Summary of Restricted Stock Unit Activity (Detail) - Restricted Stock With Service Based Vesting Conditions - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
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, 2015	2,147,209
Shares, Granted	1,321,224
Shares, Vested	(751,203)
Shares, Forfeited	(272,264)
Shares, Non-vested units as of December 31, 2016	2,444,966	2,147,209
Shares, Non-vested units expected to vest at December 31, 2016	2,444,966
Weighted Average Grant Date Fair Value, Non-vested units as of December 31, 2015	$ 93.89
Weighted Average Grant Date Fair Value, Granted	84.18	$ 119.86	$ 64.37
Weighted Average Grant Date Fair Value, Vested	80.42
Weighted Average Grant Date Fair Value, Forfeited	94.52
Weighted Average Grant Date Fair Value, Non-vested units as of December 31, 2016	92.70	$ 93.89
Weighted Average Grant Date Fair Value, Non-vested units expected to vest at December 31, 2016	$ 92.70
Weighted Average Remaining Years, Non-vested units as of December 31, 2015	1 year 4 months 24 days	2 years 9 months 18 days
Aggregate Intrinsic Value, Non-vested units as of December 31, 2015	$ 224,942
Aggregate Intrinsic Value, Non-vested units as of December 31, 2016	202,541	$ 224,942
Aggregate Intrinsic Value, Non-vested units expected to vest at December 31, 2016	$ 202,541