Common Stock and Earnings per Share (Details 1) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Basic
Net Income	$ 5,341	$ 6,092	$ 5,962	$ 5,908	$ 5,491	$ 6,060	$ 5,739	$ 5,719	$ 23,303	$ 23,009	$ 20,310
Weighted-average common shares outstanding (in shares)									11,378,216	11,326,968	11,295,693
Basic earnings per share (in dollars per share)	$ 0.47	$ 0.53	$ 0.53	$ 0.52	$ 0.48	$ 0.54	$ 0.51	$ 0.50	$ 2.05	$ 2.03	$ 1.8
Diluted
Net Income	$ 5,341	$ 6,092	$ 5,962	$ 5,908	$ 5,491	$ 6,060	$ 5,739	$ 5,719	$ 23,303	$ 23,009	$ 20,310
Weighted-average common shares outstanding (in shares)									11,378,216	11,326,968	11,295,693
Effect of dilutive restricted stock, stock options and SARs (in shares)									178,998	148,652	135,873
Weighted-average common shares outstanding assuming dilution (in shares)									11,557,214	11,475,620	11,431,566
Diluted earnings per share (in dollars per share)	$ 0.46	$ 0.53	$ 0.52	$ 0.51	$ 0.48	$ 0.53	$ 0.50	$ 0.50	$ 2.02	$ 2.01	$ 1.78