Allowance for Credit Losses - Activity in Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	$ 114,419	$ 106,178
Loans charged-off	(3,379)	(2,511)
Charged-off loans recovered	2,001	1,019
Net (charge-offs) recoveries	(1,378)	(1,492)
Provision for loan losses	2,402	729
Ending balance	115,443	105,415
Commercial and industrial
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	50,820	48,767
Loans charged-off	(1,714)	(1,251)
Charged-off loans recovered	848	526
Net (charge-offs) recoveries	(866)	(725)
Provision for loan losses	1,334	375
Ending balance	51,288	48,417
Commercial real estate loans
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	55,851	48,006
Loans charged-off	(414)	(105)
Charged-off loans recovered	142	89
Net (charge-offs) recoveries	(272)	(16)
Provision for loan losses	723	464
Ending balance	56,302	48,454
Residential mortgage
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	3,702	4,625
Loans charged-off	(130)	(81)
Charged-off loans recovered	448	15
Net (charge-offs) recoveries	318	(66)
Provision for loan losses	(428)	(350)
Ending balance	3,592	4,209
Consumer
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	4,046	4,780
Loans charged-off	(1,121)	(1,074)
Charged-off loans recovered	563	389
Net (charge-offs) recoveries	(558)	(685)
Provision for loan losses	773	240
Ending balance	4,261	4,335
Unallocated
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	0	0
Loans charged-off	0	0
Charged-off loans recovered	0	0
Net (charge-offs) recoveries	0	0
Provision for loan losses		0
Ending balance	$ 0	$ 0

Amount, after recoveries, of loans and leases that have been written-off.

No definition available.

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- Definition

A valuation allowance for financing receivables that are expected to be uncollectible.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953423-111524

+ Details

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- Definition

Amount of recovery of financing receivables doubtful of collection that were previously charged off.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(4)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953423-111524

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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 direct write-downs of financing receivables charged against the allowance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953423-111524

+ Details

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.11)
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953423-111524

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