Loans and reserve for credit losses (Schedule of Payment Defaults on Troubled Debt Restructurings on Financing Receivables) (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014 loan	Jun. 30, 2013 loan
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of loans	0	2
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 0	$ 3,500
Commercial Real Estate
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of loans	0	2
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	0	3,500
Construction
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of loans	0	0
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	0	0
Residential real estate
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of loans	0	0
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	0	0
Commercial and industrial loans
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of loans	0	0
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	0	0
Consumer Loans
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of loans	0	0
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 0	$ 0