Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Statement of Comprehensive Income [Abstract]
Revenues	[1]	$ 130	$ 84,683	$ 10,650
Operating expenses:
Research and development		182,945	159,188	138,693
General and administrative		66,983	117,307	89,057
Other operating income, net		(2,790)	(4,754)	(2,324)
Total operating expenses		247,138	271,741	225,426
Loss from operations		(247,008)	(187,058)	(214,776)
Interest income, net		23,453	7,053	1,165
Other income (expense), net		1,846	1,887	(161)
Impairment of other investments		(12,923)	(5,000)	(36,447)
Total other income (loss), net		12,376	3,940	(35,443)
Net loss		(234,632)	(183,118)	(250,219)
Other comprehensive loss:
Net unrealized gain (loss) on marketable securities		7,505	(5,976)	(1,879)
Comprehensive loss		$ (227,127)	$ (189,094)	$ (252,098)
Net loss per common share, basic (in dollars per share)		$ (0.93)	$ (0.74)	$ (1.84)
Net loss per common share, diluted (in dollars per share)		$ (0.93)	$ (0.74)	$ (1.84)
Weighted-average shares used to compute net loss per common share, basic (in shares)		250,983	247,080	135,918
Weighted-average shares used to compute net loss per common share, diluted (in shares)		250,983	247,080	135,918

[1] Includes related-party revenue of zero, $84,653 and $10,509 for the years ended December 31, 2023, 2022 and 2021, respectively.