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Loans Held for Investment - Schedule of Loans by Segment (Details) - USD ($) $ in Millions | Mar. 31, 2025 | Dec. 31, 2024 | Mar. 31, 2024 | Dec. 31, 2023
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Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Deferred loan fees and costs | $ (10.6) | $ (11.1) |  |
Allowance for credit losses | (215.3) | (204.1) | $ (227.7) | $ (227.7)
Net loans held for investment | 17,162.0 | 17,640.8 |  |
Financing Receivable, Loan in Process | 0.5 | 19.1 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 17,377.3 | 17,844.9 |  |
Nonaccrual loans | 116.5 | 56.9 |  |
30 to 59 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Nonaccrual loans | 14.8 | 13.5 |  |
60 to 89 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Nonaccrual loans | 28.3 | 6.2 |  |
Equal to or Greater than 90 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Nonaccrual loans | 76.9 | 40.5 |  |
Commercial real estate |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 29.9 | 7.7 |  |
Nonaccrual loans | 82.9 | 55.4 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process | 9,196.1 | 9,263.2 |  |
Commercial real estate | 30 to 59 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 1.4 | 4.9 |  |
Commercial real estate | 60 to 89 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 28.5 | 2.8 |  |
Commercial 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 | 0.0 | 0.0 |  |
Commercial real estate | Financial Asset, Not Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 9,083.3 | 9,200.1 |  |
Total construction loans |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 3.6 | 3.7 |  |
Nonaccrual loans | 4.0 | 3.3 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process | 1,097.3 | 1,244.6 |  |
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 | 3.7 |  |
Total construction loans | 60 to 89 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 0.0 | 0.0 |  |
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 |  |
Total construction loans | Financial Asset, Not Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 1,089.7 | 1,237.6 |  |
Residential |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 11.8 | 9.7 |  |
Nonaccrual loans | 16.6 | 15.4 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process | 2,161.4 | 2,191.6 |  |
Residential | 30 to 59 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 10.7 | 6.6 |  |
Residential | 60 to 89 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 0.4 | 2.7 |  |
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 | 0.7 | 0.4 |  |
Residential | Financial Asset, Not Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 2,133.0 | 2,166.5 |  |
Agricultural |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 17.2 | 10.4 |  |
Nonaccrual loans | 20.5 | 5.3 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process | 678.1 | 701.1 |  |
Agricultural | 30 to 59 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 10.1 | 7.6 |  |
Agricultural | 60 to 89 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 7.0 | 2.8 |  |
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 | 0.1 | 0.0 |  |
Agricultural | Financial Asset, Not Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 640.4 | 685.4 |  |
Total real estate |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Allowance for credit losses | (146.0) | (139.4) | (152.9) | (160.1)
Financing Receivable, Loan in Process | 62.5 | 31.5 |  |
Nonaccrual loans | 124.0 | 79.4 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process | 13,132.9 | 13,400.5 |  |
Total real estate | 30 to 59 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 25.8 | 22.8 |  |
Total real estate | 60 to 89 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 35.9 | 8.3 |  |
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 | 0.8 | 0.4 |  |
Total real estate | Financial Asset, Not Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 12,946.4 | 13,289.6 |  |
Indirect consumer |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 8.9 | 11.7 |  |
Nonaccrual loans | 4.5 | 3.9 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process | 680.2 | 725.0 |  |
Indirect consumer | 30 to 59 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 7.2 | 8.4 |  |
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 | 2.6 |  |
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 | 0.7 |  |
Indirect consumer | Financial Asset, Not Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 666.8 | 709.4 |  |
Total consumer loans |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Allowance for credit losses | (15.9) | (16.8) | (12.6) | (13.0)
Financing Receivable, Loan in Process | 11.4 | 15.0 |  |
Nonaccrual loans | 5.1 | 4.5 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process | 886.8 | 936.6 |  |
Total consumer loans | 30 to 59 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 8.4 | 9.7 |  |
Total consumer loans | 60 to 89 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 2.2 | 3.3 |  |
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 | 2.0 |  |
Total consumer loans | Financial Asset, Not Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 870.3 | 917.1 |  |
Commercial |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Allowance for credit losses | (46.3) | (38.9) | (58.0) | (50.2)
Financing Receivable, Loan in Process | 7.0 | 14.8 |  |
Nonaccrual loans | 31.3 | 33.5 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process | 2,770.6 | 2,829.4 |  |
Commercial | 30 to 59 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 4.4 | 11.2 |  |
Commercial | 60 to 89 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 1.3 | 3.0 |  |
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 | 1.3 | 0.6 |  |
Commercial | Financial Asset, Not Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 2,732.3 | 2,781.1 |  |
Agricultural |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Allowance for credit losses | (7.1) | (9.0) | $ (4.2) | $ (4.4)
Financing Receivable, Loan in Process | 12.3 | 5.2 |  |
Nonaccrual loans | 31.5 | 20.9 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process | 595.8 | 687.9 |  |
Agricultural | 30 to 59 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 11.0 | 2.4 |  |
Agricultural | 60 to 89 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 1.2 | 2.8 |  |
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 | 0.1 | 0.0 |  |
Agricultural | Financial Asset, Not Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 552.0 | 661.8 |  |
Other, including overdrafts |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 0.0 | 0.0 |  |
Nonaccrual loans | 0.0 | 0.0 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process | 1.8 | 1.6 |  |
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 |  |
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 |  |
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 |  |
Other, including overdrafts | Financial Asset, Not Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 1.8 | 1.6 |  |
Loans And Leases Held For Investment [Member] |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 93.2 | 66.5 |  |
Nonaccrual loans | 191.9 | 138.3 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process | 17,387.9 | 17,856.0 |  |
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 | 49.6 | 46.1 |  |
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 | 40.6 | 17.4 |  |
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 | 3.0 | 3.0 |  |
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 | 17,102.8 | 17,651.2 |  |
Consumer Loan |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 0.7 | 1.1 |  |
Nonaccrual loans | 0.6 | 0.6 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process | 132.4 | 134.0 |  |
Consumer Loan | 30 to 59 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 0.5 | 0.6 |  |
Consumer Loan | 60 to 89 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 0.2 | 0.2 |  |
Consumer Loan | 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 | 0.3 |  |
Consumer Loan | Financial Asset, Not Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 131.1 | 132.3 |  |
Credit Card Receivable [Member] |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 1.8 | 2.2 |  |
Nonaccrual loans | 0.0 | 0.0 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process | 74.2 | 77.6 |  |
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 |  |
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 | 0.4 | 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 | 1.0 |  |
Credit Card Receivable [Member] | Financial Asset, Not Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | $ 72.4 | $ 75.4 |  |

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