Loans and reserve for credit losses (Troubled Debt Restructurings on Financing Receivables) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014 loan	Mar. 31, 2013 loan
Financing Receivable, Modifications [Line Items]
Number of loans	0	30
TDR outstanding recorded investment	$ 0	$ 28,701
Commercial Real Estate
Financing Receivable, Modifications [Line Items]
Number of loans	0	5
TDR outstanding recorded investment	0	27,677
Construction
Financing Receivable, Modifications [Line Items]
Number of loans	0	2
TDR outstanding recorded investment	0	115
Residential real estate
Financing Receivable, Modifications [Line Items]
Number of loans	0	3
TDR outstanding recorded investment	0	152
Commercial and industrial loans
Financing Receivable, Modifications [Line Items]
Number of loans	0	8
TDR outstanding recorded investment	0	399
Consumer Loans
Financing Receivable, Modifications [Line Items]
Number of loans	0	12
TDR outstanding recorded investment	$ 0	$ 358