Stock Option Information Related to Equity Incentive Plan (Detail) (USD $)	12 Months Ended
	Dec. 31, 2011 Year
Options
Outstanding, beginning of period	3,112,253
Granted	385,645
Exercised	(985,143)
Forfeited	(68,444)
Expired	(4,951)
Outstanding, end of period	2,439,360
Vested and expected to vest, end of period	2,332,192
Exercisable, end of period	1,404,132
Weighted Average Exercise Price
Outstanding, beginning of period	$ 37.88
Granted	$ 59.17
Exercised	$ 33.96
Forfeited	$ 44.31
Expired	$ 38.31
Outstanding, end of period	$ 42.64
Vested and expected to vest, end of period	$ 42.31
Exercisable, end of period	$ 40.09
Weighted Average Remaining Contractual Life in Years
Outstanding, end of period	3.51
Vested and expected to vest, end of period	3.41
Exercisable, end of period	2.17
Aggregate Intrinsic Value of In-The-Money Options
Outstanding, end of period	$ 18,838,493
Vested and expected to vest, end of period	18,412,929
Exercisable, end of period	$ 12,326,931