Loans - Distribution of Fixed Rate Loans and Variable Rate Loans by Major Loan Category (Detail) $ in Thousands	Dec. 31, 2020 USD ($)
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Distribution of fixed rate loans by major loan category, Fixed Rate	$ 128,948
Distribution of variable rate loans by major loan category, Variable Rate	46,640
Agricultural Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Distribution of fixed rate loans by major loan category, Fixed Rate	102,993
Distribution of variable rate loans by major loan category, Variable Rate	86,166
Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Distribution of fixed rate loans by major loan category, Fixed Rate	81,089
Distribution of variable rate loans by major loan category, Variable Rate	13,269
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Distribution of fixed rate loans by major loan category, Fixed Rate	456,997
Distribution of variable rate loans by major loan category, Variable Rate	131,828
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Distribution of fixed rate loans by major loan category, Fixed Rate	163,688
Distribution of variable rate loans by major loan category, Variable Rate	25,558
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Distribution of fixed rate loans by major loan category, Fixed Rate	48,558
Distribution of variable rate loans by major loan category, Variable Rate	3,982
Other Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Distribution of fixed rate loans by major loan category, Fixed Rate	15,705
Distribution of variable rate loans by major loan category, Variable Rate	$ 52