Allowance for Loan Losses - Schedule of Troubled Debt Restructurings (Detail) $ in Thousands	12 Months Ended
Dec. 31, 2018 USD ($) Contract	Dec. 31, 2017 USD ($) Contract	Dec. 31, 2016 USD ($) Contract
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of Contracts \| Contract	2	1	9
Pre- Modification Outstanding Recorded Investment	$ 133	$ 13	$ 1,537
Post-Modification Outstanding Recorded Investment	$ 133	$ 13	$ 1,537
Commercial and Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of Contracts \| Contract			4
Pre- Modification Outstanding Recorded Investment			$ 529
Post-Modification Outstanding Recorded Investment			$ 529
Residential Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of Contracts \| Contract	1	1	2
Pre- Modification Outstanding Recorded Investment	$ 23	$ 13	$ 308
Post-Modification Outstanding Recorded Investment	$ 23	$ 13	$ 308
Farm Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of Contracts \| Contract	1		3
Pre- Modification Outstanding Recorded Investment	$ 110		$ 700
Post-Modification Outstanding Recorded Investment	$ 110		$ 700

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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

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