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Loans - Recorded Investment in Nonaccrual Loans by Portfolio Class of Loans (Detail) - USD ($) $ in Thousands | Sep. 30, 2020 | Dec. 31, 2019 | Sep. 30, 2019
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Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Investment in nonaccrual loans | $ 7,870 | $ 3,400 | $ 3,275
Consumer Real Estate [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Investment in nonaccrual loans | 1,523 | 1,209 |
Agricultural Real Estate [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Investment in nonaccrual loans | 3,775 | 88 |
Agricultural [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Investment in nonaccrual loans | 517 | 1,769 |
Commercial Real Estate [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Investment in nonaccrual loans | 685 | 37 |
Commercial and Industrial [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Investment in nonaccrual loans | 1,328 | 288 |
Consumer [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Investment in nonaccrual loans | $ 42 | $ 9 |

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