Immunic (IMUX) 10-K 20 Mar 15 2014 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2014	Feb. 27, 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	VTL
Entity Registrant Name	VITAL THERAPIES INC
Entity Central Index Key	1280776
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		23,993,389
Entity Public Float			$399.10

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Current assets:
Cash and cash equivalents	$102,238	$38,186
Restricted cash	1,592	963
Deferred financing costs		3,506
Other current assets and prepaid expenses	986	1,200
Total current assets	104,816	43,855
Property and equipment, net	3,068	2,467
Other assets	198	263
Total assets	108,082	46,585
Current liabilities:
Accounts payable	1,153	1,224
Accrued expenses	8,875	3,253
Future purchase rights liabilities		2,600
Other current liabilities	250	369
Total current liabilities	10,278	7,446
Other long-term liabilities	241	321
Commitments and contingencies
Stockholders' equity (deficit):
Preferred stock, $0.0001 par value; 20,000,000 and 25,000,000 (4,498,599 undesignated) authorized at December 31, 2014 and 2013, respectively; no shares issued and outstanding at December 31, 2014 and 2013
Common stock, $0.0001 par value; 130,000,000 and 29,250,000 shares authorized at December 31, 2014 and 2013, respectively; 23,982,786 and 606,238 shares issued and outstanding at December 31, 2014 and 2013, respectively	2
Additional paid-in capital	248,305	58,413
Accumulated other comprehensive income	89	96
Accumulated deficit	-150,833	-103,166
Total stockholders' equity (deficit)	97,563	-44,657
Total liabilities, redeemable convertible preferred stock, and stockholders' equity (deficit)	108,082	46,585
Convertible Preferred Stock (Junior) [Member]
Current liabilities:
Convertible preferred stock		1,359
Redeemable Convertible Preferred Stock (Senior) [Member]
Current liabilities:
Convertible preferred stock		$82,116

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Preferred stock, par value	$0.00	$0.00
Preferred stock, shares authorized	20,000,000	25,000,000
Preferred stock, shares authorized undesignated		4,498,599
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$0.00	$0.00
Common stock, shares authorized	130,000,000	29,250,000
Common stock, shares issued	23,982,786	606,238
Common stock, shares outstanding	23,982,786	606,238
Convertible Preferred Stock (Junior) [Member]
Convertible preferred stock, par value	$0.00	$0.00
Convertible preferred stock, shares designated	0	3,501,401
Convertible preferred stock, shares issued		3,501,400
Convertible preferred stock, shares outstanding		3,501,401
Redeemable Convertible Preferred Stock (Senior) [Member]
Convertible preferred stock, par value	$0.00	$0.00
Convertible preferred stock, shares designated	0	17,000,000
Convertible preferred stock, shares issued		10,212,007
Convertible preferred stock, shares outstanding		10,212,007

Consolidated_Statements_of_Ope

Consolidated Statements of Operations (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating expenses:
Research and development	$39,479	$21,787	$5,097
General and administrative	10,863	9,615	4,483
Total operating expenses	50,342	31,402	9,580
Loss from operations	-50,342	-31,402	-9,580
Other income (expense):
Interest income	19	5	4
Interest expense			-413
Other income (expense), net	56	-15	7
Revaluation of preferred stock warrant liabilities			180
Revaluation of future purchase rights liabilities	2,600	-1,306	3,101
Total other income (expense)	2,675	-1,316	2,879
Net loss	-47,667	-32,718	-6,701
Amortization of deemed dividend	-4,744	-64
Accretion to redemption value of redeemable convertible preferred stock	-4,410	-6,303	-942
Net loss attributable to common stockholders	($56,821)	($39,085)	($7,643)
Net loss per share attributable to common stockholders, basic and diluted	($3.54)	($74.86)	($17.89)
Weighted-average common shares outstanding, basic and diluted	16,054,452	522,102	427,117

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Loss (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Comprehensive Income [Abstract]
Net loss	($47,667)	($32,718)	($6,701)
Other comprehensive (loss) income:
Foreign currency translation	-7	8	5
Total comprehensive loss	($47,674)	($32,710)	($6,696)

Consolidated_Statements_of_Red

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (USD $)	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Redeemable Convertible Preferred Stock (Senior) [Member]	Redeemable Convertible Preferred Stock (Senior) [Member]	Redeemable Convertible Preferred Stock (Senior) [Member]	Junior Convertible, and senior Redeemable Convertible Preferred Stock [Member]	Junior Convertible, and senior Redeemable Convertible Preferred Stock [Member]	Junior Convertible, and senior Redeemable Convertible Preferred Stock [Member]
In Thousands, except Share data							Common Stock [Member]	Additional Paid-in Capital [Member]		Convertible Preferred Stock (Junior) [Member]	Redeemable Convertible Preferred Stock (Senior) [Member]
Beginning balance at Dec. 31, 2011									$54,658
Beginning balance at Dec. 31, 2011	-54,853		8,811	83	-63,747
Beginning balance (in shares) at Dec. 31, 2011									90,267
Beginning balance (in shares) at Dec. 31, 2011		9,097
Private placement of convertible preferred stock										1,326	23,965
Private placement of convertible preferred stock (shares)										3,501,400	3,518,199
Net loss	-6,701				-6,701
Other comprehensive income (loss)	5			5
Stock-based compensation	144		144
Conversion of preferred stock to common stock	54,715		54,715						-54,715
Conversion of preferred stock to common stock (shares)		458,070							-90,267
Accretion to redemption value of redeemable convertible preferred stock	-942		-942						942
Ending balance at Dec. 31, 2012									26,176
Ending balance at Dec. 31, 2012	-7,632		62,728	88	-70,448
Ending balance (in shares) at Dec. 31, 2012									7,019,599
Ending balance (in shares) at Dec. 31, 2012		467,167
Private placement of convertible preferred stock						905		905			50,996
Private placement of convertible preferred stock (shares)											6,693,808
Net loss	-32,718				-32,718
Other comprehensive income (loss)	8			8
Exercise of stock options, net of repurchase liability	135		135
Exercise of stock options, net of repurchase liability (shares)		139,071
Stock-based compensation	948		948
Amortization of deemed dividend	-64
Accretion to redemption value of redeemable convertible preferred stock	-6,303		-6,303						6,303
Ending balance at Dec. 31, 2013									83,475
Ending balance at Dec. 31, 2013	-44,657		58,413	96	-103,166
Ending balance (in shares) at Dec. 31, 2013									13,713,407
Ending balance (in shares) at Dec. 31, 2013		606,238
Private placement of convertible preferred stock											18,167
Private placement of convertible preferred stock (shares)											2,296,016
Net loss	-47,667				-47,667
Other comprehensive income (loss)	-7			-7
Exercise of stock options and release of stock option early exercise repurchase liability	956		956
Exercise of stock options and release of stock option early exercise repurchase liability (shares)		142,041
Exercise of stock options, net of repurchase liability (shares)	142,041
Stock-based compensation	2,510		2,510
Amortization of deemed dividend	-4,744		-4,744						4,744
Conversion of preferred stock to common stock						110,796	1	110,795			-110,796
Conversion of preferred stock to common stock (shares)							16,009,423				-16,009,423
Accretion to redemption value of redeemable convertible preferred stock	-4,410		-4,410						4,410
Initial public offering, net issuance costs	51,933	1	51,932
Initial public offering, net issuance costs (shares)		5,175,000
Adjustment for fractional shares	0	0	0	0	0				0
Adjustment for fractional shares (shares)		84
Issuance of common stock, net of issuance costs	32,853		32,853
Issuance of common stock, net of issuance costs (shares)		2,050,000
Ending balance at Dec. 31, 2014	$97,563	$2	$248,305	$89	($150,833)
Ending balance (in shares) at Dec. 31, 2014		23,982,786

Consolidated_Statement_of_Cash

Consolidated Statement of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities:
Net loss	($47,667)	($32,718)	($6,701)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,087	799	651
Stock-based compensation	2,510	948	144
Non-cash interest expense			382
Revaluation of preferred stock warrant liabilities			-180
Revaluation of future purchase rights liabilities	-2,600	1,306	-3,101
Gain on sale of equipment			-7
Other	21	-17	41
Changes in operating assets and liabilities:
Other assets and prepaid expenses	279	-1,141	-242
Accounts payable	46	-91	-219
Accrued expenses	5,499	2,266	-12
Net cash used in operating activities	-40,825	-28,648	-9,244
Cash flows from investing activities:
Purchases of short-term investments		-2,999	-13,992
Sales of short-term investments		17,000
Proceeds from sale of equipment			20
Increase in restricted cash	-631	-608	-355
Purchases of property and equipment	-1,409	-1,484	-261
Net cash (used in) provided by investing activities	-2,040	11,909	-14,588
Cash flows from financing activities:
Proceeds from debt, net of issuance costs			6,934
Deferred financing costs		-3,112
Principal payments on term loan			-533
Proceeds from issuance of common stock, net of issuance costs	87,899
Proceeds from issuance of preferred stock, net of issuance costs	18,167	53,195	21,100
Proceeds from exercise of stock options	852	135
Proceeds from early exercise of stock options		227
Net cash provided by financing activities	106,918	50,445	27,501
Effect of exchange rate changes on cash and cash equivalents	-1	3	5
Net change in cash and cash equivalents	64,052	33,709	3,674
Cash and cash equivalents, beginning of period	38,186	4,477	803
Cash and cash equivalents, end of period	102,238	38,186	4,477
Supplemental cash flow information:
Cash paid for interest			32
Supplemental disclosure of non-cash investing and financing activities:
Deferred offering costs included in liabilities		394
Purchase of property and equipment included in liabilities	277	170	502
Leasehold improvements paid for by landlord		478
Release of stock option early exercise repurchase liability	104
Conversion of debt for redeemable convertible preferred stock			7,296
Conversion of redeemable convertible preferred stock to common stock	110,796		54,715
Valuation of future purchase rights upon issuance		1,294	3,101
Beneficial conversion underlying the senior preferred stock		969
Accretion to redemption value of redeemable convertible preferred stock	4,410	6,303	942
Amortization of deemed dividend	$4,744	$64

Description_of_Business_and_Ba

Description of Business and Basis of Financial Statements	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Description of Business and Basis of Financial Statements	1. Description of Business and Basis of Financial Statements
	Description of Business
	We are a biotherapeutic company focused on developing a cell-based therapy targeting the treatment of all forms of acute liver failure. Our product candidate, currently in Phase 3 clinical trials, the ELAD® System or ELAD, is an extracorporeal human cell-based bio-artificial liver therapy designed to allow the patient’s own liver to regenerate to a healthy state, or to stabilize the patient until transplant. Since inception, we have devoted essentially all of our efforts to product development, clinical testing and pilot manufacturing and have not realized revenues from our planned principal operations. Our business, operating results, financial condition, and growth prospects are subject to significant risks and uncertainties, including failing to obtain regulatory approval to commercialize and failing to secure additional funding to complete development of and to commercialize our product candidate.
	We began operations as a California corporation on May 23, 2003 through the acquisition of the assets and business of VitaGen, Inc. and in June 2003 changed our name to Vital Therapies, Inc. In January 2004, we were re-incorporated in Delaware. Our headquarters are located in San Diego, California.
	Basis of Presentation and Consolidation
	The accompanying consolidated financial statements have been prepared in conformity with United States generally accepted accounting principles, or GAAP, and include the accounts of Vital Therapies, Inc. and its wholly-owned subsidiaries located in the United Kingdom (currently inactive) and China. All intercompany accounts and transactions have been eliminated in consolidation. We manage our operations as a single segment for the purposes of assessing performance and making operating decisions.
	We previously were classified as a “development stage entity” under GAAP and, as such, were required to present inception-to-date information in our statements of operations, comprehensive loss, stockholders’ equity, and cash flows. In June 2014, the Financial Accounting Standards Board, or FASB, issued an accounting standards update that eliminates the concept of a development stage entity from GAAP and removes the related incremental reporting requirements, which we elected to early adopt. See Note 2 for additional information on this standard.

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 GAAP requires us to make certain estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Actual results could differ materially from those estimates and assumptions.
	Cash and Cash Equivalents
	Cash and cash equivalents consist of cash and highly-liquid investments with original maturities of three months or less when acquired and are stated at cost, which approximates market value.
	Restricted Cash
	Restricted cash relates to amounts reserved for various clinical trial obligations and lease arrangements at December 31, 2014 and 2013, respectively, as well as for certain provisions of the junior preferred stock agreement at December 31, 2013.
	Fair Value of Financial Instruments
	Fair value is defined as the price that would be received to sell an asset or be paid to transfer a liability in an orderly transaction between market participants on the measurement date. Accounting guidance establishes a fair value hierarchy that requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. The standard describes three levels of inputs that may be used to measure fair value:
	Level 1—Quoted prices in active markets for identical assets or liabilities. Our Level 1 assets consisted of U.S. treasuries and money market funds for the periods presented. We had no Level 1 liabilities for any period presented.
	Level 2—Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in markets with insufficient volume or infrequent transactions (less active markets), or model-derived valuations in which all significant inputs are observable or can be derived principally from or corroborated with observable market data for substantially the full term of the assets or liabilities. We had no Level 2 assets or liabilities for any period presented.
	Level 3—Unobservable inputs to the valuation methodology that are significant to the measurement of the fair value of assets or liabilities. Our Level 3 liabilities included preferred stock warrants and future purchase rights liabilities during the periods presented. We had no Level 3 assets in any period presented. We estimated the fair value of the preferred stock warrants and the future purchase rights using a binomial lattice model depending on the underlying attributes of the preferred stock warrants or future purchase rights, as applicable. Upon the completion of our initial public offering, or IPO, in April 2014, the future purchase rights liabilities terminated. See “Future Purchase Rights Liabilities” below.
	The carrying value of cash and cash equivalents, restricted cash, other current assets and prepaid expenses, accounts payable, and accrued expenses approximate fair value due to the short period of time to maturity.
	The future purchase rights were recorded at their estimated fair value at the date of issuance. The binomial lattice model used in the determination of the estimated fair value of the future purchase rights was based on various assumptions, including the estimated fair value of our senior preferred and common stock. We recorded subsequent adjustments to reflect the increase or decrease in estimated fair value at each reporting date as a gain or loss.
	Deferred Financing Costs
	Deferred financing costs represent direct costs associated with the issuance of our corporate securities. Direct costs include, but are not limited to, the legal, accounting and printing costs. Indirect costs associated with the issuance of corporate securities are expensed as incurred. Deferred financing costs as of December 31, 2013 were offset against the proceeds from our IPO in April 2014.
	Property and Equipment, Depreciation and Amortization
	Property and equipment are recorded at cost and depreciated using the straight-line method over the estimated useful lives of the assets (generally three to five years). Leasehold improvements are stated at cost and amortized on a straight-line basis over the lesser of the remaining term of the related lease or the estimated useful lives of the assets. Construction in progress is not depreciated until the underlying asset is placed in service. Repairs and maintenance costs are charged to expense as incurred.
	Impairment of Long-lived Assets
	Long-lived assets consist primarily of property and equipment. We review long-lived assets when events and circumstances indicate that the carrying amount of an asset may not be recoverable. If an asset is considered to be impaired, the impairment recognized is the amount by which the carrying value of the asset exceeds its fair value.
	Redeemable Convertible Preferred Stock
	Our junior convertible and senior redeemable convertible preferred stock were classified as mezzanine in accordance with authoritative guidance for the classification and measurement of potentially redeemable securities, as the preferred stock was conditionally redeemable at the holder’s option or upon certain change in control events that are outside our control, including liquidation, sale, or transfer of control of the company. In conjunction with our IPO in April 2014, all shares of our junior convertible and senior redeemable convertible preferred stock were converted to common stock.
	Warrants to Purchase Redeemable Convertible Preferred Stock
	We classify our preferred stock warrants that are either puttable or that are redeemable as liabilities on the consolidated balance sheets at fair value. At the end of each reporting period, changes in fair value during the period are recorded as a component of other income (expense), net. In February 2012, a final valuation adjustment was recognized for these preferred stock warrants prior to their conversion to common stock warrants in conjunction with a junior preferred stock offering.
	Future Purchase Rights Liabilities
	The future purchase rights liabilities were recorded at their estimated fair value on the date of issuance as a discount on the underlying preferred stock and are re-measured to reflect changes in the estimated fair value at each reporting date, with any decrease or increase in the estimated fair value being recorded as other income or expense, respectively. The fair value of these liabilities was estimated using a binomial lattice model based on the characteristics of the common and preferred stock on the valuation date, probabilities related to our operations and clinical development, as well as assumptions for volatility, remaining expected life, risk-free interest rate and, in some cases, credit spread. Changes in the fair value of the future purchase rights fluctuated in conjunction with increases or decreases in the implied fair value of our common stock, and the number of preferred and common shares and future purchase rights outstanding relative to our enterprise value at each reporting date. In April 2014, the remaining future purchase rights terminated upon the conversion of all senior preferred stock to common stock in conjunction with our IPO and the remaining balance of the future purchase rights liabilities was recorded as other income in our consolidated statement of operations for the period.
	Research and Development
	Research and development costs consist primarily of employee-related expenses, costs incurred for clinical trial sites, contractors and contract research organizations engaged in the development of the ELAD System, expenses associated with obtaining regulatory approvals, and the cost of acquiring and manufacturing clinical trial materials. All research and development costs are expensed as incurred.
	Stock-based Compensation
	We measure and recognize compensation expense for all stock-based payments made to employees and directors based on estimated fair value, net of an estimated forfeiture rate, and to consultants based on estimated fair value. Currently, our stock-based awards consist only of stock options; however, future grants under our equity compensation plans may consist of shares of restricted stock and restricted stock units. We estimate the fair value of stock options granted using the Black-Scholes-Merton, or BSM, option pricing model, which requires the use of estimates to value employee stock-based compensation at the date of grant.
	We recognize stock-based compensation cost for employees and directors on a straight-line basis over the requisite service period of the award. Stock-based compensation expense is recognized only for those awards that are ultimately expected to vest. We estimate forfeitures based on an analysis of our historical employee turnover and will continue to evaluate the appropriateness of the forfeiture rate based on actual forfeiture experience, analysis of employee turnover and other factors. We will revise the forfeiture estimate, if necessary, in subsequent periods if actual forfeitures differ from those estimates. Changes in forfeiture estimates, which have not been material to date, impact compensation cost in the period in which the change in estimate occurs.
	The fair value of options granted to consultants is estimated using the BSM option pricing model and is re-measured at each reporting date with changes in fair value recognized as expense in the consolidated statements of operations.
	The BSM option pricing model requires the input of highly subjective assumptions, including the risk-free interest rate, the expected dividend yield of our common stock, the expected volatility of the price of our common stock, and the expected term of the option. These estimates involve inherent uncertainties and the application of management’s judgment. If factors change and different assumptions are used, our stock-based compensation expense could be materially different in the future. These assumptions are estimated as follows:
	Risk-free Interest Rate
	We base the risk-free interest rate assumption on zero-coupon U.S. treasury instruments appropriate for the expected term of the stock option grants.
	Expected Dividend Yield
	We base the expected dividend yield assumption on the fact that we have never paid cash dividends and have no present intention to pay cash dividends. Consequently, we used an expected dividend yield of zero.
	Expected Volatility
	The expected stock price volatility for our common stock is estimated based on volatilities of a peer group of similar publicly-traded, biotechnology companies by taking the average historic price volatility for the peers for a period equivalent to the expected term of the stock option grants. We do not use our average historic price volatility as we have only been a publicly-traded company since April 2014.
	Expected Term
	The expected term represents the period of time that options are expected to be outstanding. As we do not have sufficient historical experience for determining the expected term of the stock option awards granted we have determined the expected life assumption using either the simplified method, which is an average of the contractual term of the option and its ordinary vesting period, or the comparable average expected term utilizing those companies in the peer group as noted above.
	Common Stock Valuation
	Due to the absence of a public market trading our common stock prior to the completion of our IPO in April 2014, it is necessary to estimate the fair value of the common stock underlying our stock-based awards when performing fair value calculations using the BSM option pricing model. The fair value of the common stock underlying our stock-based awards was assessed for each grant date by our board of directors. All options to purchase shares of our common stock have been granted with an exercise price per share no less than the fair value per share of our common stock underlying those options on the date of grant.
	In the absence of a public trading market for our common stock prior to our IPO, we determined the estimated fair value of our common stock using methodologies, approaches, and assumptions consistent with the American Institute of Certified Public Accountants, or AICPA, Audit and Accounting Practice Aid Series: Valuation of Privately Held Company Equity Securities Issued as Compensation, or the AICPA Practice Aid.
	Leases
	We lease all of our office space and enter into various other lease agreements in conducting our business. At the inception of each lease, we evaluate the lease agreement to determine whether the lease is an operating or capital lease. Some of our lease agreements may contain renewal options, tenant improvement allowances, rent holidays or rent escalation clauses. When such items are included in a lease agreement, we record a deferred rent asset or liability equal to the difference between the rent expense and future minimum lease payments due. The rent expense related to operating leases is recognized on a straight-line basis in the statements of operations over the terms of the leases. In cases where the lessor grants leasehold improvement allowances that reduce our rent expense, we capitalize the improvements as incurred and recognize deferred rent, which is amortized over the shorter of the lease term or the expected useful life of the improvements.
	Comprehensive Loss
	Comprehensive loss is defined as the change in equity during a period from transactions and other events and circumstances from non-owner sources. Comprehensive loss has been reflected in the consolidated statements of comprehensive loss and as a separate component of the consolidated statements of redeemable convertible preferred stock and stockholders’ equity (deficit) for all periods presented.
	Foreign Currency Translation and Transactions
	The functional currencies of each our subsidiaries in the United Kingdom (currently inactive) and China is the local currency. Assets and liabilities of the subsidiaries are translated at the rate of exchange at the balance sheet date. Expenses are translated at the average rate of exchange rates in effect during the reporting period. Gains and losses resulting from foreign currency translation are included in accumulated other comprehensive income in the accompanying consolidated balance sheets. Gains and losses resulting from foreign currency transactions are included in the results of operations, which to date, have not been significant.
	Income Taxes
	We account for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the consolidated financial statements. Under this method, deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period that includes the enactment date.
	We recognize net deferred tax assets to the extent we believe these assets are more likely than not to be realized. In making such a determination, management considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax-planning strategies, and results of recent operations. If management determines that we would be able to realize our deferred tax assets in the future in excess of their net recorded amount, management would make an adjustment to the deferred tax asset valuation allowance, which would reduce the provision for income taxes. As of December 31, 2014 and 2013, respectively, we maintained a full valuation allowance against our entire balance of deferred tax assets.
	We record uncertain tax positions in accordance with ASC 740 on the basis of a two-step process whereby (1) management determines whether it is more likely than not that the tax positions will be sustained on the basis of the technical merits of the position and (2) for those tax positions that meet the more-likely-than-not recognition threshold, management recognizes the largest amount of tax benefit that is more than 50 percent likely to be realized upon ultimate settlement with the related tax authority. We recognize interest and penalties related to unrecognized tax benefits, if any, within income tax expense and any accrued interest and penalties are included within the related tax liability line.
	Net Loss Per Share
	Basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding for the period, without consideration for common stock equivalents. Excluded from the weighted-average number of shares outstanding are shares that have been issued upon the early exercise of stock options and are subject to future vesting, which was a total of 24,444 shares as of December 31, 2014. Diluted net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock and common stock equivalents outstanding for the period determined using the treasury-stock method. Common stock equivalents are comprised of redeemable convertible preferred stock, warrants for the purchase of common stock, and options outstanding under our stock option plan. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding as the common stock equivalents are anti-dilutive due to our net loss position.
	Potentially dilutive securities not included in the calculation of diluted net loss per share attributable to common stockholders because to do so would be anti-dilutive are as follows (in common stock equivalent shares):
		As of December 31,
		2014		2013		2012
	Redeemable convertible preferred stock		—		13,713,407		7,019,599
	Options to purchase common stock		3,210,693		3,098,573		2,336,314
	Warrants to purchase common stock		250,646		250,646		250,646
	Recently Issued and Adopted Accounting Pronouncements
	In August 2014, the FASB issued Accounting Standards Update, or ASU, No. 2014-15, “Presentation of Financial Statements—Going Concern (Subtopic 205-40): Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern,” or ASU 2014-15. ASU 2014-15 will require management to assess, at each annual and interim reporting period, the entity’s ability to continue as a going concern. The amendments in ASU 2014-15 do not have any application to an entity’s financial statements, but only to disclosure in the related notes. ASU 2014-15 is effective for annual periods ending after December 15, 2016 and early application is permitted. We intend to apply ASU 2014-15 beginning with the first quarter of fiscal year 2016.
In June 2014, the FASB issued ASU No. 2014-10, “Development Stage Entities (Topic 915) — Elimination of Certain Financial Reporting Requirements, Including an Amendment to Variable Interest Entities Guidance in Topic 810, Consolidation,” or ASU 2014-10, which eliminates the concept of a development stage entity in its entirety from current accounting guidance and provides for certain amendments to the consolidation guidance in Topic 810 in the Accounting Standards Codification, or ASC. Prior to the issuance of this guidance, we were considered a development stage entity and as a result we included certain inception-to-date disclosures in our financial statements. The guidance related to the elimination of the concept of a development stage entity is effective for public companies for annual reporting periods beginning after December 15, 2014, and interim periods therein. The amendment of the consolidation guidance in Topic 810 is effective for public companies for annual reporting periods beginning after December 15, 2015. Early adoption of the new standard is permitted. We adopted ASU No. 2014-10 during the quarter ended June 30, 2014. As such, all inception-to-date disclosures have not been included in these consolidated financial statements.

Other_Financial_Information

Other Financial Information	12 Months Ended
	Dec. 31, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Other Financial Information	3. Other Financial Information
	Property and Equipment
	Property and equipment, leasehold improvements, and related accumulated depreciation and amortization were as follows (in thousands):
		December 31,
		2014			2013
	Manufacturing and laboratory equipment	$	3,177		$	3,229
	Office furniture and equipment		113			112
	Clinical equipment		2,115			1,606
	Computer equipment and software		152			122
	Leasehold improvements		3,367			2,830
	Construction in progress		922			323
			9,846			8,222
	Less: accumulated depreciation and amortization		(6,778	)		(5,755	)
	Total	$	3,068		$	2,467
	Depreciation and amortization expense was $1.1 million, $851,000 and $651,000 for the years ended December 31, 2014, 2013 and 2012, respectively.
	In cases where our lessor grants to us leasehold improvement allowances that reduce our rent expense, we capitalize the improvements as incurred and recognize deferred rent, which is amortized over the shorter of the lease term or the expected useful life of the improvements. During the year ended December 31, 2013, we capitalized $478,000 in such leasehold improvements.
	Accrued Expenses
	Accrued expenses consist of (in thousands):
		December 31,
		2014			2013
	Accrued clinical and related costs	$	6,072		$	2,067
	Accrued compensation and related taxes		2,554			512
	Accrued offering costs		—			496
	Accrued other		249			178
	Total	$	8,875		$	3,253

Debt

Debt	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Debt	4. Debt
	Term Loan and Troubled Debt Restructuring
	In September 2008, we entered into a term loan with CIT Healthcare LLC (the Term Loan) at a fixed interest rate of approximately 10.6% that provided a maximum of $4.0 million to be used for capital expenditures.
	In May 2012, CIT Healthcare LLC agreed to modify the scheduled payment terms of the Term Loan and deferred 50% of the remaining monthly payments to a final balloon payment due at the end of the original loan term. These modifications were determined to meet the definition of a troubled debt restructuring. The outstanding debt and accrued interest were paid in full in accordance with the amended provisions in October 2012.

Commitments_and_Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	5. Commitments and Contingencies
	Operating Leases
	We lease office, manufacturing and research and development facilities, and equipment under various non-cancellable operating lease agreements. Facility leases generally provide for periodic rent increases and many contain escalation clauses and renewal options. Certain leases require us to pay property taxes and routine maintenance.
	Future minimum annual obligations under all non-cancellable operating lease commitments at December 31, 2014 are as follows (in thousands):
		Year Ending December 31, 2014
		Total		2015		2016		2017		2018		2019
	Operating lease obligations	$	2,200	$	856	$	853	$	491	$	—	$	—
	Total rent expense under our operating leases was $835,000, $659,000 and $459,000 during the years ended December 31, 2014, 2013 and 2012, respectively.
	We recognize rent expense for our facility operating leases on a straight-line basis. We account for the difference between the minimum lease payments and the straight-line rent expense as deferred rent. Current and long-term deferred rent totaled $126,000 and $241,000 at December 31, 2014 and $142,000 and $321,000 at December 31, 2013, respectively.
	Purchase Commitments
	The following table summarizes our purchase obligations at December 31, 2014 (in thousands):
		Payments Due by Period
		Total		Less Than		3-Feb		5-Mar		More Than
				1 Year		Years		Years		5 Years
	Purchase obligations	$	758	$	758	$	—	$	—	$	—
	As of December 31, 2014, our purchase obligations include existing purchase commitments for future minimum payments of $391,000 with a vendor for raw materials that will be manufactured and utilized on an as needed basis. During the years ended December 31, 2014, 2013 and 2012, we purchased $1.2 million, $724,000 and $462,000, respectively, of materials from this vendor. Our purchase obligations also include a purchase order with a vendor for cartridges that will be manufactured and delivered on an agreed upon schedule during 2015 for a future payment of $367,000. During the years ended December 31, 2014 and 2013, we purchased $1.2 million and $439,000 of materials from this vendor. During the year ended 2012, we purchased no material from this vendor. If we cancel any future cartridge shipment, we would be required to pay 50% of the scheduled invoice amount for that shipment.
	Legal Proceedings
	We are not currently a party to any litigation, nor are we aware of any pending or threatened litigation against us that we believe would materially affect our business, operating results, financial condition or cash flows. Our industry is characterized by frequent claims and litigation, including claims regarding patent and other intellectual property rights, as well as for product liability. As a result, in the future, we may be involved in various legal proceedings from time to time.

Fair_Value

Fair Value	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Fair Value	6. Fair Value
	The following fair value hierarchy table presents information about each major category of our financial assets and liabilities measured at fair value on a recurring basis (in thousands):
		Fair Value Measurement at December 31, 2014
		Fair Value			Level 1			Level 2		Level 3
	Assets
	Money market funds	$	101,592		$	101,592		$	—	$	—
		Fair Value Measurement at December 31, 2013
		Fair Value			Level 1			Level 2		Level 3
	Assets
	Money market funds	$	37,158		$	37,158		$	—	$	—
	Liabilities
	Future purchase rights	$	2,600		$	—		$	—	$	2,600
	We report the change in fair value during each period as a non-operating gain or loss. There were no transfers between Level 1, Level 2 or Level 3 for our assets or liabilities during any period presented. The following table summarizes the changes in Level 3 preferred stock warrant liabilities measured at fair value on a recurring basis for the year ended December 31, 2012 (in thousands):
		Fair Value of
		Preferred Stock
		Warrant Liabilities
	Balance at January 1, 2012	$	180
	Revaluation of warrants		(180	)
	Balance at December 31, 2012	$	—
	The preferred stock warrants were converted to common stock warrants in February 2012 (see Note 2).
	The following table summarizes the changes in Level 3 future purchase rights liabilities measured at fair value on a recurring basis for the three years ended December 31, 2014 (in thousands):
		Fair Value of
		Future Purchase
		Rights Liabilities
	Balance at January 1, 2012	$	—
	Initial valuation of future purchase rights		3,101
	Re-measurement of future purchase rights		(3,101	)
	Balance at December 31, 2012		—
	Initial valuation of additional future purchase rights		1,294
	Re-measurement of future purchase rights		1,306
	Balance at December 31, 2013		2,600
	Re-measurement of future purchase rights		(2,600	)
	Balance at December 31, 2014	$	—
	We valued the future purchase rights liabilities in the periods ended December 31, 2013 and 2012 using a binomial lattice option pricing model with the following assumptions:
		December 31,
		2013			2012
	Common stock fair value	$	5.93		$	1.17
	Preferred stock price	$	8		$	8
	Volatility		85	%		80	%
	Risk-free interest rate		0.38	%		0.36	%
	Contractual life (years)		2.08			3.08
	Number of nodes		25			37
	Dividend yield		0	%		0	%

Redeemable_Convertible_Preferr

Redeemable Convertible Preferred Stock

12 Months Ended

Dec. 31, 2014

Equity [Abstract]

Redeemable Convertible Preferred Stock

7. Redeemable Convertible Preferred Stock

Junior Convertible Preferred Stock

In February 2012, we entered into a securities purchase agreement for the sale of junior convertible preferred stock. In conjunction with the junior preferred stock financing, previously issued shares of redeemable convertible Series A, Series B, Series C, and Series D preferred stock and related preferred stock warrants converted into shares of common stock and common stock warrants, respectively. As a result, we reclassified the aggregate value of the Series A, Series B, Series C, and Series D preferred stock of $54.7 million to stockholders’ equity (deficit).

The junior preferred stock financing totaled $1.5 million of convertible, but not redeemable, preferred stock at approximately $0.43 a share, for an aggregate of 3,501,400 shares. During February and March 2012, we received proceeds of $1.3 million, net of issuance costs of $40,000. In conjunction with the completion of our IPO in April 2014, all shares of our junior convertible preferred stock were converted into common stock on a one-to-one basis and the remaining unamortized issuance costs of $31,000 were recognized as accretion to redemption value of the junior convertible preferred stock in the statement of operations.

Senior Redeemable Convertible Preferred Stock

In September 2012, we entered into the Senior Preferred Purchase Agreement that authorized the multi-stage issuance of 14,765,632 shares of our senior redeemable convertible preferred stock for $8.00 per share. Prior to termination upon the completion of our IPO in April 2014, 10,767,007 shares were issued under the Senior Preferred Purchase. Pursuant to the Senior Preferred Purchase Agreement, we granted the investors in the senior preferred stock financing the right, subject to the satisfaction of certain conditions, to purchase additional shares of senior preferred stock for a purchase price of $8.00 per share at multiple subsequent closings in accordance with a schedule provided in the Senior Preferred Purchase Agreement, referred to as the future stock purchase rights. Where applicable, the purchase price under the Senior Preferred Stock Purchase Agreement was allocated to the future purchase rights and any related stock options at their estimated fair value, as described under “Future Purchase Rights” below.

In connection with the senior preferred stock financing, we have entered into a Fourth Amended and Restated Investors’ Rights Agreement in August 2013 (the “Senior Preferred IRA”). The Senior Preferred IRA contains customary registration rights and related provisions, including customary market standoff provisions.

From September to October 2012, we issued 2,606,250 shares of senior preferred stock for proceeds of $19.8 million, net of issuance costs of $240,000. We also issued 911,949 shares of senior preferred stock upon the conversion of a loan entered into during 2012 that included $7.2 million of principal and $146,000 of accrued interest.

In February 2013, we closed another senior preferred stock financing and issued 305,571 shares of senior preferred stock for proceeds of $2.3 million, net of issuance costs of $134,000 incurred by us for services rendered by a third-party professional services firm that is also utilized by certain of our investors.

In May 2013, we closed an additional senior preferred stock financing and issued 158,150 shares of senior preferred stock for proceeds of $1.2 million, net of issuance costs of $28,000.

In June 2013, we closed a further senior preferred stock financing and issued 3,830,050 shares of senior preferred stock for proceeds of $30.6 million, net of issuance costs of $90,000.

In December 2013, we amended the terms of the Senior Preferred Stock Purchase Agreement to provide for a partial acceleration of existing future preferred stock financing closings under the Senior Preferred Stock Purchase Agreement and the sale of additional shares of senior preferred stock to certain of our existing investors and to certain of our directors and officers (the December 2013 Amendment). Pursuant to the Senior Preferred Stock Purchase Agreement, as amended by the December 2013 Amendment, we issued 2.4 million of senior preferred stock for proceeds of $19.1 million, net of issuance costs of $102,000, in December 2013.

Pursuant to the Senior Preferred Stock Purchase Agreement, in January 2014 we issued an additional 555,000 shares of senior redeemable convertible preferred stock for proceeds of $4.3 million, net of issuance costs of $135,000. Also in January 2014, we completed the sale of 1.5 million shares of our senior redeemable convertible preferred stock at a price of $8.00 per share in a private placement to new investors for proceeds of $12.0 million, net of issuance costs of $31,000.

In February 2014, we completed a pre-emptive rights offering, triggered by the private placement for 241,016 shares of our senior redeemable convertible preferred stock at a price of $8.00 per share for proceeds of $1.9 million, net of issuance costs of $35,000.

In conjunction with the completion of our IPO on April 2014, all the outstanding shares of our senior redeemable convertible preferred stock were converted into common stock on a one-to-one basis and the remaining unamortized discounts of $3.8 million and issuance costs of $727,000 were recognized as a deemed dividend and accretion to redemption value of the redeemable convertible preferred stock, respectively, in the statement of operations.

Future Purchase Rights

Pursuant to the Senior Preferred Purchase Agreement, we granted to the investors in the senior preferred stock financing the future purchase rights, subject to the satisfaction of certain conditions, to purchase additional shares of senior preferred stock for a purchase price of $8.00 per share at multiple subsequent closings in accordance with a schedule provided in the Senior Preferred Purchase Agreement. These future purchase rights for additional shares of our senior preferred stock were legally detachable from the shares of the underlying senior preferred stock and, as a result, were considered freestanding instruments accounted for separately from the shares of senior preferred stock. As the future purchase rights were exercisable for shares of our redeemable convertible preferred stock, the future purchase rights were instruments that embodied obligations to transfer assets and were classified as liabilities under the accounting guidance that distinguishes liabilities from equity.

The following table summarizes the number of shares subject to purchase under future purchase rights initially granted, the fair value per share of the senior preferred stock subject to the rights as initially granted, the initial grant date fair value recorded, the fair value of our common stock used in determining such value, and beneficial conversion amounts underlying the preferred stock that were recorded in connection with certain purchases of such preferred stock under the Senior Preferred Purchase Agreement and the related stock options granted to certain members of our board of directors (in thousands except share and per share amounts):

Issuance Date

Number of

Fair Value

Grant Date Fair

Common Stock

Beneficial

Shares

per Share

Value Recorded

Value Used in

Conversion on

Subject to

of Rights

Determining

Underlying

Future Purchase

Fair Value

Preferred Stock/

Rights Granted

Options

25-Sep-12

3,750,000

$

2.8

$

3,101

$

2.3

$

—

28-Feb-13

891,250

$

2.83

$

864

$

6.85

$

513

30-Apr-13

461,271

$

2.4

$

379

$

6.85

$

192

26-Jun-13

66,250

$

0.76

$

50

$

6.82

$

264

In conjunction with the issuance of senior preferred stock during the year ended December 31, 2013, we estimated the fair value of the future purchase rights for the shares issued to be $1.3 million. The future purchase rights were recorded at their estimated fair value, with the remaining amount of the proceeds allocated to the senior preferred stock, resulting in the senior preferred stock being recorded at an amount per share less than the fair value of our common stock at that time. Accordingly, we recorded an aggregate beneficial conversion amount underlying the senior preferred stock of $705,000, an amount equal to the number of shares of senior preferred stock sold on that date multiplied by the difference between the estimated fair value of the underlying common stock and the value allocated to the senior preferred stock on that date. The beneficial conversion amount was recorded as an offset to additional paid-in capital and was being amortized as a deemed dividend over the redemption period using an effective interest rate method.

In connection with the issuance of senior preferred stock in June 2013 discussed above, we also granted to certain members of our board of directors who participated in the senior preferred stock financings one common stock option for each share of preferred stock purchased through June 2013. An aggregate of 86,917 common stock options were granted to these board members, which were valued at $4.91 per share utilizing the BSM option pricing model. After allocation of the proceeds to the underlying future purchase rights as noted above, the remaining amount of the proceeds were allocated between the common stock options and the senior preferred stock acquired using the relative fair value method. As the allocated value per share of the senior preferred stock acquired was less than the fair value of our common stock on such date, we recorded a beneficial conversion associated with the options granted, on the underlying senior preferred stock of $264,000. This beneficial conversion was also recorded as an offset to additional paid-in capital and was being amortized as a deemed dividend over the redemption period using an effective interest rate method.

All remaining future purchase rights associated with our preferred stock were terminated and the remaining unamortized beneficial conversion balance of $878,000 was recognized as a reduction to equity at the effective date of our IPO in April 2014.

Certificate of Incorporation

The material terms of our amended restated certificate of incorporation, which became effective as of the closing of our IPO in April 2014, are as follows:

Authorized Shares

Our amended and restated certificate of incorporation authorizes the company to issue 150,000,000 shares of stock consisting of 130,000,000 shares of common stock, par value of $0.0001 per share and 20,000,000 shares of preferred stock, par value $0.0001 per share.

Dividends

Subject to preferences that may be applicable to any then outstanding preferred stock, holders of common stock are entitled to receive ratably those dividends, if any, as may be declared from time to time by our board of directors out of legally available funds.

Liquidation Preference

In the event of our liquidation, dissolution or winding up, holders of common stock will be entitled to share ratably in the net assets legally available for distribution to stockholders after the payment of all of our debts and other liabilities and the satisfaction of any liquidation preferences that may be granted to the holders of any then outstanding shares of preferred stock.

Rights and Preferences

Holders of common stock have no preemptive, conversion or subscription rights, and there are no redemption or sinking fund provisions applicable to the common stock. The rights, preferences and privileges of the holders of common stock are subject to, and may be adversely affected by, the rights of the holders of shares of any series of preferred stock, which we may designate and issue in the future.

Voting Rights

Each holder of common stock is entitled to one vote for each share on all matters submitted to a vote of the stockholders, including the election of directors. Our amended and restated certificate of incorporation and amended and restated bylaws do not provide for cumulative voting rights. Because of this absence of cumulative voting, the holders of a majority of the shares of common stock entitled to vote in any election of directors can elect all of the directors standing for election, if they should so choose. In addition, our amended and restated certificate of incorporation also provides that our directors may be removed only for cause by the affirmative vote of the holders of at least 75% of the combined voting power of all our stockholders entitled to vote on the election of directors, voting together as a single class.

Subject to supermajority votes for some matters, matters shall be decided by the affirmative vote of our stockholders having a majority in voting power of the votes cast by the stockholders present or represented and voting on such matter, provided that the holders of our common stock are not allowed to vote on any amendment to our certificate of incorporation that relates solely to the terms of one or more series of preferred stock if the holders of such affected series are entitled, either separately or together with the holders or one or more such series, to approve such amendment. The affirmative vote of the holders of at least 75% of the votes that all of our stockholders would be entitled to cast in any annual election of directors and, in some cases, the affirmative vote of a majority of minority stockholders entitled to vote in any annual election of directors are required to amend or repeal our bylaws, amend or repeal certain provisions of our certificate of incorporation, approve certain transactions with certain affiliates, or approve the sale or liquidation of the company. The vote of a majority of minority of stockholders applies when an individual or entity and its affiliates or associates together own more than 50% of the voting power of our then outstanding capital stock, excluding any such person that owned 15% or more of our outstanding voting stock immediately prior to our IPO, and such a vote would require the approval of the majority of our voting stock, excluding the voting stock held by such a majority holder.

Warrants

We issued warrants to purchase redeemable convertible preferred stock in connection with financing activities or for consulting services. In connection with the junior preferred stock financing in February 2012, all warrants to purchase Series B, Series C, and Series D preferred stock converted to common stock warrants. The common stock warrants outstanding as of December 31, 2014, have a weighted-average exercise price of $95.21 and expire between February 2016 and September 2019. Our warrant activity is as follows for the three years ended December 31, 2014:

Number

Weighted-

Outstanding

average

Exercise Price

Balance outstanding — January 1, 2012

252,308

$

95.84

Expiration of warrants

(1,662

)

$

191.69

Balance outstanding — December 31, 2012, 2013 and 2014

250,646

$

95.21

Common_Stock

Common Stock	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Common Stock	8. Common Stock
	In April 2014, we completed an IPO selling 4,500,000 shares of our common stock at $12.00 per share and received net proceeds of $50.2 million after underwriters’ discounts and commissions. In addition, we incurred $5.8 million in offering expenses, resulting in total costs of $9.6 million and net offering proceeds to us of $44.4 million. In May 2014, the underwriters exercised their option to purchase an additional 675,000 shares of our common stock at $12.00 per share in full. As a result, we received an additional $7.5 million in net proceeds after underwriters’ discounts and commissions of $567,000, for total net proceeds of $51.9 million from the IPO.
	In October 2014, we completed a follow-on public offering selling 2,000,000 shares of our common stock at $17.50 per share and received net proceeds of $32.6 million after underwriters’ discounts and commissions. In addition, we incurred $511,000 in offering expenses, resulting in total costs of $3.0 million and net offering proceeds to us of $32.0 million. In November 2014, the underwriters exercised a portion of their option and purchased an additional 50,000 shares of our common stock at $17.50 per share. As a result, we received an additional $814,000 in net proceeds after underwriters’ discounts and commissions, for total net proceeds from the follow-on public offering of $32.9 million, net of discounts, commissions and costs, from the offering.
	Stock Reserved for Future Issuance
	Shares reserved for future issuance at December 31, 2014 are as follows:
		Number of
		Shares
	Exercise of common stock warrants		250,646
	Common stock options outstanding		3,210,693
	Common stock options available for future grant		373,803
	Total common shares reserved for future issuance		3,835,142

Stock_Compensation_Plans

Stock Compensation Plans	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock Compensation Plans	9. Stock Compensation Plans
	Equity Incentive Plans
	Our 2014 Equity Incentive Plan, or the 2014 Plan, became effective in April 2014 and replaced our 2012 Stock Option Plan, or the 2012 Plan, with respect to future awards. The 2014 Plan provides for the grant of stock options, restricted stock, restricted stock units, stock appreciation rights, performance awards and performance units to employees, directors, and consultants. Option grants under the 2014 Plan generally have a ten-year term and vest over four years. Shares available for grant under the 2014 Plan include any shares remaining available or becoming available in the future under the 2012 Plan due to cancellation or forfeiture. In addition, the 2014 Plan provides for annual increases in the number of shares available for issuance thereunder beginning upon its effective date in April 2014, and on each annual anniversary, equal to the lower of:
		•		1,200,000 shares of our common stock;
		•		3% of the outstanding shares of our common stock on the second-to-the-last day prior to each anniversary date of the effectiveness date of our IPO; or
		•		an amount as our board of directors may determine.
	Our 2012 Stock Option Plan, or the 2012 Plan, provided for the grant of stock options, restricted stock, restricted stock units, stock purchase rights, and performance awards to employees, directors, and consultants. Option grants under the 2012 Plan generally have a ten-year term, vest over four years and are exercisable immediately, subject to a repurchase right that lapses as the option vests. Options to purchase 55,516 shares of our common stock had been exercised prior to vesting under the 2012 Plan, of which 24,444 shares were unvested and subject to repurchase as of December 31, 2014. During 2014, 20,715 shares vested resulting in a release of the repurchase liability of $104,000. We have not repurchased any shares related to these early exercises for which our repurchase liability was $123,000 as of December 31, 2014.
	Prior to the adoption of the 2012 Plan, we granted incentive awards under the 2004 Stock Option Plan. In February 2012 and in connection with the junior preferred stock financing, 27,230 outstanding options from the 2004 Stock Option Plan were canceled, which represented all options outstanding at the time of cancellation. In conjunction with the cancellation of options, we expensed previously unrecognized compensation cost of $27,000.
	As of December, 2014, the aggregate number of shares outstanding or available for grant under the 2012 and 2014 Plans was 3,584,496 shares.
	The following table summarizes stock option activity:
			Options			Weighted-		Weighted-		Aggregate
						Average		Average		Intrinsic
						Exercise		Remaining		Value (In
						Price		Contractual		thousands)
								Term (Years)
	Outstanding as of January 1, 2014			3,098,573		$	6.71
	Granted			326,324		$	16.85
	Exercised			(142,041	)	$	6
	Forfeited			(72,163	)	$	8.11
	Outstanding as of December 31, 2014			3,210,693		$	7.54		8	$	55,845
	Options vested and expected to vest as of December 31, 2014			3,129,706		$	7.45		7.9	$	54,722
	Options exercisable as of December 31, 2014			2,981,319		$	6.64		7.9	$	54,529
	The aggregate intrinsic value of options is calculated as the difference between the exercise price of the options and the fair value of our common stock for those shares that had exercise prices lower than the fair value of our common stock as of December 31, 2014. The number of options vested and expected to vest is calculated as the total number of options vested plus the number of unvested options remaining after applying our estimated forfeiture rate. As of December 31, 2014, there was $5.8 million of total compensation cost related to unvested stock option awards not yet recognized, which is expected to be recognized over a remaining weighted-average vesting period of 2.2 years.
	The following table summarizes information about stock options (in thousands):
			Year Ended
			December 31,
			2014			2013		2012
	Aggregate intrinsic value of options exercised		$	1,972		$	633	$	—
	We have not capitalized or recognized an income tax benefit from the exercise of any stock options as we continue to record a full valuation allowance on our deferred tax assets.
	Stock-based Compensation Expense
	The weighted-average grant date fair value of stock options granted to employees and directors during the years ended December 31, 2014, 2013 and 2012 was $11.87, $5.53, $0.47, respectively. The following are the ranges of underlying assumptions used to determine the fair value of stock options granted to employees and non-employees:
			Years Ended December 31,
			2014			2013		2012
	Employees and Directors:
	Risk-free interest rate			1.53% - 1.89%			0.76% - 1.10%		0.76% - 0.99%
	Expected dividend yield			0%			0%		0%
	Expected volatility			80%  - 85%			90% - 100%		100%
	Expected term of options (years)			6 – 6.2			5 - 5.5		5 - 6
	Range of common stock value		$	7.55 – $24.04		$	6.77 - $9.94	$	0.43 - $1.17
			Years Ended December 31,
			2014			2013		2012
	Non-Employees:
	Risk-free interest rate			0.11% - 1.27%			0.13% - 0.86%		0.17% - 0.57%
	Expected dividend yield			0%			0%		0%
	Expected volatility			73% - 85%			90% - 100%		100%
	Expected term of options (years)			1 - 4			1 - 4		1 - 4
	Range of common stock value		$	11.31 - $27.24		$	5.93 - $9.94	$	1.17
	December 31, 2012 Valuation Analysis
	During the first quarter of 2013, we commenced an analysis of the enterprise value of our company and the fair value of our common stock as of December 31, 2012, which utilized an Option Pricing Model, or OPM. OPM is appropriate to use when the range of possible future outcomes is so difficult to predict that any such forecast would be highly speculative, or there is a substantially contemporaneous sale of stock to a third party. OPM treats common stock and convertible preferred stock as call options on the enterprise value, with exercise prices based on the liquidation preference of the convertible preferred stock. Therefore, the common stock has value only if the funds available for distribution to the stockholders exceed the value of the liquidation preference to be received by holders of our redeemable convertible preferred stock at the time of a liquidity event, such as a merger, sale or an initial public offering, or IPO, assuming the enterprise has funds available to make a liquidation preference meaningful and collectible by the stockholders. The common stock is modeled to be a call option with a claim on the enterprise at an exercise price equal to the remaining value immediately after the convertible preferred stock is liquidated. OPM uses the BSM option pricing model to price the call option.
	The OPM considered the relative rights and preferences of the various securities, including the seniority of the liquidation preferences for preferred equity, and the potential for dilution caused by the conversion of the preferred equity. Additionally, our preferred stockholders have various rights that give them greater control and influence over future liquidity, financing and other decisions relating to our company than the holders of our common stock. The OPM applied a percentage of participation for each class of shares for each valuation interval based on BSM option pricing models and a 25.4% discount for lack of marketability was applied for the common stockholders. The resulting implied per share value of our common stock was $1.17 per share as of December 31, 2012, which was utilized to determine the BSM fair value for the purpose of calculating stock-based compensation expense related to the options granted in September and December 2012 at an exercise price of $8.00 per share.
	2013 and 2014 Valuation Analyses
	Due to our management’s and board of directors’ decision to pursue an IPO, coupled with our belief that we could reasonably estimate the form and timing of potential liquidity events, we utilized a Probability Weighted Expected Return Method, or PWERM, for our 2013 and 2014 valuations prior to the completion of our IPO in April 2014. Under this method, the implied fair value of our common stock is estimated based upon an analysis of future values assuming various outcomes. The value is based on the probability-weighted present value of expected future investment returns considering each of the possible outcomes available to us as well as the rights of each share class. The possible outcomes considered are based upon an analysis of future scenarios as described below:
		•		closing of an initial public offering;
		•		sale to a strategic acquirer;
		•		continuation as a private company with subsequent liquidation event; and
		•		dissolution.
	Critical assumptions required to perform the PWERM include the following:
		•		Scenarios: Expected future events were identified.
		•		Scenario probabilities: Estimates of the probability of occurrence of each event were identified.
		•		Valuation: Expected future values under each scenario were estimated.
		•		Timing: Expected timing to the event under each scenario were estimated.
		•		Risk adjusted discount rates: Risk-adjusted discount rates were selected for each equity class based on the rights and preferences of each equity class and market data.
		•		Discounts: Appropriate minority or marketability discounts, if any, required to estimate the per share value of the various equity classes were determined.
	In determining the implied fair value of our common stock in the IPO scenario, we assumed that the redeemable convertible preferred stock then outstanding would be converted into common stock. In allocating value to our common stock in the merger or sale scenario, we first allocated to our outstanding shares of redeemable convertible preferred stock the greater of the liquidation preference of the redeemable convertible preferred stock and the amount that would have been payable had all such shares of redeemable convertible preferred stock been converted to common stock.
There is inherent uncertainty in these estimates and, if we had made different assumptions, the fair value of the underlying common stock and amount of our stock-based compensation expense, net loss and net loss per share amounts would have differed.
March 31, 2013 Valuation Analysis
Our analysis considered the following probability-weighted scenarios:
Scenario		Weight
IPO by December 31, 2013			25	%
Sale by December 31, 2013			20	%
Private company			30	%
Dissolution			25	%
A 13% discount for lack of marketability was applied for common stockholders. The resulting implied fair value of $6.85 per share was utilized to determine the BSM fair value for the purpose of calculating stock-based compensation expense related to the options granted in March 2013 at an exercise price of $8.00 per share.
June 30, 2013 Valuation Analysis
Our analysis considered the following probability-weighted scenarios:
Scenario		Weight
IPO by November 15, 2013			35	%
Sale by November 15, 2013			10	%
Private company			30	%
Dissolution			25	%
A 9% discount for lack of marketability was applied for common stockholders. The resulting implied fair value of $6.82 per share was utilized to determine the BSM fair value for the purpose of calculating stock-based compensation expense related to the options granted in May, June, and July 2013 at an exercise price of $8.00 per share. The decrease in implied fair value of our common stock from March 31, 2013 was primarily due to dilution from the issuance of substantially more shares of our redeemable convertible senior preferred stock during the second quarter of 2013 that have superior rights to our common stock.
September 3, 2013 Valuation Analysis
Our analysis considered the following probability-weighted scenarios:
Scenario		Weight
IPO by November 15, 2013			50	%
Sale by November 15, 2013			10	%
Private company			25	%
Dissolution			15	%
A 7% discount for lack of marketability was applied for common stockholders. The resulting implied fair value of $9.94 per share was utilized to determine the BSM fair value for the purpose of calculating stock-based compensation expense related to the options granted in September 2013 at an exercise price of $10.50 per share. The implied fair value of our common stock increased from June 30, 2013 primarily due to the increased likelihood of an IPO scenario as a result of progress made toward a public offering. In addition, we decreased our discount for lack of marketability reflecting a decrease in the expected time to liquidity.
September 30, 2013 Valuation Analysis
Our analysis considered the following probability-weighted scenarios:
Scenario		Weight
IPO by November 15, 2013.			50	%
Sale by November 15, 2013			10	%
Private company			25	%
Dissolution			15	%
A 6% discount for lack of marketability was applied for common stockholders, which resulted in an implied fair value of $10.02 per share. This increase in implied fair value of our common stock from September 3, 2013 was associated with a slight decrease in our discount for lack of marketability due to a decrease in the expected time to liquidity. There were no changes to our probability-weighted scenarios as no significant changes occurred from our September 3, 2013 valuation analysis.
December 1, 2013 Valuation Analysis
Our analysis considered the following probability-weighted scenarios:
Scenario		Weight
IPO by May 15, 2014			20	%
Sale by September 30, 2015			10	%
Private company			50	%
Dissolution			20	%
A discount for lack of marketability was applied for common stockholders of 10%, 21% and 28% for the IPO, sale and private company scenarios, respectively. The resulting implied fair value of $6.77 per share was utilized to determine the BSM fair value for the purpose of calculating stock-based compensation expense related to the options granted in December 2013 at an exercise price of $8.00 per share. The decrease in fair value of our common stock from September 30, 2013 was primarily related to the increases in discount for lack of marketability due to an increase in the expected time to a liquidity event associated with the projected timing of an IPO or a sale of our company.
December 31, 2013 Valuation Analysis
Our analysis considered the following probability-weighted scenarios:
Scenario		Weight
IPO by May 15, 2014			20	%
Sale by September 30, 2015			10	%
Private company			50	%
Dissolution			20	%
A discount for lack of marketability was applied for common stockholders of 9%, 20% and 28% for the IPO, sale and private company scenarios, respectively, which resulted in an implied fair value of $5.93 per share. The decrease in fair value of our common stock from December 1, 2013 was primarily related to dilution from the issuance of additional shares of our redeemable convertible senior preferred stock in December 2013, partially offset by a slight decrease in discount for lack of marketability for the IPO and sale scenarios reflecting a decrease in the expected time to liquidity.
February 12, 2014 Valuation Analysis
Our analysis considered the following probability-weighted scenarios:
Scenario		Weight
IPO by May 15, 2014			25	%
Sale by September 30, 2015			10	%
Private company			50	%
Dissolution			15	%
A discount for lack of marketability was applied for common stockholders of 8%, 20% and 28% for the IPO, sale and private company scenarios, respectively, which resulted in an implied fair value of $7.55 per share. The increase in fair value of our common stock from December 31, 2013 was primarily related to the increase in likelihood of an IPO scenario based on progress toward a public offering, coupled with a slight decrease in discount for lack of marketability for the IPO and sale scenarios. These were partially offset by dilution from the issuance of additional shares of our senior redeemable convertible preferred stock in January 2014.
March 31, 2014 Valuation Analysis
Our analysis considered the following probability-weighted scenarios:
Scenario		Weight
IPO by April 15, 2014			65	%
Sale by September 30, 2015			10	%
Private company			15	%
Dissolution			10	%
A discount for lack of marketability was applied for common stockholders of 2%, 17% and 27% for the IPO, sale and private company scenarios, respectively, which resulted in an implied fair value of $11.30 per share. The increase in fair value of our common stock from December 31, 2013 and February 12, 2014, was related to the increase in likelihood of an IPO scenario as significant progress had been completed toward a public offering and the decrease in discount for lack of marketability for the IPO scenario that reflected the proximity to the projected time to liquidity. These were slightly offset by dilution from the issuance of additional shares of our senior redeemable convertible preferred stock in January and February 2014, as applicable.
The following table summarizes the allocation of stock-based compensation expense to employees and non-employees (in thousands):
		Years Ended December 31,
		2014			2013		2012
Employees and Directors:
Research and development		$	763		$	262	$	45
General and administrative			937			503		94
Totals		$	1,700		$	765	$	139
		Years Ended December 31,
		2014			2013		2012
Non-Employees:
Research and development		$	757		$	149	$	5
General and administrative			53			34		—
Totals		$	810		$	183	$	5

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income Taxes	10. Income Taxes
	Our net loss before income tax was subject to tax in the following jurisdictions for the following periods (in thousands):
		Year Ended December 31,
		2014			2013			2012
	United States	$	(47,482	)	$	(32,524	)	$	(6,321	)
	Foreign		(185	)		(194	)		(380	)
		$	(47,667	)	$	(32,718	)	$	(6,701	)
	Our rate reconciliation consists of the following:
		Year Ended December 31,
		2014			2013			2012
	Federal statutory rate		35	%		35	%		35	%
	State tax (net of federal benefit)		5.4	%		5.3	%		5.8	%
	Research and development credits		3.8	%		3.9	%		1.8	%
	Warrants/purchase rights liabilities		2.2	%		(1.6	%)		19.9	%
	Foreign net operating losses		(0.4	%)		(1.2	%)		(0.6	%)
	382 limited net operating losses and credits		—			(0.6	%)		(415.2	%)
	Change in valuation allowance		(45.1	%)		(40.0	%)		355.5	%
	Other		(0.9	%)		(0.8	%)		(2.2	%)
	Effective tax rate		0	%		0	%		0	%
	Significant components of our deferred tax assets are shown below. A valuation allowance has been established as realization of such deferred tax assets has not met the more likely-than-not threshold requirement. If our judgment changes and it is determined that we will be able to realize these deferred tax assets, the tax benefits relating to any reversal of the valuation allowance on deferred tax assets will be accounted for as a reduction to income tax expense.
		December 31,
		2014			2013
		(in thousands)
	Deferred tax assets:
	Net operating loss carryforwards	$	33,517		$	15,073
	Research and development tax credits		3,269			1,426
	Stock compensation		879			181
	Foreign net operating loss carryforwards		377			504
	Other, net		1,715			1,066
	Total deferred tax assets		39,757			18,250
	Less valuation allowance		(39,757	)		(18,250	)
		$	—		$	—
	We have a history of incurring net operating losses each year since inception that is due to our history as a development stage company with no realized revenues from our planned principal operations. These cumulative operating losses provide significant negative evidence in the determination of whether or not we will be able to realize our deferred tax assets such as our net operating losses and other favorable temporary differences. As a result, we have maintained a full valuation allowance against the entire balance of deferred tax assets since the date of inception. The valuation allowance increased by $21.5 million and $13.1 million for the years ended December 31, 2014 and 2013, respectively.
	As of December 31, 2014, we had available net operating loss, or NOL, carryforwards of approximately $84.8 million and $79.4 million for federal and state income tax purposes, respectively. The federal and state NOLs begin to expire in 2023 and 2015, respectively. As of December 31, 2014, we have federal and state research and development tax credits available for income tax purposes of approximately $2.3 million and $1.4 million, respectively. The federal research and development credits begin to expire in 2023 and the state research and development tax credits do not expire. These carryforwards are net of the Section 382 and 383 limitations discussed below.
	As of December 31, 2014, we also have available NOLs from our Chinese subsidiary of approximately $1.5 million. The Chinese NOLs begin to expire in 2015.
	Sections 382 and 383 of the Internal Revenue Code (the IRC) limit a company’s ability to utilize certain net operating losses and tax credit carryforwards in the event of a cumulative change in ownership in excess of 50%, as defined. We experienced changes in ownership, as defined in Section 382, in February 2012 and in December 2013. As a result, the deferred tax asset associated with our federal and state net operating loss carryforwards and federal and state research credits have been reduced based on the Section 382 limitations. The amount of the reduction in our deferred tax assets is based on the estimated amount of the NOL carryforwards and federal and state research credits we believe cannot be used based on the estimated amount of our Section 382 annual limitation. We have reduced our deferred tax assets by $23.8 million and have estimated that approximately $58.7 million and $56.2 million of our federal and state NOLs, respectively, cannot be used in future years as a result of this change in ownership. Additionally, we have estimated that approximately $2.2 million and $1.6 million of our federal and state research credits, respectively, cannot be used in future years. We have not experienced any additional changes as defined in Section 382 through December 31, 2014. If additional Section 382 changes occur, limitations against the utilization of net operating losses and credits could further impact our future cash flows, but would not impact our 2014 consolidated financial statements, due to the existence of a full valuation allowance against our deferred tax assets.
	Approximately $1.8 million of both the federal and state NOL carryforwards reflected above relate to excess tax deductions for stock compensation, the income tax benefit of which will be recorded as additional paid-in capital if and when realized.
	The following table summarizes the activity related to our unrecognized tax benefits (in thousands):
		Year Ended
		December 31,
		2014			2013
	Balance at beginning of year	$	407		$	—
	Additions based on tax positions related to the current year		533			337
	Changes for prior period tax positions		(2	)		70
	Balance at end of year	$	938		$	407
	We do not anticipate any significant changes in the amount of unrecognized tax benefits over the next twelve months. Due to the full valuation allowance we have on our net deferred tax asset balance, there are no unrecognized tax benefits that would impact the effective tax rate if recognized.
	We are subject to U.S. federal, California and various other states and Chinese income taxes. We are no longer subject to U.S. federal or state income tax examination by tax authorities for tax returns filed for the years ended on or before December 31, 2009. However, to the extent allowed by law, the taxing authorities may have the right to examine the period from 2003 through 2014 where NOLs were generated and carried forward, and make adjustments to the amount of the NOL carryforward. We are not currently under examination by any federal or state jurisdictions.

Related_Party_Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2014
Related Party Transactions [Abstract]
Related Party Transactions	11. Related Party Transactions
	Directors
	During the years ended December 31, 2014, 2013 and 2012, we paid an aggregate of $33,500, $39,000, and $7,000, respectively, to a member of our board of directors for consulting services and services rendered as chair of our Clinical Advisory Board.
	One member of our board of directors was a partner and is no longer practicing law as of the end of 2013 with a firm that provides certain legal services to us. For the years ended December 31, 2013 and 2012, we incurred an aggregate of $100,000 and $73,000, respectively, in fees for these services.
	Clinical Advisory Board and Scientific Advisory Board
	Certain members of our Clinical Advisory Board and Scientific Advisory Board hold positions at medical institutions where we conduct business. During the years ended December 31, 2014 and 2013, we incurred an estimated aggregate of $1.7 million and $824,000, respectively, in fees to these institutions, primarily for clinical trial costs. As of December 31, 2014 and 2013, accounts payable and accrued expenses combined included $1.6 million and $643,000, respectively, due to these institutions.

Selected_Quarterly_Data

Selected Quarterly Data	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Data	12. Selected Quarterly Data (unaudited)
	The following financial information reflects all normal recurring adjustments, which are, in the opinion of management, necessary for a fair statement of the results of the interim periods. Summarized quarterly data for 2014 and 2013 are as follows (in thousands, except per share data):
			For the Quarters Ended
			March 31			June 30			September 30			December 31			Total Year
	2014:00:00
	Operating expenses		$	11,876		$	11,638		$	12,810		$	14,018		$	50,342
	Net loss		$	(10,748	)	$	(10,167	)	$	(12,798	)	$	(13,954	)	$	(47,667	)
	Net loss attributable to common stockholders		$	(13,818	)	$	(16,251	)	$	(12,798	)	$	(13,954	)	$	(56,821	)
	Basic and diluted net loss per share attributable to common stockholders (1)		$	(24.49	)	$	(0.91	)	$	(0.59	)	$	(0.59	)
	2013:00:00
	Operating expenses		$	4,926		$	7,063		$	9,165		$	10,248		$	31,402
	Net loss		$	(9,358	)	$	(6,144	)	$	(6,977	)	$	(10,239	)	$	(32,718	)
	Net loss attributable to common stockholders		$	(10,331	)	$	(7,267	)	$	(9,034	)	$	(12,453	)	$	(39,085	)
	Basic and diluted net loss per share attributable to common stockholders (1)		$	(22.11	)	$	(14.33	)	$	(16.31	)	$	(22.28	)
	-1	Net loss per share is computed independently for each of the quarters presented. Therefore, the sum of the quarterly per share calculations will not necessarily equal the annual per share calculation.

Description_of_Business_and_Ba1

Description of Business and Basis of Financial Statements (Policies)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Basis of Presentation and Consolidation	Basis of Presentation and Consolidation
	The accompanying consolidated financial statements have been prepared in conformity with United States generally accepted accounting principles, or GAAP, and include the accounts of Vital Therapies, Inc. and its wholly-owned subsidiaries located in the United Kingdom (currently inactive) and China. All intercompany accounts and transactions have been eliminated in consolidation. We manage our operations as a single segment for the purposes of assessing performance and making operating decisions.
	We previously were classified as a “development stage entity” under GAAP and, as such, were required to present inception-to-date information in our statements of operations, comprehensive loss, stockholders’ equity, and cash flows. In June 2014, the Financial Accounting Standards Board, or FASB, issued an accounting standards update that eliminates the concept of a development stage entity from GAAP and removes the related incremental reporting requirements, which we elected to early adopt. See Note 2 for additional information on this standard.
Use of Estimates	Use of Estimates
	The preparation of financial statements in conformity with GAAP requires us to make certain estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Actual results could differ materially from those estimates and assumptions.
Cash and Cash Equivalents	Cash and Cash Equivalents
	Cash and cash equivalents consist of cash and highly-liquid investments with original maturities of three months or less when acquired and are stated at cost, which approximates market value.
Restricted Cash	Restricted Cash
	Restricted cash relates to amounts reserved for various clinical trial obligations and lease arrangements at December 31, 2014 and 2013, respectively, as well as for certain provisions of the junior preferred stock agreement at December 31, 2013.
Fair Value of Financial Instruments	Fair Value of Financial Instruments
	Fair value is defined as the price that would be received to sell an asset or be paid to transfer a liability in an orderly transaction between market participants on the measurement date. Accounting guidance establishes a fair value hierarchy that requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. The standard describes three levels of inputs that may be used to measure fair value:
	Level 1—Quoted prices in active markets for identical assets or liabilities. Our Level 1 assets consisted of U.S. treasuries and money market funds for the periods presented. We had no Level 1 liabilities for any period presented.
	Level 2—Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in markets with insufficient volume or infrequent transactions (less active markets), or model-derived valuations in which all significant inputs are observable or can be derived principally from or corroborated with observable market data for substantially the full term of the assets or liabilities. We had no Level 2 assets or liabilities for any period presented.
	Level 3—Unobservable inputs to the valuation methodology that are significant to the measurement of the fair value of assets or liabilities. Our Level 3 liabilities included preferred stock warrants and future purchase rights liabilities during the periods presented. We had no Level 3 assets in any period presented. We estimated the fair value of the preferred stock warrants and the future purchase rights using a binomial lattice model depending on the underlying attributes of the preferred stock warrants or future purchase rights, as applicable. Upon the completion of our initial public offering, or IPO, in April 2014, the future purchase rights liabilities terminated. See “Future Purchase Rights Liabilities” below.
	The carrying value of cash and cash equivalents, restricted cash, other current assets and prepaid expenses, accounts payable, and accrued expenses approximate fair value due to the short period of time to maturity.
	The future purchase rights were recorded at their estimated fair value at the date of issuance. The binomial lattice model used in the determination of the estimated fair value of the future purchase rights was based on various assumptions, including the estimated fair value of our senior preferred and common stock. We recorded subsequent adjustments to reflect the increase or decrease in estimated fair value at each reporting date as a gain or loss.
Deferred Financing Costs	Deferred Financing Costs
	Deferred financing costs represent direct costs associated with the issuance of our corporate securities. Direct costs include, but are not limited to, the legal, accounting and printing costs. Indirect costs associated with the issuance of corporate securities are expensed as incurred. Deferred financing costs as of December 31, 2013 were offset against the proceeds from our IPO in April 2014.
Property and Equipment, Depreciation and Amortization	Property and Equipment, Depreciation and Amortization
	Property and equipment are recorded at cost and depreciated using the straight-line method over the estimated useful lives of the assets (generally three to five years). Leasehold improvements are stated at cost and amortized on a straight-line basis over the lesser of the remaining term of the related lease or the estimated useful lives of the assets. Construction in progress is not depreciated until the underlying asset is placed in service. Repairs and maintenance costs are charged to expense as incurred.
Impairment of Long-lived Assets	Impairment of Long-lived Assets
	Long-lived assets consist primarily of property and equipment. We review long-lived assets when events and circumstances indicate that the carrying amount of an asset may not be recoverable. If an asset is considered to be impaired, the impairment recognized is the amount by which the carrying value of the asset exceeds its fair value.
Redeemable Convertible Preferred Stock	Redeemable Convertible Preferred Stock
	Our junior convertible and senior redeemable convertible preferred stock were classified as mezzanine in accordance with authoritative guidance for the classification and measurement of potentially redeemable securities, as the preferred stock was conditionally redeemable at the holder’s option or upon certain change in control events that are outside our control, including liquidation, sale, or transfer of control of the company. In conjunction with our IPO in April 2014, all shares of our junior convertible and senior redeemable convertible preferred stock were converted to common stock.
Warrants to Purchase Redeemable Convertible Preferred Stock	Warrants to Purchase Redeemable Convertible Preferred Stock
	We classify our preferred stock warrants that are either puttable or that are redeemable as liabilities on the consolidated balance sheets at fair value. At the end of each reporting period, changes in fair value during the period are recorded as a component of other income (expense), net. In February 2012, a final valuation adjustment was recognized for these preferred stock warrants prior to their conversion to common stock warrants in conjunction with a junior preferred stock offering.
Future Purchase Rights Liabilities	Future Purchase Rights Liabilities
	The future purchase rights liabilities were recorded at their estimated fair value on the date of issuance as a discount on the underlying preferred stock and are re-measured to reflect changes in the estimated fair value at each reporting date, with any decrease or increase in the estimated fair value being recorded as other income or expense, respectively. The fair value of these liabilities was estimated using a binomial lattice model based on the characteristics of the common and preferred stock on the valuation date, probabilities related to our operations and clinical development, as well as assumptions for volatility, remaining expected life, risk-free interest rate and, in some cases, credit spread. Changes in the fair value of the future purchase rights fluctuated in conjunction with increases or decreases in the implied fair value of our common stock, and the number of preferred and common shares and future purchase rights outstanding relative to our enterprise value at each reporting date. In April 2014, the remaining future purchase rights terminated upon the conversion of all senior preferred stock to common stock in conjunction with our IPO and the remaining balance of the future purchase rights liabilities was recorded as other income in our consolidated statement of operations for the period.
Research and Development	Research and Development
	Research and development costs consist primarily of employee-related expenses, costs incurred for clinical trial sites, contractors and contract research organizations engaged in the development of the ELAD System, expenses associated with obtaining regulatory approvals, and the cost of acquiring and manufacturing clinical trial materials. All research and development costs are expensed as incurred.
Stock-based Compensation	Stock-based Compensation
	We measure and recognize compensation expense for all stock-based payments made to employees and directors based on estimated fair value, net of an estimated forfeiture rate, and to consultants based on estimated fair value. Currently, our stock-based awards consist only of stock options; however, future grants under our equity compensation plans may consist of shares of restricted stock and restricted stock units. We estimate the fair value of stock options granted using the Black-Scholes-Merton, or BSM, option pricing model, which requires the use of estimates to value employee stock-based compensation at the date of grant.
	We recognize stock-based compensation cost for employees and directors on a straight-line basis over the requisite service period of the award. Stock-based compensation expense is recognized only for those awards that are ultimately expected to vest. We estimate forfeitures based on an analysis of our historical employee turnover and will continue to evaluate the appropriateness of the forfeiture rate based on actual forfeiture experience, analysis of employee turnover and other factors. We will revise the forfeiture estimate, if necessary, in subsequent periods if actual forfeitures differ from those estimates. Changes in forfeiture estimates, which have not been material to date, impact compensation cost in the period in which the change in estimate occurs.
	The fair value of options granted to consultants is estimated using the BSM option pricing model and is re-measured at each reporting date with changes in fair value recognized as expense in the consolidated statements of operations.
	The BSM option pricing model requires the input of highly subjective assumptions, including the risk-free interest rate, the expected dividend yield of our common stock, the expected volatility of the price of our common stock, and the expected term of the option. These estimates involve inherent uncertainties and the application of management’s judgment. If factors change and different assumptions are used, our stock-based compensation expense could be materially different in the future. These assumptions are estimated as follows:
	Risk-free Interest Rate
	We base the risk-free interest rate assumption on zero-coupon U.S. treasury instruments appropriate for the expected term of the stock option grants.
	Expected Dividend Yield
	We base the expected dividend yield assumption on the fact that we have never paid cash dividends and have no present intention to pay cash dividends. Consequently, we used an expected dividend yield of zero.
	Expected Volatility
	The expected stock price volatility for our common stock is estimated based on volatilities of a peer group of similar publicly-traded, biotechnology companies by taking the average historic price volatility for the peers for a period equivalent to the expected term of the stock option grants. We do not use our average historic price volatility as we have only been a publicly-traded company since April 2014.
	Expected Term
	The expected term represents the period of time that options are expected to be outstanding. As we do not have sufficient historical experience for determining the expected term of the stock option awards granted we have determined the expected life assumption using either the simplified method, which is an average of the contractual term of the option and its ordinary vesting period, or the comparable average expected term utilizing those companies in the peer group as noted above.
	Common Stock Valuation
	Due to the absence of a public market trading our common stock prior to the completion of our IPO in April 2014, it is necessary to estimate the fair value of the common stock underlying our stock-based awards when performing fair value calculations using the BSM option pricing model. The fair value of the common stock underlying our stock-based awards was assessed for each grant date by our board of directors. All options to purchase shares of our common stock have been granted with an exercise price per share no less than the fair value per share of our common stock underlying those options on the date of grant.
	In the absence of a public trading market for our common stock prior to our IPO, we determined the estimated fair value of our common stock using methodologies, approaches, and assumptions consistent with the American Institute of Certified Public Accountants, or AICPA, Audit and Accounting Practice Aid Series: Valuation of Privately Held Company Equity Securities Issued as Compensation, or the AICPA Practice Aid.
Leases	Leases
	We lease all of our office space and enter into various other lease agreements in conducting our business. At the inception of each lease, we evaluate the lease agreement to determine whether the lease is an operating or capital lease. Some of our lease agreements may contain renewal options, tenant improvement allowances, rent holidays or rent escalation clauses. When such items are included in a lease agreement, we record a deferred rent asset or liability equal to the difference between the rent expense and future minimum lease payments due. The rent expense related to operating leases is recognized on a straight-line basis in the statements of operations over the terms of the leases. In cases where the lessor grants leasehold improvement allowances that reduce our rent expense, we capitalize the improvements as incurred and recognize deferred rent, which is amortized over the shorter of the lease term or the expected useful life of the improvements.
Comprehensive Loss	Comprehensive Loss
	Comprehensive loss is defined as the change in equity during a period from transactions and other events and circumstances from non-owner sources. Comprehensive loss has been reflected in the consolidated statements of comprehensive loss and as a separate component of the consolidated statements of redeemable convertible preferred stock and stockholders’ equity (deficit) for all periods presented.
Foreign Currency Translation and Transactions	Foreign Currency Translation and Transactions
	The functional currencies of each our subsidiaries in the United Kingdom (currently inactive) and China is the local currency. Assets and liabilities of the subsidiaries are translated at the rate of exchange at the balance sheet date. Expenses are translated at the average rate of exchange rates in effect during the reporting period. Gains and losses resulting from foreign currency translation are included in accumulated other comprehensive income in the accompanying consolidated balance sheets. Gains and losses resulting from foreign currency transactions are included in the results of operations, which to date, have not been significant.
Income Taxes	Income Taxes
	We account for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the consolidated financial statements. Under this method, deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period that includes the enactment date.
	We recognize net deferred tax assets to the extent we believe these assets are more likely than not to be realized. In making such a determination, management considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax-planning strategies, and results of recent operations. If management determines that we would be able to realize our deferred tax assets in the future in excess of their net recorded amount, management would make an adjustment to the deferred tax asset valuation allowance, which would reduce the provision for income taxes. As of December 31, 2014 and 2013, respectively, we maintained a full valuation allowance against our entire balance of deferred tax assets.
	We record uncertain tax positions in accordance with ASC 740 on the basis of a two-step process whereby (1) management determines whether it is more likely than not that the tax positions will be sustained on the basis of the technical merits of the position and (2) for those tax positions that meet the more-likely-than-not recognition threshold, management recognizes the largest amount of tax benefit that is more than 50 percent likely to be realized upon ultimate settlement with the related tax authority. We recognize interest and penalties related to unrecognized tax benefits, if any, within income tax expense and any accrued interest and penalties are included within the related tax liability line.
Net Loss Per Share	Net Loss Per Share
	Basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding for the period, without consideration for common stock equivalents. Excluded from the weighted-average number of shares outstanding are shares that have been issued upon the early exercise of stock options and are subject to future vesting, which was a total of 24,444 shares as of December 31, 2014. Diluted net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock and common stock equivalents outstanding for the period determined using the treasury-stock method. Common stock equivalents are comprised of redeemable convertible preferred stock, warrants for the purchase of common stock, and options outstanding under our stock option plan. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding as the common stock equivalents are anti-dilutive due to our net loss position.
	Potentially dilutive securities not included in the calculation of diluted net loss per share attributable to common stockholders because to do so would be anti-dilutive are as follows (in common stock equivalent shares):
		As of December 31,
		2014		2013		2012
	Redeemable convertible preferred stock		—		13,713,407		7,019,599
	Options to purchase common stock		3,210,693		3,098,573		2,336,314
	Warrants to purchase common stock		250,646		250,646		250,646
Recently Issued and Adopted Accounting Pronouncements	Recently Issued and Adopted Accounting Pronouncements
	In August 2014, the FASB issued Accounting Standards Update, or ASU, No. 2014-15, “Presentation of Financial Statements—Going Concern (Subtopic 205-40): Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern,” or ASU 2014-15. ASU 2014-15 will require management to assess, at each annual and interim reporting period, the entity’s ability to continue as a going concern. The amendments in ASU 2014-15 do not have any application to an entity’s financial statements, but only to disclosure in the related notes. ASU 2014-15 is effective for annual periods ending after December 15, 2016 and early application is permitted. We intend to apply ASU 2014-15 beginning with the first quarter of fiscal year 2016.
	In June 2014, the FASB issued ASU No. 2014-10, “Development Stage Entities (Topic 915) — Elimination of Certain Financial Reporting Requirements, Including an Amendment to Variable Interest Entities Guidance in Topic 810, Consolidation,” or ASU 2014-10, which eliminates the concept of a development stage entity in its entirety from current accounting guidance and provides for certain amendments to the consolidation guidance in Topic 810 in the Accounting Standards Codification, or ASC. Prior to the issuance of this guidance, we were considered a development stage entity and as a result we included certain inception-to-date disclosures in our financial statements. The guidance related to the elimination of the concept of a development stage entity is effective for public companies for annual reporting periods beginning after December 15, 2014, and interim periods therein. The amendment of the consolidation guidance in Topic 810 is effective for public companies for annual reporting periods beginning after December 15, 2015. Early adoption of the new standard is permitted. We adopted ASU No. 2014-10 during the quarter ended June 30, 2014. As such, all inception-to-date disclosures have not been included in these consolidated financial statements.

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Schedule of Potentially Dilutive Securities Not Included in Calculation of Diluted Net Loss per Share	Potentially dilutive securities not included in the calculation of diluted net loss per share attributable to common stockholders because to do so would be anti-dilutive are as follows (in common stock equivalent shares):
		As of December 31,
		2014		2013		2012
	Redeemable convertible preferred stock		—		13,713,407		7,019,599
	Options to purchase common stock		3,210,693		3,098,573		2,336,314
	Warrants to purchase common stock		250,646		250,646		250,646

Other_Financial_Information_Ta

Other Financial Information (Tables)	12 Months Ended
	Dec. 31, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Property and Equipment, Leasehold Improvements, and Related Accumulated Depreciation and Amortization	Property and equipment, leasehold improvements, and related accumulated depreciation and amortization were as follows (in thousands):
		December 31,
		2014			2013
	Manufacturing and laboratory equipment	$	3,177		$	3,229
	Office furniture and equipment		113			112
	Clinical equipment		2,115			1,606
	Computer equipment and software		152			122
	Leasehold improvements		3,367			2,830
	Construction in progress		922			323
			9,846			8,222
	Less: accumulated depreciation and amortization		(6,778	)		(5,755	)
	Total	$	3,068		$	2,467
Schedule of Accrued Expenses	Accrued expenses consist of (in thousands):
		December 31,
		2014			2013
	Accrued clinical and related costs	$	6,072		$	2,067
	Accrued compensation and related taxes		2,554			512
	Accrued offering costs		—			496
	Accrued other		249			178
	Total	$	8,875		$	3,253

Commitments_and_Contingencies_

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Future Minimum Annual Obligations Under All Non-Cancellable Operating Lease Commitments	Future minimum annual obligations under all non-cancellable operating lease commitments at December 31, 2014 are as follows (in thousands):
		Year Ending December 31, 2014
		Total		2015		2016		2017		2018		2019
	Operating lease obligations	$	2,200	$	856	$	853	$	491	$	—	$	—
Summaries of Purchase Obligations	The following table summarizes our purchase obligations at December 31, 2014 (in thousands):
		Payments Due by Period
		Total		Less Than		3-Feb		5-Mar		More Than
				1 Year		Years		Years		5 Years
	Purchase obligations	$	758	$	758	$	—	$	—	$	—

Fair_Value_Tables

Fair Value (Tables)	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Schedule of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis	The following fair value hierarchy table presents information about each major category of our financial assets and liabilities measured at fair value on a recurring basis (in thousands):
		Fair Value Measurement at December 31, 2014
		Fair Value			Level 1			Level 2		Level 3
	Assets
	Money market funds	$	101,592		$	101,592		$	—	$	—
		Fair Value Measurement at December 31, 2013
		Fair Value			Level 1			Level 2		Level 3
	Assets
	Money market funds	$	37,158		$	37,158		$	—	$	—
	Liabilities
	Future purchase rights	$	2,600		$	—		$	—	$	2,600
Schedule of Changes in Level 3 Future Purchase Rights Liabilities Measured at Fair Value on Recurring Basis	The following table summarizes the changes in Level 3 preferred stock warrant liabilities measured at fair value on a recurring basis for the year ended December 31, 2012 (in thousands):
		Fair Value of
		Preferred Stock
		Warrant Liabilities
	Balance at January 1, 2012	$	180
	Revaluation of warrants		(180	)
	Balance at December 31, 2012	$	—
	The preferred stock warrants were converted to common stock warrants in February 2012 (see Note 2).
	The following table summarizes the changes in Level 3 future purchase rights liabilities measured at fair value on a recurring basis for the three years ended December 31, 2014 (in thousands):
		Fair Value of
		Future Purchase
		Rights Liabilities
	Balance at January 1, 2012	$	—
	Initial valuation of future purchase rights		3,101
	Re-measurement of future purchase rights		(3,101	)
	Balance at December 31, 2012		—
	Initial valuation of additional future purchase rights		1,294
	Re-measurement of future purchase rights		1,306
	Balance at December 31, 2013		2,600
	Re-measurement of future purchase rights		(2,600	)
	Balance at December 31, 2014	$	—
Schedule of Future Purchase Rights Liabilities Using Binomial Lattice Option Pricing Model	We valued the future purchase rights liabilities in the periods ended December 31, 2013 and 2012 using a binomial lattice option pricing model with the following assumptions:
		December 31,
		2013			2012
	Common stock fair value	$	5.93		$	1.17
	Preferred stock price	$	8		$	8
	Volatility		85	%		80	%
	Risk-free interest rate		0.38	%		0.36	%
	Contractual life (years)		2.08			3.08
	Number of nodes		25			37
	Dividend yield		0	%		0	%

Redeemable_Convertible_Preferr1

Redeemable Convertible Preferred Stock (Tables)	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Number of Shares Subject to Purchase	The following table summarizes the number of shares subject to purchase under future purchase rights initially granted, the fair value per share of the senior preferred stock subject to the rights as initially granted, the initial grant date fair value recorded, the fair value of our common stock used in determining such value, and beneficial conversion amounts underlying the preferred stock that were recorded in connection with certain purchases of such preferred stock under the Senior Preferred Purchase Agreement and the related stock options granted to certain members of our board of directors (in thousands except share and per share amounts):
	Issuance Date	Number of			Fair Value		Grant Date Fair		Common Stock		Beneficial
		Shares			per Share		Value Recorded		Value Used in		Conversion on
		Subject to			of Rights				Determining		Underlying
		Future Purchase							Fair Value		Preferred Stock/
		Rights Granted									Options
	25-Sep-12		3,750,000		$	2.8	$	3,101	$	2.3	$	—
	28-Feb-13		891,250		$	2.83	$	864	$	6.85	$	513
	30-Apr-13		461,271		$	2.4	$	379	$	6.85	$	192
	26-Jun-13		66,250		$	0.76	$	50	$	6.82	$	264
Warrant Activity	Our warrant activity is as follows for the three years ended December 31, 2014:
		Number			Weighted-
		Outstanding			average
					Exercise Price
	Balance outstanding — January 1, 2012		252,308		$	95.84
	Expiration of warrants		(1,662	)	$	191.69
	Balance outstanding — December 31, 2012, 2013 and 2014		250,646		$	95.21

Common_Stock_Tables

Common Stock (Tables)	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Shares Reserved for Future Issuance	Shares reserved for future issuance at December 31, 2014 are as follows:
		Number of
		Shares
	Exercise of common stock warrants		250,646
	Common stock options outstanding		3,210,693
	Common stock options available for future grant		373,803
	Total common shares reserved for future issuance		3,835,142

Stock_Compensation_Plans_Table

Stock Compensation Plans (Tables)	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of Stock Option Activity	The following table summarizes stock option activity:
		Options			Weighted-		Weighted-		Aggregate
					Average		Average		Intrinsic
					Exercise		Remaining		Value (In
					Price		Contractual		thousands)
							Term (Years)
	Outstanding as of January 1, 2014		3,098,573		$	6.71
	Granted		326,324		$	16.85
	Exercised		(142,041	)	$	6
	Forfeited		(72,163	)	$	8.11
	Outstanding as of December 31, 2014		3,210,693		$	7.54		8	$	55,845
	Options vested and expected to vest as of December 31, 2014		3,129,706		$	7.45		7.9	$	54,722
	Options exercisable as of December 31, 2014		2,981,319		$	6.64		7.9	$	54,529
Schedule of Stock Options	The following table summarizes information about stock options (in thousands):
		Year Ended
		December 31,
		2014			2013		2012
	Aggregate intrinsic value of options exercised	$	1,972		$	633	$	—
Ranges of Underlying Assumptions Used to Determine Fair Value of Stock Options Granted to Employees and Non-Employees	The following are the ranges of underlying assumptions used to determine the fair value of stock options granted to employees and non-employees:
		Years Ended December 31,
		2014			2013		2012
	Employees and Directors:
	Risk-free interest rate		1.53% - 1.89%			0.76% - 1.10%		0.76% - 0.99%
	Expected dividend yield		0%			0%		0%
	Expected volatility		80%  - 85%			90% - 100%		100%
	Expected term of options (years)		6 – 6.2			5 - 5.5		5 - 6
	Range of common stock value	$	7.55 – $24.04		$	6.77 - $9.94	$	0.43 - $1.17
		Years Ended December 31,
		2014			2013		2012
	Non-Employees:
	Risk-free interest rate		0.11% - 1.27%			0.13% - 0.86%		0.17% - 0.57%
	Expected dividend yield		0%			0%		0%
	Expected volatility		73% - 85%			90% - 100%		100%
	Expected term of options (years)		1 - 4			1 - 4		1 - 4
	Range of common stock value	$	11.31 - $27.24		$	5.93 - $9.94	$	1.17
Schedule of Stock-based Compensation Expense Valuation Analysis Probability-Weighted Scenarios	March 31, 2013 Valuation Analysis
	Our analysis considered the following probability-weighted scenarios:
	Scenario	Weight
	IPO by December 31, 2013		25	%
	Sale by December 31, 2013		20	%
	Private company		30	%
	Dissolution		25	%
	June 30, 2013 Valuation Analysis
	Our analysis considered the following probability-weighted scenarios:
	Scenario	Weight
	IPO by November 15, 2013		35	%
	Sale by November 15, 2013		10	%
	Private company		30	%
	Dissolution		25	%
	September 3, 2013 Valuation Analysis
	Our analysis considered the following probability-weighted scenarios:
	Scenario	Weight
	IPO by November 15, 2013		50	%
	Sale by November 15, 2013		10	%
	Private company		25	%
	Dissolution		15	%
	September 30, 2013 Valuation Analysis
	Our analysis considered the following probability-weighted scenarios:
	Scenario	Weight
	IPO by November 15, 2013.		50	%
	Sale by November 15, 2013		10	%
	Private company		25	%
	Dissolution		15	%
	December 1, 2013 Valuation Analysis
	Our analysis considered the following probability-weighted scenarios:
	Scenario	Weight
	IPO by May 15, 2014		20	%
	Sale by September 30, 2015		10	%
	Private company		50	%
	Dissolution		20	%
	December 31, 2013 Valuation Analysis
	Our analysis considered the following probability-weighted scenarios:
	Scenario	Weight
	IPO by May 15, 2014		20	%
	Sale by September 30, 2015		10	%
	Private company		50	%
	Dissolution		20	%
	February 12, 2014 Valuation Analysis
	Our analysis considered the following probability-weighted scenarios:
	Scenario	Weight
	IPO by May 15, 2014		25	%
	Sale by September 30, 2015		10	%
	Private company		50	%
	Dissolution		15	%
	March 31, 2014 Valuation Analysis
	Our analysis considered the following probability-weighted scenarios:
	Scenario	Weight
	IPO by April 15, 2014		65	%
	Sale by September 30, 2015		10	%
	Private company		15	%
	Dissolution		10	%
Schedule of Stock-based Compensation Expense to Employees and Non-Employees	The following table summarizes the allocation of stock-based compensation expense to employees and non-employees (in thousands):
		Years Ended December 31,
		2014			2013		2012
	Employees and Directors:
	Research and development	$	763		$	262	$	45
	General and administrative		937			503		94
	Totals	$	1,700		$	765	$	139
		Years Ended December 31,
		2014			2013		2012
	Non-Employees:
	Research and development	$	757		$	149	$	5
	General and administrative		53			34		—
	Totals	$	810		$	183	$	5

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Net Loss before Income Tax Based on Jurisdictions	Our net loss before income tax was subject to tax in the following jurisdictions for the following periods (in thousands):
		Year Ended December 31,
		2014			2013			2012
	United States	$	(47,482	)	$	(32,524	)	$	(6,321	)
	Foreign		(185	)		(194	)		(380	)
		$	(47,667	)	$	(32,718	)	$	(6,701	)
Income Tax Rate Reconciliation	Our rate reconciliation consists of the following:
		Year Ended December 31,
		2014			2013			2012
	Federal statutory rate		35	%		35	%		35	%
	State tax (net of federal benefit)		5.4	%		5.3	%		5.8	%
	Research and development credits		3.8	%		3.9	%		1.8	%
	Warrants/purchase rights liabilities		2.2	%		(1.6	%)		19.9	%
	Foreign net operating losses		(0.4	%)		(1.2	%)		(0.6	%)
	382 limited net operating losses and credits		—			(0.6	%)		(415.2	%)
	Change in valuation allowance		(45.1	%)		(40.0	%)		355.5	%
	Other		(0.9	%)		(0.8	%)		(2.2	%)
	Effective tax rate		0	%		0	%		0	%
Deferred Tax Assets	Significant components of our deferred tax assets are shown below. A valuation allowance has been established as realization of such deferred tax assets has not met the more likely-than-not threshold requirement. If our judgment changes and it is determined that we will be able to realize these deferred tax assets, the tax benefits relating to any reversal of the valuation allowance on deferred tax assets will be accounted for as a reduction to income tax expense.
		December 31,
		2014			2013
		(in thousands)
	Deferred tax assets:
	Net operating loss carryforwards	$	33,517		$	15,073
	Research and development tax credits		3,269			1,426
	Stock compensation		879			181
	Foreign net operating loss carryforwards		377			504
	Other, net		1,715			1,066
	Total deferred tax assets		39,757			18,250
	Less valuation allowance		(39,757	)		(18,250	)
		$	—		$	—
Unrecognized Tax Benefit	The following table summarizes the activity related to our unrecognized tax benefits (in thousands):
		Year Ended
		December 31,
		2014			2013
	Balance at beginning of year	$	407		$	—
	Additions based on tax positions related to the current year		533			337
	Changes for prior period tax positions		(2	)		70
	Balance at end of year	$	938		$	407

Selected_Quarterly_Data_Tables

Selected Quarterly Data (Tables)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Summarized Quarterly Information	Summarized quarterly data for 2014 and 2013 are as follows (in thousands, except per share data):
			For the Quarters Ended
			March 31			June 30			September 30			December 31			Total Year
	2014:00:00
	Operating expenses		$	11,876		$	11,638		$	12,810		$	14,018		$	50,342
	Net loss		$	(10,748	)	$	(10,167	)	$	(12,798	)	$	(13,954	)	$	(47,667	)
	Net loss attributable to common stockholders		$	(13,818	)	$	(16,251	)	$	(12,798	)	$	(13,954	)	$	(56,821	)
	Basic and diluted net loss per share attributable to common stockholders (1)		$	(24.49	)	$	(0.91	)	$	(0.59	)	$	(0.59	)
	2013:00:00
	Operating expenses		$	4,926		$	7,063		$	9,165		$	10,248		$	31,402
	Net loss		$	(9,358	)	$	(6,144	)	$	(6,977	)	$	(10,239	)	$	(32,718	)
	Net loss attributable to common stockholders		$	(10,331	)	$	(7,267	)	$	(9,034	)	$	(12,453	)	$	(39,085	)
	Basic and diluted net loss per share attributable to common stockholders (1)		$	(22.11	)	$	(14.33	)	$	(16.31	)	$	(22.28	)
	-1	Net loss per share is computed independently for each of the quarters presented. Therefore, the sum of the quarterly per share calculations will not necessarily equal the annual per share calculation.

Summary_of_Significant_Account2

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Summary Of Significant Accounting Policies [Line Items]
Expected dividend yield	0.00%	0.00%	0.00%
Early Exercise of Stock Options [Member]
Summary Of Significant Accounting Policies [Line Items]
Shares issued upon early exercise of stock options and are subject to future vesting	24,444
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives	3 years
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Cash equivalents, highly-liquid investments maturity	3 months
Property and equipment, estimated useful lives	5 years

Summary_of_Significant_Account3

Summary of Significant Accounting Policies - Schedule of Potentially Dilutive Securities Not Included in Calculation of Diluted Net Loss per Share (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Redeemable Convertible Preferred Stock (Senior) [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities not included in the calculation of diluted net loss per share		13,713,407	7,019,599
Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities not included in the calculation of diluted net loss per share	3,210,693	3,098,573	2,336,314
Warrants to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities not included in the calculation of diluted net loss per share	250,646	250,646	250,646

Other_Financial_Information_Sc

Other Financial Information - Schedule of Property and Equipment, Leasehold Improvements, and Related Accumulated Depreciation and Amortization (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$9,846	$8,222
Less: accumulated depreciation and amortization	-6,778	-5,755
Property and equipment, net	3,068	2,467
Manufacturing and Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	3,177	3,229
Office Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	113	112
Clinical Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,115	1,606
Computer Equipment and Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	152	122
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	3,367	2,830
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$922	$323

Other_Financial_Information_Ad

Other Financial Information - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property, Plant and Equipment [Abstract]
Depreciation and amortization expense	$1,100,000	$851,000	$651,000
Capitalized leasehold improvements		$478,000

Other_Financial_Information_Sc1

Other Financial Information - Schedule of Accrued Expenses (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Payables and Accruals [Abstract]
Accrued clinical and related costs	$6,072	$2,067
Accrued compensation and related taxes	2,554	512
Accrued offering costs		496
Accrued other	249	178
Total	$8,875	$3,253

Debt_Additional_Information_De

Debt - Additional Information (Detail) (Term Loan [Member], USD $)	31-May-12	Sep. 30, 2008
Term Loan [Member]
Debt Instrument [Line Items]
Debt instrument , interest rate		10.60%
Debt instrument, principal		$4,000,000
Debt instrument, percentage of remaining monthly payments deferred	50.00%

Commitments_and_Contingencies_1

Commitments and Contingencies - Future Minimum Annual Obligations Under All Non-Cancellable Operating Lease Commitments (Detail) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified
Leases [Abstract]
Total	$2,200
2015	856
2016	853
2017	$491

Commitments_and_Contingencies_2

Commitments and Contingencies - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Leased Assets [Line Items]
Total rent expense under operating leases	$835,000	$659,000	$459,000
Current deferred rent	126,000	142,000
Other long-term liabilities	241,000	321,000
Purchase obligations	758,000
Cartridges [Member]
Operating Leased Assets [Line Items]
Purchase obligations	367,000
Purchase commitment, required percentage of scheduled invoice payable upon cancellation	50.00%
Materials [Member]
Operating Leased Assets [Line Items]
Purchase commitment, purchased	1,200,000	439,000
Raw Materials [Member]
Operating Leased Assets [Line Items]
Purchase obligations	391,000
Purchase commitment, purchased	$1,200,000	$724,000	$462,000

Commitments_and_Contingencies_3

Commitments and Contingencies - Summaries of Purchase Obligations (Detail) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified
Commitments and Contingencies Disclosure [Abstract]
Total	$758
Payments Due, Less Than 1 Year	758
Payments Due, 2-3 Years	0
Payments Due, 3-5 Years	0
Payments Due, More Than 5 Years	$0

Fair_Value_Schedule_of_Financi

Fair Value - Schedule of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Liabilities
Liabilities		$2,600
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member]
Assets
Assets	101,592	37,158
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Future Purchase Rights [Member]
Liabilities
Liabilities		2,600
Fair Value [Member] | Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member]
Assets
Assets	101,592	37,158
Fair Value [Member] | Fair Value, Measurements, Recurring [Member] | Future Purchase Rights [Member]
Liabilities
Liabilities		$2,600

Fair_Value_Additional_Informat

Fair Value - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014
Debt Instrument Fair Value Carrying Value [Abstract]
Fair value transfers of assets and liabilities between levels	$0

Fair_Value_Schedule_of_Changes

Fair Value - Schedule of Changes in Level 3 Future Purchase Rights Liabilities Measured at Fair Value on Recurring Basis (Detail) (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]
Revaluation of warrants			($180)
Balance at January 1, 2012	2,600
Re-measurement of future purchase rights	-2,600	1,306	-3,101
Balance at December 31, 2012		2,600
Fair Value Of Future Purchase Rights Liabilities [Member] | Level 3 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at January 1, 2012			180
Revaluation of warrants			-180
Balance at January 1, 2012	2,600
Initial valuation of additional future purchase rights		1,294	3,101
Re-measurement of future purchase rights	-2,600	1,306	-3,101
Balance at December 31, 2012		$2,600

Fair_Value_Schedule_of_Future_

Fair Value - Schedule of Future Purchase Rights Liabilities Using Binomial Lattice Option Pricing Model (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 31, 2014	Feb. 12, 2014	Dec. 01, 2013	Sep. 30, 2013	Sep. 03, 2013	Jun. 30, 2013	Mar. 31, 2013
		Nodes	Nodes
Fair Value Disclosures [Abstract]
Common stock fair value		$5.93	$1.17	$11.30	$7.55	$6.77	$10.02	$9.94	$6.82	$6.85
Preferred stock price		$8	$8
Volatility		85.00%	80.00%
Risk-free interest rate		0.38%	0.36%
Contractual life (years)		2 years 29 days	3 years 29 days
Number of nodes		25	37
Dividend yield	0.00%	0.00%	0.00%

Redeemable_Convertible_Preferr2

Redeemable Convertible Preferred Stock - Additional Information (Detail) (USD $)

1 Months Ended

12 Months Ended

0 Months Ended

6 Months Ended

0 Months Ended

2 Months Ended

1 Months Ended

2 Months Ended

3 Months Ended

1 Months Ended

Feb. 29, 2012

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2012

Jun. 30, 2013

Jun. 30, 2013

Feb. 29, 2012

Feb. 29, 2012

Apr. 30, 2014

Feb. 28, 2014

Jun. 30, 2013

31-May-13

Feb. 28, 2013

Oct. 31, 2012

Mar. 31, 2014

Dec. 31, 2013

Jan. 31, 2014

Sep. 30, 2012

Dec. 31, 2011

Vote

Class of Stock [Line Items]

Reclassification of aggregate value of preferred stock to stockholders' equity (deficit)

$97,563,000

($44,657,000)

($7,632,000)

($44,657,000)

($54,853,000)

Convertible preferred stock, terms of conversion

In conjunction with the junior preferred stock financing, previously issued shares of redeemable convertible Series A, Series B, Series C, and Series D preferred stock and related preferred stock warrants converted into shares of common stock and common stock warrants, respectively.

Issuance costs

3,112,000

Preferred stock, authorized

20,000,000

25,000,000

25,000,000

Aggregate conversion amount of preferred stock

878,000

Aggregate common stock options granted to stock, value per share

$11.87

$5.53

$0.47

Shares authorized

150,000,000

Common stock, shares authorized

130,000,000

29,250,000

29,250,000

Common stock, par value

$0.00

$0.00

$0.00

Preferred stock, par value

$0.00

$0.00

$0.00

Common stock voting right

1

Minimum percentage of combined voting power

75.00%

Minimum percentage of affirmative vote consent of shareholders

75.00%

Weighted-average exercise per share

$95.21

Minimum [Member]

Class of Stock [Line Items]

Common stock warrants expiration period

29-Feb-16

Maximum [Member]

Class of Stock [Line Items]

Common stock warrants expiration period

30-Sep-19

Preferred Stock [Member]

Class of Stock [Line Items]

Reclassification of aggregate value of preferred stock to stockholders' equity (deficit)

54,700,000

54,700,000

54,700,000

Common Stock Options [Member] | Director [Member]

Class of Stock [Line Items]

Aggregate conversion amount of preferred stock

264,000

Aggregate common stock options granted to stock

86,917

Aggregate common stock options granted to stock, value per share

$4.91

Future Purchase Rights [Member]

Class of Stock [Line Items]

Estimated fair value of shares

1,300,000

1,300,000

Nonredeemable Convertible Preferred Stock [Member]

Class of Stock [Line Items]

Net proceeds from issuance of preferred stock

1,500,000

Convertible preferred stock, price per share

$0.43

Convertible preferred stock, shares issued

3,501,400

Net proceeds from issuance of preferred stock

1,300,000

Issuance costs

40,000

Convertible Preferred Stock (Junior) [Member]

Class of Stock [Line Items]

Issuance costs

31,000

Preferred stock converted into common stock

One-to-one basis

Redeemable Convertible Preferred Stock (Senior) [Member]

Class of Stock [Line Items]

Convertible preferred stock, shares issued

241,016

3,830,050

158,150

305,571

2,606,250

Issuance costs

727,000

35,000

90,000

28,000

134,000

240,000

Preferred stock converted into common stock

All the outstanding shares of our senior redeemable convertible preferred stock were converted into common stock on a one-to-one basis

Proceeds from issuance of preferred stock

1,900,000

30,600,000

1,200,000

2,300,000

19,800,000

Debt conversion, shares issued

911,949

Discounts and commissions

3,800,000

Aggregate conversion amount of preferred stock

705,000

Redeemable Convertible Preferred Stock (Senior) [Member] | Debt Principal [Member]

Class of Stock [Line Items]

Debt conversion, amount

7,200,000

Redeemable Convertible Preferred Stock (Senior) [Member] | Accrued Interest [Member]

Class of Stock [Line Items]

Debt conversion, amount

146,000

Redeemable Convertible Preferred Stock (Senior) [Member] | December 2013 Amendment [Member]

Class of Stock [Line Items]

Convertible preferred stock, shares issued

2,400,000

Issuance costs

102,000

Proceeds from issuance of preferred stock

19,100,000

Redeemable Convertible Preferred Stock (Senior) [Member] | Preferred Stock Purchase Agreement [Member]

Class of Stock [Line Items]

Convertible preferred stock, shares issued

10,767,007

555,000

Issuance costs

135,000

Preferred stock, authorized

14,765,632

Preferred stock, stated value per share

$8

Proceeds from issuance of preferred stock

4,300,000

Redeemable Convertible Preferred Stock (Senior) [Member] | Preferred Stock Purchase Agreement [Member] | Private Placement [Member]

Class of Stock [Line Items]

Convertible preferred stock, price per share

$8

Convertible preferred stock, shares issued

1,500,000

Issuance costs

31,000

Proceeds from issuance of preferred stock

$12,000,000

Redeemable Convertible Preferred Stock (Senior) [Member] | Future Purchase Rights [Member]

Class of Stock [Line Items]

Convertible preferred stock, price per share

$8

Redeemable_Convertible_Preferr3

Redeemable Convertible Preferred Stock - Number of Shares Subject to Purchase (Detail) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2014	Mar. 31, 2014	Feb. 12, 2014	Dec. 01, 2013	Sep. 30, 2013	Sep. 03, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012
Temporary Equity [Line Items]
Common Stock Value Used in Determining Fair Value	$5.93		$11.30	$7.55	$6.77	$10.02	$9.94	$6.82	$6.85	$1.17
Beneficial Conversion on Underlying Preferred Stock/ Options	$969
September 25, 2012 [Member]
Temporary Equity [Line Items]
Issuance Date		25-Sep-12
Number of Shares Subject to Future Purchase Rights Granted		3,750,000
Fair Value per Share of Rights		$2.80
Grant Date Fair Value Recorded		3,101
Common Stock Value Used in Determining Fair Value		$2.30
February 28, 2013 [Member]
Temporary Equity [Line Items]
Issuance Date		28-Feb-13
Number of Shares Subject to Future Purchase Rights Granted		891,250
Fair Value per Share of Rights		$2.83
Grant Date Fair Value Recorded		864
Common Stock Value Used in Determining Fair Value		$6.85
Beneficial Conversion on Underlying Preferred Stock/ Options		513
April 30, 2013 [Member]
Temporary Equity [Line Items]
Issuance Date		30-Apr-13
Number of Shares Subject to Future Purchase Rights Granted		461,271
Fair Value per Share of Rights		$2.40
Grant Date Fair Value Recorded		379
Common Stock Value Used in Determining Fair Value		$6.85
Beneficial Conversion on Underlying Preferred Stock/ Options		192
June 26, 2013 [Member]
Temporary Equity [Line Items]
Issuance Date		26-Jun-13
Number of Shares Subject to Future Purchase Rights Granted		66,250
Fair Value per Share of Rights		$0.76
Grant Date Fair Value Recorded		50
Common Stock Value Used in Determining Fair Value		$6.82
Beneficial Conversion on Underlying Preferred Stock/ Options		$264

Redeemable_Convertible_Preferr4

Redeemable Convertible Preferred Stock - Warrant Activity (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2011
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Number of warrants Outstanding, beginning balance	252,308	250,646	250,646
Expiration of warrants	-1,662
Number of warrants Outstanding, ending balance	250,646	250,646	250,646
Expiration of warrants	$191.69
Weighted- average Exercise Price of warrants	$95.21	$95.21	$95.21	$95.84

Common_Stock_Additional_Inform

Common Stock - Additional Information (Detail) (USD $)	12 Months Ended	1 Months Ended
	Dec. 31, 2013	Apr. 30, 2014	Nov. 30, 2014	31-May-14	Oct. 31, 2014
Class of Stock [Line Items]
Total costs	$3,112,000
IPO [Member]
Class of Stock [Line Items]
Common stock sold, shares		4,500,000
Common stock sold, per share		$12
Net proceeds from IPO after underwriters' discounts and commissions		50,200,000
Estimated offering expenses		5,800,000
Total costs		9,600,000
Net estimated offering proceeds		44,400,000
Underwriters [Member]
Class of Stock [Line Items]
Common stock sold, per share			$17.50	$12
Net proceeds from IPO after underwriters' discounts and commissions			814,000	7,500,000
Underwriting discounts and commission				567,000
Net estimated offering proceeds				51,900,000
Over-Allotment Option [Member]
Class of Stock [Line Items]
Common stock sold, shares			50,000	675,000
Follow On Public Offering [Member]
Class of Stock [Line Items]
Common stock sold, shares					2,000,000
Common stock sold, per share					$17.50
Net proceeds from IPO after underwriters' discounts and commissions					32,600,000
Estimated offering expenses					511,000
Total costs					3,000,000
Net estimated offering proceeds			$32,900,000		$32,000,000

Common_Stock_Shares_Reserved_f

Common Stock - Shares Reserved for Future Issuance (Detail)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Equity [Abstract]
Exercise of common stock warrants	250,646	250,646	250,646	252,308
Common stock options outstanding	3,210,693	3,098,573
Common stock options available for future grant	373,803
Total common shares reserved for future issuance	3,835,142

Stock_Compensation_Plans_Addit

Stock Compensation Plans - Additional Information (Detail) (USD $)	0 Months Ended				1 Months Ended		12 Months Ended			0 Months Ended
	Sep. 30, 2013	Sep. 03, 2013	Mar. 31, 2013	Dec. 31, 2012	Jun. 30, 2013	Feb. 29, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 31, 2014	Dec. 31, 2013	Feb. 12, 2014	Dec. 01, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock exercised							142,041
Release of repurchase liability for shares vested							$104,000
Stock option cancelled						27,230
Unrecognized compensation cost expensed						27,000
Compensation cost related to unvested stock option awards							5,800,000
Remaining weighted-average vesting period							2 years 2 months 12 days
Weighted-average grant date fair value of stock options granted to employees and directors							$11.87	$5.53	$0.47
Discount for lack of marketability	6.00%	7.00%	13.00%	25.40%	9.00%
Fair value of per share	$10.02	$9.94	$6.85	$1.17	$6.82			$5.93	$1.17	11.3	5.93	7.55	6.77
Exercise price		$10.50	$8	$8	$8				$8				8
IPO by April 15, 2014 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Discount for lack of marketability										2.00%	9.00%
Sale [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Discount for lack of marketability										17.00%	20.00%	20.00%	21.00%
Private Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Discount for lack of marketability										27.00%	28.00%	28.00%	28.00%
IPO by May 15, 2014 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Discount for lack of marketability												8.00%	10.00%
Two Thousand Twelve Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option grants under Equity Incentive Plans, term							10 years
Option vesting under Equity Incentive Plans, term							4 years
Common stock exercised							55,516
Unvested common stock option to repurchase							24,444
Number of shares vested							20,715
Release of repurchase liability for shares vested							104,000
Stock option repurchase liability							$123,000
Two Thousand And Fourteen Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option grants under Equity Incentive Plans, term							10 years
Option vesting under Equity Incentive Plans, term							4 years
Shares of common stock for annual increase in shares available for issuance							1,200,000
Percentage of outstanding shares of common stock for annual increase in shares available for issuance							3.00%
2012 and 2014 Equity Incentive Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate number of shares outstanding or available for grant under the plan							3,584,496

Stock_Compensation_Plans_Summa

Stock Compensation Plans - Summary of Stock Option Activity (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Options, Outstanding, Beginning balance	3,098,573
Options, Granted	326,324
Options, Exercised	-142,041
Options, Forfeited	-72,163
Options, Outstanding, Ending balance	3,210,693
Options vested and expected to vest, Ending balance	3,129,706
Options exercisable, Ending balance	2,981,319
Outstanding, Weighted-Average Exercise Price, Beginning balance	$6.71
Granted, Weighted-Average Exercise Price	$16.85
Exercised, Weighted-Average Exercise Price	$6
Forfeited, Weighted-Average Exercise Price	$8.11
Outstanding, Weighted-Average Exercise Price, Ending balance	$7.54
Options vested and expected to vest, Weighted-Average Exercise Price, Ending balance	$7.45
Options exercisable, Weighted-Average Exercise Price, Ending balance	$6.64
Outstanding, Weighted-Average Remaining Contractual Term (Years), Ending balance	8 years
Options vested and expected to vest , Weighted-Average Remaining Contractual Term (Years), Ending balance	7 years 10 months 24 days
Options exercisable, Weighted-Average Remaining Contractual Term (Years), Ending balance	7 years 10 months 24 days
Outstanding, Aggregate Intrinsic Value, Ending balance	$55,845
Options vested and expected to vest , Aggregate Intrinsic Value, Ending balance	54,722
Options exercisable, Aggregate Intrinsic Value, Ending balance	$54,529

Stock_Compensation_Plans_Sched

Stock Compensation Plans - Schedule of Stock Options (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Aggregate intrinsic value of options exercised	$1,972	$633

Stock_Compensation_Plans_Range

Stock Compensation Plans - Ranges of Underlying Assumptions Used to Determine Fair Value of Stock Options Granted to Employees and Non-Employees (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 31, 2014	Feb. 12, 2014	Dec. 01, 2013	Sep. 30, 2013	Sep. 03, 2013	Jun. 30, 2013	Mar. 31, 2013
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Method Used [Line Items]
Range of common stock value		5.93	1.17	$11.30	$7.55	$6.77	$10.02	$9.94	$6.82	$6.85
Employees and Directors [Member]
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Method Used [Line Items]
Risk-free interest rate, minimum	1.53%	0.76%	0.76%
Risk-free interest rate, maximum	1.89%	1.10%	0.99%
Expected dividend yield	0.00%	0.00%	0.00%
Expected volatility, minimum	80.00%	90.00%
Expected volatility, maximum	85.00%	100.00%
Expected volatility			100.00%
Employees and Directors [Member] | Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Method Used [Line Items]
Expected term of options (years)	6 years	5 years	5 years
Range of common stock value	7.55	6.77	0.43
Employees and Directors [Member] | Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Method Used [Line Items]
Expected term of options (years)	6 years 2 months 12 days	5 years 6 months	6 years
Range of common stock value	24.04	9.94	1.17
Non-Employees [Member]
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Method Used [Line Items]
Risk-free interest rate, minimum	0.11%	0.13%	0.17%
Risk-free interest rate, maximum	1.27%	0.86%	0.57%
Expected dividend yield	0.00%	0.00%	0.00%
Expected volatility, minimum	73.00%	90.00%
Expected volatility, maximum	85.00%	100.00%
Expected volatility			100.00%
Range of common stock value			1.17
Non-Employees [Member] | Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Method Used [Line Items]
Expected term of options (years)	1 year	1 year	1 year
Range of common stock value	11.31	5.93
Non-Employees [Member] | Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Method Used [Line Items]
Expected term of options (years)	4 years	4 years	4 years
Range of common stock value	27.24	9.94

Stock_Compensation_Plans_Sched1

Stock Compensation Plans - Schedule of Stock-based Compensation Expense Valuation Analysis Probability-Weighted Scenarios (Detail)	0 Months Ended
	Mar. 31, 2014	Feb. 12, 2014	Dec. 31, 2013	Dec. 01, 2013	Sep. 30, 2013	Sep. 03, 2013	Jun. 30, 2013	Mar. 31, 2013
IPO by May 15, 2014 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Probability-weighted scenarios, percentage		25.00%	20.00%	20.00%
Sale by September 30, 2015 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Probability-weighted scenarios, percentage	10.00%	10.00%	10.00%	10.00%
Private Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Probability-weighted scenarios, percentage	15.00%	50.00%	50.00%	50.00%	25.00%	25.00%	30.00%	30.00%
Dissolution [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Probability-weighted scenarios, percentage	10.00%	15.00%	20.00%	20.00%	15.00%	15.00%	25.00%	25.00%
IPO by April 15, 2014 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Probability-weighted scenarios, percentage	65.00%
IPO by December 31, 2013 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Probability-weighted scenarios, percentage								25.00%
Sale by December 31, 2013 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Probability-weighted scenarios, percentage								20.00%
IPO by November 15, 2013 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Probability-weighted scenarios, percentage					50.00%	50.00%	35.00%
Sale by November 15, 2013 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Probability-weighted scenarios, percentage					10.00%	10.00%	10.00%

Stock_Compensation_Plans_Sched2

Stock Compensation Plans - Schedule of Stock-based Compensation Expense to Employees and Non-Employees (Detail) (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, Compensation Cost [Line Items]
Stock-based compensation expense	$2,510	$948	$144
Employees and Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	1,700	765	139
Non-Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	810	183	5
Research and Development [Member] | Employees and Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	763	262	45
Research and Development [Member] | Non-Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	757	149	5
General and Administrative [Member] | Employees and Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	937	503	94
General and Administrative [Member] | Non-Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$53	$34

Income_Taxes_Net_Loss_before_I

Income Taxes - Net Loss before Income Tax Based on Jurisdictions (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
United States	($47,482)	($32,524)	($6,321)
Foreign	-185	-194	-380
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest, Total	($47,667)	($32,718)	($6,701)

Income_Taxes_Income_Tax_Rate_R

Income Taxes - Income Tax Rate Reconciliation (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Federal statutory rate	35.00%	35.00%	35.00%
State tax (net of federal benefit)	5.40%	5.30%	5.80%
Research and development credits	3.80%	3.90%	1.80%
Warrants/purchase rights liabilities	2.20%	-1.60%	19.90%
Foreign net operating losses	-0.40%	-1.20%	-0.60%
382 limited net operating losses and credits		-0.60%	-415.20%
Change in valuation allowance	-45.10%	-40.00%	355.50%
Other	-0.90%	-0.80%	-2.20%
Effective tax rate	0.00%	0.00%	0.00%

Income_Taxes_Deferred_Tax_Asse

Income Taxes - Deferred Tax Assets (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Deferred tax assets:
Net operating loss carryforwards	$33,517	$15,073
Research and development tax credits	3,269	1,426
Stock compensation	879	181
Foreign net operating loss carryforwards	377	504
Other, net	1,715	1,066
Total deferred tax assets	39,757	18,250
Less valuation allowance	-39,757	-18,250
Deferred Tax Assets, Net of Valuation Allowance, Total	$0	$0

Income_Tax_Additional_Informat

Income Tax - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Feb. 28, 2012
Valuation allowance increase	$21,500,000	$13,100,000
Deferred Tax Assets Gross	39,757,000	18,250,000
State Administration of Taxation, China [Member]
Net operating loss carryforwards	1,500,000
Domestic Tax Authority [Member]
Net operating loss carryforwards	84,800,000
Domestic Tax Authority [Member] | Research and development Tax Credit Carryforward [Member]
Tax credit carry forward	2,300,000
State and Local Jurisdiction [Member]
Net operating loss carryforwards	79,400,000
State and Local Jurisdiction [Member] | Research and development Tax Credit Carryforward [Member]
Tax credit carry forward	1,400,000
Domestic Tax Authority and State and Local Jurisdiction [Member]
Net operating loss carryforwards related to excess tax deductions for stock compensation	1,800,000
Change in ownership, as defined in Section 382 [Member]
Deferred Tax Assets Gross			-23,800,000
Change in ownership, as defined in Section 382 [Member] | Domestic Tax Authority [Member]
Net operating loss carryforwards			-58,700,000
Change in ownership, as defined in Section 382 [Member] | Domestic Tax Authority [Member] | Research and development Tax Credit Carryforward [Member]
Tax credit carry forward			-2,200,000
Change in ownership, as defined in Section 382 [Member] | State and Local Jurisdiction [Member]
Net operating loss carryforwards			-56,200,000
Change in ownership, as defined in Section 382 [Member] | State and Local Jurisdiction [Member] | Research and development Tax Credit Carryforward [Member]
Tax credit carry forward			($1,600,000)

Income_Taxes_Unrecognized_Tax_

Income Taxes - Unrecognized Tax Benefit (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Balance at beginning of year	$407
Additions based on tax positions related to the current year	533	337
Changes for prior period tax positions	-2	70
Balance at end of year	$938	$407

Related_Party_Transactions_Add

Related Party Transactions - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Director [Member] | Service Fees [Member]
Related Party Transaction [Line Items]
Related party transaction, expense		$100,000	$73,000
Director [Member] | Chairmans Fee [Member]
Related Party Transaction [Line Items]
Related party transaction, expense	33,500	39,000	7,000
Clinical Advisory Board
Related Party Transaction [Line Items]
Related party transaction, expense	1,700,000	824,000
Related party, accounts payable and accrued expenses	$1,600,000	$643,000

Selected_Quarterly_Data_Summar

Selected Quarterly Data - Summarized Quarterly Information (Detail) (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]
Operating expenses	$14,018	$12,810	$11,638	$11,876	$10,248	$9,165	$7,063	$4,926	$50,342	$31,402	$9,580
Net loss	-13,954	-12,798	-10,167	-10,748	-10,239	-6,977	-6,144	-9,358	-47,667	-32,718	-6,701
Net loss attributable to common stockholders	($13,954)	($12,798)	($16,251)	($13,818)	($12,453)	($9,034)	($7,267)	($10,331)	($56,821)	($39,085)	($7,643)
Basic and diluted net loss per share attributable to common stockholders	($0.59)	($0.59)	($0.91)	($24.49)	($22.28)	($16.31)	($14.33)	($22.11)	($3.54)	($74.86)	($17.89)