CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Collaboration revenue	$ 567	$ 441	$ 1,722	$ 1,103
Operating expenses:
Research and development	20,417	25,691	77,197	69,056
General and administrative	8,423	6,038	24,986	16,431
Total operating expenses	28,840	31,729	102,183	85,487
Loss from operations	(28,273)	(31,288)	(100,461)	(84,384)
Other income:
Interest income	41	1,661	1,558	4,635
Total other income	41	1,661	1,558	4,635
Net loss	$ (28,232)	$ (29,627)	$ (98,903)	$ (79,749)
Net loss per share-basic and diluted	$ (0.62)	$ (0.67)	$ (2.19)	$ (1.92)
Weighted-average common shares outstanding-basic and diluted	45,227,231	43,904,812	45,196,459	41,503,545