Stock-based compensation - Summary of Restricted Stock Units (Detail) - Restricted stock units shares in Thousands	6 Months Ended
	Jun. 30, 2020 $ / shares shares
Shares (in thousands)
Unvested balance at beginning of period (in shares) | shares	1,127
Granted (in shares) | shares	879
Vested (in shares) | shares	(318)
Forfeited (in shares) | shares	(95)
Unvested balance at end of period (in shares) | shares	1,593
Weighted- average grant date fair value
Unvested balance at beginning of period (in dollars per share) | $ / shares	$ 146.10
Granted (in dollars per share) | $ / shares	72.59
Vested (in dollars per share) | $ / shares	143.73
Forfeited (in dollars per share) | $ / shares	132.84
Unvested balance at end of period (in dollars per share) | $ / shares	$ 106.81