CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Collaboration revenue	$ 567	$ 392	$ 1,155	$ 662
Operating expenses:
Research and development	27,471	22,827	56,780	43,368
General and administrative	8,793	5,538	16,563	10,390
Total operating expenses	36,264	28,365	73,343	53,758
Loss from operations	(35,697)	(27,973)	(72,188)	(53,096)
Other income:
Interest income	357	1,703	1,517	2,974
Total other income	357	1,703	1,517	2,974
Net loss	$ (35,340)	$ (26,270)	$ (70,671)	$ (50,122)
Net loss per share-basic and diluted	$ (0.78)	$ (0.61)	$ (1.56)	$ (1.25)
Weighted-average common shares outstanding-basic and diluted	45,207,934	43,075,587	45,180,096	40,230,484