CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Expenses
Research and development	$ 8,207us-gaap_ResearchAndDevelopmentExpense	$ 4,960us-gaap_ResearchAndDevelopmentExpense
General and administrative	3,779us-gaap_GeneralAndAdministrativeExpense	2,685us-gaap_GeneralAndAdministrativeExpense
Restructuring costs	0us-gaap_RestructuringCharges	334us-gaap_RestructuringCharges
Total operating expenses	11,986us-gaap_OperatingExpenses	7,979us-gaap_OperatingExpenses
Loss from operations	(11,986)us-gaap_OperatingIncomeLoss	(7,979)us-gaap_OperatingIncomeLoss
Other income (expense), net	46us-gaap_OtherNonoperatingIncomeExpense	(202)us-gaap_OtherNonoperatingIncomeExpense
Change in fair value of warrant liability	0us-gaap_FairValueAdjustmentOfWarrants	(5,475)us-gaap_FairValueAdjustmentOfWarrants
Net loss	(11,940)us-gaap_NetIncomeLoss	(13,656)us-gaap_NetIncomeLoss
Unrealized gain (loss) on available-for-sale investments	5	10
Comprehensive loss	$ (11,935)us-gaap_ComprehensiveIncomeNetOfTax	$ (13,646)us-gaap_ComprehensiveIncomeNetOfTax
Basic and diluted net loss per share	$ (0.77)us-gaap_EarningsPerShareBasicAndDiluted	$ (1.01)us-gaap_EarningsPerShareBasicAndDiluted
Weighted average number of shares used in computing net loss per share, basic and diluted	15,453,534	13,457,400

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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