Loans and reserve for credit losses (Average Recorded Investment in Impaired Financing Receivables) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Financing Receivable, Recorded Investment [Line Items]
Impaired Financing Receivable, Average Recorded Investment	$ 38,495	$ 65,981
Commercial Real Estate Owner Occupied
Financing Receivable, Recorded Investment [Line Items]
Impaired Financing Receivable, Average Recorded Investment	7,868	15,209
Commercial Real Estate Non Owner Occupied
Financing Receivable, Recorded Investment [Line Items]
Impaired Financing Receivable, Average Recorded Investment	22,806	28,250
Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Impaired Financing Receivable, Average Recorded Investment	30,674	43,459
Construction
Financing Receivable, Recorded Investment [Line Items]
Impaired Financing Receivable, Average Recorded Investment	1,863	6,514
Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Impaired Financing Receivable, Average Recorded Investment	428	4,836
Commercial and Industrial
Financing Receivable, Recorded Investment [Line Items]
Impaired Financing Receivable, Average Recorded Investment	5,530	9,384
Consumer Loans
Financing Receivable, Recorded Investment [Line Items]
Impaired Financing Receivable, Average Recorded Investment	$ 0	$ 1,788