Stock-Based Compensation Expense - Summary of Stock Option Activity (Detail) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) $ / shares shares
Shares
Beginning balance outstanding | shares	12,726
Granted | shares	2,997
Exercised | shares	(1,493)
Forfeited or expired | shares	(441)
Ending balance outstanding | shares	13,789
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Beginning balance outstanding, weighted-average exercise price | $ / shares	$ 25.24
Granted, weighted-average exercise price | $ / shares	52.67
Exercised, weighted-average exercise price | $ / shares	17.94
Forfeited or expired, weighted-average exercise price | $ / shares	33.59
Ending balance outstanding, weighted-average exercise price | $ / shares	$ 31.73
Exercisable, Shares | shares	4,556
Options vested or expected to vest | shares	12,499
Exercisable, weighted-average exercise price | $ / shares	$ 20.94
Options vested or expected to vest, weighted-average exercise price | $ / shares	$ 30.60
Outstanding, weighted-average remaining contractual term (in years)	7 years 4 months 10 days
Exercisable, weighted-average remaining contractual term (in years)	5 years 10 months 6 days
Options vested or expected to vest, weighted-average remaining contractual term (in years)	7 years 2 months 23 days
Outstanding, aggregate intrinsic value | $	$ 146,270
Exercisable, aggregate intrinsic value | $	82,716
Options vested or expected to vest, aggregate intrinsic value | $	$ 141,643