Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Operating expenses:
Research and development	$ 1,549	$ 3,175	$ 7,921	$ 11,694
General and administrative	1,767	3,526	7,173	9,130
Restructuring costs	299		715
Total operating expenses	3,615	6,701	15,809	20,824
Loss from operations	(3,615)	(6,701)	(15,809)	(20,824)
Other income (expense)
Interest income	91	78	289	187
Interest expense	(268)	(459)	(955)	(1,509)
Change in fair value of warrants		(20)	29	82
Total other income (expense), net	(177)	(401)	(637)	(1,240)
Loss before benefit from income taxes	(3,792)	(7,102)	(16,446)	(22,064)
Benefit from income taxes			477
Net loss	$ (3,792)	$ (7,102)	$ (15,969)	$ (22,064)
Net loss per share (basic and diluted) (in dollars per share)	$ (0.11)	$ (0.22)	$ (0.47)	$ (0.74)
Weighted-average common shares (basic and diluted) (in shares)	34,377,329	31,937,628	34,295,240	29,847,972