Loans - Contractual Aging of Recorded Investment in Past Due Loans by Portfolio Classification of Loans (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
Recorded Investment > 90 Days and Accruing	0	0	0
30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,898	749
60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	568	131
Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,847	575
Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	5,313	1,455
Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,137,303	1,855,964
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	416,044	395,805	202,370
Consumer Real Estate [Member] | 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,056	228
Consumer Real Estate [Member] | 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	167
Consumer Real Estate [Member] | Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	216	246
Consumer Real Estate [Member] | Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,439	474
Consumer Real Estate [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	414,605	395,331
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 Real Estate [Member] | 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	189	436
Agricultural Real Estate [Member] | 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	216
Agricultural Real Estate [Member] | Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,550
Agricultural Real Estate [Member] | Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,955	436
Agricultural Real Estate [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	202,832	197,597
Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	128,818	118,504	105,722
Agricultural [Member] | 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	435
Agricultural [Member] | 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	88
Agricultural [Member] | Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	831
Agricultural [Member] | Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,354
Agricultural [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	127,464	118,504
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 Real Estate [Member] | 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1
Commercial Real Estate [Member] | Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	180	180
Commercial Real Estate [Member] | Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	181	180
Commercial Real Estate [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,061,723	846,930
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	260,000	240,138	225,382
Commercial and Industrial [Member] | 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	203	21
Commercial and Industrial [Member] | 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	52	131
Commercial and Industrial [Member] | Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	23	149
Commercial and Industrial [Member] | Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	278	301
Commercial and Industrial [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	259,722	239,837
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	71,063	57,829	$ 55,619
Consumer [Member] | 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	14	64
Consumer [Member] | 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	45
Consumer [Member] | Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	47
Consumer [Member] | Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	106	64
Consumer [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 70,957	$ 57,765