CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Expenses
Research and development	$ 26,071us-gaap_ResearchAndDevelopmentExpense	$ 19,797us-gaap_ResearchAndDevelopmentExpense	$ 15,081us-gaap_ResearchAndDevelopmentExpense
General and administrative	12,699us-gaap_GeneralAndAdministrativeExpense	11,177us-gaap_GeneralAndAdministrativeExpense	5,417us-gaap_GeneralAndAdministrativeExpense
Restructuring costs	334us-gaap_RestructuringCharges	1,025us-gaap_RestructuringCharges	0us-gaap_RestructuringCharges
Total operating expenses	39,104us-gaap_OperatingExpenses	31,999us-gaap_OperatingExpenses	20,498us-gaap_OperatingExpenses
Loss from operations	(39,104)us-gaap_OperatingIncomeLoss	(31,999)us-gaap_OperatingIncomeLoss	(20,498)us-gaap_OperatingIncomeLoss
Other income (expense), net	(77)us-gaap_OtherNonoperatingIncomeExpense	(1,084)us-gaap_OtherNonoperatingIncomeExpense	251us-gaap_OtherNonoperatingIncomeExpense
Change in fair value of warrant liability	(4,517)us-gaap_FairValueAdjustmentOfWarrants	(19,799)us-gaap_FairValueAdjustmentOfWarrants	0us-gaap_FairValueAdjustmentOfWarrants
Loss before income taxes	(43,698)	(52,882)	(20,247)
Income tax benefit (expense)	0us-gaap_IncomeTaxExpenseBenefit	23us-gaap_IncomeTaxExpenseBenefit	(39)us-gaap_IncomeTaxExpenseBenefit
Net loss	(43,698)us-gaap_NetIncomeLoss	(52,859)us-gaap_NetIncomeLoss	(20,286)us-gaap_NetIncomeLoss
Unrealized gain (loss) on available-for-sale investments	(14)	13	0
Comprehensive loss	$ (43,684)us-gaap_ComprehensiveIncomeNetOfTax	$ (52,872)us-gaap_ComprehensiveIncomeNetOfTax	$ (20,286)us-gaap_ComprehensiveIncomeNetOfTax
Basic and diluted net loss per share (in dollars per share)	$ (3.24)us-gaap_EarningsPerShareBasicAndDiluted	$ (4.78)us-gaap_EarningsPerShareBasicAndDiluted	$ (3.00)us-gaap_EarningsPerShareBasicAndDiluted
Weighted average number of shares used in computing net loss per share, basic and diluted (in shares)	13,483,467	11,057,040	6,762,985

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Average number of shares or units issued and outstanding that are used in calculating basic and diluted earnings per share (EPS).

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