Loans and Leases - Summary of Loans and Leases, Net of Unearned Income (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned income	$ 11,404,099	$ 11,247,038
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned income	3,817,189	3,815,708
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned income	2,397,731	2,318,015
Commercial Leases [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned income	180,207	177,824
Total Commercial Loans and Leases [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned income	6,395,127	6,311,547
Direct Installment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned income	1,653,621	1,644,621
Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned income	1,299,097	1,263,053
Indirect Installment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned income	905,204	875,551
Consumer Lines of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned income	1,108,418	1,110,976
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned income	42,632	41,290
Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned income	9,915,931	9,666,145
Originated Loans [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned income	3,082,385	3,031,810
Originated Loans [Member] | Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned income	2,281,075	2,197,793
Originated Loans [Member] | Commercial Leases [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned income	180,207	177,824
Originated Loans [Member] | Total Commercial Loans and Leases [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned income	5,543,667	5,407,427
Originated Loans [Member] | Direct Installment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned income	1,594,846	1,579,770
Originated Loans [Member] | Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned income	877,437	817,586
Originated Loans [Member] | Indirect Installment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned income	903,780	873,645
Originated Loans [Member] | Consumer Lines of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned income	953,569	946,427
Originated Loans [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned income	42,632	41,290
Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned income	1,488,168	1,580,893
Acquired Loans [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned income	734,804	783,898
Acquired Loans [Member] | Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned income	116,656	120,222
Acquired Loans [Member] | Total Commercial Loans and Leases [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned income	851,460	904,120
Acquired Loans [Member] | Direct Installment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned income	58,775	64,851
Acquired Loans [Member] | Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned income	421,660	445,467
Acquired Loans [Member] | Indirect Installment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned income	1,424	1,906
Acquired Loans [Member] | Consumer Lines of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned income	$ 154,849	$ 164,549