Loans and reserve for credit losses (Details 6) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Impaired Financing Receivable, Average Recorded Investment	$ 57,510	$ 77,075	$ 61,231	$ 77,010
Commercial Real Estate Owner Occupied [Member]
Impaired Financing Receivable, Average Recorded Investment	15,179	15,768	15,447	15,583
Commercial Real Estate Non Owner Occupied [Member]
Impaired Financing Receivable, Average Recorded Investment	28,089	37,917	27,685	37,920
Commerical real estate [Member]
Impaired Financing Receivable, Average Recorded Investment	43,268	53,685	43,132	53,503
Construction [Member]
Impaired Financing Receivable, Average Recorded Investment	2,479	5,142	4,897	5,142
Residential real estate [Member]
Impaired Financing Receivable, Average Recorded Investment	2,751	6,173	3,447	6,160
Commercial and Industrial [Member]
Impaired Financing Receivable, Average Recorded Investment	8,043	10,801	8,563	10,933
Consumer Loans [Member]
Impaired Financing Receivable, Average Recorded Investment	$ 969	$ 1,274	$ 1,192	$ 1,272