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Loans - Impaired Loans Classified as Troubled Debt Restructured (Detail) $ in Thousands | 12 Months Ended
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Dec. 31, 2020 USD ($) Contract | Dec. 31, 2019 USD ($) Contract
Consumer Real Estate [Member] |  |
Financing Receivable Modifications [Line Items] |  |
Number of Contracts Modified in the Last 12 Months | Contract |  | 1
Pre-Modification Outstanding Recorded Investment |  | $ 74
Post-Modification Outstanding Recorded Investment |  | $ 74
Agricultural Real Estate [Member] |  |
Financing Receivable Modifications [Line Items] |  |
Number of Contracts Modified in the Last 12 Months | Contract | 2 |
Pre-Modification Outstanding Recorded Investment | $ 5,380 |
Post-Modification Outstanding Recorded Investment | $ 5,380 |
Commercial and Industrial [Member] |  |
Financing Receivable Modifications [Line Items] |  |
Number of Contracts Modified in the Last 12 Months | Contract | 1 | 4
Pre-Modification Outstanding Recorded Investment | $ 50 | $ 812
Post-Modification Outstanding Recorded Investment | $ 50 | $ 812
Agricultural [Member] |  |
Financing Receivable Modifications [Line Items] |  |
Number of Contracts Modified in the Last 12 Months | Contract | 1 |
Pre-Modification Outstanding Recorded Investment | $ 164 |
Post-Modification Outstanding Recorded Investment | $ 164 |
Commercial Real Estate [Member] |  |
Financing Receivable Modifications [Line Items] |  |
Number of Contracts Modified in the Last 12 Months | Contract | 2 |
Pre-Modification Outstanding Recorded Investment | $ 981 |
Post-Modification Outstanding Recorded Investment | $ 981 |

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