Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Statement of Comprehensive Income [Abstract]
Revenue	[1]	$ 25	$ 3	$ 117	$ 36,297
Operating expenses:
Research and development		43,849	41,607	135,950	121,156
General and administrative		15,507	26,084	53,816	90,959
Other operating income, net		(292)	(1,251)	(2,149)	(3,544)
Total operating expenses		59,064	66,440	187,617	208,571
Loss from operations		(59,039)	(66,437)	(187,500)	(172,274)
Interest income, net		6,608	2,251	16,369	3,600
Other income (expense), net		1,578	(1,068)	2,352	(1,047)
Impairment of other investments		0	(5,000)	(12,923)	(5,000)
Total other income (loss), net		8,186	(3,817)	5,798	(2,447)
Net loss		(50,853)	(70,254)	(181,702)	(174,721)
Other comprehensive loss:
Net unrealized gain (loss) on marketable securities		1,198	(1,645)	6,418	(8,373)
Comprehensive loss		$ (49,655)	$ (71,899)	$ (175,284)	$ (183,094)
Net loss per common share, basic (in dollars per share)		$ (0.20)	$ (0.28)	$ (0.73)	$ (0.71)
Net loss per common share, diluted (in dollars per share)		$ (0.20)	$ (0.28)	$ (0.73)	$ (0.71)
Weighted-average shares used to compute net loss per common share, basic (in shares)		251,318	248,320	250,377	246,285
Weighted-average shares used to compute net loss per common share, diluted (in shares)		251,318	248,320	250,377	246,285

[1] (1)    Including related-party revenue of zero for both the three months ended September 30, 2023 and 2022, and zero and $36,299 for the nine months ended September 30, 2023 and 2022, respectively.