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Variable Interest Entities (Details) $ in Millions		9 Months Ended
Variable Interest Entities (Details) $ in Millions	Dec. 05, 2025	Sep. 30, 2026 USD ($) debtInstrument	Dec. 31, 2025 USD ($)	Sep. 02, 2025
Variable Interest Entity [Line Items]
Assets held-in-trust		$ 992.6	$ 1,006.5
Subsidiary - HG Global
Variable Interest Entity [Line Items]
Purchase of surplus notes		$ 503.0
Subsidiary - HG Global \| Maximum
Variable Interest Entity [Line Items]
Percentage of par value of policy reinsured		15.00%
Outrigger Re
Variable Interest Entity [Line Items]
Short-term investments, at fair value		$ 48.0	$ 245.7
Bamboo SPV \| Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Ownership interest	27.90%	27.90%
Bamboo CRV \| Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Partnership interest, carrying value		$ 290.0
PassportCard/DavidShield \| Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Ownership interest		53.80%
Partnership interest, carrying value		$ 189.5
Equity method investments, fair value		$ 170.0
Number of private debt instruments \| debtInstrument		2
Fair Value		$ 19.5
BroadStreet \| Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Ownership interest		10.90%
Partnership interest, carrying value		$ 176.8
Limited Partnerships \| Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Partnership interest, carrying value		$ 392.1
Subsidiary - WM Outrigger Re \| Preferred Stock
Variable Interest Entity [Line Items]
Basic ownership		100.00%	100.00%
Subsidiary - Distinguished Managing General Agent
Variable Interest Entity [Line Items]
Basic ownership		55.30%	55.50%	55.50%