Quarterly Financial Data (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 Financial Data
Interest income	$ 19,988	$ 19,977	$ 20,258	$ 20,431	$ 20,821	$ 21,237	$ 21,704	$ 21,706	$ 80,654	$ 85,468	$ 91,003
Interest expense	1,838	1,958	2,111	2,267	2,487	2,621	2,723	2,897	8,174	10,728	17,469
Net interest income	18,150	18,019	18,147	18,164	18,334	18,616	18,981	18,809	72,480	74,740	73,534
Provision for loan and lease losses	2,382	2,210	1,343	4,100	3,140	3,649	5,556	5,134	10,035	17,479	21,565
Net interest income after provision for loan and lease losses	15,768	15,809	16,804	14,064	15,194	14,967	13,425	13,675	62,445	57,261	51,969
Noninterest income	10,378	10,861	8,000	11,021	8,978	8,974	8,696	7,759	40,260	34,407	34,418
Noninterest expense	19,712	19,058	18,636	18,876	17,563	17,295	16,406	16,746	76,282	68,010	67,349
Income before income taxes	6,434	7,612	6,168	6,209	6,609	6,646	5,715	4,688	26,423	23,658	19,038
Income taxes	1,358	1,842	1,405	946	1,349	1,402	1,199	826	5,551	4,776	3,282
Net income	$ 5,076	$ 5,770	$ 4,763	$ 5,263	$ 5,260	$ 5,244	$ 4,516	$ 3,862	$ 20,872	$ 18,882	$ 15,756
Net income per share data:
Basic	$ 0.30	$ 0.34	$ 0.28	$ 0.31	$ 0.32	$ 0.31	$ 0.27	$ 0.23	$ 1.25	$ 1.13	$ 0.95
Diluted	$ 0.30	$ 0.34	$ 0.28	$ 0.31	$ 0.32	$ 0.31	$ 0.27	$ 0.23	$ 1.24	$ 1.13	$ 0.95
Dividends declared	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.80	$ 0.80	$ 0.80