Loans - Contractual Aging of Recorded Investment in Past Due Loans by Portfolio Classification of Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 2,536,837	$ 2,580,674
Total Financing Receivables	2,535,291	2,578,472
30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,146	2,657
60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	186	4,735
Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,553	4,182
Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,885	11,574
Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,530,406	2,566,898
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	524,055	521,895
Total Financing Receivables	524,270	521,908
Consumer Real Estate [Member] | 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,854	1,914
Consumer Real Estate [Member] | 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	128	137
Consumer Real Estate [Member] | Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,091	670
Consumer Real Estate [Member] | Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,073	2,721
Consumer Real Estate [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	520,197	519,187
Agricultural Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	220,328	223,791
Total Financing Receivables	220,051	223,479
Agricultural Real Estate [Member] | 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due		3,429
Agricultural Real Estate [Member] | Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due		55
Agricultural Real Estate [Member] | Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due		3,484
Agricultural Real Estate [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	220,051	219,995
Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	137,252	132,560
Total Financing Receivables	137,587	132,763
Agricultural [Member] | 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	35
Agricultural [Member] | 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	13	1,132
Agricultural [Member] | Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	91	2,977
Agricultural [Member] | Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	139	4,109
Agricultural [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	137,448	128,654
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,301,160	1,337,766
Total Financing Receivables	1,298,929	1,335,075
Commercial Real Estate [Member] | 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due		380
Commercial Real Estate [Member] | Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	360	255
Commercial Real Estate [Member] | Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	360	635
Commercial Real Estate [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,298,569	1,334,440
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Financing Receivables	286,404	284,894
Commercial and Industrial [Member] | 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	50	145
Commercial and Industrial [Member] | 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	28
Commercial and Industrial [Member] | Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	11	199
Commercial and Industrial [Member] | Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	89	344
Commercial and Industrial [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	286,315	284,550
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	67,394	79,591
Total Financing Receivables	68,050	80,353
Consumer [Member] | 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	207	218
Consumer [Member] | 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	17	37
Consumer [Member] | Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due		26
Consumer [Member] | Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	224	281
Consumer [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 67,826	$ 80,072