Stock Options Activity (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Shares
Outstanding at January 1, 2014	2,516,618
Granted	514,905
Exercised	(489,047)
Forfeited	(163,917)
Outstanding at December 31, 2014	2,378,559	2,516,618
Vested and expected to vest at December 31, 2014	2,279,445
Exercisable at December 31, 2014	1,157,805
Weighted Average Price
Outstanding at January 1, 2014	$ 39.60
Granted	$ 72.77
Exercised	$ 34.59
Forfeited	$ 52.59
Outstanding at December 31, 2014	$ 46.91	$ 39.60
Vested and expected to vest at December 31, 2014	$ 46.24
Exercisable at December 31, 2014	$ 36.70
Weighted-Average Remaining Contractual Term
Weighted-Average Remaining Contractual Term	6 years 8 months 9 days	6 years 10 months 13 days
Vested and expected to vest at December 31, 2014	6 years 7 months 6 days
Exercisable at December 31, 2014	5 years 2 months 1 day
Aggregate Intrinsic Value
Outstanding at January 1, 2014	$ 86,200,655
Outstanding at December 31, 2014	73,561,785	86,200,655
Vested and expected to vest at December 31, 2014	72,026,247
Exercisable at December 31, 2014	$ 47,631,234