Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating expenses:
Research and development	$ 9,777	$ 14,428	$ 20,929
General and administrative	8,739	12,383	8,792
Restructuring costs	1,019
Total operating expenses	19,535	26,811	29,721
Loss from operations	(19,535)	(26,811)	(29,721)
Other income (expense)
Interest income	366	282	117
Interest expense	(1,116)	(1,918)	(2,446)
Change in fair value of warrants	29	143	234
Total other income (expense), net	(721)	(1,493)	(2,095)
Loss before benefit from income taxes	(20,256)	(28,304)	(31,816)
Benefit from income taxes	477		3,075
Net loss	$ (19,779)	$ (28,304)	$ (28,741)
Net loss per share (basic and diluted) (in dollars per share)	$ (0.58)	$ (0.91)	$ (1.02)
Weighted-average common shares (basic and diluted) (in shares)	34,315,931	30,940,831	28,273,331