Loans and reserve for credit losses (Post Modification Recorded in Investment for Troubled Debt Restructurings on Financing Receivables) (Details1) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2013
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Rate reduction	$ 0	$ 3,983
Term extension	3	2,471
Rate reduction and term extension	0	21,500
Total	3	27,954
Commercial Real Estate
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Rate reduction	0	3,809
Term extension	0	2,368
Rate reduction and term extension	0	21,500
Total	0	27,677
Construction
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Rate reduction	0	0
Term extension	0	0
Rate reduction and term extension	0	0
Total	0	0
Residential real estate
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Rate reduction	0	0
Term extension	0	0
Rate reduction and term extension	0	0
Total	0	0
Commercial and industrial loans
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Rate reduction	0	174
Term extension	3	103
Rate reduction and term extension	0	0
Total	3	277
Consumer Loans
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Rate reduction	0	0
Term extension	0	0
Rate reduction and term extension	0	0
Total	$ 0	$ 0