Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Operating expenses:
Research and development	$ 7,743	$ 23,193	$ 25,194	$ 62,900
General and administrative	4,494	4,514	12,239	14,706
Restructuring charges	(587)		(704)
Total operating expenses	11,650	27,707	36,729	77,606
Loss from operations	(11,650)	(27,707)	(36,729)	(77,606)
Other income:
Interest income	229	1,425	1,494	4,211
Total other income	229	1,425	1,494	4,211
Net loss	(11,421)	(26,282)	(35,235)	(73,395)
Other comprehensive (loss) income:
Unrealized (loss) gain on marketable securities	(104)	(51)	2	235
Total other comprehensive (loss) income	(104)	(51)	2	235
Comprehensive loss	$ (11,525)	$ (26,333)	$ (35,233)	$ (73,160)
Basic and diluted net loss per common share	$ (0.17)	$ (0.38)	$ (0.51)	$ (1.10)
Weighted average common shares outstanding used to calculate basic and diluted net loss per common share	68,887,092	68,701,043	68,884,894	66,454,750