Ultragenyx Pharmaceutical (RARE) 10-Q 3 Aug 18 2018 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2018	Jul. 30, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q2
Trading Symbol	RARE
Entity Registrant Name	Ultragenyx Pharmaceutical Inc.
Entity Central Index Key	1,515,673
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		50,182,357

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 110,854	$ 100,488
Short-term investments	436,278	134,005
Accounts receivable	17,425	5,172
Inventory	3,342	757
Prepaid expenses and other current assets	36,844	29,161
Total current assets	604,743	269,583
Property and equipment, net	20,858	21,837
Long-term investments		9,975
Intangible assets, net	132,776	141,545
Goodwill	44,406	44,406
Other assets	3,239	3,407
Total assets	806,022	490,753
Current liabilities:
Accounts payable	10,314	8,886
Accrued liabilities	55,735	62,128
Total current liabilities	66,049	71,014
Deferred tax liabilities	31,166	31,166
Other liabilities	4,836	5,119
Total liabilities	102,051	107,299
Stockholders’ equity:
Preferred stock — 25,000,000 shares authorized; nil outstanding as of June 30, 2018 and December 31, 2017
Common stock — 250,000,000 shares authorized; 50,116,056 and 44,167,071 shares issued and outstanding as of June 30, 2018 and December 31, 2017, respectively	50	44
Additional paid-in capital	1,559,722	1,221,762
Accumulated other comprehensive loss	(654)	(5,680)
Accumulated deficit	(855,147)	(832,672)
Total stockholders’ equity	703,971	383,454
Total liabilities and stockholders’ equity	$ 806,022	$ 490,753

CONDENSED CONSOLIDATED BALANCE3

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - shares	Jun. 30, 2018	Dec. 31, 2017
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	50,116,056	44,167,071
Common stock, shares outstanding	50,116,056	44,167,071

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues:
Total revenues	$ 12,794		$ 23,471
Operating expenses:
Cost of sales	141		366
Research and development	76,835	$ 58,436	152,339	$ 109,705
Selling, general and administrative	30,718	20,005	62,153	38,690
Total operating expenses	107,694	78,441	214,858	148,395
Loss from operations	(94,900)	(78,441)	(191,387)	(148,395)
Other income (expense), net:
Interest income	2,448	1,151	4,185	2,233
Gain from sale of priority review vouchers	40,322		170,322
Other income (expense)	(496)	4,413	(5,454)	4,995
Loss before income taxes	(52,626)	(72,877)	(22,334)	(141,167)
Provision for income taxes	(102)	(14)	(141)	(14)
Net loss	$ (52,728)	$ (72,891)	$ (22,475)	$ (141,181)
Net loss per share, basic and diluted	$ (1.06)	$ (1.72)	$ (0.46)	$ (3.35)
Shares used in computing net loss per share, basic and diluted	49,819,528	42,346,830	49,046,838	42,095,750
Collaboration and License
Revenues:
Total revenues	$ 10,519		$ 19,881
Product Sales
Revenues:
Total revenues	$ 2,275		$ 3,590

CONDENSED CONSOLIDATED STATEME5

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (52,728)	$ (72,891)	$ (22,475)	$ (141,181)
Other comprehensive loss:
Foreign currency translation adjustments	225	(4,403)	(64)	(5,051)
Transfer of cumulative translation adjustment for the substantial liquidation of foreign subsidiaries			5,272
Unrealized gain (loss) on available-for-sale securities	67	(51)	(182)	(77)
Other comprehensive income (loss):	292	(4,454)	5,026	(5,128)
Total comprehensive loss	$ (52,436)	$ (77,345)	$ (17,449)	$ (146,309)

CONDENSED CONSOLIDATED STATEME6

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Operating activities:
Net loss	$ (22,475)	$ (141,181)
Adjustments to reconcile net loss to net cash used in operating activities:
Gain from sale of priority review vouchers	(170,322)
Stock-based compensation	38,360	31,293
Amortization of premium (discount) on investment securities, net	(913)	1,051
Depreciation and amortization	12,240	2,216
Foreign currency remeasurement (gain) loss	5,846	(4,604)
Other	(145)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(22,382)	469
Other assets	(102)	101
Accounts payable	1,376	6,353
Accrued liabilities and other liabilities	(7,039)	(5,725)
Net cash used in operating activities	(165,556)	(110,027)
Investing activities:
Purchase of property and equipment	(1,852)	(861)
Proceeds from sale of priority review vouchers	170,322
Purchase of investments	(408,683)	(207,208)
Proceeds from the sale of investments	4,954	21,642
Proceeds from maturities of investments	112,162	154,730
Net cash used in investing activities	(123,097)	(31,697)
Financing activities:
Proceeds from issuance of common stock in connection with a public offering, net	270,969
Proceeds from issuance of common stock in connection with at-the-market offering, net	11,789	67,616
Proceeds from issuance of common stock from equity awards, net	16,829	2,879
Net cash provided by financing activities	299,587	70,495
Effect of exchange rate changes on cash	(647)	(361)
Net increase (decrease) in cash, cash equivalents and restricted cash	10,287	(71,590)
Cash, cash equivalents and restricted cash at beginning of period	103,041	164,607
Cash, cash equivalents and restricted cash at end of period	$ 113,328	$ 93,017

Organization

Organization	6 Months Ended
	Jun. 30, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization	1. Organization Ultragenyx Pharmaceutical Inc. (the Company) is a biopharmaceutical company and was 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 rare and ultra-rare diseases, with a focus on serious, debilitating genetic diseases. The Company has two approved therapies. Crysvita ® Mepsevii™ (vestronidase alfa), the first medicine approved for the treatment of children and adults with MPS VII, also known as Sly syndrome. In addition to the approved treatments for XLH and MPS VII, the Company has six ongoing clinical development programs. Crysvita is being studied for the treatment of tumor induced osteomalacia (TIO), a rare disease that impairs bone mineralization. UX007 is being studied in patients with glucose transporter type-1 deficiency syndrome (Glut1 DS), a brain energy deficiency, who are experiencing movement disorders; it is also being studied in patients severely affected by long-chain fatty acid oxidation disorders (LC-FAOD), a genetic disorder in which the body is unable to convert long chain fatty acids into energy. The company has three gene therapy pipeline candidates: DTX 301 is a n adeno-associated virus 8 (AAV8) gene therapy product candidate in development for the treatment of patients with deficiency, the most common urea cycle disorder; DTX 401 is an AAV8 gene therapy product candidate for the treatment of patients with glycogen storage disease type Ia (GSDIa); and . 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 activities. Management expects to incur additional losses in the future to conduct product research and development and recognizes the need to raise additional capital to fully implement its business plan. Through June 30, 2018, the Company has relied primarily on the proceeds from equity offerings to finance its operations. The Company intends to 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 will need to reevaluate its operating plans.

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2018
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 amounts of the Company and our 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 21, 2018 with the United States Securities and Exchange Commission (SEC). The results of operations for the three and six months ended June 30, 2018 are not necessarily indicative of the results to be expected for the year ending December 31, 2018. The condensed consolidated balance sheet as of December 31, 2017 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 sales return reserves, clinical trial accruals, fair value of assets and liabilities, income taxes, and stock-based compensation. 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. In November 2016, the Financial Statement of Cash Flows (Topic 230): Restricted Cash June 30, June 30, 2018 2017 Cash and cash equivalents $ 110,854 $ 90,751 Restricted cash included in prepaid expenses and other current assets 652 461 Restricted cash included in other assets 1,822 1,805 Total cash, cash equivalents, and restricted cash shown in the statements of cash flows $ 113,328 $ 93,017 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 are 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 also receives 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 its results of operations, 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 significant or material changes to prior period estimates of revenues and expenses. The terms of the Company’s collaboration 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 Contract with Customers, 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. Variable 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. Revenue is recognized by measuring the progress toward complete satisfaction of the performance obligations using an input measure. Product sales The Company sells Mepsevii 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 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. Limited historical data is available for use in developing estimates of the amount of the reduction for reserve in gross revenue. The estimates applied are periodically reviewed and adjusted as necessary. Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases

Financial Instruments

Financial Instruments	6 Months Ended
	Jun. 30, 2018
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 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): June 30, 2018 Gross Unrealized Fair Value Hierarchy Amortized Cost Gains Losses Estimated Fair Value Money market funds Level 1 $ 94,565 $ — $ — $ 94,565 Time deposits Level 2 10,000 — — 10,000 Corporate bonds Level 2 160,606 — (311 ) 160,295 Commercial paper Level 2 71,708 — — 71,708 Asset-backed securities Level 2 30,210 — (35 ) 30,175 U.S. Government Treasury and agency securities Level 2 174,316 1 (217 ) 174,100 Total $ 541,405 $ 1 $ (563 ) $ 540,843 December 31, 2017 Gross Unrealized Fair Value Hierarchy Amortized Cost Gains Losses Estimated Fair Value Money market funds Level 1 $ 79,670 $ — $ — $ 79,670 Corporate bonds Level 2 39,330 — (90 ) 39,240 U.S. Government Treasury and agency securities Level 2 105,029 — (290 ) 104,739 Total $ 224,029 $ — $ (380 ) $ 223,649 At June 30, 2018, the remaining contractual maturities of available-for-sale securities were at or less than one year. There have been no significant realized gains or losses on available-for-sale securities for the periods presented. All marketable securities with unrealized losses at have a loss that was considered to be temporary in nature. The Company does not intend to sell the investments that are in an unrealized loss position before recovery of their amortized cost basis.

Balance Sheet Components

Balance Sheet Components	6 Months Ended
	Jun. 30, 2018
Investments Debt And Equity Securities [Abstract]
Balance Sheet Components	4. Balance Sheet Components Inventory Inventory consists of the following (in thousands): June 30, December 31, 2018 2017 Work-in-progress $ 2,880 $ 737 Finished goods 462 20 Total inventory $ 3,342 $ 757 Accrued Liabilities Accrued liabilities consist of the following (in thousands): June 30, December 31, 2018 2017 Research and clinical study expenses $ 22,761 $ 17,141 Payroll and related expenses 23,479 26,527 Repayment liability under collaboration agreement — 3,681 Contract liabilities 1,244 5,986 Other 8,251 8,793 Total accrued liabilities $ 55,735 $ 62,128

Revenue

Revenue	6 Months Ended
	Jun. 30, 2018
Revenue From Contract With Customer [Abstract]
Revenue	5. Revenue The following table disaggregates total revenues from external customers by collaboration and license revenue and product sales (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Collaboration and license revenue: KHK (Crysvita) $ 1,577 $ — $ 1,592 $ — Bayer 8,942 — 18,289 — Total collaboration and license revenue 10,519 — 19,881 — Product sales: Crysvita 26 — 26 — Mepsevii 2,007 — 3,126 — UX007 242 — 438 — Total product sales 2,275 — 3,590 — Total revenues $ 12,794 $ — $ 23,471 $ — The following table disaggregates total revenues based on geographic location (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 United States $ 11,838 $ — $ 21,852 $ — Europe 930 — 1,593 — All other 26 — 26 — Total revenues $ 12,794 $ — $ 23,471 $ — The following table presents changes in the contract liabilities for the six months ended June 30, 2018 (in thousands): December 31, 2017 Additions Deductions June 30, 2018 Contract liabilities $ 5,986 $ 14,135 $ (18,877 ) $ 1,244 The Company’s largest accounts receivables balance accounted for 81% of the June 30, 2018 total accounts receivable balance compared to 97% as of December 31, 2017.

License and Research Agreements

License and Research Agreements	6 Months Ended
	Jun. 30, 2018
Research Grant Agreement [Abstract]
License and Research Agreements	6 . License and Research Agreements Kyowa Hakko Kirin Collaboration and License Agreement In August 2013, the Company entered into a collaboration and license agreement with Kyowa Hakko Kirin Co., Ltd. (KHK). Under the terms of this collaboration and license agreement, as amended, the Company and KHK will 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 and Switzerland, or the European territory, and the Company will have the right to develop and commercialize such products in the field of orphan diseases in Mexico and Central and South America, or Latin America. In the field of orphan diseases, and except for ongoing studies being conducted by KHK, the Company will be the lead party for development activities in the profit share territory and in the European territory until the applicable transition date; the Company will also be 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 KHK. The Company will share 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 KHK, and KHK shall be responsible for 100% of the costs for development activities in Japan and Korea. On the applicable transition date in the profit share territory and the European territory, KHK 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 KHK. Crysvita was approved in the European Union in November 2017 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 KHK share commercial responsibilities and profits in the profit share territory until the applicable transition date. Under the collaboration agreement, KHK will manufacture and supply Crysvita for commercial use in the profit share territory. The remaining profit or loss after supply costs from commercializing products in the profit-share territory, until the applicable transition date, are shared between the Company and KHK on a 50/50 basis. Thereafter, the Company will be entitled to receive a tiered double-digit revenue share in the mid-to-high 20% range. The Company is considered the agent in the arrangement as KHK 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. The Company recognizes a pro-rata share of collaboration revenue, net of supply costs, in the period the sale occurs. The Company concluded that its portion of KHK’s sales in the Profit Share Territory is analogous to a royalty and therefore recorded $1.1 million as collaboration revenue, similar to a royalty, during the three and six months ended June 30, 2018. Royalty revenue related to sales in European Territory KHK has the commercial responsibility for in the European territory. The Company is entitled to receive a royalty of up to 10% on net sales in the European territory. The Company’s Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Company's share of collaboration revenue in profit share territory $ 1,065 $ — $ 1,065 $ — Royalty revenue in European territory 512 — 527 — Total $ 1,577 $ — $ 1,592 $ — Product revenue related to sales in Other Territories The Company is responsible for commercializing in Latin America. The Company is considered the principal in the arrangement 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. Product sales are recorded net of estimated product returns and other deductions. Under KHK manufactures and supplies for commercial use in the Latin America territory. The Company also pays to KHK a low single-digit royalty on net sales. In May 2017, the Company signed an agreement with a wholly-owned subsidiary of KHK pursuant to which the Company was granted the right to commercialize Crysvita in Turkey. KHK’s subsidiary has the option to assume responsibility for commercialization efforts from the Company, after a certain minimum period. The Company is considered the principal in the arrangement as the Company controls the product before it is transferred to the customer; accordingly, the Company will record revenue on a gross basis for sales made in Turkey, including named patient sales, until KHK’s subsidiary assumes responsibility for commercialization efforts. Cost sharing payments Under the collaboration agreement, KHK and the Company shares certain development and commercialization costs. Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Research and development $ 9,420 $ 7,934 $ 17,656 $ 15,325 Selling, general and administrative 4,068 593 7,850 1,141 Total $ 13,488 $ 8,527 $ 25,506 $ 16,466 Collaboration receivable As of June 30, 2018 and December 31, 2017, the Company had receivables from KHK in the amount of $15.0 million and $10.3 million, respectively, for this collaboration arrangement. Takeda License and Collaboration and Purchase Agreements As of June 30, 2018, the research and development under the initial development plan pursuant to the collaboration and license agreement with Takeda Pharmaceutical Limited (Takeda) had been completed. The Company was responsible for the costs under the initial development plan. A significant portion of the work under the initial development plan was performed by Takeda, and as a result, the Company paid $10.6 million to Takeda for performance of their services. The Company concluded that the payments to Takeda were not in return for a distinct service that Takeda had transferred to the Company, therefore, the payments made to Takeda were accounted for as a reduction in the total transaction price of $14.3 million. As of June 30, 2018, the Company concluded that the remaining $3.7 million of the transaction price should not be constrained because it is probable that a significant reversal in the amount to be recognized will not occur. The unconstrained transaction price was allocated to the distinct performance obligations on a relative standalone selling price basis. The Company recorded $0.4 million and $0.3 million for the three months ended June 30, 2018 and June 30, 2017, respectively, and $1.2 million and $0.3 million for the six months ended June 30, 2018 and June 30, 2017, respectively, as a reduction of research and development expenses by measuring the progress toward complete satisfaction of the individual performance obligation using an input measure. Costs incurred by the Company associated with co-development activities performed under this collaboration are included in research and development expense in the accompanying consolidated statements of operations. The Company had no repayment liability as of June 30, 2018 and a $3.7 million repayment liability as of December 31, 2017 and no contract liability as of June 30, 2018 and a $0.6 million contract liability as of December 31, 2017. Bayer HealthCare LLC The Company has an agreement with Bayer Healthcare LLC (Bayer) to research, develop and commercialize adeno-associated virus gene therapy products for 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 Company is responsible for the development of DTX201 under the agreement through a proof-of-concept (POC) clinical trial, in accordance with the mutually agreed upon research budget. Upon the successful demonstration of clinical POC, the agreement requires that Bayer use commercially reasonable efforts to manage and fund 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 to fund 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 and the second milestone in April 2018 and has received $15.0 million for such milestones to date. As of the acquisition date of Dimension Therapeutics, Inc. on November 7, 2017, the Company valued the contract under ASC 805, Business Combinations, The Company evaluated the agreement under ASC 606 and recorded a contract liability as of November 7, 2017 of $2.5 million. It was determined that the performance obligations under the agreement includes (i) research and development services to be provided over the research term, (ii) a development and commercialization license and (iii) the Company’s participation in certain committees. It was determined that these performance obligations are not distinct in the context of the contract and therefore are a single performance obligation. The Company calculated the transaction price by including the unconstrained milestones along with the estimated payments for research and development services and recorded $9.0 million and $18.3 million as collaboration and license revenue for the three and six months ended June 30, 2018, respectively, by measuring the progress toward complete satisfaction of the performance obligation using an input measure. The performance obligation under the contract is expected to be substantially complete by end of 2019. As of June 30, 2018 and December 31, 2017, the Company had a $1.2 million and a $5.4 million contract liability, respectively.

Stock-Based Awards

Stock-Based Awards	6 Months Ended
	Jun. 30, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Awards	7 . 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 June 30, 2018, there were 1,915,493 shares reserved under the 2014 Plan for the future issuance of equity awards and 2,246,823 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 June 30, Six Months Ended June 30, 2018 2017 2018 2017 Research and development $ 11,644 $ 10,034 $ 22,891 $ 18,577 Selling, general and administrative 7,919 6,760 15,469 12,716 Total stock-based compensation $ 19,563 $ 16,794 $ 38,360 $ 31,293

Net Loss Per Share

Net Loss Per Share	6 Months Ended
	Jun. 30, 2018
Earnings Per Share [Abstract]
Net Loss Per Share	8 . 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 June 30, Six Months Ended June 30, 2018 2017 2018 2017 Options to purchase common stock and RSUs 7,735,231 5,767,660 7,479,526 5,536,816 Employee stock purchase plan 9,369 6,760 4,710 3,399 Common stock warrants 149,700 149,700 149,700 149,700 7,894,300 5,924,120 7,633,936 5,689,915

Equity Transactions

Equity Transactions	6 Months Ended
	Jun. 30, 2018
Equity [Abstract]
Equity Transactions	9 . 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 can sell up to $150.0 million in aggregate proceeds of common stock from time to time, through Cowen as its sales agent. In March 2018, the Company and Cowen entered into an amendment to the ATM sales agreement to sell, from time to time, the remaining $72.6 million in common stock under the sales agreement under the Company’s new registration statement that was filed with the SEC on February 21, 2018. During the three and six months ended June 30, 2018, 240,417 shares were sold pursuant to the sales agreement, resulting in net proceeds of approximately $11.8 million, after commissions and other offering costs. In January 2018, the Company completed an underwritten public offering in which 5,043,860 shares of common stock were sold, which includes 657,895 shares purchased by the underwriters pursuant to an option granted to them in connection with the offering, at a public offering price of $57.00 per share. The total proceeds that the Company received from the offering were approximately $271.0 million, net of underwriting discounts and commissions.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Loss	6 Months Ended
	Jun. 30, 2018
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease [Abstract]
Accumulated Other Comprehensive Loss	10 . Accumulated Other Comprehensive Loss Total accumulated other comprehensive loss consisted of the following (in thousands): June 30, December 31, 2018 2017 Foreign currency translation adjustments $ (90 ) $ (5,298 ) Unrealized loss on securities available-for-sale (564 ) (382 ) Total accumulated other comprehensive loss $ (654 ) $ (5,680 )

Gain from Sale of Priority Revi

Gain from Sale of Priority Review Vouchers	6 Months Ended
	Jun. 30, 2018
Goodwill And Intangible Assets Disclosure [Abstract]
Gain from Sale of Priority Review Vouchers	11 . Gain from Sale of Priority Review Vouchers In January 2018, the Company completed the sale of a Rare Pediatric Disease Priority Review Voucher (PRV) it received in connection with the approval of Mepsevii for $130.0 million. In June 2018, the Company also completed the sale of the PRV it received in connection with the approval of Crysvita for $80.6 million, net, which was shared equally with KHK. As the PRVs did not have a carrying value, the gain recognized was equal to the net proceeds received. The Company recorded its portion of the net proceeds in other income of $40.3 million and $170.3 million for the three and six months ended June 30, 2018, respectively, as a gain from the sale of the priority review vouchers.

Summary of Significant Accoun18

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements include the amounts of the Company and our 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 21, 2018 with the United States Securities and Exchange Commission (SEC). The results of operations for the three and six months ended June 30, 2018 are not necessarily indicative of the results to be expected for the year ending December 31, 2018. The condensed consolidated balance sheet as of December 31, 2017 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 sales return reserves, clinical trial accruals, fair value of assets and liabilities, income taxes, and stock-based compensation. 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. In November 2016, the Financial Statement of Cash Flows (Topic 230): Restricted Cash June 30, June 30, 2018 2017 Cash and cash equivalents $ 110,854 $ 90,751 Restricted cash included in prepaid expenses and other current assets 652 461 Restricted cash included in other assets 1,822 1,805 Total cash, cash equivalents, and restricted cash shown in the statements of cash flows $ 113,328 $ 93,017
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 are 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 also receives 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 its results of operations, 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 significant or material changes to prior period estimates of revenues and expenses. The terms of the Company’s collaboration 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 Contract with Customers, 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. Variable 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. Revenue is recognized by measuring the progress toward complete satisfaction of the performance obligations using an input measure. Product sales The Company sells Mepsevii 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 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. Limited historical data is available for use in developing estimates of the amount of the reduction for reserve in gross revenue. The estimates applied are periodically reviewed and adjusted as necessary.
Recent Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases

Summary of Significant Accoun19

Summary of Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2018
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): June 30, June 30, 2018 2017 Cash and cash equivalents $ 110,854 $ 90,751 Restricted cash included in prepaid expenses and other current assets 652 461 Restricted cash included in other assets 1,822 1,805 Total cash, cash equivalents, and restricted cash shown in the statements of cash flows $ 113,328 $ 93,017

Financial Instruments (Tables)

Financial Instruments (Tables)	6 Months Ended
	Jun. 30, 2018
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): June 30, 2018 Gross Unrealized Fair Value Hierarchy Amortized Cost Gains Losses Estimated Fair Value Money market funds Level 1 $ 94,565 $ — $ — $ 94,565 Time deposits Level 2 10,000 — — 10,000 Corporate bonds Level 2 160,606 — (311 ) 160,295 Commercial paper Level 2 71,708 — — 71,708 Asset-backed securities Level 2 30,210 — (35 ) 30,175 U.S. Government Treasury and agency securities Level 2 174,316 1 (217 ) 174,100 Total $ 541,405 $ 1 $ (563 ) $ 540,843 December 31, 2017 Gross Unrealized Fair Value Hierarchy Amortized Cost Gains Losses Estimated Fair Value Money market funds Level 1 $ 79,670 $ — $ — $ 79,670 Corporate bonds Level 2 39,330 — (90 ) 39,240 U.S. Government Treasury and agency securities Level 2 105,029 — (290 ) 104,739 Total $ 224,029 $ — $ (380 ) $ 223,649

Balance Sheet Components (Table

Balance Sheet Components (Tables)	6 Months Ended
	Jun. 30, 2018
Investments Debt And Equity Securities [Abstract]
Summary of Inventory	Inventory consists of the following (in thousands): June 30, December 31, 2018 2017 Work-in-progress $ 2,880 $ 737 Finished goods 462 20 Total inventory $ 3,342 $ 757
Accrued Liabilities	Accrued liabilities consist of the following (in thousands): June 30, December 31, 2018 2017 Research and clinical study expenses $ 22,761 $ 17,141 Payroll and related expenses 23,479 26,527 Repayment liability under collaboration agreement — 3,681 Contract liabilities 1,244 5,986 Other 8,251 8,793 Total accrued liabilities $ 55,735 $ 62,128

Revenue (Tables)

Revenue (Tables)	6 Months Ended
	Jun. 30, 2018
Revenue From Contract With Customer [Abstract]
Summary of Disaggregation of Total Revenues	The following table disaggregates total revenues from external customers by collaboration and license revenue and product sales (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Collaboration and license revenue: KHK (Crysvita) $ 1,577 $ — $ 1,592 $ — Bayer 8,942 — 18,289 — Total collaboration and license revenue 10,519 — 19,881 — Product sales: Crysvita 26 — 26 — Mepsevii 2,007 — 3,126 — UX007 242 — 438 — Total product sales 2,275 — 3,590 — Total revenues $ 12,794 $ — $ 23,471 $ — The following table disaggregates total revenues based on geographic location (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 United States $ 11,838 $ — $ 21,852 $ — Europe 930 — 1,593 — All other 26 — 26 — Total revenues $ 12,794 $ — $ 23,471 $ —
Summary of Changes in Contract Liabilities	The following table presents changes in the contract liabilities for the six months ended June 30, 2018 (in thousands): December 31, 2017 Additions Deductions June 30, 2018 Contract liabilities $ 5,986 $ 14,135 $ (18,877 ) $ 1,244

License and Research Agreemen23

License and Research Agreements (Tables)	6 Months Ended
	Jun. 30, 2018
Research Grant Agreement [Abstract]
Schedule of Collaboration Revenue	The Company’s Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Company's share of collaboration revenue in profit share territory $ 1,065 $ — $ 1,065 $ — Royalty revenue in European territory 512 — 527 — Total $ 1,577 $ — $ 1,592 $ —
Schedule of Cost Sharing Payments	Under the collaboration agreement, KHK and the Company shares certain development and commercialization costs. Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Research and development $ 9,420 $ 7,934 $ 17,656 $ 15,325 Selling, general and administrative 4,068 593 7,850 1,141 Total $ 13,488 $ 8,527 $ 25,506 $ 16,466

Stock-Based Awards (Tables)

Stock-Based Awards (Tables)	6 Months Ended
	Jun. 30, 2018
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 June 30, Six Months Ended June 30, 2018 2017 2018 2017 Research and development $ 11,644 $ 10,034 $ 22,891 $ 18,577 Selling, general and administrative 7,919 6,760 15,469 12,716 Total stock-based compensation $ 19,563 $ 16,794 $ 38,360 $ 31,293

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	6 Months Ended
	Jun. 30, 2018
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 June 30, Six Months Ended June 30, 2018 2017 2018 2017 Options to purchase common stock and RSUs 7,735,231 5,767,660 7,479,526 5,536,816 Employee stock purchase plan 9,369 6,760 4,710 3,399 Common stock warrants 149,700 149,700 149,700 149,700 7,894,300 5,924,120 7,633,936 5,689,915

Accumulated Other Comprehensi26

Accumulated Other Comprehensive Loss (Tables)	6 Months Ended
	Jun. 30, 2018
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease [Abstract]
Schedule of Total Accumulated Other Comprehensive Loss	Total accumulated other comprehensive loss consisted of the following (in thousands): June 30, December 31, 2018 2017 Foreign currency translation adjustments $ (90 ) $ (5,298 ) Unrealized loss on securities available-for-sale (564 ) (382 ) Total accumulated other comprehensive loss $ (654 ) $ (5,680 )

Organization - Additional Infor

Organization - Additional Information (Details)	6 Months Ended
	Jun. 30, 2018Segment
United States of America
Organization And Nature Of Business [Line Items]
Number of reportable segments	1

Summary of Significant Accoun28

Summary of Significant Accounting Policies - Summary of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Cash and cash equivalents	$ 110,854	$ 100,488	$ 90,751
Restricted cash included in prepaid expenses and other current assets	$ 652		$ 461
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	$ 1,822		$ 1,805
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	$ 113,328	$ 103,041	$ 93,017	$ 164,607

Financial Instruments - Summary

Financial Instruments - Summary of Financial Assets Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	$ 541,405	$ 224,029
Gross Unrealized Gains	1
Gross Unrealized Losses	(563)	(380)
Estimated Fair Value	540,843	223,649
Money Market Funds | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	94,565	79,670
Estimated Fair Value	94,565	79,670
Asset-backed Securities | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	30,210
Gross Unrealized Losses	(35)
Estimated Fair Value	30,175
Time Deposits | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	10,000
Estimated Fair Value	10,000
Corporate Bonds | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	160,606	39,330
Gross Unrealized Losses	(311)	(90)
Estimated Fair Value	160,295	39,240
Commercial Paper | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	71,708
Estimated Fair Value	71,708
U.S. Government Treasury and Agency Securities | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	174,316	105,029
Gross Unrealized Gains	1
Gross Unrealized Losses	(217)	(290)
Estimated Fair Value	$ 174,100	$ 104,739

Financial Instruments - Additio

Financial Instruments - Additional Information (Details)	6 Months Ended
	Jun. 30, 2018USD ($)
Schedule Of Available For Sale Securities [Line Items]
Significant realized gains or losses on available-for-sale securities	$ 0
Maximum
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale securities remaining contractual maturities	1 year

Balance Sheet Components - Summ

Balance Sheet Components - Summary of Inventory (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Investments Debt And Equity Securities [Abstract]
Work-in-progress	$ 2,880	$ 737
Finished goods	462	20
Total inventory	$ 3,342	$ 757

Balance Sheet Components - Accr

Balance Sheet Components - Accrued Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Research and clinical study expenses	$ 22,761	$ 17,141
Payroll and related expenses	23,479	26,527
Repayment liability under collaboration agreement		3,681
Contract liabilities	1,244	5,986
Other	8,251	8,793
Total accrued liabilities	$ 55,735	$ 62,128

Revenue - Summary of Disaggrega

Revenue - Summary of Disaggregation of Total Revenues from External Customers (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Total revenues
Total revenues	$ 12,794	$ 23,471
Bayer HealthCare LLC
Total revenues
Total revenues	9,000	18,300
Collaboration and License
Total revenues
Total revenues	10,519	19,881
Collaboration and License | Kyowa Hakko Kirin Collaboration
Total revenues
Total revenues	1,577	1,592
Collaboration and License | Bayer HealthCare LLC
Total revenues
Total revenues	8,942	18,289
Product Sales
Total revenues
Total revenues	2,275	3,590
Product Sales | Crysvita
Total revenues
Total revenues	26	26
Product Sales | Mepsevii
Total revenues
Total revenues	2,007	3,126
Product Sales | UX007
Total revenues
Total revenues	$ 242	$ 438

Revenue - Summary of Disaggre34

Revenue - Summary of Disaggregation of Total Revenues (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Disaggregation Of Revenue [Line Items]
Total revenues	$ 12,794	$ 23,471
United States
Disaggregation Of Revenue [Line Items]
Total revenues	11,838	21,852
Europe
Disaggregation Of Revenue [Line Items]
Total revenues	930	1,593
All other
Disaggregation Of Revenue [Line Items]
Total revenues	$ 26	$ 26

Revenue - Summary of Changes in

Revenue - Summary of Changes in Contract Liabilities (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018USD ($)
Disaggregation Of Revenue [Abstract]
Contract liabilities, Beginning balance	$ 5,986
Additions	14,135
Deductions	(18,877)
Contract liabilities, Ending balance	$ 1,244

Revenue - Additional Informatio

Revenue - Additional Information (Details)	Jun. 30, 2018	Dec. 31, 2017
Disaggregation Of Revenue [Abstract]
Percentage of gross accounts receivable balance	81.00%	97.00%

License and Research Agreemen37

License and Research Agreements - Additional Information (Details) - USD ($)	Nov. 07, 2017	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue		$ 12,794,000		$ 23,471,000
Contract liability		1,244,000		1,244,000		$ 5,986,000
Research and development		76,835,000	$ 58,436,000	152,339,000	$ 109,705,000
Dimension
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Business acquisition date	Nov. 7, 2017
Research and development		4,400,000		$ 8,800,000
Amortization completion year				2,019
Dimension | Contract Asset
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Business combination recognized intangible assets	$ 13,500,000
Bayer HealthCare LLC
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue		9,000,000		$ 18,300,000
Contract liability	$ 2,500,000	1,200,000		1,200,000		5,400,000
Kyowa Hakko Kirin Collaboration
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development		9,420,000	7,934,000	17,656,000	15,325,000
Kyowa Hakko Kirin Collaboration | License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue		1,100		1,100
License agreement receivable		15,000,000		$ 15,000,000		10,300,000
Kyowa Hakko 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 Hakko Kirin Collaboration | Maximum | License Agreement | European Territory
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of royalty on net sales entitled to receive				10.00%
Takeda License and Collaboration and Purchase Agreements
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development amount paid				$ 10,600,000
Collaborative agreement reduction in transaction price				14,300,000
Remaining transaction price				3,700,000
Research and development		400,000	$ 300,000	1,200,000	$ 300,000
Repayment liability		0		0		3,700,000
Contract liability		0		0		$ 600,000
Research, Develop and Commercialize Adeno Associated Virus Gene Therapy Products | Bayer HealthCare LLC
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments received				15,000,000
Research, Develop and Commercialize Adeno Associated Virus Gene Therapy Products | Maximum | Bayer HealthCare LLC
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future contingent milestone payments		$ 232,000,000		$ 232,000,000

License and Research Agreemen38

License and Research Agreements - Share of Collaboration Revenue Related to Crysvita (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	$ 12,794	$ 23,471
Collaboration and License
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	10,519	19,881
Collaboration and License | Kyowa Hakko Kirin Collaboration
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	1,577	1,592
Collaboration and License | Kyowa Hakko Kirin Collaboration | Profit Share Territory
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	1,065	1,065
Collaboration and License | Kyowa Hakko Kirin Collaboration | Royalty Revenue in European Territory
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	$ 512	$ 527

License and Research Agreemen39

License and Research Agreements - Schedule of Cost Sharing Payments (Details) - Kyowa Hakko Kirin Collaboration - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Cost Sharing Payments [Line Items]
Research and development	$ 9,420	$ 7,934	$ 17,656	$ 15,325
Selling, general and administrative	4,068	593	7,850	1,141
Total	$ 13,488	$ 8,527	$ 25,506	$ 16,466

Stock-Based Awards - Additional

Stock-Based Awards - Additional Information (Details)	6 Months Ended
	Jun. 30, 2018shares
2014 Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share reserved for future issuance	1,915,493
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	2,246,823

Stock-Based Awards - Summary of

Stock-Based Awards - Summary of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 19,563	$ 16,794	$ 38,360	$ 31,293
Research and development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	11,644	10,034	22,891	18,577
Selling, general and administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 7,919	$ 6,760	$ 15,469	$ 12,716

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		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	7,894,300	5,924,120	7,633,936	5,689,915
Options to Purchase Common Stock and RSUs [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	7,735,231	5,767,660	7,479,526	5,536,816
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	149,700	149,700	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	9,369	6,760	4,710	3,399

Equity Transactions - Additiona

Equity Transactions - Additional Information (Details) - USD ($)	1 Months Ended			3 Months Ended	6 Months Ended
	Mar. 31, 2018	Jan. 31, 2018	Jul. 31, 2017	Jun. 30, 2018	Jun. 30, 2018
Stockholders Equity [Line Items]
Net proceeds from sale of common stock					$ 270,969,000
ATM Sales Agreement
Stockholders Equity [Line Items]
Common stock shares sold				240,417	240,417
Net proceeds from sale of common stock				$ 11,800,000	$ 11,800,000
ATM Sales Agreement | Maximum
Stockholders Equity [Line Items]
Option to sell common stock for cash			$ 150,000,000
Amended ATM Sales Agreement
Stockholders Equity [Line Items]
Remaining option to sell common stock for cash	$ 72,600,000
Underwritten Public Offering
Stockholders Equity [Line Items]
Common stock shares sold		5,043,860
Net proceeds from sale of common stock		$ 271,000,000
Shares purchased by underwriters		657,895
Public offering price		$ 57

Accumulated Other Comprehensi44

Accumulated Other Comprehensive Income (Loss) - Schedule of Total Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income Loss Net Of Tax [Abstract]
Foreign currency translation adjustments	$ (90)	$ (5,298)
Unrealized loss on securities available-for-sale	(564)	(382)
Total accumulated other comprehensive loss	$ (654)	$ (5,680)

Gain from Sale of Priority Re45

Gain from Sale of Priority Review Vouchers - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jan. 31, 2018	Jun. 30, 2018	Jun. 30, 2018
Finite Lived Intangible Assets [Line Items]
Sale of PRV				$ 170,322
Gain from sale of priority review vouchers			$ 40,322	$ 170,322
Mepsevii
Finite Lived Intangible Assets [Line Items]
Sale of PRV		$ 130,000
Crysvita
Finite Lived Intangible Assets [Line Items]
Sale of PRV	$ 80,600