CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Statement Of Income And Comprehensive Income [Abstract]
Collaboration revenue	$ 3,684
Operating expenses:
Research and development	47,948	$ 21,378
General and administrative	17,300	8,279
Total operating expenses	65,248	29,657
Loss from operations	(61,564)	(29,657)
Other income (expense):
Changes in fair value of convertible preferred stock tranche liability		(876)
Interest income	4,349	542
Total other income (expense)	4,349	(334)
Net loss and net loss attributable to common stockholders-basic and diluted	$ (57,215)	$ (29,991)
Net loss per share attributable to common stockholders-basic and diluted	$ (2.00)	$ (12.10)
Weighted average common shares outstanding-basic and diluted	28,551,807	2,479,432