Loans - Distribution of Fixed Rate Loans and Variable Rate Loans by Major Loan Category (Detail) $ in Thousands	Sep. 30, 2019 USD ($)
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Distribution of fixed rate loans by major loan category, Fixed Rate	$ 71,645
Distribution of variable rate loans by major loan category, Variable Rate	87,429
Agricultural Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Distribution of fixed rate loans by major loan category, Fixed Rate	94,620
Distribution of variable rate loans by major loan category, Variable Rate	106,171
Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Distribution of fixed rate loans by major loan category, Fixed Rate	70,049
Distribution of variable rate loans by major loan category, Variable Rate	40,221
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Distribution of fixed rate loans by major loan category, Fixed Rate	323,791
Distribution of variable rate loans by major loan category, Variable Rate	178,346
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Distribution of fixed rate loans by major loan category, Fixed Rate	76,229
Distribution of variable rate loans by major loan category, Variable Rate	53,921
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Distribution of fixed rate loans by major loan category, Fixed Rate	45,069
Distribution of variable rate loans by major loan category, Variable Rate	4,483
Other Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Distribution of fixed rate loans by major loan category, Fixed Rate	8,070
Distribution of variable rate loans by major loan category, Variable Rate	$ 97