Loans - Contractual Aging of Recorded Investment in Past Due Loans by Portfolio Classification of Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022	Jun. 30, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	$ 2,515,793	$ 2,356,387	$ 2,034,818
Recorded Investment > 90 Days and Accruing		0	0
30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	7,573	3,197
60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	498	674
Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,613	2,154
Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	9,684	6,025
Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,506,109	2,350,362
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	506,842
Loans after net deferred loan fees and costs	506,842	494,423	410,468
Consumer Real Estate [Member] | 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,287	1,536
Consumer Real Estate [Member] | 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	5	635
Consumer Real Estate [Member] | Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	443	90
Consumer Real Estate [Member] | Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,735	2,261
Consumer Real Estate [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	505,107	492,162
Agricultural Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	230,531	220,514	199,650
Agricultural Real Estate [Member] | 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	5,047	118
Agricultural Real Estate [Member] | 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1	2
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	5,048	1,670
Agricultural Real Estate [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	225,483	218,844
Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	128,593
Loans after net deferred loan fees and costs	128,593	128,926	127,340
Agricultural [Member] | 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	750	433
Agricultural [Member] | 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	462
Agricultural [Member] | Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due		152
Agricultural [Member] | Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,212	585
Agricultural [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	127,381	128,341
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,278,445
Loans after net deferred loan fees and costs	1,278,445	1,150,511	977,588
Commercial Real Estate [Member] | 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	434	74
Commercial Real Estate [Member] | Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	255	180
Commercial Real Estate [Member] | Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	689	254
Commercial Real Estate [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,277,756	1,150,257
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	282,244	272,119	264,124
Commercial and Industrial [Member] | 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	26	953
Commercial and Industrial [Member] | Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	855	182
Commercial and Industrial [Member] | Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	881	1,135
Commercial and Industrial [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	281,363	270,984
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	89,138	89,894	$ 55,648
Consumer [Member] | 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	29	83
Consumer [Member] | 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	30	37
Consumer [Member] | Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	60
Consumer [Member] | Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	119	120
Consumer [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 89,019	$ 89,774