Ardelyx (ARDX) 10-K 5 Mar 15 2014 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2014	Feb. 26, 2015	Jun. 30, 2014
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	FALSE
Document Period End Date	31-Dec-14
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY
Trading Symbol	ARDX
Entity Registrant Name	Ardelyx, Inc.
Entity Central Index Key	1437402
Current Fiscal Year End Date	-19
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		18,598,133
Entity Public Float			$96,062,968

Balance_Sheets

Balance Sheets (USD $)	Dec. 31, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$107,286,000	$34,435,000
Accounts receivable	2,584,000	6,436,000
Prepaid expenses and other current assets	1,209,000	965,000
Total current assets	111,079,000	41,836,000
Property and equipment, net	2,131,000	530,000
Other assets	104,000	358,000
Restricted cash	100,000	180,000
Total assets	113,414,000	42,904,000
Current liabilities:
Accounts payable	3,129,000	2,284,000
Accrued compensation and benefits	1,648,000	927,000
Accrued and other liabilities	780,000	100,000
Deferred revenue, current portion	15,979,000	13,828,000
Total current liabilities	21,536,000	17,139,000
Other long-term liabilities	122,000
Deferred revenue, non-current	31,074,000	26,470,000
Convertible preferred stock warrant liability		6,456,000
Liabilities related to early exercise of options	0	163,000
Total liabilities	52,732,000	50,228,000
Commitments and contingencies (Note 12)
Convertible preferred stock, $0.0001 par value per share—no shares and 108,829,748 shares authorized as of December 31, 2014 and 2013, respectively; no shares and 11,517,222 shares issued and outstanding as of December 31, 2014 and 2013, respectively		56,155,000
Stockholders’ equity (deficit):
Preferred stock, $0.0001 par value; 5,000,000 shares and no shares authorized as of December 31, 2014 and 2013, respectively; no shares issued and outstanding as of December 31, 2014 and 2013
Common stock, $0.0001 par value per share—300,000,000 and 130,360,121 shares authorized as of December 31, 2014 and 2013, respectively; 18,589,245 and 1,225,481 shares issued and outstanding as of December 31, 2014 and 2013, respectively	2,000
Additional paid-in capital	132,547,000	5,174,000
Accumulated deficit	-71,867,000	-68,653,000
Total stockholders’ equity (deficit)	60,682,000	-63,479,000
Total liabilities, convertible preferred stock, and stockholders’ equity (deficit)	$113,414,000	$42,904,000

Balance_Sheets_Parenthetical

Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Statement Of Financial Position [Abstract]
Convertible preferred stock, par value	$0.00	$0.00
Convertible preferred stock, shares authorized	0	108,829,748
Convertible preferred stock, shares issued	0	11,517,222
Convertible preferred stock, shares outstanding	0	11,517,222
Preferred stock, par value	$0.00	$0.00
Preferred stock, shares authorized	5,000,000	0
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$0.00	$0.00
Common stock, shares authorized	300,000,000	130,360,121
Common stock, shares issued	18,589,245	1,225,481
Common stock, shares outstanding	18,589,245	1,225,481

Statements_of_Operations_and_C

Statements of Operations and Comprehensive Loss (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenue:
Licensing revenue	$18,394	$8,063	$3,182
Collaborative development revenue	13,229	20,865	2,228
Total revenue	31,623	28,928	5,410
Operating expenses:
Research and development	25,900	28,093	10,184
General and administrative	7,287	3,700	4,031
Total operating expenses	33,187	31,793	14,215
Loss from operations	-1,564	-2,865	-8,805
Other income (expense), net	10	-52	-30
Change in fair value of preferred stock warrant liability	-1,593	-3,506	-950
Loss before provision for income taxes	-3,147	-6,423	-9,785
Provision for income taxes	-67	-141
Net loss and comprehensive loss	($3,214)	($6,564)	($9,785)
Net loss per common share, basic and diluted	($0.31)	($5.82)	($11.32)
Shares used to compute net loss per common share, basic and diluted	10,248,337	1,127,948	864,020

Statements_of_Convertible_Pref

Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (USD $)	Total	Convertible Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Deficit
In Thousands, except Share data
Balance, amount at Dec. 31, 2011	($48,255)	$56,155		$4,049	($52,304)
Balance, shares at Dec. 31, 2011		11,517,222	659,485
Exercise of stock options and vesting of early exercised stock options, net of repurchases, amount	175			175
Exercise of stock options and vesting of early exercised stock options, net of repurchases, shares	342,131		342,131
Stock-based compensation	473			473
Net loss	-9,785				-9,785
Balance, amount at Dec. 31, 2012	-57,392	56,155		4,697	-62,089
Balance, shares at Dec. 31, 2012		11,517,222	1,001,616
Exercise of stock options and vesting of early exercised stock options, net of repurchases, amount	125			125
Exercise of stock options and vesting of early exercised stock options, net of repurchases, shares	223,865		223,865
Stock-based compensation	352			352
Net loss	-6,564				-6,564
Balance, amount at Dec. 31, 2013	-63,479	56,155		5,174	-68,653
Balance, shares at Dec. 31, 2013		11,517,222	1,225,481
Conversion of convertible preferred stock to common stock in connection with initial public offering, amount	56,155	-56,155	1	56,154
Conversion of convertible preferred stock to common stock in connection with initial public offering, shares		-11,517,222	11,517,222
Net exercise and conversion of preferred stock warrants to common stock in connection with initial public offering, amount	8,049			8,049
Net exercise and conversion of preferred stock warrants to common stock in connection with initial public offering, shares			571,244
Exercise of stock options and vesting of early exercised stock options, net of repurchases, amount	238			238
Exercise of stock options and vesting of early exercised stock options, net of repurchases, shares	336,398		336,398
Issuance of common stock in connection with initial public offering, net of offering costs, amount	61,241		1	61,240
Issuance of common stock in connection with initial public offering, net of offering costs, shares			4,928,900
Issuance of common stock for services, amount	208			208
Issuance of common stock for services, shares	10,000		10,000
Stock-based compensation	1,484			1,484
Net loss	-3,214				-3,214
Balance, amount at Dec. 31, 2014	$60,682		$2	$132,547	($71,867)
Balance, shares at Dec. 31, 2014			18,589,245

Statements_of_Cash_Flows

Statements of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating activities
Net loss	($3,214)	($6,564)	($9,785)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization expense	302	592	675
Stock-based compensation	1,692	352	473
Change in fair value of preferred stock warrant liability	1,593	3,506	950
Changes in operating assets and liabilities:
Accounts receivable	3,852	-3,364	-3,072
Prepaid expenses and other assets	96	-438	-790
Accounts payable	831	1,138	-105
Accrued compensation and benefits	721	-38	760
Accrued and other liabilities	647	-1,009	212
Deferred revenue	6,755	7,636	32,662
Other long-term liabilities	122
Net cash provided by operating activities	13,397	1,811	21,980
Investing activities
Purchases of property and equipment	-1,856	-278	-128
Net cash used in investing activities	-1,856	-278	-128
Financing activities
Proceeds from issuance of common stock upon initial public offering, net	61,241
Proceeds from issuance of common stock from exercise of options, including early exercise of stock options	71	1	290
Repurchase of unvested common stock	-2	-2	-20
Net cash provided by (used in) financing activities	61,310	-1	270
Net increase in cash and cash equivalents	72,851	1,532	22,122
Cash and cash equivalents at beginning of period	34,435	32,903	10,781
Cash and cash equivalents at end of period	107,286	34,435	32,903
Supplementary disclosure of cash flow information
Income taxes paid		160
Supplementary disclosure of non-cash financing information:
Services settled through the issuance of common stock	208
Reclassification of convertible preferred warrant liability to additional paid-in capital	8,049
Conversion of convertible preferred stock to common stock at closing of initial public offering	$56,155

Organization_and_Basis_of_Pres

Organization and Basis of Presentation	12 Months Ended
	Dec. 31, 2014
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Basis of Presentation	1. Organization and Basis of Presentation
	Ardelyx, Inc. (the “Company”) is a clinical stage biopharmaceutical company focused on the discovery, development and commercialization of innovative, minimally-systemic, small molecule therapeutics that work exclusively in the gastrointestinal tract to treat cardio-renal, gastrointestinal and metabolic diseases. The Company has developed a drug discovery and design platform enabling it, in a rapid and cost-efficient manner, to discover and design novel drug candidates. The Company was incorporated in Delaware on October 17, 2007, under the name Nteryx and changed its name to Ardelyx, Inc. in June 2008.
	The Company operates in only one business segment, which is the development of biopharmaceutical products.
	Reverse Stock Split
	On June 18, 2014, the Company’s Amended and Restated Certificate of Incorporation became effective resulting in a reverse split of the Company’s common stock and convertible preferred stock at a 1-for-9 ratio (the “Reverse Stock Split”). The par value and the authorized shares of the common stock and convertible preferred stock were not adjusted as a result of the Reverse Stock Split. All issued and outstanding common stock, convertible preferred stock, warrants for preferred stock, options for common stock and per share amounts contained in the financial statements have been retroactively adjusted to reflect this Reverse Stock Split for all periods presented.
	Initial Public Offering
	On June 18, 2014, the Company’s registration statement on Form S-1 (File No. 333-196090) relating to the initial public offering (the “IPO”) of its common stock was declared effective by the SEC, and the IPO closed on June 24, 2014. The Company sold 4,928,900 shares of its common stock, which included the exercise in full by the underwriters of the IPO of their option to purchase 642,900 additional shares of the Company’s common stock, and the Company received cash proceeds of $61.2 million from the IPO, net of $7.8 million underwriting discounts and commissions and expenses paid by the Company.
	On June 24, 2014, prior to the closing of the IPO, all outstanding shares of convertible preferred stock converted into 11,517,222 shares of common stock with the related carrying value of $56.2 million being reclassified to common stock and additional paid-in capital. In addition, all convertible preferred stock warrants were net exercised and the related convertible preferred stock warrant liability was reclassified to additional paid-in capital.
	On June 24, 2014, the Company’s Amended and Restated Certificate of Incorporation became effective and the number of shares of capital stock the Company is authorized to issue was increased to 305,000,000 shares, of which 300,000,000 shares may be common stock and 5,000,000 shares may be preferred stock. Both the common stock and preferred stock have a par value of $0.0001 per share. There are no shares of preferred stock outstanding at December 31, 2014.

Summary_of_Significant_Account

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies
	Use of Estimates
	The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and judgments that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to revenue recognition, clinical trial accruals, 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 may differ from those estimates.
	Cash and Cash Equivalents
	The Company considers all highly liquid investments purchased with an original maturity date of 90 days or less on the date of purchase to be cash equivalents. The Company invests its cash in bank deposits and money market accounts.
	Restricted Cash
	The Company is required to guarantee the credit limit on its corporate credit card with a certificate of deposit of $0.1 million. The collateral will be released upon the cancellation of the corporate credit card.
	Concentration of Credit Risk
	Financial instruments that potentially expose the Company to concentrations of credit risk consist principally of cash, cash equivalents, and certificates of deposit. Cash and cash equivalents, as well as certificates of deposit held with financial institutions, may exceed the Federal Deposit Insurance Corporation insurance limits. The Company is exposed to credit risk in the event of default by the financial institutions holding its cash and cash equivalents to the extent of the amounts on its balance sheets. The Company has not experienced any losses on its cash, cash equivalents and certificates of deposit during the years ended December 31, 2014, 2013 and 2012.
	Accounts receivable are unsecured and are concentrated with one collaboration partner in the pharmaceutical industry, AstraZeneca AB (“AstraZeneca”). Accordingly, the Company may be exposed to credit risk generally associated with pharmaceutical companies or specific to the license and collaboration agreement with AstraZeneca. To date the Company has not experienced any losses related to its receivables.
	Fair Value of Financial Instruments
	Fair value accounting is applied for all financial assets and liabilities and non-financial assets and liabilities that are recognized at fair value in the financial statements on a recurring basis (at least annually).
	Property and Equipment
	Property and equipment are stated at cost, less accumulated depreciation and amortization. Depreciation is computed using the straight-line method over the estimated useful lives of the respective assets, generally three to five years. Leasehold improvements are amortized over the lesser of the estimated useful lives or the related remaining lease term.
	Impairment of Long-Lived Assets
	The Company reviews long-lived assets, including property and equipment, for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. If indicators of impairment exist, an impairment loss would be recognized when estimated, undiscounted future cash flows expected to result from the use of the asset and its eventual disposition are less than its carrying amount. The impairment charge is determined based upon the excess of the carrying value of the asset over its fair value, with fair value determined based upon an estimate of discounted future cash flows or another appropriate measure of fair value. The Company has not recorded any impairment of long-lived assets during any of the periods presented.
	Income Taxes
	The Company uses the asset and 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. 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.
	Revenue Recognition
	Revenue from research activities made under collaboration partnership agreements are recognized as the services are provided and when there is persuasive evidence that an arrangement exists, delivery has occurred, the price is fixed or determinable, and collectability is reasonably assured. Revenue generated from research and licensing agreements typically includes up-front signing or license fees, cost reimbursements, research services, minimum sublicense fees, milestone payments, and royalties on future licensees’ product sales.
	For revenue agreements with multiple-element arrangements, such as license and development agreements, the Company allocates revenue to each unit of accounting based on the relative selling price of each unit. When applying the relative selling price method, the Company determines the selling price for each deliverable using vendor-specific objective evidence or third-party evidence. If neither exists, the Company uses its best estimate of selling price for that deliverable. Revenue allocated is then recognized when the four basic revenue recognition criteria are met for each deliverable.
	The Company recognizes revenue from upfront payments ratably over the term of its estimated period of performance under the agreement which is recorded as licensing revenue. Reimbursements for development costs incurred under the Company’s license agreement with AstraZeneca are classified as collaborative development revenue. The Company recognizes cost reimbursement revenue under collaboration partnership agreements as the related research and development costs for services are rendered. Deferred revenue represents the portion of research or license payments received which has not been earned.
	Revenues from milestones, if they are nonrefundable and deemed substantive, are recognized upon successful accomplishment of the milestones. To the extent that non-substantive milestones are achieved and the Company has remaining performance obligations, milestones are deferred and recognized as revenue over the estimated remaining period of performance. The Company will recognize revenue associated with the non-substantive milestones upon achievement of the milestone if there are no undelivered units and it has no remaining performance obligations. The Company will account for sales-based milestones as royalties that will be recognized as revenue upon achievement of the milestone.
	Stock-Based Compensation
	The Company measures its stock-based payment awards made to employees and directors based on the estimated fair values of the awards and recognizes the compensation expense over the requisite service period. The Company has selected the Black-Scholes option-pricing model to estimate the fair value of its stock-based awards. Stock-based compensation expense is recognized using the straight-line method. Stock-based compensation expense is based on the value of the portion of stock-based payment awards that is ultimately expected to vest. As such, the Company’s stock-based compensation is reduced for the estimated forfeitures at the date of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates.
	The Company accounts for compensation expense related to stock options granted to non-employees based on the fair values estimated using the Black-Scholes model. Stock options granted to non-employees are remeasured at each reporting date until the award is vested.
	Research and Development Costs
	Research and development expenditures are expensed as incurred. Major components of research and development expenses consist of personnel costs, materials and supplies, and allocations of facilities-related costs, as well as fees paid to consultants and third parties that conduct certain research and development activities on the Company’s behalf. Payments made to other entities are under agreements that are generally cancelable by the Company. Nonrefundable advance payments for goods or services to be rendered 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.
	Convertible Preferred Stock Warrant Liability
	The Company accounts for freestanding warrants to purchase shares of convertible preferred stock that were contingently redeemable as liabilities in the balance sheets at their estimated fair value. Convertible preferred stock warrants are subject to remeasurement at each balance sheet date, and any change in fair value is recognized as a component of other expense, net in the statements of operations and comprehensive loss. The Company continued to adjust the carrying value of the warrants until the closing of the IPO, at which time the warrants were net exercised for shares of the Company’s common stock and the liability was reclassified to stockholders’ equity (deficit).
	Comprehensive Loss
	Comprehensive loss is composed of two components: net loss and other comprehensive loss. Other comprehensive income (loss) refers to gains and losses that under GAAP are recorded as an element of stockholders’ equity (deficit), but are excluded from net loss. The Company did not record any transactions within other comprehensive income (loss) in the periods presented and, therefore, the net loss and comprehensive loss were the same for all periods presented.
	Net Loss per Share
	Basic net loss per common share is calculated by dividing the net loss by the weighted-average number of common shares outstanding during the period, without consideration of common stock equivalents. Diluted net loss per common share in the periods presented is the same as basic net loss per common share, since the effects of potentially dilutive securities are antidilutive.
	Recent Accounting Pronouncements
	In July 2013, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update (“ASU”) 2013-11, Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists. The ASU concludes an unrecognized tax benefit should be presented as a reduction of a deferred tax asset when settlement in this manner is available under the law. The Company adopted this amendment as of January 1, 2014, which did not have a significant impact on the balance sheet.
	In May 2014, the FASB issued Accounting Standards Update 2014-09, Revenue from Contracts with Customers (“ASU 2014-09”), which converges the FASB and the International Accounting Standards Board standards on revenue recognition and will replace nearly all existing revenue recognition under U.S. GAAP. The core principle of ASU 2014-09 is that an entity should recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. This guidance is effective for the fiscal years and interim reporting periods beginning after December 15, 2016, at which time the Company may adopt the new standard under the full retrospective method or the modified retrospective method. Early adoption is not permitted. The Company has not yet selected a transition method nor has the Company determined the impact of the new standard on its financial statements and related disclosures.
	In August 2014, the Financial Accounting Standards Board issued Accounting Standards Update No. 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern (“ASU 2014-15”). ASU 2014-15 requires management to evaluate whether there is substantial doubt about an entity’s ability to continue as a going concern and to provide related footnote disclosures. In doing so, companies will have reduced diversity in the timing and content of footnote disclosures than under today’s guidance. ASU 2014-15 is effective for the Company in the first quarter of 2016 with early adoption permitted. The Company does not believe the impact of adopting ASU 2014-15 on its financial statements will be material.

Fair_Value_Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements
	Pursuant to the accounting guidance for fair value measurement and its subsequent updates, fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (i.e., the “exit price”) in an orderly transaction between market participants at the measurement date. The accounting guidance establishes a hierarchy for inputs used in measuring fair value that minimizes the use of unobservable inputs by requiring the use of observable market data when available. Observable inputs are inputs that market participants would use in pricing the asset or liability based on active market data. Unobservable inputs are inputs that reflect the assumptions market participants would use in pricing the asset or liability based on the best information available in the circumstances.
	The three-level hierarchy for the inputs to valuation techniques is briefly summarized as follows:
	Level 1	–		Valuations are based on quoted prices in active markets for identical assets or liabilities and readily accessible by us at the reporting date. Examples of assets and liabilities utilizing Level 1 inputs are certain money market funds, U.S. Treasuries and trading securities with quoted prices on active markets.
	Level 2	–		Valuations based on inputs other than the quoted prices in active markets that are observable either directly or indirectly in active markets. Examples of assets and liabilities utilizing Level 2 inputs are U.S. government agency bonds, corporate bonds, commercial paper, certificates of deposit and over-the-counter derivatives.
	Level 3	–		Valuations based on unobservable inputs in which there is little or no market data, which require us to develop our own assumptions.
	The following table sets forth the fair value of the Company’s financial assets and liabilities measured on a recurring basis by level within the fair value hierarchy:
		December 31, 2014
		Total			Level 1		Level 2		Level 3
					(in thousands)
	Assets:
	Money market funds	$	105,410		$	105,410	$	—	$	—
	Certificates of deposit		100			—		100		—
	Total	$	105,510		$	105,410	$	100	$	—
		December 31, 2013
		Total			Level 1		Level 2		Level 3
					(in thousands)
	Assets:
	Money market funds	$	32,472		$	32,472	$	—	$	—
	Certificates of deposit		180			—		180		—
	Total	$	32,652		$	32,472	$	180	$	—
	Liabilities:
	Convertible preferred stock warrant liability	$	6,456		$	—	$	—	$	6,456
	Total	$	6,456		$	—	$	—	$	6,456
	Where quoted prices are available in an active market, securities are classified as Level 1. The Company classifies money market funds as Level 1. When quoted market prices are not available for the specific security, then the Company estimates fair value by using benchmark yields, reported trades, broker/dealer quotes, and issuer spreads. The Company classifies certificates of deposit as Level 2. In certain cases where there is limited activity or less transparency around inputs to valuation, securities are classified as Level 3. There were no transfers between Level 1 and Level 2 during the periods presented.
	Level 3 liabilities that were measured at fair value on a recurring basis consist of the preferred stock warrant liability, which was measured using the probability weighted expected return method that calculated the probability of the Company going public or being acquired, and the option-pricing method for remaining private in the near to mid-term. The fair value of the preferred stock warrant liability as of December 31, 2013 was estimated using such scenarios that were weighted based on the Company’s estimate of the probability of each scenario: 20% for IPO; 10% for merger and 70% for stay private as of December 31, 2013. At the end of each reporting period, the change in estimated fair value during the period is recorded in change in fair value of convertible preferred stock warrant liability in the statements of operations and comprehensive income (loss). Generally, increases or decreases in the fair value of the underlying convertible preferred stock would result in a directionally similar impact in the fair value measurement of the warrant liability. The preferred stock warrant liability was remeasured prior to the net exercise of the warrants using the IPO price. The preferred stock warrants were net exercised and converted to common stock 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 preferred stock warrants which were measured at fair value on a recurring basis (in thousands):
		Preferred Stock
		Warrant Liability
		(in thousands)
	Balance at December 31, 2012	$	2,950
	Net increase in fair value of warrant liabilities upon revaluation		3,506
	Balance at December 31, 2013	$	6,456
	Net increase in fair value of warrant liabilities upon revaluation		1,593
	Reclassification of warrant liability to additional paid-in capital upon completion of IPO		(8,049	)
	Balance at December 31, 2014	$	—

Property_and_Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2014
Property Plant And Equipment [Abstract]
Property and Equipment	4. Property and Equipment
	Property and equipment consist of the following:
		December 31,
		2014			2013
		(in thousands)
	Laboratory equipment	$	3,039		$	2,315
	Office equipment and furniture		229			91
	Construction in progress		362			—
	Leasehold improvements		2,135			1,456
	Property and equipment, gross		5,765			3,862
	Less: accumulated depreciation and amortization		(3,634	)		(3,332	)
	Total property and equipment, net	$	2,131		$	530
	Depreciation and amortization expense totaled $0.3 million, $0.6 million and $0.7 million for the years ended December 31, 2014, 2013 and 2012.

Collaboration_and_Licensing_Ag

Collaboration and Licensing Agreements	12 Months Ended
	Dec. 31, 2014
Collaboration And Licensing Agreements [Abstract]
Collaboration and Licensing Agreements	5. Collaboration and Licensing agreements
	AstraZeneca AB
	In October 2012, the Company entered into a license agreement (the “License Agreement”) pursuant to which the Company and AstraZeneca collaborate to research, develop, and commercialize the Company’s small molecule NHE3 inhibitors program, which includes the Company’s lead product candidate, tenapanor, as well as back-up compounds. Pursuant to the agreement, the Company granted a worldwide exclusive right and license to exploit such licensed compounds solely for development and commercialization purposes.
	The Company is currently responsible for certain development activities from the effective date of the agreement through completion of the chronic kidney disease (“CKD”) Phase 2a clinical trial. AstraZeneca reimburses the Company for its internal and external development-related costs. The Company is also obligated to participate on a Development Collaboration Committee through the completion of all Phase 2 clinical trials for tenapanor. As part of the transaction, the Company has an option to co-promote the product in the United States, subject to agreed limitations.
	Upon product sales, the Company is eligible to receive royalties that adjust depending on sales volume with tiered royalty percentage ranges starting in the high single digits and moving into double digits in mid-teens as net sales increase, subject to reductions in certain specified circumstances.
	Under the License Agreement, the Company has the option to participate in the funding of the first Phase 3 clinical development program for the first indication of tenapanor by investing a co-funding amount of $20.0 million, $30.0 million or $40.0 million to acquire an increase of 1%, 2% or 3%, respectively, in the royalties payable to us by AstraZeneca on net sales of tenapanor at all tiers. The selected co-funding amount would be paid ratably over the estimated period of the Phase 3 clinical development program. The Company may exercise this right only for a limited period of 60 days following AstraZeneca’s determination to proceed to the first Phase 3 clinical development program for tenapanor for a specific indication.
	The Company identified the deliverables within the arrangement as a license to the technology, the initial supply of the compound of the licensed product for use in development, and ongoing development activities through completion of all Phase 2 clinical trials for tenapanor, which are accounted for as a single unit of accounting. The Company concluded that the license is not a separate unit of accounting. It does not have stand-alone value to AstraZeneca, separable from the development services to be performed pursuant to the agreement, as AstraZeneca is unable to use the license for its intended purpose without the Company’s performance of the development services, which included the initial supply of the compound. As a result, the Company will recognize revenue from the up-front payment on a straight-line basis over the period from the effective date of the agreement through the completion of all Phase 2 clinical trials for tenapanor (the estimated period of performance).
	Under the License Agreement, AstraZeneca paid the Company an up-front license fee of $35.0 million in October 2012. In December 2013, AstraZeneca and the Company entered into an amendment to the License Agreement to acknowledge the intention of AstraZeneca to commence development of tenapanor for the treatment of hyperphosphatemia in CKD-5D patients, and to provide additional clarification for the payment of certain development milestones (the “License Amendment”). The License Amendment was not deemed to be a material modification to the arrangement since there were no changes in the total arrangement consideration or key provisions, only a change in the allocation of payments. AstraZeneca made a payment of $15.0 million in December 2013 pursuant to the amendment. The payment was combined with the unamortized upfront payment and is being recognized as revenue on a straight-line basis over the estimated period of performance.
	In May 2014, the Company received from AstraZeneca a $25.0 million payment as a result of the dosing of the first patient in the Phase 2b clinical trial in hyperphosphatemia. As the $25.0 million did not meet the criteria to be considered the achievement of a substantive milestone for accounting purposes, the amount was recorded as deferred revenue when received and is being recognized as revenue on a straight-line basis over the remaining estimated period of performance under the AstraZeneca collaboration partnership agreement.
	The estimated period of performance is currently estimated to be December 2017, which was changed during the quarter ended September 30, 2014 from December 2016 due to the extension of the estimated completion date of the Phase 2 CKD clinical trials. The expected period of performance is reviewed quarterly and adjusted, as needed, to reflect our current assumptions regarding the timing of clinical studies.
	AstraZeneca reimburses the Company for its internal and external development-related costs. These reimbursements are recognized as collaborative development revenue when the development-related costs are incurred.
	As of December 31, 2014, the Company was eligible to receive future contingent payments up to a total of $795.0 million, which is comprised of future development milestones up to an additional $197.5 million and launch, commercialization, and sales milestones up to an additional $597.5 million. The contingent payments are triggered upon the activities expected to be undertaken by AstraZeneca. Revenue from milestones, if they are nonrefundable and deemed substantive, are recognized upon successful accomplishment of the milestone. The Company will recognize revenue associated with non-substantive milestones upon achievement of the milestones if there are no undelivered units and it has no remaining performance obligation. To the extent that non-substantive milestones are achieved and the Company has remaining performance obligations, milestones are deferred and recognized as revenue over the estimated remaining period of performance.
	For the years ended December 31, 2014, 2013 and 2012, the Company recognized revenue of $18.4 million, $8.1 million and $3.2 million, respectively, related to amortization of the up-front and other license fees, and $13.2 million, $20.9 million and $2.2 million, respectively, for collaborative development services. As of December 31, 2014, the Company had total deferred revenue of $47.1 million related to the AstraZeneca license agreement.
	Sanofi SA
	In February 2014, the Company entered into a License Option and License Agreement with Sanofi SA (“Option and License Agreement”) for its phosphate transport NaP2b inhibitor program. NaP2b is an intestinal phosphate transporter whose activity accounts for a significant portion of dietary phosphate absorption in humans. The inhibition of NaP2b is believed to have utility for the treatment of hyperphosphatemia (elevated serum phosphate) in patients with CKD-5D. Under the Option and License Agreement, the Company granted Sanofi an exclusive worldwide license to conduct research utilizing the Company’s small molecule NaP2b inhibitors. In addition, Sanofi has the option to obtain an exclusive license to develop, manufacture and commercialize the Company’s NaP2b inhibitors. Sanofi is advancing this program towards first-in-human clinical trials. Under the Option and License Agreement, Sanofi is responsible for all of the costs and expenses for research and preclinical activities and, should it exercise its option, for the development and commercialization efforts under the program. Under the Option and License Agreement, the Company received a payment of $1.25 million and is responsible for up to $0.2 million of patent costs after which any additional patent costs will be fully reimbursed to the Company by Sanofi.
	The Company received the payment of $1.25 million in March 2014, which was fully recognized as licensing revenue in May 2014 after the Company completed its obligation to provide to Sanofi the background know-how, listed patents, and materials described in the License Option and License Agreement.
	The Company has the potential to earn future development, regulatory and commercial milestone payments of up to $196.8 million if Sanofi continues to advance the program into development and through commercialization. If a NaP2b inhibitor is commercialized by Sanofi as a result of this program, the Company will receive tiered royalties ranging from mid-single digits into the low double digits. As part of the arrangement with Sanofi, the Company retains an option to participate in co-promotional activities in the United States. Future potential milestone payments do not meet the criteria to be considered substantive milestones, and therefore will be treated as other contingent consideration and recognized as revenue as they are achieved as the Company has no performance obligations under the License Option and License Agreement. No milestones have been received since the inception of the agreement.

Convertible_Preferred_Stock

Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2014
Class Of Stock Disclosures [Abstract]
Convertible Preferred Stock	6. Convertible Preferred Stock
	On June 24, 2014, prior to the closing of the IPO, all outstanding shares of convertible preferred stock converted into 11,517,222 shares of common stock with the related carrying value of $56.2 million reclassified to common stock and additional paid-in capital.
	Convertible preferred stock as of December 31, 2013 consisted of the following:
	Convertible Preferred Stock:	Shares		Shares		Net		Aggregate
		Authorized		Issued and		Carrying		Liquidation
				Outstanding		Value		Preference
		(In thousands, except share data)
	Series A		25,231,213		2,803,462	$	25,957	$	28,764
	Series B		83,598,535		8,713,760		30,198		30,310
	Total convertible preferred stock		108,829,748		11,517,222	$	56,155	$	59,074

Preferred_Stock_Warrants

Preferred Stock Warrants	12 Months Ended
	Dec. 31, 2014
Class Of Stock Disclosures [Abstract]
Preferred Stock Warrants	7. Preferred Stock Warrants
	In connection with the closing of the Series B financing in August 2011, the Company issued warrants for the purchase of 574,953 shares of Series B convertible preferred stock. The exercise price of the warrants was $0.09 per share. The preferred stock warrant liability was measured at fair value on a recurring basis. Changes in fair value were recorded in change in fair value of preferred stock warrant liability in the Statements of Operations and Comprehensive Loss. As a result of the low exercise price for the warrants, the Company used the intrinsic value of the warrants as a proxy for the fair value for financial reporting purposes. The Company revalued the warrants as of December 31, 2012 using their intrinsic value given their low exercise price. As of December 31, 2013 and for the period in 2014 up to the IPO date, the Company revalued the warrants using a hybrid of the option pricing method and the probability-weighted expected return method. The hybrid methodology was applied to reflect two exit scenarios, IPO and merger using a market approach and the income approach was used in the stay private scenario. The scenarios were weighted based on the Company’s estimate of the probability of each scenario: 20% for IPO; 10% for merger and 70% for stay private for the year ended December 31, 2013. As of December 31, 2013, the fair value of this convertible preferred stock warrant liability amounted to $6.5 million. Just prior to the IPO close date of June 24, 2014, the preferred stock warrant liability was remeasured prior to the net exercise of the warrants using the IPO price. The preferred stock warrants were net exercised.

Equity_Incentive_Plans

Equity Incentive Plans	12 Months Ended
	Dec. 31, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Equity Incentive Plans	8. Equity Incentive Plans
	2008 Plan
	The Company granted options under its 2008 Stock Incentive Plan (the “2008 Plan”) until June 2014 when it was terminated as to future awards, although it continues to govern the terms of options that remain outstanding under the 2008 Plan. The 2008 Plan provided for the granting of incentive and nonstatutory stock options, and stock purchase rights to employees, directors and consultants at the discretion of the Board of Directors. Stock options granted generally vest over a period of four years from the date of grant. In connection with the Board of Directors and stockholders approval of the 2014 Plan, all remaining shares available for future award under the 2008 Plan were transferred to 2014 Plan, and the 2008 Plan was terminated.
	2014 Plan
	The 2014 Equity Incentive Award Plan (“2014 Plan”) became effective on June 18, 2014, immediately prior to the time the Company’s Registration Statement on Form S-1 became effective. Under the 2014 Plan, 1,419,328 shares of common stock were initially reserved for issuance pursuant to a variety of stock-based compensation awards, including stock options, stock appreciation rights, or SARs, restricted stock awards, restricted stock unit awards, deferred stock awards, deferred stock unit awards, dividend equivalent awards, stock payment awards and performance awards. In addition, 35,221 shares that had been available for future awards under the 2008 Plan as of June 18, 2014, were added to the initial reserve available under the 2014 Plan, bringing the total reserve upon the effective date of the 2014 Plan to 1,454,549. The number of shares initially reserved for issuance or transfer pursuant to awards under the 2014 Plan will be increased by (i) the number of shares represented by awards outstanding under 2008 Plan on June 18, 2014, that are either forfeited or lapse unexercised or that are repurchased for the original purchase price thereof, up to a maximum of 1,153,279 shares, and (ii) if approved by the Administrator of the 2014 Plan, an annual increase on the first day of each fiscal year ending in 2024, equal to the lesser of (A) four percent (4.0%) of the shares of stock outstanding (on an as converted basis) on the last day of the immediately preceding fiscal year and (B) such smaller number of shares of stock as determined by our board of directors; provided, however, that no more than 10,683,053 shares of stock may be issued upon the exercise of incentive stock options.  Effective January 1, 2015, the 2014 Plan share reserve was increased by 743,569 shares.
	Stock Plan Activity
	The following table summarizes activity under the 2008 Plan and the 2014 Plan, including grants to nonemployees and restricted stock issued:
						Options Issued and
						Outstanding
		Shares Available for Grant				Number of Shares							Weighted- Average		Aggregate
													Exercise Price per		Intrinsic Value
													Share
															(in thousands)
	Balances at December 31, 2011		19,798					1,598,513				$		0.57
	Options authorized		114,428					—
	Options granted		(81,233	)				81,233						3.46
	Options exercised		—					(342,131	)					0.52
	Options canceled		43,848					(43,848	)					0.52
	Balance at December 31, 2012		96,841					1,293,767				$		0.77
	Options granted		(99,552	)				99,552						3.42
	Options exercised		—					(223,865	)					0.56
	Options canceled		6,625					(6,625	)					2.23
	Balance at December 31, 2013		3,914					1,162,829				$		1.03
	Options authorized		1,452,661					—
	Options granted		(188,888	)				188,888						24.41
	Options exercised		—					(336,398	)					0.71
	Options canceled		4,084					(4,084	)					2.21
	Options repurchased		3,511					(3,511	)					0.55
	Issuance of common stock for services		(10,000	)				—						—
	Balance at December 31, 2014		1,265,282					1,007,724				$		5.51		$	14,839
	Vested and expected to vest at December 31, 2014							990,889				$		5.27		$	14,746
	Vested at December 31, 2014							643,217				$		1.21		$	11,376
	The weighted-average grant-date estimated fair value of options granted during the years ended December 31, 2014, 2013 and 2012 was $18.53, $2.68 and $2.56 per share. The aggregate intrinsic value was calculated as the difference between the exercise price of the options and the estimated fair value of the Company’s common stock of $18.89 per share as of December 31, 2014.
	2014 Employee Stock Purchase Plan
	The Company adopted the 2014 Employee Stock Purchase Plan (ESPP) and initially reserved 202,762 shares of common stock as of its effective date of June 18, 2014. If approved by the Administrator of the ESPP, on the first day of each calendar year, ending in 2024, the number of shares in the reserve will increase by an amount equal to the lesser of (i) one percent (1.0%) of the shares of common stock outstanding on the last day of the immediately preceding fiscal year and (ii) such number of shares of common stock as determined by the board of directors; provided, however, no more than 2,230,374 shares of our common stock may be issued under the ESPP. Effective January 1, 2015, the ESPP share reserve was increased by 185,892. Under the ESPP, participants are offered the option to purchase shares of the Company’s common stock at a discount during a series of successive offering periods normally commencing on March 1 and September 1 of each year. The initial offering period commenced on September 1, 2014 and will end on February 27, 2015.
	As of December 31, 2014, no shares of common stock have been issued to employees participating in the ESPP and 202,762 shares were available for issuance under the ESPP.
	The following table illustrates the weighted-average assumptions for the Black-Scholes option-pricing model used in determining the fair value of ESPP purchase rights granted to employees:
		Year Ended December 31, 2014
	Expected term (years)		0.5
	Volatility		73	%
	Risk-free interest rate		0.05	%
	Dividend yield		—	%
	Liability for Early Exercise of Stock Options
	As of December 31, 2014 and 2013, there were zero and 286,217 shares of common stock outstanding, respectively, subject to the Company’s right of repurchase at prices ranging from $0.27 to $1.08 per share. As of December 31, 2014 and 2013, the Company recorded zero and $0.2 million, respectively, as liabilities associated with shares issued with repurchase rights.
	Modification of Stock Awards
	During September 2014, the Company entered into a Transition and Separation Agreement with its Chief Scientific Officer, Dominique Charmot, under which certain restricted shares that were subject to vesting and repurchase by the Company have become fully vested as of Dr. Charmot’s separation from the Company as an employee and director on December 23, 2014. This resulted in the acceleration of the vesting for 58,969 shares of restricted stock. As a result of the acceleration, the Company has recorded a stock-based compensation charge of $0.8 million during the year ended December 31, 2014 to reflect the revised service period for the restricted stock and related vesting of shares that would otherwise not have vested.
	Stock-based Compensation
	Total stock-based compensation recognized was as follows (in thousands):
		Year Ended December 31,
		2014			2013				2012
					(in thousands)
	Research and development	$	1,376		$	200			$	221
	General and administrative		316			152				252
	Total stock-based compensation	$	1,692		$	352			$	473
	As of December 31, 2014, there was $3.2 million of unrecognized stock-based compensation expense, net of estimated forfeitures, related to unvested share options with a weighted-average remaining recognition period of 2.3 years.
	In determining the 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. The Company used the simplified method to determine the expected term, which is calculated as the average of the time-to-vesting and the contractual life of the options.
	Expected Volatility— The Company was privately held prior to its IPO in June 2014 and thus a sufficient trading history does not exist for the Company’s common stock. 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. 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.
	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 to employees was estimated at the date of grant using a Black-Scholes option-pricing model with the following weighted-average assumptions:
		Year Ended December 31
		2014			2013				2012
	Expected term (years)		5.97			6.07				5.73
Volatility		94	%		98	%			97	%
Risk-free interest rate		1.79	%		1.35	%			0.79	%
Dividend yield		—	%		—	%			—	%
The weighted-average, estimated grant-date fair value of employee stock options granted during the years ended December 31, 2014, 2013 and 2012 was $18.57, $2.68 and $2.56 per share, respectively.
Options Granted to Nonemployees
The Company has granted options to purchase shares of common stock to consultants in exchange for services performed. The Company granted options to purchase 10,000 and 3,333 shares with average exercise prices of $20.77 and $3.43 per share, respectively, during the years ended December 31, 2014 and 2013, respectively. These options vest upon grant or various terms up to three years. The Company recognized non-employees stock compensation expense of $0.1 million, $2,000 and zero during the years ended December 31, 2014, 2013 and 2012, respectively. The fair value of non-employees’ options was measured using the Black-Scholes option-pricing model reflecting the same assumptions as applied to employee options in each of the reported years, other than the expected life, which is assumed to be the remaining contractual life of the option.
Issuance of Common Stock for Services
During the year ended December 31, 2014, the Company issued 10,000 shares of common stock to consultants in exchange for services performed.  The shares issued were valued at $0.2 million based on the fair value of the common stock on the date of grant.

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income Taxes
	9. Income Taxes
	The following is a reconciliation of the statutory federal income tax rate to the Company’s effective tax rate:
		Year Ended December 31,
		2014			2013			2012
	Expected income tax provision at the federal statutory rate		35	%		35	%		35	%
	State taxes, net of federal benefit		4.6			(1.4	)		—
	Change in valuation allowance		(17.9	)		(22.6	)		(38.6	)
	Nondeductible expenses		(20.6	)		(20.8	)		(5.2	)
	Tax credits		—			7.3			4.4
	Other		(3.2	)		0.3			4.4
	Income tax provision		(2.1	)%		(2.2	)%		—	%
	Significant components of the Company’s deferred tax assets are as follows:
		December 31,
		2014			2013
		(in thousands)
	Deferred tax assets:
	Net operating loss carryforwards	$	11,262		$	13,069
	Deferred revenue		11,099			9,723
	Research credits		1,260			1,734
	Other		1,201			475
	Gross deferred tax assets		24,822			25,001
	Valuation allowance		(24,741	)		(25,001	)
	Total deferred tax assets		81			—
	Deferred tax liabilities		(81	)		—
	Net deferred tax assets	$	—		$	—
	Realization of deferred tax assets is dependent on future earnings, if any, the timing and amount of which are uncertain. Accordingly, the deferred tax assets have been fully offset by a valuation allowance. The valuation allowance decreased by $0.3 million for the year ended December 31, 2014. The valuation allowance increased by $1.5 million for the year ended December 31, 2013.
	At December 31, 2014, the Company had net operating loss carryforwards for federal income tax purposes of approximately $28.0 million that expire beginning in 2028 if not utilized, and federal research and development tax credit carryforwards of approximately $2.1 million that expire beginning in 2029 if not utilized. In addition, the Company had net operating loss carryforwards for state income tax purposes of approximately $25.6 million that expire beginning in 2018 if not utilized, and state research and development tax credit carryforwards of approximately $2.3 million, which do not expire.
	The future utilization of the net operating loss and tax credit carryforwards and credits may be subject to an annual limitation, pursuant to Internal Revenue Code Sections 382 and 383, as a result of ownership changes that may have occurred previously or that could occur in the future.  Due to the existence of the valuation allowance, future changes under Sections 382 and 383 will not impact the Company’s effective tax rate.
	A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows:
		December 31,
		2014			2013			2012
					(in thousands)
	Balance at beginning of year	$	1,411		$	1,064		$	807
	Additions based on tax positions related to prior year		405			—			—
	Additions based on tax positions related to current year		999			347			257
	Balance at end of year	$	2,815		$	1,411		$	1,064
	The unrecognized tax benefits, if recognized and in absence of full valuation allowance, would impact the income tax provision by $2.8 million, $1.4 million and $1.1 million as of December 31, 2014, 2013 and 2012, respectively.
	The Company has elected to include interest and penalties as a component of tax expense. During the years ended December 31, 2014, 2013 and 2012, the Company did not recognize accrued interest and penalties related to unrecognized tax benefits. Although the timing and outcome of income tax audit is highly uncertain, the Company does not anticipate that the amount of existing unrecognized tax benefits will significantly change during the next 12 months.
	The Company files income tax returns in the U.S. federal and California tax jurisdictions. Due to the Company’s net operating loss and tax credit carryforwards, the income tax returns remain open to U.S. federal and California state tax examinations.   The Company is not currently under examination in any tax jurisdiction.

Net_Loss_per_Share

Net Loss per Share	12 Months Ended
	Dec. 31, 2014
Earnings Per Share [Abstract]
Net Loss per Share
	10. Net Loss per Share
	Basic net loss per share is calculated by dividing net loss by the weighted-average number of common shares outstanding during the period, less shares subject to repurchase, and excludes any dilutive effects of share-based awards and warrants. Diluted net loss per common share is computed giving effect to all potential dilutive common shares, including common stock issuable upon exercise of stock options, and unvested restricted common stock and stock units. As the Company had net losses for the years ended December 31, 2014, 2013 and 2012, all potential common shares were determined to be anti-dilutive.
	The following table sets forth the computation of net loss per common share (in thousands, except share and per share amounts):
		December 31,
		2014			2013			2012
	Numerator:
	Net loss	$	(3,214	)	$	(6,564	)	$	(9,785	)
	Denominator:
	Weighted average number of shares outstanding—basic and diluted		10,248,337			1,127,948			864,020
	Net loss per share—basic and diluted	$	(0.31	)	$	(5.82	)	$	(11.32	)
	Potentially dilutive securities that were not included in the diluted per share calculations because they would be anti-dilutive were as follows:
		December 31,
		2014			2013			2012
	Convertible preferred stock		—			11,517,222			11,517,222
	Options to purchase common stock		1,007,724			1,162,829			1,293,767
	Warrants to purchase convertible preferred stock		—			574,953			574,953
	Total		1,007,724			13,255,004			13,385,942

Related_Party_Transactions

Related Party Transactions (Clinical Operations Consulting Arrangement, Spouse of Executive Officer)	12 Months Ended
	Dec. 31, 2014
Clinical Operations Consulting Arrangement | Spouse of Executive Officer
Related Party Transaction [Line Items]
Related Party Transactions
	11. Related Party Transactions
	As part of the consulting arrangement with the spouse of an executive of the Company to provide research and development services related to clinical operations, the Company incurred expenses of $0.2 million for services rendered during each of the years ended December 31, 2014 and 2013, and $0.1 million for services rendered during the year ended December 31, 2012, respectively.

Commitments_and_Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2014
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	12. Commitments and Contingencies
	The Company has a lease agreement for a facility in Fremont, California that was amended in December 2012 to extend the lease agreement to September 2016. In September 2014, the Company signed the second amendment to its facility lease agreement in Fremont, California to add space and to extend the lease term through September 2019. In addition, the amended lease agreement provides for a tenant improvement allowance of up to $0.6 million. The extended lease has rent escalation clauses through the lease term. Rent increases, including the impact of a rent holiday and leasehold improvement allowance from the landlord, will be recognized as deferred rent and amortized on a straight-line basis over the term of the lease.
	Under the terms of the lease agreement, the Company provided the lessor with a security deposit in the amount of $0.1 million. The lessor shall be entitled to draw on the security deposit in the event of any uncured default by the Company under the terms of the lease.
	The future minimum payments under the noncancelable operating lease at December 31, 2014, are as follows (in thousands):
	Year ending December 31,	Amounts
	2015	$	843
	2016		868
	2017		895
	2018		921
	2019		653
	Total	$	4,180
	Rent expense under operating leases was $0.6 million, $0.5 million and $0.4 million for the years ended December 31, 2014, 2013 and 2012, respectively.
	The Company entered into a series of purchase commitments for research and development equipment at December 31, 2014 totaling $0.7 million, all of which will be due within the next year.  The Company has capital expenditure commitments for $1.2 million related to expansion of office space.
	Guarantees and Indemnifications
	As permitted under Delaware law and in accordance with the Company’s bylaws, the Company indemnifies its officers and directors for certain events or occurrences while the officer or director is or was serving in such capacity. The maximum amount of potential future indemnification is unlimited; however, the Company currently holds director and officer liability insurance. This insurance allows the transfer of the risk associated with the Company’s exposure and may enable it to recover a portion of any future amounts paid. The Company may terminate the indemnification agreements with its officers and directors upon a 90-day written notification, but termination will not affect claims for indemnification related to events occurring prior to the effective date of termination. The Company believes the fair value of these indemnification agreements is minimal. Accordingly, the Company has not recorded any liabilities associated with these indemnification agreements as of December 31, 2014 or 2013.

Selected_Quarterly_Financial_D

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data (Unaudited)	13. Selected Quarterly Financial Data (Unaudited)
	Selected quarterly financial results from operations for the years ended December 31, 2014 and 2013 are as follows (in thousands, except per share amounts):
		2014 Quarter End
		March 31,			June 30			September 30			December 31
	Total revenue	$	8,550		$	9,137		$	7,598		$	6,338
	Operating expenses		9,014			6,386			7,517			10,270
	Net income (loss)		(3,071	)		3,753			74			(3,970	)
	Net income (loss) per share:
	Basic		(2.44	)		0.2			—			(0.21	)
	Diluted		(2.44	)		0.18			—			(0.21	)
		2013 Quarter End
		March 31,			June 30			September 30			December 31
	Total revenue	$	6,556		$	7,291		$	6,593		$	8,488
	Operating expenses		6,966			8,142			7,479			9,206
	Net loss		(470	)		(891	)		(934	)		(4,269	)
	Basic and diluted net loss per common share		(0.45	)		(0.81	)		(0.81	)		(3.53	)

Subsequent_Events

Subsequent Events	12 Months Ended
	Dec. 31, 2014
Subsequent Events [Abstract]
Subsequent Events	14. Subsequent Events
	None.

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates
	The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and judgments that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to revenue recognition, clinical trial accruals, 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 may differ from those estimates.
Cash and Cash Equivalents	Cash and Cash Equivalents
	The Company considers all highly liquid investments purchased with an original maturity date of 90 days or less on the date of purchase to be cash equivalents. The Company invests its cash in bank deposits and money market accounts.
Restricted Cash	Restricted Cash
	The Company is required to guarantee the credit limit on its corporate credit card with a certificate of deposit of $0.1 million. The collateral will be released upon the cancellation of the corporate credit card.
Concentration of Credit Risk	Concentration of Credit Risk
	Financial instruments that potentially expose the Company to concentrations of credit risk consist principally of cash, cash equivalents, and certificates of deposit. Cash and cash equivalents, as well as certificates of deposit held with financial institutions, may exceed the Federal Deposit Insurance Corporation insurance limits. The Company is exposed to credit risk in the event of default by the financial institutions holding its cash and cash equivalents to the extent of the amounts on its balance sheets. The Company has not experienced any losses on its cash, cash equivalents and certificates of deposit during the years ended December 31, 2014, 2013 and 2012.
	Accounts receivable are unsecured and are concentrated with one collaboration partner in the pharmaceutical industry, AstraZeneca AB (“AstraZeneca”). Accordingly, the Company may be exposed to credit risk generally associated with pharmaceutical companies or specific to the license and collaboration agreement with AstraZeneca. To date the Company has not experienced any losses related to its receivables.
Fair Value of Financial Instruments	Fair Value of Financial Instruments
	Fair value accounting is applied for all financial assets and liabilities and non-financial assets and liabilities that are recognized at fair value in the financial statements on a recurring basis (at least annually).
Property and Equipment	Property and Equipment
	Property and equipment are stated at cost, less accumulated depreciation and amortization. Depreciation is computed using the straight-line method over the estimated useful lives of the respective assets, generally three to five years. Leasehold improvements are amortized over the lesser of the estimated useful lives or the related remaining lease term.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets
	The Company reviews long-lived assets, including property and equipment, for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. If indicators of impairment exist, an impairment loss would be recognized when estimated, undiscounted future cash flows expected to result from the use of the asset and its eventual disposition are less than its carrying amount. The impairment charge is determined based upon the excess of the carrying value of the asset over its fair value, with fair value determined based upon an estimate of discounted future cash flows or another appropriate measure of fair value. The Company has not recorded any impairment of long-lived assets during any of the periods presented.
Income Taxes	Income Taxes
	The Company uses the asset and 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. 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.
Revenue Recognition	Revenue Recognition
	Revenue from research activities made under collaboration partnership agreements are recognized as the services are provided and when there is persuasive evidence that an arrangement exists, delivery has occurred, the price is fixed or determinable, and collectability is reasonably assured. Revenue generated from research and licensing agreements typically includes up-front signing or license fees, cost reimbursements, research services, minimum sublicense fees, milestone payments, and royalties on future licensees’ product sales.
	For revenue agreements with multiple-element arrangements, such as license and development agreements, the Company allocates revenue to each unit of accounting based on the relative selling price of each unit. When applying the relative selling price method, the Company determines the selling price for each deliverable using vendor-specific objective evidence or third-party evidence. If neither exists, the Company uses its best estimate of selling price for that deliverable. Revenue allocated is then recognized when the four basic revenue recognition criteria are met for each deliverable.
	The Company recognizes revenue from upfront payments ratably over the term of its estimated period of performance under the agreement which is recorded as licensing revenue. Reimbursements for development costs incurred under the Company’s license agreement with AstraZeneca are classified as collaborative development revenue. The Company recognizes cost reimbursement revenue under collaboration partnership agreements as the related research and development costs for services are rendered. Deferred revenue represents the portion of research or license payments received which has not been earned.
	Revenues from milestones, if they are nonrefundable and deemed substantive, are recognized upon successful accomplishment of the milestones. To the extent that non-substantive milestones are achieved and the Company has remaining performance obligations, milestones are deferred and recognized as revenue over the estimated remaining period of performance. The Company will recognize revenue associated with the non-substantive milestones upon achievement of the milestone if there are no undelivered units and it has no remaining performance obligations. The Company will account for sales-based milestones as royalties that will be recognized as revenue upon achievement of the milestone.
Stock-Based Compensation	Stock-Based Compensation
	The Company measures its stock-based payment awards made to employees and directors based on the estimated fair values of the awards and recognizes the compensation expense over the requisite service period. The Company has selected the Black-Scholes option-pricing model to estimate the fair value of its stock-based awards. Stock-based compensation expense is recognized using the straight-line method. Stock-based compensation expense is based on the value of the portion of stock-based payment awards that is ultimately expected to vest. As such, the Company’s stock-based compensation is reduced for the estimated forfeitures at the date of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates.
	The Company accounts for compensation expense related to stock options granted to non-employees based on the fair values estimated using the Black-Scholes model. Stock options granted to non-employees are remeasured at each reporting date until the award is vested.
Research and Development Costs	Research and Development Costs
	Research and development expenditures are expensed as incurred. Major components of research and development expenses consist of personnel costs, materials and supplies, and allocations of facilities-related costs, as well as fees paid to consultants and third parties that conduct certain research and development activities on the Company’s behalf. Payments made to other entities are under agreements that are generally cancelable by the Company. Nonrefundable advance payments for goods or services to be rendered 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.
Convertible Preferred Stock Warrant Liability	Convertible Preferred Stock Warrant Liability
	The Company accounts for freestanding warrants to purchase shares of convertible preferred stock that were contingently redeemable as liabilities in the balance sheets at their estimated fair value. Convertible preferred stock warrants are subject to remeasurement at each balance sheet date, and any change in fair value is recognized as a component of other expense, net in the statements of operations and comprehensive loss. The Company continued to adjust the carrying value of the warrants until the closing of the IPO, at which time the warrants were net exercised for shares of the Company’s common stock and the liability was reclassified to stockholders’ equity (deficit).
Comprehensive Loss	Comprehensive Loss
	Comprehensive loss is composed of two components: net loss and other comprehensive loss. Other comprehensive income (loss) refers to gains and losses that under GAAP are recorded as an element of stockholders’ equity (deficit), but are excluded from net loss. The Company did not record any transactions within other comprehensive income (loss) in the periods presented and, therefore, the net loss and comprehensive loss were the same for all periods presented.
Net Loss per Share	Net Loss per Share
	Basic net loss per common share is calculated by dividing the net loss by the weighted-average number of common shares outstanding during the period, without consideration of common stock equivalents. Diluted net loss per common share in the periods presented is the same as basic net loss per common share, since the effects of potentially dilutive securities are antidilutive.
Recent Accounting Pronouncements	Recent Accounting Pronouncements
	In July 2013, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update (“ASU”) 2013-11, Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists. The ASU concludes an unrecognized tax benefit should be presented as a reduction of a deferred tax asset when settlement in this manner is available under the law. The Company adopted this amendment as of January 1, 2014, which did not have a significant impact on the balance sheet.
	In May 2014, the FASB issued Accounting Standards Update 2014-09, Revenue from Contracts with Customers (“ASU 2014-09”), which converges the FASB and the International Accounting Standards Board standards on revenue recognition and will replace nearly all existing revenue recognition under U.S. GAAP. The core principle of ASU 2014-09 is that an entity should recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. This guidance is effective for the fiscal years and interim reporting periods beginning after December 15, 2016, at which time the Company may adopt the new standard under the full retrospective method or the modified retrospective method. Early adoption is not permitted. The Company has not yet selected a transition method nor has the Company determined the impact of the new standard on its financial statements and related disclosures.
	In August 2014, the Financial Accounting Standards Board issued Accounting Standards Update No. 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern (“ASU 2014-15”). ASU 2014-15 requires management to evaluate whether there is substantial doubt about an entity’s ability to continue as a going concern and to provide related footnote disclosures. In doing so, companies will have reduced diversity in the timing and content of footnote disclosures than under today’s guidance. ASU 2014-15 is effective for the Company in the first quarter of 2016 with early adoption permitted. The Company does not believe the impact of adopting ASU 2014-15 on its financial statements will be material.

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Summary of Fair Value Measurements of Company's Financial Assets and Liabilities	The following table sets forth the fair value of the Company’s financial assets and liabilities measured on a recurring basis by level within the fair value hierarchy:
		December 31, 2014
		Total			Level 1		Level 2		Level 3
					(in thousands)
	Assets:
	Money market funds	$	105,410		$	105,410	$	—	$	—
	Certificates of deposit		100			—		100		—
	Total	$	105,510		$	105,410	$	100	$	—
		December 31, 2013
		Total			Level 1		Level 2		Level 3
					(in thousands)
	Assets:
	Money market funds	$	32,472		$	32,472	$	—	$	—
	Certificates of deposit		180			—		180		—
	Total	$	32,652		$	32,472	$	180	$	—
	Liabilities:
	Convertible preferred stock warrant liability	$	6,456		$	—	$	—	$	6,456
	Total	$	6,456		$	—	$	—	$	6,456
Summary of Changes in Estimated Fair Value of Preferred Stock Warrant Liability	The following table sets forth a summary of the changes in the estimated fair value of the Company’s preferred stock warrants which were measured at fair value on a recurring basis (in thousands):
		Preferred Stock
		Warrant Liability
		(in thousands)
	Balance at December 31, 2012	$	2,950
	Net increase in fair value of warrant liabilities upon revaluation		3,506
	Balance at December 31, 2013	$	6,456
	Net increase in fair value of warrant liabilities upon revaluation		1,593
	Reclassification of warrant liability to additional paid-in capital upon completion of IPO		(8,049	)
	Balance at December 31, 2014	$	—

Property_and_Equipment_Tables

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2014
Property Plant And Equipment [Abstract]
Summary of Property and Equipment	Property and equipment consist of the following:
		December 31,
		2014			2013
		(in thousands)
	Laboratory equipment	$	3,039		$	2,315
	Office equipment and furniture		229			91
	Construction in progress		362			—
	Leasehold improvements		2,135			1,456
	Property and equipment, gross		5,765			3,862
	Less: accumulated depreciation and amortization		(3,634	)		(3,332	)
	Total property and equipment, net	$	2,131		$	530

Convertible_Preferred_Stock_Ta

Convertible Preferred Stock (Tables)	12 Months Ended
	Dec. 31, 2014
Class Of Stock Disclosures [Abstract]
Summary of Convertible Preferred Stock	Convertible preferred stock as of December 31, 2013 consisted of the following:
	Convertible Preferred Stock:	Shares		Shares		Net		Aggregate
		Authorized		Issued and		Carrying		Liquidation
				Outstanding		Value		Preference
		(In thousands, except share data)
	Series A		25,231,213		2,803,462	$	25,957	$	28,764
	Series B		83,598,535		8,713,760		30,198		30,310
	Total convertible preferred stock		108,829,748		11,517,222	$	56,155	$	59,074

Equity_Incentive_Plans_Tables

Equity Incentive Plans (Tables)	12 Months Ended
	Dec. 31, 2014
Summary of Activity Under 2008 Plan and 2014 Plan, Including Grants to Nonemployees and Restricted Stock Issued	The following table summarizes activity under the 2008 Plan and the 2014 Plan, including grants to nonemployees and restricted stock issued:
						Options Issued and
						Outstanding
		Shares Available for Grant				Number of Shares							Weighted- Average		Aggregate
													Exercise Price per		Intrinsic Value
													Share
															(in thousands)
	Balances at December 31, 2011		19,798					1,598,513				$		0.57
	Options authorized		114,428					—
	Options granted		(81,233	)				81,233						3.46
	Options exercised		—					(342,131	)					0.52
	Options canceled		43,848					(43,848	)					0.52
	Balance at December 31, 2012		96,841					1,293,767				$		0.77
	Options granted		(99,552	)				99,552						3.42
	Options exercised		—					(223,865	)					0.56
	Options canceled		6,625					(6,625	)					2.23
	Balance at December 31, 2013		3,914					1,162,829				$		1.03
	Options authorized		1,452,661					—
	Options granted		(188,888	)				188,888						24.41
	Options exercised		—					(336,398	)					0.71
	Options canceled		4,084					(4,084	)					2.21
	Options repurchased		3,511					(3,511	)					0.55
	Issuance of common stock for services		(10,000	)				—						—
	Balance at December 31, 2014		1,265,282					1,007,724				$		5.51		$	14,839
	Vested and expected to vest at December 31, 2014							990,889				$		5.27		$	14,746
	Vested at December 31, 2014							643,217				$		1.21		$	11,376
Summary of Weighted Average Assumptions to Estimate Fair Value of Stock Option Awards and Employee Stock Purchase Plan	The fair value of stock option awards to employees was estimated at the date of grant using a Black-Scholes option-pricing model with the following weighted-average assumptions:
		Year Ended December 31
		2014			2013				2012
	Expected term (years)		5.97			6.07				5.73
	Volatility		94	%		98	%			97	%
	Risk-free interest rate		1.79	%		1.35	%			0.79	%
	Dividend yield		—	%		—	%			—	%
Summary of Stock-Based Compensation Recognized	Total stock-based compensation recognized was as follows (in thousands):
		Year Ended December 31,
		2014			2013				2012
					(in thousands)
	Research and development	$	1,376		$	200			$	221
	General and administrative		316			152				252
	Total stock-based compensation	$	1,692		$	352			$	473
2014 Employee Stock Purchase Plan
Summary of Weighted Average Assumptions to Estimate Fair Value of Stock Option Awards and Employee Stock Purchase Plan	The following table illustrates the weighted-average assumptions for the Black-Scholes option-pricing model used in determining the fair value of ESPP purchase rights granted to employees:
		Year Ended December 31, 2014
	Expected term (years)		0.5
	Volatility		73	%
	Risk-free interest rate		0.05	%
	Dividend yield		—	%

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Reconciliation of Statutory Federal Income Tax Rate to the Company's Effective Tax Rate	The following is a reconciliation of the statutory federal income tax rate to the Company’s effective tax rate:
		Year Ended December 31,
		2014			2013			2012
	Expected income tax provision at the federal statutory rate		35	%		35	%		35	%
	State taxes, net of federal benefit		4.6			(1.4	)		—
	Change in valuation allowance		(17.9	)		(22.6	)		(38.6	)
	Nondeductible expenses		(20.6	)		(20.8	)		(5.2	)
	Tax credits		—			7.3			4.4
	Other		(3.2	)		0.3			4.4
	Income tax provision		(2.1	)%		(2.2	)%		—	%
Significant Components of the Company's Deferred Tax Assets	Significant components of the Company’s deferred tax assets are as follows:
		December 31,
		2014			2013
		(in thousands)
	Deferred tax assets:
	Net operating loss carryforwards	$	11,262		$	13,069
	Deferred revenue		11,099			9,723
	Research credits		1,260			1,734
	Other		1,201			475
	Gross deferred tax assets		24,822			25,001
	Valuation allowance		(24,741	)		(25,001	)
	Total deferred tax assets		81			—
	Deferred tax liabilities		(81	)		—
	Net deferred tax assets	$	—		$	—
Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits	A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows:
		December 31,
		2014			2013			2012
					(in thousands)
	Balance at beginning of year	$	1,411		$	1,064		$	807
	Additions based on tax positions related to prior year		405			—			—
	Additions based on tax positions related to current year		999			347			257
	Balance at end of year	$	2,815		$	1,411		$	1,064

Net_Loss_per_Share_Tables

Net Loss per Share (Tables)	12 Months Ended
	Dec. 31, 2014
Earnings Per Share [Abstract]
Computation of Net Loss Per Common Share	The following table sets forth the computation of net loss per common share (in thousands, except share and per share amounts):
		December 31,
		2014			2013			2012
	Numerator:
	Net loss	$	(3,214	)	$	(6,564	)	$	(9,785	)
	Denominator:
	Weighted average number of shares outstanding—basic and diluted		10,248,337			1,127,948			864,020
	Net loss per share—basic and diluted	$	(0.31	)	$	(5.82	)	$	(11.32	)
Calculation of Anti-dilutive Potentially Dilutive Securities Not Included in Diluted Per Share	Potentially dilutive securities that were not included in the diluted per share calculations because they would be anti-dilutive were as follows:
		December 31,
		2014			2013			2012
	Convertible preferred stock		—			11,517,222			11,517,222
	Options to purchase common stock		1,007,724			1,162,829			1,293,767
	Warrants to purchase convertible preferred stock		—			574,953			574,953
	Total		1,007,724			13,255,004			13,385,942

Commitments_and_Contingencies_

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2014
Commitments And Contingencies Disclosure [Abstract]
Schedule of Future Minimum Payments Under the Noncancelable Operating Lease	The future minimum payments under the noncancelable operating lease at December 31, 2014, are as follows (in thousands):
	Year ending December 31,	Amounts
	2015	$	843
	2016		868
	2017		895
	2018		921
	2019		653
	Total	$	4,180

Selected_Quarterly_Financial_D1

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Schedule of Selected Quarterly Financial Results from Operations	Selected quarterly financial results from operations for the years ended December 31, 2014 and 2013 are as follows (in thousands, except per share amounts):
		2014 Quarter End
		March 31,			June 30			September 30			December 31
	Total revenue	$	8,550		$	9,137		$	7,598		$	6,338
	Operating expenses		9,014			6,386			7,517			10,270
	Net income (loss)		(3,071	)		3,753			74			(3,970	)
	Net income (loss) per share:
	Basic		(2.44	)		0.2			—			(0.21	)
	Diluted		(2.44	)		0.18			—			(0.21	)
		2013 Quarter End
		March 31,			June 30			September 30			December 31
	Total revenue	$	6,556		$	7,291		$	6,593		$	8,488
	Operating expenses		6,966			8,142			7,479			9,206
	Net loss		(470	)		(891	)		(934	)		(4,269	)
	Basic and diluted net loss per common share		(0.45	)		(0.81	)		(0.81	)		(3.53	)

Organization_and_Basis_of_Pres1

Organization and Basis of Presentation - Additional Information (Details) (USD $)	0 Months Ended	12 Months Ended	0 Months Ended
	Jun. 18, 2014	Dec. 31, 2014	Jun. 24, 2014	Dec. 31, 2013
		Segment
Organization And Basis Of Presentation [Line Items]
Date of incorporation		17-Oct-07
Place of incorporation		Delaware
Number of operating segments		1
Reverse stock split, description		On June 18, 2014, the Companybs Amended and Restated Certificate of Incorporation became effective resulting in a reverse split of the Companybs common stock and convertible preferred stock at a 1-for-9 ratio (the bReverse Stock Splitb). The par value and the authorized shares of the common stock and convertible preferred stock were not adjusted as a result of the Reverse Stock Split. All issued and outstanding common stock, convertible preferred stock, warrants for preferred stock, options for common stock and per share amounts contained in the financial statements have been retroactively adjusted to reflect this Reverse Stock Split for all periods presented.
Reverse stock split ratio	0.11
Net proceeds from the IPO	$61,200,000
Underwriting discounts and commissions and expenses	7,800,000
Convertible preferred stock converted to common stock, value		56,155,000
Shares authorized			305,000,000
Common stock, shares authorized		300,000,000	300,000,000	130,360,121
Preferred stock, shares authorized		5,000,000	5,000,000	0
Common stock, par value		$0.00		$0.00
Preferred stock, par value		$0.00		$0.00
Preferred stock, shares outstanding		0		0
Common Stock
Organization And Basis Of Presentation [Line Items]
Stock issued during period, shares, new issues		4,928,900
Convertible preferred stock converted to common stock, shares			11,517,222
Convertible preferred stock converted to common stock, value			$56,200,000
IPO
Organization And Basis Of Presentation [Line Items]
Stock issued during period, shares, new issues			4,928,900
Additional common stock issued on exercise of option by Underwriters			642,900

Summary_of_Significant_Account2

Summary of Significant Accounting Policies - Additional Information (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Organization And Basis Of Presentation [Line Items]
Cash and cash equivalents original maturity dates	90 days or less
Restricted cash	$100	$180
Minimum
Organization And Basis Of Presentation [Line Items]
Property and equipment, estimated useful lives	3 years
Maximum
Organization And Basis Of Presentation [Line Items]
Property and equipment, estimated useful lives	5 years
Certificate of Deposit
Organization And Basis Of Presentation [Line Items]
Restricted cash	$100

Fair_Value_Measurements_Summar

Fair Value Measurements - Summary of Fair Value Measurements of Company's Financial Assets and Liabilities (Details) (Fair Value, Recurring, USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Assets:
Assets at fair value	$105,510	$32,652
Liabilities:
Liabilities at fair value		6,456
Convertible preferred stock warrant liability
Liabilities:
Liabilities at fair value		6,456
Level 1
Assets:
Assets at fair value	105,410	32,472
Liabilities:
Liabilities at fair value		0
Level 1 | Convertible preferred stock warrant liability
Liabilities:
Liabilities at fair value		0
Level 2
Assets:
Assets at fair value	100	180
Liabilities:
Liabilities at fair value		0
Level 2 | Convertible preferred stock warrant liability
Liabilities:
Liabilities at fair value		0
Level 3
Assets:
Assets at fair value	0	0
Liabilities:
Liabilities at fair value		6,456
Level 3 | Convertible preferred stock warrant liability
Liabilities:
Liabilities at fair value		6,456
Money Market Funds
Assets:
Assets at fair value	105,410	32,472
Money Market Funds | Level 1
Assets:
Assets at fair value	105,410	32,472
Money Market Funds | Level 2
Assets:
Assets at fair value	0	0
Money Market Funds | Level 3
Assets:
Assets at fair value	0	0
Certificate of Deposit
Assets:
Assets at fair value	100	180
Certificate of Deposit | Level 1
Assets:
Assets at fair value	0	0
Certificate of Deposit | Level 2
Assets:
Assets at fair value	100	180
Certificate of Deposit | Level 3
Assets:
Assets at fair value	$0	$0

Fair_Value_Measurements_Additi

Fair Value Measurements - Additional Information (Details)	12 Months Ended
	Dec. 31, 2013
Fair Value Disclosures [Abstract]
Fair value of preferred stock warrant liability, probability of IPO scenario, percentage	20.00%
Fair value of preferred stock warrant liability, probability of merger scenario, percentage	10.00%
Fair value of preferred stock warrant liability, probability of stay private scenario, percentage	70.00%

Fair_Value_Measurements_Summar1

Fair Value Measurements - Summary of Changes in Estimated Fair Value of Preferred Stock Warrant Liability (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Net increase in fair value of warrant liabilities upon revaluation	$1,593	$3,506	$950
Reclassification of warrant liability to additional paid-in capital upon completion of IPO	-8,049
Fair Value, Recurring | Preferred stock warrant liability
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning balance	6,456	2,950
Net increase in fair value of warrant liabilities upon revaluation	1,593	3,506
Reclassification of warrant liability to additional paid-in capital upon completion of IPO	-8,049
Ending balance	$0	$6,456

Property_and_Equipment_Summary

Property and Equipment - Summary of Property and Equipment (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Property Plant And Equipment [Line Items]
Property and equipment, gross	$5,765	$3,862
Less: accumulated depreciation and amortization	-3,634	-3,332
Total property and equipment, net	2,131	530
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	3,039	2,315
Office Equipment and Furniture
Property Plant And Equipment [Line Items]
Property and equipment, gross	229	91
Construction in Progress
Property Plant And Equipment [Line Items]
Property and equipment, gross	362
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	$2,135	$1,456

Property_and_Equipment_Additio

Property and Equipment - Additional Information (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property Plant And Equipment [Abstract]
Depreciation and amortization expense	$302	$592	$675

Collaboration_and_Licensing_Ag1

Collaboration and Licensing Agreements - Additional Information (Details) (USD $)	1 Months Ended			12 Months Ended
In Millions, unless otherwise specified	Feb. 28, 2014	31-May-14	Oct. 31, 2012	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2012
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Patent costs under responsibility of the company	$0.20
AstraZeneca
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Deferred Revenue, Additions		25	35	15
Future potential payments to be received					795
Deferred revenue					47.1
AstraZeneca | Future Development Milestones
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Future potential payments to be received					197.5
AstraZeneca | Launch, Commercialization, and Sales Milestones
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Future potential payments to be received					597.5
AstraZeneca | Amortization of Up-Front and Other License Fees
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Revenue recognized				8.1	18.4	3.2
AstraZeneca | Collaborative Development Services
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Revenue recognized				20.9	13.2	2.2
AstraZeneca | First Phase 3 Clinical Development Program
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Exercise of right, limited period					60 days
AstraZeneca | First Phase 3 Clinical Development Program | Funding Agreement One
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Co-funding amount					20
Royalties payable percentage					1.00%
AstraZeneca | First Phase 3 Clinical Development Program | Funding Agreement Two
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Co-funding amount					30
Royalties payable percentage					2.00%
AstraZeneca | First Phase 3 Clinical Development Program | Funding Agreement Three
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Co-funding amount					40
Royalties payable percentage					3.00%
Sanofi
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Future potential payments to be received					196.8
Revenue recognized		$1.25

Convertible_Preferred_Stock_Ad

Convertible Preferred Stock - Additional Information (Details) (USD $)	12 Months Ended	0 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Jun. 24, 2014
Class Of Stock [Line Items]
Convertible preferred stock converted to common stock, value	$56,155
Common Stock
Class Of Stock [Line Items]
Convertible preferred stock converted to common stock, shares		11,517,222
Convertible preferred stock converted to common stock, value		$56,200

Convertible_Preferred_Stock_Su

Convertible Preferred Stock - Summary of Convertible Preferred Stock (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, except Share data, unless otherwise specified
Class Of Stock [Line Items]
Convertible Preferred Stock Shares Authorized	0	108,829,748
Convertible Preferred Stock Shares Issued and Outstanding		11,517,222
Convertible Preferred Stock Net Carrying Value		$56,155
Convertible Preferred Stock Aggregate Liquidation Preference		59,074
Series A Convertible Preferred Stock
Class Of Stock [Line Items]
Convertible Preferred Stock Shares Authorized		25,231,213
Convertible Preferred Stock Shares Issued and Outstanding		2,803,462
Convertible Preferred Stock Net Carrying Value		25,957
Convertible Preferred Stock Aggregate Liquidation Preference		28,764
Series B Convertible Preferred Stock
Class Of Stock [Line Items]
Convertible Preferred Stock Shares Authorized		83,598,535
Convertible Preferred Stock Shares Issued and Outstanding		8,713,760
Convertible Preferred Stock Net Carrying Value		30,198
Convertible Preferred Stock Aggregate Liquidation Preference		$30,310

Preferred_Stock_Warrants_Addit

Preferred Stock Warrants - Additional Information (Details) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2013	Aug. 31, 2011
Class Of Stock [Line Items]
Fair value of preferred stock warrant liability, probability of IPO scenario, percentage	20.00%
Fair value of preferred stock warrant liability, probability of merger scenario, percentage	10.00%
Fair value of preferred stock warrant liability, probability of stay private scenario, percentage	70.00%
Convertible preferred stock warrant liability	$6,456
Series B Convertible Preferred Stock
Class Of Stock [Line Items]
Company issued warrants		574,953
Exercise price of the warrants		$0.09

Equity_Incentive_Plans_Additio

Equity Incentive Plans - Additional Information (Details) (USD $)	12 Months Ended			0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jan. 01, 2015	Jun. 18, 2014	Dec. 31, 2011
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period	4 years
Common stock reserved	1,454,549
Weighted-average grant-date estimated fair value of options granted	$18.53	$2.68	$2.56
Estimated fair value of common stock	$18.89
Employee stock purchase plan initial offering commenced period	1-Sep-14
Employee stock purchase plan initial offering ending period	27-Feb-15
Shares available for future grant	1,265,282	3,914	96,841			19,798
Common stock outstanding subject to repurchase	0	286,217
Liabilities related to early exercise of options	$0	$163,000
Stock-based compensation charge	800,000
Unrecognized stock based compensation expense	3,200,000
Unrecognized stock based compensation expense, weighted-average remaining recognition period	2 years 3 months 18 days
Options Issued and Outstanding Number of Shares, Options granted	188,888	99,552	81,233
Issuance of common stock for services (Shares)	10,000
Issuance of common stock for services, amount	208,000
2014 Equity Incentive Award Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved	1,419,328
Increase in shares reserved for issuance, maximum shares to be issued up on exercise of stock options	10,683,053
Possible increase in shares reserved for issuance as percentage of outstanding stock	4.00%
2008 Stock Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved	35,221
2014 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved	202,762
Increase in shares reserved for issuance, maximum shares to be issued up on exercise of stock options	2,230,374
Possible increase in shares reserved for issuance as percentage of outstanding stock	1.00%
Shares available for future grant	202,762
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based award accelerated vesting number of shares	58,969
Employees Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average grant-date estimated fair value of options granted	$18.57	$2.68	$2.56
Nonemployees Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average grant-date estimated fair value of options granted	$20.77	$3.43
Stock-based compensation charge	$100,000	$2,000	$0
Options Issued and Outstanding Number of Shares, Options granted	10,000	3,333
Subsequent Event | 2014 Equity Incentive Award Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Increase in shares reserved for issuance, maximum shares to be issued up on exercise of stock options				743,569
Subsequent Event | 2014 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Increase in shares reserved for issuance, maximum shares to be issued up on exercise of stock options				185,892
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Repurchase price of common stock		$1.08
Maximum | 2008 Stock Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Increase in shares reserved for issuance, maximum shares to be issued up on exercise of stock options					1,153,279
Maximum | Nonemployees Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period	3 years
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Repurchase price of common stock		$0.27

Equity_Incentive_Plans_Summary

Equity Incentive Plans - Summary of Activity Under 2008 Plan and 2014 Plan, Including Grants to Nonemployees and Restricted Stock Issued (Details) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Shares Available for Grant
Shares Available for Grant, Beginning balance	3,914	96,841	19,798
Shares Available for Grant, Options authorized	1,452,661		114,428
Shares Available for Grant, Options granted	-188,888	-99,552	-81,233
Shares Available for Grant, Options exercised	0	0	0
Shares Available for Grant, Options canceled	4,084	6,625	43,848
Shares Available for Grant, Options repurchased	3,511
Shares Available for Grant, Ending balance	1,265,282	3,914	96,841
Shares Available for Grant, Issuance of common stock for services	-10,000
Options Issued and Outstanding
Options Issued and Outstanding Number of Shares, Beginning balance	1,162,829	1,293,767	1,598,513
Options Issued and Outstanding Number of Shares, Options authorized	0		0
Options Issued and Outstanding Number of Shares, Options granted	188,888	99,552	81,233
Options Issued and Outstanding Number of Shares, Options exercised	-336,398	-223,865	-342,131
Options Issued and Outstanding Number, Options cancelled	-4,084	-6,625	-43,848
Options Issued and Outstanding Number of Shares, Options repurchased	-3,511
Options Issued and Outstanding Number of Shares, Issuance of common stock for services	0
Options Issued and Outstanding Number of Shares, Ending balance	1,007,724	1,162,829	1,293,767
Options Issued and Outstanding Number of Shares, Expected to vest	990,889
Options Issued and Outstanding Number of Shares, Vested	643,217
Options Issued and Outstanding Weighted Average Exercise Price per Share
Options Issued and Outstanding Weighted Average Exercise Price per Share, Beginning balance	$1.03	$0.77	$0.57
Options Issued and Outstanding Weighted Average Exercise Price per Share, Options granted	$24.41	$3.42	$3.46
Options Issued and Outstanding Weighted Average Exercise Price per Share, Options exercised	$0.71	$0.56	$0.52
Options Issued and Outstanding Weighted Average Exercise Price per Share, Options canceled	$2.21	$2.23	$0.52
Options Issued and Outstanding Weighted Average Exercise Price per Share, Options repurchased	$0.55
Options Issued and Outstanding Weighted Average Exercise Price per Share, Issuance of common stock for services	$0
Options Issued and Outstanding Weighted Average Exercise Price per Share, Ending balance	$5.51	$1.03	$0.77
Options Issued and Outstanding Weighted Average Exercise Price per Share, Expected to vest	$5.27
Options Issued and Outstanding Weighted Average Exercise Price per Share, Vested	$1.21
Aggregate Intrinsic Value
Aggregate Intrinsic Value, Ending balance	$14,839
Aggregate Intrinsic Value, Expected to Vest	14,746
Aggregate Intrinsic Value, Vested	$11,376

Equity_Incentive_Plans_Summary1

Equity Incentive Plans - Summary of Weighted Average Assumptions to Estimate Fair value of Stock Option Awards and Employee Stock Purchase Plan (Details)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	5 years 11 months 19 days	6 years 26 days	5 years 8 months 23 days
Volatility	94.00%	98.00%	97.00%
Risk-free interest rate	1.79%	1.35%	0.79%
Dividend yield	0.00%	0.00%	0.00%
2014 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	6 months
Volatility	73.00%
Risk-free interest rate	0.05%
Dividend yield	0.00%

Equity_Incentive_Plans_Summary2

Equity Incentive Plans - Summary of Stock-Based Compensation Recognized (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation	$1,692	$352	$473
Research and Development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation	1,376	200	221
General and Administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation	$316	$152	$252

Income_Taxes_Reconciliation_of

Income Taxes - Reconciliation of Statutory Federal Income Tax Rate to the Company's Effective Tax Rate (Details)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Expected income tax provision at the federal statutory rate	35.00%	35.00%	35.00%
State taxes, net of federal benefit	4.60%	-1.40%
Change in valuation allowance	-17.90%	-22.60%	-38.60%
Nondeductible expenses	-20.60%	-20.80%	-5.20%
Tax credits		7.30%	4.40%
Other	-3.20%	0.30%	4.40%
Income tax provision	-2.10%	-2.20%	0.00%

Income_Taxes_Significant_Compo

Income Taxes - Significant Components of the Company's Deferred Tax Assets (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Deferred tax assets:
Net operating loss carryforwards	$11,262	$13,069
Deferred revenue	11,099	9,723
Research credits	1,260	1,734
Other	1,201	475
Gross deferred tax assets	24,822	25,001
Valuation allowance	-24,741	-25,001
Total deferred tax assets	81
Deferred tax liabilities	-81
Net deferred tax assets	$0	$0

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Line Items]
Increase (decrease) in deferred tax valuation allowance	($300,000)	$1,500,000
Unrecognized tax benefits that would affect the effective tax rate if recognized	2,800,000	1,400,000	1,100,000
Accrued interest and penalties related to unrecognized tax benefits	0	0	0
Federal Tax Authority
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	28,000,000
Operating loss carryforward expiration year	expire beginning in 2028
Federal Tax Authority | Research and Development Tax Credit
Income Tax Disclosure [Line Items]
Tax credit carryforwards	2,100,000
Tax credit carryforward expiration year	2029
State Tax Authority
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	25,600,000
Operating loss carryforward expiration year	expire beginning in 2018
State Tax Authority | Research and Development Tax Credit
Income Tax Disclosure [Line Items]
Tax credit carryforwards	$2,300,000

Income_Taxes_Reconciliation_of1

Income Taxes - Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Balance at beginning of year	$1,411	$1,064	$807
Additions based on tax positions related to prior year	405
Additions based on tax positions related to current year	999	347	257
Balance at end of year	$2,815	$1,411	$1,064

Net_Loss_per_Share_Computation

Net Loss per Share - Computation of Net Loss Per Common Share (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Numerator:
Net loss	($3,970)	$74	$3,753	($3,071)	($4,269)	($934)	($891)	($470)	($3,214)	($6,564)	($9,785)
Denominator:
Weighted average number of shares outstandingbbasic and diluted									10,248,337	1,127,948	864,020
Net loss per sharebbasic and diluted					($3.53)	($0.81)	($0.81)	($0.45)	($0.31)	($5.82)	($11.32)

Net_Loss_per_Share_Summary_of_

Net Loss per Share - Summary of Antidilutive Securities Excluded from Computation of Diluted Net Income (Loss) per Share (Details)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, shares	1,007,724	13,255,004	13,385,942
Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, shares	0	11,517,222	11,517,222
Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, shares	1,007,724	1,162,829	1,293,767
Warrants to Purchase Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, shares	0	574,953	574,953

Related_Party_Transactions_Add

Related Party Transactions - Additional Information (Details) (Clinical Operations Consulting Arrangement, Spouse of Executive Officer, USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Clinical Operations Consulting Arrangement | Spouse of Executive Officer
Related Party Transaction [Line Items]
Research and development service expenses	$0.20	$0.20	$0.10

Commitments_and_Contingencies_1

Commitments and Contingencies - Additional Information (Details) (USD $)	1 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Loss Contingencies [Line Items]
Lease expiration date	30-Sep-16
Amount provided lessor with irrevocable letter of credit		$100,000
Rent expense under operating leases		600,000	500,000	400,000
Number of days for written terminate indemnification agreement		90 days
Liabilities recorded associated with indemnification agreement		52,732,000	50,228,000
Guarantees and Indemnifications
Loss Contingencies [Line Items]
Liabilities recorded associated with indemnification agreement		0	0
Research and Development Equipment
Loss Contingencies [Line Items]
Purchase commitments		700,000
Office Space
Loss Contingencies [Line Items]
Purchase commitments		1,200,000
Amended Facility Lease Agreement
Loss Contingencies [Line Items]
Lease expiration date		30-Sep-19
Lease improvement allowance maximum amount		$600,000

Commitments_and_Contingencies_2

Commitments and Contingencies - Schedule of Future Minimum Payments Under the Non cancelable Operating Lease (Details) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified
Commitments And Contingencies Disclosure [Abstract]
2015	$843
2016	868
2017	895
2018	921
2019	653
Total	$4,180

Selected_Quarterly_Financial_D2

Selected Quarterly Financial Data (Unaudited) - Schedule of Selected Quarterly Financial Results from Operations (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Information Disclosure [Abstract]
Total revenue	$6,338	$7,598	$9,137	$8,550	$8,488	$6,593	$7,291	$6,556	$31,623	$28,928	$5,410
Operating expenses	10,270	7,517	6,386	9,014	9,206	7,479	8,142	6,966	33,187	31,793	14,215
Net income (loss)	($3,970)	$74	$3,753	($3,071)	($4,269)	($934)	($891)	($470)	($3,214)	($6,564)	($9,785)
Net income (loss) per share:
Basic	($0.21)		$0.20	($2.44)
Diluted	($0.21)		$0.18	($2.44)
Basic and diluted net loss per common share					($3.53)	($0.81)	($0.81)	($0.45)	($0.31)	($5.82)	($11.32)