Loans and allowance for credit losses (Details 6) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	$ 675,926	$ 691,164
30-59 days past due	6,529	3,757
60-89 days past due	1,905	2,102
90 days or more past due	121	270
Total past due	8,555	6,129
Non-accrual	19,156	14,626
Total loans	703,637	711,919
Percent of total loans, Current	96.10%	97.10%
Percent of total loans, 30-59 days past due	0.90%	0.50%
Percent of total loans, 60-89 days past due	0.30%	0.30%
Percent of total loans, 90 days or more past due	0.00%	0.00%
Percent of total loans, Total past due	1.20%	0.80%
Percent of total loans, Non accrual	2.70%	2.10%
Construction Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	57,666	60,642
30-59 days past due	935	0
60-89 days past due	0	0
90 days or more past due	0	0
Total past due	935	0
Non-accrual	8,211	3,949
Total loans	66,812	64,591
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	261,491	265,182
30-59 days past due	4,246	2,765
60-89 days past due	998	1,724
90 days or more past due	0	20
Total past due	5,244	4,509
Non-accrual	3,745	5,166
Total loans	270,480	274,857
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	293,871	299,295
30-59 days past due	1,027	639
60-89 days past due	755	0
90 days or more past due	117	0
Total past due	1,899	639
Non-accrual	6,377	4,671
Total loans	302,147	304,605
Commercial Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	52,894	55,576
30-59 days past due	201	330
60-89 days past due	134	247
90 days or more past due	4	250
Total past due	339	827
Non-accrual	781	792
Total loans	54,014	57,195
Consumer Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	10,004	10,469
30-59 days past due	120	23
60-89 days past due	18	131
90 days or more past due	0	0
Total past due	138	154
Non-accrual	42	48
Total loans	$ 10,184	$ 10,671