Stock-based compensation - Summary of Restricted Stock Units (Detail) - Restricted stock units shares in Thousands	9 Months Ended
	Sep. 30, 2021 $ / shares shares
Shares (in thousands)
Unvested balance at beginning of period (in shares) | shares	1,495
Granted (in shares) | shares	3,268
Vested (in shares) | shares	(501)
Forfeited (in shares) | shares	(724)
Unvested balance at end of period (in shares) | shares	3,538
Weighted- average grant date fair value
Unvested balance at beginning of period (in dollars per share) | $ / shares	$ 102.34
Granted (in dollars per share) | $ / shares	26.81
Vested (in dollars per share) | $ / shares	114.58
Forfeited (in dollars per share) | $ / shares	60.33
Unvested balance at end of period (in dollars per share) | $ / shares	$ 39.43