Stock Option Information Related to Equity Incentive Plan (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012
Options
Outstanding, beginning of period	2,439,360
Granted	399,462
Exercised	(704,631)
Forfeited	(67,710)
Expired	(6,068)
Outstanding, end of period	2,060,413
Vested and expected to vest, end of period	1,986,049
Exercisable, end of period	1,091,812
Weighted average exercise price
Outstanding, beginning of period	$ 42.64
Granted	$ 63.82
Exercised	$ 34.99
Forfeited	$ 49.81
Expired	$ 36.21
Outstanding, end of period	$ 49.15
Vested and expected to vest, end of period	$ 48.78
Exercisable, end of period	$ 44.50
Weighted Average Remaining Contractual Life in Years
Outstanding, end of period	3 years 10 months 30 days
Vested and expected to vest, end of period	3 years 10 months 11 days
Exercisable, end of period	2 years 8 months 11 days
Aggregate Intrinsic Value of In-The-Money Options
Outstanding, end of period	$ 18,509,590
Vested and expected to vest, end of period	18,329,727
Exercisable, end of period	$ 12,891,111