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Loans - Impaired Loans Classified as Troubled Debt Restructured (Detail) $ in Thousands | 3 Months Ended | 9 Months Ended
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Sep. 30, 2021 USD ($) Contract Loan | Sep. 30, 2020 USD ($) Contract Loan | Sep. 30, 2021 USD ($) Contract Loan | Sep. 30, 2020 USD ($) Contract Loan
Financing Receivable Modifications [Line Items] |  |  |  |
Number of Contracts Modified in the Last three Months | Loan | 1 | 1 | 2 | 6
Agricultural Real Estate [Member] |  |  |  |
Financing Receivable Modifications [Line Items] |  |  |  |
Number of Contracts Modified in the Last three Months | Contract |  |  |  | 2
Pre-Modification Outstanding Recorded Investment |  |  |  | $ 5,380
Post-Modification Outstanding Recorded Investment |  |  |  | $ 5,380
Agricultural [Member] |  |  |  |
Financing Receivable Modifications [Line Items] |  |  |  |
Number of Contracts Modified in the Last three 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 three Months | Contract |  |  | 1 | 2
Pre-Modification Outstanding Recorded Investment |  |  | $ 382 | $ 981
Post-Modification Outstanding Recorded Investment |  |  | $ 382 | $ 981
Commercial and Industrial [Member] |  |  |  |
Financing Receivable Modifications [Line Items] |  |  |  |
Number of Contracts Modified in the Last three Months | Contract | 1 | 1 | 1 | 1
Pre-Modification Outstanding Recorded Investment | $ 1,000 | $ 50 | $ 1,000 | $ 50
Post-Modification Outstanding Recorded Investment | $ 1,000 | $ 50 | $ 1,000 | $ 50

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