Stock Option Information Related to Equity Incentive Plan (Detail) (USD $)	6 Months Ended
	Jun. 30, 2011 Year Investment
Shares
Outstanding, beginning of period	3,112,253
Granted	365,583
Exercised	(707,770)
Forfeited	(23,823)
Expired	(1,426)
Outstanding, end of period	2,744,817
Vested and expected to vest, end of period	2,599,938
Exercisable, end of period	1,642,080
Weighted Average Exercise Price
Outstanding, beginning of period	$ 37.88
Granted	$ 59.97
Exercised	$ 33.89
Forfeited	$ 42.20
Expired	$ 35.53
Outstanding, end of period	$ 41.81
Vested and expected to vest, end of period	$ 41.41
Exercisable, end of period	$ 39.16
Weighted Average Remaining Contractual Life in Years
Outstanding, end of period	3.70
Vested and expected to vest, end of period	3.56
Exercisable, end of period	2.30
Aggregate Intrinsic Value of In-The-Money Options
Outstanding, end of period	$ 49,351,094
Vested and expected to vest, end of period	47,762,256
Exercisable, end of period	$ 33,733,082