Loans and allowance for credit losses (Details 4) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Current	$ 748,133	$ 760,733
30-59 days past due	6,517	17,198
60-89 days past due	3,831	9,026
90 days or more past due	3,519	2,723
Total past due	13,867	28,947
Non accrual	47,958	51,370
Total	809,958	841,050
Current	92.40%	90.50%
30-59 days past due	0.80%	2.00%
60-89 days past due	0.50%	1.10%
90 days or more past due	0.40%	0.30%
Total past due	1.70%	3.40%
Non accrual	5.90%	6.10%
Commercial Loan [Member]
Current	61,278	64,581
30-59 days past due	46	1,350
60-89 days past due	9	1,819
90 days or more past due	62	66
Total past due	117	3,235
Non accrual	1,609	1,669
Total	63,004	69,485
Consumer Loan [Member]
Current	13,837	14,492
30-59 days past due	51	112
60-89 days past due	23	6
90 days or more past due	184	1
Total past due	258	119
Non accrual	55	28
Total	14,150	14,639
Residential Real Estate [Member]
Current	279,299	289,459
30-59 days past due	4,133	4,417
60-89 days past due	1,029	5,291
90 days or more past due	1,232	2,331
Total past due	6,394	12,039
Non accrual	20,400	20,106
Total	306,093	321,604
Commercial Real Estate [Member]
Current	297,782	289,760
30-59 days past due	2,287	10,073
60-89 days past due	1,898	1,594
90 days or more past due	2,041	0
Total past due	6,226	11,667
Non accrual	11,636	14,012
Total	315,644	315,439
Construction Loans [Member]
Current	95,937	102,441
30-59 days past due	0	1,246
60-89 days past due	872	316
90 days or more past due	0	325
Total past due	872	1,887
Non accrual	14,258	15,555
Total	$ 111,067	$ 119,883