Ultragenyx Pharmaceutical (RARE) 10-Q 12 May 15 2015 Q1 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	3 Months Ended
	Mar. 31, 2015	6-May-15
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	FALSE
Document Period End Date	31-Mar-15
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Trading Symbol	RARE
Entity Registrant Name	Ultragenyx Pharmaceutical Inc.
Entity Central Index Key	1515673
Current Fiscal Year End Date	-19
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		35,902,599

CONDENSED_CONSOLIDATED_BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Current assets:
Cash and cash equivalents	$178,040	$24,324
Short-term investments	164,526	163,163
Prepaid expenses and other current assets	6,877	5,929
Restricted cash	1,071
Total current assets	350,514	193,416
Property and equipment, net	3,514	3,033
Restricted cash	1,031	744
Other assets	781	774
Total assets	355,840	197,967
Current liabilities:
Accounts payable	5,755	4,857
Accrued liabilities	8,398	7,575
Deferred rent—current portion	90	85
Total current liabilities	14,243	12,517
Other liabilities	478	505
Total liabilities	14,721	13,022
Commitments and contingencies (Note 9)
Stockholders’ equity:
Preferred stock, par value of $0.001 per share—25,000,000 shares authorized; nil outstanding as of March 31, 2015 and December 31, 2014
Common stock, par value of $0.001 per share—250,000,000 shares authorized; 35,612,019 and 31,934,682 shares issued and outstanding as of March 31, 2015 and December 31, 2014	36	32
Additional paid-in capital	501,597	324,128
Accumulated other comprehensive loss	-94	-174
Accumulated deficit	-160,420	-139,041
Total stockholders’ equity	341,119	184,945
Total liabilities and stockholders’ equity	$355,840	$197,967

CONDENSED_CONSOLIDATED_BALANCE1

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Statement Of Financial Position [Abstract]
Preferred stock, par value	$0.00	$0.00
Preferred stock, shares authorized	25,000,000	25,000,000
Preferred stock, shares outstanding	0	0
Common stock, par value	$0.00	$0.00
Common stock, shares authorized	250,000,000	250,000,000
Common stock, shares issued	35,612,019	31,934,682
Common stock, shares outstanding	35,612,019	31,934,682

CONDENSED_CONSOLIDATED_STATEME

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Operating expenses:
Research and development	$17,364	$8,353
General and administrative	4,138	1,986
Total operating expenses	21,502	10,339
Loss from operations	-21,502	-10,339
Other income (expense), net:
Interest income	273	93
Other expense, net	-150	-3,384
Total other income (expense), net	123	-3,291
Net loss	-21,379	-13,630
Net loss attributable to common stockholders	($21,379)	($18,438)
Net loss per share attributable to common stockholders, basic and diluted	($0.63)	($0.85)
Shares used in computing net loss per share attributable to common stockholders, basic and diluted	34,008,830	21,582,435

CONDENSED_CONSOLIDATED_STATEME1

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Unaudited) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Statement Of Income And Comprehensive Income [Abstract]
Net loss	($21,379)	($13,630)
Other comprehensive income:
Unrealized gain (loss) on available-for-sale securities	80	-57
Total comprehensive loss	($21,299)	($13,687)

CONDENSED_CONSOLIDATED_STATEME2

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Operating activities:
Net loss	($21,379,000)	($13,630,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	201,000	117,000
Amortization of premium (discount) on investment securities, net	965,000	479,000
Stock-based compensation	2,408,000	795,000
Revaluation of convertible preferred stock warrant liability	0	3,324,000
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	-948,000	-2,391,000
Other assets	-7,000	-187,000
Accounts payable	437,000	2,058,000
Accrued liabilities and other liabilities	664,000	-1,186,000
Net cash used in operating activities	-17,659,000	-10,621,000
Investing activities:
Purchase of property and equipment	-459,000	-569,000
Purchase of investments	-77,254,000	-87,998,000
Proceeds from the sale of investments	12,766,000
Proceeds from maturities of investments	62,240,000	23,462,000
Increase in restricted cash	-1,358,000	-293,000
Net cash used in investing activities	-4,065,000	-65,398,000
Financing activities:
Proceeds from issuance of common stock, net of issuance costs	175,440,000	128,385,000
Payment of preferred stock dividend		-4,346,000
Net cash provided by financing activities	175,440,000	124,039,000
Net increase in cash and cash equivalents	153,716,000	48,020,000
Cash and cash equivalents at beginning of period	24,324,000	7,427,000
Cash and cash equivalents at end of period	178,040,000	55,447,000
Supplemental disclosures of non-cash investing and financing information:
Reclassification of warrant liability to equity upon conversion to common stock warrants		6,743,000
Conversion of Series A and Series B preferred stock to common stock		$129,360,000

Organization

Organization	3 Months Ended
	Mar. 31, 2015
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization	1	Organization
	Ultragenyx Pharmaceutical Inc. (the Company) is a biopharmaceutical company 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 2 extension study of sialic acid, extended release (SA-ER) in patients with 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 triheptanoin in patients with glucose transporter type-1 deficiency syndrome (Glut1 DS), a brain energy deficiency; a Phase 2 clinical study of triheptanoin 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 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 genetic diseases that impair bone growth mineralization. The Company is in the clinical stage as of December 31, 2014, and since inception has been engaged in developing its product candidates, raising capital and recruiting personnel. The Company operates in the United States of America in one reportable segment.
	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 estimated offering expenses payable of approximately $0.6 million, net proceeds were $174.5 million.

Summary_of_Significant_Account

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2	Summary of Significant Accounting Policies
	Basis of Presentation
	The accompanying unaudited condensed consolidated financial statements include the amounts of the Company and our wholly-owned subsidiary and have been prepared in accordance with U.S. general accepted accounting principles (“U.S. GAAP”) for interim financial information and in accordance with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by generally accepted accounting principles for complete financial statements. The unaudited interim consolidated financial statements have been prepared on the same basis as the annual financial statements. In the opinion of management, the accompanying unaudited condensed consolidated financial statements reflect all adjustments (consisting only of normal recurring adjustments) considered necessary for a fair presentation. These financial statements should be read in conjunction with the audited financial statements and notes thereto for the preceding fiscal year contained in the Company’s Annual Report on Form 10-K filed on March 27, 2015 with the SEC.
	The results of operations for the three months ended March 31, 2015 are not necessarily indicative of the results to be expected for the year ending December 31, 2015. The condensed balance sheet as of December 31, 2014 has been derived from audited financial statements at that date but does not include all of the information required by U.S. GAAP for complete financial statements.
	Use of Estimates
	The preparation of condensed consolidated financial statements in conformity with U.S. 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 financial statements and the accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to clinical study accruals, fair value of assets and liabilities, convertible preferred stock and related 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.
	Short-Term 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. Unrealized gains and losses are excluded from earnings and were 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 marketable securities 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 short-term investments. The Company’s cash, cash equivalents, and short-term 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.
	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.
	Recently Issued 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. We are currently assessing the future impact of this ASU in the financial statements.

Fair_Value_Measurements

Fair Value Measurements	3 Months Ended
	Mar. 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 condensed consolidated balance sheets are categorized based upon the level of judgment associated with the inputs used to measure their fair values. Fair value is defined as the exchange price that would be received for an asset or an exit price that would be paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The authoritative guidance on fair value measurements establishes a three-tier fair value hierarchy for disclosure of fair value measurements as follows:
	Level 1—Inputs are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date;
	Level 2—Inputs are observable, unadjusted quoted prices in active markets for similar assets or liabilities, unadjusted quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the related assets or liabilities; and
	Level 3—Unobservable inputs that are significant to the measurement of the fair value of the assets or liabilities that are supported by little or no market data.
	The following tables set forth the fair value of the Company’s financial assets and liabilities remeasured on a recurring basis based on the three-tier fair value hierarchy (in thousands):
		31-Mar-15
		Level 1		Level 2			Level 3		Total
	Financial Assets:
	Money market funds	$	142,829	$	—		$	—	$	142,829
	Corporate bonds		—		170,452			—		170,452
	Asset backed securities		—		9,520			—		9,520
	U.S. Government agency securities		—		2,998			—		2,998
	Commercial paper		—		2,497			—		2,497
	Total financial assets	$	142,829	$	185,467		$	—	$	328,296
		31-Dec-14
		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
	The convertible preferred stock warrant liability was classified as a Level 3 liability. As of January 30, 2014, the Company determined the estimated fair value of the warrants using the Black-Scholes option-pricing model. Inputs used to determine the fair value included the value of the Company’s common stock upon closing of the IPO of $21.00, the remaining contractual term of the warrants of 7.0 years, risk-free interest rate of 2.19% and expected volatility of 70%. Generally, increases (decreases) in the equity value of the Company would result in a directionally similar impact to the fair value measurement of the preferred stock warrant liability. The preferred stock warrants were converted to common stock warrants upon the completion of the IPO and are no longer subject to remeasurement.
	The following table sets forth a summary of the changes in the estimated fair value of the Company’s convertible preferred stock warrants, which were measured at fair value on a recurring basis until their conversion to common stock warrants and related reclassification to additional paid-in capital (in thousands):
		Three Months Ended March 31,
		2015		2014
	Fair value, beginning of period	$	—	$	3,419
	Change in fair value recorded as a loss in other expense, net		—		3,324
	Reclassification of warrant liability to additional paid-in capital		—		(6,743	)
	Fair value, end of period	$	—	$	—
	The Company recorded $0 and $3.3 million in other expense for the three months ended March 31, 2015 and 2014, representing the change in fair value of the warrants for the respective periods.

Balance_Sheet_Components

Balance Sheet Components	3 Months Ended
	Mar. 31, 2015
Investments Debt And Equity Securities [Abstract]
Balance Sheet Components	4.Balance Sheet Components
	Cash Equivalents and Short-term Investments
	The fair values of cash equivalents and short-term investments classified as available-for-sale securities, consisted of the following (in thousands):
		31-Mar-15
					Gross Unrealized
		Amortized			Gains			Losses			Estimated
		Cost									Fair Value
	Money market funds classified as cash equivalents	$	142,829		$	—		$	—		$	142,829
	Corporate bonds classified as cash equivalents		20,941			—			—			20,941
	Commercial paper classified as short-term investments		2,497			2			(2	)		2,497
	Corporate bonds classified as short-term investments		149,607			8			(104	)		149,511
	Asset backed securities classified as short-term investments		9,522			—			(2	)		9,520
	U.S. Government agency securities classified as short-term		2,994			4			—			2,998
	investments
	Total	$	328,390		$	14		$	(108	)	$	328,296
		31-Dec-14
					Gross Unrealized
		Amortized			Gains			Losses			Estimated
		Cost									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		4,488			1			(4	)		4,485
	investments
	Other classified as cash equivalents		209			—			—			209
	Total	$	175,979		$	6		$	(180	)	$	175,805
	At March 31, 2015, the remaining contractual maturities of available-for-sale securities were less than two years. There have been no significant realized gains or losses on available-for-sale securities for the periods presented.
	Accrued Liabilities
	Accrued liabilities consist of the following (in thousands):
			March 31,			December 31,
			2015			2014
	Research and clinical study expenses		$	4,271		$	2,703
	Payroll and related expenses			3,217			4,205
	Other			910			667
	Total accrued liabilities		$	8,398		$	7,575

License_and_Research_Agreement

License and Research Agreements	3 Months Ended
	Mar. 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). 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.
	Under the collaboration and license agreement, the Company paid Nobelpharma $111,000 (10 million Yen) for the license, which was recorded as research and development expense in 2010, and also issued 76,567 shares of common stock to Nobelpharma with a minimal value. The Company is required to pay Nobelpharma royalties based on net sales upon product sales commencement. In addition, the Company is required to make certain payments to Nobelpharma based upon achievement of certain development and approval milestones. The Company paid $495,000 in development milestone payments since the inception of the agreement through March 31, 2015. The remaining total aggregate payments, if all milestones are achieved by Nobelpharma, would be 200 million Yen (approximately $1.7 million based on the exchange rate at March 31, 2015). The Company will pay a high 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. Net sales, as defined in the collaboration and license agreement, represent the net sales of products whereby the licensed compound is the active ingredient. If the products include other active ingredients, the portion of the net sales allocated to the licensed compound would be used in determining the royalty payments.
	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.
	Under the license agreement, the Company paid SLU an up-front fee of $10,000, which was recorded as research and development expense in 2010. The Company will be required to make a milestone payment of $100,000 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, AAIPharma 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 License Agreement
	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. Under the license agreement, the Company paid HRG an up-front fee of $25,000 which was recorded as research and development expense during the year ended December 31, 2012. The Company may make future payments that aggregate up to $300,000 and 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.
	Under the license agreement, the Company paid St. Jude an up-front fee of $10,000 which was recorded as research and development expense during the year ended December 31, 2012. Additionally, 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. Under the license agreement, the Company paid BRI an up-front fee of $250,000 which was recorded as research and development expense during the year ended December 31, 2012. 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 $750,000.
	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). 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 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. On the applicable transition date in the relevant territory, KHK will become the lead party and be responsible for these costs. 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 recognized $1.4 million and $710,000 for its share of the costs as research and development expenses for the three months ended March 31, 2015 and 2014, respectively. As of March 31, 2015 and 2014, the Company had a receivable in the amount of $1.5 million and $878,000 from KHK and an accrued liability of $25,000 and $201,000, respectively, for this collaboration arrangement.

Common_Stock_Warrants

Common Stock Warrants	3 Months Ended
	Mar. 31, 2015
Warrants And Rights Note Disclosure [Abstract]
Common Stock Warrants	6	Common Stock Warrants
	Upon the closing of the Company’s IPO in February 2014, the convertible preferred stock warrants were converted into warrants to purchase common stock. Accordingly, the warrants were reclassified from a liability to permanent equity and were no longer subject to remeasurement.
	The table sets forth the outstanding common stock warrants for the periods presented:
	Outstanding at March 31,		Outstanding at December 31,		Date Issued	Term	Exercise Price
	2015		2014
		83,167		83,167	Jun-10	10 years	$	3.006
		174,651		174,651	Feb-11	10 years		3.006
		66,533		66,533	Jun-11	10 years		3.006
		324,351		324,351

StockBased_Compensation

Stock-Based Compensation	3 Months Ended
	Mar. 31, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	7	Stock-Based Compensation
	2014 Incentive Plan
	In 2014, the Company adopted the 2014 Incentive Plan (the 2014 Plan), which became effective upon the closing of the Company’s IPO in February 2014. The 2014 Plan provides for automatic annual increases in shares available for grant, beginning on January 1, 2015 through January 1, 2024. As of March 31, 2015, there were 2,595,430 shares reserved under the 2014 Plan for the future issuance of equity awards.
	The table below sets forth the functional classification of stock-based compensation expense, net of estimated forfeitures, for the periods presented (in thousands):
		Three Months Ended March 31,
		2015		2014
	Research and development	$	1,841	$	705
	General and administrative		567		90
	Total stock-based compensation	$	2,408	$	795

Defined_Contribution_Plan

Defined Contribution Plan	3 Months Ended
	Mar. 31, 2015
Defined Contribution Pension And Other Postretirement Plans Disclosure [Abstract]
Defined Contribution Plan	8	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 $123,000 as contribution expenses for the three months ended March 31, 2015.

Commitment_and_Contingencies

Commitment and Contingencies	3 Months Ended
	Mar. 31, 2015
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	9	Commitments and Contingencies
	Commitments
	The Company has various manufacturing, clinical, research, and other contracts with vendors in the conduct of the normal course of its business. All other significant contracts as of March 31, 2015 were 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.
	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 such 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 such claims, and their resolution could be material to the Company for any particular period, depending upon the level of income or loss for the period, as well as the Company’s consolidated balance sheet.

Net_Loss_per_Share_Attributabl

Net Loss per Share Attributable to Common Stockholders	3 Months Ended
	Mar. 31, 2015
Earnings Per Share [Abstract]
Net Loss per Share Attributable to Common Stockholders	10	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 (in thousands, except share and per share data):
		Three Months Ended
		March 31,
		2015			2014
	Numerator:
	Net loss	$	(21,379	)	$	(13,630	)
	Accretion and dividends on convertible preferred stock		—			(4,808	)
	Net loss attributable to common stockholders	$	(21,379	)	$	(18,438	)
	Denominator:
	Weighted-average common shares outstanding		34,008,830			21,582,435
	Less: weighted-average unvested common shares subject to repurchase		—			—
	Weighted-average shares used to compute net loss per share attributable		34,008,830			21,582,435
	to common stockholders, basic and diluted
	Net loss per share attributable to common stockholders, basic and diluted	$	(0.63	)	$	(0.85	)
	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:
		Three Months Ended March 31,
		2015			2014
	Convertible preferred stock (as if converted)		—			6,532,828
	Stock options to purchase common stock		2,698,846			2,315,345
	Unvested restricted stock units		33,856			—
	Convertible preferred stock warrants (as if converted)		—			117,820
	Common stock warrants		324,351			235,639
			3,057,053			9,201,632

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation
	The accompanying unaudited condensed consolidated financial statements include the amounts of the Company and our wholly-owned subsidiary and have been prepared in accordance with U.S. general accepted accounting principles (“U.S. GAAP”) for interim financial information and in accordance with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by generally accepted accounting principles for complete financial statements. The unaudited interim consolidated financial statements have been prepared on the same basis as the annual financial statements. In the opinion of management, the accompanying unaudited condensed consolidated financial statements reflect all adjustments (consisting only of normal recurring adjustments) considered necessary for a fair presentation. These financial statements should be read in conjunction with the audited financial statements and notes thereto for the preceding fiscal year contained in the Company’s Annual Report on Form 10-K filed on March 27, 2015 with the SEC.
	The results of operations for the three months ended March 31, 2015 are not necessarily indicative of the results to be expected for the year ending December 31, 2015. The condensed balance sheet as of December 31, 2014 has been derived from audited financial statements at that date but does not include all of the information required by U.S. GAAP for complete financial statements.
Use of Estimates	Use of Estimates
	The preparation of condensed consolidated financial statements in conformity with U.S. 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 financial statements and the accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to clinical study accruals, fair value of assets and liabilities, convertible preferred stock and related 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	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.
Short-Term Investments
	Short-Term 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. Unrealized gains and losses are excluded from earnings and were 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 marketable securities is included in interest income.
Concentration of Credit Risk and Other Risks and Uncertainties	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 short-term investments. The Company’s cash, cash equivalents, and short-term 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.
Income Taxes	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	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.
Recently Issued Accounting Pronouncements	Recently Issued 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. We are currently assessing the future impact of this ASU in the financial statements.

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Summary of Financial Assets and Liabilities Measured on Recurring Basis	The following tables set 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):
		31-Mar-15
		Level 1		Level 2			Level 3		Total
	Financial Assets:
	Money market funds	$	142,829	$	—		$	—	$	142,829
	Corporate bonds		—		170,452			—		170,452
	Asset backed securities		—		9,520			—		9,520
	U.S. Government agency securities		—		2,998			—		2,998
	Commercial paper		—		2,497			—		2,497
	Total financial assets	$	142,829	$	185,467		$	—	$	328,296
		31-Dec-14
		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
Summary of Changes in Estimated Fair Value	The following table sets forth a summary of the changes in the estimated fair value of the Company’s convertible preferred stock warrants, which were measured at fair value on a recurring basis until their conversion to common stock warrants and related reclassification to additional paid-in capital (in thousands):
		Three Months Ended March 31,
		2015		2014
	Fair value, beginning of period	$	—	$	3,419
	Change in fair value recorded as a loss in other expense, net		—		3,324
	Reclassification of warrant liability to additional paid-in capital		—		(6,743	)
	Fair value, end of period	$	—	$	—

Balance_Sheet_Components_Table

Balance Sheet Components (Tables)	3 Months Ended
	Mar. 31, 2015
Investments Debt And Equity Securities [Abstract]
Summary of Fair Values of Cash Equivalents and Short-Term Investments Classified as Available-for-Sale Securities	The fair values of cash equivalents and short-term investments classified as available-for-sale securities, consisted of the following (in thousands):
		31-Mar-15
					Gross Unrealized
		Amortized			Gains			Losses			Estimated
		Cost									Fair Value
	Money market funds classified as cash equivalents	$	142,829		$	—		$	—		$	142,829
	Corporate bonds classified as cash equivalents		20,941			—			—			20,941
	Commercial paper classified as short-term investments		2,497			2			(2	)		2,497
	Corporate bonds classified as short-term investments		149,607			8			(104	)		149,511
	Asset backed securities classified as short-term investments		9,522			—			(2	)		9,520
	U.S. Government agency securities classified as short-term		2,994			4			—			2,998
	investments
	Total	$	328,390		$	14		$	(108	)	$	328,296
		31-Dec-14
					Gross Unrealized
		Amortized			Gains			Losses			Estimated
		Cost									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		4,488			1			(4	)		4,485
	investments
	Other classified as cash equivalents		209			—			—			209
	Total	$	175,979		$	6		$	(180	)	$	175,805
Accrued Liabilities	Accrued liabilities consist of the following (in thousands):
			March 31,			December 31,
			2015			2014
	Research and clinical study expenses		$	4,271		$	2,703
	Payroll and related expenses			3,217			4,205
	Other			910			667
	Total accrued liabilities		$	8,398		$	7,575

Common_Stock_Warrants_Tables

Common Stock Warrants (Tables)	3 Months Ended
	Mar. 31, 2015
Warrants And Rights Note Disclosure [Abstract]
Summary of Outstanding Warrants	The table sets forth the outstanding common stock warrants for the periods presented:
	Outstanding at March 31,		Outstanding at December 31,		Date Issued	Term	Exercise Price
	2015		2014
		83,167		83,167	Jun-10	10 years	$	3.006
		174,651		174,651	Feb-11	10 years		3.006
		66,533		66,533	Jun-11	10 years		3.006
		324,351		324,351

StockBased_Compensation_Tables

Stock-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Functional Classification of Stock-Based Compensation Expense, Net of Estimated Forfeitures	The table below sets forth the functional classification of stock-based compensation expense, net of estimated forfeitures, for the periods presented (in thousands):
		Three Months Ended March 31,
		2015		2014
	Research and development	$	1,841	$	705
	General and administrative		567		90
	Total stock-based compensation	$	2,408	$	795

Net_Loss_per_Share_Attributabl1

Net Loss per Share Attributable to Common Stockholders (Tables)	3 Months Ended
	Mar. 31, 2015
Earnings Per Share [Abstract]
Computation of Basic and Diluted Net Loss per Share	The following table sets forth the computation of the basic and diluted net loss per share attributable to common stockholders (in thousands, except share and per share data):
		Three Months Ended
		March 31,
		2015			2014
	Numerator:
	Net loss	$	(21,379	)	$	(13,630	)
	Accretion and dividends on convertible preferred stock		—			(4,808	)
	Net loss attributable to common stockholders	$	(21,379	)	$	(18,438	)
	Denominator:
	Weighted-average common shares outstanding		34,008,830			21,582,435
	Less: weighted-average unvested common shares subject to repurchase		—			—
	Weighted-average shares used to compute net loss per share attributable		34,008,830			21,582,435
	to common stockholders, basic and diluted
	Net loss per share attributable to common stockholders, basic and diluted	$	(0.63	)	$	(0.85	)
Outstanding Shares of Common Stock Equivalents Excluded from Computation of Diluted Net Loss per Share	The following weighted-average outstanding common stock equivalents were excluded from the computation of diluted net loss per share attributable to common stockholders for the periods presented because including them would have been antidilutive:
		Three Months Ended March 31,
		2015			2014
	Convertible preferred stock (as if converted)		—			6,532,828
	Stock options to purchase common stock		2,698,846			2,315,345
	Unvested restricted stock units		33,856			—
	Convertible preferred stock warrants (as if converted)		—			117,820
	Common stock warrants		324,351			235,639
			3,057,053			9,201,632

Organization_Additional_Inform

Organization - Additional Information (Details) (USD $)	1 Months Ended	3 Months Ended
In Millions, except Share data, unless otherwise specified	Feb. 28, 2015	Mar. 31, 2015	Dec. 31, 2014
		Segment
Organization And Nature Of Business [Line Items]
Common stock, shares issued	3,450,000	35,612,019	31,934,682
Purchase of additional shares by underwriters	450,000
Common stock issued price per share	$54
Proceeds from public offering before offering expenses	$175.10
Underwriting discounts and commissions	11.2
Offering expenses	0.6
Proceeds from public offering, net	$174.50
United States of America
Organization And Nature Of Business [Line Items]
Number of reportable segments		1

Summary_of_Significant_Account2

Summary of Significant Accounting Policies - Additional Information (Details) (USD $)	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Unrecognized tax benefits related to interest or penalties	$0

Fair_Value_Measurements_Summar

Fair Value Measurements - Summary of Financial Assets and Liabilities Measured on Recurring Basis (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Financial Assets:
Fair value	$328,296	$175,805
Money Market Funds
Financial Assets:
Fair value	142,829	8,627
Asset Backed Securities
Financial Assets:
Fair value	9,520	9,542
Other
Financial Assets:
Fair value		209
Level 1
Financial Assets:
Fair value	142,829	8,627
Level 1 | Money Market Funds
Financial Assets:
Fair value	142,829	8,627
Level 2
Financial Assets:
Fair value	185,467	167,178
Level 2 | Asset Backed Securities
Financial Assets:
Fair value	9,520	9,542
Level 2 | Other
Financial Assets:
Fair value		209
Corporate Bonds
Financial Assets:
Fair value	170,452	152,942
Corporate Bonds | Level 2
Financial Assets:
Fair value	170,452	152,942
US Government Corporations and Agencies Securities
Financial Assets:
Fair value	2,998	4,485
US Government Corporations and Agencies Securities | Level 2
Financial Assets:
Fair value	2,998	4,485
Commercial Paper
Financial Assets:
Fair value	2,497
Commercial Paper | Level 2
Financial Assets:
Fair value	$2,497

Fair_Value_Measurements_Additi

Fair Value Measurements - Additional Information (Details) (USD $)	3 Months Ended		0 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Jan. 30, 2014
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Revaluation of convertible preferred stock warrant liability	$0	$3,324,000
Black-Scholes Option Pricing Model
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Estimated fair value of common stock, per share			$21
Expected time			7 years
Expected risk free interest rate			2.19%
Expected volatility			70.00%

Fair_Value_Measurements_Summar1

Fair Value Measurements - Summary of Changes in Estimated Fair Value (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014
Fair Value Disclosures [Abstract]
Fair value, beginning of period	$3,419
Change in fair value recorded as a loss in other expense, net	3,324
Reclassification of warrant liability to additional paid-in capital	($6,743)

Balance_Sheet_Components_Summa

Balance Sheet Components - Summary of Fair Values of Cash Equivalents and Short-Term Investments Classified as Available-for-Sale Securities (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$328,390	$175,979
Gross Unrealized Gains	14	6
Gross Unrealized Losses	-108	-180
Estimated Fair Value	328,296	175,805
Money Market Funds Classified as Cash Equivalents
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	142,829	8,627
Estimated Fair Value	142,829	8,627
Corporate Bonds Classified as Cash Equivalents
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	20,941	3,806
Gross Unrealized Gains		1
Estimated Fair Value	20,941	3,807
Commercial Paper Classified as Short-Term Investments
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	2,497
Gross Unrealized Gains	2
Gross Unrealized Losses	-2
Estimated Fair Value	2,497
Corporate Bonds Classified as Short-Term Investments
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	149,607	149,303
Gross Unrealized Gains	8	4
Gross Unrealized Losses	-104	-172
Estimated Fair Value	149,511	149,135
Asset Backed Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	9,522	9,546
Gross Unrealized Losses	-2	-4
Estimated Fair Value	9,520	9,542
US Government Corporations and Agencies Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	2,994	4,488
Gross Unrealized Gains	4	1
Gross Unrealized Losses		-4
Estimated Fair Value	2,998	4,485
Other Classified as Cash Equivalents
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		209
Estimated Fair Value		$209

Balance_Sheet_Components_Addit

Balance Sheet Components - Additional Information (Details) (USD $)	3 Months Ended
	Mar. 31, 2015
Schedule Of Available For Sale Securities [Line Items]
Significant realized gains or losses on available-for-sale securities	$0
Maximum
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale securities remaining contractual maturities	2 years

Balance_Sheet_Components_Accru

Balance Sheet Components - Accrued Liabilities (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Payables And Accruals [Abstract]
Research and clinical study expenses	$4,271	$2,703
Payroll and related expenses	3,217	4,205
Other	910	667
Total accrued liabilities	$8,398	$7,575

License_and_Research_Agreement1

License and Research Agreements - Additional Information (Details)

Mar. 31, 2015

Feb. 28, 2015

Dec. 31, 2014

Sep. 30, 2010

Sep. 30, 2010

Mar. 31, 2015

Mar. 31, 2015

Nov. 30, 2010

Mar. 31, 2015

Dec. 31, 2012

Mar. 31, 2015

Mar. 31, 2015

Dec. 31, 2012

Mar. 31, 2015

Jun. 30, 2013

Dec. 31, 2012

Mar. 31, 2015

Mar. 31, 2015

Mar. 31, 2015

Mar. 31, 2014

USD ($)

USD ($)

Nobelpharma License Agreement

Nobelpharma License Agreement

Nobelpharma License Agreement

Nobelpharma License Agreement

Saint Louis University License Agreement

Saint Louis University License Agreement

H I B M Research Group License Agreement

H I B M Research Group License Agreement

H I B M Research Group License Agreement

St. Jude Children's Research Hospital License Agreement

St. Jude Children's Research Hospital License Agreement

Baylor Research Institute License Agreement

Baylor Research Institute License Agreement

Baylor Research Institute License Agreement

Baylor Research Institute License Agreement

Kyowa Hakko Kirin Collaboration

Kyowa Hakko Kirin Collaboration

USD ($)

JPY (¥)

USD ($)

JPY (¥)

USD ($)

USD ($)

USD ($)

Maximum

Development and Approval Milestones

USD ($)

Maximum

USD ($)

USD ($)

Development Milestones

Sales Milestones

License Agreement

License Agreement

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

License agreement

$111,000

¥ 10,000,000

$495,000

$10,000

$100,000

$25,000

$10,000

$250,000

$1,400,000

$710,000

Common stock, shares issued

35,612,019

3,450,000

31,934,682

76,567

76,567

Remaining total aggregate payments

1,700,000

200,000,000

Future contingent milestone payments

300,000

10,500,000

7,500,000

Payments for royalty on net sales

1.00%

1.00%

Payment of option exercise fee

750,000

License agreement receivable

1,500,000

878,000

Accrued liabilities

$8,398,000

$7,575,000

$25,000

$201,000

Common_Stock_Warrants_Summary_

Common Stock Warrants - Summary of Outstanding Warrants (Details) (Common Stock [Member], USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Class Of Warrant Or Right [Line Items]
Number of Warrants Outstanding	324,351	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	$3.01	$3.01
February 2011 Common Stock Warrant [Member]
Class Of Warrant Or Right [Line Items]
Number of Warrants Outstanding	174,651	174,651
Date Issued	2011-02	2011-02
Term	10 years	10 years
Exercise Price	$3.01	$3.01
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	$3.01	$3.01

StockBased_Compensation_Additi

Stock-Based Compensation - Additional Information (Details) (2014 Incentive Plan)	3 Months Ended
	Mar. 31, 2015
2014 Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share reserved for future issuance	2,595,430
Automatic increases in shares available for grant effective date	1-Jan-15
Shares available for grant, ending date	1-Jan-24

StockBased_Compensation_Functi

Stock-Based Compensation - Functional Classification of Stock-Based Compensation Expense, Net of Estimated Forfeitures (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$2,408	$795
Research and development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	1,841	705
General and administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$567	$90

Defined_Contribution_Plan_Addi

Defined Contribution Plan - Additional Information (Details) (USD $)	3 Months Ended
	Mar. 31, 2015
Defined Contribution Pension And Other Postretirement Plans Disclosure [Abstract]
Contribution expenses	$123,000

Net_Loss_per_Share_Attributabl2

Net Loss per Share Attributable to Common Stockholders - Computation of Basic and Diluted Net Loss per Share (Details) (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Numerator:
Net loss	($21,379)	($13,630)
Accretion and dividends on convertible preferred stock		-4,808
Net loss attributable to common stockholders	($21,379)	($18,438)
Denominator:
Weighted-average common shares outstanding	34,008,830	21,582,435
Weighted-average shares used to compute net loss per share attributable to common stockholders, basic and diluted	34,008,830	21,582,435
Net loss per share attributable to common stockholders, basic and diluted	($0.63)	($0.85)

Net_Loss_per_Share_Attributabl3

Net Loss per Share Attributable to Common Stockholders - Outstanding Shares of Common Stock Equivalents Excluded from Computation of Diluted Net Loss per Share (Details)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	3,057,053	9,201,632
Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share		6,532,828
Stock options to purchase common stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	2,698,846	2,315,345
Convertible Preferred Stock Warrants (as if converted)
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share		117,820
Unvested Restricted Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	33,856
Common Stock Warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	324,351	235,639