Loans - Risk Category of Loans by Portfolio Class (Detail) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021	Sep. 30, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	$ 2,142,616	$ 1,857,419	$ 1,495,562
Agricultural Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	204,787	198,033	179,051
Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	128,818	118,504	105,722
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	1,061,904	847,110	$ 727,418
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	229,338	208,049
Other Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	30,662	32,089
1-2 [Member] | Agricultural Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	9,608	8,720
1-2 [Member] | Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	5,358	4,178
1-2 [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	14,227	10,894
1-2 [Member] | Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	1,195	4,604
3 [Member] | Agricultural Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	50,781	42,180
3 [Member] | Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	33,381	38,623
3 [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	303,291	238,132
3 [Member] | Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	66,129	46,547
3 [Member] | Other Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	11,110	11,408
4 [Member] | Agricultural Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	127,806	129,301
4 [Member] | Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	88,476	75,164
4 [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	705,358	568,038
4 [Member] | Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	155,223	152,736
4 [Member] | Other Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	19,552	20,681
5 [Member] | Agricultural Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	5,024	4,599
5 [Member] | Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	240	227
5 [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	15,322	14,509
5 [Member] | Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	3,214	986
6 [Member] | Agricultural Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	11,568	13,233
6 [Member] | Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	1,363	312
6 [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	23,706	15,537
6 [Member] | Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	$ 3,577	$ 3,176