Loans - Distribution of Fixed Rate Loans and Variable Rate Loans by Major Loan Category (Detail) $ in Thousands	Mar. 31, 2021 USD ($)
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Distribution of fixed rate loans by major loan category, Fixed Rate	$ 127,467
Distribution of variable rate loans by major loan category, Variable Rate	48,208
Agricultural Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Distribution of fixed rate loans by major loan category, Fixed Rate	105,009
Distribution of variable rate loans by major loan category, Variable Rate	74,936
Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Distribution of fixed rate loans by major loan category, Fixed Rate	87,924
Distribution of variable rate loans by major loan category, Variable Rate	12,098
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Distribution of fixed rate loans by major loan category, Fixed Rate	492,252
Distribution of variable rate loans by major loan category, Variable Rate	126,502
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Distribution of fixed rate loans by major loan category, Fixed Rate	172,598
Distribution of variable rate loans by major loan category, Variable Rate	30,360
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Distribution of fixed rate loans by major loan category, Fixed Rate	50,558
Distribution of variable rate loans by major loan category, Variable Rate	3,887
Other Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Distribution of fixed rate loans by major loan category, Fixed Rate	14,084
Distribution of variable rate loans by major loan category, Variable Rate	$ 4