Description of the business - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accumulated deficit	$ (3,348,057)				$ (3,348,057)		$ (2,900,547)
Net loss	(241,702)	$ (205,808)	$ (21,465)	$ (202,611)	(447,510)	$ (224,076)
Net cash used in operating activities					(348,975)	$ (166,378)
Cash, cash equivalents and marketable securities	$ 941,600				$ 941,600