STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating expenses:
Research and development	$ 133,028	$ 85,594	$ 35,906
General and administrative	45,796	18,001	11,216
Total operating expenses	178,824	103,595	47,122
Loss from operations	(178,824)	(103,595)	(47,122)
Change in fair value—preferred stock tranche obligation	0	0	5,649
Other income (expense), net	7,663	3,924	183
Interest expense	(5,744)	(3,137)	0
Loss before income taxes	(176,905)	(102,808)	(41,290)
Income tax benefit	(92)	0	0
Net loss	(176,813)	(102,808)	(41,290)
Other comprehensive income (loss):
Net unrealized gain (loss) on available-for-sale-investments, net of tax	346	(140)	(13)
Total comprehensive loss	$ (176,467)	$ (102,948)	$ (41,303)
Net loss per share, basic and diluted (in USD per share)	$ (3.72)	$ (4.64)	$ (19.32)
Weighted-average number of shares outstanding, basic and diluted (in shares)	47,521,237	22,146,192	2,137,690