Stock-based compensation - Summary of Restricted Stock Units (Detail) - Restricted stock units shares in Thousands	3 Months Ended
	Mar. 31, 2021 $ / shares shares
Shares (in thousands)
Unvested balance at beginning of period (in shares) | shares	1,495
Granted (in shares) | shares	990
Vested (in shares) | shares	(294)
Forfeited (in shares) | shares	(118)
Unvested balance at end of period (in shares) | shares	2,073
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	29.17
Vested (in dollars per share) | $ / shares	108.85
Forfeited (in dollars per share) | $ / shares	84.63
Unvested balance at end of period (in dollars per share) | $ / shares	$ 67.48