CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement of Comprehensive Income [Abstract]
Collaboration revenue	$ 1,677	$ 567	$ 33,169	$ 1,722
Operating expenses:
Research and development	23,987	20,417	69,439	77,197
General and administrative	8,351	8,423	26,054	24,986
Total operating expenses	32,338	28,840	95,493	102,183
Loss from operations	(30,661)	(28,273)	(62,324)	(100,461)
Other income:
Interest income	53	41	143	1,558
Total other income	53	41	143	1,558
Net loss	$ (30,608)	$ (28,232)	$ (62,181)	$ (98,903)
Net loss per share-basic and diluted	$ (0.54)	$ (0.62)	$ (1.14)	$ (2.19)
Weighted-average common shares outstanding-basic and diluted	57,106,639	45,227,231	54,704,410	45,196,459