CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Collaboration revenue	$ 1,666	$ 5,322
Operating expenses:
Research and development	89,398	47,948
General and administrative	22,211	17,300
Total operating expenses	111,609	65,248
Loss from operations	(109,943)	(59,926)
Other income:
Interest income	6,027	4,349
Total other income	6,027	4,349
Net loss	$ (103,916)	$ (55,577)
Net loss per share-basic and diluted	$ (2.47)	$ (1.95)
Weighted average common shares outstanding-basic and diluted	42,117,690	28,551,807