Loans - Recorded Investment in Nonaccrual Loans by Portfolio Class of Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investment in nonaccrual loans	$ 8,581	$ 8,076	$ 8,139
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investment in nonaccrual loans	861	824
Agricultural Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investment in nonaccrual loans	6,266	6,477
Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investment in nonaccrual loans	20	20
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investment in nonaccrual loans	1,152	600
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investment in nonaccrual loans	273	149
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investment in nonaccrual loans	$ 9	$ 6