Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
Revenue	$ 0	$ 0	$ 0	$ 0
Operating expenses:
Research and development	4,458	4,208	7,744	8,712
General and administrative	2,826	2,166	5,633	4,492
Total operating expenses	7,284	6,374	13,377	13,204
Loss from operations	(7,284)	(6,374)	(13,377)	(13,204)
Other income (expense):
Interest income (expense), net	32	40	69	75
Other expense, net	(26)	(73)	(50)	(90)
Change in fair value of warrant liability	3,501	(135)	(5,252)	(404)
Total other income (expense), net	3,507	(168)	(5,233)	(419)
Net loss	(3,777)	(6,542)	(18,610)	(13,623)
Other comprehensive loss:
Unrealized gain (loss) from available for sale securities		4		(2)
Comprehensive loss	(3,777)	(6,538)	(18,610)	(13,625)
Net loss attributable to common stockholders—basic and diluted	$ (3,697)	$ (5,454)	$ (18,124)	$ (11,285)
Net loss per common share—basic and diluted	$ (0.13)	$ (0.25)	$ (0.64)	$ (0.51)
Weighted-average shares used to compute loss per common share—basic and diluted	28,740,030	22,183,804	28,208,030	22,050,572