Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Fixed maturities, at amortized cost	$ 7,761.7	$ 7,811.8
Fixed maturities, allowance for credit losses	7.1	9.6
Equity securities, at cost	232.4	247.6
Premium receivables, allowance for credit losses	12.0	13.1
Long-term Debt	$ 1,183.5	$ 1,195.1
Common stock, par value (in dollars per share)	$ 0.10	$ 0.10
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock, shares issued (in shares)	64,054,430	63,912,762
Common stock, shares outstanding (in shares)	64,054,430	63,912,762