Stock-based compensation - Summary of Stock Option Activity Under Plan (Detail) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) $ / shares shares
Shares (in thousands)
Outstanding at beginning of period (in shares) | shares	4,643
Granted (in shares) | shares	1,594
Exercised (in shares) | shares	(354)
Canceled or forfeited (in shares) | shares	(400)
Outstanding at end of period (in shares) | shares	5,483
Exercisable at end of period (in shares) | shares	2,853
Vested and expected to vest at end of period (in shares) | shares	5,483
Weighted- average exercise price per share
Outstanding at beginning of period (in dollars per share) | $ / shares	$ 108.56
Granted (in dollars per share) | $ / shares	129.76
Exercised (in dollars per share) | $ / shares	50.36
Canceled or forfeited (in dollars per share) | $ / shares	138.61
Outstanding at end of period (in dollars per share) | $ / shares	116.30
Exercisable at end of period (in dollars per share) | $ / shares	94.77
Vested and expected to vest at end of period (in dollars per share) | $ / shares	$ 116.30
Weighted- average contractual life (in years)
Outstanding at December 31, 2019	7 years 3 months 18 days
Exercisable at December 31, 2019	6 years
Vested and expected to vest at December 31, 2019	7 years 3 months 18 days
Aggregate intrinsic value (in thousands)
Outstanding at end of period | $	$ 68,511
Exercisable at end of period | $	64,899
Vested and expected to vest at end of period | $	$ 68,511