Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Operating expenses:
Research and development	$ 3,175	$ 4,911	$ 11,694	$ 15,415
General and administrative	3,526	2,180	9,130	6,497
Total operating expenses	6,701	7,091	20,824	21,912
Loss from operations	(6,701)	(7,091)	(20,824)	(21,912)
Other income (expense)
Interest expense	(459)	(784)	(1,509)	(1,879)
Interest income	78	33	187	83
Change in fair value of warrants	(20)	38	82	168
Loss before benefit from income taxes	(7,102)	(7,804)	(22,064)	(23,540)
Net loss	$ (7,102)	$ (7,804)	$ (22,064)	$ (23,540)
Net loss per share - basic and diluted (in dollars per share)	$ (0.22)	$ (0.27)	$ (0.74)	$ (0.84)
Weighted-average shares outstanding -basic and diluted (in shares)	31,937,628	28,754,458	29,847,972	28,110,587