Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Revenue	$ 0	$ 0	$ 0	$ 0
Operating expenses:
Research and development	4,563	3,488	12,307	12,200
General and administrative	2,426	2,225	8,059	6,717
Total operating expenses	6,989	5,713	20,366	18,917
Loss from operations	(6,989)	(5,713)	(20,366)	(18,917)
Other income (expense):
Interest income, net	19	39	88	114
Other expense, net	(21)	(52)	(71)	(142)
Change in fair value of warrant liability	17,776	(269)	12,524	(673)
Total other income (expense), net	17,774	(282)	12,541	(701)
Net income (loss)	10,785	(5,995)	(7,825)	(19,618)
Other comprehensive income (loss):
Unrealized gain from available for sale securities		1
Comprehensive income (loss)	10,785	(5,994)	(7,825)	(19,618)
Net income (loss) attributable to common stockholders—basic	10,650	(5,080)	(7,657)	(16,380)
Net (loss) attributable to common stockholders—diluted	$ (7,126)	$ (5,080)	$ (20,181)	$ (16,380)
Net income (loss) per common share—basic	$ 0.36	$ (0.23)	$ (0.27)	$ (0.74)
Net loss per common share—diluted	$ (0.24)	$ (0.23)	$ (0.68)	$ (0.74)
Weighted-average shares used to compute income (loss) per common share—basic	29,737,632	22,552,341	28,723,500	22,219,666
Weighted-average shares used to compute income (loss) per common share—diluted	29,737,632	22,552,341	29,515,700	22,219,666