Statements of Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Operating expenses:
Research and development	$ 2,413	$ 3,798	$ 6,372	$ 8,519
General and administrative	2,318	3,198	5,404	5,603
Restructuring costs	416		416
Total operating expenses	5,147	6,996	12,192	14,122
Loss from operations	(5,147)	(6,996)	(12,192)	(14,122)
Other income (expense)
Interest income	101	61	198	109
Interest expense	(320)	(504)	(689)	(1,050)
Change in fair value of warrants	22	(7)	29	102
Total other income (expense), net	(197)	(450)	(462)	(839)
Loss before benefit from income taxes	(5,344)	(7,446)	(12,654)	(14,961)
Benefit from income taxes			477
Net loss	$ (5,344)	$ (7,446)	$ (12,177)	$ (14,961)
Net loss per share (basic and diluted) (in dollars per share)	$ (0.16)	$ (0.26)	$ (0.36)	$ (0.52)
Weighted-average common shares (basic and diluted) (in shares)	34,277,601	28,802,112	34,253,515	28,785,827