CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement Of Income And Comprehensive Income [Abstract]
Collaboration revenue	$ 2,187	$ 567	$ 31,492	$ 1,155
Operating expenses:
Research and development	23,697	27,471	45,452	56,780
General and administrative	9,042	8,793	17,703	16,563
Total operating expenses	32,739	36,264	63,155	73,343
Loss from operations	(30,552)	(35,697)	(31,663)	(72,188)
Other income:
Interest income	52	357	90	1,517
Total other income	52	357	90	1,517
Net loss	$ (30,500)	$ (35,340)	$ (31,573)	$ (70,671)
Net loss per share-basic and diluted	$ (0.54)	$ (0.78)	$ (0.59)	$ (1.56)
Weighted-average common shares outstanding-basic and diluted	56,497,461	45,207,934	53,429,634	45,180,096