Investments - Schedule of Investment Income and Expenses (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Net Investment Income [Line Items]
Income from equity method investments	$ 1.7	$ 0.7	$ 1.9	$ 1.2
Gross investment income	20.3	18.9	40.9	36.4
Interest expense on funds held under reinsurance	(12.3)	(5.7)	(20.2)	(10.8)
Investment expenses	(0.8)	(0.4)	(1.4)	(0.6)
Net investment income	7.2	12.8	19.3	25.0
Cash and cash equivalents
Net Investment Income [Line Items]
Investment income, interest	10.3	12.1	23.6	23.8
Fixed maturity securities
Net Investment Income [Line Items]
Investment income, interest	$ 8.3	$ 6.1	$ 15.4	$ 11.4

Investment Expense, Interest On Funds Held Under Reinsurance

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Amount, before investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

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Amount of income (loss) for proportionate share of equity method investee's income (loss).

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Amount before accretion (amortization) of purchase discount (premium) of interest income on nonoperating securities.

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Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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