Summary of Restricted Stock Unit Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Restricted Stock With Service Based Vesting Conditions
Schedule of Share based Compensation Arrangements by Share based Payment Award, Equity Instruments, Other Than Options, Restricted Stock Units [Line Items]
Shares, Non-vested units as of December 31, 2018	3,147,523
Shares, Granted	1,937,858
Shares, Vested	(1,136,627)
Shares, Forfeited	(363,370)
Shares, Non-vested units as of December 31, 2019	3,585,384	3,147,523
Weighted Average Grant Date Fair Value, Non-vested units as of December 31, 2018	$ 87.42
Weighted Average Grant Date Fair Value, Granted	91.28	$ 84.63	$ 87.88
Weighted Average Grant Date Fair Value, Vested	91.20
Weighted Average Grant Date Fair Value, Forfeited	89.39
Weighted Average Grant Date Fair Value, Non-vested units as of December 31, 2019	$ 88.54	$ 87.42
Weighted Average Remaining Years, Non-vested units	2 years 7 months 6 days	2 years 7 months 6 days
Aggregate Intrinsic Value, Non-vested units	$ 303,144	$ 268,012
Restricted Stock With Performance Conditions
Schedule of Share based Compensation Arrangements by Share based Payment Award, Equity Instruments, Other Than Options, Restricted Stock Units [Line Items]
Shares, Non-vested units as of December 31, 2018	256,418
Shares, Granted	99,010
Shares, Vested	(125,687)
Shares, Forfeited	(2,857)
Shares, Non-vested units as of December 31, 2019	226,884	256,418
Weighted Average Grant Date Fair Value, Non-vested units as of December 31, 2018	$ 84.85
Weighted Average Grant Date Fair Value, Granted	94.53	$ 83.57	$ 87.42
Weighted Average Grant Date Fair Value, Vested	84.85
Weighted Average Grant Date Fair Value, Forfeited	83.57
Weighted Average Grant Date Fair Value, Non-vested units as of December 31, 2019	$ 89.09	$ 84.85