Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Statement of Financial Position [Abstract]
Fixed maturities, at amortized cost	$ 7,575.3	$ 7,358.2
Fixed maturities, allowance for credit losses	7.5	7.5
Equity securities, at cost	302.4	618.7
Premium receivables, allowance for credit losses	12.5	13.6
Long-term Debt	$ 1,204.1	$ 1,152.1
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)	63,884,152	63,684,628
Common stock, shares outstanding (in shares)	63,884,152	63,684,628