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Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2016	May 04, 2016
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2016
Document Fiscal Year Focus	2016
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		39,020,576

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 70,763	$ 93,569
Short-term investments	341,092	343,428
Restricted cash	1,291	150
Prepaid expenses and other current assets	17,088	13,060
Total current assets	430,234	450,207
Property and equipment, net	13,418	7,373
Restricted cash	2,537	2,135
Long-term investments	75,932	99,259
Other assets	2,063	595
Total assets	524,184	559,569
Current liabilities:
Accounts payable	6,012	2,942
Accrued liabilities	23,565	24,784
Deferred rent—current portion	303	192
Total current liabilities	29,880	27,918
Other liabilities	4,480	561
Total liabilities	34,360	28,479
Stockholders’ equity:
Preferred stock — 25,000,000 shares authorized; nil outstanding as of March 31, 2016 and December 31, 2015
Common stock — 250,000,000 shares authorized; 38,992,346 and 38,882,394 shares issued and outstanding as of March 31, 2016 and December 31, 2015, respectively	39	39
Additional paid-in capital	827,109	816,578
Accumulated other comprehensive income (loss)	92	(868)
Accumulated deficit	(337,416)	(284,659)
Total stockholders’ equity	489,824	531,090
Total liabilities and stockholders’ equity	$ 524,184	$ 559,569

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - shares	Mar. 31, 2016	Dec. 31, 2015
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	38,992,346	38,882,394
Common stock, shares outstanding	38,992,346	38,882,394

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Operating expenses:
Research and development	$ 40,415	$ 17,364
General and administrative	13,207	4,138
Total operating expenses	53,622	21,502
Loss from operations	(53,622)	(21,502)
Other income (expense), net:
Interest income	984	273
Other expense, net	(119)	(150)
Total other income (expense), net	865	123
Net loss	$ (52,757)	$ (21,379)
Net loss per share, basic and diluted	$ (1.35)	$ (0.63)
Shares used in computing net loss per share, basic and diluted	38,970,151	34,008,830

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (52,757)	$ (21,379)
Other comprehensive income:
Unrealized gain (loss) on available-for-sale securities	960	80
Total comprehensive loss	$ (51,797)	$ (21,299)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Operating activities:
Net loss	$ (52,757)	$ (21,379)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	544	201
Amortization of premium (discount) on investment securities, net	1,828	965
Stock-based compensation	10,217	2,408
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(4,028)	(948)
Other assets	(1,468)	(7)
Accounts payable	2,638	437
Accrued liabilities and other liabilities	(1,869)	664
Net cash used in operating activities	(44,895)	(17,659)
Investing activities:
Purchase of property and equipment	(1,477)	(459)
Purchase of investments	(118,130)	(77,254)
Proceeds from the sale of investments	11,494	12,766
Proceeds from maturities of investments	131,431	62,240
Increase in restricted cash	(1,543)	(1,358)
Net cash provided by (used in) investing activities	21,775	(4,065)
Financing activities:
Proceeds from issuance of common stock, net	314	175,440
Net cash provided by financing activities	314	175,440
Net increase (decrease) in cash and cash equivalents	(22,806)	153,716
Cash and cash equivalents at beginning of period	93,569	24,324
Cash and cash equivalents at end of period	$ 70,763	$ 178,040

Organization

3 Months Ended

Mar. 31, 2016

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 metabolic genetic diseases. The Company is currently conducting a Phase 3 study of aceneuramic acid extended-release (Ace-ER) in patients with GNE myopathy, which is also known as hereditary inclusion body myopathy (HIBM), a progressive muscle-wasting disorder; a Phase 3 study of recombinant human beta-glucuronidase (rhGUS) in patients with mucopolysaccharidosis 7, or MPS 7, a rare lysosomal storage disease; a Phase 2 clinical study for UX007 in patients with glucose transporter type-1 deficiency syndrome (Glut1 DS), a brain energy deficiency; 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; and Phase 2 and Phase 3 studies of KRN23, an antibody targeting fibroblast growth factor 23, or FGF23, in patients with X-linked hypophosphatemia (XLH) and tumor-induced osteomalacia (TIO), both rare diseases that impair bone mineralization. The Company operates as one reportable segment.

Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2016

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. general 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 26, 2016 with the United States Securities and Exchange Commission (SEC).

The results of operations for the three months ended March 31, 2016 are not necessarily indicative of the results to be expected for the year ending December 31, 2016. The condensed balance sheet as of December 31, 2015 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 preparation of condensed 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 condensed consolidated financial statements and the accompanying notes. 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.

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 recognize the assets and liabilities arising from leases on the balance sheet. 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 March 2016, the FASB issued ASU No. 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. This guidance is effective for annual reporting periods beginning after December 15, 2016, and interim periods within those annual periods. 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, 2016

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 condensed consolidated 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 the 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, 2016
	Level 1		Level 2		Level 3		Total
Financial Assets:
Money market funds	$	44,133	$	—	$	—	$	44,133
Corporate bonds		—		318,215		—		318,215
Asset-backed securities		—		38,998		—		38,998
U.S. Government Treasury and agency securities		13,979		47,598		—		61,577
Commercial paper		—		9,985		—		9,985
Total financial assets	$	58,112	$	414,796	$	—	$	472,908

	December 31, 2015
	Level 1		Level 2		Level 3		Total
Financial Assets:
Money market funds	$	53,254	$	—	$	—	$	53,254
Corporate bonds		—		370,445		—		370,445
Asset-backed securities		—		29,302		—		29,302
U.S. Government Treasury and agency securities		—		47,452		—		47,452
Commercial paper		—		13,887		—		13,887
Total financial assets	$	53,254	$	461,086	$	—	$	514,340

- 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, 2016

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, 2016
			Gross Unrealized
	Amortized Cost		Gains		Losses			Estimated Fair Value
Money market funds classified as cash equivalents	$	44,133	$	—	$	—		$	44,133
Corporate bonds classified as cash equivalents		11,753		—		(2	)		11,751
Commercial paper classified as short-term investments		9,985		—		—			9,985
Corporate bonds classified as short-term investments		262,257		121		(94	)		262,284
Asset-backed securities classified as short-term investments		29,737		9		(8	)		29,738
U.S. Government Treasury and agency securities classified as short-term investments		39,095		4		(14	)		39,085
Corporate bonds classified as long-term investments		44,129		78		(27	)		44,180
Asset-backed securities classified as long-term investments		9,246		14		—			9,260
U.S. Government Treasury and agency securities classified as long-term investments		22,481		18		(7	)		22,492
Total	$	472,816	$	244	$	(152	)	$	472,908

	December 31, 2015
			Gross Unrealized
	Amortized Cost		Gains		Losses			Estimated Fair Value
Money market funds classified as cash equivalents	$	53,254	$	—	$	—		$	53,254
Corporate bonds classified as cash equivalents		18,403		—		(4	)		18,399
Commercial paper classified as short-term investments		13,887		—		—			13,887
Corporate bonds classified as short-term investments		282,386		9		(397	)		281,998
Asset-backed securities classified as short-term investments		15,019		—		(27	)		14,992
U.S. Government Treasury and agency securities classified as short-term investments		32,628		—		(77	)		32,551
Corporate bonds classified as long-term investments		70,309		2		(263	)		70,048
Asset-backed securities classified as long-term investments		14,337		—		(27	)		14,310
U.S. Government Treasury and agency securities classified as long-term investments		14,985		—		(84	)		14,901
Total	$	515,208	$	11	$	(879	)	$	514,340

At March 31, 2016, the remaining contractual maturities of available-for-sale securities were less than three years. There have been no significant realized gains or losses on available-for-sale securities for the periods presented.

Accrued Liabilities

Accrued liabilities consist of the following (in thousands):

	March 31,		December 31,
	2016		2015
Research and clinical study expenses	$	13,179	$	9,764
Payroll and related expenses		5,339		9,423
Other		5,047		5,597
Total accrued liabilities	$	23,565	$	24,784

License and Research Agreements

3 Months Ended

Mar. 31, 2016

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), which was amended in August 2015. Under the terms of this collaboration and license agreement, the Company and KHK will collaborate on the development and commercialization of certain products containing KRN23, an antibody directed towards FGF23, 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, provided that the core development plan related to Japan and Korea shall be 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. The Company is obligated to provide assistance in accordance with the agreed upon development plan as well as participate on various committees. If KRN23 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 KRN23 in the European territory, and the Company will develop and commercialize KRN23 in Latin America. KHK will manufacture and supply KRN23 for clinical use globally and will manufacture and supply KRN23 for commercial use in the profit share territory and Latin America.

The Company is accounting for the agreement as a collaboration arrangement as defined in ASC 808, Collaborative Agreements; accordingly, the Company’s expenses were reduced by $4.9 million and $1.5 million for the three months ended March 31, 2016 and 2015, respectively, for its share of the costs as research and development. As of March 31, 2016 and December 31, 2015, the Company had receivables in the amount of $4.9 million and $3.8 million, respectively, for this collaboration arrangement.

Stock-Based Awards

3 Months Ended

Mar. 31, 2016

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Awards

6.	Stock-Based Awards

2014 Incentive Plan

In 2014, the Company adopted the 2014 Incentive Plan (the 2014 Plan), which became effective upon the closing of the Company’s IPO in February 2014. 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, 2016, there were 2,238,250 shares reserved under the 2014 Plan for the future issuance of equity awards. The Company also had 1,380,922 shares reserved for the 2014 Employee Stock Purchase Plan, for which no shares had been issued.

Stock-Based Compensation Expense

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,
	2016		2015
Research and development	$	6,575	$	1,841
General and administrative		3,642		567
Total stock-based compensation	$	10,217	$	2,408

Net Loss Per Share

3 Months Ended

Mar. 31, 2016

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,
	2016		2015
Stock options to purchase common stock		3,829,812		2,698,846
Unvested restricted stock units		211,261		33,856
Common stock warrants		149,700		324,351
		4,190,773		3,057,053

Summary of Significant Accounting Policies (Policies)	3 Months Ended
Summary of Significant Accounting Policies (Policies)	Mar. 31, 2016
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. general 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 26, 2016 with the United States Securities and Exchange Commission (SEC). The results of operations for the three months ended March 31, 2016 are not necessarily indicative of the results to be expected for the year ending December 31, 2016. The condensed balance sheet as of December 31, 2015 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 preparation of condensed 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 condensed consolidated financial statements and the accompanying notes. 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.
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 recognize the assets and liabilities arising from leases on the balance sheet. 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 March 2016, the FASB issued ASU No. 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. This guidance is effective for annual reporting periods beginning after December 15, 2016, and interim periods within those annual periods. 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, 2016

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, 2016
	Level 1		Level 2		Level 3		Total
Financial Assets:
Money market funds	$	44,133	$	—	$	—	$	44,133
Corporate bonds		—		318,215		—		318,215
Asset-backed securities		—		38,998		—		38,998
U.S. Government Treasury and agency securities		13,979		47,598		—		61,577
Commercial paper		—		9,985		—		9,985
Total financial assets	$	58,112	$	414,796	$	—	$	472,908

	December 31, 2015
	Level 1		Level 2		Level 3		Total
Financial Assets:
Money market funds	$	53,254	$	—	$	—	$	53,254
Corporate bonds		—		370,445		—		370,445
Asset-backed securities		—		29,302		—		29,302
U.S. Government Treasury and agency securities		—		47,452		—		47,452
Commercial paper		—		13,887		—		13,887
Total financial assets	$	53,254	$	461,086	$	—	$	514,340

Balance Sheet Components (Tables)

3 Months Ended

Mar. 31, 2016

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, 2016
			Gross Unrealized
	Amortized Cost		Gains		Losses			Estimated Fair Value
Money market funds classified as cash equivalents	$	44,133	$	—	$	—		$	44,133
Corporate bonds classified as cash equivalents		11,753		—		(2	)		11,751
Commercial paper classified as short-term investments		9,985		—		—			9,985
Corporate bonds classified as short-term investments		262,257		121		(94	)		262,284
Asset-backed securities classified as short-term investments		29,737		9		(8	)		29,738
U.S. Government Treasury and agency securities classified as short-term investments		39,095		4		(14	)		39,085
Corporate bonds classified as long-term investments		44,129		78		(27	)		44,180
Asset-backed securities classified as long-term investments		9,246		14		—			9,260
U.S. Government Treasury and agency securities classified as long-term investments		22,481		18		(7	)		22,492
Total	$	472,816	$	244	$	(152	)	$	472,908

	December 31, 2015
			Gross Unrealized
	Amortized Cost		Gains		Losses			Estimated Fair Value
Money market funds classified as cash equivalents	$	53,254	$	—	$	—		$	53,254
Corporate bonds classified as cash equivalents		18,403		—		(4	)		18,399
Commercial paper classified as short-term investments		13,887		—		—			13,887
Corporate bonds classified as short-term investments		282,386		9		(397	)		281,998
Asset-backed securities classified as short-term investments		15,019		—		(27	)		14,992
U.S. Government Treasury and agency securities classified as short-term investments		32,628		—		(77	)		32,551
Corporate bonds classified as long-term investments		70,309		2		(263	)		70,048
Asset-backed securities classified as long-term investments		14,337		—		(27	)		14,310
U.S. Government Treasury and agency securities classified as long-term investments		14,985		—		(84	)		14,901
Total	$	515,208	$	11	$	(879	)	$	514,340

Accrued Liabilities

Accrued liabilities consist of the following (in thousands):

	March 31,		December 31,
	2016		2015
Research and clinical study expenses	$	13,179	$	9,764
Payroll and related expenses		5,339		9,423
Other		5,047		5,597
Total accrued liabilities	$	23,565	$	24,784

Stock-Based Awards (Tables)

3 Months Ended

Mar. 31, 2016

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,
	2016		2015
Research and development	$	6,575	$	1,841
General and administrative		3,642		567
Total stock-based compensation	$	10,217	$	2,408

Net Loss Per Share (Tables)

3 Months Ended

Mar. 31, 2016

Earnings Per Share [Abstract]

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

	Three Months Ended March 31,
	2016		2015
Stock options to purchase common stock		3,829,812		2,698,846
Unvested restricted stock units		211,261		33,856
Common stock warrants		149,700		324,351
		4,190,773		3,057,053

Organization - Additional Information (Details)	3 Months Ended
Organization - Additional Information (Details)	Mar. 31, 2016 Segment
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Number of reportable segments	1

Fair Value Measurements - Summary of Financial Assets Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Financial Assets:
Fair value	$ 472,908	$ 514,340
Money Market Funds
Financial Assets:
Fair value	44,133	53,254
Asset Backed Securities
Financial Assets:
Fair value	38,998	29,302
Level 1
Financial Assets:
Fair value	58,112	53,254
Level 1 \| Money Market Funds
Financial Assets:
Fair value	44,133	53,254
Level 2
Financial Assets:
Fair value	414,796	461,086
Level 2 \| Asset Backed Securities
Financial Assets:
Fair value	38,998	29,302
Corporate Bonds
Financial Assets:
Fair value	318,215	370,445
Corporate Bonds \| Level 2
Financial Assets:
Fair value	318,215	370,445
US Government Treasury and Agencies Securities
Financial Assets:
Fair value	61,577	47,452
US Government Treasury and Agencies Securities \| Level 1
Financial Assets:
Fair value	13,979
US Government Treasury and Agencies Securities \| Level 2
Financial Assets:
Fair value	47,598	47,452
Commercial Paper
Financial Assets:
Fair value	9,985	13,887
Commercial Paper \| Level 2
Financial Assets:
Fair value	$ 9,985	$ 13,887

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, 2016	Dec. 31, 2015
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 472,816	$ 515,208
Gross Unrealized Gains	244	11
Gross Unrealized Losses	(152)	(879)
Estimated Fair Value	472,908	514,340
Money Market Funds Classified as Cash Equivalents
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	44,133	53,254
Estimated Fair Value	44,133	53,254
Corporate Bonds Classified as Cash Equivalents
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	11,753	18,403
Gross Unrealized Losses	(2)	(4)
Estimated Fair Value	11,751	18,399
Commercial Paper Classified as Short-Term Investments
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	9,985	13,887
Estimated Fair Value	9,985	13,887
Corporate Bonds Classified as Short-Term Investments
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	262,257	282,386
Gross Unrealized Gains	121	9
Gross Unrealized Losses	(94)	(397)
Estimated Fair Value	262,284	281,998
Asset Backed Securities Classified as Short-Term Investments
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	29,737	15,019
Gross Unrealized Gains	9
Gross Unrealized Losses	(8)	(27)
Estimated Fair Value	29,738	14,992
U.S. Government Treasury and Agency Securities Classified as Short-Term Investments
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	39,095	32,628
Gross Unrealized Gains	4
Gross Unrealized Losses	(14)	(77)
Estimated Fair Value	39,085	32,551
Corporate Bonds Classified as Long-Term Investments
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	44,129	70,309
Gross Unrealized Gains	78	2
Gross Unrealized Losses	(27)	(263)
Estimated Fair Value	44,180	70,048
Asset Backed Securities Classified as Long-Term Investments
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	9,246	14,337
Gross Unrealized Gains	14
Gross Unrealized Losses		(27)
Estimated Fair Value	9,260	14,310
U.S. Government Treasury and Agency Securities Classified as Long-Term Investments
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	22,481	14,985
Gross Unrealized Gains	18
Gross Unrealized Losses	(7)	(84)
Estimated Fair Value	$ 22,492	$ 14,901

Balance Sheet Components - Additional Information (Details)	3 Months Ended
	Mar. 31, 2016 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	3 years

Balance Sheet Components - Accrued Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Payables And Accruals [Abstract]
Research and clinical study expenses	$ 13,179	$ 9,764
Payroll and related expenses	5,339	9,423
Other	5,047	5,597
Total accrued liabilities	$ 23,565	$ 24,784

License and Research Agreements - Additional Information (Details) - Kyowa Hakko Kirin Collaboration - License Agreement - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Reduction in research and development cost	$ 4.9	$ 1.5
License agreement receivable	$ 4.9		$ 3.8

Stock-Based Awards - Additional Information (Details)	3 Months Ended
Stock-Based Awards - Additional Information (Details)	Mar. 31, 2016 shares
2014 Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share reserved for future issuance	2,238,250
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	1,380,922
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, 2016	Mar. 31, 2015
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 10,217	$ 2,408
Research and development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	6,575	1,841
General and administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 3,642	$ 567

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, 2016	Mar. 31, 2015
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	4,190,773	3,057,053
Stock options to purchase common stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	3,829,812	2,698,846
Unvested 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	211,261	33,856
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	324,351