Loans and Leases and the Allowance for Credit Losses - Allocation of Allowance for Credit Losses on Basis of Company's Impairment Methodology (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Loans And Leases Receivable [Line Items]
Allowance for credit losses	$ 927,065	$ 925,860
Allocated [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	852,733	852,085
Unallocated [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	74,332	73,775
Individually Evaluated for Impairment [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	111,343	131,656
Collectively Evaluated for Impairment [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	735,265	717,064
Purchased Impaired [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	6,125	3,365
Commercial, Financial, Leasing, etc. [Member] | Allocated [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	268,867	246,759
Commercial, Financial, Leasing, etc. [Member] | Individually Evaluated for Impairment [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	36,451	33,669
Commercial, Financial, Leasing, etc. [Member] | Collectively Evaluated for Impairment [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	230,309	212,930
Commercial, Financial, Leasing, etc. [Member] | Purchased Impaired [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	2,107	160
Commercial Real Estate [Member] | Allocated [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	324,264	337,101
Commercial Real Estate [Member] | Individually Evaluated for Impairment [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	31,798	55,291
Commercial Real Estate [Member] | Collectively Evaluated for Impairment [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	291,365	280,789
Commercial Real Estate [Member] | Purchased Impaired [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	1,101	1,021
Residential Real Estate [Member] | Allocated [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	85,311	88,807
Residential Real Estate [Member] | Individually Evaluated for Impairment [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	22,628	20,502
Residential Real Estate [Member] | Collectively Evaluated for Impairment [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	60,989	66,684
Residential Real Estate [Member] | Purchased Impaired [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	1,694	1,621
Consumer loans [Member] | Allocated [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	174,291	179,418
Consumer loans [Member] | Individually Evaluated for Impairment [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	20,466	22,194
Consumer loans [Member] | Collectively Evaluated for Impairment [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	152,602	156,661
Consumer loans [Member] | Purchased Impaired [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	$ 1,223	$ 563