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	Sep. 30, 2013	Dec. 31, 2012
Loans And Leases Receivable [Line Items]
Allowance for credit losses	$ 916,370	$ 925,860
Allocated [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	841,636	852,085
Unallocated [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	74,734	73,775
Individually Evaluated for Impairment [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	100,823	131,656
Collectively Evaluated for Impairment [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	734,338	717,064
Purchased Impaired [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	6,475	3,365
Commercial, Financial, Leasing, etc. [Member] | Allocated [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	263,295	246,759
Commercial, Financial, Leasing, etc. [Member] | Individually Evaluated for Impairment [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	25,530	33,669
Commercial, Financial, Leasing, etc. [Member] | Collectively Evaluated for Impairment [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	234,912	212,930
Commercial, Financial, Leasing, etc. [Member] | Purchased Impaired [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	2,853	160
Commercial Real Estate [Member] | Allocated [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	333,453	337,101
Commercial Real Estate [Member] | Individually Evaluated for Impairment [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	34,139	55,291
Commercial Real Estate [Member] | Collectively Evaluated for Impairment [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	298,579	280,789
Commercial Real Estate [Member] | Purchased Impaired [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	735	1,021
Residential Real Estate [Member] | Allocated [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	82,705	88,807
Residential Real Estate [Member] | Individually Evaluated for Impairment [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	21,517	20,502
Residential Real Estate [Member] | Collectively Evaluated for Impairment [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	59,645	66,684
Residential Real Estate [Member] | Purchased Impaired [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	1,543	1,621
Consumer loans [Member] | Allocated [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	162,183	179,418
Consumer loans [Member] | Individually Evaluated for Impairment [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	19,637	22,194
Consumer loans [Member] | Collectively Evaluated for Impairment [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	141,202	156,661
Consumer loans [Member] | Purchased Impaired [Member]
Loans And Leases Receivable [Line Items]
Allowance for credit losses	$ 1,344	$ 563