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Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2018	May 03, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q1
Trading Symbol	RARE
Entity Registrant Name	Ultragenyx Pharmaceutical Inc.
Entity Central Index Key	0001515673
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		49,772,297

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 226,730	$ 100,488
Short-term investments	314,616	134,005
Accounts receivable	3,671	5,172
Inventory	2,068	757
Restricted cash	542	461
Prepaid expenses and other current assets	33,953	28,700
Total current assets	581,580	269,583
Property and equipment, net	20,830	21,837
Restricted cash	1,931	2,092
Long-term investments	29,907	9,975
Intangible assets, net	137,122	141,545
Goodwill	44,406	44,406
Other assets	1,574	1,315
Total assets	817,350	490,753
Current liabilities:
Accounts payable	7,569	8,886
Accrued liabilities	49,291	61,427
Deferred rent—current portion	723	701
Total current liabilities	57,583	71,014
Deferred tax liabilities	31,166	31,166
Other liabilities	4,944	5,119
Total liabilities	93,693	107,299
Stockholders’ equity:
Preferred stock — 25,000,000 shares authorized; nil outstanding as of March 31, 2018 and December 31, 2017
Common stock — 250,000,000 shares authorized; 49,665,203 and 44,167,071 shares issued and outstanding as of March 31, 2018 and December 31, 2017, respectively	50	44
Additional paid-in capital	1,526,972	1,221,762
Accumulated other comprehensive loss	(946)	(5,680)
Accumulated deficit	(802,419)	(832,672)
Total stockholders’ equity	723,657	383,454
Total liabilities and stockholders’ equity	$ 817,350	$ 490,753

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - shares	Mar. 31, 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	49,665,203	44,167,071
Common stock, shares outstanding	49,665,203	44,167,071

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues:
Collaboration and license	$ 9,362
Product sales	1,315
Total revenues	10,677
Operating expenses:
Cost of sales	225
Research and development	75,504	$ 51,269
Selling, general and administrative	31,435	18,685
Total operating expenses	107,164	69,954
Loss from operations	(96,487)	(69,954)
Other income (expense), net:
Interest income	1,737	1,082
Gain from sale of priority review voucher	130,000
Other income (expense)	(4,958)	582
Income (loss) before income taxes	30,292	(68,290)
Provision for income taxes	(39)
Net income (loss)	$ 30,253	$ (68,290)
Net income (loss) per share:
Basic	$ 0.63	$ (1.63)
Diluted	$ 0.62	$ (1.63)
Shares used in computing net income (loss) per share:
Basic	48,190,511	41,841,612
Diluted	49,077,742	41,841,612

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ 30,253	$ (68,290)
Other comprehensive income (loss):
Foreign currency translation adjustments	(289)	(648)
Transfer of cumulative translation adjustment for the substantial liquidation of a foreign subsidiary	5,272
Unrealized loss on available-for-sale securities	(249)	(26)
Other comprehensive income (loss):	4,734	(674)
Total comprehensive income (loss)	$ 34,987	$ (68,964)

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating activities:
Net income (loss)	$ 30,253	$ (68,290)
Adjustments to reconcile net income (loss) to net cash used in operating activities:
Gain from sale of priority review voucher	(130,000)
Stock-based compensation	18,797	14,499
Amortization of premium (discount) on investment securities, net	(239)	549
Depreciation and amortization	6,160	1,161
Foreign currency remeasurement (gain) loss	4,773	(648)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(5,063)	930
Other assets	(259)	75
Accounts payable	(1,317)	2,989
Accrued liabilities and other liabilities	(12,583)	(12,470)
Net cash used in operating activities	(89,478)	(61,205)
Investing activities:
Purchase of property and equipment	(475)	(485)
Proceeds from sale of priority review voucher	130,000
Purchase of investments	(260,830)	(87,527)
Proceeds from the sale of investments		12,415
Proceeds from maturities of investments	60,277	64,977
Net cash used in investing activities	(71,028)	(10,620)
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	11,808	67,591
Proceeds from issuance of common stock from equity awards, net	3,642	1,378
Net cash provided by financing activities	286,419	68,969
Effect of exchange rate changes on cash	249	17
Net increase (decrease) in cash, cash equivalents and restricted cash	126,162	(2,839)
Cash, cash equivalents and restricted cash at beginning of period	103,041	164,607
Cash, cash equivalents and restricted cash at end of period	$ 229,203	$ 161,768

Organization

3 Months Ended

Mar. 31, 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® (burosumab) is approved by the U.S. Food and Drug Administration (FDA) for the treatment of X-linked hypophosphatemia (XLH) in adult and pediatric patients one year of age and older, and has received European conditional marketing authorization for the treatment of XLH with radiographic evidence of bone disease in children 1 year of age and older and adolescents with growing skeletons. The Company has also received FDA approval for Mepsevii™ (vestronidase alfa), the first medicine approved for the treatment of children and adults with MPS VII, also known as Sly syndrome.

The Company is conducting Phase 2 and Phase 3 studies of Crysvita, an antibody targeting fibroblast growth factor 23 (FGF23), in pediatric and adult patients with XLH and a Phase 2 study in tumor induced osteomalacia (TIO), both rare diseases that impair bone mineralization; a Phase 3 study for UX007 in patients with glucose transporter type-1 deficiency syndrome (Glut1 DS), a brain energy deficiency, who are experiencing movement disorders; a Phase 2 clinical study of UX007 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; a Phase 1/2 open label clinical study of DTX 301, an adeno-associated virus 8 (AAV8) gene therapy product candidate designed for the treatment of patients with ornithine transcarbamylase (OTC) deficiency, the most common urea cycle disorder; and has an active IND for DTX 401, an AAV8 gene therapy clinical candidate for the treatment of patients with glycogen storage disease type Ia, or 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 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 March 31, 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 Accounting Policies

3 Months Ended

Mar. 31, 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 months ended March 31, 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 March 31, 2018 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 its obligations under its facility leases.

In November 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash, which requires restricted cash to be presented with cash and cash equivalents on the statement of cash flows and disclosure of how the statement of cash flows reconciles to the balance sheet if restricted cash is shown separately from cash and cash equivalents on the balance sheet. The Company adopted the standard as of January 1, 2018 on a retrospective basis, wherein the statement of cash flow of each period presented was adjusted to reflect the effects of applying the new guidance. 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):

	March 31,		March 31,
	2018		2017
Cash and cash equivalents	$	226,730	$	159,501
Restricted cash, current		542		271
Restricted cash, non-current		1,931		1,996
Total cash, cash equivalents, and restricted cash shown in the statements of cash flows	$	229,203	$	161,768

Goodwill

In January 2017, the FASB issued ASU No. 2017-04, Goodwill and Other - Simplifying the Test for Goodwill Impairment, which eliminated the requirement to determine the fair value of individual assets and liabilities of a reporting unit to measure goodwill impairment. Under this guidance, goodwill impairment testing shall be performed by comparing the fair value of the reporting unit with its carrying amount and recognizing an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value. The Company had early adopted the new goodwill guidance as of January 1, 2018 on a prospective basis. The adoption did not have an effect on the Consolidated Financial Statements on the adoption date.

Revenue Recognition

Product sales

The Company sells Mepsevii through a limited number of distributors. Under Accounting Standards Codification (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 Mepsevii and UX007 on a “named patient” basis, which are allowed in certain countries prior to the commercial approval of the product in the territory. 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 when the uncertainty associated with the variable consideration is subsequently resolved. Product sales are recorded net of estimated government-mandated rebates and chargebacks, distribution fees, estimated product returns and other deductions.

Provisions for returns and other adjustments are provided for in the period the related revenue is recorded. Historical data are not yet readily available and reliable for use in estimating the amount of the reduction in gross revenue. The estimates applied are periodically reviewed and will be adjusted as necessary.

Collaboration and license revenue

The Company has certain license and collaboration agreements that are within the scope of ASC 808, Collaborative Agreements, which provides guidance on the presentation and disclosure of collaborative arrangements. Funding received related to research and development services and pre-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 Company 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 under these license or collaborations agreements, royalty revenue is recorded as the underlying sales occur.

The Company also recognizes collaboration and license revenue under certain of the Company’s license or collaboration agreements that are within the scope of ASC 606. The terms of these agreements may contain multiple performance obligations, which may include licenses and research and development activities. The Company evaluates these agreements under ASC 606 to determine the distinct performance obligations.

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.

Recently Issued Accounting Pronouncements

In February 2016, the FASB issued ASU No. 2016-02, Leases, which requires an entity that is a lessee to record a right of use asset and a corresponding lease liability on the balance sheet for all leases with terms longer than 12 months. This guidance also requires disclosures about the amount, timing, and uncertainty of cash flows arising from leases. This guidance is effective for annual reporting periods beginning after December 15, 2018, and interim periods within those annual periods, using a modified retrospective approach, and early adoption is permitted. The Company is evaluating the effect that this guidance will have on its Consolidated Financial Statements and related disclosures.

Financial Instruments

3 Months Ended

Mar. 31, 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):

	March 31, 2018
				Gross Unrealized
	Fair Value Hierarchy	Amortized Cost		Gains		Losses			Estimated Fair Value
Money market funds	Level 1	$	158,296	$	—	$	—		$	158,296
Time deposits	Level 2		10,000		—		—			10,000
Corporate bonds	Level 2		90,462		—		(289	)		90,173
Commercial paper	Level 2		79,388		—		—			79,388
Asset-backed securities	Level 2		30,928		—		(59	)		30,869
U.S. Government Treasury and agency securities	Level 2		160,388		—		(283	)		160,105
Total		$	529,462	$	—	$	(631	)	$	528,831

	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 March 31, 2018, the remaining contractual maturities of available-for-sale securities were less than two years. 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 March 31, 2018 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.

Financial Instruments (Tables)

3 Months Ended

Mar. 31, 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):

	March 31, 2018
				Gross Unrealized
	Fair Value Hierarchy	Amortized Cost		Gains		Losses			Estimated Fair Value
Money market funds	Level 1	$	158,296	$	—	$	—		$	158,296
Time deposits	Level 2		10,000		—		—			10,000
Corporate bonds	Level 2		90,462		—		(289	)		90,173
Commercial paper	Level 2		79,388		—		—			79,388
Asset-backed securities	Level 2		30,928		—		(59	)		30,869
U.S. Government Treasury and agency securities	Level 2		160,388		—		(283	)		160,105
Total		$	529,462	$	—	$	(631	)	$	528,831

	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

3 Months Ended

Mar. 31, 2018

Investments Debt And Equity Securities [Abstract]

Balance Sheet Components

4.	Balance Sheet Components

Inventory

Inventory consists of the following (in thousands):

	March 31,		December 31,
	2018		2017
Work-in-progress	$	1,808	$	737
Finished goods		260		20
Total inventory	$	2,068	$	757

Accrued Liabilities

Accrued liabilities consist of the following (in thousands):

	March 31,		December 31,
	2018		2017
Research and clinical study expenses	$	21,680	$	17,141
Payroll and related expenses		16,774		26,527
Repayment liability under collaboration agreement		3,460		3,681
Contract liability		—		5,986
Other		7,377		8,092
Total accrued liabilities	$	49,291	$	61,427

License and Research Agreements

3 Months Ended

Mar. 31, 2018

Research Grant Agreement [Abstract]

License and Research Agreements

5.	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. The Company has the primary responsibility for conducting certain research and development services. Crysvita was approved in the European Union in November 2017 and was approved by the FDA in April 2018. The Company and KHK will share commercial responsibilities and profits in the profit share territory until the applicable transition date and KHK will commercialize Crysvita in the European territory. The Company will develop and commercialize Crysvita in Latin America.

KHK will manufacture and supply Crysvita for clinical use globally and will manufacture and supply Crysvita for commercial use in the profit share territory and Latin America. The remaining profit or loss from commercializing products in the profit-share territory, until the applicable transition date, will be 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 in the profit share territory. Net proceeds from any sale of the priority review voucher issued in connection with the approval of Crysvita will be shared equally with KHK. The Company will also be entitled to receive a royalty of up to 10% on net sales in the European territory. In Latin America, the Company will pay 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 accounting for the agreement as a collaboration agreement as defined in ASC 808, Collaborative Agreements. The Company’s expenses were reduced by $8.2 million and $7.4 million for the three months ended March 31, 2018 and 2017, respectively, for KHK’s share of the research and development expenses and were reduced by $3.8 million and $0.5 million for the three months ended March 31, 2018 and 2017, respectively, for KHK’s share of the selling, general and administrative expenses. As of March 31, 2018 and December 31, 2017, the Company had receivables in the amount of $12.3 million and $10.3 million, respectively, for this collaboration arrangement.

Takeda License and Collaboration and Purchase Agreements

In June 2016, the Company executed a collaboration and license agreement with Takeda Pharmaceutical Company Limited (Takeda). Pursuant to the agreement, which became effective in July 2016, the Company obtained an exclusive license for a pre-clinical compound from Takeda in a pre-determined field of use. The Company is responsible for the development costs for the pre-clinical compound and the identified option product pursuant to an initial development plan. Because the license to the pre-clinical compound has no alternative future use, the estimated fair value of $0.7 million was recorded as a research and development expense upon acquisition. Any products resulting from the pre-clinical compound or the identified option product is referred to in this report as the “licensed product.” The Company discontinued the development efforts on the pre-clinical compound in the pre-determined field of use and the identified option product.

As part of the agreement, the Company and Takeda established a five-year research collaboration whereby the parties may mutually agree to add additional option products candidates to the collaboration, in which case the Company will bear the cost of the development activities, with certain exceptions.

In July 2016, the Company consummated a common stock purchase agreement, executed in conjunction with the collaboration and license agreement, whereby Takeda purchased 374,590 shares of the Company’s common stock for $40.0 million in cash. The fair market value of the common stock issued to Takeda was $27.3 million, based on the closing stock price of $72.95 on the date of issuance, resulting in a $12.7 million premium paid to the Company. The Company also received a put option to require Takeda to purchase an additional $25.0 million in shares of the Company’s common stock which was exercised in October 2016, whereby Takeda purchased 352,530 shares of the Company’s common stock for $25.0 million in cash. Takeda is subject to a five-year standstill (subject to customary exceptions or release). The Company estimated the fair value of the put options to be $0.9 million and recorded the put options in additional paid-in capital.

The research and license agreement and the stock purchase agreement are being accounted for as one arrangement because they were entered into at the same time with interrelated financial terms. The Company analogized to Topic 606 for the accounting for the arrangements. The Company concluded that there are multiple promised goods and services under the collaboration agreement, including obligations related to research and development services with respect to licensed products as well as committee participation, which were determined to represent distinct performance obligations. The total consideration received from Takeda was $14.3 million and was comprised of the $12.7 million premium on the sale of the common stock, the $0.9 million estimated fair value of the put options, and the $0.7 million estimated fair value of the pre-clinical compound.

The Company is responsible for the costs under the initial development plan. A significant portion of this work is performed by Takeda which is substantively complete as of March 31, 2018. The Company concluded that the payment to Takeda is not in return for a distinct service that Takeda transfers to the Company, therefore, the payment made to Takeda is accounted for as a reduction in the transaction price. As of March 31, 2018, the Company concluded that $3.3 million of the estimated 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 $0.8 million for the three months ended March 31, 2018 and none for the three months ended March 31, 2017 as a reduction of research and development expenses by measuring the progress toward complete satisfaction of the individual performance obligation using an input measure. The Company will continue to re-evaluate the application of the constraint to the transaction price at each reporting period end date.

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. As of March 31, 2018 and December 31, 2017, the Company had a repayment liability in the amount of $3.5 million and $3.7 million, respectively, and no contract liability as of March 31, 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. In December 2017, the first milestone was achieved and the Company subsequently received the $5.0 million milestone from Bayer.

As of the acquisition date of November 7, 2017, the Company valued the contract under ASC 805, Business Combinations, and recorded an intangible asset of $13.5 million. The intangible asset will be amortized to research and development expense over the remainder of the research term which is expected to be complete in 2019. The Company recorded a research and development expense of $4.4 million for the three months ended March 31, 2018 for the amortization of the intangible asset.

The Company evaluated the agreement under ASC 606 Revenue from Contracts with Customers, 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 $9.3 million as collaboration and license revenue for the three months ended March 31, 2018, 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 March 31, 2018 and December 31, 2017, the Company had a $0.8 million of contract asset and a $5.4 million of contract liability, respectively.

Stock-Based Awards

3 Months Ended

Mar. 31, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Awards

6.	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 March 31, 2018, there were 1,828,073 shares reserved under the 2014 Plan for the future issuance of equity awards and 2,292,906 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 March 31,
	2018		2017
Research and development	$	11,247	$	8,543
Selling, general and administrative		7,550		5,956
Total stock-based compensation	$	18,797	$	14,499

Net Income (Loss) Per Share

3 Months Ended

Mar. 31, 2018

Earnings Per Share [Abstract]

Net Income (Loss) Per Share

7.	Net Income (Loss) Per Share

Basic net income (loss) per share has been computed by dividing the net income (loss) by the weighted-average number of shares of common stock outstanding during the period. Diluted net income (loss) per share is calculated by dividing net income (loss) by the weighted-average number of shares of common stock and potential dilutive securities outstanding during the period. For the three months ended March 31, 2017, there was no difference between basic and diluted net loss per share since the effect of the dilutive securities would be antidilutive and therefore were excluded from the diluted net loss per share calculation. The following table sets forth the computation of the basic and diluted net income (loss) per share (in thousands, except share and per share data):

	Three Months Ended March 31,
	2018		2017
Net income (loss), basic and diluted	$	30,253	$	(68,290	)
Weighted-average shares used in computing net income (loss) per share, basic		48,190,511		41,841,612
Weighted-average effect of dilutive securities:
Options to purchase common stock and RSUs		742,796		—
Employee stock purchase plan		3,683		—
Common stock warrants		140,752		—
Weighted-average shares used in computing net income (loss) per share, diluted		49,077,742		41,841,612
Net income (loss) per share:
Basic	$	0.63	$	(1.63	)
Diluted	$	0.62	$	(1.63	)

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 March 31,
	2018		2017
Options to purchase common stock and RSUs		5,150,737		5,303,718
Employee stock purchase plan		—		24,590
Common stock warrants		—		149,700
		5,150,737		5,478,008

Equity Transactions

3 Months Ended

Mar. 31, 2018

Equity [Abstract]

Equity Transactions

8.	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 months ended March 31, 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 Income (Loss)

3 Months Ended

Mar. 31, 2018

Other Comprehensive Income Loss Net Of Tax Period Increase Decrease [Abstract]

Accumulated Other Comprehensive Income (Loss)

9.	Accumulated Other Comprehensive Income (Loss)

Total accumulated other comprehensive income (loss) consisted of the following (in thousands):

	March 31,			December 31,
	2018			2017
Foreign currency translation adjustments	$	(315	)	$	(5,298	)
Unrealized loss on securities available-for-sale		(631	)		(382	)
Total accumulated other comprehensive loss	$	(946	)	$	(5,680	)

Gain from Sale of Priority Review Voucher

3 Months Ended

Mar. 31, 2018

Goodwill And Intangible Assets Disclosure [Abstract]

Gain from Sale of Priority Review Voucher

10.	Gain from Sale of Priority Review Voucher

On January 10, 2018, the Company completed the sale of a Rare Pediatric Disease Priority Review Voucher (PRV) to Novartis Pharma AG for $130.0 million. The Company received the PRV from the FDA in connection with the approval of Mepsevii. The full amount was received and recorded as a gain from sale of PRV as the PRV did not have a carrying value at the time of the sale.

Summary of Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2018

Accounting Policies [Abstract]

Basis of Presentation

Use of Estimates

Cash, Cash Equivalents and Restricted Cash

Restricted cash primarily consists of money market accounts as collateral for its obligations under its facility leases.

	March 31,		March 31,
	2018		2017
Cash and cash equivalents	$	226,730	$	159,501
Restricted cash, current		542		271
Restricted cash, non-current		1,931		1,996
Total cash, cash equivalents, and restricted cash shown in the statements of cash flows	$	229,203	$	161,768

Goodwill

Revenue Recognition

Product sales

Collaboration and license revenue

Recent Issued Accounting Pronouncements

Recently Issued Accounting Pronouncements

Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 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):

	March 31,		March 31,
	2018		2017
Cash and cash equivalents	$	226,730	$	159,501
Restricted cash, current		542		271
Restricted cash, non-current		1,931		1,996
Total cash, cash equivalents, and restricted cash shown in the statements of cash flows	$	229,203	$	161,768

Balance Sheet Components (Tables)

3 Months Ended

Mar. 31, 2018

Investments Debt And Equity Securities [Abstract]

Summary of Inventory

Inventory consists of the following (in thousands):

	March 31,		December 31,
	2018		2017
Work-in-progress	$	1,808	$	737
Finished goods		260		20
Total inventory	$	2,068	$	757

Accrued Liabilities

Accrued liabilities consist of the following (in thousands):

	March 31,		December 31,
	2018		2017
Research and clinical study expenses	$	21,680	$	17,141
Payroll and related expenses		16,774		26,527
Repayment liability under collaboration agreement		3,460		3,681
Contract liability		—		5,986
Other		7,377		8,092
Total accrued liabilities	$	49,291	$	61,427

Stock-Based Awards (Tables)

3 Months Ended

Mar. 31, 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 March 31,
	2018		2017
Research and development	$	11,247	$	8,543
Selling, general and administrative		7,550		5,956
Total stock-based compensation	$	18,797	$	14,499

Net Income (Loss) Per Share (Tables)

3 Months Ended

Mar. 31, 2018

Earnings Per Share [Abstract]

Computation of Basic and Diluted Net Income (Loss) Per Share

The following table sets forth the computation of the basic and diluted net income (loss) per share (in thousands, except share and per share data):

	Three Months Ended March 31,
	2018		2017
Net income (loss), basic and diluted	$	30,253	$	(68,290	)
Weighted-average shares used in computing net income (loss) per share, basic		48,190,511		41,841,612
Weighted-average effect of dilutive securities:
Options to purchase common stock and RSUs		742,796		—
Employee stock purchase plan		3,683		—
Common stock warrants		140,752		—
Weighted-average shares used in computing net income (loss) per share, diluted		49,077,742		41,841,612
Net income (loss) per share:
Basic	$	0.63	$	(1.63	)
Diluted	$	0.62	$	(1.63	)

Outstanding Shares of Common Stock Equivalents Excluded from Computation of Diluted Net Loss per Share

	Three Months Ended March 31,
	2018		2017
Options to purchase common stock and RSUs		5,150,737		5,303,718
Employee stock purchase plan		—		24,590
Common stock warrants		—		149,700
		5,150,737		5,478,008

Accumulated Other Comprehensive Income (Loss) (Tables)

3 Months Ended

Mar. 31, 2018

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):

	March 31,			December 31,
	2018			2017
Foreign currency translation adjustments	$	(315	)	$	(5,298	)
Unrealized loss on securities available-for-sale		(631	)		(382	)
Total accumulated other comprehensive loss	$	(946	)	$	(5,680	)

Organization - Additional Information (Details)	3 Months Ended
Organization - Additional Information (Details)	Mar. 31, 2018 Segment
United States of America
Organization And Nature Of Business [Line Items]
Number of reportable segments	1

Summary of Significant Accounting Policies - Summary of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Cash and cash equivalents	$ 226,730	$ 100,488	$ 159,501
Restricted cash, current	542	461	271
Restricted cash, non-current	1,931	2,092	1,996
Total cash, cash equivalents, and restricted cash shown in the statements of cash flows	$ 229,203	$ 103,041	$ 161,768	$ 164,607

Financial Instruments - Summary of Financial Assets Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	$ 529,462	$ 224,029
Gross Unrealized Losses	(631)	(380)
Estimated Fair Value	528,831	223,649
Money Market Funds \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	158,296	79,670
Estimated Fair Value	158,296	79,670
Asset-backed Securities \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	30,928
Gross Unrealized Losses	(59)
Estimated Fair Value	30,869
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	90,462	39,330
Gross Unrealized Losses	(289)	(90)
Estimated Fair Value	90,173	39,240
Commercial Paper \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	79,388
Estimated Fair Value	79,388
U.S. Government Treasury and Agency Securities \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	160,388	105,029
Gross Unrealized Losses	(283)	(290)
Estimated Fair Value	$ 160,105	$ 104,739

Financial Instruments - Additional Information (Details)	3 Months Ended
	Mar. 31, 2018 USD ($)
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	2 years

Balance Sheet Components - Summary of Inventory (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Investments Debt And Equity Securities [Abstract]
Work-in-progress	$ 1,808	$ 737
Finished goods	260	20
Total inventory	$ 2,068	$ 757

Balance Sheet Components - Accrued Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Research and clinical study expenses	$ 21,680	$ 17,141
Payroll and related expenses	16,774	26,527
Repayment liability under collaboration agreement	3,460	3,681
Contract liability		5,986
Other	7,377	8,092
Total accrued liabilities	$ 49,291	$ 61,427

License and Research Agreements - Additional Information (Details) - USD ($)		1 Months Ended			3 Months Ended
	Nov. 07, 2017	Oct. 31, 2016	Jul. 31, 2016	Jun. 30, 2016	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock purchased					49,665,203		44,167,071
Contract liability							$ 5,986,000
Research and development					$ 75,504,000	$ 51,269,000
Dimension
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Business acquisition date	Nov. 07, 2017
Research and development					$ 4,400,000
Amortization completion year					2019
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]
Contract liability	$ 2,500,000						5,400,000
Collaboration and license revenue					$ 9,300,000
Contract asset					800,000
Kyowa Hakko Kirin Collaboration \| License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Reduction in research and development cost					8,200,000	7,400,000
Reduction in selling, general and administrative expenses					3,800,000	$ 500,000
License agreement receivable					$ 12,300,000		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]
Reduction in research and development cost			$ 800,000
Estimated fair value of license recorded as research and development expense			$ 700,000	$ 700,000
Research collaboration agreement, period				5 years
Common stock purchased			374,590
Common stock value			$ 40,000,000
Common closing stock price per share			$ 72.95
Common stock shares issued premium amount			$ 12,700,000
Option to purchase additional common stock, value			25,000,000
Common stock purchase agreement, terms					Takeda is subject to a five-year standstill (subject to customary exceptions or release).
Total arrangement consideration received			14,300,000
Estimated transaction price			3,300,000
Repayment liability					$ 3,500,000		3,700,000
Contract liability					0		$ 600,000
Takeda License and Collaboration and Purchase Agreements \| Put Option
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Estimated fair value of future options			900,000
Common stock issued upon option exercised in period, shares		352,530
Common stock issued upon option exercised in period, value		$ 25,000,000
Takeda License and Collaboration and Purchase Agreements \| Common Stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Fair market value of shares issued			$ 27,300,000
Research, Develop and Commercialize Adeno Associated Virus Gene Therapy Products \| Bayer HealthCare LLC
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments received					5,000,000
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

Stock-Based Awards - Additional Information (Details)	3 Months Ended
Stock-Based Awards - Additional Information (Details)	Mar. 31, 2018 shares
2014 Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share reserved for future issuance	1,828,073
Automatic increases in shares available for grant effective date	Jan. 01, 2015
Shares available for grant, ending date	Jan. 01, 2024
2014 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share reserved for future issuance	2,292,906

Stock-Based Awards - Summary of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 18,797	$ 14,499
Research and development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	11,247	8,543
Selling, general and administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 7,550	$ 5,956

Net Income (Loss) per Share - Computation of Basic and Diluted Net Income (Loss) Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Net income (loss), basic and diluted	$ 30,253	$ (68,290)
Weighted-average shares used in computing net income (loss) per share, basic	48,190,511	41,841,612
Weighted-average effect of dilutive securities:
Weighted-average shares used in computing net income (loss) per share, diluted	49,077,742	41,841,612
Net income (loss) per share:
Basic	$ 0.63	$ (1.63)
Diluted	$ 0.62	$ (1.63)
Options to Purchase Common Stock and RSUs [Member]
Weighted-average effect of dilutive securities:
Weighted Average Number Diluted Shares Outstanding Adjustment	742,796
Common Stock Warrants
Weighted-average effect of dilutive securities:
Weighted Average Number Diluted Shares Outstanding Adjustment	140,752
Employee Stock Purchase Plan
Weighted-average effect of dilutive securities:
Weighted Average Number Diluted Shares Outstanding Adjustment	3,683

Net Income (Loss) Per Share - Outstanding Shares of Common Stock Equivalents Excluded from Computation of Diluted Net Loss per Share (Details) - shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	5,150,737	5,478,008
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	5,150,737	5,303,718
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
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		24,590

Equity Transactions - Additional Information (Details) - USD ($)	1 Months Ended			3 Months Ended
	Mar. 31, 2018	Jan. 31, 2018	Jul. 31, 2016	Mar. 31, 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
Net proceeds from sale of common stock				$ 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		$ 57.00

Accumulated Other Comprehensive Income (Loss) - Schedule of Total Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income Loss Net Of Tax [Abstract]
Foreign currency translation adjustments	$ (315)	$ (5,298)
Unrealized loss on securities available-for-sale	(631)	(382)
Total accumulated other comprehensive loss	$ (946)	$ (5,680)

Gain from Sale of Priority Review Voucher - Additional Information (Details) - USD ($) $ in Thousands		3 Months Ended
	Jan. 10, 2018	Mar. 31, 2018
Goodwill And Intangible Assets Disclosure [Abstract]
Sale of PRV	$ 130,000	$ 130,000