Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
License and collaboration revenue	$ 20,340	$ 0	$ 0
Operating expenses:
Research and development	282,001	244,650	216,097
General and administrative	78,801	64,402	79,584
Total operating expenses	360,802	309,052	295,681
Loss from operations	(340,462)	(309,052)	(295,681)
Interest and other income, net	367	2,447	4,717
Loss before provision for income taxes	(340,095)	(306,605)	(290,964)
Provision for income taxes	46	15	12
Net loss	(340,141)	(306,620)	(290,976)
Other comprehensive (loss) gain:
Unrealized (loss) gain on available-for-sale securities	(664)	76	560
Comprehensive loss	$ (340,805)	$ (306,544)	$ (290,416)
Net loss per common share:
Basic and diluted net loss per common share	$ (3.63)	$ (4.15)	$ (5.67)
Weighted-average shares outstanding used to calculate basic and diluted net loss per common share	93,670	73,973	51,308