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
	Mar. 31, 2013
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Rate reduction	$ 3,983
Term extension	3,166
Rate reduction and term extension	21,552
Total	28,701
Commercial Real Estate
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Rate reduction	3,809
Term extension	2,368
Rate reduction and term extension	21,500
Total	27,677
Construction
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Rate reduction	0
Term extension	115
Rate reduction and term extension	0
Total	115
Residential real estate
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Rate reduction	0
Term extension	152
Rate reduction and term extension	0
Total	152
Commercial and industrial loans
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Rate reduction	174
Term extension	173
Rate reduction and term extension	52
Total	399
Consumer Loans
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Rate reduction	0
Term extension	358
Rate reduction and term extension	0
Total	$ 358