Loans - Investment in Loans Related to Allowance for Loan Losses by Portfolio Segment Disaggregated Based on Impairment Methodology (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial:	$ 5,624,833	$ 4,907,076	$ 4,772,617
Commercial Real Estate	3,835,589	3,467,336	3,371,268
Consumer Real Estate	863,215	808,204	785,205
Consumer and Other	378,229	358,116	325,322
Unearned discounts	(22,489)	(25,032)	(21,869)
Total loans	10,679,377	9,515,700	9,232,543
Loans Individually Evaluated for Impairment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial:	205,485	210,273	126,402
Commercial Real Estate	101,566	136,601	147,196
Consumer Real Estate	689	745	802
Consumer and Other	252	278	365
Unearned discounts	0	0	0
Total loans	307,992	347,897	274,765
Loans Collectively Evaluated for Impairment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial:	5,419,348	4,696,803	4,646,215
Commercial Real Estate	3,734,023	3,330,735	3,224,072
Consumer Real Estate	862,526	807,459	784,403
Consumer and Other	377,977	357,838	324,957
Unearned discounts	(22,489)	(25,032)	(21,869)
Total loans	$ 10,371,385	$ 9,167,803	$ 8,957,778

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Amount before allowance of other consumer installment loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

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Amount before allowance of consumer real estate loans. Includes, but not limited to, construction financing, residential mortgage loans, and home equity lines of credit. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

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Amount of deferred interest and fee income, unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of acquired loans. Excludes amounts for loans and leases covered under loss sharing agreements.

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Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

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Amount before allowance of loans issued to commercial and industrial institutions. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes real estate loans and loans covered under loss sharing agreements.

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Amount before allowance of commercial loans issued to businesses to acquire, develop, construct, improve, or refinance land or building. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans covered under loss sharing agreements.

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