CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Statement of Financial Position [Abstract]
Fixed maturities, available for sale, amortized cost	$ 5,857.7	$ 5,842.5
Equity securities at cost	77.8	78.8
Limited partnership interests, carried under Fair Value Options	$ 1,125.6	$ 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)	67,124,719	67,032,164
Treasury stock (in shares)	26,170,486	26,167,246