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	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	$ 86,103	$ 92,231
Allowance for credit losses	744,753	742,951
Allowance for credit losses	916,768	916,676	927,117	925,860
Purchased Impaired [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	9,980	6,479
Allocated [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	840,836	841,661
Unallocated [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	75,932	75,015
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	21,578	24,614
Allowance for credit losses	249,499	246,096
Commercial, Financial, Leasing, etc. [Member] | Purchased Impaired [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	5,758	2,673
Commercial, Financial, Leasing, etc. [Member] | Allocated [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	276,835	273,383
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	26,157	27,563
Allowance for credit losses	298,048	296,781
Commercial Real Estate [Member] | Purchased Impaired [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	600	634
Commercial Real Estate [Member] | Allocated [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	324,805	324,978
Residential Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	18,243	21,127
Allowance for credit losses	56,797	55,864
Residential Real Estate [Member] | Purchased Impaired [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	2,022	1,665
Residential Real Estate [Member] | Allocated [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	77,062	78,656
Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	20,125	18,927
Allowance for credit losses	140,409	144,210
Consumer loans [Member] | Purchased Impaired [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	1,600	1,507
Consumer loans [Member] | Allocated [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	$ 162,134	$ 164,644