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Loans - Amortized Cost of Nonaccrual Loans by Portfolio Class of Loans (Detail) - USD ($) $ in Thousands | Sep. 30, 2023 | Dec. 31, 2022 | Sep. 30, 2022
--- | --- | --- | ---
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Investment in nonaccrual loans |  | $ 4,689 | $ 5,470
Consumer Real Estate [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Investment in nonaccrual loans |  | 612 |
Agricultural Real Estate [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Investment in nonaccrual loans |  | 1,921 |
Agricultural [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Investment in nonaccrual loans |  | 152 |
Commercial Real Estate [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Investment in nonaccrual loans |  | 903 |
Commercial and Industrial [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Investment in nonaccrual loans |  | 1,096 |
Consumer [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Investment in nonaccrual loans |  | $ 5 |
Nonaccrual With No Allowance For Credit Loss [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Investment in nonaccrual loans | $ 22,447 |  |
Nonaccrual With No Allowance For Credit Loss [Member] | Consumer Real Estate [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Investment in nonaccrual loans | 689 |  |
Nonaccrual With No Allowance For Credit Loss [Member] | Agricultural Real Estate [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Investment in nonaccrual loans | 15,948 |  |
Nonaccrual With No Allowance For Credit Loss [Member] | Agricultural [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Investment in nonaccrual loans | 4,695 |  |
Nonaccrual With No Allowance For Credit Loss [Member] | Commercial Real Estate [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Investment in nonaccrual loans | 254 |  |
Nonaccrual With No Allowance For Credit Loss [Member] | Commercial and Industrial [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Investment in nonaccrual loans | 854 |  |
Nonaccrual With No Allowance For Credit Loss [Member] | Consumer [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Investment in nonaccrual loans | 7 |  |
Nonaccrual [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Investment in nonaccrual loans | 22,447 |  |
Nonaccrual [Member] | Consumer Real Estate [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Investment in nonaccrual loans | 689 |  |
Nonaccrual [Member] | Agricultural Real Estate [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Investment in nonaccrual loans | 15,948 |  |
Nonaccrual [Member] | Agricultural [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Investment in nonaccrual loans | 4,695 |  |
Nonaccrual [Member] | Commercial Real Estate [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Investment in nonaccrual loans | 254 |  |
Nonaccrual [Member] | Commercial and Industrial [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Investment in nonaccrual loans | 854 |  |
Nonaccrual [Member] | Consumer [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Investment in nonaccrual loans | $ 7 |  |

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