Stock-based compensation - Summary of Restricted Stock Units (Detail) - Restricted stock units shares in Thousands	12 Months Ended
	Dec. 31, 2019 $ / shares shares
Shares (in thousands)
Unvested balance at beginning of period (in shares) | shares	931
Granted (in shares) | shares	570
Vested (in shares) | shares	(251)
Forfeited (in shares) | shares	(123)
Unvested balance at end of period (in shares) | shares	1,127
Weighted-average grant date fair value
Unvested balance at beginning of period (in dollars per share) | $ / shares	$ 155.99
Granted (in dollars per share) | $ / shares	128.87
Vested (in dollars per share) | $ / shares	138.93
Forfeited (in dollars per share) | $ / shares	155.68
Unvested balance at end of period (in dollars per share) | $ / shares	$ 146.10