Fair Value of Financial Instruments - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Percentage of level 3 invested assets in total investment portfolio	9.50%		9.50%		9.50%
Net investment gains (losses) included in net income	$ (6.6)	$ 3.2	$ (7.6)	$ 5.6
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Net investment gains (losses) included in net income	$ (0.4)	$ 0.2	$ 0.1	$ 0.2