Allowance for Loan Losses - Impaired Loans Excluding PCI Loans - Recorded Investment and Unpaid Principal Balances (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	$ 1,831	$ 3,146
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	1,855	3,218
Impaired financing receivables, with an allowance recorded, Recorded Investment	405	451
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance	409	455
Impaired financing receivables, with an allowance recorded, Related Allowance	93	91
Impaired financing receivables, Recorded Investment, Total	2,236	3,597
Impaired financing receivables, Unpaid Principal Balance, Total	2,264	3,673
Impaired financing receivables, Related Allowance, Total	93	91
Commercial and Agriculture [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment		367
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance		367
Impaired financing receivables, Recorded Investment, Total		367
Impaired financing receivables, Unpaid Principal Balance, Total		367
Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	149	168
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	149	168
Impaired financing receivables, with an allowance recorded, Recorded Investment	230	258
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance	230	258
Impaired financing receivables, with an allowance recorded, Related Allowance	8	9
Impaired financing receivables, Recorded Investment, Total	379	426
Impaired financing receivables, Unpaid Principal Balance, Total	379	426
Impaired financing receivables, Related Allowance, Total	8	9
Commercial Real Estate Non Owner Occupied [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	55	374
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	55	374
Impaired financing receivables, Recorded Investment, Total	55	374
Impaired financing receivables, Unpaid Principal Balance, Total	55	374
Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	993	1,571
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	1,017	1,643
Impaired financing receivables, with an allowance recorded, Recorded Investment	175	193
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance	179	197
Impaired financing receivables, with an allowance recorded, Related Allowance	85	82
Impaired financing receivables, Recorded Investment, Total	1,168	1,764
Impaired financing receivables, Unpaid Principal Balance, Total	1,196	1,840
Impaired financing receivables, Related Allowance, Total	85	82
Farm Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	634	666
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	634	666
Impaired financing receivables, Recorded Investment, Total	634	666
Impaired financing receivables, Unpaid Principal Balance, Total	$ 634	$ 666

Impaired financing receivable with and no related allowance.

No definition available.

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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.

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- Definition

Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953550-111524

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- Definition

Amount of allowance for credit losses related to recorded investment.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5212-111524

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- Definition

Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(4)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5212-111524

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- Definition

Amount of investment in impaired financing receivables for which there is no related allowance for credit losses.

+ References

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- Definition

Amount of unpaid principal balance of impaired financing receivables for which there is no related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(4)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5212-111524

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- Definition

Amount of investment in impaired financing receivables for which there is a related allowance for credit losses.

+ References

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- Definition

Unpaid principal balance of impaired financing receivables for which there is a related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(4)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5212-111524

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