Quarterly Results of Operations (Unaudited) (Details) (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
Summary of the quarterly consolidated results of operations
Interest income	$ 20,460	$ 18,719	$ 16,523	$ 16,826	$ 17,460	$ 16,011	$ 15,712	$ 15,431	$ 72,528	$ 64,614	$ 68,491
Interest expense	3,457	3,720	3,517	3,628	3,868	4,020	4,249	4,364	14,322	16,501	20,875
Net interest income	17,003	14,999	13,006	13,198	13,592	11,991	11,463	11,067	58,206	48,113	47,616
Provision for loan losses	1,715	1,041	209	559	838	1,564	1,332	1,548	3,524	5,282	11,554
Gain (loss) on sale of securities		2			23	1,115	365	274	2	1,777	533
Net income	5,170	4,850	4,910	4,613	3,522	3,417	3,093	2,765	19,543	12,797	10,455
Net income available to common shareholders	$ 5,014	$ 4,787	$ 4,804	$ 4,457	$ 3,460	$ 2,707	$ 2,816	$ 2,489	$ 19,062	$ 11,472	$ 9,049
Earnings per share
Basic	$ 0.58	$ 0.56	$ 0.65	$ 0.60	$ 0.47	$ 0.37	$ 0.38	$ 0.34	$ 2.39	$ 1.55	$ 1.23
Diluted	$ 0.56	$ 0.54	$ 0.62	$ 0.59	$ 0.46	$ 0.36	$ 0.37	$ 0.33	$ 2.30	$ 1.51	$ 1.21
Average shares outstanding:
Basic	8,617,466	8,503,475	7,434,537	7,422,860	7,421,544	7,414,043	7,406,624	7,387,072	7,974,241	7,407,258	7,373,405
Diluted	8,964,315	8,838,659	7,728,519	7,598,490	7,576,052	7,596,570	7,598,180	7,612,144	8,271,177	7,588,394	7,502,846