Loans and reserve for credit losses (Allowance for Credit Losses on Financing Receivables) (Details) (USD $) In Thousands, unless otherwise specified				3 Months Ended							3 Months Ended							3 Months Ended							3 Months Ended							3 Months Ended							3 Months Ended						3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Mar. 31, 2014 Loan Losses	Mar. 31, 2013 Loan Losses	Mar. 31, 2014 Unfunded Lending Commitments	Mar. 31, 2013 Unfunded Lending Commitments	Mar. 31, 2014 Commercial Real Estate	Dec. 31, 2013 Commercial Real Estate	Mar. 31, 2013 Commercial Real Estate	Mar. 31, 2014 Commercial Real Estate Loan Losses	Mar. 31, 2013 Commercial Real Estate Loan Losses	Mar. 31, 2014 Commercial Real Estate Unfunded Lending Commitments	Mar. 31, 2013 Commercial Real Estate Unfunded Lending Commitments	Mar. 31, 2014 Construction	Dec. 31, 2013 Construction	Mar. 31, 2013 Construction	Mar. 31, 2014 Construction Loan Losses	Mar. 31, 2013 Construction Loan Losses	Mar. 31, 2014 Construction Unfunded Lending Commitments	Mar. 31, 2013 Construction Unfunded Lending Commitments	Mar. 31, 2014 Residential real estate	Dec. 31, 2013 Residential real estate	Mar. 31, 2013 Residential real estate	Mar. 31, 2014 Residential real estate Loan Losses	Mar. 31, 2013 Residential real estate Loan Losses	Mar. 31, 2014 Residential real estate Unfunded Lending Commitments	Mar. 31, 2013 Residential real estate Unfunded Lending Commitments	Mar. 31, 2014 Commercial and Industrial	Dec. 31, 2013 Commercial and Industrial	Mar. 31, 2013 Commercial and Industrial	Mar. 31, 2014 Commercial and Industrial Loan Losses	Mar. 31, 2013 Commercial and Industrial Loan Losses	Mar. 31, 2014 Commercial and Industrial Unfunded Lending Commitments	Mar. 31, 2013 Commercial and Industrial Unfunded Lending Commitments	Mar. 31, 2014 Consumer Loans	Dec. 31, 2013 Consumer Loans	Mar. 31, 2013 Consumer Loans	Mar. 31, 2014 Consumer Loans Loan Losses	Mar. 31, 2013 Consumer Loans Loan Losses	Mar. 31, 2014 Consumer Loans Unfunded Lending Commitments	Mar. 31, 2013 Consumer Loans Unfunded Lending Commitments	Mar. 31, 2014 Unallocated	Mar. 31, 2013 Unallocated	Mar. 31, 2014 Unallocated Loan Losses	Mar. 31, 2013 Unallocated Loan Losses	Mar. 31, 2014 Unallocated Unfunded Lending Commitments	Mar. 31, 2013 Unallocated Unfunded Lending Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Allowance at the beginning of period	$ 21,722	$ 20,857		$ 20,857	$ 27,261	$ 440	$ 440	$ 8,803	$ 9,565		$ 9,565	$ 11,596	$ 48	$ 48	$ 602	$ 535		$ 535	$ 1,583	$ 268	$ 268	$ 2,227	$ 2,381		$ 2,381	$ 3,551	$ 25	$ 25	$ 6,840	$ 6,261		$ 6,261	$ 7,267	$ 75	$ 75	$ 1,243	$ 1,401		$ 1,401	$ 2,177	$ 24	$ 24	$ 714		$ 714	$ 1,087	$ 0	$ 0
Loan loss provision (credit)				0	0	0	0				(1,560)	(280)	0	0				278	316	0	0				(55)	182	0	0				(18)	125	0	0				62	86	0	0	1,300		1,293	(429)	0	0
Recoveries				2,148	990						941	178						85	124						124	117						911	512						87	59					0	0
Loans charged off				(1,283)	(3,703)						(143)	(269)						(296)	(787)						(223)	(136)						(314)	(2,228)						(307)	(283)					0	0
Allowance at the end of period	21,722	20,857		21,722	24,548	440	440	8,803	9,565		8,803	11,225	48	48	602	535		602	1,236	268	268	2,227	2,381		2,227	3,714	25	25	6,840	6,261		6,840	5,676	75	75	1,243	1,401		1,243	2,039	24	24	2,007		2,007	658	0	0
Total reserve for credit losses	$ 22,162		$ 24,988					$ 8,851		$ 11,273					$ 870		$ 1,504					$ 2,252		$ 3,739					$ 6,915		$ 5,751					$ 1,267		$ 2,063					$ 2,007	$ 658