Deferred Acquisition Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Deferred Acquisition Costs:
Balance, January 1	$ 6.2	$ 3.5
Add:
Premium taxes and other acquisition costs	14.1	9.8
Direct commissions	3.6	2.4
Less:
Amortization of net deferred acquisition costs	(17.0)	(9.5)	$ (4.9)
Balance, December 31	6.9	6.2	3.5
Other Insurance Expense:
Amortization of net deferred acquisition costs	17.0	9.5	4.9
Period costs	27.0	14.6
Total other insurance expense	$ 44.0	$ 24.1	$ 14.4