Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating expenses:
Research and development	$ 9,858	$ 9,777	$ 14,428
General and administrative	9,000	8,739	12,383
Restructuring Charges	0	1,019
Total operating expenses	18,858	19,535	26,811
Loss from operations	(18,858)	(19,535)	(26,811)
Other income (expense)
Interest income	252	366	282
Interest expense		(1,116)	(1,918)
Change in fair value of warrants		29	143
Total other income (expense), net	252	(721)	(1,493)
Loss before benefit from income taxes	(18,606)	(20,256)	(28,304)
Benefit from income taxes		477
Net loss	$ (18,606)	$ (19,779)	$ (28,304)
Net loss per share (basic and diluted) (in dollars per share)	$ (0.38)	$ (0.58)	$ (0.91)
Weighted-average common shares (basic and diluted) (in shares)	49,432,487	34,315,931	30,940,831