Summary of Stock Options Issued Pursuant to Stock Incentive Plans (Detail) (USD $)	3 Months Ended
	Mar. 31, 2014
Number of Shares
Outstanding, Beginning Balance	2,469,607
Granted	9,044
Exercised	(120,577)
Forfeited	(12,057)
Outstanding, Ending Balance	2,346,017
Number of Shares Exercisable, Ending Balance	1,665,677
Weighted-Average Exercise Price
Beginning Balance	$ 33.07
Granted	$ 60.40
Exercised	$ 23.90
Forfeited	$ 54.47
Ending Balance	$ 33.54
Weighted Average Exercise Price Exercisable, Ending Balance	$ 26.74
Weighted-Average Remaining Contractual Term (Years)
Weighted Average Remaining Contractual Term (Years), Outstanding as of end of period	5 years 8 months 9 days
Weighted Average Remaining Contractual Term (Years), Exercisable as of end of period	4 years 3 months 22 days
Aggregate Intrinsic Value of In-the-Money Options
Aggregate Intrinsic Value of In-the-Money Options, Outstanding as of end of period	$ 60,959,472
Aggregate Intrinsic Value of In-the-Money Options, Exercisable as of end of period	$ 54,047,694