Allowance for Credit Losses - Summary of Individual and Collective Allowance for Credit Losses and Loan and Lease Balances by Class (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Valuation Allowance [Line Items]
Allowance, Individually Evaluated for Impairment	$ 2,225	$ 1,179
Allowance, Collectively Evaluated for Impairment	121,971	116,773
Loans and Leases	11,626,787	11,247,038
Loans Outstanding, Individually Evaluated for Impairment	19,298	19,789
Loans Outstanding, Collectively Evaluated for Impairment	10,225,279	9,646,356
Commercial Real Estate [Member]
Valuation Allowance [Line Items]
Allowance, Individually Evaluated for Impairment	655	399
Allowance, Collectively Evaluated for Impairment	39,217	37,189
Loans and Leases	3,852,607	3,815,708
Loans Outstanding, Individually Evaluated for Impairment	13,713	13,952
Loans Outstanding, Collectively Evaluated for Impairment	3,164,506	3,017,858
Commercial and Industrial [Member]
Valuation Allowance [Line Items]
Allowance, Individually Evaluated for Impairment	1,570	780
Allowance, Collectively Evaluated for Impairment	30,735	31,865
Loans and Leases	2,453,868	2,318,015
Loans Outstanding, Individually Evaluated for Impairment	5,585	5,837
Loans Outstanding, Collectively Evaluated for Impairment	2,337,628	2,191,956
Commercial Leases [Member]
Valuation Allowance [Line Items]
Allowance, Collectively Evaluated for Impairment	2,223	2,398
Loans and Leases	190,881	177,824
Loans Outstanding, Collectively Evaluated for Impairment	190,881	177,824
Total Commercial Loans and Leases [Member]
Valuation Allowance [Line Items]
Allowance, Individually Evaluated for Impairment	2,225	1,179
Allowance, Collectively Evaluated for Impairment	72,175	71,452
Loans and Leases	6,497,356	6,311,547
Loans Outstanding, Individually Evaluated for Impairment	19,298	19,789
Loans Outstanding, Collectively Evaluated for Impairment	5,693,015	5,387,638
Direct Installment [Member]
Valuation Allowance [Line Items]
Allowance, Collectively Evaluated for Impairment	22,279	20,538
Loans and Leases	1,676,349	1,644,621
Loans Outstanding, Collectively Evaluated for Impairment	1,623,290	1,579,770
Residential Mortgages [Member]
Valuation Allowance [Line Items]
Allowance, Collectively Evaluated for Impairment	8,579	8,024
Loans and Leases	1,350,502	1,263,053
Loans Outstanding, Collectively Evaluated for Impairment	953,840	817,586
Indirect Installment [Member]
Valuation Allowance [Line Items]
Allowance, Collectively Evaluated for Impairment	8,909	7,504
Loans and Leases	942,801	875,551
Loans Outstanding, Collectively Evaluated for Impairment	941,851	873,645
Consumer Lines of Credit [Member]
Valuation Allowance [Line Items]
Allowance, Collectively Evaluated for Impairment	9,118	8,496
Loans and Leases	1,118,970	1,110,976
Loans Outstanding, Collectively Evaluated for Impairment	972,474	946,427
Other [Member]
Valuation Allowance [Line Items]
Allowance, Collectively Evaluated for Impairment	911	759
Loans and Leases	40,809	41,290
Loans Outstanding, Collectively Evaluated for Impairment	40,809	41,290
Originated Loans [Member]
Valuation Allowance [Line Items]
Loans and Leases	10,244,577	9,666,145
Originated Loans [Member] \| Commercial Real Estate [Member]
Valuation Allowance [Line Items]
Loans and Leases	3,178,219	3,031,810
Originated Loans [Member] \| Commercial and Industrial [Member]
Valuation Allowance [Line Items]
Loans and Leases	2,343,213	2,197,793
Originated Loans [Member] \| Commercial Leases [Member]
Valuation Allowance [Line Items]
Loans and Leases	190,881	177,824
Originated Loans [Member] \| Total Commercial Loans and Leases [Member]
Valuation Allowance [Line Items]
Loans and Leases	5,712,313	5,407,427
Originated Loans [Member] \| Direct Installment [Member]
Valuation Allowance [Line Items]
Loans and Leases	1,623,290	1,579,770
Originated Loans [Member] \| Residential Mortgages [Member]
Valuation Allowance [Line Items]
Loans and Leases	953,840	817,586
Originated Loans [Member] \| Indirect Installment [Member]
Valuation Allowance [Line Items]
Loans and Leases	941,851	873,645
Originated Loans [Member] \| Consumer Lines of Credit [Member]
Valuation Allowance [Line Items]
Loans and Leases	972,474	946,427
Originated Loans [Member] \| Other [Member]
Valuation Allowance [Line Items]
Loans and Leases	$ 40,809	$ 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=49124121&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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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

-Paragraph 11B

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+ 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 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4428-111522

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