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Loans Held for Investment - Schedule of Recorded Investment in Past Due Loans (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2024 | Sep. 30, 2023 | Dec. 31, 2023
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | $ 0.5 |  | $ 0.5 |  |
Accrued interest reversal | (0.4) | $ (1.0) | (2.4) | $ (1.9) |
Commercial |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 11.9 |  | 11.9 |  | $ 18.8
Nonaccrual loans | 45.2 |  | 45.2 |  | 28.2
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 9,219.3 |  | 9,219.3 |  | 8,869.2
Commercial | 30 to 59 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 5.1 |  | 5.1 |  | 12.7
Commercial | 60 to 89 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 6.8 |  | 6.8 |  | 6.1
Commercial | Equal to or Greater than 90 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 0.0 |  | 0.0
Commercial | Financial Asset, Not Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 9,162.2 |  | 9,162.2 |  | 8,822.2
Total construction loans |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 3.7 |  | 3.7 |  | 3.5
Nonaccrual loans | 0.1 |  | 0.1 |  | 17.2
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 1,307.9 |  | 1,307.9 |  | 1,826.5
Total construction loans | 30 to 59 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 3.6 |  | 3.6 |  | 3.1
Total construction loans | 60 to 89 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 0.1 |  | 0.1 |  | 0.4
Total construction loans | Equal to or Greater than 90 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 0.0 |  | 0.0
Total construction loans | Financial Asset, Not Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 1,304.1 |  | 1,304.1 |  | 1,805.8
Residential |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 4.9 |  | 4.9 |  | 15.6
Nonaccrual loans | 14.3 |  | 14.3 |  | 10.7
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 2,217.8 |  | 2,217.8 |  | 2,244.3
Residential | 30 to 59 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 2.6 |  | 2.6 |  | 11.9
Residential | 60 to 89 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 2.1 |  | 2.1 |  | 3.1
Residential | Equal to or Greater than 90 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 0.2 |  | 0.2 |  | 0.6
Residential | Financial Asset, Not Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 2,198.6 |  | 2,198.6 |  | 2,218.0
Agricultural |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 2.4 |  | 2.4 |  | 1.8
Nonaccrual loans | 4.7 |  | 4.7 |  | 5.4
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 726.4 |  | 726.4 |  | 716.8
Agricultural | 30 to 59 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 2.4 |  | 2.4 |  | 1.8
Agricultural | 60 to 89 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 0.0 |  | 0.0
Agricultural | Equal to or Greater than 90 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 0.0 |  | 0.0
Agricultural | Financial Asset, Not Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 719.3 |  | 719.3 |  | 709.6
Total real estate |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 22.9 |  | 22.9 |  | 39.7
Nonaccrual loans | 64.3 |  | 64.3 |  | 61.5
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 13,471.4 |  | 13,471.4 |  | 13,656.8
Total real estate | 30 to 59 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 13.7 |  | 13.7 |  | 29.5
Total real estate | 60 to 89 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 9.0 |  | 9.0 |  | 9.6
Total real estate | Equal to or Greater than 90 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 0.2 |  | 0.2 |  | 0.6
Total real estate | Financial Asset, Not Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 13,384.2 |  | 13,384.2 |  | 13,555.6
Indirect consumer |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 8.1 |  | 8.1 |  | 10.6
Nonaccrual loans | 3.4 |  | 3.4 |  | 2.7
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 742.2 |  | 742.2 |  | 740.9
Indirect consumer | 30 to 59 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 6.4 |  | 6.4 |  | 8.0
Indirect consumer | 60 to 89 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 1.6 |  | 1.6 |  | 2.2
Indirect consumer | Equal to or Greater than 90 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 0.1 |  | 0.1 |  | 0.4
Indirect consumer | Financial Asset, Not Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 730.7 |  | 730.7 |  | 727.6
Direct and advance lines |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 1.4 |  | 1.4 |  | 1.1
Nonaccrual loans | 0.4 |  | 0.4 |  | 0.3
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 136.9 |  | 136.9 |  | 141.6
Direct and advance lines | 30 to 59 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 1.0 |  | 1.0 |  | 0.9
Direct and advance lines | 60 to 89 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 0.4 |  | 0.4 |  | 0.2
Direct and advance lines | Equal to or Greater than 90 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 0.0 |  | 0.0
Direct and advance lines | Financial Asset, Not Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 135.1 |  | 135.1 |  | 140.2
Credit Card Receivable [Member] |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 1.9 |  | 1.9 |  | 1.8
Nonaccrual loans | 0.0 |  | 0.0 |  | 0.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 76.4 |  | 76.4 |  | 76.5
Credit Card Receivable [Member] | 30 to 59 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 0.7 |  | 0.7 |  | 0.7
Credit Card Receivable [Member] | 60 to 89 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 0.5 |  | 0.5 |  | 0.5
Credit Card Receivable [Member] | Equal to or Greater than 90 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 0.7 |  | 0.7 |  | 0.6
Credit Card Receivable [Member] | Financial Asset, Not Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 74.5 |  | 74.5 |  | 74.7
Total consumer loans |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 11.4 |  | 11.4 |  | 13.5
Nonaccrual loans | 3.8 |  | 3.8 |  | 3.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 955.5 |  | 955.5 |  | 959.0
Total consumer loans | 30 to 59 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 8.1 |  | 8.1 |  | 9.6
Total consumer loans | 60 to 89 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 2.5 |  | 2.5 |  | 2.9
Total consumer loans | Equal to or Greater than 90 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 0.8 |  | 0.8 |  | 1.0
Total consumer loans | Financial Asset, Not Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 940.3 |  | 940.3 |  | 942.5
Commercial |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 6.4 |  | 6.4 |  | 15.9
Nonaccrual loans | 81.6 |  | 81.6 |  | 11.5
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 2,919.7 |  | 2,919.7 |  | 2,906.8
Commercial | 30 to 59 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 4.3 |  | 4.3 |  | 14.5
Commercial | 60 to 89 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 1.5 |  | 1.5 |  | 1.1
Commercial | Equal to or Greater than 90 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 0.6 |  | 0.6 |  | 0.3
Commercial | Financial Asset, Not Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 2,831.7 |  | 2,831.7 |  | 2,879.4
Agricultural |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 1.8 |  | 1.8 |  | 3.1
Nonaccrual loans | 23.0 |  | 23.0 |  | 30.4
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 689.8 |  | 689.8 |  | 769.4
Agricultural | 30 to 59 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 1.6 |  | 1.6 |  | 0.1
Agricultural | 60 to 89 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 0.0 |  | 0.0
Agricultural | Equal to or Greater than 90 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 0.2 |  | 0.2 |  | 3.0
Agricultural | Financial Asset, Not Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 665.0 |  | 665.0 |  | 735.9
Other, including overdrafts |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 0.0 |  | 0.0
Nonaccrual loans | 0.0 |  | 0.0 |  | 0.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 2.5 |  | 2.5 |  | 0.1
Other, including overdrafts | 30 to 59 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 0.0 |  | 0.0
Other, including overdrafts | 60 to 89 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 0.0 |  | 0.0
Other, including overdrafts | Equal to or Greater than 90 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 0.0 |  | 0.0
Other, including overdrafts | Financial Asset, Not Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 2.5 |  | 2.5 |  | 0.1
Loans And Leases Held For Investment [Member] |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 42.5 |  | 42.5 |  | 72.2
Nonaccrual loans | 172.7 |  | 172.7 |  | 106.4
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 18,038.9 |  | 18,038.9 |  | 18,292.1
Loans And Leases Held For Investment [Member] | 30 to 59 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 27.7 |  | 27.7 |  | 53.7
Loans And Leases Held For Investment [Member] | 60 to 89 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 13.0 |  | 13.0 |  | 13.6
Loans And Leases Held For Investment [Member] | Equal to or Greater than 90 Days Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | 1.8 |  | 1.8 |  | 4.9
Loans And Leases Held For Investment [Member] | Financial Asset, Not Past Due |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |
Financing Receivable, Loan in Process | $ 17,823.7 |  | $ 17,823.7 |  | $ 18,113.5

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