Loans and reserve for credit losses (Impaired Financing Receivables) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Impaired loans with specific valuation allowances	$ 8,887	$ 27,257
Impaired loans, Without a related allowance	31,580	41,414
Impaired loans,Total recorded balance	40,467	68,671
Impaired loans, Unpaid principal balance	44,856	81,745
Impaired loans, Related allowance	783	3,799
Commercial Real Estate Owner Occupied
Financing Receivable, Impaired [Line Items]
Impaired loans with specific valuation allowances	2,772	8,538
Impaired loans, Without a related allowance	6,582	7,443
Impaired loans,Total recorded balance	9,354	15,981
Impaired loans, Unpaid principal balance	12,707	21,610
Impaired loans, Related allowance	652	988
Commercial Real Estate Non Owner Occupied
Financing Receivable, Impaired [Line Items]
Impaired loans with specific valuation allowances	1,116	3,712
Impaired loans, Without a related allowance	21,757	23,166
Impaired loans,Total recorded balance	22,873	26,878
Impaired loans, Unpaid principal balance	22,904	32,630
Impaired loans, Related allowance	13	100
Commercial Real Estate
Financing Receivable, Impaired [Line Items]
Impaired loans with specific valuation allowances	3,888	12,250
Impaired loans, Without a related allowance	28,339	30,609
Impaired loans,Total recorded balance	32,227	42,859
Impaired loans, Unpaid principal balance	35,611	54,240
Impaired loans, Related allowance	665	1,088
Construction
Financing Receivable, Impaired [Line Items]
Impaired loans with specific valuation allowances	751	2,348
Impaired loans, Without a related allowance	1,236	7,386
Impaired loans,Total recorded balance	1,987	9,734
Impaired loans, Unpaid principal balance	2,029	9,867
Impaired loans, Related allowance	0	440
Residential real estate
Financing Receivable, Impaired [Line Items]
Impaired loans with specific valuation allowances	174	4,530
Impaired loans, Without a related allowance	256	310
Impaired loans,Total recorded balance	430	4,840
Impaired loans, Unpaid principal balance	515	5,018
Impaired loans, Related allowance	62	1,141
Commercial and industrial loans
Financing Receivable, Impaired [Line Items]
Impaired loans with specific valuation allowances	4,074	6,493
Impaired loans, Without a related allowance	1,749	3,109
Impaired loans,Total recorded balance	5,823	9,602
Impaired loans, Unpaid principal balance	6,701	10,982
Impaired loans, Related allowance	56	829
Consumer Loans
Financing Receivable, Impaired [Line Items]
Impaired loans with specific valuation allowances	0	1,636
Impaired loans, Without a related allowance	0	0
Impaired loans,Total recorded balance	0	1,636
Impaired loans, Unpaid principal balance	0	1,638
Impaired loans, Related allowance	$ 0	$ 301