Loans and reserve for credit losses (Schedule of Payment Defaults on Troubled Debt Restructurings on Financing Receivables) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013 loan	Dec. 31, 2012 loan	Dec. 31, 2011 loan
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Number of loans	2	3	24
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 3,500	$ 205	$ 10,009
Commercial Real Estate
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Number of loans	2	0	1
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	3,500	0	573
Residential real estate
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Number of loans	0	0	3
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	0	0	636
Commercial and industrial loans
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Number of loans	0	1	13
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	0	193	8,729
Consumer Loans
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Number of loans	0	2	7
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 0	$ 12	$ 71