Description of the business (Detail) - USD ($) $ in Thousands, shares in Millions		1 Months Ended	3 Months Ended						6 Months Ended	9 Months Ended
	Jun. 22, 2022	Apr. 30, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2022	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Subsequent Event [Line Items]
Cash, cash equivalents and marketable securities			$ 141,000						$ 141,000	$ 141,000
Accumulated deficit			4,018,735						$ 4,018,735	4,018,735		$ 3,719,925
Net loss			76,520	$ 100,138	$ 122,152	$ 216,816	$ 241,702	$ 205,808		298,810	$ 664,326
Net cash used in operating activities										296,680	$ 495,914
Private Placement
Subsequent Event [Line Items]
Proceeds from stock offering			$ 47,900							$ 56,200
Commission fee, percentage of gross proceeds (up to)	3.00%
Shares of common stock sold (in shares)			8.7							10.7
Offering costs			$ 46,100							$ 54,100
Maximum | Private Placement
Subsequent Event [Line Items]
Proceeds from stock offering	$ 75,000
April 2022 Reduction
Subsequent Event [Line Items]
Plans to reduce workforce, as a percent		30.00%							30.00%