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Loans Held for Investment - Schedule of Recorded Investment in Impaired Loans (Details) - USD ($) $ in Millions | 3 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2024 | Mar. 31, 2023 | Dec. 31, 2023 | Dec. 31, 2022
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Provision charged to operating expense | $ (5.3) | $ (15.2) |  |
Accounts Receivable, Allowance for Credit Loss | 227.7 | 226.1 | $ 227.7 | $ 220.1
Off-Balance Sheet, Credit Loss, Liability, Credit Loss Expense (Reversal) | 8.4 | 12.2 |  |
Impaired Financing Receivable, Interest Income, Accrual Method | 0.0 | 0.0 |  |
Total real estate |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Provision charged to operating expense | 4.7 | (13.4) |  |
Accounts Receivable, Allowance for Credit Loss | 152.9 | 147.5 | 160.1 | 138.7
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 13,647.7 |  | 13,656.8 |
Commercial |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Provision charged to operating expense | (11.2) | 0.8 |  |
Accounts Receivable, Allowance for Credit Loss | 58.0 | 54.4 | 50.2 | 54.9
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 2,922.2 |  | 2,906.8 |
Agricultural |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Provision charged to operating expense | 0.5 | 1.1 |  |
Accounts Receivable, Allowance for Credit Loss | 4.2 | $ 2.4 | 4.4 | $ 3.2
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 696.0 |  | 769.4 |
Commercial |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 9,060.4 |  | 8,869.2 |
Residential |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 2,258.4 |  | 2,244.3 |
Agricultural |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 719.7 |  | 716.8 |
Total construction loans |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 1,609.2 |  | 1,826.5 |
Collateral [Member] |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 116.4 |  | 52.6 |
Collateral [Member] | Total real estate |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 53.0 |  | 45.3 |
Collateral [Member] | Commercial |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 62.3 |  | 6.6 |
Collateral [Member] | Agricultural |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 1.1 |  | 0.7 |
Collateral [Member] | Commercial |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 35.2 |  | 26.6 |
Collateral [Member] | Residential |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 0.5 |  | 0.5 |
Collateral [Member] | Agricultural |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 1.1 |  | 1.2 |
Collateral [Member] | Total construction loans |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 16.2 |  | 17.0 |
Business Assets [Member] | Collateral [Member] |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 61.1 |  | 5.2 |
Business Assets [Member] | Collateral [Member] | Total real estate |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 0.0 |  | 0.0 |
Business Assets [Member] | Collateral [Member] | Commercial |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 60.6 |  | 4.5 |
Business Assets [Member] | Collateral [Member] | Agricultural |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 0.5 |  | 0.7 |
Business Assets [Member] | Collateral [Member] | Commercial |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 0.0 |  | 0.0 |
Business Assets [Member] | Collateral [Member] | Residential |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 0.0 |  | 0.0 |
Business Assets [Member] | Collateral [Member] | Agricultural |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 0.0 |  | 0.0 |
Business Assets [Member] | Collateral [Member] | Total construction loans |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 0.0 |  | 0.0 |
Real Property [Member] | Collateral [Member] |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 54.4 |  | 46.7 |
Real Property [Member] | Collateral [Member] | Total real estate |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 53.0 |  | 45.3 |
Real Property [Member] | Collateral [Member] | Commercial |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 1.0 |  | 1.4 |
Real Property [Member] | Collateral [Member] | Agricultural |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 0.4 |  | 0.0 |
Real Property [Member] | Collateral [Member] | Commercial |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 35.2 |  | 26.6 |
Real Property [Member] | Collateral [Member] | Residential |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 0.5 |  | 0.5 |
Real Property [Member] | Collateral [Member] | Agricultural |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 1.1 |  | 1.2 |
Real Property [Member] | Collateral [Member] | Total construction loans |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 16.2 |  | 17.0 |
Other Property [Member] | Collateral [Member] |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 0.9 |  | 0.7 |
Other Property [Member] | Collateral [Member] | Total real estate |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 0.0 |  | 0.0 |
Other Property [Member] | Collateral [Member] | Commercial |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 0.7 |  | 0.7 |
Other Property [Member] | Collateral [Member] | Agricultural |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 0.2 |  | 0.0 |
Other Property [Member] | Collateral [Member] | Commercial |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 0.0 |  | 0.0 |
Other Property [Member] | Collateral [Member] | Residential |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 0.0 |  | 0.0 |
Other Property [Member] | Collateral [Member] | Agricultural |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 0.0 |  | 0.0 |
Other Property [Member] | Collateral [Member] | Total construction loans |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | $ 0.0 |  | $ 0.0 |

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