Loans and reserve for credit losses (Details 4) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
30-89 days past due	$ 7,253	$ 14,892
90 days or more past due	12,300	16,431
Total past due	19,553	31,323
Current	857,531	826,841
Total loans	877,084	858,164
Commercial Real Estate Owner Occupied [Member]
30-89 days past due	3,464	1,240
90 days or more past due	4,613	4,221
Total past due	8,077	5,461
Current	190,949	191,360
Total loans	199,026	196,821
Commercial Real Estate Non Owner Occupied [Member]
30-89 days past due	460	8,660
90 days or more past due	3,708	7,183
Total past due	4,168	15,843
Current	341,801	312,637
Total loans	345,969	328,480
Commerical real estate [Member]
30-89 days past due	3,924	9,900
90 days or more past due	8,321	11,404
Total past due	12,245	21,304
Current	532,750	503,997
Total loans	544,995	525,301
Construction [Member]
30-89 days past due	298	1,288
90 days or more past due	1,166	2,793
Total past due	1,464	4,081
Current	37,370	41,569
Total loans	38,834	45,650
Residential real estate [Member]
30-89 days past due	326	818
90 days or more past due	462	364
Total past due	788	1,182
Current	92,687	84,312
Total loans	93,475	85,494
Commercial and industrial [Member]
30-89 days past due	2,665	2,825
90 days or more past due	2,337	1,858
Total past due	5,002	4,683
Current	156,756	157,530
Total loans	161,758	162,213
Consumer Loans [Member]
30-89 days past due	40	61
90 days or more past due	14	12
Total past due	54	73
Current	37,968	39,433
Total loans	$ 38,022	$ 39,506