Quarterly Results of Operations (Unaudited) (Details) (USD $) In Thousands, except Per 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
Quarterly Results of Operations (Unaudited) [Abstract]
Interest income	$ 22,549	$ 22,636	$ 22,797	$ 22,965	$ 23,481	$ 24,386	$ 25,645	$ 24,860	$ 90,947	$ 98,372	$ 104,507
Interest expense	3,988	4,189	4,431	4,594	5,031	5,739	6,082	6,301	17,202	23,153	30,217
Net interest income	18,561	18,447	18,366	18,371	18,450	18,647	19,563	18,559	73,745	75,219	74,290
Provision for credit losses	1,108	868	835	1,005	1,464	1,182	970	1,119	3,816	4,735	6,299
Non-interest income	7,392	5,038	5,754	5,228	7,104	5,825	5,006	5,118	23,412	23,053	20,825
Non-interest expense	18,763	13,370	13,979	12,919	15,715	13,307	13,272	13,285	59,031	55,579	52,937
Income before income taxes	6,082	9,247	9,306	9,675	8,375	9,983	10,327	9,273	34,310	37,958	35,879
Income tax expense	1,904	2,992	2,894	3,092	2,536	3,054	3,257	2,934	10,882	11,781	11,113
Net Income	$ 4,178	$ 6,255	$ 6,412	$ 6,583	$ 5,839	$ 6,929	$ 7,070	$ 6,339	$ 23,428	$ 26,177	$ 24,766
Per common share:
Basic earnings per share	$ 0.55	$ 0.82	$ 0.83	$ 0.86	$ 0.76	$ 0.9	$ 0.92	$ 0.83	$ 3.06	$ 3.41	$ 3.23
Diluted earnings per share	$ 0.55	$ 0.82	$ 0.83	$ 0.86	$ 0.76	$ 0.9	$ 0.92	$ 0.83	$ 3.05	$ 3.4	$ 3.23