Stock Options Outstanding (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Number of Shares
Beginning balance	90,250	105,250	157,500
Exercised	(83,500)	(15,000)	(52,250)
Ending balance	6,750	90,250	105,250
Number of options exercisable	6,750	90,250	105,250
Granted
Expired or forfeited
Average Exercise Price
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Beginning of Period	$ 29.94	$ 29.50	$ 27.13
Granted
Exercised	$ 29.88	$ 26.90	$ 22.35
Expired or forfeited
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, End of Period	$ 30.65	$ 29.94	$ 29.50
Number of options exercisable	$ 30.65	$ 29.94	$ 29.50