Stock Option Information Related to Equity Incentive Plan (Detail) (USD $)	6 Months Ended
	Jun. 30, 2012
Options
Outstanding, beginning of period	2,439,360
Granted	387,793
Exercised	(576,461)
Forfeited	(36,629)
Expired	(4,568)
Outstanding, end of period	2,209,495
Vested and expected to vest, end of period	2,106,562
Exercisable, end of period	1,159,056
Weighted average exercise price
Outstanding, beginning of period	$ 42.64
Granted	$ 64.02
Exercised	$ 36.26
Forfeited	$ 45.86
Expired	$ 42.50
Outstanding, end of period	$ 48.00
Vested and expected to vest, end of period	$ 47.53
Exercisable, end of period	$ 43.06
Weighted Average Remaining Contractual Life in Years
Outstanding, end of period	4 years 3 months 4 days
Vested and expected to vest, end of period	4 years 2 months
Exercisable, end of period	2 years 11 months 4 days
Aggregate Intrinsic Value of In-The-Money Options
Outstanding, end of period	$ 26,284,468
Vested and expected to vest, end of period	25,861,593
Exercisable, end of period	$ 18,281,444