Loans and reserve for credit losses (Average Recorded Investment in Impaired Financing Receivables) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Financing Receivable, Recorded Investment [Line Items]
Impaired Financing Receivable, Average Recorded Investment	$ 35,191	$ 57,510	$ 36,950	$ 61,231
Commercial Real Estate Owner Occupied
Financing Receivable, Recorded Investment [Line Items]
Impaired Financing Receivable, Average Recorded Investment	6,120	15,179	7,198	15,447
Commercial Real Estate Non Owner Occupied
Financing Receivable, Recorded Investment [Line Items]
Impaired Financing Receivable, Average Recorded Investment	22,762	28,089	22,799	27,685
Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Impaired Financing Receivable, Average Recorded Investment	28,882	43,268	29,997	43,132
Construction
Financing Receivable, Recorded Investment [Line Items]
Impaired Financing Receivable, Average Recorded Investment	1,351	2,479	1,563	4,897
Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Impaired Financing Receivable, Average Recorded Investment	443	2,751	439	3,447
Commercial and Industrial
Financing Receivable, Recorded Investment [Line Items]
Impaired Financing Receivable, Average Recorded Investment	4,515	8,043	4,951	8,563
Consumer Loans
Financing Receivable, Recorded Investment [Line Items]
Impaired Financing Receivable, Average Recorded Investment	$ 0	$ 969	$ 0	$ 1,192