Description of the business - Additional Information (Detail) $ in Thousands			3 Months Ended						9 Months Ended
	Nov. 04, 2021 USD ($) company	Sep. 30, 2021 USD ($)	Sep. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Subsequent Event [Line Items]
Accumulated deficit		$ (3,564,873)	$ (3,564,873)						$ (3,564,873)		$ (2,900,547)
Net loss			(216,816)	$ (241,702)	$ (205,808)	$ (194,745)	$ (21,465)	$ (202,611)	(664,326)	$ (418,821)
Net cash used in operating activities									(495,914)	(315,158)
Cash, cash equivalents and marketable securities		970,700	970,700						970,700
Stock-based compensation expense			$ 28,338			$ 38,818			$ 101,863	$ 123,640
Unrestricted Stock Awards | July 2021 reduction
Subsequent Event [Line Items]
Stock-based compensation expense		$ 2,500
Subsequent Event
Subsequent Event [Line Items]
Number of independent publicly traded companies | company	2
Payments for advance to affiliate	$ 441,500