Loans and reserve for credit losses (Schedule of Payment Defaults on Troubled Debt Restructurings on Financing Receivables) (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013 loan
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of loans	2
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 3,500
Commercial Real Estate
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of loans	2
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	3,500
Construction
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of loans	0
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	0
Residential real estate
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of loans	0
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	0
Commercial and industrial loans
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of loans	0
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	0
Consumer Loans
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of loans	0
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 0