Share-Based Compensation - Stock Option Information Related to Equity Incentive Plan (Detail) (USD $)	6 Months Ended
	Jun. 30, 2013
Options
Outstanding, beginning of period	2,060,413
Granted	304,675
Exercised	(515,693)
Forfeited	(29,096)
Expired	(953)
Outstanding, end of period	1,819,346
Vested and expected to vest, end of period	1,755,204
Exercisable, end of period	901,146
Weighted Average Exercise Price
Outstanding, beginning of period	$ 49.15
Granted	$ 71.15
Exercised	$ 46.84
Forfeited	$ 54.41
Expired	$ 51.86
Outstanding, end of period	$ 53.40
Vested and expected to vest, end of period	$ 52.96
Exercisable, end of period	$ 44.57
Weighted Average Remaining Contractual Life in Years
Outstanding, end of period	4 years 5 months 15 days
Vested and expected to vest, end of period	4 years 4 months 26 days
Exercisable, end of period	3 years 3 months 3 days
Aggregate Intrinsic Value of In-The- Money Options
Outstanding, end of period	$ 54,437,326
Vested and expected to vest, end of period	53,284,085
Exercisable, end of period	$ 34,920,695