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Income Taxes - Narrative (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2024 | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Income Tax Contingency [Line Items] |  |  |  |
Net deferred tax benefit |  | $ 68.0 |  |
Non-U.S. pre-tax income (loss) |  | 282.7 | $ 450.0 | $ (94.4)
Net income tax payments to US |  | 34.3 | $ 42.7 | $ 10.3
P&C Insurance and Reinsurance (Ark/WM Outrigger) | Ark Insurance Holdings Limited - Segment |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |
Net deferred tax benefit |  | 51.0 |  |
Financial Guarantee (HG Global) | HG Global |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |
Net deferred tax benefit |  | 17.0 |  |
Deferred tax liabilities |  | 5.0 |  |
Tax benefit | $ 5.0 |  |  |
Domestic Tax Jurisdiction |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |
Separate return limitation year operating loss carryforwards |  | 7.8 |  |
Separate return limitation year internal revenue |  | 0.7 |  |
Foreign Tax Jurisdiction |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |
Tax credit carryforwards |  | $ 2.8 |  |

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