Loans and reserve for credit losses (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Commercial real estate:
Owner occupied, Amount	$ 199,026	$ 196,821
Non-owner occupied and other, Amount	345,969	328,480
Total commercial real estate loans	544,995	525,301
Construction, Amount	38,834	45,650
Residential real estate, Amount	93,475	85,494
Commerical and industrial, Amount	161,758	162,213
Consumer, Amount	38,022	39,506
Total loans, Amount	877,084	858,164
Less:
Deferred loan fees, Amount	(1,771)	(1,846)
Reserve for loan losses, Amount	(24,548)	(27,261)	(43,951)	(43,905)
Loans, net, Amount	$ 850,765	$ 829,057
Owner occupied, Percent	22.70%	22.90%
Non-owner occupied and other, Percent	39.40%	38.30%
Total commercial real estate loans, Percent	62.10%	61.20%
Construction, Percent	4.40%	5.30%
Residential real estate, Percent	10.70%	10.00%
Commerical and industrial, Percent	18.40%	18.90%
Consumer, Percent	4.40%	4.60%
Total loans, Percent	100.00%	100.00%