Loans - Contractual Aging of Recorded Investment in Past Due Loans by Portfolio Classification of Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	$ 2,446,652	$ 2,356,387	$ 1,962,220
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	9,537	3,197
60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	654	674
Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,762	2,154
Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	12,953	6,025
Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,433,699	2,350,362
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	502,968
Loans after net deferred loan fees and costs	502,968	494,423	410,064
Consumer Real Estate [Member] | 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	850	1,536
Consumer Real Estate [Member] | 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due		635
Consumer Real Estate [Member] | Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	111	90
Consumer Real Estate [Member] | Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	961	2,261
Consumer Real Estate [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	502,007	492,162
Agricultural Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	227,599	220,514	195,901
Agricultural Real Estate [Member] | 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	231	118
Agricultural Real Estate [Member] | 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	283	2
Agricultural Real Estate [Member] | Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,511	1,550
Agricultural Real Estate [Member] | Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,025	1,670
Agricultural Real Estate [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	225,574	218,844
Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	131,677
Loans after net deferred loan fees and costs	131,677	128,926	140,847
Agricultural [Member] | 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due		433
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		585
Agricultural [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	131,677	128,341
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,223,163
Loans after net deferred loan fees and costs	1,223,163	1,150,511	909,408
Commercial Real Estate [Member] | 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	8,383	74
Commercial Real Estate [Member] | Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	267	180
Commercial Real Estate [Member] | Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	8,650	254
Commercial Real Estate [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,214,513	1,150,257
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	270,857	272,119	248,362
Commercial and Industrial [Member] | 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due		953
Commercial and Industrial [Member] | 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	346
Commercial and Industrial [Member] | Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	854	182
Commercial and Industrial [Member] | Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,200	1,135
Commercial and Industrial [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	269,657	270,984
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	90,388	89,894	$ 57,638
Consumer [Member] | 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	73	83
Consumer [Member] | 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	25	37
Consumer [Member] | Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	19
Consumer [Member] | Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	117	120
Consumer [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 90,271	$ 89,774