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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, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Income Tax Contingency [Line Items]
Net deferred tax benefit							$ (68.0)
Effective tax rate (in percent)	(27.60%)	9.60%	15.40%	9.30%
Bermuda
Income Tax Contingency [Line Items]
Deferred tax liabilities					$ 5.1
Deferred tax expense (benefit)					(5.1)
LUXEMBOURG
Income Tax Contingency [Line Items]
Deferred tax expense (benefit)					$ (78.1)
P&C Insurance and Reinsurance (Ark/WM Outrigger) \| Ark
Income Tax Contingency [Line Items]
Net deferred tax benefit							(51.0)
HG Global
Income Tax Contingency [Line Items]
Net deferred tax benefit							$ (17.0)
Deferred tax liabilities						$ 5.0
Deferred tax expense (benefit)						$ (5.0)