Allowance for Credit Losses - Summary of Individual and Collective Allowance for Credit Losses and Loan and Lease Balances by Class (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Valuation Allowance [Line Items]
Allowance, Individually Evaluated for Impairment	$ 2,181	$ 1,179
Allowance, Collectively Evaluated for Impairment	119,066	116,773
Loans and Leases	11,404,099	11,247,038
Loans Outstanding, Individually Evaluated for Impairment	18,576	19,789
Loans Outstanding, Collectively Evaluated for Impairment	9,897,355	9,646,356
Commercial Real Estate [Member]
Valuation Allowance [Line Items]
Allowance, Individually Evaluated for Impairment	735	399
Allowance, Collectively Evaluated for Impairment	38,057	37,189
Loans and Leases	3,817,189	3,815,708
Loans Outstanding, Individually Evaluated for Impairment	12,865	13,952
Loans Outstanding, Collectively Evaluated for Impairment	3,069,520	3,017,858
Commercial and Industrial [Member]
Valuation Allowance [Line Items]
Allowance, Individually Evaluated for Impairment	1,446	780
Allowance, Collectively Evaluated for Impairment	31,357	31,865
Loans and Leases	2,397,731	2,318,015
Loans Outstanding, Individually Evaluated for Impairment	5,711	5,837
Loans Outstanding, Collectively Evaluated for Impairment	2,275,364	2,191,956
Commercial Leases [Member]
Valuation Allowance [Line Items]
Allowance, Collectively Evaluated for Impairment	2,576	2,398
Loans and Leases	180,207	177,824
Loans Outstanding, Collectively Evaluated for Impairment	180,207	177,824
Total Commercial Loans and Leases [Member]
Valuation Allowance [Line Items]
Allowance, Individually Evaluated for Impairment	2,181	1,179
Allowance, Collectively Evaluated for Impairment	71,990	71,452
Loans and Leases	6,395,127	6,311,547
Loans Outstanding, Individually Evaluated for Impairment	18,576	19,789
Loans Outstanding, Collectively Evaluated for Impairment	5,525,091	5,387,638
Direct Installment [Member]
Valuation Allowance [Line Items]
Allowance, Collectively Evaluated for Impairment	21,204	20,538
Loans and Leases	1,653,621	1,644,621
Loans Outstanding, Collectively Evaluated for Impairment	1,594,846	1,579,770
Residential Mortgages [Member]
Valuation Allowance [Line Items]
Allowance, Collectively Evaluated for Impairment	8,471	8,024
Loans and Leases	1,299,097	1,263,053
Loans Outstanding, Collectively Evaluated for Impairment	877,437	817,586
Indirect Installment [Member]
Valuation Allowance [Line Items]
Allowance, Collectively Evaluated for Impairment	7,657	7,504
Loans and Leases	905,204	875,551
Loans Outstanding, Collectively Evaluated for Impairment	903,780	873,645
Consumer Lines of Credit [Member]
Valuation Allowance [Line Items]
Allowance, Collectively Evaluated for Impairment	8,890	8,496
Loans and Leases	1,108,418	1,110,976
Loans Outstanding, Collectively Evaluated for Impairment	953,569	946,427
Other [Member]
Valuation Allowance [Line Items]
Allowance, Collectively Evaluated for Impairment	854	759
Loans and Leases	42,632	41,290
Loans Outstanding, Collectively Evaluated for Impairment	42,632	41,290
Originated Loans [Member]
Valuation Allowance [Line Items]
Loans and Leases	9,915,931	9,666,145
Originated Loans [Member] \| Commercial Real Estate [Member]
Valuation Allowance [Line Items]
Loans and Leases	3,082,385	3,031,810
Originated Loans [Member] \| Commercial and Industrial [Member]
Valuation Allowance [Line Items]
Loans and Leases	2,281,075	2,197,793
Originated Loans [Member] \| Commercial Leases [Member]
Valuation Allowance [Line Items]
Loans and Leases	180,207	177,824
Originated Loans [Member] \| Total Commercial Loans and Leases [Member]
Valuation Allowance [Line Items]
Loans and Leases	5,543,667	5,407,427
Originated Loans [Member] \| Direct Installment [Member]
Valuation Allowance [Line Items]
Loans and Leases	1,594,846	1,579,770
Originated Loans [Member] \| Residential Mortgages [Member]
Valuation Allowance [Line Items]
Loans and Leases	877,437	817,586
Originated Loans [Member] \| Indirect Installment [Member]
Valuation Allowance [Line Items]
Loans and Leases	903,780	873,645
Originated Loans [Member] \| Consumer Lines of Credit [Member]
Valuation Allowance [Line Items]
Loans and Leases	953,569	946,427
Originated Loans [Member] \| Other [Member]
Valuation Allowance [Line Items]
Loans and Leases	$ 42,632	$ 41,290

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (g)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524

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Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

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- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

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The balance of financing receivables that were individually evaluated for impairment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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-Topic 310

-SubTopic 10

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5074-111524

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