Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Operating expenses:
Research and development	$ 23,043	$ 28,509	$ 64,114	$ 67,649
General and administrative	9,577	8,209	26,765	24,515
Total operating expenses	32,620	36,718	90,879	92,164
Loss from operations	(32,620)	(36,718)	(90,879)	(92,164)
Other (expense) income:
Interest income	2	12	21	706
Other income (expense)	5	(74)	(41)	(123)
Total other (expense) income, net	7	(62)	(20)	583
Net loss	(32,613)	(36,780)	(90,899)	(91,581)
Comprehensive loss	$ (32,613)	$ (36,780)	$ (90,899)	$ (91,581)
Net loss per share — basic and diluted	$ (0.75)	$ (1.01)	$ (2.13)	$ (2.59)
Weighted-average number of common shares outstanding — basic and diluted	43,623	36,444	42,588	35,409