CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating expenses:
Research and development	$ 112,042	$ 135,001	$ 86,597
General and administrative	45,321	34,962	21,563
Total operating expenses	157,363	169,963	108,160
Loss from operations	(157,363)	(169,963)	(108,160)
Interest income	1,134	6,049	4,719
Loss before (provision) benefit for income taxes	(156,229)	(163,914)	(103,441)
(Provision) benefit for income taxes	(5,152)	2,047	214
Net loss	$ (161,381)	$ (161,867)	$ (103,227)
Net loss per share attributable to common shareholders-basic and diluted	$ (2.61)	$ (2.99)	$ (3.49)
Weighted average common shares outstanding-basic and diluted	61,842,722	54,049,477	29,547,427
Comprehensive loss:
Net loss	$ (161,381)	$ (161,867)	$ (103,227)
Other comprehensive income (loss):
Unrealized gain (loss) on short-term investments and currency translation adjustments, net of tax	(67)	37	(4)
Total other comprehensive income	(67)	37	(4)
Total comprehensive loss	$ (161,448)	$ (161,830)	$ (103,231)