Loans and reserve for credit losses (Details 1) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Allowance for Loan Losses
Balance at Beginning of period	$ 27,261	$ 43,905
Loan loss provision (credit)	0	1,100
Recoveries	990	460
Loans charged off	(3,703)	(1,514)
Balance at end of period	24,548	43,951
Reserve for unfunded loan commitments
Balance at beginning of year	440	1,550
Provision (credit) for unfunded loan commitments	0	0
Balance at end of year	440	1,550
Reserve for credit losses
Reserve for loan losses	24,548	43,951
Reserve for unfunded lending commitments	440	1,550
Total reserve for credit losses	24,988	45,501
Commerical real estate [Member]
Allowance for Loan Losses
Balance at Beginning of period	11,596	21,648
Loan loss provision (credit)	(280)	667
Recoveries	178	6
Loans charged off	(269)	(7)
Balance at end of period	11,225	22,314
Reserve for unfunded loan commitments
Balance at beginning of year	48	28
Provision (credit) for unfunded loan commitments	0	0
Balance at end of year	48	28
Reserve for credit losses
Reserve for loan losses	11,225	22,314
Reserve for unfunded lending commitments	48	28
Total reserve for credit losses	11,273	22,342
Construction [Member]
Allowance for Loan Losses
Balance at Beginning of period	1,583	5,398
Loan loss provision (credit)	316	(489)
Recoveries	124	151
Loans charged off	(787)	0
Balance at end of period	1,236	5,060
Reserve for unfunded loan commitments
Balance at beginning of year	268	29
Provision (credit) for unfunded loan commitments	0	0
Balance at end of year	268	29
Reserve for credit losses
Reserve for loan losses	1,236	5,060
Reserve for unfunded lending commitments	268	29
Total reserve for credit losses	1,504	5,089
Residential real estate [Member]
Allowance for Loan Losses
Balance at Beginning of period	3,551	3,259
Loan loss provision (credit)	182	1,132
Recoveries	117	34
Loans charged off	(136)	(561)
Balance at end of period	3,714	3,864
Reserve for unfunded loan commitments
Balance at beginning of year	25	184
Provision (credit) for unfunded loan commitments	0	0
Balance at end of year	25	184
Reserve for credit losses
Reserve for loan losses	3,714	3,864
Reserve for unfunded lending commitments	25	184
Total reserve for credit losses	3,739	4,048
Commercial and industrial [Member]
Allowance for Loan Losses
Balance at Beginning of period	7,267	11,291
Loan loss provision (credit)	125	(919)
Recoveries	512	180
Loans charged off	(2,228)	(644)
Balance at end of period	5,676	9,908
Reserve for unfunded loan commitments
Balance at beginning of year	75	487
Provision (credit) for unfunded loan commitments	0	0
Balance at end of year	75	487
Reserve for credit losses
Reserve for loan losses	5,676	9,908
Reserve for unfunded lending commitments	75	487
Total reserve for credit losses	5,751	10,395
Consumer Loans [Member]
Allowance for Loan Losses
Balance at Beginning of period	2,177	2,292
Loan loss provision (credit)	86	709
Recoveries	59	89
Loans charged off	(283)	(302)
Balance at end of period	2,039	2,788
Reserve for unfunded loan commitments
Balance at beginning of year	24	822
Provision (credit) for unfunded loan commitments	0	0
Balance at end of year	24	822
Reserve for credit losses
Reserve for loan losses	2,039	2,788
Reserve for unfunded lending commitments	24	822
Total reserve for credit losses	2,063	3,610
Unallocated [Member]
Allowance for Loan Losses
Balance at Beginning of period	1,087	17
Loan loss provision (credit)	(429)	0
Recoveries	0	0
Loans charged off	0	0
Balance at end of period	658	17
Reserve for unfunded loan commitments
Balance at beginning of year	0	0
Provision (credit) for unfunded loan commitments	0	0
Balance at end of year	0	0
Reserve for credit losses
Reserve for loan losses	658	17
Reserve for unfunded lending commitments	0	0
Total reserve for credit losses	$ 658	$ 17