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, 2013	Dec. 31, 2012	Jun. 30, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	$ 4,772,617	$ 4,828,612	$ 4,309,889
Commercial Real Estate	3,371,268	3,319,795	3,119,902
Consumer Real Estate	785,205	777,347	762,060
Consumer and Other	325,322	319,745	317,003
Unearned Discounts	(21,869)	(21,651)	(19,091)
Total loans	9,232,543	9,223,848	8,489,763
Loans Individually Evaluated for Impairment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	126,402	128,544	183,964
Commercial Real Estate	147,196	165,152	198,000
Consumer Real Estate	802	864	1,279
Consumer and Other	365	400	439
Unearned Discounts
Total loans	274,765	294,960	383,682
Loans Collectively Evaluated for Impairment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	4,646,215	4,700,068	4,125,925
Commercial Real Estate	3,224,072	3,154,643	2,921,902
Consumer Real Estate	784,403	776,483	760,781
Consumer and Other	324,957	319,345	316,564
Unearned Discounts	(21,869)	(21,651)	(19,091)
Total loans	$ 8,957,778	$ 8,928,888	$ 8,106,081

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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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