Share-Based Compensation - Stock Option Information Related to Equity Incentive Plan (Detail) (USD $)	9 Months Ended
	Sep. 30, 2014
Options
Outstanding, beginning of period	1,514,159
Granted	239,383
Exercised	(283,498)
Forfeited	(21,975)
Outstanding, end of period	1,448,069
Vested and expected to vest, end of period	1,397,466
Exercisable, end of period	727,829
Weighted Average Exercise Price
Outstanding, beginning of period	$ 55.27
Granted	$ 108.27
Exercised	$ 47.56
Forfeited	$ 71.17
Outstanding, end of period	$ 65.30
Vested and expected to vest, end of period	$ 64.55
Exercisable, end of period	$ 50.48
Weighted Average Remaining Contractual Life in Years
Outstanding, end of period	4 years 3 months
Vested and expected to vest, end of period	4 years 2 months 12 days
Exercisable, end of period	3 years 0 months 29 days
Aggregate Intrinsic Value of In-The- Money Options
Outstanding, end of period	$ 67,825,947
Vested and expected to vest, end of period	66,495,669
Exercisable, end of period	$ 44,843,070