Unpaid Loss and Loss Adjustment Expense - Activity (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Unpaid loss and LAE at beginning of period			$ 262.3	$ 256.2
Less: Reinsurance recoverable at beginning of period			120.2	124.6
Net unpaid loss and LAE at beginning of period			142.1	131.6
Add: Incurred loss and LAE, net of reinsurance, related to:
Current year			220.6	219.0
Prior years			(6.3)	(3.6)
Total incurred	$ 77.9	$ 75.9	214.3	215.4
Deduct: Paid loss and LAE, net of reinsurance, related to:
Current year			138.7	133.4
Prior years			63.5	71.6
Total paid			202.2	205.0
Unpaid loss and LAE, net of reinsurance recoverable, at end of period	154.2	142.0	154.2	142.0
Reinsurance recoverable at end of period	140.0	113.1	140.0	113.1
Unpaid loss and LAE, gross of reinsurance recoverable, at end of period	$ 294.2	$ 255.1	$ 294.2	$ 255.1