CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Fixed maturities, available for sale, amortized cost	$ 5,985.5	$ 5,842.5
Equity securities at cost	56.2	78.8
Fair value option of limited partnership interests	$ 1,137.8	$ 1,121.3
Preferred stock, par value (in usd per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	1,000,000	1,000,000
Preferred stock, shares issued (in shares)	0	0
Common stock, par value (in usd per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	75,000,000	75,000,000
Common stock, shares issued (in shares)	67,323,432	67,032,164
Treasury stock (in shares)	26,510,547	26,167,246
Fair Value, Recurring
Fair value option of limited partnership interests	$ 33.5	$ 28.9