Loans and reserve for credit losses (Allowance for Credit Losses on Financing Receivables) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended					3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended					3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended					3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended					3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended					3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended				3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014 Loan Losses	Jun. 30, 2013 Loan Losses	Jun. 30, 2014 Loan Losses	Jun. 30, 2013 Loan Losses	Jun. 30, 2014 Unfunded Lending Commitments	Jun. 30, 2013 Unfunded Lending Commitments	Jun. 30, 2014 Unfunded Lending Commitments	Jun. 30, 2013 Unfunded Lending Commitments	Jun. 30, 2014 Commercial Real Estate	Dec. 31, 2013 Commercial Real Estate	Jun. 30, 2013 Commercial Real Estate	Jun. 30, 2014 Commercial Real Estate Loan Losses	Jun. 30, 2013 Commercial Real Estate Loan Losses	Jun. 30, 2014 Commercial Real Estate Loan Losses	Jun. 30, 2013 Commercial Real Estate Loan Losses	Jun. 30, 2014 Commercial Real Estate Unfunded Lending Commitments	Jun. 30, 2013 Commercial Real Estate Unfunded Lending Commitments	Jun. 30, 2014 Commercial Real Estate Unfunded Lending Commitments	Jun. 30, 2013 Commercial Real Estate Unfunded Lending Commitments	Jun. 30, 2014 Construction	Dec. 31, 2013 Construction	Jun. 30, 2013 Construction	Jun. 30, 2014 Construction Loan Losses	Jun. 30, 2013 Construction Loan Losses	Jun. 30, 2014 Construction Loan Losses	Jun. 30, 2013 Construction Loan Losses	Jun. 30, 2014 Construction Unfunded Lending Commitments	Jun. 30, 2013 Construction Unfunded Lending Commitments	Jun. 30, 2014 Construction Unfunded Lending Commitments	Jun. 30, 2013 Construction Unfunded Lending Commitments	Jun. 30, 2014 Residential real estate	Dec. 31, 2013 Residential real estate	Jun. 30, 2013 Residential real estate	Jun. 30, 2014 Residential real estate Loan Losses	Jun. 30, 2013 Residential real estate Loan Losses	Jun. 30, 2014 Residential real estate Loan Losses	Jun. 30, 2013 Residential real estate Loan Losses	Jun. 30, 2014 Residential real estate Unfunded Lending Commitments	Jun. 30, 2013 Residential real estate Unfunded Lending Commitments	Jun. 30, 2014 Residential real estate Unfunded Lending Commitments	Jun. 30, 2013 Residential real estate Unfunded Lending Commitments	Jun. 30, 2014 Commercial and Industrial	Dec. 31, 2013 Commercial and Industrial	Jun. 30, 2013 Commercial and Industrial	Jun. 30, 2014 Commercial and Industrial Loan Losses	Jun. 30, 2013 Commercial and Industrial Loan Losses	Jun. 30, 2014 Commercial and Industrial Loan Losses	Jun. 30, 2013 Commercial and Industrial Loan Losses	Jun. 30, 2014 Commercial and Industrial Unfunded Lending Commitments	Jun. 30, 2013 Commercial and Industrial Unfunded Lending Commitments	Jun. 30, 2014 Commercial and Industrial Unfunded Lending Commitments	Jun. 30, 2013 Commercial and Industrial Unfunded Lending Commitments	Jun. 30, 2014 Consumer Loans	Dec. 31, 2013 Consumer Loans	Jun. 30, 2013 Consumer Loans	Jun. 30, 2014 Consumer Loans Loan Losses	Jun. 30, 2013 Consumer Loans Loan Losses	Jun. 30, 2014 Consumer Loans Loan Losses	Jun. 30, 2013 Consumer Loans Loan Losses	Jun. 30, 2014 Consumer Loans Unfunded Lending Commitments	Jun. 30, 2013 Consumer Loans Unfunded Lending Commitments	Jun. 30, 2014 Consumer Loans Unfunded Lending Commitments	Jun. 30, 2013 Consumer Loans Unfunded Lending Commitments	Jun. 30, 2014 Unallocated	Jun. 30, 2013 Unallocated	Jun. 30, 2014 Unallocated Loan Losses	Jun. 30, 2013 Unallocated Loan Losses	Jun. 30, 2014 Unallocated Loan Losses	Jun. 30, 2013 Unallocated Loan Losses	Jun. 30, 2014 Unallocated Unfunded Lending Commitments	Jun. 30, 2013 Unallocated Unfunded Lending Commitments	Jun. 30, 2014 Unallocated Unfunded Lending Commitments	Jun. 30, 2013 Unallocated Unfunded Lending Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Allowance at the beginning of period			$ 20,857		$ 21,722	$ 24,548	$ 20,857	$ 27,261	$ 440	$ 440	$ 440	$ 440	$ 7,960	$ 9,565		$ 8,803	$ 11,225	$ 9,565	$ 11,596	$ 48	$ 48	$ 48	$ 48	$ 728	$ 535		$ 602	$ 1,236	$ 535	$ 1,583	$ 268	$ 268	$ 268	$ 268	$ 2,067	$ 2,381		$ 2,227	$ 3,714	$ 2,381	$ 3,551	$ 25	$ 25	$ 25	$ 25	$ 6,616	$ 6,261		$ 6,840	$ 5,676	$ 6,261	$ 7,267	$ 75	$ 75	$ 75	$ 75	$ 1,181	$ 1,401		$ 1,243	$ 2,039	$ 1,401	$ 2,177	$ 24	$ 24	$ 24	$ 24	$ 714		$ 2,007	$ 658	$ 714	$ 1,087	$ 0	$ 0	$ 0	$ 0
Loan loss provision (credit)	0	1,000	0	1,000	0	1,000	0	1,000	0	0	0	0				82	261	(1,478)	(19)	0	0	0	0				(163)	226	115	542	0	0	0	0				(215)	(570)	(270)	(388)	0	0	0	0				255	887	237	1,012	0	0	0	0				129	(276)	191	(190)	0	0	0	0	800		(88)	472	1,205	43	0	0	0	0
Recoveries					1,119	1,040	3,267	2,030								60	37	1,001	215								289	39	374	163								157	71	281	188								546	834	1,457	1,346								67	59	154	118							0	0	0	0
Loans charged off					(2,370)	(3,894)	(3,653)	(7,597)								(985)	(811)	(1,128)	(1,080)								0	(659)	(296)	(1,446)								(101)	(243)	(324)	(379)								(1,026)	(2,049)	(1,340)	(4,277)								(258)	(132)	(565)	(415)							0	0	0	0
Allowance at the end of period	20,471		20,471		20,471	22,694	20,471	22,694	440	440	440	440	7,960	9,565		7,960	10,712	7,960	10,712	48	48	48	48	728	535		728	842	728	842	268	268	268	268	2,067	2,381		2,068	2,972	2,068	2,972	25	25	25	25	6,616	6,261		6,615	5,348	6,615	5,348	75	75	75	75	1,181	1,401		1,181	1,690	1,181	1,690	24	24	24	24	1,919		1,919	1,130	1,919	1,130	0	0	0	0
Total reserve for credit losses	$ 20,911	$ 23,134	$ 20,911	$ 23,134									$ 8,008		$ 10,760									$ 996		$ 1,110									$ 2,093		$ 2,997									$ 6,690		$ 5,423									$ 1,205		$ 1,714									$ 1,919	$ 1,130