Loans - Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial:	$ 5,876,899	$ 5,767,743	$ 5,510,887
Commercial mortgages	3,222,107	3,080,202
Construction	718,991	629,988
Land	280,749	291,907
Total commercial real estate	4,221,847	4,002,097	4,020,478
Home equity loans	339,336	342,725
Home equity lines of credit	226,874	220,128
Other	305,460	286,198
Total consumer real estate	871,670	849,051	847,068
Total real estate	5,093,517	4,851,148
Consumer installment	408,928	385,479
Other	4,044	8,122
Total consumer and other	412,972	393,601	391,480
Unearned discounts	(24,438)	(24,957)	(23,147)
Total loans	$ 11,358,950	$ 10,987,535	$ 10,746,766
Total commercial and industrial percentage of total loans	51.70%	52.50%
Commercial mortgages percentage of total loans	28.40%	28.00%
Construction percentage of total loans	6.30%	5.70%
Land percentage of total loans	2.50%	2.70%
Total commercial real estate percentage of total loans	37.20%	36.40%
Home equity loans percentage of total loans	3.00%	3.10%
Home equity lines of credit percentage of total loans	2.00%	2.00%
Other percentage of total loans	2.70%	2.60%
Total consumer real estate percentage of total loans	7.70%	7.70%
Total real estate percentage of total loans	44.90%	44.10%
Consumer installment percentage of total loans	3.60%	3.50%
Other percentage of total loans	0.00%	0.10%
Total consumer and other percentage of total loans	3.60%	3.60%
Unearned discounts percentage of total loans	(0.20%)	(0.20%)
Total loans percentage	100.00%	100.00%
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial:	$ 5,533,383	$ 5,429,206
Total commercial and industrial percentage of total loans	48.70%	49.40%
Leases [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial:	$ 343,516	$ 338,537
Total commercial and industrial percentage of total loans	3.00%	3.10%

Loans and Leases Receivable Consumer Home Equity Lines Of Credit

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Loans And Leases Receivable Real Estate

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Loans Receivable, Commercial Real Estate, Land

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Percentage Of Commercial And Industrial Loans To Loans

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Percentage Of Commercial Real Estate Construction Loans To Loans

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Percentage Of Loans And Leases Receivable Consumer Other To Loans

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Percentage Of Unearned Discounts To Loans

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount before allowance of revolving, open-end loan, extended under a line of credit and secured by the borrower's residential property. 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 installment and revolving loans issued to individuals, including, but not limited to credit card, automobile, boat, student, durable home appliance 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 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 other loans and leases not otherwise specified in the taxonomy. 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 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 construction loans. 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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Amount before allowance of mortgage loans on existing 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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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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