Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating expenses:
Research and development	$ 20,929	$ 25,622	$ 13,365
General and administrative	8,792	7,467	5,150
Total operating expenses	29,721	33,089	18,515
Loss from operations	(29,721)	(33,089)	(18,515)
Other income (expense)
Interest expense	(2,446)	(2,077)	(1,566)
Interest income	117	5	3
Change in fair value of warrants	234	(110)	348
Loss on extinguishment of debt		(1,036)
Loss before benefit from income taxes	(31,816)	(36,307)	(19,730)
Benefit from income taxes	3,075	5,972	3,653
Net loss	$ (28,741)	$ (30,335)	$ (16,077)
Net loss per share (basic and diluted) (in dollars per share)	$ (1.02)	$ (1.38)	$ (1.41)
Weighted-average shares outstanding (basic and diluted) (in shares)	28,273,331	22,017,229	11,394,971