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Document and Entity Information - USD ($) $ in Billions	12 Months Ended
Document and Entity Information - USD ($) $ in Billions	Dec. 31, 2015	Feb. 19, 2016	Jun. 30, 2015
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2015
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	FY
Trading Symbol	RARE
Entity Registrant Name	Ultragenyx Pharmaceutical Inc.
Entity Central Index Key	0001515673
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		38,979,564
Entity Public Float			$ 2.3

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 93,569	$ 24,324
Short-term investments	343,428	163,163
Restricted cash	150
Prepaid expenses and other current assets	13,060	5,929
Total current assets	450,207	193,416
Property and equipment, net	7,373	3,033
Restricted cash	2,135	744
Long-term investments	99,259
Other assets	595	774
Total assets	559,569	197,967
Current liabilities:
Accounts payable	2,942	4,857
Accrued liabilities	24,784	7,575
Deferred rent—current portion	192	85
Total current liabilities	27,918	12,517
Other liabilities	561	505
Total liabilities	28,479	13,022
Commitments and contingencies (Note 12)
Stockholders’ equity:
Preferred stock, par value of $0.001 per share—25,000,000 shares authorized; nil outstanding as of December 31, 2015 and 2014
Common stock, par value of $0.001 per share—250,000,000 shares authorized; 38,882,394 and 31,934,682 shares issued and outstanding as of December 31, 2015 and 2014	39	32
Additional paid-in capital	816,578	324,128
Accumulated other comprehensive loss	(868)	(174)
Accumulated deficit	(284,659)	(139,041)
Total stockholders’ equity	531,090	184,945
Total liabilities and stockholders’ equity	$ 559,569	$ 197,967

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating expenses:
Research and development	$ 114,737	$ 45,967	$ 27,829
General and administrative	33,001	10,811	4,451
Total operating expenses	147,738	56,778	32,280
Loss from operations	(147,738)	(56,778)	(32,280)
Other income (expense), net:
Interest income	2,320	608	216
Other expense, net	(200)	(3,632)	(3,006)
Total other income (expense), net	2,120	(3,024)	(2,790)
Net loss	(145,618)	(59,802)	(35,070)
Net loss attributable to common stockholders	$ (145,618)	$ (64,610)	$ (50,289)
Net loss per share attributable to common stockholders, basic and diluted	$ (3.96)	$ (2.25)	$ (14.87)
Shares used in computing net loss per share attributable to common stockholders, basic and diluted	36,782,603	28,755,758	3,382,489

CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND SHAREHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Series A Redeemable Convertible Preferred Stock	Series B Convertible Preferred Stock	Employee Stock Option	Founders Stock	Common Stock	Additional Paid-in Capital	Additional Paid-in Capital Employee Stock Option	Additional Paid-in Capital Founders Stock	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance at Dec. 31, 2012	$ (27,047)					$ 3	$ 8				$ (27,058)
Beginning balance, shares at Dec. 31, 2012						3,458,928
Beginning balance at Dec. 31, 2012		$ 37,458	$ 73,929
Beginning balance, shares at Dec. 31, 2012		34,349,894	27,081,680
Issuance of common stock upon exercise of stock options and warrants	$ 171					$ 1	170
Issuance of common stock upon exercise of stock options and warrants , shares	307,366					307,361
Employee stock-based compensation				$ 389	$ 268			$ 389	$ 268
Accretion on convertible preferred stock	$ (13,543)	$ 13,543					(835)				(12,708)
Unrealized gain (loss) on available-for-sale securities	11									$ 11
Net loss	(35,070)										(35,070)
Ending balance at Dec. 31, 2013	(74,821)					$ 4				11	(74,836)
Ending balance, shares at Dec. 31, 2013						3,766,289
Ending balance at Dec. 31, 2013		$ 51,001	$ 73,929
Ending balance, shares at Dec. 31, 2013		34,349,894	27,081,680
Conversion of convertible preferred stock to common stock at initial public offering	129,360	$ (55,431)	$ (73,929)			$ 19	129,341
Conversion of convertible preferred stock to common stock at initial public offering, shares		(34,349,894)	(27,081,680)			19,598,486
Reclassification of preferred stock warrant liability	6,743						6,743
Issuance of common stock in connection with initial public offering, net of issuance costs and preferred stock dividend	121,711					$ 7	121,704
Issuance of common stock in connection with initial public offering, net of issuance costs and preferred stock dividend, shares						6,624,423
Issuance of common stock in connection with underwritten public offering, net of issuance costs	60,239					$ 2	60,237
Issuance of common stock in connection with underwritten public offering, net of issuance costs, shares						1,613,879
Issuance of common stock upon exercise of stock options and warrants	$ 736						736
Issuance of common stock upon exercise of stock options and warrants , shares	305,090					331,605
Employee stock-based compensation	$ 5,394						5,394
Accretion on convertible preferred stock	(4,430)	$ 4,430					(27)				(4,403)
Unrealized gain (loss) on available-for-sale securities	(185)									(185)
Net loss	(59,802)										(59,802)
Ending balance at Dec. 31, 2014	$ 184,945					$ 32	324,128			(174)	(139,041)
Ending balance, shares at Dec. 31, 2014	31,934,682					31,934,682
Issuance of common stock in connection with underwritten public offering, net of issuance costs	$ 461,136					$ 6	461,130
Issuance of common stock in connection with underwritten public offering, net of issuance costs, shares						5,980,000
Issuance of common stock upon exercise of stock options and warrants	$ 7,355					$ 1	7,354
Issuance of common stock upon exercise of stock options and warrants , shares	795,825					957,587
Employee stock-based compensation	$ 24,884						24,884
Restricted stock units vested during the period, net	(918)						(918)
Restricted stock units vested during the period, net of shares						10,125
Unrealized gain (loss) on available-for-sale securities	(694)									(694)
Net loss	(145,618)										(145,618)
Ending balance at Dec. 31, 2015	$ 531,090					$ 39	$ 816,578			$ (868)	$ (284,659)
Ending balance, shares at Dec. 31, 2015	38,882,394					38,882,394

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating activities:
Net loss	$ (145,618)	$ (59,802)	$ (35,070)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,384	684	444
Amortization of premium on investment securities	5,637	3,600	1,413
Stock-based compensation	24,884	5,394	657
Revaluation of convertible preferred stock warrant liability	0	3,324	2,901
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(7,131)	(4,081)	(1,593)
Other assets	179	(411)	(2,615)
Accounts payable	(1,982)	3,177	237
Accrued expenses and other liabilities	16,670	3,481	2,426
Net cash used in operating activities	(105,977)	(44,634)	(31,200)
Investing activities:
Purchase of property and equipment	(4,955)	(2,149)	(407)
Purchase of investments	(624,226)	(208,972)	(63,953)
Proceeds from sale of investments	89,321	5,002
Proceeds from maturities of investments	249,050	82,972	16,601
Decrease (increase) in restricted cash	(1,541)	(293)	25
Net cash used in investing activities	(292,351)	(123,440)	(47,734)
Financing activities:
Proceeds from issuance of common stock, net	467,573	189,317	171
Payment of preferred stock dividend		(4,346)
Net cash provided by financing activities	467,573	184,971	171
Net increase (decrease) in cash and cash equivalents	69,245	16,897	(78,763)
Cash and cash equivalents at beginning of year	24,324	7,427	86,190
Cash and cash equivalents at end of year	93,569	24,324	$ 7,427
Supplemental disclosures of non-cash investing and financing information:
Costs of fixed assets included in accounts payable and accrued liabilities	$ 769	243
Reclassification of warrant liability to equity upon conversion to common stock warrants		6,743
Conversion of Series A and Series B preferred stock to common stock		$ 129,360

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2015

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Consolidation

The consolidated financial statements include the accounts of Ultragenyx Pharmaceutical Inc. and our subsidiaries. All intercompany balances and transactions have been eliminated.

Use of Estimates

The accompanying consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“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, warrants, common stock, income taxes and stock-based compensation. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Actual results could differ from those estimates.

Cash and Cash Equivalents

The Company considers all highly liquid investments with original maturities of three months or less from the date of purchase to be cash equivalents. Cash equivalents consist primarily of amounts invested in money market accounts and corporate bonds.

Investments

All investments have been classified as “available-for-sale” and are carried at estimated fair value as determined based upon quoted market prices or pricing models for similar securities. Management determines the appropriate classification of its investments in debt securities at the time of purchase and reevaluates such designation as of each balance sheet date. Investments with a maturity of one year or less from the balance sheet date are reported as short-term investments and investments with a maturity of greater than one year from the balance sheet date are reported as long-term investments. Unrealized gains and losses are excluded from earnings and are reported as a component of comprehensive loss. Realized gains and losses and declines in fair value judged to be other than temporary, if any, on available-for-sale securities are included in interest income and other expense, net, respectively. The cost of securities sold is based on the specific-identification method. Interest on investments is included in interest income.

Concentration of Credit Risk and Other Risks and Uncertainties

Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash, cash equivalents, and investments. The Company’s cash, cash equivalents, and investments are held by financial institutions that management believes are of high credit quality. The Company’s investment policy limits investments to fixed income securities denominated and payable in U.S. dollars such as U.S. government obligations, money market instruments and funds, corporate bonds, and asset-backed securities and places restrictions on maturities and concentrations by type and issuer. Such deposits may, at times, exceed federally insured limits. The Company has not experienced any losses on its deposits of cash and cash equivalents and its accounts are monitored by management to mitigate risk. The Company is exposed to credit risk in the event of default by the financial institutions holding its cash and cash equivalents, corporate bond issuers and other financial instruments to the extent recorded in the balance sheets.

Property and Equipment

Property and equipment are stated at cost, less accumulated depreciation and amortization. Depreciation and amortization is computed using the straight-line method over the estimated useful lives of the respective assets. Depreciation and amortization begins at the time the asset is placed in service. Maintenance and repairs are charged to operations as incurred. Upon sale or retirement of assets, the cost and related accumulated depreciation are removed from the balance sheet and the resulting gain or loss, if any, is reflected in operations.

The useful lives of the property and equipment are as follows:

Research and development equipment		5 years
Furniture and office equipment		5 years
Computer equipment		3 years
Software		3-5 years
Leasehold improvements		Shorter of lease term or estimated useful life

Impairment of Long-Lived Assets

The Company evaluates its long-lived assets, including property and equipment, for impairment whenever events or changes in circumstances indicate that the carrying value of these assets may not be recoverable. Recoverability of these assets is measured by comparison of the carrying amount of each asset to the future undiscounted cash flows expected to result from the use of the asset and its eventual disposition. If the asset is considered to be impaired, the amount of any impairment is measured as the difference between the carrying value and the fair value of the impaired asset. The Company has not recorded impairment of any long-lived assets since inception.

Restricted Cash

Restricted cash includes money market accounts with one of the Company’s financial institutions as collateral for its obligations under its facility leases of the Company’s corporate headquarters in Novato, California and for its facilities in Brisbane, California. Restricted cash also includes a savings account associated with a credit card agreement at one of the Company’s financial institutions.

Accruals of Research and Development Costs

The Company records accruals for estimated costs of research, preclinical and clinical studies and manufacturing development. These costs are a significant component of the Company’s research and development expenses. A substantial portion of the Company’s ongoing research and development activities are conducted by third-party service providers, including contract research organizations. The Company accrues the costs incurred under its agreements with these third parties based on actual work completed in accordance with agreements established with these third parties. The Company determines the actual costs through discussions with internal personnel and external service providers as to the progress or stage of completion of the services and the agreed-upon fee to be paid for such services. The Company makes significant judgments and estimates in determining the accrual balance in each reporting period. As actual costs become known, the Company adjusts its accruals. The Company has not experienced any material deviations between accrued clinical trial expenses and actual clinical trial expenses. However, actual services performed, number of patients enrolled, and the rate of patient enrollment may vary from the Company’s estimates, resulting in adjustments to clinical trial expense in future periods. Changes in these estimates that result in material changes to the Company’s accruals could materially affect the Company’s results of operations.

Leases

The Company enters into lease agreements for its office and laboratory facilities. These leases are classified as operating leases. Rent expense is recognized on a straight-line basis over the term of the lease and, accordingly, the Company records the difference between cash rent payments and the recognition of rent expense as a deferred rent liability. Incentives granted under the Company’s facilities leases, including allowances to fund leasehold improvements, are deferred and are recognized as adjustments to rental expense on a straight-line basis over the term of the lease.

Comprehensive Loss

Comprehensive loss is the change in stockholders’ equity (deficit) from transactions and other events and circumstances other than those resulting from investments by stockholders and distributions to stockholders. The Company’s other comprehensive loss is comprised of unrealized gains and losses on investments in available-for-sale securities.

Research and Development

Research and development costs are expensed as incurred and consist of salaries and benefits, stock-based compensation expense, lab supplies and facility costs, as well as fees paid to other nonemployees and entities that conduct certain research and development activities on the Company’s behalf. Amounts incurred in connection with license agreements are also included in research and development expense. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are deferred and capitalized. The capitalized amounts are expensed as the related goods are delivered or the services are performed.

Stock-Based Compensation

Stock-based awards issued to employees, including stock options, are recorded at fair value as of the grant date using the Black-Scholes option-pricing model and recognized as expense on a straight-line basis over the employee’s requisite service period (generally the vesting period). Because noncash stock compensation expense is based on awards ultimately expected to vest, it is reduced by an estimate for future forfeitures. Forfeitures are estimated at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from estimates.

Income Taxes

The Company uses the liability method of accounting for income taxes. Under this method, deferred tax assets and liabilities are determined based on the differences between the financial reporting and the tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. The Company must then assess the likelihood that the resulting deferred tax assets will be realized. A valuation allowance is provided when it is more likely than not that some portion or all of a deferred tax asset will not be realized. Due to the Company’s lack of earnings history, the net deferred tax assets have been fully offset by a valuation allowance.

The Company recognizes benefits of uncertain tax positions if it is more likely than not that such positions will be sustained upon examination based solely on their technical merits, as the largest amount of benefit that is more likely than not to be realized upon the ultimate settlement. The Company’s policy is to recognize interest and penalties related to the underpayment of income taxes as a component of income tax expense or benefit. To date, there have been no interest or penalties charged in relation to the unrecognized tax benefits.

Net Loss per Share Attributable to Common Stockholders

Basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding during the period, without consideration for common stock equivalents. The net loss attributable to common stockholders is calculated by adjusting the net loss of the Company for the accretion on the Series A convertible preferred stock and cumulative dividends paid on Series A and B convertible preferred stock. Diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since the effects of potentially dilutive securities are antidilutive. In periods when we have incurred a net loss, convertible preferred stock, options and warrants to purchase common stock and convertible preferred stock warrants are considered common stock equivalents, but have been excluded from the calculation of diluted net loss per share attributable to common stockholders, as their effect is antidilutive.

Recent Accounting Pronouncements

In August 2014, the FASB issued ASU No. 2014-15, Presentation of Financial Statements — Going Concern (Subtopic 205-40): Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern, which requires management to evaluate, in connection with preparing financial statements for each annual and interim reporting period, whether there are conditions or events, considered in the aggregate, that raise substantial doubt about an entity’s ability to continue as a going concern within one year after the date that the financial statements are issued and provide related disclosures. This ASU will be effective for the Company in fiscal year 2016. Early adoption is permitted. The Company is currently assessing the future impact of this ASU in the financial statements.

In November 2015, the FASB issued ASU No. 2015-17, Balance Sheet Classification of Deferred Taxes (“ASU 2015-17”), which amends existing guidance to require that deferred income tax liabilities and assets be classified as noncurrent in a classified balance sheet, and eliminates the prior guidance which required an entity to separate deferred tax liabilities and assets into a current amount and a noncurrent amount in a classified balance sheet. The standard is effective for the Company in fiscal year 2017. Early adoption is permitted. As permitted by ASU 2015-17, the Company early-adopted this standard and applied it retrospectively to all periods of the tax provision presented. As the company has full valuation allowance against the deferred assets, there is no impact to the financial statements. The Company has reflected the change of this pronouncement in Note 10, Income Taxes.

Fair Value Measurements

12 Months Ended

Dec. 31, 2015

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 Company’s financial instruments consist of Level 1 and Level 2 assets. Where quoted prices are available in an active market, securities are classified as Level 1. Money market funds are classified as Level 1. Level 2 assets consist primarily of corporate bonds, asset backed securities, commercial paper and U.S. Government agency securities based upon quoted market prices for similar movements in active markets, quoted prices for identical or similar instruments in markets that are not active and model-based valuation techniques for which all significant inputs are observable in the market or can be corroborated by observable market data for substantially the full term of the assets. Where applicable these models project future cash flows and discount the future amounts to a present value using market-based observable inputs obtained from various third party data providers, including but not limited to, benchmark yields, interest rate curves, reported trades, broker/dealer quotes and reference data.

The following table sets forth the fair value of the Company’s financial assets and liabilities remeasured on a recurring basis based on the three-tier fair value hierarchy (in thousands):

	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 agency securities		—		47,452		—		47,452
Commercial paper		—		13,887		—		13,887
Total financial assets	$	53,254	$	461,086	$	—	$	514,340

	December 31, 2014
	Level 1		Level 2		Level 3		Total
Financial Assets:
Money market funds	$	8,627	$	—	$	—	$	8,627
Corporate bonds		—		152,942		—		152,942
Asset-backed securities		—		9,542		—		9,542
U.S. Government agency securities		—		4,485		—		4,485
Other		—		209		—		209
Total financial assets	$	8,627	$	167,178	$	—	$	175,805

- 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

12 Months Ended

Dec. 31, 2015

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):

	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 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 agency securities classified as long-term investments		14,985		—		(84	)		14,901
Total	$	515,208	$	11	$	(879	)	$	514,340

	December 31, 2014
			Gross Unrealized
	Amortized Cost		Gains		Losses			Estimated Fair Value
Money market funds classified as cash equivalents	$	8,627	$	—	$	—		$	8,627
Corporate bonds classified as cash equivalents		3,806		1		—			3,807
Corporate bonds classified as short-term investments		149,303		4		(172	)		149,135
Asset backed securities classified as short-term investments		9,546		—		(4	)		9,542
U.S. Government agency securities classified as short-term investments		4,488		1		(4	)		4,485
Other classified as cash equivalents		209		—		—			209
Total	$	175,979	$	6	$	(180	)	$	175,805

At December 31, 2015, 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.

Property and Equipment, net

Property and equipment, net consists of the following (in thousands):

	December 31,
	2015			2014
Research and development equipment	$	1,302		$	712
Furniture and office equipment		944			572
Computer equipment		628			268
Software		1,622			821
Leasehold improvements		3,466			2,141
Construction-in-progress		2,276			—
Property and equipment, gross		10,238			4,514
Less accumulated depreciation		(2,865	)		(1,481	)
Property and equipment, net	$	7,373		$	3,033

Depreciation expense for the years ended December 31, 2015, 2014 and 2013 was $1.4 million, $0.7 million and $0.4 million respectively. Amortization of leasehold improvements and software is included in depreciation expense.

Accrued Liabilities

Accrued liabilities consist of the following (in thousands):

	December 31,
	2015		2014
Research and clinical trial expenses	$	9,764	$	2,703
Payroll and related expenses		9,423		4,205
Consulting service expenses		4,193		122
Other		1,404		545
Total accrued liabilities	$	24,784	$	7,575

License and Research Agreements	12 Months Ended
License and Research Agreements	Dec. 31, 2015
Research Grant Agreement [Abstract]
License and Research Agreements	5. License and Research Agreements Nobelpharma License Agreement In September 2010, the Company entered into a collaboration and license agreement with Nobelpharma Co., Ltd. (Nobelpharma), which was amended in August 2015. Under the terms of this collaboration and license agreement, each party granted the other party a worldwide exclusive license under certain of that party’s intellectual property related to the compound identified as N-acetylneuraminic acid, also known as sialic acid, to develop, manufacture, and commercialize products. Nobelpharma’s licensed territory includes Japan and certain other Asian countries, and the Company’s licensed territory includes the rest of the world. The Company is required to make certain payments to Nobelpharma based upon achievement of certain development and approval milestones. The Company may make future payments that aggregate up to 200 million Yen (approximately $1.7 million based on the exchange rate at December 31, 2015) that are contingent upon attainment of various development and approval milestones. The Company will pay a mid-single digit royalty on net sales in the Company’s territory and will receive a mid-single digit royalty on net sales in the Nobelpharma territory, excluding Japan, if such product sales are ever achieved. Saint Louis University License Agreement In November 2010, the Company entered into a license agreement with Saint Louis University (SLU). Under the terms of this license agreement, SLU granted the Company an exclusive worldwide license to make, have made, use, import, offer for sale, and sell therapeutics related to SLU’s beta-glucuronidase product for use in the treatment of human diseases. The Company will be required to make a milestone payment of $0.1 million upon approval of a glucuronidase-based enzyme therapy for treatment of MPS 7. Additionally, upon reaching a certain level of cumulative worldwide sales of the product, the Company will be required to pay to SLU a low single-digit royalty on net sales of the licensed products in any country or region, if such product sales are ever achieved. AAIPharma License Agreement In March 2011, the Company entered into a license agreement with AAIPharma Services Corp. (AAIPharma). Under the terms of this license agreement, AAI Pharma granted the Company a fully paid-up, royalty-free, exclusive, perpetual, and irrevocable license to research, develop, make, have made, use, import, offer for sale, and sell products incorporating AAIPharma’s controlled release matrix solid dose oral tablet. Under the license agreement, the Company will pay a mid-single digit percentage of any sublicense revenue received by Ultragenyx related to the sublicense of AAIPharma technology that had been initially licensed by Ultragenyx. HIBM Research Group In April 2012, the Company entered into an exclusive license agreement with HIBM Research Group (HRG). Under the terms of this license agreement, HRG granted the Company an exclusive worldwide license to certain intellectual property related to the treatment of HIBM. The Company may make future payments that aggregate up to $0.3 million that are contingent upon attainment of various development and approval milestones. Additionally, the Company will pay to HRG a royalty of less than 1% of net sales of the licensed products in the licensed territories, if such product sales are ever achieved. St. Jude Children’s Research Hospital License Agreement In September 2012, the Company entered into a license agreement with St. Jude Children’s Research Hospital (St. Jude). Under the terms of this license agreement, St. Jude granted the Company an exclusive license under certain know-how to research, develop, make, use, offer to sell, import, and otherwise commercialize and exploit St. Jude’s protective protein, cathepsin, a protein product to treat, prevent, and/or diagnose galactosialidosis and other monogenetic diseases. The Company will pay to St. Jude a royalty of less than 1% on net sales of the licensed products in the licensed territories, if such product sales are ever achieved. Baylor Research Institute License Agreement In September 2012, the Company entered into a license agreement with Baylor Research Institute (BRI). Under the terms of this license agreement, BRI exclusively licensed to the Company certain intellectual property related to triheptanoin for North America. In June 2013, the Company notified BRI that it was exercising its option pursuant to the agreement to license the rights to triheptanoin in all territories outside of the United States, Canada and Mexico and paid the option exercise fee of $0.8 million. The Company may make future payments of up to $10.5 million contingent upon attainment of various development milestones and $7.5 million contingent upon attainment of various sales milestones. Additionally, the Company will pay to BRI a mid-single digit royalty on net sales of the licensed product in the licensed territories, if such product sales are ever achieved. 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 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 $10.8 million and $4.0 million for reimbursable costs for the years ended December 31, 2015 and 2014, respectively, for its share of the costs as research and development. As of December 31, 2015 and 2014, the Company had receivables in the amount of $3.8 million and $1.3 million, respectively, for this collaboration arrangement. Arcturus Research Collaboration and License Agreement In October 2015, the Company entered into a Research Collaboration and License Agreement with Arcturus Therapeutics, Inc. (Arcturus). The Company and Arcturus will collaborate on the research and development of therapies for select rare diseases. As consideration for entering into the arrangement, the Company paid Arcturus an upfront fee of $10.0 million. Arcturus will have the primary responsibility for conducting certain research services, funded by the Company, and the Company will be responsible for development and commercialization costs.

Stock-Based Awards

12 Months Ended

Dec. 31, 2015

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Awards

8. Stock-Based Awards

2011 Equity Incentive Plan

In 2011, the Company adopted the 2011 Equity Incentive Plan (the 2011 Plan). The 2011 Plan provides for the granting of stock-based awards to employees, directors, and consultants under terms and provisions established by the board of directors. Under the terms of the 2011 Plan, options may be granted at an exercise price not less than fair market value. For employees holding more than 10% of the voting rights of all classes of stock, the exercise prices for incentive stock options must be at least 110% of fair market of the common stock on the grant date, as determined by the board of directors. The terms of options granted under the 2011 Plan may not exceed ten years. Options granted generally vest over a period of four years. Typically, the vesting schedule for option grants to newly hired employees provides that 1/4 of the grant vests upon the first anniversary of the employee’s date of hire, with the remainder of the shares vesting monthly thereafter at a rate of 1/48 of the total shares subject to the option. All other employee options typically vest in equal monthly installments over the four-year vesting schedule. In connection with the Company’s IPO, no further grants subsequent to the IPO were made under this plan and all remaining shares available for grant were transferred to the 2014 Incentive Plan.

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 had 2,250,000 shares of common stock available for future issuance at the time of its inception, which included 655,038 shares available under the 2011 Plan, which were transferred to the 2014 Plan upon adoption. The 2014 Plan provides for automatic annual increases in shares available for grant, beginning on January 1, 2015 through January 1, 2024. The 2014 Plan provides for the granting of stock-based awards to employees, directors, and consultants under similar terms, conditions and provisions as the 2011 Plan.

Stock Option Activity

The following table summarizes activity under the Company’s stock option plans, including the 2011 Plan and the 2014 Plan and related information:

	Options Outstanding
	Number of Options			Weighted- Average Exercise Price		Weighted-Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
								(In thousands)
Outstanding — December 31, 2012		1,520,967		$	0.47		9.11	$	2,038
Options granted		1,267,797			5.80
Options exercised		(307,366	)		0.55
Options cancelled		(252,515	)		1.26
Outstanding — December 31, 2013		2,228,883		$	3.41	8.91		$	19,468
Options granted		932,555			41.12
Options exercised		(305,090	)		2.14
Options cancelled		(116,873	)		8.92
Outstanding — December 31, 2014		2,739,475		$	16.15		8.43	$	79,840
Options granted		2,013,350			90.60
Options exercised		(795,825	)		8.65
Options cancelled		(130,037	)		31.49
Outstanding — December 31, 2015		3,826,963		$	56.36		8.58	$	217,386
Vested and exercisable — December 31, 2015		898,924		$	13.30		7.14	$	88,886
Vested and expected to vest — December 31, 2015		3,681,683		$	55.27		8.56	$	212,968

The aggregate intrinsic values of options outstanding, vested and exercisable, and vested and expected to vest were calculated as the difference between the exercise price of the options and the fair value of the Company’s common stock as of December 31, 2015. The total intrinsic value of options exercised during the years ended December 31, 2015, 2014 and 2013 was $59.0 million, $12.1 million and $1.0 million, respectively. Cash received from the exercise of options was $6.9 million, $0.7 million, and $0.2 million as of December 31, 2015, 2014, and 2013, respectively.

The options outstanding and exercisable by exercise price as of December 31, 2015 are as follows:

	Options Outstanding				Options Exercisable
Exercise Price	Numbers of Shares		Weighted-Average Remaining Contractual Term (in Years)		Numbers of Shares		Weighted- Average Exercise Price		Weighted-Average Remaining Contractual Term (in Years)
$0.31 to $1.32		454,420		6.11		411,883	$	0.44	6.06
$1.33 to $9.03		542,555		7.67		222,173		5.26	7.68
$9.04 to $37.65		381,173		8.18		102,800		22.56	8.14
$37.66 to $53.33		334,273		8.78		77,966		45.83	8.54
$53.34 to $59.45		362,792		8.74		80,213		55.85		8.50
$59.46 to $79.33		188,500		9.33		3,889		59.95	9.27
$79.34 to $85.96		533,500		9.39		—		—		—
$85.97 to $98.72		339,750		9.56		—		—		—
$98.73 to $115.30		316,500		9.76		—		—		—
$115.31 to $131.47		373,500		9.61		—		—		—
		3,826,963		8.58		898,924	$	13.30	7.14

The weighted-average estimated fair value of stock options granted was $54.90, $26.58 and $3.82 per share of the Company’s common stock during the years ended December 31, 2015, 2014, and 2013, respectively.

The total estimated fair value of options vested during the years ended December 31, 2015, 2014 and 2013 was $10.7 million, $2.0 million, and $0.1 million, respectively.

Restricted Stock Units

In 2015 and 2014, the Company granted 187,260 and 31,000 Restricted Stock Units (RSUs) under the 2014 Plan to employees with a weighted-average grant date fair value of $89.67 and $53.23, respectively. The fair value of the RSUs is determined on the grant date based on the fair value of the Company’s common stock. The fair value of the RSUs is recognized as expense ratably over the vesting period of two to four years. The total fair value of 18,209 shares vested during 2015 was approximately $1.0 million with an aggregate intrinsic value of the shares of $2.1 million. As of December 31, 2015, the total unrecognized compensation expense related to unvested RSUs, net of estimated forfeitures, was $14.5 million, which the Company expects to recognize over an estimated weighted-average period of 3.4 years. The total outstanding RSUs at December 31, 2015 were 197,151 shares at a weighted-average grant date fair value of $87.24.

Employee Stock Purchase Plan

In January 2014, the Company adopted the 2014 Employee Stock Purchase Plan (the ESPP) which became effective upon the closing of our IPO in February 2014. The Company reserved a total of 600,000 shares of common stock for issuance under the ESPP. Eligible employees may purchase common stock at 85% of the lesser of the fair market value of common stock on the first or last day of the purchase period. The ESPP provides for automatic annual increases in shares available for grant, beginning on January 1, 2015 through January 1, 2024. The Company has not determined the date on which the initial purchase period will commence under the ESPP.

Stock-Based Compensation Expense

Total stock-based compensation recognized was as follows (in thousands):

	Year Ended December 31,
	2015		2014		2013
Research and development	$	17,100	$	4,116	$	293
General and administrative		7,784		1,278		364
Total stock-based compensation expense	$	24,884	$	5,394	$	657

As of December 31, 2015, the total unrecognized compensation expense related to 2.9 million unvested options, net of estimated forfeitures, was $102.8 million, which the Company expects to recognize over an estimated weighted-average period of 3.25 years.

In determining the estimated fair value of the stock-based awards, the Company uses the Black-Scholes option-pricing model and assumptions discussed below. Each of these inputs is subjective and generally requires significant judgment to determine.

Expected Term—The Company’s expected term represents the period that the Company’s stock-based awards are expected to be outstanding and is determined using the simplified method (based on the mid-point between the vesting date and the end of the contractual term).

Expected Volatility—Prior to the IPO in January 2014, the Company was privately held and did not have any trading history for its common stock; accordingly, the expected volatility was estimated based on the average volatility for comparable publicly traded biopharmaceutical companies over a period equal to the expected term of the stock option grants. When selecting comparable publicly traded biopharmaceutical companies on which it has based its expected stock price volatility, the Company selected companies with comparable characteristics to it, including enterprise value, risk profiles, position within the industry, and with historical share price information sufficient to meet the expected life of the stock-based awards. The historical volatility data was computed using the daily closing prices for the selected companies’ shares during the equivalent period of the calculated expected term of the stock-based awards. In 2014, the Company modified its approach by phasing in our own common stock trading history and supplemented the remaining historical information with a blended volatility from the trading history from the common stock of the same set of comparable publicly traded biopharmaceutical companies. The Company will continue to apply this process until a sufficient amount of historical information regarding the volatility of its own stock price becomes available. Sufficient trading history does not yet exist for the Company’s common stock, therefore the estimate of expected volatility is based on the volatility of other companies with similar products under development, market, size and other factors.

Risk-Free Interest Rate—The risk-free interest rate is based on the U.S. Treasury zero coupon issues in effect at the time of grant for periods corresponding with the expected term of option.

Expected Dividend—The Company has never paid dividends on its common stock and has no plans to pay dividends on its common stock. Therefore, the Company used an expected dividend yield of zero.

The fair value of stock option awards was estimated at the date of grant using a Black-Scholes option-pricing model with the following weighted-average assumptions:

	Year Ended December 31,
	2015		2014		2013
Expected term	6.23 years		6.23 years		6.25 years
Expected volatility		65%		70%		74%
Risk-free interest rate		1.8%		1.9%	0.7% to 1.6%
Expected dividend rate		0.0%		0.0%		0.0%

Income Taxes

12 Months Ended

Dec. 31, 2015

Income Tax Disclosure [Abstract]

Income Taxes

10. Income Taxes

The Company did not record a provision or benefit for income taxes during the years ended December 31, 2015, 2014 and 2013. The Company has incurred net operating losses since inception. The Company has not reflected any benefit of such net operating loss carryforwards in the accompanying financial statements. The Company has established a full valuation allowance against its deferred tax assets due to the uncertainty surrounding the realization of such assets.

The effective tax rate of our provision for income taxes differs from the federal statutory rate as follows:

	Year Ended December 31,
	2015			2014			2013
Federal statutory income tax rate		34.0	%		34.0	%		34.0	%
State income taxes, net of federal benefit		7.5			4.6			5.0
Federal tax credits		5.9			6.7			8.2
Other		0.8			—			—
Nondeductible permanent items		—			(1.2	)		(2.9	)
Stock compensation		(1.3	)		(1.4	)		(0.6	)
Uncertain tax positions		(7.7	)		—			0.9
Change in valuation allowance		(39.2	)		(42.7	)		(44.6	)
Provision for income taxes		—			—			—

The tax effect of temporary differences that give rise to significant portions of the deferred tax assets is presented below (in thousands):

	Year Ended December 31,
	2015			2014
Deferred tax assets:
Net operating loss carryforwards	$	61,503		$	32,500
Tax credits		33,881			16,737
Stock options		6,680			1,058
Accruals and reserves		2,541			476
Fixed assets and intangibles		4,442			455
Other		432			113
Total deferred tax assets		109,479			51,339
Valuation allowance		(109,479	)		(51,339	)
Net deferred tax assets	$	—		$	—

As of December 31, 2015 and 2014, the Company had approximately $225.5 million and $89.0 million of federal net operating loss carryforwards available to reduce future taxable income that will begin to expire in 2030. As of December 31, 2015 and 2014, the Company had approximately $255.0 million and $90.1 million of state net operating loss carryforwards available to reduce future taxable income that will begin to expire in 2030.

As of December 31, 2015 and 2014, the Company had federal research tax credit carryforwards of approximately $1.7 million and $1.0 million available to reduce future tax liabilities that will begin to expire in 2030. As of December 31, 2015 and 2014, the Company had state research credit carryforwards of approximately $4.3 million and $1.6 million available to reduce future tax liabilities that will be carried forward indefinitely.

As of December 31, 2015 and 2014, the Company had federal Orphan Drug Credits of approximately $35.2 million and $21.9 million available to reduce future tax liabilities that will begin to expire in 2030.

The Company’s ability to use net operating loss and tax credit carryforwards to reduce future taxable income and liabilities may be subject to annual limitations pursuant to Internal Revenue Code Sections 382 and 383 as a result of ownership changes in the past and future. As a result of ownership changes in 2012 and 2011, $3.3 million of federal net operating loss carryforwards, $3.6 million of state net operating loss carryforwards, and $0.3 million of federal tax credits are permanently limited. Deferred tax assets for net operating losses and tax credits have been reduced and a corresponding adjustment to the valuation allowance has been recorded.

The valuation allowance increased by $58.1 million and $25.6 million during the year ended December 31, 2015 and 2014, respectively.

The Company recorded unrecognized tax benefits for uncertainties in income taxes. A reconciliation of the Company’s unrecognized tax benefits for the years ended December 31, 2015, 2014 and 2013 is as follows (in thousands):

	December 31,
	2015			2014		2013
Balance at beginning of year	$	7,275		$	3,725	$	1,551
Additions based on tax positions related to current year		15,628			3,550		2,169
Additions for tax positions of prior years		5,505			—		—
Reductions for tax positions of prior years		(4,398	)		—		5
Balance at end of year	$	24,010		$	7,275	$	3,725

The entire amount of the unrecognized tax benefits would not impact the Company’s effective tax rate if recognized. The Company has elected to include interest and penalties as a component of tax expense. During the years ended December 31, 2015 and 2014, the Company did not recognize accrued interest and penalties related to unrecognized tax benefits. The Company does not anticipate that the amount of existing unrecognized tax benefits will significantly increase or decrease during the next 12 months.

The Company files income tax returns in the U.S. federal, California, and other state tax jurisdictions. The federal and state income tax returns from inception to December 31, 2015 remain subject to examination.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2015

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

11. Commitments and Contingencies

Facilities

In December 2015, the Company entered into a lease agreement for office facilities in Brisbane, California, which provided for a tenant improvement allowance of up to $3.7 million. This operating lease is expected to commence in May 2016 and expires 122 months after the commencement date. At the end of the lease term, the Company has the option to extend the lease for two additional consecutive terms of five years each. As provided in the lease agreement, monthly lease payments are subject to annual increases as defined in the lease agreement.

Under the terms of the lease agreement and the addendum of its Brisbane office facility, the Company provided the lessor with an irrevocable letter of credit. The lessor shall be entitled to draw on the letter of credit in the event of any uncured default by the Company under the terms of the lease. Provided there has been no default on the lease, the Company may reduce the amount of the letter of credit by $0.7 million on the fifth anniversary of the commencement date. As of December 31, 2015, the current amount of restricted cash and amount of the irrevocable letter of credit in connection with the lease agreement was $1.4 million.

The Company leases office space and research, testing and manufacturing laboratory space in various facilities in Novato, California, under operating agreements expiring at various dates through 2020 and include tenant improvement allowance up to $1.5 million. Certain of the leases provide for options by the Company to extend the lease for multiple five-year renewal periods and also provide for annual minimum increases in rent, usually based on a consumer price index or annual minimum increases.

Under the terms of the lease agreement and the addendum of its Novato office facility, the Company provided the lessor with an irrevocable letter of credit. The lessor shall be entitled to draw on the letter of credit in the event of any uncured default by the Company under the terms of the lease. Provided there has been no default on the lease, the Company may reduce the amount of the letter of credit by $0.1 million on each anniversary date effective May 1, 2014. As of December 31, 2015, the current amount of restricted cash and amount of the irrevocable letter of credit in connection with the lease agreement was $0.8 million.

The Company recognizes rent expense on a straight-line basis over the noncancelable term of its operating lease. Rent expense was $1.4 million, $0.6 million, and $0.3 million during the years ended December 31, 2015, 2014 and 2013, respectively.

Other Commitments

The Company has various manufacturing, clinical, research, and other contracts with vendors in the conduct of the normal course of its business. Other than as noted below, contracts are terminable, with varying provisions regarding termination. If a contract with a specific vendor were to be terminated, the Company would only be obligated for the products or services that the Company had received at the time the termination became effective.

As of December 31, 2015, the aggregate future minimum lease payments under the noncancelable operating lease arrangements and future payments under contractually binding manufacturing and service agreements are as follows (in thousands):

Year Ending December 31,	Leases		Manufacturing and Services
2016	$	2,270	$	2,042
2017		3,877		190
2018		4,504		90
2019		3,543		83
2020		2,868		62
Thereafter		13,791		—
	$	30,853	$	2,467

Contingencies

While there are no legal proceedings the Company is aware of, the Company may become party to various claims and complaints arising in the ordinary course of business. Management does not believe that any ultimate liability resulting from any of these claims will have a material adverse effect on its results of operations, financial position, or liquidity. However, management cannot give any assurance regarding the ultimate outcome of these claims, and their resolution could be material to operating results for any particular period, depending upon the level of income for the period.

Guarantees and Indemnifications

The Company indemnifies each of its directors and officers for certain events or occurrences, subject to certain limits, while the director is or was serving at the Company’s request in such capacity, as permitted under Delaware law and in accordance with its certificate of incorporation and bylaws. The term of the indemnification period lasts as long as a director may be subject to any proceeding arising out of acts or omissions of such director in such capacity. The maximum amount of potential future indemnification is unlimited; however, the Company currently holds director liability insurance. This insurance allows the transfer of risk associated with the Company’s exposure and may enable it to recover a portion of any future amounts paid. The Company believes that the fair value of these indemnification obligations is minimal. Accordingly, it has not recognized any liabilities relating to these obligations for any period presented.

Net Loss per Share Attributable to Common Stockholders

12 Months Ended

Dec. 31, 2015

Earnings Per Share [Abstract]

Net Loss per Share Attributable to Common Stockholders

12. Net Loss per Share Attributable to Common Stockholders

The following table sets forth the computation of the basic and diluted net loss per share attributable to common stockholders during the years ended December 31, 2015, 2014 and 2013 (in thousands, except share and per share data):

	Year Ended December 31,
	2015			2014			2013
Numerator:
Net loss	$	(145,618	)	$	(59,802	)	$	(35,070	)
Accretion and dividends on convertible preferred stock		—			(4,808	)		(15,219	)
Net loss attributable to common stockholders	$	(145,618	)	$	(64,610	)	$	(50,289	)
Denominator:
Weighted-average common shares outstanding		36,782,603			28,755,758			3,583,522
Less: weighted-average unvested common shares subject to repurchase		—			—			(201,033	)
Weighted-average shares used to compute net loss per share attributable to common stockholders, basic and diluted		36,782,603			28,755,758			3,382,489
Net loss per share attributable to common stockholders, basic and diluted	$	(3.96	)	$	(2.25	)	$	(14.87	)

The following weighted-average outstanding common stock equivalents were excluded from the computation of diluted net loss per share attributable to common stockholders for the periods presented because including them would have been antidilutive:

	Year Ended December 31,
	2015		2014		2013
Convertible preferred stock		—		1,610,834		19,598,486
Stock options to purchase common stock		3,247,925		2,572,729		1,666,036
Unvested restricted stock units		120,582		9,715		—
Common stock subject to repurchase		—		—		201,033
Convertible preferred stock warrants		—		29,051		353,459
Common stock warrants		195,762		318,666		—
		3,564,269		4,540,995		21,819,014

Quarterly Financial Data (unaudited)

12 Months Ended

Dec. 31, 2015

Quarterly Financial Data [Abstract]

Quarterly Financial Data (unaudited)

13. Quarterly Financial Data (unaudited)

The following table presents certain unaudited quarterly financial information. This information has been prepared on the same basis as the audited financial statements and includes all adjustments (consisting only of normal recurring adjustments) necessary to present fairly the unaudited quarterly results of operations set forth herein (in thousands, except share and per share data):

	2015
	March 31,			June 30,			September 30,			December 31,
Operating expenses	$	21,502		$	30,142		$	39,936		$	56,158
Net loss		(21,379	)		(29,787	)		(39,232	)		(55,220	)
Net loss attributable to common stockholders		(21,379	)		(29,787	)		(39,232	)		(55,220	)
Net loss per share applicable to common stockholders, basic and diluted	$	(0.63	)	$	(0.83	)	$	(1.03	)	$	(1.42	)

	2014
	March 31,			June 30,			September 30,			December 31,
Operating expenses	$	10,339		$	13,661		$	15,835		$	16,943
Net loss		(13,630	)		(13,585	)		(15,849	)		(16,738	)
Net loss attributable to common stockholders		(18,438	)		(13,585	)		(15,849	)		(16,738	)
Net loss per share applicable to common stockholders, basic and diluted	$	(0.85	)	$	(0.45	)	$	(0.50	)	$	(0.52	)

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2015

Accounting Policies [Abstract]

Basis of Consolidation

The consolidated financial statements include the accounts of Ultragenyx Pharmaceutical Inc. and our subsidiaries. All intercompany balances and transactions have been eliminated.

Use of Estimates

Cash and Cash Equivalents

Investments

Concentration of Credit Risk and Other Risks and Uncertainties

Property and Equipment

The useful lives of the property and equipment are as follows:

Research and development equipment		5 years
Furniture and office equipment		5 years
Computer equipment		3 years
Software		3-5 years
Leasehold improvements		Shorter of lease term or estimated useful life

Impairment of Long-Lived Assets

Restricted Cash

Accruals of Research and Development Costs

Leases

Comprehensive Loss

Research and Development

Stock-Based Compensation

Income Taxes

Net Loss per Share Attributable to Common Stockholders

Recent Accounting Pronouncements

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2015

Income Tax Disclosure [Abstract]

Effective Tax Rate of Provision for Income Taxes from Federal Statutory Rate

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Schedule of Tax Effect of Temporary Differences to Significant Portions of Deferred Tax Assets

The tax effect of temporary differences that give rise to significant portions of the deferred tax assets is presented below (in thousands):

	Year Ended December 31,
	2015			2014
Deferred tax assets:
Net operating loss carryforwards	$	61,503		$	32,500
Tax credits		33,881			16,737
Stock options		6,680			1,058
Accruals and reserves		2,541			476
Fixed assets and intangibles		4,442			455
Other		432			113
Total deferred tax assets		109,479			51,339
Valuation allowance		(109,479	)		(51,339	)
Net deferred tax assets	$	—		$	—

Unrecognized Tax Benefits

A reconciliation of the Company’s unrecognized tax benefits for the years ended December 31, 2015, 2014 and 2013 is as follows (in thousands):

	December 31,
	2015			2014		2013
Balance at beginning of year	$	7,275		$	3,725	$	1,551
Additions based on tax positions related to current year		15,628			3,550		2,169
Additions for tax positions of prior years		5,505			—		—
Reductions for tax positions of prior years		(4,398	)		—		5
Balance at end of year	$	24,010		$	7,275	$	3,725

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2015

Fair Value Disclosures [Abstract]

Summary of Financial Assets Measured on Recurring Basis

The following table sets forth the fair value of the Company’s financial assets and liabilities remeasured on a recurring basis based on the three-tier fair value hierarchy (in thousands):

	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 agency securities		—		47,452		—		47,452
Commercial paper		—		13,887		—		13,887
Total financial assets	$	53,254	$	461,086	$	—	$	514,340

	December 31, 2014
	Level 1		Level 2		Level 3		Total
Financial Assets:
Money market funds	$	8,627	$	—	$	—	$	8,627
Corporate bonds		—		152,942		—		152,942
Asset-backed securities		—		9,542		—		9,542
U.S. Government agency securities		—		4,485		—		4,485
Other		—		209		—		209
Total financial assets	$	8,627	$	167,178	$	—	$	175,805

Balance Sheet Components (Tables)

12 Months Ended

Dec. 31, 2015

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):

	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 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 agency securities classified as long-term investments		14,985		—		(84	)		14,901
Total	$	515,208	$	11	$	(879	)	$	514,340

	December 31, 2014
			Gross Unrealized
	Amortized Cost		Gains		Losses			Estimated Fair Value
Money market funds classified as cash equivalents	$	8,627	$	—	$	—		$	8,627
Corporate bonds classified as cash equivalents		3,806		1		—			3,807
Corporate bonds classified as short-term investments		149,303		4		(172	)		149,135
Asset backed securities classified as short-term investments		9,546		—		(4	)		9,542
U.S. Government agency securities classified as short-term investments		4,488		1		(4	)		4,485
Other classified as cash equivalents		209		—		—			209
Total	$	175,979	$	6	$	(180	)	$	175,805

Summary of Property and Equipment

Property and equipment, net consists of the following (in thousands):

	December 31,
	2015			2014
Research and development equipment	$	1,302		$	712
Furniture and office equipment		944			572
Computer equipment		628			268
Software		1,622			821
Leasehold improvements		3,466			2,141
Construction-in-progress		2,276			—
Property and equipment, gross		10,238			4,514
Less accumulated depreciation		(2,865	)		(1,481	)
Property and equipment, net	$	7,373		$	3,033

Accrued Liabilities

Accrued liabilities consist of the following (in thousands):

	December 31,
	2015		2014
Research and clinical trial expenses	$	9,764	$	2,703
Payroll and related expenses		9,423		4,205
Consulting service expenses		4,193		122
Other		1,404		545
Total accrued liabilities	$	24,784	$	7,575

Stock-Based Awards (Tables)

12 Months Ended

Dec. 31, 2015

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Activity Under Stock Option Plans Including 2011 Plan and 2014 Plan

Stock Option Activity

The following table summarizes activity under the Company’s stock option plans, including the 2011 Plan and the 2014 Plan and related information:

	Options Outstanding
	Number of Options			Weighted- Average Exercise Price		Weighted-Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
								(In thousands)
Outstanding — December 31, 2012		1,520,967		$	0.47		9.11	$	2,038
Options granted		1,267,797			5.80
Options exercised		(307,366	)		0.55
Options cancelled		(252,515	)		1.26
Outstanding — December 31, 2013		2,228,883		$	3.41	8.91		$	19,468
Options granted		932,555			41.12
Options exercised		(305,090	)		2.14
Options cancelled		(116,873	)		8.92
Outstanding — December 31, 2014		2,739,475		$	16.15		8.43	$	79,840
Options granted		2,013,350			90.60
Options exercised		(795,825	)		8.65
Options cancelled		(130,037	)		31.49
Outstanding — December 31, 2015		3,826,963		$	56.36		8.58	$	217,386
Vested and exercisable — December 31, 2015		898,924		$	13.30		7.14	$	88,886
Vested and expected to vest — December 31, 2015		3,681,683		$	55.27		8.56	$	212,968

Summary of Options Outstanding and Exercisable by Exercise Price

The options outstanding and exercisable by exercise price as of December 31, 2015 are as follows:

	Options Outstanding				Options Exercisable
Exercise Price	Numbers of Shares		Weighted-Average Remaining Contractual Term (in Years)		Numbers of Shares		Weighted- Average Exercise Price		Weighted-Average Remaining Contractual Term (in Years)
$0.31 to $1.32		454,420		6.11		411,883	$	0.44	6.06
$1.33 to $9.03		542,555		7.67		222,173		5.26	7.68
$9.04 to $37.65		381,173		8.18		102,800		22.56	8.14
$37.66 to $53.33		334,273		8.78		77,966		45.83	8.54
$53.34 to $59.45		362,792		8.74		80,213		55.85		8.50
$59.46 to $79.33		188,500		9.33		3,889		59.95	9.27
$79.34 to $85.96		533,500		9.39		—		—		—
$85.97 to $98.72		339,750		9.56		—		—		—
$98.73 to $115.30		316,500		9.76		—		—		—
$115.31 to $131.47		373,500		9.61		—		—		—
		3,826,963		8.58		898,924	$	13.30	7.14

Summary of Stock-Based Compensation Recognized

Total stock-based compensation recognized was as follows (in thousands):

	Year Ended December 31,
	2015		2014		2013
Research and development	$	17,100	$	4,116	$	293
General and administrative		7,784		1,278		364
Total stock-based compensation expense	$	24,884	$	5,394	$	657

Fair Value of Stock Option Awards Estimated Using Black-Scholes Option-Pricing Model

The fair value of stock option awards was estimated at the date of grant using a Black-Scholes option-pricing model with the following weighted-average assumptions:

	Year Ended December 31,
	2015		2014		2013
Expected term	6.23 years		6.23 years		6.25 years
Expected volatility		65%		70%		74%
Risk-free interest rate		1.8%		1.9%	0.7% to 1.6%
Expected dividend rate		0.0%		0.0%		0.0%

Net Loss per Share Attributable to Common Stockholders (Tables)

12 Months Ended

Dec. 31, 2015

Earnings Per Share [Abstract]

Computation of Basic and Diluted Net Loss per Share

	Year Ended December 31,
	2015			2014			2013
Numerator:
Net loss	$	(145,618	)	$	(59,802	)	$	(35,070	)
Accretion and dividends on convertible preferred stock		—			(4,808	)		(15,219	)
Net loss attributable to common stockholders	$	(145,618	)	$	(64,610	)	$	(50,289	)
Denominator:
Weighted-average common shares outstanding		36,782,603			28,755,758			3,583,522
Less: weighted-average unvested common shares subject to repurchase		—			—			(201,033	)
Weighted-average shares used to compute net loss per share attributable to common stockholders, basic and diluted		36,782,603			28,755,758			3,382,489
Net loss per share attributable to common stockholders, basic and diluted	$	(3.96	)	$	(2.25	)	$	(14.87	)

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

	Year Ended December 31,
	2015		2014		2013
Convertible preferred stock		—		1,610,834		19,598,486
Stock options to purchase common stock		3,247,925		2,572,729		1,666,036
Unvested restricted stock units		120,582		9,715		—
Common stock subject to repurchase		—		—		201,033
Convertible preferred stock warrants		—		29,051		353,459
Common stock warrants		195,762		318,666		—
		3,564,269		4,540,995		21,819,014

Quarterly Financial Data (unaudited) (Tables)

12 Months Ended

Dec. 31, 2015

Quarterly Financial Data [Abstract]

Summary of Unaudited Quarterly Financial Information

	2015
	March 31,			June 30,			September 30,			December 31,
Operating expenses	$	21,502		$	30,142		$	39,936		$	56,158
Net loss		(21,379	)		(29,787	)		(39,232	)		(55,220	)
Net loss attributable to common stockholders		(21,379	)		(29,787	)		(39,232	)		(55,220	)
Net loss per share applicable to common stockholders, basic and diluted	$	(0.63	)	$	(0.83	)	$	(1.03	)	$	(1.42	)

	2014
	March 31,			June 30,			September 30,			December 31,
Operating expenses	$	10,339		$	13,661		$	15,835		$	16,943
Net loss		(13,630	)		(13,585	)		(15,849	)		(16,738	)
Net loss attributable to common stockholders		(18,438	)		(13,585	)		(15,849	)		(16,738	)
Net loss per share applicable to common stockholders, basic and diluted	$	(0.85	)	$	(0.45	)	$	(0.50	)	$	(0.52	)

Organization and Basis of Presentation - Additional Information (Details) $ / shares in Units, $ in Thousands		1 Months Ended			12 Months Ended
	Feb. 05, 2014 USD ($) shares	Jul. 31, 2015 USD ($) $ / shares shares	Feb. 28, 2015 USD ($) $ / shares shares	Jul. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2015 Segment shares	Dec. 31, 2014 USD ($) shares	Jan. 30, 2014 $ / shares
Organization And Nature Of Business [Line Items]
Net proceeds from issuance of common stock						$ 121,711
Offering expenses		$ 200	$ 600	$ 400
Common stock, shares issued \| shares		2,530,000	3,450,000	1,613,879	38,882,394	31,934,682
Purchase of additional shares by underwriters \| shares		330,000	450,000	302,602
Common stock issued price per share \| $ / shares		$ 120.00	$ 54.00	$ 40.00
Common stock sold by existing shareholders \| shares				706,072
Proceeds from public offering before offering expenses		$ 286,900	$ 175,100	$ 60,700
Underwriting discounts and commissions		16,700	11,200	3,900
Proceeds from public offering, net		$ 286,700	$ 174,500	$ 60,200
IPO
Organization And Nature Of Business [Line Items]
Effective date of registration					Jan. 30, 2014
Public offering price of the shares sold \| $ / shares							$ 21.00
Common stock issued in initial public offering \| shares	6,624,423
Net proceeds from issuance of common stock	$ 129,400
Underwriting discounts and commissions	9,700
Offering expenses	3,300
Cash dividends paid to preferred stockholders	4,300
Net proceeds from initial public offering	$ 121,700
Number of preferred stock converted into common stock \| shares	19,598,486
Over-Allotment Option
Organization And Nature Of Business [Line Items]
Common stock issued in initial public offering \| shares	864,054
United States of America
Organization And Nature Of Business [Line Items]
Number of reportable segments \| Segment					1

License and Research Agreements - Additional Information (Details) $ in Thousands, ¥ in Millions	1 Months Ended		12 Months Ended
	Oct. 31, 2015 USD ($)	Jun. 30, 2013 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2015 JPY (¥)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development			$ 114,737	$ 45,967	$ 27,829
Nobelpharma License Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Aggregate future payments			1,700			¥ 200
Saint Louis University License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future contingent milestone payments			100
H I B M Research Group License Agreement \| Development and Approval Milestones
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future contingent milestone payments			$ 300
H I B M Research Group License Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payments for royalty on net sales			1.00%
St. Jude Children's Research Hospital License Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payments for royalty on net sales			1.00%
Baylor Research Institute License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment of option exercise fee		$ 800
Baylor Research Institute License Agreement \| Development Milestones
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future contingent milestone payments			$ 10,500
Baylor Research Institute License Agreement \| Sales Milestones
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future contingent milestone payments			7,500
Kyowa Hakko Kirin Collaboration \| License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development			10,800	4,000
License agreement receivable			$ 3,800	$ 1,300
Arcturus Research Collaboration and License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development	$ 10,000

Stock-Based Awards - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Feb. 05, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total intrinsic value of options exercised	$ 59.0	$ 12.1	$ 1.0
Cash received from exercise of options	$ 6.9	$ 0.7	$ 0.2
Weighted-average estimated fair value of stock option	$ 54.90	$ 26.58	$ 3.82
Total estimated fair value of options vested	$ 10.7	$ 2.0	$ 0.1
Weighted-average period to recognize cost	3 years 3 months
Unvested options	2,900,000
Total unrecognized compensation cost	$ 102.8
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock units granted	187,260	31,000
Restricted stock units weighted average grant date fair value	$ 89.67	$ 53.23
Shares vested during the period	18,209
Total fair value of shares vested	$ 1.0
Aggregate intrinsic value	2.1
Total unrecognized compensation expense related to unvested RSUs, net of estimated forfeitures	$ 14.5
Weighted-average period to recognize cost	3 years 4 months 24 days
Restricted stock units outstanding	197,151
Restricted stock units weighted average grant date fair value	$ 87.24
Maximum \| Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock based awards vesting period	4 years
Minimum \| Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock based awards vesting period	2 years
2011 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Minimum percentage of voting rights of all classes of stock	10.00%
Percentage of statutory stock options	110.00%
Stock based awards vesting period	4 years
Share of common stock authorized for future issuance				655,038
2011 Equity Incentive Plan \| First Anniversary
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option vesting rights, percentage	25.00%
2011 Equity Incentive Plan \| Shares Vesting Monthly After First Anniversary
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option vesting rights, percentage	2.08%
2011 Equity Incentive Plan \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options expiration period	10 years
2014 Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share of common stock authorized for future issuance				2,250,000
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]
Percentage of statutory stock options	85.00%
Automatic increases in shares available for grant effective date	Jan. 01, 2015
Shares available for grant, ending date	Jan. 01, 2024
Share of common stock available for future issuance				600,000

Stock-Based Awards - Summary of Activity Under Stock Option Plans Including 2011 Plan and 2014 Plan (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Options, Outstanding, Beginning Balance	2,739,475	2,228,883	1,520,967
Number of Options, Options granted	2,013,350	932,555	1,267,797
Number of Options, Options exercised	(795,825)	(305,090)	(307,366)
Number of Options, Options cancelled	(130,037)	(116,873)	(252,515)
Number of Options, Outstanding, Ending Balance	3,826,963	2,739,475	2,228,883	1,520,967
Number of Options, Vested and exercisable — December 31, 2015	898,924
Number of Options, Vested and expected to vest — December 31, 2015	3,681,683
Weighted Average Exercise Price, Outstanding, Beginning Balance	$ 16.15	$ 3.41	$ 0.47
Weighted Average Exercise Price, Options granted	90.60	41.12	5.80
Weighted Average Exercise Price, Options exercised	8.65	2.14	0.55
Weighted Average Exercise Price, Options cancelled	31.49	8.92	1.26
Weighted Average Exercise Price, Outstanding, Ending Balance	56.36	$ 16.15	$ 3.41	$ 0.47
Weighted Average Exercise Price, Vested and exercisable — December 31, 2015	13.30
Weighted Average Exercise Price, Vested and expected to vest — December 31, 2015	$ 55.27
Weighted Average Remaining Contractual Term (Years), Outstanding	8 years 6 months 29 days	8 years 5 months 5 days	8 years 10 months 28 days	9 years 1 month 10 days
Weighted Average Remaining Contractual Term (Years), Vested and exercisable — December 31, 2015	7 years 1 month 21 days
Weighted Average Remaining Contractual Term (Years), Vested and expected to vest — December 31, 2015	8 years 6 months 22 days
Aggregate Intrinsic Value, Outstanding	$ 217,386	$ 79,840	$ 19,468	$ 2,038
Aggregate Intrinsic Value, Vested and exercisable — December 31, 2015	88,886
Aggregate Intrinsic Value, Vested and expected to vest — December 31, 2015	$ 212,968

Stock-Based Awards - Summary of Options Outstanding and Exercisable by Exercise Price (Details)	12 Months Ended
	Dec. 31, 2015 $ / shares shares
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Options Outstanding, Numbers of Shares \| shares	3,826,963
Options Outstanding, Weighted-Average Remaining Contractual Term (in Years)	8 years 6 months 29 days
Options Exercisable, Numbers of Shares \| shares	898,924
Options Exercisable, Weighted- Average Exercise Price	$ 13.30
Options Exercisable, Weighted-Average Remaining Contractual Term (in Years)	7 years 1 month 21 days
Exercise Price $0.31 to $1.32
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Exercise Price, Lower Range	$ 0.31
Exercise Price, Upper Range	$ 1.32
Options Outstanding, Numbers of Shares \| shares	454,420
Options Outstanding, Weighted-Average Remaining Contractual Term (in Years)	6 years 1 month 10 days
Options Exercisable, Numbers of Shares \| shares	411,883
Options Exercisable, Weighted- Average Exercise Price	$ 0.44
Options Exercisable, Weighted-Average Remaining Contractual Term (in Years)	6 years 22 days
Exercise Price $1.33 to $9.03
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Exercise Price, Lower Range	$ 1.33
Exercise Price, Upper Range	$ 9.03
Options Outstanding, Numbers of Shares \| shares	542,555
Options Outstanding, Weighted-Average Remaining Contractual Term (in Years)	7 years 8 months 1 day
Options Exercisable, Numbers of Shares \| shares	222,173
Options Exercisable, Weighted- Average Exercise Price	$ 5.26
Options Exercisable, Weighted-Average Remaining Contractual Term (in Years)	7 years 8 months 5 days
Exercise Price $9.04 to $37.65
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Exercise Price, Lower Range	$ 9.04
Exercise Price, Upper Range	$ 37.65
Options Outstanding, Numbers of Shares \| shares	381,173
Options Outstanding, Weighted-Average Remaining Contractual Term (in Years)	8 years 2 months 5 days
Options Exercisable, Numbers of Shares \| shares	102,800
Options Exercisable, Weighted- Average Exercise Price	$ 22.56
Options Exercisable, Weighted-Average Remaining Contractual Term (in Years)	8 years 1 month 21 days
Exercise Price $37.66 to $53.33
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Exercise Price, Lower Range	$ 37.66
Exercise Price, Upper Range	$ 53.33
Options Outstanding, Numbers of Shares \| shares	334,273
Options Outstanding, Weighted-Average Remaining Contractual Term (in Years)	8 years 9 months 11 days
Options Exercisable, Numbers of Shares \| shares	77,966
Options Exercisable, Weighted- Average Exercise Price	$ 45.83
Options Exercisable, Weighted-Average Remaining Contractual Term (in Years)	8 years 6 months 15 days
Exercise Price $53.34 to $59.45
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Exercise Price, Lower Range	$ 53.34
Exercise Price, Upper Range	$ 59.45
Options Outstanding, Numbers of Shares \| shares	362,792
Options Outstanding, Weighted-Average Remaining Contractual Term (in Years)	8 years 8 months 27 days
Options Exercisable, Numbers of Shares \| shares	80,213
Options Exercisable, Weighted- Average Exercise Price	$ 55.85
Options Exercisable, Weighted-Average Remaining Contractual Term (in Years)	8 years 6 months
Exercise Price $59.46 to $79.33
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Exercise Price, Lower Range	$ 59.46
Exercise Price, Upper Range	$ 79.33
Options Outstanding, Numbers of Shares \| shares	188,500
Options Outstanding, Weighted-Average Remaining Contractual Term (in Years)	9 years 3 months 29 days
Options Exercisable, Numbers of Shares \| shares	3,889
Options Exercisable, Weighted- Average Exercise Price	$ 59.95
Options Exercisable, Weighted-Average Remaining Contractual Term (in Years)	9 years 3 months 7 days
Exercise Price $79.34 to $85.96
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Exercise Price, Lower Range	$ 79.34
Exercise Price, Upper Range	$ 85.96
Options Outstanding, Numbers of Shares \| shares	533,500
Options Outstanding, Weighted-Average Remaining Contractual Term (in Years)	9 years 4 months 21 days
Exercise Price $85.97 to $98.72
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Exercise Price, Lower Range	$ 85.97
Exercise Price, Upper Range	$ 98.72
Options Outstanding, Numbers of Shares \| shares	339,750
Options Outstanding, Weighted-Average Remaining Contractual Term (in Years)	9 years 6 months 22 days
Exercise Price $98.73 to $115.30
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Exercise Price, Lower Range	$ 98.73
Exercise Price, Upper Range	$ 115.30
Options Outstanding, Numbers of Shares \| shares	316,500
Options Outstanding, Weighted-Average Remaining Contractual Term (in Years)	9 years 9 months 4 days
Exercise Price $115.31 to $131.47
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Exercise Price, Lower Range	$ 115.31
Exercise Price, Upper Range	$ 131.47
Options Outstanding, Numbers of Shares \| shares	373,500
Options Outstanding, Weighted-Average Remaining Contractual Term (in Years)	9 years 7 months 10 days

Income Taxes - Effective Tax Rate of Provision for Income Taxes from Federal Statutory Rate (Details)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Effective Income Tax Rate Continuing Operations Tax Rate Reconciliation [Abstract]
Federal statutory income tax rate	34.00%	34.00%	34.00%
State income taxes, net of federal benefit	7.50%	4.60%	5.00%
Federal tax credits	5.90%	6.70%	8.20%
Other	0.80%
Nondeductible permanent items		(1.20%)	(2.90%)
Stock compensation	(1.30%)	(1.40%)	(0.60%)
Uncertain tax positions	(7.70%)		0.90%
Change in valuation allowance	(39.20%)	(42.70%)	(44.60%)

Commitments and Contingencies - Summary of Future Minimum Lease Payments under Non-Cancellable Operating Leases Arrangements and Future Payments under Contractually Binding Manufacturing and Service Agreements (Details) $ in Thousands	Dec. 31, 2015 USD ($)
Commitments And Contingencies Disclosure [Abstract]
Leases, 2016	$ 2,270
Leases, 2017	3,877
Leases, 2018	4,504
Leases, 2019	3,543
Leases, 2020	2,868
Leases, Thereafter	13,791
Leases, Total	30,853
Manufacturing and Services, 2016	2,042
Manufacturing and Services, 2017	190
Manufacturing and Services, 2018	90
Manufacturing and Services, 2019	83
Manufacturing and Services, 2020	62
Manufacturing and Services, Total	$ 2,467

Net Loss per Share Attributable to Common Stockholders - Computation of Basic and Diluted Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Numerator:
Net loss	$ (55,220)	$ (39,232)	$ (29,787)	$ (21,379)	$ (16,738)	$ (15,849)	$ (13,585)	$ (13,630)	$ (145,618)	$ (59,802)	$ (35,070)
Accretion and dividends on convertible preferred stock										(4,808)	(15,219)
Net loss attributable to common stockholders	$ (55,220)	$ (39,232)	$ (29,787)	$ (21,379)	$ (16,738)	$ (15,849)	$ (13,585)	$ (18,438)	$ (145,618)	$ (64,610)	$ (50,289)
Denominator:
Weighted-average common shares outstanding									36,782,603	28,755,758	3,583,522
Less: weighted-average unvested common shares subject to repurchase											(201,033)
Weighted-average shares used to compute net loss per share attributable to common stockholders, basic and diluted									36,782,603	28,755,758	3,382,489
Net loss per share attributable to common stockholders, basic and diluted	$ (1.42)	$ (1.03)	$ (0.83)	$ (0.63)	$ (0.52)	$ (0.50)	$ (0.45)	$ (0.85)	$ (3.96)	$ (2.25)	$ (14.87)

- Definition

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

+ References + Details

Organization and Basis of Presentation	12 Months Ended
Organization and Basis of Presentation	Dec. 31, 2015
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Basis of Presentation	1. Organization and Basis of Presentation 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 (GNEM), 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 in the United States of America and has one reportable segment. In the course of its research activities, the Company has sustained operating losses and expects such losses to continue over the next several years. The Company’s ultimate success depends on the outcome of its research and development activities. Management expects to incur additional losses in the future to conduct product research and development and recognizes the need to raise additional capital to fully implement its business plan. Through December 31, 2015, the Company has relied primarily on the proceeds from equity offerings to finance its operations. On January 30, 2014, the Company’s registration statements on Form S-1 (File Nos. 333-192244 and 333-193675) relating to its initial public offering (IPO) of its common stock were declared effective by the Securities and Exchange Commission (SEC). The shares began trading on The NASDAQ Global Select Market on January 31, 2014. The public offering price of the shares sold in the offering was $21.00 per share. The IPO closed on February 5, 2014 and included 6,624,423 shares of common stock, which included 864,054 shares of common stock issued pursuant to the over-allotment option granted to the underwriters. The Company received total proceeds from the offering of $129.4 million, net of underwriting discounts and commissions of $9.7 million. After deducting offering expenses of approximately $3.3 million and a cash dividend of $4.3 million, which was paid to the preferred stockholders on the closing date, net proceeds were approximately $121.7 million. Upon the closing of the IPO, all shares of convertible preferred stock then outstanding converted into 19,598,486 shares of common stock and the Series A convertible preferred stock warrants were converted into warrants to purchase common stock. In July 2014, the Company completed an underwritten public offering in which the Company sold 1,613,879 shares of common stock, which included 302,602 shares of common stock purchased by the underwriters pursuant to an option granted to them in connection with the offering, at a public offering price of $40.00 per share. In addition, certain existing stockholders sold 706,072 shares of common stock in the underwritten public offering at the same per-share price. The total proceeds that the Company received from the offering were approximately $60.7 million, net of underwriting discounts and commissions of approximately $3.9 million. After deducting estimated offering expenses payable of approximately $0.4 million, net proceeds were $60.2 million. In February 2015, the Company completed an underwritten public offering in which the Company sold 3,450,000 shares of common stock, which included 450,000 shares of common stock purchased by the underwriters pursuant to an option granted to them in connection with the offering, at a public offering price of $54.00 per share. The total proceeds that the Company received from the offering were approximately $175.1 million, net of underwriting discounts and commissions of approximately $11.2 million. After deducting offering expenses of $0.6 million, net proceeds were $174.5 million. In July 2015, the Company completed an underwritten public offering in which the Company sold 2,530,000 shares of common stock, which included 330,000 shares of common stock purchased by the underwriters pursuant to an option granted to them in connection with the offering, at a public offering price of $120.00 per share. The total proceeds that the Company received from the offering were approximately $286.9 million, net of underwriting discounts and commissions of approximately $16.7 million. After deducting offering expenses payable of approximately $0.2 million, net proceeds were $286.7 million. The Company intends to raise additional capital through the issuance of equity, borrowings, or strategic alliances with partner companies. However, if such financing is not available at adequate levels, the Company will need to reevaluate its operating plans.

Defined Contribution Plan	12 Months Ended
Defined Contribution Plan	Dec. 31, 2015
Defined Contribution Pension And Other Postretirement Plans Disclosure [Abstract]
Defined Contribution Plan	9. Defined Contribution Plan In March 2013, the Company began to sponsor a 401(k) retirement plan, in which substantially all of its full-time employees are eligible to participate. Eligible participants may contribute a percentage of their annual compensation to this plan, subject to statutory limitations. Prior to 2015, the Company had not provided any contributions to the plan. In 2015, the Company began to make contributions to the Plan for eligible participants, and recorded $0.6 million as contribution expenses for the year ended December 31, 2015.

Common Stock Warrants (Tables)	12 Months Ended
Common Stock Warrants (Tables)	Dec. 31, 2015
Warrants And Rights Note Disclosure [Abstract]
Summary of Outstanding Warrants	ERROR: Could not retrieve Word content for note block

Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Millions			1 Months Ended	12 Months Ended
	May 31, 2021	May 01, 2014	Dec. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Disclosure Commitments And Contingencies Additional Information Details [Line Items]
Operating lease commencement date			2016-05
Rent expense				$ 1.4	$ 0.6	$ 0.3
Brisbane Office Facility
Disclosure Commitments And Contingencies Additional Information Details [Line Items]
Tenant improvement allowance			$ 3.7
Operating lease expiration period			122 months
Lease term			5 years
Restricted cash in connection with lease agreement			$ 1.4	1.4
Brisbane Office Facility \| Scenario Forecast
Disclosure Commitments And Contingencies Additional Information Details [Line Items]
Reduction in letter of credit on successful payment of lease amount	$ 0.7
Novato Office Facility
Disclosure Commitments And Contingencies Additional Information Details [Line Items]
Tenant improvement allowance			$ 1.5
Lease term			5 years
Reduction in letter of credit on successful payment of lease amount		$ 0.1
Restricted cash in connection with lease agreement			$ 0.8	$ 0.8
Operating lease expiration year				2020

Summary of Significant Accounting Policies - Summary of Useful Lives of Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2015
Research and Development Equipment
Property Plant And Equipment [Line Items]
Property plant and equipment useful life	5 years
Furniture and Office Equipment
Property Plant And Equipment [Line Items]
Property plant and equipment useful life	5 years
Computer Equipment
Property Plant And Equipment [Line Items]
Property plant and equipment useful life	3 years
Software \| Minimum
Property Plant And Equipment [Line Items]
Property plant and equipment useful life	3 years
Software \| Maximum
Property Plant And Equipment [Line Items]
Property plant and equipment useful life	5 years
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property plant and equipment useful life	Shorter of lease term or estimated useful life

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2015	Dec. 31, 2014
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	25,000,000	25,000,000
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	250,000,000	250,000,000
Common stock, shares issued	38,882,394	31,934,682
Common stock, shares outstanding	38,882,394	31,934,682

Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2015 USD ($)
Accounting Policies [Abstract]
Unrecognized tax benefits related to interest or penalties	$ 0

Fair Value Measurements - Summary of Financial Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Financial Assets:
Fair value	$ 514,340	$ 175,805
Money Market Funds
Financial Assets:
Fair value	53,254	8,627
Asset Backed Securities
Financial Assets:
Fair value	29,302	9,542
Other
Financial Assets:
Fair value		209
Level 1
Financial Assets:
Fair value	53,254	8,627
Level 1 \| Money Market Funds
Financial Assets:
Fair value	53,254	8,627
Level 2
Financial Assets:
Fair value	461,086	167,178
Level 2 \| Asset Backed Securities
Financial Assets:
Fair value	29,302	9,542
Level 2 \| Other
Financial Assets:
Fair value		209
Corporate Bonds
Financial Assets:
Fair value	370,445	152,942
Corporate Bonds \| Level 2
Financial Assets:
Fair value	370,445	152,942
US Government Corporations and Agencies Securities
Financial Assets:
Fair value	47,452	4,485
US Government Corporations and Agencies Securities \| Level 2
Financial Assets:
Fair value	47,452	$ 4,485
Commercial Paper
Financial Assets:
Fair value	13,887
Commercial Paper \| Level 2
Financial Assets:
Fair value	$ 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	Dec. 31, 2015	Dec. 31, 2014
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 515,208	$ 175,979
Gross Unrealized Gains	11	6
Gross Unrealized Losses	(879)	(180)
Estimated Fair Value	514,340	175,805
Money Market Funds Classified as Cash Equivalents
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	53,254	8,627
Estimated Fair Value	53,254	8,627
Corporate Bonds Classified as Cash Equivalents
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	18,403	3,806
Gross Unrealized Gains		1
Gross Unrealized Losses	(4)
Estimated Fair Value	18,399	3,807
Other Classified as Cash Equivalents
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		209
Estimated Fair Value		209
Commercial Paper Classified as Short-Term Investments
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	13,887
Estimated Fair Value	13,887
Corporate Bonds Classified as Short-Term Investments
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	282,386	149,303
Gross Unrealized Gains	9	4
Gross Unrealized Losses	(397)	(172)
Estimated Fair Value	281,998	149,135
Asset Backed Securities Classified as Short-Term Investments
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	15,019	9,546
Gross Unrealized Losses	(27)	(4)
Estimated Fair Value	14,992	9,542
U.S. Government Agency Securities Classified as Short-Term Investments
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	32,628	4,488
Gross Unrealized Gains		1
Gross Unrealized Losses	(77)	(4)
Estimated Fair Value	32,551	$ 4,485
Corporate Bonds Classified as Long-Term Investments
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	70,309
Gross Unrealized Gains	2
Gross Unrealized Losses	(263)
Estimated Fair Value	70,048
Asset Backed Securities Classified as Long-Term Investments
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	14,337
Gross Unrealized Losses	(27)
Estimated Fair Value	14,310
U.S. Government Agency Securities Classified as Long-Term Investments
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	14,985
Gross Unrealized Losses	(84)
Estimated Fair Value	$ 14,901

Balance Sheet Components - Summary of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 10,238	$ 4,514
Less accumulated depreciation	(2,865)	(1,481)
Property and equipment, net	7,373	3,033
Research and Development Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,302	712
Furniture and Office Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	944	572
Computer Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	628	268
Software
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,622	821
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	3,466	$ 2,141
Construction-in-progress
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 2,276

Balance Sheet Components - Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Payables And Accruals [Abstract]
Research and clinical trial expenses	$ 9,764	$ 2,703
Payroll and related expenses	9,423	4,205
Consulting service expenses	4,193	122
Other	1,404	545
Total accrued liabilities	$ 24,784	$ 7,575

Common Stock Warrants - Summary of Outstanding Warrants (Details) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Class Of Warrant Or Right [Line Items]
Number of Warrants Outstanding	149,700	324,351
June 2010 Common Stock Warrant [Member]
Class Of Warrant Or Right [Line Items]
Number of Warrants Outstanding	83,167	83,167
Date Issued	2010-06	2010-06
Term	10 years	10 years
Exercise price	$ 3.006	$ 3.006
February 2011 Common Stock Warrant [Member]
Class Of Warrant Or Right [Line Items]
Number of Warrants Outstanding		174,651
Date Issued	2011-02	2011-02
Term	10 years	10 years
Exercise price	$ 3.006	$ 3.006
June 2011 Common Stock Warrant [Member]
Class Of Warrant Or Right [Line Items]
Number of Warrants Outstanding	66,533	66,533
Date Issued	2011-06	2011-06
Term	10 years	10 years
Exercise price	$ 3.006	$ 3.006

Common Stock - Additional Information (Details)	12 Months Ended
Common Stock - Additional Information (Details)	Dec. 31, 2015 $ / shares
Dividends Common Stock [Abstract]
Common stock dividends declared	$ 0

Common Stock - Reserved Shares of Common Stock for Future Issuance (Details) - shares	Dec. 31, 2015	Dec. 31, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Reserved shares of common stock for future issuance	5,834,075	5,134,576
Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Reserved shares of common stock for future issuance	709,966	1,439,750
Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Reserved shares of common stock for future issuance	950,295	600,000
2011 Equity Incentive Plan Outstanding
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Reserved shares of common stock for future issuance	1,212,931	1,960,225
2014 Equity Incentive Plan Outstanding
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Reserved shares of common stock for future issuance	2,811,183	810,250
Common Stock Warrants Outstanding
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Reserved shares of common stock for future issuance	149,700	324,351

Defined Contribution Plan - Additional Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($)
Defined Contribution Pension And Other Postretirement Plans Disclosure [Abstract]
Contribution expenses	$ 0.6

Income Taxes - Schedule of Tax Effect of Temporary Differences to Significant Portions of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2012	Dec. 31, 2011
Deferred tax assets:
Net operating loss carryforwards	$ 61,503	$ 32,500	$ 300	$ 300
Tax credits	33,881	16,737
Stock options	6,680	1,058
Accruals and reserves	2,541	476
Fixed assets and intangibles	4,442	455
Other	432	113
Total deferred tax assets	109,479	51,339
Valuation allowance	(109,479)	(51,339)
Net deferred tax assets	$ 0	$ 0