Unaudited Condensed Statements of Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue
Operating expenses:
Research and development	4,803	10,488	13,334	22,125
General and administrative	2,989	3,420	5,827	6,552
Total operating expenses	7,792	13,908	19,161	28,677
Loss from operations	(7,792)	(13,908)	(19,161)	(28,677)
Other (expense) income:
Interest expense related to amortization of debt issuance costs and discount	(305)	(390)	(610)	(780)
Interest expense on principal	(1,232)	(1,419)	(2,461)	(2,861)
Fair value adjustment related to derivative and warrant liability	(21)	5,562	432	(4,179)
Interest and other income, net	84	123	235	238
Total other (expense) income	(1,474)	3,876	(2,404)	(7,582)
Loss before income taxes	(9,266)	(10,032)	(21,565)	(36,259)
Income tax benefit	9	39	17	47
Net loss	$ (9,257)	$ (9,993)	$ (21,548)	$ (36,212)
Net loss per share:
Basic (in dollars per share)	$ (0.33)	$ (0.65)	$ (0.78)	$ (2.41)
Diluted (in dollars per share)	$ (0.33)	$ (0.91)	$ (0.78)	$ (2.41)
Weighted average number of shares of common stock outstanding:
Basic (in shares)	28,386,119	15,317,536	27,548,657	15,056,161
Diluted (in shares)	28,386,119	16,548,751	27,548,657	15,056,161