Loans and leases and the allowance for credit losses (Details 7) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Dec. 31, 2009
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	$ 908,525	$ 902,941	$ 894,720	$ 894,667	$ 878,022
Commercial, financial, leasing, etc. [Member] | Individually evaluated for impairment [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	41,152	40,459
Commercial, financial, leasing, etc. [Member] | Collectively Evaluated For Impairment [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	182,090	171,670
Commercial, financial, leasing, etc. [Member] | Purchased Impaired [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	322	450
Commercial, financial, leasing, etc. [Member] | Allocated [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	223,564	212,579
Commercial real estate loans [Member] | Individually evaluated for impairment [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	113,009	114,082
Commercial real estate loans [Member] | Collectively Evaluated For Impairment [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	271,379	282,505
Commercial real estate loans [Member] | Purchased Impaired [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	3,305	3,975
Commercial real estate loans [Member] | Allocated [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	387,693	400,562
Residential real estate loans [Member] | Individually evaluated for impairment [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	28,000	39,000
Residential real estate loans [Member] | Collectively Evaluated For Impairment [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	56,973	46,976
Residential real estate loans [Member] | Purchased Impaired [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	247	375
Residential real estate loans [Member] | Allocated [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	85,220	86,351
Consumer loans [Member] | Individually evaluated for impairment [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	15,533	15,492
Consumer loans [Member] | Collectively Evaluated For Impairment [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	124,013	117,475
Consumer loans [Member] | Purchased Impaired [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	648	100
Consumer loans [Member] | Allocated [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	140,194	133,067
Individually evaluated for impairment [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	197,694	209,033
Collectively Evaluated For Impairment [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	634,455	618,626
Purchased Impaired [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	4,522	4,900
Allocated [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	836,671	832,559
Unallocated [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	$ 71,854	$ 70,382