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Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
Income Taxes (Details) - USD ($) $ in Millions	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2025	Dec. 31, 2023
Investments, Owned, Federal Income Tax Note [Line Items]
Net deferred tax benefit			$ 73.0			$ 68.0
Effective tax rate	9.60%	4.80%	9.30%	6.60%
Forecast
Investments, Owned, Federal Income Tax Note [Line Items]
Income tax expense (benefit) pillar two top up					$ 1.7
P&C Insurance and Reinsurance (Ark/WM Outrigger) \| Ark
Investments, Owned, Federal Income Tax Note [Line Items]
Net deferred tax benefit			$ 51.0			51.0
Financial Guarantee (HG Global) \| HG Global
Investments, Owned, Federal Income Tax Note [Line Items]
Net deferred tax benefit			22.0			$ 17.0
Deferred tax liabilities	$ 5.0		$ 5.0