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Loans - Recorded Investment in Nonaccrual Loans by Portfolio Class of Loans (Detail) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Investment in nonaccrual loans | $ 9,404 | $ 3,400
Consumer Real Estate [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Investment in nonaccrual loans | 1,546 | 1,209
Agricultural Real Estate [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Investment in nonaccrual loans | 5,575 | 88
Agricultural [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Investment in nonaccrual loans | 307 | 1,769
Commercial Real Estate [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Investment in nonaccrual loans | 665 | 37
Commercial and Industrial [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Investment in nonaccrual loans | 1,296 | 288
Consumer [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Investment in nonaccrual loans | $ 15 | $ 9

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