Unpaid Loss and Loss Adjustment Expense - Activity (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Unpaid loss and LAE at beginning of period			$ 256.2	$ 97.9
Less: Reinsurance recoverable at beginning of period			124.6	72.7
Net unpaid loss and LAE at beginning of period			131.6	25.2
Add: Incurred loss and LAE, net of reinsurance, related to:
Current year			219.0	106.9
Prior years			(3.6)	(1.1)
Total incurred	$ 75.9	$ 53.3	215.4	105.8
Deduct: Paid loss and LAE, net of reinsurance, related to:
Current year			133.4	65.9
Prior years			71.6	21.9
Total paid			205.0	87.8
Unpaid loss and LAE, net of reinsurance recoverable, at end of period	142.0	111.3	142.0	111.3
Reinsurance recoverable at end of period	113.1	109.3	113.1	109.3
Unpaid loss and LAE, gross of reinsurance recoverable, at end of period	$ 255.1	$ 220.6	$ 255.1	$ 220.6