Loans and reserve for credit losses (Allowance for Credit Losses on Financing Receivables) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Allowance for Loan and Lease Losses [Roll Forward]
Loans charged off			$ (81,400)
Balance at end of period	20,857	27,261
Total reserve for credit losses	21,297	27,701	45,455
Loan Losses
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	27,261	43,905	46,668
Loan loss provision (credit)	1,000	1,100	75,000
Recoveries	5,132	4,449	3,592
Loans charged off	(12,536)	(22,193)	(27,287)
Loans charged-off as a result of the Bulk Sale (see Note 2)			(54,068)
Balance at end of period	20,857	27,261	43,905
Unfunded Lending Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	440	1,550	941
Loan loss provision (credit)	0	(1,110)	609
Balance at end of period	440	440	1,550
Commercial Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Loans charged-off as a result of the Bulk Sale (see Note 2)			(19,216)
Balance at end of period	9,565	11,596
Total reserve for credit losses	9,613	11,644	21,676
Commercial Real Estate | Loan Losses
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	11,596	21,648	14,338
Loan loss provision (credit)	203	2,829	29,908
Recoveries	1,034	198	119
Loans charged off	(3,268)	(13,079)	(3,501)
Balance at end of period	9,565	11,596	21,648
Commercial Real Estate | Unfunded Lending Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	48	28	40
Loan loss provision (credit)	0	20	(12)
Balance at end of period	48	48	28
Construction
Allowance for Loan and Lease Losses [Roll Forward]
Loans charged-off as a result of the Bulk Sale (see Note 2)			(25,288)
Balance at end of period	535	1,583
Total reserve for credit losses	803	1,851	5,427
Construction | Loan Losses
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	1,583	5,398	12,652
Loan loss provision (credit)	159	(4,135)	22,019
Recoveries	708	584	1,551
Loans charged off	(1,915)	(264)	(5,536)
Balance at end of period	535	1,583	5,398
Construction | Unfunded Lending Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	268	29	0
Loan loss provision (credit)	0	239	29
Balance at end of period	268	268	29
Residential real estate
Allowance for Loan and Lease Losses [Roll Forward]
Loans charged-off as a result of the Bulk Sale (see Note 2)			(2,979)
Balance at end of period	2,381	3,551
Total reserve for credit losses	2,406	3,576	3,443
Residential real estate | Loan Losses
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	3,551	3,259	4,116
Loan loss provision (credit)	(1,013)	2,650	4,196
Recoveries	433	262	164
Loans charged off	(590)	(2,620)	(2,238)
Balance at end of period	2,381	3,551	3,259
Residential real estate | Unfunded Lending Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	25	184	101
Loan loss provision (credit)	0	(159)	83
Balance at end of period	25	25	184
Commercial and Industrial
Allowance for Loan and Lease Losses [Roll Forward]
Loans charged-off as a result of the Bulk Sale (see Note 2)			(6,480)
Balance at end of period	6,261	7,267
Total reserve for credit losses	6,336	7,342	11,778
Commercial and Industrial | Loan Losses
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	7,267	11,291	12,220
Loan loss provision (credit)	1,808	(2,094)	17,724
Recoveries	2,694	3,094	1,453
Loans charged off	(5,508)	(5,024)	(13,626)
Balance at end of period	6,261	7,267	11,291
Commercial and Industrial | Unfunded Lending Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	75	487	523
Loan loss provision (credit)	0	(412)	(36)
Balance at end of period	75	75	487
Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Loans charged-off as a result of the Bulk Sale (see Note 2)			(105)
Balance at end of period	1,401	2,177
Total reserve for credit losses	1,425	2,201	3,114
Consumer | Loan Losses
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	2,177	2,292	2,966
Loan loss provision (credit)	216	780	1,512
Recoveries	263	311	305
Loans charged off	(1,255)	(1,206)	(2,386)
Balance at end of period	1,401	2,177	2,292
Consumer | Unfunded Lending Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	24	822	241
Loan loss provision (credit)	0	(798)	581
Balance at end of period	24	24	822
Unallocated
Allowance for Loan and Lease Losses [Roll Forward]
Loans charged-off as a result of the Bulk Sale (see Note 2)			0
Balance at end of period	714	1,087
Total reserve for credit losses	714	1,087	17
Unallocated | Loan Losses
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	1,087	17	376
Loan loss provision (credit)	(373)	1,070	(359)
Recoveries	0	0	0
Loans charged off	0	0	0
Balance at end of period	714	1,087	17
Unallocated | Unfunded Lending Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	0	0	36
Loan loss provision (credit)	0	0	(36)
Balance at end of period	$ 0	$ 0	$ 0