Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
NET INCOME	$ 4,703	$ 4,563	$ 11,951	$ 13,246
Net earnings allocated to participating securities	(21)	(17)	(56)	(50)
Net earnings allocated to common stock	4,682	4,546	11,895	13,196
Basic earnings per common share computation:
Net earnings allocated to common stock	4,682	4,546	11,895	13,196
Net earnings allocated to common stock	4,682	4,546	11,895	13,196
Weighted average common shares outstanding, including shares considered participating securities	12,513	12,448	12,505	12,430
Less: Average participating securities	(51)	(41)	(52)	(42)
Weighted average shares	12,462	12,407	12,453	12,388
Basic earnings per common share	$ 0.38	$ 0.37	$ 0.96	$ 1.07
Diluted earnings per common share computation:
Net earnings allocated to common stock	4,682	4,546	11,895	13,196
Weighted average common shares outstanding for basic earnings per common share	12,462	12,407	12,453	12,388
Add: Dilutive effects of assumed exercises of stock options	2	4	1	4
Weighted average shares and dilutive potential common shares	12,464	12,411	12,454	12,392
Diluted earnings per common share	$ 0.38	$ 0.37	$ 0.96	$ 1.06
Distributed Earnings Allocated to Common Stock [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net earnings allocated to common stock	2,054	2,045	6,161	6,130
Basic earnings per common share computation:
Net earnings allocated to common stock	2,054	2,045	6,161	6,130
Net earnings allocated to common stock	2,054	2,045	6,161	6,130
Undistributed Earnings Allocated to Common Stock [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net earnings allocated to common stock	2,628	2,501	5,734	7,066
Basic earnings per common share computation:
Net earnings allocated to common stock	2,628	2,501	5,734	7,066
Net earnings allocated to common stock	$ 2,628	$ 2,501	$ 5,734	$ 7,066