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
Consolidated Statements of Operations and Comprehensive Loss
Product revenue	$ 10
Research revenue	178
Total revenue	188
Costs and expenses:
Cost of product revenue	3
Research and development	5,868	5,065
Selling, general and administrative	4,468	1,842
Total costs and expenses	10,339	6,907
Loss from operations	(10,151)	(6,907)
Interest expense, net	(477)	(86)
Other income, net	9	73
Net loss	(10,619)	(6,920)
Comprehensive loss	(10,619)	(6,920)
Reconciliation of net loss to net loss applicable to common stockholders:
Net loss	(10,619)	(6,920)
Accretion of redeemable convertible preferred stock to redemption value		(1,906)
Net loss applicable to common stockholders	$ (10,619)	$ (8,826)
Net loss per share applicable to common stockholders - basic and diluted	$ (0.53)	$ (6.25)
Weighted-average number of shares of common stock used in computing net loss per share applicable to common stockholders - basic and diluted	20,080,515	1,411,961