Loans and reserve for credit losses (Details 4) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
30-89 days past due	$ 5,239	$ 14,892
90 days or more past due	7,102	16,431
Total past due	12,341	31,323
Current	900,233	826,841
Total loans	912,574	858,164
Commercial Real Estate Owner Occupied [Member]
30-89 days past due	428	1,240
90 days or more past due	3,088	4,221
Total past due	3,516	5,461
Current	203,544	191,360
Total loans	207,060	196,821
Commercial Real Estate Non Owner Occupied [Member]
30-89 days past due	638	8,660
90 days or more past due	721	7,183
Total past due	1,359	15,843
Current	325,458	312,637
Total loans	326,817	328,480
Commerical real estate [Member]
30-89 days past due	1,066	9,900
90 days or more past due	3,809	11,404
Total past due	4,875	21,304
Current	529,002	503,997
Total loans	533,877	525,301
Construction [Member]
30-89 days past due	574	1,288
90 days or more past due	1,109	2,793
Total past due	1,683	4,081
Current	46,522	41,569
Total loans	48,205	45,650
Residential real estate [Member]
30-89 days past due	483	818
90 days or more past due	386	364
Total past due	869	1,182
Current	94,906	84,312
Total loans	95,775	85,494
Commercial and Industrial [Member]
30-89 days past due	3,020	2,825
90 days or more past due	1,797	1,858
Total past due	4,817	4,683
Current	192,160	157,530
Total loans	196,977	162,213
Consumer Loans [Member]
30-89 days past due	96	61
90 days or more past due	1	12
Total past due	97	73
Current	37,643	39,433
Total loans	$ 37,740	$ 39,506