Description of Business and Summary of Significant Accounting Policies - Deferred Policy Acquisition Costs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Accounting Policies [Abstract]
Deferred policy acquisition costs	$ 32.5		$ 32.5		$ 8.7
Amortization expense	$ 15.7	$ 5.3	$ 34.3	$ 12.5