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Basis of Presentation and Significant Accounting Policies (Details) $ in Millions | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2024 USD ($) segment | Dec. 31, 2023 USD ($) | Dec. 31, 2022 USD ($) | May 26, 2022 | May 25, 2022 | Jan. 01, 2021 USD ($)
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |
Number of reportable segments | segment | 4 |  |  |  |  |
Other long-term investments | $ 2,150.2 | $ 1,998.2 |  |  |  |
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List] | Other assets | Other assets |  |  |  |
Operating lease, right-of-use asset | $ 32.6 | $ 20.3 |  |  |  |
Operating Lease, Liability, Statement of Financial Position [Extensible List] | Other liabilities | Other liabilities |  |  |  |
Lease liabilities | $ 35.5 | $ 22.0 |  |  |  |
Net unrealized gains (losses) from foreign currency translation | (1.7) | (1.6) |  |  |  |
Change in fair value of contingent consideration - Ark | 61.3 | 48.7 | $ 17.3 |  |  |
P&C Insurance and Reinsurance (Ark/WM Outrigger) | Operating Segments |  |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |
Other long-term investments | 547.8 | 440.9 |  |  |  |
Contingent consideration | 155.3 | 94.0 |  |  |  | $ 22.5
Change in fair value of contingent consideration - Ark | $ 61.3 | 48.7 | $ 17.3 |  |  |
Third Point Re | P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |
Annual crediting rate | 3.00% |  |  |  |  |
Level 2 |  |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |
Variance threshold for outliers | $ 0.5 |  |  |  |  |
Variance threshold for outliers (as a percent) | 5.00% |  |  |  |  |
Level 2 | Fair value measured on a recurring basis | Other long-term investments |  |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |
Other long-term investments | $ 23.5 | 26.2 |  |  |  |
Level 3 | Fair value measured on a recurring basis | Other long-term investments |  |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |
Other long-term investments | 1,262.7 | 1,138.2 |  |  |  |
NAV | Fair value measured on a recurring basis | Other long-term investments |  |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |
Other long-term investments | 864.0 | $ 833.8 |  |  |  |
Subsidiary - HG Global |  |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |
Purchase of surplus notes | $ 503.0 |  |  |  |  |
Subsidiary - HG Global | Maximum |  |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |
Percentage of par value of policy reinsured | 15.00% |  |  |  |  |
Ark |  |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |
Percent of shares outstanding | 12.30% |  |  |  |  |
Subsidiary - Ark Insurance Holdings Limited |  |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |
Basic ownership | 72.10% | 72.00% |  |  |  |
Ownership percentage, after equity incentives | 61.90% | 61.90% |  |  |  |
Subsidiary - WM Outrigger Re | Preferred stocks |  |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |
Basic ownership | 100.00% | 100.00% |  |  |  |
Subsidiary - HG Global | Preferred stocks |  |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |
Basic ownership | 96.90% | 96.90% |  |  |  |
Subsidiary - HG Global | Common Stock |  |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |
Basic ownership | 88.40% | 88.40% |  |  |  |
Kudu |  |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |
Basic ownership | 90.40% |  |  |  |  |
Ownership percentage basic units outstanding |  | 89.60% |  | 89.30% | 99.10% |
Ownership percentage, fully diluted | 77.00% |  |  |  |  |
Ownership percentage, fully converted |  | 76.30% |  |  |  |
Bamboo |  |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |
Basic ownership | 72.80% |  |  |  |  |
Ownership percentage, fully diluted | 63.70% |  |  |  |  |

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