Summary of Stock Option Activity (Detail) (USD $)	9 Months Ended
	Sep. 30, 2013
Directors Stock Option Plan
Number of Shares
Beginning Balance	111,000
Granted
Exercised	(3,000)
Expired	(4,500)
Ending Balance	103,500
Weighted Average Exercise Price
Beginning Balance	$ 20.97
Granted
Exercised	$ 16.40
Expired	$ 16.40
Ending Balance	$ 21.30
Employee Stock Option Plan
Number of Shares
Beginning Balance	108,000
Granted
Exercised	(7,000)
Expired	(19,000)
Ending Balance	82,000
Weighted Average Exercise Price
Beginning Balance	$ 20.90
Granted
Exercised	$ 14.91
Expired	$ 18.11
Ending Balance	$ 22.06