Loans - Activity in Allowance for Loan Losses by Portfolio Segment (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 106,607	$ 98,286	$ 99,542	$ 92,438
Provision for loan losses	6,810	390	17,845	11,914
Charge-offs	(7,604)	(7,261)	(18,186)	(20,264)
Recoveries	4,560	6,897	11,172	14,224
Net charge-offs	(3,044)	(364)	(7,014)	(6,040)
Ending balance	110,373	98,312	110,373	98,312
Commercial and Industrial [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	68,725	55,672	59,192	52,790
Provision for loan losses	4,193	2,224	16,258	7,936
Charge-offs	(4,074)	(3,631)	(8,580)	(9,026)
Recoveries	1,959	4,371	3,933	6,936
Net charge-offs	(2,115)	740	(4,647)	(2,090)
Ending balance	70,803	58,636	70,803	58,636
Commercial Real Estate Portfolio Segment [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	24,935	22,046	27,163	22,590
Provision for loan losses	746	4,650	(1,470)	5,809
Charge-offs	(107)	(393)	(585)	(3,119)
Recoveries	309	477	775	1,500
Net charge-offs	202	84	190	(1,619)
Ending balance	25,883	26,780	25,883	26,780
Consumer Real Estate [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	4,702	4,659	5,178	5,230
Provision for loan losses	324	1,057	(205)	490
Charge-offs	(423)	(714)	(524)	(840)
Recoveries	201	105	355	227
Net charge-offs	(222)	(609)	(169)	(613)
Ending balance	4,804	5,107	4,804	5,107
Consumer and Other [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	8,245	6,427	8,009	5,010
Provision for loan losses	1,547	1,941	3,262	4,497
Charge-offs	(3,000)	(2,523)	(8,497)	(7,279)
Recoveries	2,091	1,944	6,109	5,561
Net charge-offs	(909)	(579)	(2,388)	(1,718)
Ending balance	8,883	7,789	8,883	7,789
Unallocated [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	0	9,482	0	6,818
Provision for loan losses	0	(9,482)	0	(6,818)
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Net charge-offs	0	0	0	0
Ending balance	$ 0	$ 0	$ 0	$ 0

Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

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- Definition

Amount of other addition (reduction) in allowance reserve for credit loss.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 15

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-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

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-Subparagraph (SX 210.9-03.7(d))

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

+ References

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- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

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-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 6

-Section L

-Subsection 1

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Amount of expense related to estimated loss from loan and lease transactions.

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