Share-Based Compensation - Stock Options Activity (Detail) - Stock Option - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Shares
Outstanding at January 1, 2015	2,378,559
Granted	525,255
Exercised	(469,497)
Forfeited	(167,884)
Outstanding at December 31, 2015	2,266,433	2,378,559
Vested and expected to vest at December 31, 2015	2,169,134
Exercisable at December 31, 2015	1,201,889
Weighted Average Price
Outstanding at January 1, 2015	$ 46.91
Granted	78.22
Exercised	40.73
Forfeited	65.82
Outstanding at December 31, 2015	54.05	$ 46.91
Vested and expected to vest at December 31, 2015	53.17
Exercisable at December 31, 2015	$ 41.72
Weighted-Average Remaining Contractual Term
Weighted-Average Remaining Contractual Term	6 years 6 months 29 days	6 years 8 months 9 days
Vested and expected to vest at December 31, 2015	6 years 5 months 23 days
Exercisable at December 31, 2015	5 years 1 month 17 days
Aggregate Intrinsic Value
Outstanding at January 1, 2015	$ 73,561,785
Outstanding at December 31, 2015	51,918,028	$ 73,561,785
Vested and expected to vest at December 31, 2015	51,531,931
Exercisable at December 31, 2015	$ 41,942,569