Loans and reserve for credit losses (Reserve for Loan Losses and Recorded Investment in Loans) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Financing Receivable, Allowance for Credit Losses [Line Items]
Reserve for loan losses Total	$ 21,722	$ 20,857
Total loans, Amount	1,007,354	996,232
Commercial Real Estate Portfolio Segment
Financing Receivable, Allowance for Credit Losses [Line Items]
Reserve for loan losses Individually evaluated for impairment	660	665
Reserve for loan losses Collectively evaluated for impairment	8,143	8,900
Reserve for loan losses Total	8,803	9,565
Recorded investment in loans Individually evaluated for impairment	29,121	32,227
Recorded investment in loans, Collectively evaluated for impairment	514,587	519,785
Total loans, Amount	543,708	552,012
Construction Portfolio Segment
Financing Receivable, Allowance for Credit Losses [Line Items]
Reserve for loan losses Individually evaluated for impairment	0	0
Reserve for loan losses Collectively evaluated for impairment	602	535
Reserve for loan losses Total	602	535
Recorded investment in loans Individually evaluated for impairment	1,739	1,987
Recorded investment in loans, Collectively evaluated for impairment	53,697	50,516
Total loans, Amount	55,436	52,503
Residential Portfolio Segment
Financing Receivable, Allowance for Credit Losses [Line Items]
Reserve for loan losses Individually evaluated for impairment	62	62
Reserve for loan losses Collectively evaluated for impairment	2,165	2,319
Reserve for loan losses Total	2,227	2,381
Recorded investment in loans Individually evaluated for impairment	426	430
Recorded investment in loans, Collectively evaluated for impairment	100,124	101,127
Total loans, Amount	100,550	101,557
Commercial and Industrial
Financing Receivable, Allowance for Credit Losses [Line Items]
Reserve for loan losses Individually evaluated for impairment	286	56
Reserve for loan losses Collectively evaluated for impairment	6,554	6,205
Reserve for loan losses Total	6,840	6,261
Recorded investment in loans Individually evaluated for impairment	5,238	5,823
Recorded investment in loans, Collectively evaluated for impairment	268,206	248,347
Total loans, Amount	273,444	254,170
Consumer Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Reserve for loan losses Individually evaluated for impairment	0	0
Reserve for loan losses Collectively evaluated for impairment	1,243	1,401
Reserve for loan losses Total	1,243	1,401
Recorded investment in loans Individually evaluated for impairment	0	0
Recorded investment in loans, Collectively evaluated for impairment	34,216	35,990
Total loans, Amount	34,216	35,990
Allocated Financing Receivables [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Reserve for loan losses Individually evaluated for impairment	1,008	783
Reserve for loan losses Collectively evaluated for impairment	18,707	19,360
Reserve for loan losses Total	19,715	20,143
Recorded investment in loans Individually evaluated for impairment	36,524	40,467
Recorded investment in loans, Collectively evaluated for impairment	970,830	955,765
Total loans, Amount	1,007,354	996,232
Unallocated Financing Receivables
Financing Receivable, Allowance for Credit Losses [Line Items]
Reserve for loan losses Total	$ 2,007	$ 714