Stock Options Activity (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012
Shares
Outstanding at January 1, 2012	4,314,044
Granted	764,700
Exercised	(1,631,923)
Forfeited/Expired	(223,079)
Outstanding at December 31, 2012	3,223,742
Vested and expected to vest at December 31, 2012	3,100,929
Exercisable at December 31, 2012	1,780,761
Weighted Average Price
Stock Options Outstanding, Weighted Average Price, Beginning	$ 29.61
Granted, Weighted Average Price	$ 42.66
Exercised, Weighted Average Price	$ 27.77
Forfeited/Expired, Weighted Average Price	$ 36.60
Stock Options Outstanding, Weighted Average Price, Ending	$ 33.16
Vested and expected to vest at December 31, 2012, Weighted Average Price	$ 32.86
Exercisable at December 31, 2012, Weighted Average Price	$ 29.00
Weighted-Average Remaining Contractual Term
Weighted-Average Remaining Contractual Term	6 years 4 months 13 days
Vested and expected to vest at December 31, 2012, Weighted-Average Remaining Contractual Term	6 years 3 months 11 days
Exercisable, Weighted-Average Remaining Contractual Term	4 years 9 months 26 days
Aggregate Intrinsic Value
Stock options outstanding, Beginning aggregate intrinsic value	$ 34,899,200
Stock options outstanding, Ending aggregate intrinsic value	43,106,153
Stock options, vested and expected to vest aggregate intrinsic value	42,398,877
Stock options, exercisable aggregate intrinsic value	$ 31,219,847