Deferred Acquisition Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Deferred Acquisition Costs:
Balance, January 1	$ 8.8	$ 6.9
Add:
Premium taxes	21.2	16.1
Direct commissions	12.7	7.6
Less:
Amortization of net deferred acquisition costs	(30.5)	(21.8)	$ (17.0)
Balance, December 31	12.2	8.8	6.9
Other Insurance Expense:
Amortization of net deferred acquisition costs	30.5	21.8	17.0
Period costs	46.3	37.4
Total other insurance expense	$ 76.8	$ 59.2	$ 44.0