Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue:
Product revenue	$ 1,747	$ 599
Research revenue	2,333	2,214	$ 119
Total revenue	4,080	2,813	119
Costs and expenses:
Cost of product revenue	6,872	1,740
Research and development	24,009	25,362	19,782
Selling, general and administrative	24,077	19,094	11,018
Total costs and expenses	54,958	46,196	30,800
Loss from operations	(50,878)	(43,383)	(30,681)
Interest expense, net	(4,098)	(1,967)	(721)
Other income, net	172	60	12
Net loss and comprehensive loss	(54,804)	(45,290)	(31,390)
Comprehensive loss	(54,804)	(45,290)	(31,390)
Accretion of redeemable convertible preferred stock to redemption value			(4,570)
Net loss applicable to common stockholders	$ (54,804)	$ (45,290)	$ (35,960)
Net loss per share applicable to common stockholders — basic and diluted	$ (2.11)	$ (2.21)	$ (4.15)
Weighted-average number of common shares used in computing net loss per share — basic and diluted	26,015,751	20,501,748	8,674,931