Loans - Risk Category of Loans by Portfolio Class (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	$ 2,529,606	$ 2,356,387	$ 2,142,616
Agricultural Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	225,370	220,514	204,787
Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	123,971	128,926	128,818
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	$ 1,301,614	1,150,511	$ 1,061,904
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs		242,301
Other Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs		29,818
1-2 [Member] | Agricultural Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs		9,912
1-2 [Member] | Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs		5,857
1-2 [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs		8,718
1-2 [Member] | Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs		780
3 [Member] | Agricultural Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs		47,405
3 [Member] | Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs		33,671
3 [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs		370,035
3 [Member] | Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs		67,506
3 [Member] | Other Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs		10,921
4 [Member] | Agricultural Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs		146,143
4 [Member] | Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs		88,992
4 [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs		737,745
4 [Member] | Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs		167,291
4 [Member] | Other Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs		18,897
5 [Member] | Agricultural Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs		10,389
5 [Member] | Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs		228
5 [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs		9,751
5 [Member] | Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs		3,592
6 [Member] | Agricultural Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs		6,665
6 [Member] | Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs		178
6 [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs		24,262
6 [Member] | Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs		$ 3,132