Stock Options Activity (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Shares
Outstanding at January 1, 2012	3,223,742
Granted	651,022
Exercised	(1,245,817)
Forfeited/Expired	(112,329)
Outstanding at December 31, 2012	2,516,618	3,223,742
Vested and expected to vest at December 31, 2012	2,400,548
Exercisable at December 31, 2012	1,086,636
Weighted Average Price
Stock Options Outstanding, Weighted Average Price, Beginning	$ 33.16
Granted, Weighted Average Price	$ 50.70
Exercised, Weighted Average Price	$ 28.41
Forfeited/Expired, Weighted Average Price	$ 43.23
Stock Options Outstanding, Weighted Average Price, Ending	$ 39.60	$ 33.16
Vested and expected to vest at December 31, 2012, Weighted Average Price	$ 39.23
Exercisable at December 31, 2012, Weighted Average Price	$ 32.47
Weighted-Average Remaining Contractual Term
Weighted-Average Remaining Contractual Term	6 years 10 months 13 days	6 years 4 months 13 days
Vested and expected to vest at December 31, 2012, Weighted-Average Remaining Contractual Term	6 years 9 months 11 days
Exercisable, Weighted-Average Remaining Contractual Term	5 years 0 months 18 days
Aggregate Intrinsic Value
Stock options outstanding, Beginning aggregate intrinsic value	$ 43,106,153
Stock options outstanding, Ending aggregate intrinsic value	86,200,655	43,106,153
Stock options, vested and expected to vest aggregate intrinsic value	83,095,331
Stock options, exercisable aggregate intrinsic value	$ 44,963,329