Statements of Operations and Comprehensive Loss (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Expenses:
Research and development	$ 9,944us-gaap_ResearchAndDevelopmentExpense	$ 4,362us-gaap_ResearchAndDevelopmentExpense
General and administrative	11,396us-gaap_GeneralAndAdministrativeExpense	13,579us-gaap_GeneralAndAdministrativeExpense
Total expenses	21,340us-gaap_CostsAndExpenses	17,941us-gaap_CostsAndExpenses
Loss from operations	(21,340)us-gaap_OperatingIncomeLoss	(17,941)us-gaap_OperatingIncomeLoss
Other income, net	27us-gaap_OtherNonoperatingIncomeExpense	6us-gaap_OtherNonoperatingIncomeExpense
Net loss and comprehensive loss	(21,313)us-gaap_NetIncomeLoss	(17,935)us-gaap_NetIncomeLoss
Convertible preferred stock dividends earned	0	(801)
Net loss attributable to common shareholders	$ (21,313)	$ (18,736)
Basic and diluted net loss per share (usd per share)	$ (2.00)us-gaap_EarningsPerShareBasicAndDiluted	$ (12.16)us-gaap_EarningsPerShareBasicAndDiluted
Shares used in computing basic and diluted net loss per share	10,667	1,540

Total costs of sales and operating expenses for the period.

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