Loans and reserve for credit losses (Details 1) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Allowance for Loan Losses
Balance at Beginning of period	$ 24,548	$ 43,951	$ 27,261	$ 43,905
Loan loss provision (credit)	1,000	0	1,000	1,100
Recoveries	1,040	717	2,030	1,177
Loans charged off	(3,894)	(6,449)	(7,597)	(7,963)
Provision For Unfunded Loan Commitments	0	0	0	0
Balance at end of period	22,694	38,219	22,694	38,219
Reserve for unfunded lending commitments
Balance at beginning of year	440	1,550	440	1,550
Balance at end of year	440	1,550	440	1,550
Reserve for credit losses
Reserve for loan losses	22,694	38,219	22,694	38,219
Reserve for unfunded lending commitments	440	1,550	440	1,550
Total reserve for credit losses	23,134	39,769	23,134	39,769
Commerical real estate [Member]
Allowance for Loan Losses
Balance at Beginning of period	11,225	22,314	11,596	21,648
Loan loss provision (credit)	261	(145)	(19)	522
Recoveries	37	7	215	13
Loans charged off	(811)	(4,073)	(1,080)	(4,080)
Provision For Unfunded Loan Commitments	0	0	0	0
Balance at end of period	10,712	18,103	10,712	18,103
Reserve for unfunded lending commitments
Balance at beginning of year	48	28	48	28
Balance at end of year	48	28	48	28
Reserve for credit losses
Reserve for loan losses	10,712	18,103	10,712	18,103
Reserve for unfunded lending commitments	48	28	48	28
Total reserve for credit losses	10,760	18,131	10,760	18,131
Construction [Member]
Allowance for Loan Losses
Balance at Beginning of period	1,236	5,060	1,583	5,398
Loan loss provision (credit)	226	(703)	542	(1,192)
Recoveries	39	231	163	382
Loans charged off	(659)	(59)	(1,446)	(59)
Provision For Unfunded Loan Commitments	0	0	0	0
Balance at end of period	842	4,529	842	4,529
Reserve for unfunded lending commitments
Balance at beginning of year	268	29	268	29
Balance at end of year	268	29	268	29
Reserve for credit losses
Reserve for loan losses	842	4,529	842	4,529
Reserve for unfunded lending commitments	268	29	268	29
Total reserve for credit losses	1,110	4,558	1,110	4,558
Residential real estate [Member]
Allowance for Loan Losses
Balance at Beginning of period	3,714	3,864	3,551	3,259
Loan loss provision (credit)	(570)	700	(388)	1,832
Recoveries	71	85	188	119
Loans charged off	(243)	(956)	(379)	(1,517)
Provision For Unfunded Loan Commitments	0	0	0	0
Balance at end of period	2,972	3,693	2,972	3,693
Reserve for unfunded lending commitments
Balance at beginning of year	25	184	25	184
Balance at end of year	25	184	25	184
Reserve for credit losses
Reserve for loan losses	2,972	3,693	2,972	3,693
Reserve for unfunded lending commitments	25	184	25	184
Total reserve for credit losses	2,997	3,877	2,997	3,877
Commercial and Industrial [Member]
Allowance for Loan Losses
Balance at Beginning of period	5,676	9,908	7,267	11,291
Loan loss provision (credit)	887	(429)	1,012	(1,348)
Recoveries	834	303	1,346	483
Loans charged off	(2,049)	(997)	(4,277)	(1,641)
Provision For Unfunded Loan Commitments	0	0	0	0
Balance at end of period	5,348	8,785	5,348	8,785
Reserve for unfunded lending commitments
Balance at beginning of year	75	487	75	487
Balance at end of year	75	487	75	487
Reserve for credit losses
Reserve for loan losses	5,348	8,785	5,348	8,785
Reserve for unfunded lending commitments	75	487	75	487
Total reserve for credit losses	5,423	9,272	5,423	9,272
Consumer Loans [Member]
Allowance for Loan Losses
Balance at Beginning of period	2,039	2,788	2,177	2,292
Loan loss provision (credit)	(276)	(7)	(190)	702
Recoveries	59	91	118	180
Loans charged off	(132)	(364)	(415)	(666)
Provision For Unfunded Loan Commitments	0	0	0	0
Balance at end of period	1,690	2,508	1,690	2,508
Reserve for unfunded lending commitments
Balance at beginning of year	24	822	24	822
Balance at end of year	24	822	24	822
Reserve for credit losses
Reserve for loan losses	1,690	2,508	1,690	2,508
Reserve for unfunded lending commitments	24	822	24	822
Total reserve for credit losses	1,714	3,330	1,714	3,330
Unallocated [Member]
Allowance for Loan Losses
Balance at Beginning of period	658	17	1,087	17
Loan loss provision (credit)	472	584	43	584
Recoveries	0	0	0	0
Loans charged off	0	0	0	0
Provision For Unfunded Loan Commitments	0	0	0	0
Balance at end of period	1,130	601	1,130	601
Reserve for unfunded lending commitments
Balance at beginning of year	0	0	0	0
Balance at end of year	0	0	0	0
Reserve for credit losses
Reserve for loan losses	1,130	601	1,130	601
Reserve for unfunded lending commitments	0	0	0	0
Total reserve for credit losses	$ 1,130	$ 601	$ 1,130	$ 601