Allowance for Loan Losses - Impaired Loans Excluding PCI Loans - Recorded Investment and Unpaid Principal Balances (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	$ 1,881	$ 1,864
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	1,953	1,939
Impaired financing receivables, with an allowance recorded, Recorded Investment	1,180	993
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance	1,184	996
Impaired financing receivables, with an allowance recorded, Related Allowance	194	141
Impaired financing receivables, Recorded Investment, Total	3,061	2,857
Impaired financing receivables, Unpaid Principal Balance, Total	3,137	2,935
Impaired financing receivables, Related Allowance, Total	194	141
Commercial and Agriculture [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	168	367
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	168	367
Impaired financing receivables, with an allowance recorded, Recorded Investment	199
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance	199
Impaired financing receivables, with an allowance recorded, Related Allowance	53
Impaired financing receivables, Recorded Investment, Total	367	367
Impaired financing receivables, Unpaid Principal Balance, Total	367	367
Impaired financing receivables, Related Allowance, Total	53
Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	187	193
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	187	193
Impaired financing receivables, with an allowance recorded, Recorded Investment	285	291
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance	285	291
Impaired financing receivables, with an allowance recorded, Related Allowance	10	12
Impaired financing receivables, Recorded Investment, Total	472	484
Impaired financing receivables, Unpaid Principal Balance, Total	472	484
Impaired financing receivables, Related Allowance, Total	10	12
Commercial Real Estate Non Owner Occupied [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	382	31
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	382	34
Impaired financing receivables, Recorded Investment, Total	382	31
Impaired financing receivables, Unpaid Principal Balance, Total	382	34
Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	892	1,017
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	964	1,089
Impaired financing receivables, with an allowance recorded, Recorded Investment	256	262
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance	260	265
Impaired financing receivables, with an allowance recorded, Related Allowance	124	122
Impaired financing receivables, Recorded Investment, Total	1,148	1,279
Impaired financing receivables, Unpaid Principal Balance, Total	1,224	1,354
Impaired financing receivables, Related Allowance, Total	124	122
Farm Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	252	256
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	252	256
Impaired financing receivables, with an allowance recorded, Recorded Investment	440	440
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance	440	440
Impaired financing receivables, with an allowance recorded, Related Allowance	7	7
Impaired financing receivables, Recorded Investment, Total	692	696
Impaired financing receivables, Unpaid Principal Balance, Total	692	696
Impaired financing receivables, Related Allowance, Total	$ 7	$ 7

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=84173941&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=84173941&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=84173941&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=84173941&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=84173941&loc=d3e5212-111524

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