Loans - Activity in Allowance for Loan Losses by Portfolio Segment (Detail) - Financial Instruments [Domain] - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 105,708	$ 95,156	$ 99,542	$ 92,438
Provision for loan losses	2,873	4,924	11,035	11,524
Charge-offs	(5,087)	(6,337)	(10,582)	(13,003)
Recoveries	3,113	4,543	6,612	7,327
Net charge-offs	(1,974)	(1,794)	(3,970)	(5,676)
Ending balance	106,607	98,286	106,607	98,286
Commercial and Industrial [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	64,713	57,054	59,192	52,790
Provision for loan losses	5,694	(248)	12,065	5,712
Charge-offs	(2,374)	(3,028)	(4,506)	(5,395)
Recoveries	692	1,894	1,974	2,565
Net charge-offs	(1,682)	(1,134)	(2,532)	(2,830)
Ending balance	68,725	55,672	68,725	55,672
Commercial Real Estate Portfolio Segment [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	27,105	21,020	27,163	22,590
Provision for loan losses	(2,464)	1,151	(2,216)	1,159
Charge-offs	0	(935)	(478)	(2,726)
Recoveries	294	810	466	1,023
Net charge-offs	294	(125)	(12)	(1,703)
Ending balance	24,935	22,046	24,935	22,046
Consumer Real Estate [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	4,907	4,533	5,178	5,230
Provision for loan losses	(286)	153	(529)	(567)
Charge-offs	(21)	(105)	(101)	(126)
Recoveries	102	78	154	122
Net charge-offs	81	(27)	53	(4)
Ending balance	4,702	4,659	4,702	4,659
Consumer and Other [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	8,983	5,691	8,009	5,010
Provision for loan losses	(71)	1,244	1,715	2,556
Charge-offs	(2,692)	(2,269)	(5,497)	(4,756)
Recoveries	2,025	1,761	4,018	3,617
Net charge-offs	(667)	(508)	(1,479)	(1,139)
Ending balance	8,245	6,427	8,245	6,427
Unallocated [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance			0
Ending balance	$ 0	$ 9,482	$ 0	$ 9,482

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

-URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5212-111524

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-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-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

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

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

-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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-Name Accounting Standards Codification

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