Loans and reserve for credit losses (Troubled Debt Restructurings on Financing Receivables) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013 loan	Dec. 31, 2012 loan	Dec. 31, 2011 loan
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of loans	10	110	358
TDR outstanding recorded investment	$ 30,157	$ 11,904	$ 75,394
Commercial Real Estate
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of loans	5	5	43
TDR outstanding recorded investment	27,677	1,761	45,921
Construction
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of loans	1	6	26
TDR outstanding recorded investment	1,243	4,832	7,334
Residential real estate
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of loans	0	12	36
TDR outstanding recorded investment	0	678	8,835
Commercial and industrial loans
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of loans	4	32	116
TDR outstanding recorded investment	1,237	3,980	11,724
Consumer Loans
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of loans	0	55	137
TDR outstanding recorded investment	$ 0	$ 653	$ 1,580