Loans - Distribution of Fixed Rate Loans and Variable Rate Loans by Major Loan Category (Detail) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Distribution of fixed rate loans by major loan category, Fixed Rate	$ 311,679	$ 329,142
Distribution of variable rate loans by major loan category, Variable Rate	212,376	192,753
Agricultural Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Distribution of fixed rate loans by major loan category, Fixed Rate	122,465	123,783
Distribution of variable rate loans by major loan category, Variable Rate	97,863	100,008
Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Distribution of fixed rate loans by major loan category, Fixed Rate	49,635	56,269
Distribution of variable rate loans by major loan category, Variable Rate	87,617	76,291
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Distribution of fixed rate loans by major loan category, Fixed Rate	959,346	1,024,989
Distribution of variable rate loans by major loan category, Variable Rate	341,814	312,777
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Distribution of fixed rate loans by major loan category, Fixed Rate	135,030	131,385
Distribution of variable rate loans by major loan category, Variable Rate	125,702	123,550
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Distribution of fixed rate loans by major loan category, Fixed Rate	67,363	79,526
Distribution of variable rate loans by major loan category, Variable Rate	31	65
Other Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Distribution of fixed rate loans by major loan category, Fixed Rate	16,200	20,552
Distribution of variable rate loans by major loan category, Variable Rate	$ 9,716	$ 9,584