Ultragenyx Pharmaceutical (RARE) 10-Q 27 Oct 20 2020 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2020	Oct. 22, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Trading Symbol	RARE
Entity Registrant Name	ULTRAGENYX PHARMACEUTICAL INC.
Entity Central Index Key	0001515673
Entity Current Reporting Status	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		61,044,688
Entity Shell Company	false
Entity File Number	001-36276
Entity Tax Identification Number	27-2546083
Entity Address, Address Line One	60 Leveroni Court
Entity Address, City or Town	Novato
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94949
City Area Code	415
Local Phone Number	483-8800
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock, $0.001 par value
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Document Quarterly Report	true
Document Transition Report	false

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 197,486	$ 433,584
Short-term investments	568,034	321,646
Accounts receivable, net	27,762	32,844
Inventory	14,457	11,546
Prepaid expenses and other current assets	64,264	51,397
Total current assets	872,003	851,017
Property and equipment, net	48,773	44,348
Investments in equity securities	129,320	27,752
Long-term investments		5,174
Right-of-use assets	37,597	30,328
Intangible assets, net	131,194	129,000
Goodwill	44,406	44,406
Other assets	5,092	3,471
Total assets	1,268,385	1,135,496
Current liabilities:
Accounts payable	10,850	12,871
Accrued liabilities	79,653	83,194
Contract liabilities, net	102,898
Short-term lease liabilities	7,785	7,235
Total current liabilities	201,186	103,300
Long-term lease liabilities	36,668	29,757
Deferred tax liabilities	33,306	33,306
Liability related to the sale of future royalties	331,034	315,369
Total liabilities	602,194	481,732
Stockholders’ equity:
Preferred stock — 25,000,000 shares authorized; nil outstanding as of September 30, 2020 and December 31, 2019
Common stock — 250,000,000 shares authorized; 60,815,690 and 57,838,220 shares issued and outstanding as of September 30, 2020 and December 31, 2019, respectively	61	58
Additional paid-in capital	2,260,682	2,086,863
Accumulated other comprehensive income (loss)	1,013	(147)
Accumulated deficit	(1,595,565)	(1,433,010)
Total stockholders’ equity	666,191	653,764
Total liabilities and stockholders’ equity	$ 1,268,385	$ 1,135,496

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - shares	Sep. 30, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Preferred stock, shares authorized	25,000,000	25,000,000
Preferred stock, shares outstanding	0	0
Common stock, shares authorized	250,000,000	250,000,000
Common stock, shares issued	60,815,690	57,838,220
Common stock, shares outstanding	60,815,690	57,838,220

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues:
Total revenues	$ 81,470	$ 25,800	$ 179,488	$ 68,121
Operating expenses:
Cost of sales	2,348	2,683	648	3,901
Research and development	87,314	100,144	280,984	274,294
Selling, general and administrative	42,123	41,006	131,891	119,647
Total operating expenses	131,785	143,833	413,523	397,842
Loss from operations	(50,315)	(118,033)	(234,035)	(329,721)
Interest income	1,338	3,319	6,054	10,468
Change in fair value of investments in equity securities	(11,520)	2,166	91,348	11,994
Non-cash interest expense on liability related to the sale of future royalties	(8,582)		(25,093)
Other income (expense)	547	(153)	308	(941)
Loss before income taxes	(68,532)	(112,701)	(161,418)	(308,200)
Provision for income taxes	(313)	(293)	(1,137)	(722)
Net loss	$ (68,845)	$ (112,994)	$ (162,555)	$ (308,922)
Net loss per share, basic and diluted	$ (1.13)	$ (1.96)	$ (2.73)	$ (5.50)
Weighted-average shares used in computing net loss per share, basic and diluted	60,687,177	57,707,694	59,564,163	56,161,996
Collaboration and License
Revenues:
Total revenues	$ 66,924	$ 21,585	$ 144,300	$ 55,070
Product Sales
Revenues:
Total revenues	11,215	$ 4,215	25,760	$ 13,051
Non-cash Collaboration Royalty Revenue
Revenues:
Total revenues	$ 3,331		$ 9,428

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (68,845)	$ (112,994)	$ (162,555)	$ (308,922)
Other comprehensive income:
Foreign currency translation adjustments	374	(234)	414	(79)
Unrealized gain (loss) on available-for-sale securities	(645)	(92)	746	641
Other comprehensive income (loss)	(271)	(326)	1,160	562
Total comprehensive loss	$ (69,116)	$ (113,320)	$ (161,395)	$ (308,360)

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance at Dec. 31, 2018	$ 608,908	$ 51	$ 1,639,773	$ (633)	$ (1,030,283)
Beginning balance, shares at Dec. 31, 2018		50,860,588
Issuance of common stock in connection with underwritten public offering, net of issuance costs	330,415	$ 6	330,409
Issuance of common stock in connection with underwritten public offering, net of issuance costs, shares		5,833,333
Issuance of common stock in connection with at-the-market offering, net of issuance costs	24,828		24,828
Issuance of common stock in connection with at-the-market offering, net of issuance costs, shares		468,685
Employee stock-based compensation	62,854		62,854
Issuance of common stock under equity plan awards, net of tax	8,620	$ 1	8,619
Issuance of common stock under equity plan awards, net of tax, shares		587,284
Other comprehensive income (loss)	562			562
Net loss	(308,922)				(308,922)
Ending balance at Sep. 30, 2019	727,265	$ 58	2,066,483	(71)	(1,339,205)
Ending balance, shares at Sep. 30, 2019		57,749,890
Beginning balance at Jun. 30, 2019	819,787	$ 58	2,045,685	255	(1,226,211)
Beginning balance, shares at Jun. 30, 2019		57,665,375
Employee stock-based compensation	19,894		19,894
Issuance of common stock under equity plan awards, net of tax	904		904
Issuance of common stock under equity plan awards, net of tax, shares		84,515
Other comprehensive income (loss)	(326)			(326)
Net loss	(112,994)				(112,994)
Ending balance at Sep. 30, 2019	727,265	$ 58	2,066,483	(71)	(1,339,205)
Ending balance, shares at Sep. 30, 2019		57,749,890
Beginning balance at Dec. 31, 2019	$ 653,764	$ 58	2,086,863	(147)	(1,433,010)
Beginning balance, shares at Dec. 31, 2019	57,838,220	57,838,220
Issuance of common stock in connection with license agreement, net of issuance costs	$ 55,268	$ 1	55,267
Issuance of common stock in connection with license agreement, net of issuance costs, shares		1,243,913
Issuance of common stock in connection with at-the-market offering, net of issuance costs	20,391		20,391
Issuance of common stock in connection with at-the-market offering, net of issuance costs, shares		283,333
Employee stock-based compensation	63,112		63,112
Issuance of common stock upon exercise of warrants and under equity plan awards, net of tax	35,051	$ 2	35,049
Issuance of common stock upon exercise of warrants and under equity plan awards, net of tax, shares		1,450,224
Other comprehensive income (loss)	1,160			1,160
Net loss	(162,555)				(162,555)
Ending balance at Sep. 30, 2020	$ 666,191	$ 61	2,260,682	1,013	(1,595,565)
Ending balance, shares at Sep. 30, 2020	60,815,690	60,815,690
Beginning balance at Jun. 30, 2020	$ 695,587	$ 60	2,220,963	1,284	(1,526,720)
Beginning balance, shares at Jun. 30, 2020		60,413,756
Employee stock-based compensation	20,527		20,527
Issuance of common stock under equity plan awards, net of tax	19,193	$ 1	19,192
Issuance of common stock under equity plan awards, net of tax, shares		401,934
Other comprehensive income (loss)	(271)			(271)
Net loss	(68,845)				(68,845)
Ending balance at Sep. 30, 2020	$ 666,191	$ 61	$ 2,260,682	$ 1,013	$ (1,595,565)
Ending balance, shares at Sep. 30, 2020	60,815,690	60,815,690

CONDENSED CONSOLIDATED STATEM_4

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Operating activities:
Net loss	$ (162,555)	$ (308,922)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	62,897	62,335
Amortization of premium (discount) on investment securities, net	217	(4,931)
Depreciation and amortization	9,128	6,370
Foreign currency remeasurement loss	167	925
Change in fair value of investments in equity securities	(91,348)	(11,994)
Non-cash collaboration royalty revenue	(9,428)
Non-cash interest expense on liability related to the sale of future royalties	25,093
Other	(28)	220
Changes in operating assets and liabilities:
Accounts receivable	5,126	(10,402)
Inventory	(2,635)	(6,604)
Prepaid expenses and other assets	(12,461)	(5,874)
Right-of-use assets	(7,261)	(15,581)
Accounts payable, accrued, and other liabilities	2,822	4,043
Contract liabilities, net	102,898
Lease liabilities	7,600	17,071
Net cash used in operating activities	(69,768)	(273,344)
Investing activities:
Purchase of property and equipment	(21,959)	(13,332)
Purchase of investments	(648,524)	(610,267)
Purchase of investments in equity securities	(10,220)	(14,339)
Purchase of convertible notes receivable	(1,880)
Proceeds from the sale of investments	40,390	35,100
Proceeds from maturities of investments	367,446	522,533
Payment for intangible assets	(2,275)
Net cash used in investing activities	(277,022)	(80,305)
Financing activities:
Proceeds from the issuance of common stock in connection with the license agreement, net	55,268
Proceeds from the issuance of common stock in connection with underwritten public offerings, net		330,415
Proceeds from the issuance of common stock in connection with at-the-market offering, net	20,391	24,828
Proceeds from the issuance of common stock from exercise of warrants and equity plan awards, net	35,051	8,620
Principal repayments of financing leases	(149)
Net cash provided by financing activities	110,561	363,863
Effect of exchange rate changes on cash	239	(502)
Net increase (decrease) in cash, cash equivalents and restricted cash	(235,990)	9,712
Cash, cash equivalents and restricted cash at beginning of period	436,244	115,525
Cash, cash equivalents and restricted cash at end of period	200,254	125,237
Supplemental disclosures of non-cash information:
Acquired lease liabilities arising from obtaining right-of-use assets	$ 13,195	$ 21,515

Organization

Organization	9 Months Ended
	Sep. 30, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization	1. Organization Ultragenyx Pharmaceutical Inc. (the Company) is a biopharmaceutical company incorporated in California on April 22, 2010. The Company subsequently reincorporated in the state of Delaware in June 2011. The Company is focused on the identification, acquisition, development, and commercialization of novel products for the treatment of serious rare and ultra-rare genetic diseases. The Company has four approved therapies. Crysvita ® Crysvita was approved by the FDA on June 18, 2020 for the treatment of FGF23-related hypophosphatemia in tumor-induced osteomalacia (TIO), associated with phosphaturic mesenchymal tumors that cannot be curatively resected or localized in adults and pediatric patients 2 years of age and older. The Company has also received FDA approval for Mepsevii™ (vestronidase alfa), the first medicine approved for the treatment of children and adults with mucopolysaccharidosis VII (MPS VII), also known as Sly syndrome. In the European Union and the United Kingdom, Mepsevii is approved under exceptional circumstances for patients of all ages for the treatment of non-neurological manifestations of MPS VII. In Brazil, Mepsevii is approved for the treatment of MPS VII for patients of all ages. Dojolvi, formerly known as UX007, was approved by FDA on June 30, 2020 for the treatment of pediatric and adult patients severely affected by long-chain fatty acid oxidation disorders (LC-FAOD). In addition to the approved treatments, the Company has two ongoing clinical development programs. DTX301 is an adeno-associated virus 8 (AAV8) gene therapy product candidate in development for the treatment of patients with ornithine transcarbamylase (OTC) deficiency, the most common urea cycle disorder; and DTX401 is an AAV8 gene therapy product candidate for the treatment of patients with glycogen storage disease type Ia (GSDIa). The Company operates as one reportable segment. The Company has sustained operating losses and expects such annual losses to continue over the next several years. The Company’s ultimate success depends on the outcome of its research and development and commercialization activities, for which it expects to incur additional losses in the future. Management recognizes that the Company will likely need to raise additional capital to fully implement its business plans. Through September 30, 2020, the Company has relied primarily on the proceeds from equity offerings and its sale of future royalties to finance its operations. The Company will likely raise additional capital through the issuance of equity, borrowings, or strategic alliances with partner companies. However, if such financing is not available at adequate levels, the Company would need to reevaluate its operating plans.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying unaudited Condensed Consolidated Financial Statements include the accounts of the Company and its wholly-owned subsidiaries and have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) for interim financial information and in accordance with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. The unaudited interim consolidated financial statements have been prepared on the same basis as the annual financial statements. In the opinion of management, the accompanying unaudited Condensed Consolidated financial Statements reflect all adjustments (consisting only of normal recurring adjustments) considered necessary for a fair presentation. These financial statements should be read in conjunction with the audited financial statements and notes thereto for the preceding fiscal year contained in the Company’s Annual Report on Form 10-K filed on February 14, 2020 with the United States Securities and Exchange Commission (SEC). The results of operations for the three and nine months ended September 30, 2020 are not necessarily indicative of the results to be expected for the year ending December 31, 2020. The Condensed Consolidated Balance Sheet as of December 31, 2019 has been derived from audited financial statements at that date, but does not include all of the information required by GAAP for complete financial statements. Use of Estimates The accompanying consolidated financial statements have been prepared in accordance with 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, and the liability related to the sale of future royalties. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Actual results could differ from those estimates. Cash, Cash Equivalents and Restricted Cash Restricted cash primarily consists of money market accounts as collateral for the Company’s obligations under its facility leases. 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 statement of cash flows (in thousands): September 30, 2020 2019 Cash and cash equivalents $ 197,486 $ 122,577 Restricted cash included in prepaid expenses and other current assets 847 161 Restricted cash included in other assets 1,921 2,499 Total cash, cash equivalents, and restricted cash shown in the statements of cash flows $ 200,254 $ 125,237 Credit Losses Effective January 1, 2020, the Company adopted Accounting Standards Update (ASU) 2016-13, Financial Instruments — Credit Losses, (Topic 326): Measurement of Credit Losses on Financial Instruments, The Company is exposed to credit losses primarily through receivables from customers and collaborators and through its available-for-sale debt 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. The Company considered the current and expected future economic and market conditions surrounding the novel coronavirus (COVID-19) pandemic and determined that the estimate of credit losses was not significantly impacted. The adoption of ASU 2016-13 did not have a material impact on the Condensed Consolidated Financial Statements and related disclosures and there was no allowance for losses on available-for-sale debt securities which were attributable to credit risk for the three and nine months ended September 30, 2020. Revenue Recognition Collaboration and license revenue The Company has certain license and collaboration agreements that are within the scope of Accounting Standards Codification (ASC) 808, Collaborative Agreements 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 statement of operations, because the provision of such services for collaborative partners are not considered to be part of the Company’s ongoing major or central operations. The Company also re cords royalty revenues under certain of the Company’s license or collaboration agreements in exchange for license of intellectual property. If the Company does not have any future performance obligations for these license or collaboration agreements, royalty revenue is recorded as the underlying sales occur. In to record collaboration revenue, the Company utilizes certain information from its , 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 terms of the Company’s collaboration and license agreements may contain multiple performance obligations, which may include licenses and research and development activities. The Company evaluates these agreements under ASC 606, Revenue from Contracts with Customers (ASC 606), to determine the distinct performance obligations. The Company analogizes to ASC 606 for the accounting for distinct performance obligations for which there is a customer relationship. Prior to recognizing revenue, the Company makes estimates of the transaction price, including variable consideration that is subject to a constraint. Amounts of variable consideration are included in the transaction price to the extent that it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur and when the uncertainty associated with the variable consideration is subsequently resolved. Total consideration may include nonrefundable upfront license fees, payments for research and development activities, reimbursement of certain third-party costs, payments based upon the achievement of specified milestones, and royalty payments based on product sales derived from the collaboration. If there are multiple distinct performance obligations, the Company allocates the transaction price to each distinct performance obligation based on its relative standalone selling price. The standalone selling price is generally determined based on the prices charged to customers or using expected cost-plus margin. The Company estimates the efforts needed to complete the performance obligations and recognizes revenue by measuring the progress towards complete satisfaction of the performance obligations using input measures. Product sales The Company sells its approved products through a limited number of distributors. Under ASC 606, revenue from product sales is recognized at the point in time when the delivery is made and when title and risk of loss transfers to these distributors. The Company also recognizes revenue from sales of certain products on a “named patient” basis, which are allowed in certain countries prior to the commercial approval of the product. Prior to recognizing revenue, the Company makes estimates of the transaction price, including any variable consideration that is subject to a constraint. Amounts of variable consideration are included in the transaction price to the extent that it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur and when the uncertainty associated with the variable consideration is subsequently resolved. Product sales are recorded net of estimated government-mandated rebates and chargebacks, estimated product returns, and other deductions. Provisions for returns and other adjustments are provided for in the period the related revenue is recorded, as estimated by management. Non-cash collaboration royalty revenue Effective January 1, 2020, the Company sold the right to receive certain royalty payments from net sales of Crysvita to RPI Finance Trust (RPI), an affiliate of Royalty Pharma, as further described in Note 7. The Company records the royalty revenue from the net sales of Crysvita in the applicable European territories on a prospective basis as non-cash royalty revenue in the Consolidated Statements of Operations over the term of the arrangement.

Financial Instruments

Financial Instruments	9 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Financial Instruments	3. Financial Instruments Financial assets and liabilities are recorded at fair value. The carrying amount of certain financial instruments, including cash and cash equivalents, accounts receivable, accounts payable and accrued liabilities approximate fair value due to their relatively short maturities. Assets and liabilities recorded at fair value on a recurring basis in the balance sheets are categorized based upon the level of judgment associated with the inputs used to measure their fair values. Fair value is defined as the exchange price that would be received for an asset or an exit price that would be paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The authoritative guidance on fair value measurements establishes a three-tier fair value hierarchy for disclosure of fair value measurements as follows: Level 1 —Inputs are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date; Level 2 —Inputs are observable, unadjusted quoted prices in active markets for similar assets or liabilities, unadjusted quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the related assets or liabilities; and Level 3 —Unobservable inputs that are significant to the measurement of the fair value of the assets or liabilities that are supported by little or no market data. The following tables set forth the fair value of the Company’s financial assets remeasured on a recurring basis based on the three-tier fair value hierarchy (in thousands): September 30, 2020 Level 1 Level 2 Level 3 Total Money market funds $ 135,764 $ — $ — $ 135,764 Repurchase agreements — 33,000 — 33,000 Time deposits — 10,000 — 10,000 Corporate bonds — 193,677 — 193,677 Commercial paper — 102,891 — 102,891 Asset-backed securities — 8,715 — 8,715 U.S. Government Treasury and agency securities 214,923 47,827 — 262,750 Investment in Arcturus common stock 128,700 — — 128,700 Total $ 479,387 $ 396,110 $ — $ 875,497 December 31, 2019 Level 1 Level 2 Level 3 Total Money market funds $ 293,309 $ — $ — $ 293,309 Repurchase agreements — 100,000 — 100,000 Time deposits — 10,000 — 10,000 Corporate bonds — 77,026 — 77,026 Commercial paper — 80,119 — 80,119 Asset-backed securities — 30,406 — 30,406 U.S. Government Treasury and agency securities 96,329 53,979 — 150,308 Investment in Arcturus equity securities 26,088 — 1,664 27,752 Total $ 415,726 $ 351,530 $ 1,664 $ 768,920 The Company determined the fair value of the Arcturus Therapeutics Holdings Inc. (Arcturus) common stock by using the quoted market price on September 30, 2020, which is a Level 1 fair value measurement. See Note 6 for additional details on the Arcturus transaction. In July 2020, the Company invested $2.5 million in DiaCarta Ltd. (DiaCarta), a private diagnostic company, in the form of a convertible promissory note that matures in two years, if not converted earlier. The Company was also issued a warrant to purchase up to $1.0 million of DiaCarta preferred stock. The fair value of the warrant to purchase shares of DiaCarta was based on unobservable inputs that are significant to the measurement of the fair value of the asset and is supported by little or no market data; accordingly, the warrant is considered a Level 3 financial asset and is remeasured on a nonrecurring basis. The Company measured the fair value of the warrant by applying the Black-Scholes option pricing method and utilizing the following inputs: stock price, strike price, volatility, risk-free interest rate, and expected term. The Company will recognize interest income on the convertible promissory note based on the effective interest rate method over the life of the note. As of September 30, 2020, the balance of the convertible promissory note was $2.0 million, including $0.1 million in interest receivable, and was recorded in other assets,

Balance Sheet Components

Balance Sheet Components	9 Months Ended
	Sep. 30, 2020
Investments Debt And Equity Securities [Abstract]
Balance Sheet Components	4. Balance Sheet Components Cash Equivalents and Investments The fair values of cash equivalents and investments classified as available-for-sale securities consisted of the following (in thousands): September 30, 2020 Gross Unrealized Amortized Cost Gains Losses Estimated Fair Value Money market funds $ 135,764 $ — $ — $ 135,764 Repurchase agreements 33,000 — — 33,000 Time deposits 10,000 — — 10,000 Corporate bonds 192,943 741 (7 ) 193,677 Commercial paper 102,890 1 — 102,891 Asset-backed securities 8,712 3 — 8,715 U.S. Government Treasury and agency securities 262,583 167 — 262,750 Total $ 745,892 $ 912 $ (7 ) $ 746,797 December 31, 2019 Gross Unrealized Amortized Cost Gains Losses Estimated Fair Value Money market funds $ 293,309 $ — $ — $ 293,309 Repurchase agreements 100,000 — — 100,000 Time deposits 10,000 — — 10,000 Corporate bonds 77,022 17 (13 ) 77,026 Commercial paper 80,119 — — 80,119 Asset-backed securities 30,375 31 — 30,406 U.S. Government Treasury and agency securities 150,184 124 — 150,308 Total $ 741,009 $ 172 $ (13 ) $ 741,168 At September 30, 2020, the remaining contractual maturities of available-for-sale securities were less than one year. There have been no realized gains or losses on available-for-sale securities for the three and nine months ended September 30, 2020 and 2019. All marketable securities with unrealized losses at 30, 2020 have been in a loss position for less than twelve months. Inventory Inventory consists of the following (in thousands): September 30, December 31, 2020 2019 Work-in-process $ 10,211 $ 8,191 Finished goods 4,246 3,355 Total inventory $ 14,457 $ 11,546 Accrued Liabilities Accrued liabilities consist of the following (in thousands): September 30, December 31, 2020 2019 Research, clinical study, and manufacturing expenses $ 20,486 $ 22,894 Payroll and related expenses 43,008 41,324 Other 16,159 18,976 Total accrued liabilities $ 79,653 $ 83,194

Revenue

Revenue	9 Months Ended
	Sep. 30, 2020
Revenue From Contract With Customer [Abstract]
Revenue	5. Revenue The following table disaggregates total revenues from customers (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Collaboration and license revenue: Crysvita collaboration revenue in profit- share territory $ 34,058 $ 19,534 $ 91,079 $ 48,721 Crysvita royalty revenue in European territory — 1,950 1,498 5,896 Daiichi Sankyo 32,866 — 51,723 — Bayer — 101 — 453 Total collaboration and license revenue 66,924 21,585 144,300 55,070 Product sales: Crysvita 3,277 1,140 7,436 2,734 Mepsevii 4,076 2,361 11,686 8,274 Dojolvi 3,862 714 6,638 2,043 Total product sales 11,215 4,215 25,760 13,051 Crysvita non-cash collaboration royalty revenue 3,331 — 9,428 — Total revenues $ 81,470 $ 25,800 $ 179,488 $ 68,121 The following table disaggregates total revenues based on geographic location (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 North America $ 72,651 $ 21,700 $ 154,939 $ 56,318 Europe 5,002 2,790 15,707 8,522 All other 3,817 1,310 8,842 3,281 Total revenues $ 81,470 $ 25,800 $ 179,488 $ 68,121 The following table presents changes in the contract assets (liabilities) (in thousands): Nine Months Ended September 30, 2020 2019 Balance of contract assets at beginning of period $ — $ 2,979 Additions (154,621 ) 452 Deductions 51,723 (3,447 ) Balance of contract liabilities at end of period, net $ (102,898 ) $ (16 ) See Note 6 for additional details on contract assets (liabilities) activities. The Company’s largest accounts receivable balance accounted for 83% and 87% of the total accounts receivable balance as of September 30, 2020 and December 31, 2019, respectively, and was due from a collaboration partner.

License and Research Agreements

License and Research Agreements	9 Months Ended
	Sep. 30, 2020
Research Grant Agreement [Abstract]
License and Research Agreements	6. License and Research Agreements Kyowa Kirin Collaboration and License Agreement In August 2013, the Company entered into a collaboration and license agreement with Kyowa Kirin Co., Ltd. (KKC or formerly Kyowa Hakko Kirin Co., Ltd. or KHK). Under the terms of this collaboration and license agreement, as amended, the Company and KKC collaborate on the development and commercialization of Crysvita in the field of orphan diseases in the United States and Canada, or the profit-share territory, and in the European Union, United Kingdom, and Switzerland, or the European territory, and the Company has the right to develop and commercialize such products in the field of orphan diseases in Mexico and Central and South America, or Latin America. Development Activities In the field of orphan diseases, and except for ongoing studies being conducted by KKC, the Company is the lead party for development activities in the profit-share territory and in the European territory until the applicable transition date; the Company is also the lead party for core development activities conducted in Japan and Korea, for which the core development plan is limited to clinical trials mutually agreed to by the Company and KKC. The Company shares the costs for development activities in the profit-share territory and the European territory conducted pursuant to the development plan before the applicable transition date equally with KKC. KKC is responsible for 100% of the costs for development activities in Japan and Korea. In April 2023, which is the transition date for the profit-share territory, and on the applicable transition date for the European territory, KKC will become the lead party and be responsible for the costs of the development activities. However, the Company will continue to share the costs of the studies commenced prior to the applicable transition date equally with KKC. Crysvita was approved in the European Union and United Kingdom in February 2018 and was approved by the FDA in April 2018. The collaboration and license agreements are within the scope of ASC 808, which provides guidance on the presentation and disclosure of collaborative arrangements. Collaboration revenue related to sales in profit-share territory The Company and KKC share commercial responsibilities and profits in the profit-share territory until April 2023. Under the collaboration agreement, KKC manufactures and supplies Crysvita for commercial use in the profit-share territory and charges the Company the transfer price of 35% of net sales through December 31, 2022, and 30% thereafter. The remaining profit or loss after supply costs from commercializing products in the profit-share territory are shared between the Company and KKC on a 50/50 basis until April 2023. Thereafter, the Company will be entitled to receive a tiered double-digit revenue share in the mid-to-high 20% range. As KKC is the principal in the sale transaction with the customer, the Company recognizes a pro-rata share of collaboration revenue, net of transfer pricing, in the period the sale occurs. The Company concluded that its portion of KKC’s sales in the profit-share territory is analogous to a royalty and therefore recorded its share as collaboration revenue, similar to a royalty. Royalty revenue related to sales in European territory KKC has the commercial responsibility for in the European territory. In December 2019, the Company sold its right to receive royalty payments based on sales in the European territory to Royalty Pharma, effective January 1, 2020, as further described in Note 7. Prior to the Company’s sale of the royalty, the Company received a royalty of up to 10% on net sales in the European territory, which was recognized as the underlying sales occur. Beginning in 2020, the Company records the royalty revenue as non-cash royalty revenues. September The Company’s Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Company's share of revenue in profit- share territory $ 34,058 $ 19,534 $ 91,079 $ 48,721 Royalty revenue in European territory — 1,950 1,498 5,896 Non-cash royalty revenue in European territory 3,331 — 9,428 — Total $ 37,389 $ 21,484 $ 102,005 $ 54,617 Product revenue related to sales in other territories The Company is responsible for commercializing in Latin America and Turkey. The Company is considered the principal in these territories as the Company controls the product before it is transferred to the customer. Accordingly, the Company records revenue on a gross basis related to the sale of once the product is delivered and the risk and title of the product is transferred to the distributor. The Company recorded product sales of $3.3 million and $7.4 million for the three and nine months ended September 30, 2020, respectively, and $1.1 million and $2.7 million for the three and nine months ended September 30, 2019, respectively, net of estimated product returns and other deductions. KKC has the option to assume responsibility for commercialization efforts in Turkey from the Company, after a certain minimum period. Under KKC manufactures and supplies for sales in the above territories and is based on 35% of the net sales through December 31, 2022 and 30% thereafter. The Company also pays to KKC a low single-digit royalty on net sales in Latin America Cost sharing payments Under the collaboration agreement, KKC and the Company share certain development and commercialization costs. Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Research and development $ 5,156 $ 7,124 $ 15,814 $ 20,118 Selling, general and administrative 5,492 5,633 18,509 16,009 Total $ 10,648 $ 12,757 $ 34,323 $ 36,127 Collaboration receivable The Company had accounts receivable from KKC in the amount of $23.2 million and $28.5 million from profit-share revenue and royalties and other receivables recorded in prepaid and other current assets of $12.9 million and $17.8 million and accrued liabilities of $1.6 million and $0.9 million from commercial and development activity reimbursements, as of September Bayer HealthCare LLC The Company has an agreement with Bayer Healthcare LLC (Bayer) to research, develop and commercialize AAV gene therapy products for the treatment of hemophilia A (DTX 201). Under this agreement, Bayer has been granted an exclusive license to develop and commercialize one or more novel gene therapies for hemophilia A. The agreement requires that Bayer use commercially reasonable efforts to conduct and fund a proof-of-concept (POC) clinical trial and any subsequent clinical trials and commercialization of gene therapy products for treatment of hemophilia A. Bayer will have worldwide rights to commercialize the potential future product. Bayer is responsible for funding certain research and development services performed by the Company in the performance of its obligations under the annual research plan and budget. Under the terms of the agreement with Bayer, the Company is eligible to receive development and commercialization milestone payments of up to $232.0 million, as well as, royalty payments ranging in the high single-digit to low double-digit percentages, not exceeding the mid-teens, of net sales of licensed products. The Company achieved the first milestone in December 2017, the second milestone in April 2018, and has received $15.0 million for such milestones to date. The Company’s obligations under the contract were completed by end of December 31, 2019 and no revenue was recorded for the three and nine months ended September September Arcturus The Company has a Research Collaboration and License Agreement with Arcturus to research and develop therapies for select rare diseases. Pursuant to the agreement, the Company incurred none and $0.7 million for the three and nine months ended September In May 2020, the Company exercised an option to purchase 600,000 shares of Arcturus’ common stock at $16.00 per share, or a total purchase price of $9.6 million. Accordingly, after the exercise of the option, the Company owned 3,000,000 shares, or 14.6%, of Arcturus’ then outstanding common stock. The purchase was made pursuant to the equity purchase agreement between the parties entered into in June 2019 in connection with the amendment to the research collaboration and license agreement. The Arcturus common stock is restricted from sale or transfer by the Company for six months from the exercise date, subject to certain conditions. The Company has elected to apply the fair value option to account for the equity investment in Arcturus. The Company had accounted for the option to purchase additional shares of Arcturus common stock at fair value based on the Black-Scholes option pricing method. The changes in the fair value of the Company’s investment in Arcturus securities were as follows (in thousands): Arcturus common stock Fair value of option to purchase additional shares of Arcturus common stock Total Acquisition of investment in Arcturus securities in June 2019 $ 13,872 $ 467 $ 14,339 Change in fair value 12,216 1,197 13,413 December 31, 2019 26,088 1,664 27,752 Change in fair value 67,400 23,948 91,348 Transfer of value upon option exercise 35,212 (25,612 ) 9,600 September 30, 2020 $ 128,700 $ — $ 128,700 The Company recorded $11.5 million in unrealized loss for the three months ended September 2020 from the fair value adjustment on the investment in Arcturus common stock. GeneTx In August 2019, the Company entered into a Program Agreement and a Unitholder Option Agreement with GeneTx Biotherapeutics, LLC (GeneTx) to collaborate on the development of GeneTx’s GTX-102, an antisense oligonucleotide (ASO) for the treatment of Angelman syndrome. Pursuant to the terms of the Unitholder Option Agreement, the Company made an upfront payment of $20.0 million for an exclusive option to acquire GeneTx, which was exercisable any time prior to 30 days following FDA acceptance of the IND for GTX-102. Pursuant to the agreement, upon acceptance of the IND, which occurred in January 2020, the Company elected to extend the option period by paying an option extension payment of $25.0 million (option extension premium) during the prior quarter ended March 31, 2020. The Company has a right to acquire GeneTx for a payment of $125.0 million, at any time, until the earlier of 30 months from the first dosing of a patient in a planned Phase 1/2 study (subject to extensions) or 90 days after results are available from that study. This exclusive option to acquire GeneTx can be extended under certain circumstances, by up to four additional three-month periods, by paying an additional extension fee for each three-month period. During the exclusive option period, GeneTx is responsible for conducting the program based on the development plan agreed between the parties and, subject to the terms in the Program Agreement, has the decision-making authority on all matters in connection with the research, development, manufacturing and regulatory activities with respect to the Program. The Company will provide support, at its discretion, including strategic guidance and clinical expertise. The Company and GeneTx will collaborate on the management of the Phase 1/2 study in patients with Angelman syndrome. If the Company acquires GeneTx, the Company will then be responsible for all development and commercialization activities from the date of acquisition. The Company would also be required to make payments upon achievement of certain development and commercial milestones, as well as royalties, depending upon the success of the program. Although GeneTx is a variable interest entity, the Company is not the primary beneficiary as it currently does not have the power to direct the activities that would most significantly impact the economic performance of GeneTx. Prior to product regulatory approval, all consideration paid to GeneTx represents rights to potential future benefits associated with GeneTx’s in-process research and development activities, which have not reached technological feasibility and have no alternative future use. Accordingly, for the nine months ended September 30, 2020, the Company recorded the option extension payment of $25.0 million as an in-process research and development expense. REGENXBIO, Inc. In March 2020, the Company executed a License Agreement with REGENXBIO, Inc. (REGENEX), for an exclusive, sublicensable, worldwide license to REGENX’s NAV AAV8 and AAV9 Vectors for the development and commercialization of gene therapy treatments for a rare metabolic disorder. In return for these rights, the Company made an upfront payment of $7.0 million, which was recorded as an in-process research and development expense during the prior quarter ended March 31, 2020. 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 Daiichi Sankyo In March 2020, the Company executed a License and Technology Access Agreement (the License Agreement) with Daiichi Sankyo Co., Ltd. (Daiichi Sankyo). Pursuant to the License Agreement, the Company granted Daiichi Sankyo a non-exclusive license to intellectual property, including know-how and patent applications, with respect to its HeLa PCL and HEK293 transient transfection manufacturing technology platforms for AAV-based gene therapy products. The Company retains the exclusive right to use the manufacturing technology for its current target indications and additional indications identified now and in the future. The Company will provide certain technical assistance and technology transfer services during the technology transfer period of three years to enable Daiichi Sankyo to use the technologies for its internal gene therapy programs. Daiichi Sankyo has an option to extend the technology transfer period including know-how improvements by two additional one-year periods by paying a fixed amount for each additional year. Daiichi Sankyo will be responsible for the manufacturing, development, and commercialization of products manufactured with the licensed technology; however, the Company has the option to co-develop and co-commercialize rare disease products at the IND stage. Ultragenyx may also provide strategic consultation to Daiichi Sankyo on the development of both AAV-based gene therapy products and other products for rare diseases. Under the terms of the License Agreement, Daiichi Sankyo made an upfront payment of $125.0 million and will pay an additional $25.0 million upon completion of the technology transfer of the HeLa PCL and HEK293 platforms, as well as single-digit royalties on net sales of products manufactured in either system. Daiichi Sankyo will reimburse the Company for all costs associated with the transfer of the manufacturing technology. The Company also entered into a Stock Purchase Agreement (SPA) with Daiichi Sankyo, pursuant to which Daiichi Sankyo purchased 1,243,913 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 (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, The License Agreement, the Sublicense Agreement, and the SPA are being accounted for as one arrangement because they were entered into at or near the same time and negotiated in contemplation of one another. The Company evaluated the License Agreement and the Sublicense Agreement under ASC 606 and determined that the performance obligations under the agreements are (i) intellectual property with respect to its HeLa PCL and HEK293 transient transfection manufacturing technology platforms together with the initial technical assistance and technology transfer services, which are expected to be completed over a period of 18 to 21 months, 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 determined that the total transaction price of the License Agreement was $183.6 million which was comprised of the $19.7 million premium from the SPA, the $125.0 million upfront payment, the $25.0 million in unconstrained milestone payments, $8.0 million from the Sublicense Agreement, and the $5.9 million estimated reimbursement amount for delivering the license and technology services. The Company allocated the total transaction price to the two performance obligations on a relative stand-alone selling price basis. Revenue allocated to the intellectual property and the technology transfer services will be recognized over an initial estimated period of 18 to 21 months, measuring the progress toward complete satisfaction of the individual performance obligation using an input measure. Revenue for know-how and improvements after the completion of technology transfer will be recognized over the remaining technology transfer period (i.e., months 19-36) on a straight-line basis, as it is expected that Daiichi Sankyo will receive and consume the benefits consistently throughout the period. The performance obligations are estimated to be substantially complete by March 2023. The estimated period to complete the technology transfer services and the related milestones payments, if any, are subject to revised estimates which could be impacted by limitations or delays from the COVID-19 pandemic, successful scale-up of the manufacturing, and other changes that may impact timing. Royalties from commercial sales will be accounted for as revenue upon achievement of such sales, assuming all other revenue recognition criteria are met. For the three and nine months ended September 30, 2020, the Company recognized $32.9 million and $51.7 million, respectively, in revenue related to this arrangement. Accordingly, the Company had recorded $102.9 million as contract liabilities, net, as of 30, 2020.

Liability Related to the Sale o

Liability Related to the Sale of Future Royalties	9 Months Ended
	Sep. 30, 2020
Deferred Revenue Disclosure [Abstract]
Liability Related to the Sale of Future Royalties	7. Liability Related to the Sale of Future Royalties In December 2019, the Company entered into a Royalty Purchase Agreement with RPI. Pursuant to the agreement, RPI paid $320.0 million to the Company in consideration for the right to receive royalty payments effective January 1, 2020, arising from the net sales of Crysvita in the European Union, the United Kingdom, As RPI’s rate of return is explicitly limited due to the cap on royalties they may receive, proceeds from the transaction were recorded as a liability (liability related to sale of future royalties on the Consolidated Balance Sheets). The Company amortizes $320.0 million, net of transaction cost of $5.8 million using the effective interest method over the estimated life of the arrangement. In order to determine the amortization of the liability, the Company is required to estimate the total amount of future royalty payments to be received by the Company and paid to RPI, subject to the capped amount, over the life of the arrangement. The excess of future estimated royalty payments (subject to the capped amount), over the $314.2 million of net proceeds, is recorded as non-cash interest expense over the life of the arrangement. Consequently, the Company estimates an imputed interest on the unamortized portion of the liability and records interest expense relating to the transaction. The Company records the royalty revenue from the net sales of Crysvita in the applicable European territories as non-cash royalty revenue in the Consolidated Statements of Operations. The Company periodically assesses the expected royalty payments using a combination of historical results, internal projections and forecasts from external sources. To the extent such payments are greater or less than the Company’s initial estimates or the timing of such payments is materially different than its original estimates, the Company will prospectively adjust the amortization of the liability and the effective interest rate. The Company’s effective annual interest rate was approximately 10.3% and 10.1% as of September There are a number of factors that could materially affect the amount and timing of royalty payments from KKC in the applicable European territories, most of which are not within the Company’s control. Such factors include, but are not limited to, the success of KKC’s sales and promotion of Crysvita, changing standards of care, delays or disruptions related to the COVID-19 pandemic, the introduction of competing products, pricing for reimbursement in various European territories, manufacturing or other delays, intellectual property matters, adverse events that result in governmental health authority imposed restrictions on the use of Crysvita, significant changes in foreign exchange rates as the royalty payments are made in U.S. dollars (USD) while significant portions of the underlying European sales of Crysvita are made in currencies other than USD, and other events or circumstances that could result in reduced royalty payments from European sales of Crysvita, all of which would result in a reduction of non-cash royalty revenue and the non-cash interest expense over the life of the arrangement. Conversely, if sales of Crysvita in Europe are more than expected, the non-cash royalty revenue and the non-cash interest expense recorded by the Company would be greater over the term of the arrangement. The following table shows the activity within the liability account (in thousands): Liability related to the sale of future royalties Proceeds from sale of future royalties in December 2019 $ 314,234 Non-cash interest expense 1,135 December 31, 2019 315,369 Non-cash collaboration royalty revenue (9,428 ) Non-cash interest expense 25,093 September 30, 2020 $ 331,034

Stock-Based Awards

Stock-Based Awards	9 Months Ended
	Sep. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Awards	8 . Stock-Based Awards The 2014 Incentive Plan (the 2014 Plan) provides for automatic annual increases in shares available for grant, beginning on January 1, 2015 through January 1, 2024. As of September 30, 2020 were 3,186,920 shares reserved under the 2014 Plan for the future issuance of equity awards and 3,287,825 shares reserved for the 2014 Employee Stock Purchase Plan. The table below sets forth the stock-based compensation expense for the periods presented (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Cost of sales $ 133 $ 319 $ 313 $ 404 Research and development 11,533 10,629 35,318 33,891 Selling, general and administrative 8,675 8,959 27,291 28,040 Total stock-based compensation expense $ 20,341 $ 19,907 $ 62,922 $ 62,335

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Net Loss Per Share	9 . Net Loss Per Share Basic net loss per share has been computed by dividing the net loss by the weighted-average number of shares of common stock outstanding during the period. Diluted net loss per share is calculated by dividing net loss by the weighted-average number of shares of common stock and potential dilutive securities outstanding during the period. The following weighted-average outstanding common stock equivalents were excluded from the computation of diluted net loss per share for the periods presented because including them would have been antidilutive: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Options to purchase common stock and restricted stock units 8,627,419 8,155,406 8,637,904 7,936,664 Employee stock purchase plan 35,282 33,094 19,701 18,547 Common stock warrants — 149,700 39,337 149,700 8,662,701 8,338,200 8,696,942 8,104,911

Equity Transactions

Equity Transactions	9 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Equity Transactions	10 . Equity Transactions In July 2017, the Company entered into an At-The-Market, or ATM, sales agreement with Cowen and Company, LLC (Cowen), whereby the Company could sell up to $150.0 million in aggregate proceeds of common stock from time to time, with Cowen as its sales agent. During the three months ended June 30, 2020, the Company sold 283,333 shares of common stock, resulting in net proceeds of $20.4 million, after commissions and other offering costs. As of June 30, 2020, the Company had completed the sale of all available amounts under the ATM facility. During the three and nine months ended September 30, 2019, the Company sold none and 468,685 shares of common stock, respectively, resulting in net proceeds of approximately none and $ 24.8 million, respectively, after commissions and other offering costs. In February 2019, the Company completed an underwritten public offering in which 5,833,333 shares of common stock were sold, which included 760,869 shares purchased by the underwriters pursuant to an option granted to them in connection with the offering, at a public offering price of $60.00 per share. The total proceeds that the Company received from the offering were approximately $330.4 million, net of underwriting discounts and commissions.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	9 Months Ended
	Sep. 30, 2020
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease [Abstract]
Accumulated Other Comprehensive Income (Loss)	11 . Accumulated Other Comprehensive Income (Loss) Total accumulated other comprehensive income (loss) consisted of the following (in thousands): September 30, December 31, 2020 2019 Foreign currency translation adjustments $ 108 $ (306 ) Unrealized gain on available-for-sale securities 905 159 Total accumulated other comprehensive income (loss) $ 1,013 $ (147 )

Subsequent Event

Subsequent Event	9 Months Ended
	Sep. 30, 2020
Subsequent Events [Abstract]
Subsequent Event	12. Subsequent Event On October 23, 2020, the Company announced that it had entered into a strategic collaboration and license agreement (the collaboration agreement) with Solid Biosciences, Inc. (Solid) to focus on the development and commercialization of new gene therapies for Duchenne muscular dystrophy (Duchenne) using its HeLa producer cell line (PCL) manufacturing platform. Under the terms of the collaboration agreement, Solid granted the Company 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 and other diseases resulting from lack of functional dystrophin. The Company also entered into a stock purchase agreement and investor agreement with Solid in connection with the collaboration agreement, and purchased 7,825,797 shares of Solid’s common stock for an aggregate purchase price of $40.0 million. The Company will pay Solid up to $255.0 million in cumulative milestone payments per product upon achievement of specified milestone events, and tiered royalties on worldwide net sales at low double-digit to mid-teens percentages. Upon achievement of proof-of-concept, Solid has the right to opt-in to co-fund collaboration programs in return for participation in a profit share or increased royalty payments.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited Condensed Consolidated Financial Statements include the accounts of the Company and its wholly-owned subsidiaries and have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) for interim financial information and in accordance with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. The unaudited interim consolidated financial statements have been prepared on the same basis as the annual financial statements. In the opinion of management, the accompanying unaudited Condensed Consolidated financial Statements reflect all adjustments (consisting only of normal recurring adjustments) considered necessary for a fair presentation. These financial statements should be read in conjunction with the audited financial statements and notes thereto for the preceding fiscal year contained in the Company’s Annual Report on Form 10-K filed on February 14, 2020 with the United States Securities and Exchange Commission (SEC). The results of operations for the three and nine months ended September 30, 2020 are not necessarily indicative of the results to be expected for the year ending December 31, 2020. The Condensed Consolidated Balance Sheet as of December 31, 2019 has been derived from audited financial statements at that date, but does not include all of the information required by GAAP for complete financial statements.
Use of Estimates	Use of Estimates The accompanying consolidated financial statements have been prepared in accordance with 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, and the liability related to the sale of future royalties. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Actual results could differ from those estimates.
Cash, Cash Equivalents, and Restricted Cash	Cash, Cash Equivalents and Restricted Cash Restricted cash primarily consists of money market accounts as collateral for the Company’s obligations under its facility leases. 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 statement of cash flows (in thousands): September 30, 2020 2019 Cash and cash equivalents $ 197,486 $ 122,577 Restricted cash included in prepaid expenses and other current assets 847 161 Restricted cash included in other assets 1,921 2,499 Total cash, cash equivalents, and restricted cash shown in the statements of cash flows $ 200,254 $ 125,237
Credit Losses	Credit Losses Effective January 1, 2020, the Company adopted Accounting Standards Update (ASU) 2016-13, Financial Instruments — Credit Losses, (Topic 326): Measurement of Credit Losses on Financial Instruments, The Company is exposed to credit losses primarily through receivables from customers and collaborators and through its available-for-sale debt 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. The Company considered the current and expected future economic and market conditions surrounding the novel coronavirus (COVID-19) pandemic and determined that the estimate of credit losses was not significantly impacted. The adoption of ASU 2016-13 did not have a material impact on the Condensed Consolidated Financial Statements and related disclosures and there was no allowance for losses on available-for-sale debt securities which were attributable to credit risk for the three and nine months ended September 30, 2020.
Revenue Recognition	Revenue Recognition Collaboration and license revenue The Company has certain license and collaboration agreements that are within the scope of Accounting Standards Codification (ASC) 808, Collaborative Agreements 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 statement of operations, because the provision of such services for collaborative partners are not considered to be part of the Company’s ongoing major or central operations. The Company also re cords royalty revenues under certain of the Company’s license or collaboration agreements in exchange for license of intellectual property. If the Company does not have any future performance obligations for these license or collaboration agreements, royalty revenue is recorded as the underlying sales occur. In to record collaboration revenue, the Company utilizes certain information from its , 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 terms of the Company’s collaboration and license agreements may contain multiple performance obligations, which may include licenses and research and development activities. The Company evaluates these agreements under ASC 606, Revenue from Contracts with Customers (ASC 606), to determine the distinct performance obligations. The Company analogizes to ASC 606 for the accounting for distinct performance obligations for which there is a customer relationship. Prior to recognizing revenue, the Company makes estimates of the transaction price, including variable consideration that is subject to a constraint. Amounts of variable consideration are included in the transaction price to the extent that it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur and when the uncertainty associated with the variable consideration is subsequently resolved. Total consideration may include nonrefundable upfront license fees, payments for research and development activities, reimbursement of certain third-party costs, payments based upon the achievement of specified milestones, and royalty payments based on product sales derived from the collaboration. If there are multiple distinct performance obligations, the Company allocates the transaction price to each distinct performance obligation based on its relative standalone selling price. The standalone selling price is generally determined based on the prices charged to customers or using expected cost-plus margin. The Company estimates the efforts needed to complete the performance obligations and recognizes revenue by measuring the progress towards complete satisfaction of the performance obligations using input measures. Product sales The Company sells its approved products through a limited number of distributors. Under ASC 606, revenue from product sales is recognized at the point in time when the delivery is made and when title and risk of loss transfers to these distributors. The Company also recognizes revenue from sales of certain products on a “named patient” basis, which are allowed in certain countries prior to the commercial approval of the product. Prior to recognizing revenue, the Company makes estimates of the transaction price, including any variable consideration that is subject to a constraint. Amounts of variable consideration are included in the transaction price to the extent that it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur and when the uncertainty associated with the variable consideration is subsequently resolved. Product sales are recorded net of estimated government-mandated rebates and chargebacks, estimated product returns, and other deductions. Provisions for returns and other adjustments are provided for in the period the related revenue is recorded, as estimated by management. Non-cash collaboration royalty revenue Effective January 1, 2020, the Company sold the right to receive certain royalty payments from net sales of Crysvita to RPI Finance Trust (RPI), an affiliate of Royalty Pharma, as further described in Note 7. The Company records the royalty revenue from the net sales of Crysvita in the applicable European territories on a prospective basis as non-cash royalty revenue in the Consolidated Statements of Operations over the term of the arrangement.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2020
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 statement of cash flows (in thousands): September 30, 2020 2019 Cash and cash equivalents $ 197,486 $ 122,577 Restricted cash included in prepaid expenses and other current assets 847 161 Restricted cash included in other assets 1,921 2,499 Total cash, cash equivalents, and restricted cash shown in the statements of cash flows $ 200,254 $ 125,237

Financial Instruments (Tables)

Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Summary of Financial Assets Measured on Recurring Basis	The following tables set forth the fair value of the Company’s financial assets remeasured on a recurring basis based on the three-tier fair value hierarchy (in thousands): September 30, 2020 Level 1 Level 2 Level 3 Total Money market funds $ 135,764 $ — $ — $ 135,764 Repurchase agreements — 33,000 — 33,000 Time deposits — 10,000 — 10,000 Corporate bonds — 193,677 — 193,677 Commercial paper — 102,891 — 102,891 Asset-backed securities — 8,715 — 8,715 U.S. Government Treasury and agency securities 214,923 47,827 — 262,750 Investment in Arcturus common stock 128,700 — — 128,700 Total $ 479,387 $ 396,110 $ — $ 875,497 December 31, 2019 Level 1 Level 2 Level 3 Total Money market funds $ 293,309 $ — $ — $ 293,309 Repurchase agreements — 100,000 — 100,000 Time deposits — 10,000 — 10,000 Corporate bonds — 77,026 — 77,026 Commercial paper — 80,119 — 80,119 Asset-backed securities — 30,406 — 30,406 U.S. Government Treasury and agency securities 96,329 53,979 — 150,308 Investment in Arcturus equity securities 26,088 — 1,664 27,752 Total $ 415,726 $ 351,530 $ 1,664 $ 768,920

Balance Sheet Components (Table

Balance Sheet Components (Tables)	9 Months Ended
	Sep. 30, 2020
Investments Debt And Equity Securities [Abstract]
Summary of Cash Equivalents and Investments Classified as Available For Sale Securities	The fair values of cash equivalents and investments classified as available-for-sale securities consisted of the following (in thousands): September 30, 2020 Gross Unrealized Amortized Cost Gains Losses Estimated Fair Value Money market funds $ 135,764 $ — $ — $ 135,764 Repurchase agreements 33,000 — — 33,000 Time deposits 10,000 — — 10,000 Corporate bonds 192,943 741 (7 ) 193,677 Commercial paper 102,890 1 — 102,891 Asset-backed securities 8,712 3 — 8,715 U.S. Government Treasury and agency securities 262,583 167 — 262,750 Total $ 745,892 $ 912 $ (7 ) $ 746,797 December 31, 2019 Gross Unrealized Amortized Cost Gains Losses Estimated Fair Value Money market funds $ 293,309 $ — $ — $ 293,309 Repurchase agreements 100,000 — — 100,000 Time deposits 10,000 — — 10,000 Corporate bonds 77,022 17 (13 ) 77,026 Commercial paper 80,119 — — 80,119 Asset-backed securities 30,375 31 — 30,406 U.S. Government Treasury and agency securities 150,184 124 — 150,308 Total $ 741,009 $ 172 $ (13 ) $ 741,168
Summary of Inventory	Inventory consists of the following (in thousands): September 30, December 31, 2020 2019 Work-in-process $ 10,211 $ 8,191 Finished goods 4,246 3,355 Total inventory $ 14,457 $ 11,546
Accrued Liabilities	Accrued liabilities consist of the following (in thousands): September 30, December 31, 2020 2019 Research, clinical study, and manufacturing expenses $ 20,486 $ 22,894 Payroll and related expenses 43,008 41,324 Other 16,159 18,976 Total accrued liabilities $ 79,653 $ 83,194

Revenue (Tables)

Revenue (Tables)	9 Months Ended
	Sep. 30, 2020
Revenue From Contract With Customer [Abstract]
Summary of Disaggregation of Total Revenues	The following table disaggregates total revenues from customers (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Collaboration and license revenue: Crysvita collaboration revenue in profit- share territory $ 34,058 $ 19,534 $ 91,079 $ 48,721 Crysvita royalty revenue in European territory — 1,950 1,498 5,896 Daiichi Sankyo 32,866 — 51,723 — Bayer — 101 — 453 Total collaboration and license revenue 66,924 21,585 144,300 55,070 Product sales: Crysvita 3,277 1,140 7,436 2,734 Mepsevii 4,076 2,361 11,686 8,274 Dojolvi 3,862 714 6,638 2,043 Total product sales 11,215 4,215 25,760 13,051 Crysvita non-cash collaboration royalty revenue 3,331 — 9,428 — Total revenues $ 81,470 $ 25,800 $ 179,488 $ 68,121 The following table disaggregates total revenues based on geographic location (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 North America $ 72,651 $ 21,700 $ 154,939 $ 56,318 Europe 5,002 2,790 15,707 8,522 All other 3,817 1,310 8,842 3,281 Total revenues $ 81,470 $ 25,800 $ 179,488 $ 68,121
Summary of Changes in Contract Assets (Liabilities)	The following table presents changes in the contract assets (liabilities) (in thousands): Nine Months Ended September 30, 2020 2019 Balance of contract assets at beginning of period $ — $ 2,979 Additions (154,621 ) 452 Deductions 51,723 (3,447 ) Balance of contract liabilities at end of period, net $ (102,898 ) $ (16 )

License and Research Agreemen_2

License and Research Agreements (Tables)	9 Months Ended
	Sep. 30, 2020
Research Grant Agreement [Abstract]
Share of Collaboration and Royalty Revenue Related to Crysvita	The Company’s Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Company's share of revenue in profit- share territory $ 34,058 $ 19,534 $ 91,079 $ 48,721 Royalty revenue in European territory — 1,950 1,498 5,896 Non-cash royalty revenue in European territory 3,331 — 9,428 — Total $ 37,389 $ 21,484 $ 102,005 $ 54,617
Schedule of Cost Sharing Payments	Under the collaboration agreement, KKC and the Company share certain development and commercialization costs. Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Research and development $ 5,156 $ 7,124 $ 15,814 $ 20,118 Selling, general and administrative 5,492 5,633 18,509 16,009 Total $ 10,648 $ 12,757 $ 34,323 $ 36,127
Schedule of Changes in Fair Value of Investment in Arcturus Securities	The changes in the fair value of the Company’s investment in Arcturus securities were as follows (in thousands): Arcturus common stock Fair value of option to purchase additional shares of Arcturus common stock Total Acquisition of investment in Arcturus securities in June 2019 $ 13,872 $ 467 $ 14,339 Change in fair value 12,216 1,197 13,413 December 31, 2019 26,088 1,664 27,752 Change in fair value 67,400 23,948 91,348 Transfer of value upon option exercise 35,212 (25,612 ) 9,600 September 30, 2020 $ 128,700 $ — $ 128,700

Liability Related to the Sale_2

Liability Related to the Sale of Future Royalties (Tables)	9 Months Ended
	Sep. 30, 2020
Deferred Revenue Disclosure [Abstract]
Schedule of Activity Within Liability Related to Sale of Future Royalties	The following table shows the activity within the liability account (in thousands): Liability related to the sale of future royalties Proceeds from sale of future royalties in December 2019 $ 314,234 Non-cash interest expense 1,135 December 31, 2019 315,369 Non-cash collaboration royalty revenue (9,428 ) Non-cash interest expense 25,093 September 30, 2020 $ 331,034

Stock-Based Awards (Tables)

Stock-Based Awards (Tables)	9 Months Ended
	Sep. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Stock-Based Compensation Expense	The table below sets forth the stock-based compensation expense for the periods presented (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Cost of sales $ 133 $ 319 $ 313 $ 404 Research and development 11,533 10,629 35,318 33,891 Selling, general and administrative 8,675 8,959 27,291 28,040 Total stock-based compensation expense $ 20,341 $ 19,907 $ 62,922 $ 62,335

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Outstanding Shares of Common Stock Equivalents Excluded from Computation of Diluted Net Loss per Share	The following weighted-average outstanding common stock equivalents were excluded from the computation of diluted net loss per share for the periods presented because including them would have been antidilutive: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Options to purchase common stock and restricted stock units 8,627,419 8,155,406 8,637,904 7,936,664 Employee stock purchase plan 35,282 33,094 19,701 18,547 Common stock warrants — 149,700 39,337 149,700 8,662,701 8,338,200 8,696,942 8,104,911

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) (Tables)	9 Months Ended
	Sep. 30, 2020
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease [Abstract]
Schedule of Total Accumulated Other Comprehensive Income (Loss)	Total accumulated other comprehensive income (loss) consisted of the following (in thousands): September 30, December 31, 2020 2019 Foreign currency translation adjustments $ 108 $ (306 ) Unrealized gain on available-for-sale securities 905 159 Total accumulated other comprehensive income (loss) $ 1,013 $ (147 )

Organization - Additional Infor

Organization - Additional Information (Details)	9 Months Ended
	Sep. 30, 2020Segment
United States of America
Organization And Nature Of Business [Line Items]
Number of reportable segments	1

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Summary of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Cash and cash equivalents	$ 197,486	$ 433,584	$ 122,577
Restricted cash included in prepaid expenses and other current assets	$ 847		$ 161
Restricted Cash and Cash Equivalents, Current, Asset, Statement of Financial Position [Extensible List]	us-gaap:PrepaidExpensesAndOtherCurrentAssetsMember		us-gaap:PrepaidExpensesAndOtherCurrentAssetsMember
Restricted cash included in other assets	$ 1,921		$ 2,499
Restricted Cash and Cash Equivalents, Noncurrent, Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherNoncurrentAssetsMember		us-gaap:OtherNoncurrentAssetsMember
Total cash, cash equivalents, and restricted cash shown in the statements of cash flows	$ 200,254	$ 436,244	$ 125,237	$ 115,525

Financial Instruments - Summary

Financial Instruments - Summary of Financial Assets Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	$ 875,497	$ 768,920
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	479,387	415,726
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	396,110	351,530
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value		1,664
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	135,764	293,309
Money Market Funds | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	135,764	293,309
Asset-backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	8,715	30,406
Asset-backed Securities | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	8,715	30,406
Repurchase Agreements
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	33,000	100,000
Repurchase Agreements | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	33,000	100,000
Time Deposits
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	10,000	10,000
Time Deposits | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	10,000	10,000
Corporate Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	193,677	77,026
Corporate Bonds | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	193,677	77,026
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	102,891	80,119
Commercial Paper | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	102,891	80,119
U.S. Government Treasury and Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	262,750	150,308
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	214,923	96,329
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	47,827	53,979
Investment in Arcturus Common Stock
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	128,700
Investment in Arcturus Common Stock | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	$ 128,700
Investment in Arcturus Equity Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value		27,752
Investment in Arcturus Equity Securities | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value		26,088
Investment in Arcturus Equity Securities | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value		$ 1,664

Financial Instruments - Additio

Financial Instruments - Additional Information (Details) - DiaCarta Ltd. - Convertible Promissory Note - USD ($)	1 Months Ended	9 Months Ended
	Jul. 31, 2020	Sep. 30, 2020
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Investment amount	$ 2,500,000
Debt instrument maturity period	2 years
Debt instrument, face amount		$ 2,000,000
Interest receivable		100,000
Allocated fair value of warrant		$ 600,000
Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Warrants issued to purchase preferred stock	$ 1,000,000

Balance Sheet Components - Summ

Balance Sheet Components - Summary of Cash Equivalents and Investments Classified as Available For Sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 745,892	$ 741,009
Gross Unrealized Gains	912	172
Gross Unrealized Losses	(7)	(13)
Estimated Fair Value	746,797	741,168
Money Market Funds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	135,764	293,309
Estimated Fair Value	135,764	293,309
Asset-backed Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	8,712	30,375
Gross Unrealized Gains	3	31
Estimated Fair Value	8,715	30,406
Repurchase Agreements
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	33,000	100,000
Estimated Fair Value	33,000	100,000
Time Deposits
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	10,000	10,000
Estimated Fair Value	10,000	10,000
Corporate Bonds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	192,943	77,022
Gross Unrealized Gains	741	17
Gross Unrealized Losses	(7)	(13)
Estimated Fair Value	193,677	77,026
Commercial Paper
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	102,890	80,119
Gross Unrealized Gains	1
Estimated Fair Value	102,891	80,119
U.S. Government Treasury and Agency Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	262,583	150,184
Gross Unrealized Gains	167	124
Estimated Fair Value	$ 262,750	$ 150,308

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Schedule Of Available For Sale Securities [Line Items]
Significant realized gains or losses on available-for-sale securities	$ 0	$ 0	$ 0	$ 0
Maximum
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale securities remaining contractual maturities			1 year

Balance Sheet Components - Su_2

Balance Sheet Components - Summary of Inventory (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Investments Debt And Equity Securities [Abstract]
Work-in-process	$ 10,211	$ 8,191
Finished goods	4,246	3,355
Total inventory	$ 14,457	$ 11,546

Balance Sheet Components - Accr

Balance Sheet Components - Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
Research, clinical study, and manufacturing expenses	$ 20,486	$ 22,894
Payroll and related expenses	43,008	41,324
Other	16,159	18,976
Total accrued liabilities	$ 79,653	$ 83,194

Revenue - Summary of Disaggrega

Revenue - Summary of Disaggregation of Total Revenues from Customers (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Total revenues
Total revenues	$ 81,470	$ 25,800	$ 179,488	$ 68,121
Collaboration and License
Total revenues
Total revenues	66,924	21,585	144,300	55,070
Collaboration and License | Crysvita
Total revenues
Total revenues	34,058	19,534	91,079	48,721
Collaboration and License | Royalty Revenue in European Territory | Crysvita
Total revenues
Total revenues		1,950	1,498	5,896
Collaboration and License | Daiichi Sankyo
Total revenues
Total revenues	32,866		51,723
Collaboration and License | Bayer HealthCare LLC
Total revenues
Total revenues		101		453
Product Sales
Total revenues
Total revenues	11,215	4,215	25,760	13,051
Product Sales | Crysvita
Total revenues
Total revenues	3,277	1,140	7,436	2,734
Product Sales | Mepsevii
Total revenues
Total revenues	4,076	2,361	11,686	8,274
Product Sales | Dojolvi
Total revenues
Total revenues	3,862	$ 714	6,638	$ 2,043
Non-cash Collaboration Royalty Revenue
Total revenues
Total revenues	3,331		9,428
Non-cash Collaboration Royalty Revenue | Crysvita
Total revenues
Total revenues	$ 3,331		$ 9,428

Revenue - Summary of Disaggre_2

Revenue - Summary of Disaggregation of Total Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation Of Revenue [Line Items]
Total revenues	$ 81,470	$ 25,800	$ 179,488	$ 68,121
North America
Disaggregation Of Revenue [Line Items]
Total revenues	72,651	21,700	154,939	56,318
Europe
Disaggregation Of Revenue [Line Items]
Total revenues	5,002	2,790	15,707	8,522
All other
Disaggregation Of Revenue [Line Items]
Total revenues	$ 3,817	$ 1,310	$ 8,842	$ 3,281

Revenue - Summary of Changes in

Revenue - Summary of Changes in Contract Assets (Liabilities) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Disaggregation Of Revenue [Abstract]
Contract assets		$ 2,979
Additions	$ (154,621)	452
Deductions	51,723	(3,447)
Contract liabilities	$ (102,898)	$ (16)

Revenue - Additional Informatio

Revenue - Additional Information (Details)	Sep. 30, 2020	Dec. 31, 2019
Disaggregation Of Revenue [Abstract]
Percentage of gross accounts receivable balance	83.00%	87.00%

License and Research Agreemen_3

License and Research Agreements - Additional Information (Details)	Jan. 01, 2023	Aug. 31, 2019USD ($)	Sep. 30, 2020USD ($)$ / sharesshares	Mar. 31, 2020USD ($)shares	Sep. 30, 2019USD ($)	Sep. 30, 2020USD ($)Quarter$ / sharesshares	Sep. 30, 2019USD ($)	Dec. 31, 2022	Dec. 31, 2019USD ($)shares
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue			$ 81,470,000		$ 25,800,000	$ 179,488,000	$ 68,121,000
Research and development			$ 87,314,000		100,144,000	$ 280,984,000	274,294,000
Common stock, shares issued | shares			60,815,690			60,815,690			57,838,220
Proceeds from issuance of common stock in connection with license agreement						$ 55,268,000
Issuance of common stock in connection with license agreement, net of issuance costs						55,268,000
Daiichi Sankyo
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue			$ 102,900,000			102,900,000
Revenue recognized			32,900,000			$ 51,700,000
Common Stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Issuance of common stock in connection with license agreement, net of issuance costs, shares | shares						1,243,913
Issuance of common stock in connection with license agreement, net of issuance costs						$ 1,000
Prepaid and Other Current Assets | Daiichi Sankyo
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Receivable related to Daiichi Sankyo license agreement			900,000			900,000
Product Sales
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue			11,215,000		4,215,000	25,760,000	13,051,000
Kyowa Kirin Collaboration | Collaboration and Royalty
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue			37,389,000		21,484,000	102,005,000	54,617,000
Kyowa Kirin Collaboration | Profit Share Territory | Collaboration and Royalty
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue			34,058,000		19,534,000	91,079,000	48,721,000
Kyowa Kirin Collaboration | European Territory | Collaboration and Royalty
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue					1,950,000	1,498,000	5,896,000
Kyowa Kirin Collaboration | License Agreement | Prepaid and Other Current Assets
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License agreement other receivables			12,900,000			12,900,000			$ 17,800,000
Kyowa Kirin Collaboration | License Agreement | Product Sales
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue			3,300,000		1,100,000	7,400,000	2,700,000
Kyowa Kirin Collaboration | License Agreement | Profit Share Revenue
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License agreement accounts receivable			23,200,000			23,200,000			28,500,000
Kyowa Kirin Collaboration | License Agreement | Commercial And Development Activity Reimbursements
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License agreement accrued liabilities			1,600,000			$ 1,600,000			$ 900,000
Kyowa Kirin Collaboration | License Agreement | Scenario Forecast
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Profit loss sharing percentage on net sales	30.00%							35.00%
Kyowa Kirin Collaboration | License Agreement | Japan and Korea
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of cost for developing activities						100.00%
Kyowa Kirin Collaboration | License Agreement | Profit Share Territory
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Remaining profit or loss share percentage on commercializing products						50.00%
Tiered double-digit revenue share percentage entitled to receive						20.00%
Kyowa Kirin Collaboration | License Agreement | European Territory
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of royalty on net sales receives						10.00%
Research, Develop and Commercialize AAV Gene Therapy Products | Bayer HealthCare LLC
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue			0		100,000	$ 0	500,000
Milestone payments received						15,000,000
Research, Develop and Commercialize AAV Gene Therapy Products | Bayer HealthCare LLC | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future contingent milestone payments			$ 232,000,000			232,000,000
Arcturus
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development					$ 0	$ 0	$ 700,000
Number of option exercised | shares						600,000
Option exercise price | $ / shares						$ 16
Purchase price						$ 9,600,000
Common stock, shares issued | shares			3,000,000			3,000,000
Percentage of outstanding common stock						14.60%
Common stock sale or transfer reduced restriction period						6 months
Arcturus | Common Stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Unrealized loss			$ (11,500,000)
Program Agreement and Unitholder Option Agreement | GeneTx Biotherapeutics LLC
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development						$ 25,000,000
Upfront payment for exclusive option to acquisition		$ 20,000,000
Business acquisition option exercise period, description						the Company made an upfront payment of $20.0 million for an exclusive option to acquire GeneTx, which was exercisable any time prior to 30 days following FDA acceptance of the IND for GTX-102.
Option extension Premium				$ 25,000,000
Business acquisition, consideration transferred		$ 125,000,000
Exercise of option extension, right to acquire condition						The Company has a right to acquire GeneTx for a payment of $125.0 million, at any time, until the earlier of 30 months from the first dosing of a patient in a planned Phase 1/2 study (subject to extensions) or 90 days after results are available from that study.
Program Agreement and Unitholder Option Agreement | GeneTx Biotherapeutics LLC | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Extension period available for right to acquisition | Quarter						4
License Agreement | REGENXBIO, Inc.
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment for in-process research and development expense				$ 7,000,000
Annual fees payable						$ 100,000
License Agreement | REGENXBIO, Inc. | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future contingent milestone payments			14,000,000			14,000,000
License and Technology Access Agreement | Daiichi Sankyo
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received						125,000,000
Deferred revenue			25,000,000			25,000,000
Premium from stock purchase agreement						19,700,000
Transaction price of license agreement						183,600,000
Estimated reimbursement of delivering license and technology services						5,900,000
License and Technology Access Agreement | HeLA PCL Platform | Daiichi Sankyo
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue			$ 25,000,000			25,000,000
License and Technology Access Agreement | Sublicense Agreement | Daiichi Sankyo
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue from sublicense agreement						8,000,000
Stock Purchase Agreement | Daiichi Sankyo
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Issuance of common stock in connection with license agreement, net of issuance costs, shares | shares				1,243,913
Proceeds from issuance of common stock in connection with license agreement				$ 75,000,000
Issuance of common stock in connection with license agreement, net of issuance costs						$ 55,300,000
Stock price | $ / shares			$ 44.43			$ 44.43
Premium from stock purchase agreement						$ 19,700,000
Sublicense Agreement | Daiichi Sankyo
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received						$ 8,000,000

License and Research Agreemen_4

License and Research Agreements - Share of Collaboration and Royalty Revenue Related to Crysvita (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	$ 81,470	$ 25,800	$ 179,488	$ 68,121
Collaboration and Royalty | Kyowa Kirin Collaboration
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	37,389	21,484	102,005	54,617
Collaboration and Royalty | Kyowa Kirin Collaboration | Profit Share Territory
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	34,058	19,534	91,079	48,721
Collaboration and Royalty | Kyowa Kirin Collaboration | Royalty Revenue in European Territory
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue		$ 1,950	1,498	$ 5,896
Non-cash Collaboration Royalty Revenue
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	3,331		9,428
Non-cash Collaboration Royalty Revenue | Kyowa Kirin Collaboration | Royalty Revenue in European Territory
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	$ 3,331		$ 9,428

License and Research Agreemen_5

License and Research Agreements - Schedule of Cost Sharing Payments (Details) - Kyowa Kirin Collaboration - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Cost Sharing Payments [Line Items]
Research and development	$ 5,156	$ 7,124	$ 15,814	$ 20,118
Selling, general and administrative	5,492	5,633	18,509	16,009
Total	$ 10,648	$ 12,757	$ 34,323	$ 36,127

License and Research Agreemen_6

License and Research Agreements - Schedule of Changes in Fair Value of Investment in Arcturus Securities (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Arcturus common stock, Beginning balance	$ 768,920
Arcturus common stock, Ending balance	875,497	$ 768,920
Arcturus
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Arcturus common stock, Beginning balance	27,752
Arcturus common stock, Acquisition of investment in Arcturus securities in June 2019		14,339
Arcturus common stock, Change in fair value	91,348	13,413
Arcturus common stock, Transfer of value upon option exercise	9,600
Arcturus common stock, Purchase price of option exercise	9,600
Arcturus common stock, Ending balance	128,700	27,752
Fair value of option to purchase additional shares of Arcturus common stock, Beginning balance	1,664
Fair value of option to purchase additional shares of Arcturus common stock, Acquisition of investment in Arcturus securities in June 2019		467
Fair value of option to purchase additional shares of Arcturus common stock, Change in fair value	23,948	1,197
Fair value of option to purchase additional shares of Arcturus common stock, Transfer of value upon option exercise	(25,612)
Fair value of option to purchase additional shares of Arcturus common stock, Ending balance		1,664
Arcturus | Common Stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Arcturus common stock, Beginning balance	26,088
Arcturus common stock, Acquisition of investment in Arcturus securities in June 2019		13,872
Arcturus common stock, Change in fair value	67,400	12,216
Arcturus common stock, Transfer of value upon option exercise	35,212
Arcturus common stock, Ending balance	$ 128,700	$ 26,088

Liability Related to the Sale_3

Liability Related to the Sale of Future Royalties - Additional Information (Details) - Royalty Purchase Agreement - RPI Finance Trust (RPI) - USD ($)	1 Months Ended	9 Months Ended
	Dec. 31, 2019	Sep. 30, 2020
Liability Related To Sale Of Future Royalties [Line Items]
Proceeds from sale of future royalties	$ 320,000,000
Royalty payment termination description		The agreement with RPI will automatically terminate, and the payment of royalties to RPI will cease, in the event aggregate royalty payments received by RPI are equal to or greater than $608.0 million prior to December 31, 2030, or in the event aggregate royalty payments received by RPI are less than $608.0 million prior to December 31, 2030, when aggregate royalty payments received by RPI are equal to $800.0 million.
Royalties transaction costs net	5,800,000
Proceeds from the sale of future royalties, net	$ 314,200,000
Effective annual interest rate	10.10%	10.30%
Minimum [Member]
Liability Related To Sale Of Future Royalties [Line Items]
Royalty agreement termination threshold amount	$ 608,000,000
Maximum
Liability Related To Sale Of Future Royalties [Line Items]
Royalty agreement termination threshold amount	$ 800,000,000

Liability Related to the Sale_4

Liability Related to the Sale of Future Royalties - Schedule of Activity Within Liability Related to Sale of Future Royalties (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Dec. 31, 2019
Deferred Revenue Disclosure [Abstract]
Proceeds from sale of future royalties in December 2019			$ 314,234
Non-cash collaboration royalty revenue		$ (9,428)
Non-cash interest expense	$ 8,582	25,093	1,135
Liability related to the sale of future royalties at end of year	$ 331,034	$ 331,034	$ 315,369

Stock-Based Awards - Additional

Stock-Based Awards - Additional Information (Details)	9 Months Ended
	Sep. 30, 2020shares
2014 Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share reserved for future issuance	3,186,920
Automatic increases in shares available for grant effective date	Jan. 1, 2015
Shares available for grant, ending date	Jan. 1, 2024
2014 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share reserved for future issuance	3,287,825

Stock-Based Awards - Summary of

Stock-Based Awards - Summary of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 20,341	$ 19,907	$ 62,922	$ 62,335
Cost of sales
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	133	319	313	404
Research and development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	11,533	10,629	35,318	33,891
Selling, general and administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 8,675	$ 8,959	$ 27,291	$ 28,040

Net Loss Per Share - Outstandin

Net Loss Per Share - Outstanding Shares of Common Stock Equivalents Excluded from Computation of Diluted Net Loss per Share (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	8,662,701	8,338,200	8,696,942	8,104,911
Options to Purchase Common Stock and Restricted Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	8,627,419	8,155,406	8,637,904	7,936,664
Common Stock Warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share		149,700	39,337	149,700
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	35,282	33,094	19,701	18,547

Equity Transactions - Additiona

Equity Transactions - Additional Information (Details) - USD ($)	1 Months Ended		3 Months Ended		9 Months Ended
	Feb. 28, 2019	Jul. 31, 2017	Jun. 30, 2020	Sep. 30, 2019	Sep. 30, 2019
Stockholders Equity [Line Items]
Net proceeds from sale of common stock					$ 330,415,000
ATM Sales Agreement
Stockholders Equity [Line Items]
Option to sell common stock for cash		$ 150,000,000
Common stock shares sold			283,333	0	468,685
Net proceeds from sale of common stock			$ 20,400,000	$ 0	$ 24,800,000
Underwritten Public Offering
Stockholders Equity [Line Items]
Common stock shares sold	5,833,333
Net proceeds from sale of common stock	$ 330,400,000
Shares purchased by underwriters	760,869
Public offering price	$ 60

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Loss) - Schedule of Total Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Accumulated Other Comprehensive Income Loss Net Of Tax [Abstract]
Foreign currency translation adjustments	$ 108	$ (306)
Unrealized gain on available-for-sale securities	905	159
Total accumulated other comprehensive income (loss)	$ 1,013	$ (147)

Subsequent Event - Additional I

Subsequent Event - Additional Information (Details) - Subsequent Event - Collaboration Agreement	Oct. 30, 2020USD ($)shares
Subsequent Event [Line Items]
Number of common stock purchased | shares	7,825,797
Aggregate purchase price	$ 40,000,000
Maximum
Subsequent Event [Line Items]
cumulative milestone payments	$ 255,000,000