STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Collaboration revenue				$ 146
Operating expenses:
Research and development	$ 8,641	$ 8,263	$ 28,115	25,935
General and administrative	4,807	4,307	13,707	15,355
Total operating expenses	13,448	12,570	41,822	41,290
Loss from operations	(13,448)	(12,570)	(41,822)	(41,144)
Other income, net	203	150	523	462
Change in fair value of derivative liabilities		(165)		46
Non-cash inducement warrant expense	(60,751)		(60,751)
Net loss	(73,996)	(12,585)	(102,050)	(40,636)
Preferred stock dividends		(6,074)		(16,656)
Net loss applicable to common stockholders	$ (73,996)	$ (18,659)	$ (102,050)	$ (57,292)
Basic and diluted net loss per share	$ (0.43)	$ (0.13)	$ (0.62)	$ (0.41)
Weighted average common shares outstanding used to compute basic and diluted net loss per share	170,613,712	141,185,404	164,053,029	141,020,025