Loans and reserve for credit losses (Past Due Financing Receivables) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 days past due	$ 2,260	$ 14,892
90 days or more past due	5,270	16,431
Total past due	7,530	31,323
Current	988,702	826,841
Total loans	996,232	858,164
Commercial Real Estate Owner Occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 days past due	959	1,240
90 days or more past due	2,905	4,221
Total past due	3,864	5,461
Current	201,134	191,360
Total loans	204,998	196,821
Commercial Real Estate Non Owner Occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 days past due	0	8,660
90 days or more past due	0	7,183
Total past due	0	15,843
Current	347,014	312,637
Total loans	347,014	328,480
Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 days past due	959	9,900
90 days or more past due	2,905	11,404
Total past due	3,864	21,304
Current	548,148	503,997
Total loans	552,012	525,301
Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 days past due	215	1,288
90 days or more past due	119	2,793
Total past due	334	4,081
Current	52,169	41,569
Total loans	52,503	45,650
Residential real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 days past due	436	818
90 days or more past due	163	364
Total past due	599	1,182
Current	100,958	84,312
Total loans	101,557	85,494
Commercial and Industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 days past due	597	2,825
90 days or more past due	2,077	1,858
Total past due	2,674	4,683
Current	251,496	157,530
Total loans	254,170	162,213
Consumer Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 days past due	53	61
90 days or more past due	6	12
Total past due	59	73
Current	35,931	39,433
Total loans	$ 35,990	$ 39,506