Description of the business - Narrative (Detail) - USD ($)	1 Months Ended	3 Months Ended
	Apr. 30, 2022	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Subsequent Event [Line Items]
Cash, cash equivalents and marketable securities		$ 266,600,000
Accumulated deficit		3,842,077,000		$ 3,719,925,000
Net loss		122,152,000	$ 205,808,000
Net cash used in operating activities		$ (125,296,000)	$ (203,327,000)
April 2022 Reduction | Subsequent Event
Subsequent Event [Line Items]
Anticipated cost savings associated with restructuring	$ 160,000,000
Anticipated cost savings associated with restructuring, period of recognition	2 years
Plans to reduce workforce, as a percent	30.00%