Summary of Stock Option Activity (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding Beginning balance, Shares	1,784,660	1,818,640	1,749,003
Granted, Shares	188,407	196,469	166,247
Exercised, Shares	(277,687)	(223,022)	(94,115)
Expired, Shares		(5,093)	(2,495)
Forfeited, Shares		(2,334)
Outstanding Ending balance, Shares	1,695,380	1,784,660	1,818,640
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Outstanding Beginning balance, Weighted Average Exercise Price	$ 33.05	$ 30.94	$ 29.74
Granted, Weighted Average Exercise Price	$ 49.03	$ 37.33	$ 34.09
Exercised, Weighted Average Exercise Price	$ 34.72	$ 18.93	$ 13.99
Expired, Weighted Average Exercise Price		$ 43.33	$ 44.08
Forfeited, Weighted Average Exercise Price		$ 36.69
Outstanding Ending balance,Weighted Average Exercise Price	$ 34.55	$ 33.05	$ 30.94
Exercisable at end of period	1,178,657	1,100,300	907,598