Loans and reserve for credit losses (Average Recorded Investiment in Impaired Financing Receivables) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	$ 49,980	$ 73,710	$ 112,363
Commercial Real Estate Owner Occupied
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	12,922	15,521	20,123
Commercial Real Estate Non Owner Occupied
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	25,655	33,267	32,555
Commercial Real Estate
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	38,577	48,788	52,678
Construction
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	2,283	7,272	35,997
Residential real estate
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	1,596	5,685	5,908
Commercial and Industrial
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	7,039	10,500	17,011
Consumer Loans
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	$ 485	$ 1,465	$ 769