Loans and allowance for credit losses (Details 4) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Current	$ 753,758	$ 760,733
30-59 days past due	6,578	17,198
60-89 days past due	3,577	9,026
90 days or more past due	4,675	2,723
Total past due	14,830	28,947
Nonaccrual	39,442	51,370
Total loans	808,030	841,050
Current	93.30%	90.50%
30-59 days past due	0.80%	2.00%
60-89 days past due	0.40%	1.10%
90 days or more past due	0.60%	0.30%
Total past due	1.80%	3.40%
Non accrual	4.90%	6.10%
Commercial Loan [Member]
Current	59,756	64,581
30-59 days past due	69	1,350
60-89 days past due	82	1,819
90 days or more past due	67	66
Total past due	218	3,235
Nonaccrual	1,557	1,669
Total loans	61,531	69,485
Consumer Loan [Member]
Current	13,228	14,492
30-59 days past due	174	112
60-89 days past due	11	6
90 days or more past due	45	1
Total past due	230	119
Nonaccrual	54	28
Total loans	13,512	14,639
Residential Real Estate [Member]
Current	281,610	289,459
30-59 days past due	4,274	4,417
60-89 days past due	1,113	5,291
90 days or more past due	1,012	2,331
Total past due	6,399	12,039
Nonaccrual	14,440	20,106
Total loans	302,449	321,604
Commercial Real Estate [Member]
Current	303,008	289,760
30-59 days past due	971	10,073
60-89 days past due	2,371	1,594
90 days or more past due	3,551	0
Total past due	6,893	11,667
Nonaccrual	11,916	14,012
Total loans	321,817	315,439
Construction Loans [Member]
Current	96,156	102,441
30-59 days past due	1,090	1,246
60-89 days past due	0	316
90 days or more past due	0	325
Total past due	1,090	1,887
Nonaccrual	11,475	15,555
Total loans	$ 108,721	$ 119,883