Condensed Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Operating expenses:
Research and development	$ 13,498	$ 7,247	$ 32,987	$ 21,846
General and administrative	4,214	5,672	13,878	14,960
Total operating expenses	17,712	12,919	46,865	36,806
Loss from operations	(17,712)	(12,919)	(46,865)	(36,806)
Interest expense.	(89)	(130)	(298)	(399)
Other income, net	399	248	1,141	543
Net loss	$ (17,402)	$ (12,801)	$ (46,022)	$ (36,662)
Net loss per common share (basic and diluted) (in dollars per share)	$ (0.77)	$ (0.57)	$ (2.04)	$ (1.68)
Weighted-average shares outstanding (basic and diluted)	22,550,438	22,494,075	22,541,137	21,854,685
Other comprehensive loss:
Unrealized gain (loss) on investments	$ (96)	$ 71	$ 504	$ 70
Total comprehensive loss	$ (17,498)	$ (12,730)	$ (45,518)	$ (36,592)