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Loans - Contractual Aging at Amortized Cost in Past Due Loans by Portfolio Segment (Detail) - USD ($) $ in Thousands | Sep. 30, 2025 | Dec. 31, 2024
--- | --- | ---
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | $ 2,659,727 | $ 2,562,545
Total Financing Receivables | 2,658,275 | 2,560,795
30 to 59 Days Past Due [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 3,360 | 3,769
60 to 89 Days Past Due [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 362 | 712
Greater Than 90 Days [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 2,166 | 1,117
Past Due [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 5,888 | 5,598
Current [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 2,652,387 | 2,555,197
Consumer Real Estate [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 522,416 | 520,114
Total Financing Receivables | 522,930 | 520,392
Consumer Real Estate [Member] | 30 to 59 Days Past Due [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 2,472 | 2,533
Consumer Real Estate [Member] | 60 to 89 Days Past Due [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 250 | 547
Consumer Real Estate [Member] | Greater Than 90 Days [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 1,387 | 559
Consumer Real Estate [Member] | Past Due [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 4,109 | 3,639
Consumer Real Estate [Member] | Current [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 518,821 | 516,753
Agricultural Real Estate [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 222,145 | 216,401
Total Financing Receivables | 221,923 | 216,137
Agricultural Real Estate [Member] | 30 to 59 Days Past Due [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 336 | 651
Agricultural Real Estate [Member] | Greater Than 90 Days [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 376 |
Agricultural Real Estate [Member] | Past Due [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 712 | 651
Agricultural Real Estate [Member] | Current [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 221,211 | 215,486
Agricultural [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 179,361 | 152,080
Total Financing Receivables | 179,699 | 152,381
Agricultural [Member] | 30 to 59 Days Past Due [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 109 | 44
Agricultural [Member] | Greater Than 90 Days [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 50 | 79
Agricultural [Member] | Past Due [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 159 | 123
Agricultural [Member] | Current [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 179,540 | 152,258
Commercial Real Estate [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 1,355,166 | 1,310,811
Total Financing Receivables | 1,352,690 | 1,308,461
Commercial Real Estate [Member] | 30 to 59 Days Past Due [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 290 | 54
Commercial Real Estate [Member] | 60 to 89 Days Past Due [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due |  | 141
Commercial Real Estate [Member] | Greater Than 90 Days [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 140 | 360
Commercial Real Estate [Member] | Past Due [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 430 | 555
Commercial Real Estate [Member] | Current [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 1,352,260 | 1,307,906
Commercial and Industrial [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Financing Receivables | 295,815 | 274,819
Commercial and Industrial [Member] | 30 to 59 Days Past Due [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due |  | 122
Commercial and Industrial [Member] | 60 to 89 Days Past Due [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 101 | 5
Commercial and Industrial [Member] | Greater Than 90 Days [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 197 | 57
Commercial and Industrial [Member] | Past Due [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 298 | 184
Commercial and Industrial [Member] | Current [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 295,517 | 274,635
Consumer [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 60,469 | 63,009
Total Financing Receivables | 61,132 | 63,627
Consumer [Member] | 30 to 59 Days Past Due [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 153 | 365
Consumer [Member] | 60 to 89 Days Past Due [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 11 | 19
Consumer [Member] | Greater Than 90 Days [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 16 | 62
Consumer [Member] | Past Due [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 180 | 446
Consumer [Member] | Current [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 60,952 | 63,181
Other Loan [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 24,086 | 24,978
Total Financing Receivables | 24,086 | 24,978
Other Loan [Member] | Past Due [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | 0 |
Other Loan [Member] | Current [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total Past Due | $ 24,086 | $ 24,978

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