Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating expenses:
Research and development	$ 34,504	$ 16,777	$ 13,832
General and administrative	13,112	6,777	5,710
Total operating expenses	47,616	23,554	19,542
Loss from operations	(47,616)	(23,554)	(19,542)
Other income (expense):
Interest income (expense), net	(386)	(832)	(444)
Change in fair value of warrant liabilities	29	36	(28)
Total other income (expense)	(357)	(796)	(472)
Net loss	(47,973)	(24,350)	(20,014)
Accretion to redemption value of redeemable convertible preferred stock	(15)	(416)	(1,637)
Net loss attributable to common stockholders	$ (47,988)	$ (24,766)	$ (21,651)
Net loss per share attributable to common stockholders, basic and diluted	$ (3.03)	$ (29.69)	$ (28.39)
Weighted average common stock shares outstanding, basic and diluted	15,838,353	834,221	762,761