Loans and reserve for credit losses (Average Recorded Investment in Impaired Financing Receivables) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Financing Receivable, Recorded Investment [Line Items]
Impaired Financing Receivable, Average Recorded Investment	$ 33,613	$ 48,082	$ 34,583	$ 57,031
Commercial Real Estate Owner Occupied
Financing Receivable, Recorded Investment [Line Items]
Impaired Financing Receivable, Average Recorded Investment	6,010	13,948	6,134	14,579
Commercial Real Estate Non Owner Occupied
Financing Receivable, Recorded Investment [Line Items]
Impaired Financing Receivable, Average Recorded Investment	22,586	25,062	22,637	26,656
Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Impaired Financing Receivable, Average Recorded Investment	28,596	39,010	28,771	41,235
Construction
Financing Receivable, Recorded Investment [Line Items]
Impaired Financing Receivable, Average Recorded Investment	963	1,927	1,221	4,220
Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Impaired Financing Receivable, Average Recorded Investment	391	560	403	2,698
Commercial and Industrial
Financing Receivable, Recorded Investment [Line Items]
Impaired Financing Receivable, Average Recorded Investment	3,663	6,585	4,188	7,984
Consumer Loans
Financing Receivable, Recorded Investment [Line Items]
Impaired Financing Receivable, Average Recorded Investment	$ 0	$ 0	$ 0	$ 894