Loans and leases and the allowance for credit losses (Details 6) (USD $) In Thousands	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2009
Allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	$ 907,589	$ 903,703	$ 902,941	$ 894,667	$ 891,265	$ 878,022
Individually evaluated for impairment [Member]
Allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	200,674		209,033
Individually evaluated for impairment [Member] | Commercial, financial, leasing [Member]
Allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	32,656		40,459
Individually evaluated for impairment [Member] | Commercial real estate loans [Member]
Allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	118,545		114,082
Individually evaluated for impairment [Member] | Residential real estate loans [Member]
Allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	34,000		39,000
Individually evaluated for impairment [Member] | Consumer loans [Member]
Allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	15,473		15,492
Collectively evaluated for impairment [Member]
Allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	629,624		618,626
Collectively evaluated for impairment [Member] | Commercial, financial, leasing [Member]
Allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	177,052		171,670
Collectively evaluated for impairment [Member] | Commercial real estate loans [Member]
Allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	278,862		282,505
Collectively evaluated for impairment [Member] | Residential real estate loans [Member]
Allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	52,297		46,976
Collectively evaluated for impairment [Member] | Consumer loans [Member]
Allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	121,413		117,475
Purchased Impaired [Member]
Allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	5,342		4,900
Purchased Impaired [Member] | Commercial, financial, leasing [Member]
Allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	171		450
Purchased Impaired [Member] | Commercial real estate loans [Member]
Allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	3,704		3,975
Purchased Impaired [Member] | Residential real estate loans [Member]
Allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	1,044		375
Purchased Impaired [Member] | Consumer loans [Member]
Allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	423		100
Allocated [Member]
Allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	835,640		832,559
Commercial, financial, leasing [Member]
Allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	209,879	215,659	212,579
Commercial real estate loans [Member]
Allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	401,111	391,107	400,562
Residential real estate loans [Member]
Allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	87,341	87,526	86,351
Consumer loans [Member]
Allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	137,309	137,351	133,067
Unallocated [Member]
Allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	$ 71,949	$ 72,060	$ 70,382