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Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2017	May 01, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2017
Document Fiscal Year Focus	2017
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		42,312,906

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 159,501	$ 161,120
Short-term investments	265,689	219,028
Restricted cash	271	1,411
Prepaid expenses and other current assets	19,224	20,136
Total current assets	444,685	401,695
Property and equipment, net	16,517	17,055
Restricted cash	1,996	2,076
Long-term investments	80,862	117,963
Other assets	1,762	1,837
Total assets	545,822	540,626
Current liabilities:
Accounts payable	8,345	5,364
Accrued liabilities	42,773	54,554
Deferred rent—current portion	637	341
Total current liabilities	51,755	60,259
Other liabilities	5,589	6,393
Total liabilities	57,344	66,652
Stockholders’ equity:
Preferred stock — 25,000,000 shares authorized; nil outstanding as of March 31, 2017 and December 31, 2016
Common stock — 250,000,000 shares authorized; 42,273,429 and 41,240,230 shares issued and outstanding as of March 31, 2017 and December 31, 2016, respectively	42	41
Additional paid-in capital	1,087,028	1,003,561
Accumulated other comprehensive income	231	905
Accumulated deficit	(598,823)	(530,533)
Total stockholders’ equity	488,478	473,974
Total liabilities and stockholders’ equity	$ 545,822	$ 540,626

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - shares	Mar. 31, 2017	Dec. 31, 2016
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	42,273,429	41,240,230
Common stock, shares outstanding	42,273,429	41,240,230

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Operating expenses:
Research and development	$ 51,269	$ 40,415
General and administrative	18,685	13,207
Total operating expenses	69,954	53,622
Loss from operations	(69,954)	(53,622)
Other income (expense), net:
Interest income	1,082	984
Other income (expense), net	582	(119)
Total other income (expense), net	1,664	865
Net loss	$ (68,290)	$ (52,757)
Net loss per share, basic and diluted	$ (1.63)	$ (1.35)
Shares used in computing net loss per share, basic and diluted	41,841,612	38,970,151

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (68,290)	$ (52,757)
Other comprehensive income (loss):
Foreign currency translation adjustments	(648)
Unrealized gain (loss) on available-for-sale securities	(26)	960
Other comprehensive income (loss):	(674)	960
Total comprehensive loss	$ (68,964)	$ (51,797)

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Operating activities:
Net loss	$ (68,290)	$ (52,757)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	14,499	10,217
Amortization of premium on investment securities, net	549	1,828
Depreciation and amortization	1,161	544
Foreign currency remeasurement gain	(648)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	930	(4,028)
Other assets	75	(1,468)
Accounts payable	2,989	2,638
Accrued liabilities and other liabilities	(12,470)	(1,869)
Net cash used in operating activities	(61,205)	(44,895)
Investing activities:
Purchase of property and equipment	(485)	(1,477)
Purchase of investments	(87,527)	(118,130)
Proceeds from the sale of investments	12,415	11,494
Proceeds from maturities of investments	64,977	131,431
(Increase) decrease in restricted cash	1,220	(1,543)
Net cash provided by (used in) investing activities	(9,400)	21,775
Financing activities:
Proceeds from issuance of common stock in connection with at-the-market offering, net	67,591
Proceeds from issuance of common stock from equity awards, net	1,378	314
Net cash provided by financing activities	68,969	314
Effect of exchange rate changes on cash	17
Net decrease in cash and cash equivalents	(1,619)	(22,806)
Cash and cash equivalents at beginning of period	161,120	93,569
Cash and cash equivalents at end of period	$ 159,501	$ 70,763

Organization

3 Months Ended

Mar. 31, 2017

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 completed a Phase 3 study of recombinant human beta-glucuronidase (rhGUS) in patients with mucopolysaccharidosis 7 (MPS 7), a rare lysosomal storage disease, and is conducting a Phase 3 study of aceneuramic acid extended-release (Ace-ER) in patients with GNE myopathy, a progressive muscle-wasting disorder; Phase 2 and Phase 3 studies of burosumab (KRN23 or UX023), an antibody targeting fibroblast growth factor 23 (FGF23), in pediatric and adult patients with X-linked hypophosphatemia (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; and 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. The Company operates as one reportable segment.

Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2017

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 17, 2017 with the United States Securities and Exchange Commission (SEC).

The results of operations for the three months ended March 31, 2017 are not necessarily indicative of the results to be expected for the year ending December 31, 2017. The condensed consolidated balance sheet as of December 31, 2016 has been derived from audited financial statements at that date, but does not include all of the information required by GAAP for complete financial statements.

Use of Estimates

The accompanying consolidated financial statements have been prepared in accordance with GAAP. The preparation of the consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent liabilities and the reported amounts of expenses in the consolidated financial statements and the accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to clinical trial accruals, fair value of assets and liabilities, income taxes, 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.

Revenue Recognition

In May 2014, the Financial Accounting Standards Board (FASB), issued Accounting Standards Update (ASU) 2014-09, Revenue from Contracts with Customers (ASC 606), to supersede nearly all existing revenue recognition guidance under GAAP. The core principle of ASU 2014-09 is to recognize revenues when promised goods or services are transferred to customers in an amount that reflects the consideration that is expected to be received for those goods or services. ASU 2014-09 defines a five-step process to achieve this core principle and, in doing so, it is possible more judgment and estimates may be required within the revenue recognition process than are required under existing GAAP, including identifying performance obligations in a contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. In March, April, May and December 2016, the FASB issued ASU 2016-08, Revenue from Contracts with Customers: Principal versus Agent Considerations, ASU 2016-10, Revenue from Contracts with Customers: Identifying Performance Obligations and Licensing, ASU 2016-12, Revenue from Contracts with Customers: Narrow-Scope Improvements and Practical Expedients to provide supplemental adoption guidance and clarification to ASU 2014-09, and ASU 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers, respectively. The effective date for these new standards is the same as the effective date and transition requirements for ASU 2014-09. The Company has early adopted the new revenue standard as of January 1, 2017 using a full retrospective application to each prior reporting period presented. Through January 1, 2017, the Company had recorded a cumulative inception to date total of $0.1 million of revenues. The adoption did not have an effect on the Consolidated Financial Statements on the adoption date and no adjustment to prior year consolidated financial statements was required.

Product sales revenue

The Company recognizes revenue from sales of rhGUS (UX003) on a “named patient” basis, which is allowed in certain countries prior to the commercial approval of the product in the territory. Under ASC 606, revenue from product sales is recognized at the point in time when the product is shipped to the customer. 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.

License and collaboration revenue

The Company has license and collaboration agreements with Kyowa Hakko Kirin Co., Ltd. (KHK) and Takeda Pharmaceutical Company Limited (Takeda). The license and collaboration agreements 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 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.

Stock-Based Compensation

In March 2016, the FASB issued ASU 2016-09, Compensation — Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting, which simplifies several aspects of the accounting for employee share-based payments, including income tax consequences, application of award forfeitures to expense, classification on the statement of cash flows, and classification of awards as either equity or liabilities. The Company adopted ASU 2016-09 as of January 1, 2017. On January 1, 2017, there was $19.7 million of cumulative unrecognized excess tax benefits which was fully offset by a corresponding increase in the valuation allowance. The adoption did not have any other impact on the Consolidated Financial Statements on the adoption date.

Recently Issued Accounting Pronouncements

In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842), 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.

In October 2016, the FASB issued ASU 2016-16, Income Taxes - Intra-Entity Transfers of Assets Other Than Inventory, which requires entities to recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs. The standard is effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. Early adoption is permitted as of the beginning of a fiscal year. The new standard must be adopted using a modified retrospective transition method which is a cumulative-effective adjustment to retained earnings as of the beginning of the first effective reporting period. The Company is evaluating the effect that this guidance will have on its Consolidated Financial Statements and related disclosures.

Fair Value Measurements

3 Months Ended

Mar. 31, 2017

Fair Value Disclosures [Abstract]

Fair Value Measurements

3.Fair Value Measurements

Financial assets and liabilities are recorded at fair value. The carrying amount of certain financial instruments, including cash and cash equivalents, accounts 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, 2017
	Level 1		Level 2		Level 3		Total
Financial Assets:
Money market funds	$	114,551	$	—	$	—	$	114,551
Corporate bonds		—		232,429		—		232,429
Commercial paper		—		13,958		—		13,958
Asset-backed securities		—		15,234		—		15,234
U.S. Government Treasury and agency securities		—		121,806		—		121,806
Total financial assets	$	114,551	$	383,427	$	—	$	497,978

	December 31, 2016
	Level 1		Level 2		Level 3		Total
Financial Assets:
Money market funds	$	123,536	$	—	$	—	$	123,536
Corporate bonds		—		207,726		—		207,726
Commercial paper		—		11,970		—		11,970
Asset-backed securities		—		27,713		—		27,713
U.S. Government Treasury and agency securities		—		111,931		—		111,931
Total financial assets	$	123,536	$	359,340	$	—	$	482,876

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Balance Sheet Components

3 Months Ended

Mar. 31, 2017

Investments Debt And Equity Securities [Abstract]

Balance Sheet Components

4.	Balance Sheet Components

Cash Equivalents and Investments

The fair values of cash equivalents, short-term investments, and long-term investments classified as available-for-sale securities, consisted of the following (in thousands):

	March 31, 2017
			Gross Unrealized
	Amortized Cost		Gains		Losses			Estimated Fair Value
Money market funds	$	114,551	$	—	$	—		$	114,551
Corporate bonds		232,549		29		(149	)		232,429
Commercial paper		13,958		—		—			13,958
Asset-backed securities		15,241		—		(7	)		15,234
U.S. Government Treasury and agency securities		122,122		—		(316	)		121,806
Total	$	498,421	$	29	$	(472	)	$	497,978

	December 31, 2016
			Gross Unrealized
	Amortized Cost		Gains		Losses			Estimated Fair Value
Money market funds	$	123,536	$	—	$	—		$	123,536
Corporate bonds		207,909		14		(197	)		207,726
Commercial paper		11,970		—		—			11,970
Asset-backed securities		27,712		3		(2	)		27,713
U.S. Government Treasury and agency securities		112,166		10		(245	)		111,931
Total	$	483,293	$	27	$	(444	)	$	482,876

At March 31, 2017, 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, 2017 have been in a loss position for less than twelve months or the loss is not material and were 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.

Accrued Liabilities

Accrued liabilities consist of the following (in thousands):

	March 31,		December 31,
	2017		2016
Research and clinical study expenses	$	14,459	$	18,593
Payroll and related expenses		10,514		17,226
Repayment liability under collaboration agreement		13,063		13,650
Other		4,737		5,085
Total accrued liabilities	$	42,773	$	54,554

License and Research Agreements

3 Months Ended

Mar. 31, 2017

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 certain products containing burosumab in the field of orphan diseases in the United States and Canada, or the profit share territory, and in the European Union, Switzerland, and Turkey, 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. If burosumab is approved, the Company and KHK will share commercial responsibilities and profits in the profit share territory until the applicable transition date, KHK will commercialize burosumab in the European territory, and the Company will develop and commercialize burosumab in Latin America.

KHK will manufacture and supply burosumab for clinical use globally and will manufacture and supply burosumab 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. 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.

The Company’s expenses were reduced by $7.4 million and $4.6 million for the three month periods ended March 31, 2017 and 2016, respectively, for its share of the costs as research and development and were reduced by $0.5 million and $0.3 million for the three month periods ended March 31, 2017 and 2016, respectively, for its share of the costs as general and administrative expenditures. As of March 31, 2017 and December 31, 2016, the Company had receivables in the amount of $7.9 million and $8.6 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, which includes an option to an additional field of use for this product with the terms to be negotiated, and an option to a specified product candidate (identified option product). 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. Under the license for the pre-clinical compound, the Company may be required to make future milestone payments to Takeda of up to $7.5 million if certain development milestones are met, $75.0 million if certain regulatory milestones are met, and $150.0 million if certain commercial milestones are met, as well as royalties with respect to net sales in the high-single digits to low-teens. Any products resulting from the pre-clinical compound or the identified option product is referred to in this report as the “licensed 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 at the then-current 30-day volume-weighted average price (VWAP). The put option 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 valuation was performed using a Monte Carlo simulation approach using the term of the put options and an equity volatility of approximately 70%.

The Company also granted Takeda an exclusive option for Asian rights, for a limited period, to any licensed products and any additional products resulting from the collaboration, as well as an option to exclusively license one of the Company’s products for development and commercialization in Japan. If Takeda exercises any of its option rights to license a product pursuant to the agreement, Takeda will pay for the development costs within the licensed territory, will share in a portion of the global development costs, and will make a milestone payment upon regulatory approval. Takeda will also owe royalties on net sales in the licensed territory for any licensed product, depending on the development stage when the product is licensed as well as sales levels. The royalties related to the option to license the Company’s product, as well as the additional product are subject to future good faith negotiations at the time that the option is exercised.

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 ASC 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, which is expected to be performed over a period of approximately one and a half years. A significant portion of this work is expected to be performed by Takeda which has an estimated cost of approximately $10.0 million to $15.5 million and is subject to changes as development activities are adjusted and cost estimates are refined. 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, 2017, the Company concluded that the total amount of funding to be returned to Takeda for the development work is uncertain and therefore concluded that the transaction price should be fully constrained. The Company could not conclude it is probable that a significant reversal in the amount recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. When evaluating whether the transaction price should be constrained, the Company evaluated ASC 606-10-32-12 and noted its experience with similar types of contracts is limited, and the contract has a large number and broad range of possible consideration amounts. Therefore, the Company has noted that the qualitative factors in ASC 606-10-32-12 (c) and (e) are both met. Based on the high level of uncertainty in the amount of transaction price that is refundable to Takeda, the Company concluded that the transaction price should be fully constrained through March 31, 2017. Therefore, the total consideration received from Takeda of $14.3 million was recorded as a refund liability. The Company will continue to re-evaluate the application of the constraint to the transaction price at each reporting period end date. The accounting result under ASC 606 was consistent with the conclusions under the prior revenue recognition standard.

Once the transaction price is no longer constrained, any excess of the total consideration received over the repayment obligation to Takeda will be classified as a contract liability, allocated to the distinct performance obligations on a relative standalone selling price basis, and recognized as a reduction of research and development expenses over time by measuring the progress toward complete satisfaction of the individual performance obligation using an input measure. The performance obligations are estimated to be substantially complete by March 2018. 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, 2017, the Company recorded a repayment liability under a collaboration agreement in the amount of $13.1 million. The Company acknowledges that the FASB added a project to its agenda in November 2016 to evaluate the interaction between ASC 808 and ASC 606 and some of the conclusions reached by the Company may change if new guidance is provided by FASB.

Stock-Based Awards

3 Months Ended

Mar. 31, 2017

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, 2017, there were 1,892,354 shares reserved under the 2014 Plan for the future issuance of equity awards. The Company also had 1,844,853 shares reserved for the 2014 Employee Stock Purchase Plan, for which no shares had been issued.

The table below sets forth the functional classification of stock-based compensation expense, net of estimated forfeitures, for the periods presented (in thousands):

	Three Months Ended March 31,
	2017		2016
Research and development	$	8,543	$	6,575
General and administrative		5,956		3,642
Total stock-based compensation	$	14,499	$	10,217

- Definition

The entire disclosure for compensation-related costs for equity-based compensation, which may include disclosure of policies, compensation plan details, allocation of equity compensation, incentive distributions, equity-based arrangements to obtain goods and services, deferred compensation arrangements, employee stock ownership plan details and employee stock purchase plan details.

+ References + Details

Net Loss Per Share

3 Months Ended

Mar. 31, 2017

Earnings Per Share [Abstract]

Net Loss Per Share

7.	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 March 31,
	2017		2016
Options to purchase common stock and restricted stock units		5,303,718		4,041,073
Employee stock purchase plan		24,590		—
Common stock warrants		149,700		149,700
		5,478,008		4,190,773

Equity Transactions

3 Months Ended

Mar. 31, 2017

Equity [Abstract]

Equity Transactions

8.	Equity Transactions

In July 2016, the Company entered into an At-The-Market, or ATM, sales agreement, with Cowen and Company, LLC (Cowen), whereby the Company could sell up to $150.0 million in aggregate proceeds of common stock from time to time, through Cowen as its sales agent. During the three months ended March 31, 2017, the Company sold 912,351 shares of common stock, resulting in net proceeds of approximately $67.6 million, after commissions and other offering costs, which completed the sales of the total amount authorized in the agreement.

- Definition

The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Reference 14: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Glossary Preferred Stock
-URI http://asc.fasb.org/extlink&oid=6521494

Reference 15: http://www.xbrl.org/2003/role/presentationRef
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+ Details

Accumulated Other Comprehensive Income (Loss)

3 Months Ended

Mar. 31, 2017

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):

	Three Months Ended March 31, 2017
	Unrealized Gain (Loss) on Securities Available-for-Sale			Foreign Currency Translation Adjustments			Accumulated Other Comprehensive Income (Loss)
December 31, 2016	$	(417	)	$	1,322		$	905
Current period other comprehensive loss		(26	)		(648	)		(674	)
March 31, 2017	$	(443	)	$	674		$	231

	Three Months Ended March 31, 2016
	Unrealized Gain (Loss) on Securities Available-for-Sale			Foreign Currency Translation Adjustments		Accumulated Other Comprehensive Income (Loss)
December 31, 2015	$	(868	)	$	—	$	(868	)
Current period other comprehensive income		960			—		960
March 31, 2016	$	92		$	—	$	92

- Definition

The entire disclosure for comprehensive income, which includes, but is not limited to, 1) the amount of income tax expense or benefit allocated to each component of other comprehensive income, including reclassification adjustments, 2) the reclassification adjustments for each classification of other comprehensive income and 3) the ending accumulated balances for each component of comprehensive income.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Reclassification Adjustments
-URI http://asc.fasb.org/extlink&oid=6522872

+ Details

Summary of Significant Accounting Policies (Policies)	3 Months Ended
Summary of Significant Accounting Policies (Policies)	Mar. 31, 2017
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 17, 2017 with the United States Securities and Exchange Commission (SEC). The results of operations for the three months ended March 31, 2017 are not necessarily indicative of the results to be expected for the year ending December 31, 2017. The condensed consolidated balance sheet as of December 31, 2016 has been derived from audited financial statements at that date, but does not include all of the information required by GAAP for complete financial statements.
Use of Estimates	Use of Estimates The accompanying consolidated financial statements have been prepared in accordance with GAAP. The preparation of the consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent liabilities and the reported amounts of expenses in the consolidated financial statements and the accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to clinical trial accruals, fair value of assets and liabilities, income taxes, 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.
Revenue Recognition	Revenue Recognition In May 2014, the Financial Accounting Standards Board (FASB), issued Accounting Standards Update (ASU) 2014-09, Revenue from Contracts with Customers (ASC 606), to supersede nearly all existing revenue recognition guidance under GAAP. The core principle of ASU 2014-09 is to recognize revenues when promised goods or services are transferred to customers in an amount that reflects the consideration that is expected to be received for those goods or services. ASU 2014-09 defines a five-step process to achieve this core principle and, in doing so, it is possible more judgment and estimates may be required within the revenue recognition process than are required under existing GAAP, including identifying performance obligations in a contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. In March, April, May and December 2016, the FASB issued ASU 2016-08, Revenue from Contracts with Customers: Principal versus Agent Considerations, ASU 2016-10, Revenue from Contracts with Customers: Identifying Performance Obligations and Licensing, ASU 2016-12, Revenue from Contracts with Customers: Narrow-Scope Improvements and Practical Expedients to provide supplemental adoption guidance and clarification to ASU 2014-09, and ASU 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers, respectively. The effective date for these new standards is the same as the effective date and transition requirements for ASU 2014-09. The Company has early adopted the new revenue standard as of January 1, 2017 using a full retrospective application to each prior reporting period presented. Through January 1, 2017, the Company had recorded a cumulative inception to date total of $0.1 million of revenues. The adoption did not have an effect on the Consolidated Financial Statements on the adoption date and no adjustment to prior year consolidated financial statements was required. Product sales revenue The Company recognizes revenue from sales of rhGUS (UX003) on a “named patient” basis, which is allowed in certain countries prior to the commercial approval of the product in the territory. Under ASC 606, revenue from product sales is recognized at the point in time when the product is shipped to the customer. 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. License and collaboration revenue The Company has license and collaboration agreements with Kyowa Hakko Kirin Co., Ltd. (KHK) and Takeda Pharmaceutical Company Limited (Takeda). The license and collaboration agreements 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 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.
Stock-Based Compensation	Stock-Based Compensation In March 2016, the FASB issued ASU 2016-09, Compensation — Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting, which simplifies several aspects of the accounting for employee share-based payments, including income tax consequences, application of award forfeitures to expense, classification on the statement of cash flows, and classification of awards as either equity or liabilities. The Company adopted ASU 2016-09 as of January 1, 2017. On January 1, 2017, there was $19.7 million of cumulative unrecognized excess tax benefits which was fully offset by a corresponding increase in the valuation allowance. The adoption did not have any other impact on the Consolidated Financial Statements on the adoption date.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842), 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. In October 2016, the FASB issued ASU 2016-16, Income Taxes - Intra-Entity Transfers of Assets Other Than Inventory, which requires entities to recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs. The standard is effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. Early adoption is permitted as of the beginning of a fiscal year. The new standard must be adopted using a modified retrospective transition method which is a cumulative-effective adjustment to retained earnings as of the beginning of the first effective reporting period. The Company is evaluating the effect that this guidance will have on its Consolidated Financial Statements and related disclosures.

Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2017

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, 2017
	Level 1		Level 2		Level 3		Total
Financial Assets:
Money market funds	$	114,551	$	—	$	—	$	114,551
Corporate bonds		—		232,429		—		232,429
Commercial paper		—		13,958		—		13,958
Asset-backed securities		—		15,234		—		15,234
U.S. Government Treasury and agency securities		—		121,806		—		121,806
Total financial assets	$	114,551	$	383,427	$	—	$	497,978

	December 31, 2016
	Level 1		Level 2		Level 3		Total
Financial Assets:
Money market funds	$	123,536	$	—	$	—	$	123,536
Corporate bonds		—		207,726		—		207,726
Commercial paper		—		11,970		—		11,970
Asset-backed securities		—		27,713		—		27,713
U.S. Government Treasury and agency securities		—		111,931		—		111,931
Total financial assets	$	123,536	$	359,340	$	—	$	482,876

Balance Sheet Components (Tables)

3 Months Ended

Mar. 31, 2017

Investments Debt And Equity Securities [Abstract]

Summary of Fair Values of Cash Equivalents, Short-Term Investments and Long-Term Investments Classified as Available-for-Sale Securities

The fair values of cash equivalents, short-term investments, and long-term investments classified as available-for-sale securities, consisted of the following (in thousands):

	March 31, 2017
			Gross Unrealized
	Amortized Cost		Gains		Losses			Estimated Fair Value
Money market funds	$	114,551	$	—	$	—		$	114,551
Corporate bonds		232,549		29		(149	)		232,429
Commercial paper		13,958		—		—			13,958
Asset-backed securities		15,241		—		(7	)		15,234
U.S. Government Treasury and agency securities		122,122		—		(316	)		121,806
Total	$	498,421	$	29	$	(472	)	$	497,978

	December 31, 2016
			Gross Unrealized
	Amortized Cost		Gains		Losses			Estimated Fair Value
Money market funds	$	123,536	$	—	$	—		$	123,536
Corporate bonds		207,909		14		(197	)		207,726
Commercial paper		11,970		—		—			11,970
Asset-backed securities		27,712		3		(2	)		27,713
U.S. Government Treasury and agency securities		112,166		10		(245	)		111,931
Total	$	483,293	$	27	$	(444	)	$	482,876

Accrued Liabilities

Accrued liabilities consist of the following (in thousands):

	March 31,		December 31,
	2017		2016
Research and clinical study expenses	$	14,459	$	18,593
Payroll and related expenses		10,514		17,226
Repayment liability under collaboration agreement		13,063		13,650
Other		4,737		5,085
Total accrued liabilities	$	42,773	$	54,554

Stock-Based Awards (Tables)

3 Months Ended

Mar. 31, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Functional Classification of Stock-Based Compensation Expense, Net of Estimated Forfeitures

The table below sets forth the functional classification of stock-based compensation expense, net of estimated forfeitures, for the periods presented (in thousands):

	Three Months Ended March 31,
	2017		2016
Research and development	$	8,543	$	6,575
General and administrative		5,956		3,642
Total stock-based compensation	$	14,499	$	10,217

Net Loss Per Share (Tables)

3 Months Ended

Mar. 31, 2017

Earnings Per Share [Abstract]

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

	Three Months Ended March 31,
	2017		2016
Options to purchase common stock and restricted stock units		5,303,718		4,041,073
Employee stock purchase plan		24,590		—
Common stock warrants		149,700		149,700
		5,478,008		4,190,773

Accumulated Other Comprehensive Income (Loss) (Tables)

3 Months Ended

Mar. 31, 2017

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):

	Three Months Ended March 31, 2017
	Unrealized Gain (Loss) on Securities Available-for-Sale			Foreign Currency Translation Adjustments			Accumulated Other Comprehensive Income (Loss)
December 31, 2016	$	(417	)	$	1,322		$	905
Current period other comprehensive loss		(26	)		(648	)		(674	)
March 31, 2017	$	(443	)	$	674		$	231

	Three Months Ended March 31, 2016
	Unrealized Gain (Loss) on Securities Available-for-Sale			Foreign Currency Translation Adjustments		Accumulated Other Comprehensive Income (Loss)
December 31, 2015	$	(868	)	$	—	$	(868	)
Current period other comprehensive income		960			—		960
March 31, 2016	$	92		$	—	$	92

Organization - Additional Information (Details)	3 Months Ended
Organization - Additional Information (Details)	Mar. 31, 2017 Segment
United States of America
Organization And Nature Of Business [Line Items]
Number of reportable segments	1

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Jan. 01, 2017
Accounting Standards Update 2016-09
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Unrecognized excess tax benefits which was fully offset by increase in valuation allowance		$ 19.7
New Accounting Pronouncement, Early Adoption, Effect \| Accounting Standards Update 2014-09
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Revenue recognized	$ 0.1

Fair Value Measurements - Summary of Financial Assets Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Financial Assets:
Fair value	$ 497,978	$ 482,876
Money Market Funds
Financial Assets:
Fair value	114,551	123,536
Asset-backed Securities
Financial Assets:
Fair value	15,234	27,713
Corporate Bonds
Financial Assets:
Fair value	232,429	207,726
Commercial Paper
Financial Assets:
Fair value	13,958	11,970
U.S. Government Treasury and Agency Securities
Financial Assets:
Fair value	121,806	111,931
Level 1
Financial Assets:
Fair value	114,551	123,536
Level 1 \| Money Market Funds
Financial Assets:
Fair value	114,551	123,536
Level 2
Financial Assets:
Fair value	383,427	359,340
Level 2 \| Asset-backed Securities
Financial Assets:
Fair value	15,234	27,713
Level 2 \| Corporate Bonds
Financial Assets:
Fair value	232,429	207,726
Level 2 \| Commercial Paper
Financial Assets:
Fair value	13,958	11,970
Level 2 \| U.S. Government Treasury and Agency Securities
Financial Assets:
Fair value	$ 121,806	$ 111,931

Balance Sheet Components - Summary of Fair Values of Cash Equivalents, Short-Term Investments and Long-Term Investments Classified as Available-for-Sale Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 498,421	$ 483,293
Gross Unrealized Gains	29	27
Gross Unrealized Losses	(472)	(444)
Estimated Fair Value	497,978	482,876
Money Market Funds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	114,551	123,536
Estimated Fair Value	114,551	123,536
Commercial Paper
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	13,958	11,970
Estimated Fair Value	13,958	11,970
Corporate Bonds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	232,549	207,909
Gross Unrealized Gains	29	14
Gross Unrealized Losses	(149)	(197)
Estimated Fair Value	232,429	207,726
Asset-Backed Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	15,241	27,712
Gross Unrealized Gains		3
Gross Unrealized Losses	(7)	(2)
Estimated Fair Value	15,234	27,713
U.S. Government Treasury and Agency Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	122,122	112,166
Gross Unrealized Gains		10
Gross Unrealized Losses	(316)	(245)
Estimated Fair Value	$ 121,806	$ 111,931

Balance Sheet Components - Additional Information (Details)	3 Months Ended
	Mar. 31, 2017 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 - Accrued Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Payables And Accruals [Abstract]
Research and clinical study expenses	$ 14,459	$ 18,593
Payroll and related expenses	10,514	17,226
Repayment liability under collaboration agreement	13,063	13,650
Other	4,737	5,085
Total accrued liabilities	$ 42,773	$ 54,554

License and Research Agreements - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended			3 Months Ended
	Oct. 31, 2016	Jul. 31, 2016	Jun. 30, 2016	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock purchased				42,273,429		41,240,230
Liability under collaboration arrangement				$ 13,063		$ 13,650
Kyowa Hakko Kirin Collaboration \| License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Reduction in research and development cost				7,400	$ 4,600
Reduction in general and administrative cost				500	$ 300
License agreement receivable				$ 7,900		$ 8,600
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]
Estimated fair value of license recorded as research and development expense			$ 700
Research collaboration agreement, period			5 years
Common stock purchased		374,590
Common stock value		$ 40,000
Common closing stock price per share		$ 72.95
Common stock shares issued premium amount		$ 12,700
Option to purchase additional common stock, value		$ 25,000
Volume weighted average price, period		30 days
Total arrangement consideration received		$ 14,300		$ 14,300
Initial development plan period				Approximately one and a half years
Liability under collaboration arrangement				$ 13,100
Takeda License and Collaboration and Purchase Agreements \| Put Option
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Estimated fair value of future options		$ 900
Common stock issued upon option exercised in period, shares	352,530
Common stock issued upon option exercised in period, value	$ 25,000
Takeda License and Collaboration and Purchase Agreements \| Put Option \| Monte Carlo Simulation
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Equity volatility percentage		70.00%
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
Takeda License and Collaboration and Purchase Agreements \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Estimated approximate cost for expected work performed		15,500
Takeda License and Collaboration and Purchase Agreements \| Maximum \| Development Milestones
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future contingent milestone payments			$ 7,500
Takeda License and Collaboration and Purchase Agreements \| Maximum \| Regulatory Milestones
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future contingent milestone payments			75,000
Takeda License and Collaboration and Purchase Agreements \| Maximum \| Commercial Milestones
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future contingent milestone payments			$ 150,000
Takeda License and Collaboration and Purchase Agreements \| Minimum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Estimated approximate cost for expected work performed		$ 10,000

Stock-Based Awards - Additional Information (Details)	3 Months Ended
Stock-Based Awards - Additional Information (Details)	Mar. 31, 2017 shares
2014 Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share reserved for future issuance	1,892,354
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	1,844,853
Shares issued	0

Stock-Based Awards - Functional Classification of Stock-Based Compensation Expense, Net of Estimated Forfeitures (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 14,499	$ 10,217
Research and development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	8,543	6,575
General and administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 5,956	$ 3,642

Net 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, 2017	Mar. 31, 2016
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	5,478,008	4,190,773
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
Options to Purchase Common Stock and Restricted Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	5,303,718	4,041,073
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

Equity Transactions - Additional Information (Details) - ATM Sales Agreement - USD ($)	1 Months Ended	3 Months Ended
	Jul. 31, 2016	Mar. 31, 2017
Stockholders Equity [Line Items]
Common stock shares sold		912,351
Net proceeds from sale of common stock		$ 67,600,000
Maximum
Stockholders Equity [Line Items]
Option to sell common stock for cash	$ 150,000,000

Accumulated Other Comprehensive Income (Loss) - Schedule of Total Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 473,974
Current period other comprehensive income (loss)	(674)	$ 960
Ending balance	488,478
Unrealized Gain (Loss) on Securities Available-for-Sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(417)	(868)
Current period other comprehensive income (loss)	(26)	960
Ending balance	(443)	92
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	1,322
Current period other comprehensive income (loss)	(648)
Ending balance	674
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	905	(868)
Current period other comprehensive income (loss)	(674)	960
Ending balance	$ 231	$ 92