Investments - Additional Information (Details) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2025 USD ($) security	Sep. 30, 2024 USD ($)	Sep. 30, 2025 USD ($) security	Sep. 30, 2024 USD ($)	Dec. 31, 2024 USD ($)
Investments, Debt and Equity Securities [Abstract]
Gross unrealized losses	$ 0.1		$ 0.1		$ 1.3
Pre-tax net realized capital gains (less than for 2024)	$ 0.2	$ 0.1	$ 0.3	$ 0.1
Number of debt securities held, unrealized loss position \| security	51		51
Gross unrealized losses, twelve months or more	$ 0.1		$ 0.1		0.5
Allowance for credit losses	0.0		0.0
Restricted investments	$ 80.8		$ 80.8		$ 81.3

Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount, excluding accrued interest, of increase (decrease) in allowance for credit loss on financing receivable. Excludes net investment in lease.

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Amount of realized gain (loss) on investment.

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Investments which are not defined as or included in marketable (debt, equity, or other) securities whose use is restricted in whole or in part, generally by contractual agreements or regulatory requirements. For use in an unclassified balance sheet.

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