Deferred Acquisition Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Deferred Acquisition Costs:
Balance, January 1	$ 6.9	$ 6.2
Add:
Premium taxes	16.1	14.1
Direct commissions	7.6	3.6
Less:
Amortization of net deferred acquisition costs	(21.8)	(17.0)	$ (9.5)
Balance, December 31	8.8	6.9	6.2
Other Insurance Expense:
Amortization of net deferred acquisition costs	21.8	17.0	9.5
Period costs	37.4	27.0
Total other insurance expense	$ 59.2	$ 44.0	$ 24.1