unvested, Beginning Balance	1,624,599
PSOs cancelled	(243,601)
Outstanding, Number of Shares, Unvested, Ending Balance	1,380,998	1,624,599
Vested and exercisable December 31, 2023	117,865
Vested and expected to vest December 31, 2023	983,173
Outstanding, Weighted-Average Grant Date Fair Value, Unvested, Beginning Balance	$ 67.37
Weighted Average Exercise Price ,PSOs cancelled	67.37
Weighted- Average Exercise Price,Outstanding December 31, 2023	67.37	$ 67.37
Weighted- Average Exercise Price,Weighted Average Exercise Price	67.37
Weighted Average Exercise Price, Vested and expected to vest December 31, 2023	$ 67.37
Weighted-Average Remaining Contractual Term,Outstanding at December 31, 2023	3 years 1 month 24 days	4 years 1 month 20 days
Weighted-Average Remaining Contractual Term,Vested and expected to vest December 31, 2023	3 years 1 month 20 days
Weighted Average Remaining Contractual Term (Years), Vested and exercisable - December 31, 2023	3 years 1 month 2 days
Aggregate Intrinsic Value, Outstanding	$ 0	$ 0
Aggregate Intrinsic Value, Vested and exercisable - December 31, 2023	0
Aggregate Intrinsic Value, Vested and expected to vest - December 31, 2023	$ 0

Stock-Based Awards - Summary _2

Stock-Based Awards - Summary of Activity Under Restricted Stock Units (RSUs) from 2014 Plan (Details) - Restricted Stock Units	12 Months Ended
	Dec. 31, 2023 $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding, Number of Shares, Unvested, Beginning Balance | shares	2,129,153
Number of shares, granted | shares	2,447,170
Number of shares, vested | shares	(738,130)
Number of shares, cancelled | shares	(394,081)
Outstanding, Number of Shares, Unvested, Ending Balance | shares	3,444,112
Outstanding, Weighted-Average Grant Date Fair Value, Unvested, Beginning Balance | $ / shares	$ 75.11
Weighted-Average Grant Date Fair Value, granted | $ / shares	44.52
Weighted-Average Grant Date Fair Value, vested | $ / shares	73.99
Weighted-Average Grant Date Fair Value, cancelled | $ / shares	61.22
Weighted- Average Exercise Price,Outstanding December 31, 2023 | $ / shares	$ 55.21

Stock-Based Awards - Summary _3

Stock-Based Awards - Summary of Activity Under PSUs from 2014 Plan (Details) - Performance Stock Units	12 Months Ended
	Dec. 31, 2023 $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding, Number of Shares, Unvested, Beginning Balance | shares	209,230
Number of shares, granted | shares	362,470
Number of shares, vested | shares	(27,581)
Number of shares, cancelled | shares	(38,013)
Outstanding, Number of Shares, Unvested, Ending Balance | shares	506,106
Outstanding, Weighted-Average Grant Date Fair Value, Unvested, Beginning Balance | $ / shares	$ 98.09
Weighted-Average Grant Date Fair Value, granted | $ / shares	50.29
Weighted-Average Grant Date Fair Value, vested | $ / shares	141.86
Weighted-Average Grant Date Fair Value, cancelled | $ / shares	106.8
Weighted- Average Exercise Price,Outstanding December 31, 2023 | $ / shares	$ 60.82

Stock-Based Awards - Summary _4

Stock-Based Awards - Summary of Stock-Based Compensation Recognized (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 135,213	$ 130,368	$ 104,979
Cost of sales
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	1,166	902	871
Research and development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	74,531	74,464	59,097
Selling, general and administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 59,516	$ 55,002	$ 45,011

Stock-Based Awards - Fair Value

Stock-Based Awards - Fair Value of Stock Option Awards Granted Estimated Using Black-Scholes Option-Pricing Model (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term in years	6 years 25 days	6 years 25 days	6 years 21 days
Expected volatility	55%	56%	60%
Risk-free interest rate	4.20%	2%	1%
Expected dividend rate	0%	0%	0%
Granted [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term in years		3 years 7 months 6 days
Expected volatility		57%
Risk-free interest rate		1.50%
Expected dividend rate		0%

Defined Contribution Plan - Add

Defined Contribution Plan - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Contribution Pension And Other Post Retirement Plan Disclosure [Abstract]
Contribution expenses	$ 9.7	$ 9	$ 5.5

Income Taxes - Components of Co

Income Taxes - Components of Company's Loss Before Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Domestic	$ 608,166	$ 703,411	$ 455,314
Foreign	298	(1,686)	(2,333)
Total loss before income taxes	$ 608,464	$ 701,725	$ 452,981

Income Taxes - Components of _2

Income Taxes - Components of Company's Income Tax Provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Current provision for income taxes:
State	$ (3,187)	$ 6,062	$ (14)
International	3,127	1,274	1,058
Total current tax provision	(60)	7,336	1,044
Deferred tax provision:
State	(1,608)	(1,640)
International	(157)
Total deferred tax provision	(1,765)	(1,640)
Total (benefit from) provision for income taxes	$ (1,825)	$ 5,696	$ 1,044

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2012	Dec. 31, 2011
Tax Credit Carryforward [Line Items]
Current state income tax expense	$ (60)	$ 7,336	$ 1,044
Deferred tax assets net operating loss, federal tax credits				$ 200	$ 200
Deferred tax assets net operating loss carryforwards	266,253	231,835
Valuation allowance increased	141,300	193,800
Effective income tax rate unrecognized tax benefits	1,300
Deferred tax liability increase (decrease), net	(1,600)
Deferred income tax expense	1,608	1,640
Recognized accrued interest and penalties	200	0	$ 0
Undistributed earnings of foreign subsidiaries	10,800
Federal
Tax Credit Carryforward [Line Items]
Deferred tax assets operating loss carryforwards subject to expiration	$ 1,004,800	756,600
Operating loss carryforwards expiration year	2031
Tax credit carryforwards	$ 46,900	32,600
Tax credit carryforwards expiration year	2030
Deferred tax assets net operating loss carryforwards				3,600	3,600
Federal | Orphan Drug Credits [Member]
Tax Credit Carryforward [Line Items]
Deferred tax assets operating loss carryforwards subject to expiration	$ 269,600	239,300
Operating loss carryforwards expiration year	2031
State
Tax Credit Carryforward [Line Items]
Current state income tax expense	$ 4,800	6,100
Deferred tax assets operating loss carryforwards subject to expiration	$ 659,900	710,000
Operating loss carryforwards expiration year	2031
Tax credit carryforwards	$ 74,400	$ 59,900
Deferred tax assets net operating loss carryforwards				$ 3,600	$ 3,600
International
Tax Credit Carryforward [Line Items]
Current state income tax expense	$ 3,000

Income Taxes - Effective Tax Ra

Income Taxes - Effective Tax Rate of Provision for Income Taxes from Federal Statutory Rate (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal statutory income tax rate	21%	21%	21%
State income taxes, net of federal benefit	0.80%	(0.40%)
Federal tax credits	7.30%	5.90%	7.20%
Other	(0.70%)	(0.10%)	0.50%
Nondeductible permanent items	(0.30%)	(0.60%)	(0.80%)
Stock-based compensation	(1.80%)	(1.20%)	1.30%
Uncertain tax positions	(1.40%)	(1.20%)	(1.40%)
Change in valuation allowance	(24.10%)	(24.00%)	(27.90%)
Foreign rate differential	(0.50%)	(0.20%)	(0.10%)
Provision for income taxes	0.30%	(0.80%)	(0.20%)

Income Taxes - Schedule of Tax

Income Taxes - Schedule of Tax Effect of Temporary Differences to Significant Portions of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets:
Loss carryforwards	$ 266,253	$ 231,835
Tax credits	305,198	260,546
Stock options	44,795	39,784
Accruals and reserves	27,694	27,029
Fixed assets and intangibles	33,853	39,233
Liabilities for sales of future royalties	205,400	214,900
Basis difference in equity investments	8,423	8,971
Capitalized research and development costs	149,898	75,335
Other	281	3,028
Gross deferred tax assets	1,041,795	900,661
Valuation allowance	(1,035,836)	(894,518)
Total deferred tax assets	5,959	6,143
Deferred tax liabilities:
Gross deferred tax liabilities	(36,017)	(37,810)
Net deferred tax liabilities	(30,058)	(31,667)
Right-of-use Lease Assets
Deferred tax liabilities:
Gross deferred tax liabilities	(5,329)	(6,143)
In-process Research and Development [Member]
Deferred tax liabilities:
Gross deferred tax liabilities	$ (30,688)	$ (31,667)

Income Taxes - Unrecognized Tax

Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 66,794	$ 55,360	$ 46,662
Additions based on tax positions related to current year	12,562	11,316	8,542
Additions for tax positions of prior years	642	377	356
Reductions for tax positions of prior years	0	(259)	(200)
Balance at end of year	$ 79,998	$ 66,794	$ 55,360

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2023
Manufacturing and Services
Commitments And Contingencies Disclosure Line Items
Contractual Obligation Maturity Period	12 months

Commitments and Contingencies_2

Commitments and Contingencies - Summary of Aggregate Payments under Contractually Binding Manufacturing and Service Agreements (Details) - Manufacturing and Services $ in Thousands	Dec. 31, 2023 USD ($)
Commitments And Contingencies Disclosure Line Items
2024	$ 27,899
2025	5,718
Contractual Obligation, Total	$ 33,617

Related Party Transaction - Add

Related Party Transaction - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jul. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Related Party Transaction Line Items
Contribution amount paid	$ 1,000
Contribution period	4 years
Research and development		$ 648,449	$ 705,789	$ 497,153
Non Profit Foundation
Related Party Transaction Line Items
Research and development		$ 300	$ 300

Net Loss per Share - Computatio

Net Loss per Share - Computation of Basic and Diluted Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Numerator:
Net loss	$ (606,639)	$ (707,421)	$ (454,025)
Denominator:
Weighted-average shares used to computing net loss per share, basic	73,543,862	69,914,225	67,795,540
Weighted-average shares used to computing net loss per share, diluted	73,543,862	69,914,225	67,795,540
Net loss per share, basic	$ (8.25)	$ (10.12)	$ (6.7)
Net loss per share, diluted	$ (8.25)	$ (10.12)	$ (6.7)

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	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	14,160,736	11,298,516	8,217,574
Options to Purchase Common Stock, RSUs, and PSUs
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	14,152,286	11,290,935	8,214,063
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	8,450	7,581	3,511

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Loss) - Schedule of Total Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Cumulative foreign currency translation adjustment	$ (606)	$ (845)
Unrealized gain (loss) on securities available-for-sale	1,253	(5,728)
Total accumulated other comprehensive income (loss)	$ 647	$ (6,573)