Stock Compensation Plans - Stock Option Transactions Under Various Stock-Based Employee Compensation Plans (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Outstanding, Beginning Balance, Shares	3,232,423
Granted, Shares	87,000
Exercised, Shares	(522,032)	(682,263)	(586,563)
Forfeited, Shares	(12,200)
Expired, Shares	(10,600)
Outstanding, Ending Balance, Shares	2,774,591	3,232,423
Exercisable, Ending Balance, Shares	1,622,891
Outstanding, Beginning Balance, Weighted Average Exercise Price	$ 32.89
Granted, Weighted Average Exercise Price	$ 51.04
Exercised, Weighted-Average Exercise Price	$ 31.12
Forfeited, Weighted Average Exercise Price	$ 43.89
Expired, Weighted Average Exercise Price	$ 28.13
Outstanding, Ending Balance, Weighted Average Exercise Price	$ 33.76	$ 32.89
Exercisable, Ending Balance, Weighted Average Exercise Price	$ 27.54
Outstanding, Ending balance, Weighted Average Remaining Contractual Term	6 years 7 months 28 days
Exercisable, Ending Balance, Weighted Average Remaining Contractual Term	5 years 7 months 17 days