Loans and reserve for credit losses (Past Due Financing Receivables) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 days past due	$ 3,904	$ 2,260
90 days or more past due	2,986	5,270
Total past due	6,890	7,530
Current	1,000,464	988,702
Total loans	1,007,354	996,232
Commercial Real Estate Owner Occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 days past due	2,035	959
90 days or more past due	1,054	2,905
Total past due	3,089	3,864
Current	192,022	201,134
Total loans	195,111	204,998
Commercial Real Estate Non Owner Occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 days past due	792	0
90 days or more past due	0	0
Total past due	792	0
Current	347,805	347,014
Total loans	348,597	347,014
Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 days past due	2,827	959
90 days or more past due	1,054	2,905
Total past due	3,881	3,864
Current	539,827	548,148
Total loans	543,708	552,012
Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 days past due	0	215
90 days or more past due	39	119
Total past due	39	334
Current	55,397	52,169
Total loans	55,436	52,503
Residential real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 days past due	362	436
90 days or more past due	235	163
Total past due	597	599
Current	99,953	100,958
Total loans	100,550	101,557
Commercial and Industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 days past due	621	597
90 days or more past due	1,607	2,077
Total past due	2,228	2,674
Current	271,216	251,496
Total loans	273,444	254,170
Consumer Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 days past due	94	53
90 days or more past due	51	6
Total past due	145	59
Current	34,071	35,931
Total loans	$ 34,216	$ 35,990