Selected Quarterly Financial Data (Unaudited) - Summary (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
License and collaboration revenues	$ 299	$ 71,793	$ 0	$ 0	$ 1,707	$ 11,424	$ 0	$ 267	$ 72,092	$ 13,398	$ 3,335
Loss from operations	(197,075)	(79,499)	(164,186)	(132,421)	(106,336)	(88,678)	(84,862)	(89,487)	(573,181)	(369,363)	(222,104)
Net loss	$ (199,620)	$ (80,054)	$ (166,430)	$ (135,680)	$ (101,087)	$ (87,336)	$ (82,859)	$ (86,655)	$ (581,784)	$ (357,937)	$ (213,256)
Basic and diluted net loss per share (USD per share)	$ (3.72)	$ (1.55)	$ (3.23)	$ (2.67)	$ (2.08)	$ (1.96)	$ (1.89)	$ (2.02)