Stock Option Information Related to Equity Incentive Plan (Detail) (USD $)	9 Months Ended
	Sep. 30, 2011 Year Investment
Shares
Outstanding, beginning of period	3,112,253
Granted	373,493
Exercised	(837,448)
Forfeited	(43,770)
Expired	(1,426)
Outstanding, end of period	2,603,102
Vested and expected to vest, end of period	2,478,035
Exercisable, end of period	1,545,346
Weighted Average Exercise Price
Outstanding, beginning of period	$ 37.88
Granted	$ 59.71
Exercised	$ 33.93
Forfeited	$ 42.56
Expired	$ 35.53
Outstanding, end of period	$ 42.20
Vested and expected to vest, end of period	$ 41.84
Exercisable, end of period	$ 39.72
Weighted Average Remaining Contractual Life in Years
Outstanding, end of period	3.54
Vested and expected to vest, end of period	3.42
Exercisable, end of period	2.17
Aggregate Intrinsic Value of In-The-Money Options
Outstanding, end of period	$ 10,788,138
Vested and expected to vest, end of period	10,504,466
Exercisable, end of period	$ 7,085,746