Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Basic earnings per common share computation
Net income per consolidated statements of income	$ 4,297	$ 4,347	$ 4,347
Net earnings allocated to participating securities	(20)	(16)
Net earnings allocated to common stock	4,277	4,331
Net earnings allocated to common stock	4,277	4,331
Weighted average common shares outstanding, including shares considered participating securities	12,493	12,402
Less: Average participating securities	(49)	(40)
Weighted average shares	12,444	12,362
Basic earnings per common share	$ 0.34	$ 0.35	$ 0.35
Diluted earnings per common share computation
Net earnings allocated to common stock	4,277	4,331
Weighted average common shares outstanding for basic earnings per common share	12,444	12,362
Add: Dilutive effects of assumed exercises of stock options	1	4
Weighted average shares and dilutive potential common shares	12,445	12,366
Diluted earnings per common share	$ 0.34	$ 0.35	$ 0.35
Distributed earnings allocated to common stock [Member]
Basic earnings per common share computation
Net earnings allocated to common stock	2,053	2,041
Net earnings allocated to common stock	2,053	2,041
Undistributed earnings allocated to common stock [Member]
Basic earnings per common share computation
Net earnings allocated to common stock	2,224	2,290
Net earnings allocated to common stock	$ 2,224	$ 2,290