Statements of Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Operating expenses:
Research and development	$ 3,798	$ 5,577	$ 8,519	$ 10,505
General and administrative	3,198	2,264	5,603	4,316
Total operating expenses	6,996	7,841	14,122	14,821
Loss from operations	(6,996)	(7,841)	(14,122)	(14,821)
Other income (expense)
Interest expense	(504)	(548)	(1,050)	(1,095)
Interest income	61	33	109	50
Change in fair value of warrants	(7)	(62)	102	130
Loss before benefit from income taxes	(7,446)	(8,418)	(14,961)	(15,736)
Net loss	$ (7,446)	$ (8,418)	$ (14,961)	$ (15,736)
Net loss per share - basic and diluted (in dollars per share)	$ (0.26)	$ (0.29)	$ (0.52)	$ (0.57)
Weighted-average shares outstanding - basic and diluted (in shares)	28,802,112	28,744,004	28,785,827	27,785,113