Loans and reserve for credit losses (Allowance for Credit Losses on Financing Receivables) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended					3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended					3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended					3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended					3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended					3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended				3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014 Loan Losses	Sep. 30, 2013 Loan Losses	Sep. 30, 2014 Loan Losses	Sep. 30, 2013 Loan Losses	Sep. 30, 2014 Unfunded Lending Commitments	Sep. 30, 2013 Unfunded Lending Commitments	Sep. 30, 2014 Unfunded Lending Commitments	Sep. 30, 2013 Unfunded Lending Commitments	Sep. 30, 2014 Commercial Real Estate	Dec. 31, 2013 Commercial Real Estate	Sep. 30, 2013 Commercial Real Estate	Sep. 30, 2014 Commercial Real Estate Loan Losses	Sep. 30, 2013 Commercial Real Estate Loan Losses	Sep. 30, 2014 Commercial Real Estate Loan Losses	Sep. 30, 2013 Commercial Real Estate Loan Losses	Sep. 30, 2014 Commercial Real Estate Unfunded Lending Commitments	Sep. 30, 2013 Commercial Real Estate Unfunded Lending Commitments	Sep. 30, 2014 Commercial Real Estate Unfunded Lending Commitments	Sep. 30, 2013 Commercial Real Estate Unfunded Lending Commitments	Sep. 30, 2014 Construction	Dec. 31, 2013 Construction	Sep. 30, 2013 Construction	Sep. 30, 2014 Construction Loan Losses	Sep. 30, 2013 Construction Loan Losses	Sep. 30, 2014 Construction Loan Losses	Sep. 30, 2013 Construction Loan Losses	Sep. 30, 2014 Construction Unfunded Lending Commitments	Sep. 30, 2013 Construction Unfunded Lending Commitments	Sep. 30, 2014 Construction Unfunded Lending Commitments	Sep. 30, 2013 Construction Unfunded Lending Commitments	Sep. 30, 2014 Residential real estate	Dec. 31, 2013 Residential real estate	Sep. 30, 2013 Residential real estate	Sep. 30, 2014 Residential real estate Loan Losses	Sep. 30, 2013 Residential real estate Loan Losses	Sep. 30, 2014 Residential real estate Loan Losses	Sep. 30, 2013 Residential real estate Loan Losses	Sep. 30, 2014 Residential real estate Unfunded Lending Commitments	Sep. 30, 2013 Residential real estate Unfunded Lending Commitments	Sep. 30, 2014 Residential real estate Unfunded Lending Commitments	Sep. 30, 2013 Residential real estate Unfunded Lending Commitments	Sep. 30, 2014 Commercial and Industrial	Dec. 31, 2013 Commercial and Industrial	Sep. 30, 2013 Commercial and Industrial	Sep. 30, 2014 Commercial and Industrial Loan Losses	Sep. 30, 2013 Commercial and Industrial Loan Losses	Sep. 30, 2014 Commercial and Industrial Loan Losses	Sep. 30, 2013 Commercial and Industrial Loan Losses	Sep. 30, 2014 Commercial and Industrial Unfunded Lending Commitments	Sep. 30, 2013 Commercial and Industrial Unfunded Lending Commitments	Sep. 30, 2014 Commercial and Industrial Unfunded Lending Commitments	Sep. 30, 2013 Commercial and Industrial Unfunded Lending Commitments	Sep. 30, 2014 Consumer Loans	Dec. 31, 2013 Consumer Loans	Sep. 30, 2013 Consumer Loans	Sep. 30, 2014 Consumer Loans Loan Losses	Sep. 30, 2013 Consumer Loans Loan Losses	Sep. 30, 2014 Consumer Loans Loan Losses	Sep. 30, 2013 Consumer Loans Loan Losses	Sep. 30, 2014 Consumer Loans Unfunded Lending Commitments	Sep. 30, 2013 Consumer Loans Unfunded Lending Commitments	Sep. 30, 2014 Consumer Loans Unfunded Lending Commitments	Sep. 30, 2013 Consumer Loans Unfunded Lending Commitments	Sep. 30, 2014 Unallocated	Sep. 30, 2013 Unallocated	Sep. 30, 2014 Unallocated Loan Losses	Sep. 30, 2013 Unallocated Loan Losses	Sep. 30, 2014 Unallocated Loan Losses	Sep. 30, 2013 Unallocated Loan Losses	Sep. 30, 2014 Unallocated Unfunded Lending Commitments	Sep. 30, 2013 Unallocated Unfunded Lending Commitments	Sep. 30, 2014 Unallocated Unfunded Lending Commitments	Sep. 30, 2013 Unallocated Unfunded Lending Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Allowance at the beginning of period			$ 20,857		$ 20,471	$ 22,694	$ 20,857	$ 27,261	$ 440	$ 440	$ 440	$ 440	$ 6,983	$ 9,565		$ 7,960	$ 10,712	$ 9,565	$ 11,596	$ 48	$ 48	$ 48	$ 48	$ 1,000	$ 535		$ 728	$ 842	$ 535	$ 1,583	$ 268	$ 268	$ 268	$ 268	$ 1,884	$ 2,381		$ 2,068	$ 2,972	$ 2,381	$ 3,551	$ 25	$ 25	$ 25	$ 25	$ 7,352	$ 6,261		$ 6,615	$ 5,348	$ 6,261	$ 7,267	$ 75	$ 75	$ 75	$ 75	$ 1,099	$ 1,401		$ 1,181	$ 1,690	$ 1,401	$ 2,177	$ 24	$ 24	$ 24	$ 24	$ 714		$ 1,919	$ 1,130	$ 714	$ 1,087	$ 0	$ 0	$ 0	$ 0
Loan loss provision (credit)	0	0	0	1,000	0	0	0	1,000	0	0	0	0				(1,203)	1,049	(2,681)	1,030	0	0	0	0				(597)	(201)	(482)	341	0	0	0	0				6	(202)	(264)	(590)	0	0	0	0				469	(23)	706	989	0	0	0	0				211	185	402	(5)	0	0	0	0	2,300		1,114	(808)	2,319	(765)	0	0	0	0
Recoveries					2,123	982	5,390	3,012								317	79	1,318	294								869	249	1,243	412								349	28	630	216								512	554	1,969	1,900								76	72	230	190							0	0	0	0
Loans charged off					(1,243)	(2,023)	(4,896)	(9,620)								(91)	(656)	(1,219)	(1,736)								0	(292)	(296)	(1,738)								(539)	(129)	(863)	(508)								(244)	(534)	(1,584)	(4,811)								(369)	(412)	(934)	(827)							0	0	0	0
Allowance at the end of period	21,351		21,351		21,351	21,653	21,351	21,653	440	440	440	440	6,983	9,565		6,983	11,184	6,983	11,184	48	48	48	48	1,000	535		1,000	598	1,000	598	268	268	268	268	1,884	2,381		1,884	2,669	1,884	2,669	25	25	25	25	7,352	6,261		7,352	5,345	7,352	5,345	75	75	75	75	1,099	1,401		1,099	1,535	1,099	1,535	24	24	24	24	3,033		3,033	322	3,033	322	0	0	0	0
Total reserve for credit losses	$ 21,791	$ 22,093	$ 21,791	$ 22,093									$ 7,031		$ 11,232									$ 1,268		$ 866									$ 1,909		$ 2,694									$ 7,427		$ 5,420									$ 1,123		$ 1,559									$ 3,033	$ 322