Consolidated 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	Dec. 31, 2012
Operating expenses:
Research and development	$ 21,784us-gaap_ResearchAndDevelopmentExpense	$ 15,802us-gaap_ResearchAndDevelopmentExpense	$ 6,323us-gaap_ResearchAndDevelopmentExpense
Selling, general and administrative	26,149	13,332	7,206
Total operating expenses	47,933us-gaap_OperatingExpenses	29,134us-gaap_OperatingExpenses	13,529us-gaap_OperatingExpenses
Loss from operations	(47,933)us-gaap_OperatingIncomeLoss	(29,134)us-gaap_OperatingIncomeLoss	(13,529)us-gaap_OperatingIncomeLoss
Interest (expense) income, net	(126)us-gaap_InvestmentIncomeInterest	90us-gaap_InvestmentIncomeInterest	19us-gaap_InvestmentIncomeInterest
Other income (expense), net	122us-gaap_OtherNonoperatingIncomeExpense
Loss from equity method investment	(1,583)
Net loss	(49,520)us-gaap_NetIncomeLoss	(29,044)us-gaap_NetIncomeLoss	(13,510)us-gaap_NetIncomeLoss
Net loss per share-basic and diluted (in dollars per share)	$ (2.19)us-gaap_EarningsPerShareBasicAndDiluted	$ (1.80)us-gaap_EarningsPerShareBasicAndDiluted	$ (2.33)us-gaap_EarningsPerShareBasicAndDiluted
Weighted average number of shares used in net loss per share-basic and diluted	22,647	16,160	5,810
Net loss	(49,520)	(29,044)	(13,510)
Other comprehensive loss:
Unrealized gains (losses) on available-for-sale securities	(36)	16	(6)
Comprehensive loss	(49,556)us-gaap_ComprehensiveIncomeNetOfTax	(29,028)us-gaap_ComprehensiveIncomeNetOfTax	(13,516)us-gaap_ComprehensiveIncomeNetOfTax
Non-cash stock-based compensation expenses included in operating expenses are as follows:
Stock-based compensation expense	12,407us-gaap_ShareBasedCompensation	5,094us-gaap_ShareBasedCompensation	1,382us-gaap_ShareBasedCompensation
Research and development
Non-cash stock-based compensation expenses included in operating expenses are as follows:
Stock-based compensation expense	7,578	2,361	1,143
Selling, general and administrative
Non-cash stock-based compensation expenses included in operating expenses are as follows:
Stock-based compensation expense	$ 4,829	$ 2,733	$ 239

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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