Loans and leases and the allowance for credit losses (Details 7) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	$ 917,028	$ 908,290
Unallocated [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	73,158	71,595
Allocated [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	843,870	836,695
Allocated [Member] | Commercial, financial, leasing [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	244,728	234,022
Allocated [Member] | Commercial real estate loans [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	341,521	367,637
Allocated [Member] | Residential real estate [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	93,269	91,915
Allocated [Member] | Consumer loans [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	164,352	143,121
Individually evaluated for impairment [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	153,075	165,579
Individually evaluated for impairment [Member] | Commercial, financial, leasing [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	38,961	48,517
Individually evaluated for impairment [Member] | Commercial real estate loans [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	64,143	71,784
Individually evaluated for impairment [Member] | Residential real estate [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	27,258	29,420
Individually evaluated for impairment [Member] | Consumer loans [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	22,713	15,858
Collectively Evaluated For Impairment [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	684,606	663,674
Collectively Evaluated For Impairment [Member] | Commercial, financial, leasing [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	205,594	185,048
Collectively Evaluated For Impairment [Member] | Commercial real estate loans [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	275,671	291,271
Collectively Evaluated For Impairment [Member] | Residential real estate [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	62,182	60,742
Collectively Evaluated For Impairment [Member] | Consumer loans [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	141,159	126,613
Purchased Impaired [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	6,189	7,442
Purchased Impaired [Member] | Commercial, financial, leasing [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	173	457
Purchased Impaired [Member] | Commercial real estate loans [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	1,707	4,582
Purchased Impaired [Member] | Residential real estate [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	3,829	1,753
Purchased Impaired [Member] | Consumer loans [Member]
Allocation of allowance for credit losses on the basis of the Company's impairment methodology
Allowance for credit losses	$ 480	$ 650