Loans - Restructured in Troubled Debt (Detail) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2018 USD ($) Loans	Dec. 31, 2017 USD ($) Loans
Financing Receivable, Modifications [Line Items]
Number of Loans \| Loans	19	19
Loan Balance	$ 17,360	$ 17,303
Specific Reserve	$ 6,446	$ 5,689
Commercial, Industrial, and Agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| Loans	10	10
Loan Balance	$ 5,150	$ 5,213
Specific Reserve	$ 278	$ 245
Commercial Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| Loans	9	9
Loan Balance	$ 12,210	$ 12,090
Specific Reserve	$ 6,168	$ 5,444
Residential Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| Loans	0	0
Loan Balance	$ 0	$ 0
Specific Reserve	$ 0	$ 0
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| Loans	0	0
Loan Balance	$ 0	$ 0
Specific Reserve	$ 0	$ 0
Credit Cards [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| Loans	0	0
Loan Balance	$ 0	$ 0
Specific Reserve	$ 0	$ 0

Financing receivable modifications specific reserve.

No definition available.

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Balance Type:	credit
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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
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- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953676-111524

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=82895541&loc=d3e18845-111554

+ Details

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