Loans and allowance for credit losses (Details 6) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	$ 686,756	$ 691,164
30-59 days past due	4,703	3,757
60-89 days past due	3,019	2,102
90 days or more past due	5	270
Total past due	7,727	6,129
Non-accrual	15,176	14,626
Total loans	709,659	711,919
Percent of total loans, Current	96.80%	97.10%
Percent of total loans, 30-59 days past due	0.70%	0.50%
Percent of total loans, 60-89 days past due	0.40%	0.30%
Percent of total loans, 90 days or more past due	0.00%	0.00%
Percent of total loans, Total past due	1.10%	0.80%
Percent of total loans, Non accrual	2.10%	2.10%
Construction Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	60,108	60,642
30-59 days past due	106	0
60-89 days past due	154	0
90 days or more past due	0	0
Total past due	260	0
Non-accrual	7,980	3,949
Total loans	68,348	64,591
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	271,171	265,182
30-59 days past due	1,526	2,765
60-89 days past due	1,450	1,724
90 days or more past due	0	20
Total past due	2,976	4,509
Non-accrual	3,037	5,166
Total loans	277,184	274,857
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	290,697	299,295
30-59 days past due	1,885	639
60-89 days past due	1,307	0
90 days or more past due	0	0
Total past due	3,192	639
Non-accrual	3,873	4,671
Total loans	297,762	304,605
Commercial Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	55,071	55,576
30-59 days past due	1,146	330
60-89 days past due	9	247
90 days or more past due	5	250
Total past due	1,160	827
Non-accrual	261	792
Total loans	56,492	57,195
Consumer Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	9,709	10,469
30-59 days past due	40	23
60-89 days past due	99	131
90 days or more past due	0	0
Total past due	139	154
Non-accrual	25	48
Total loans	$ 9,873	$ 10,671