Unpaid Loss and Loss Adjustment Expense - Activity in the Liability for Unpaid Loss and LAE (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Unpaid loss and LAE at beginning of period			$ 298.1	$ 262.3
Less: Reinsurance recoverable at beginning of period			149.5	120.2
Net unpaid loss and LAE at beginning of period			148.6	142.1
Add: Incurred loss and LAE, net of reinsurance, related to:
Current year			271.4	220.6
Prior years			(18.9)	(6.3)
Total incurred	$ 89.6	$ 77.9	252.5	214.3
Deduct: Paid loss and LAE, net of reinsurance, related to:
Current year			171.2	138.7
Prior years			65.9	63.5
Total paid			237.1	202.2
Unpaid loss and LAE, net of reinsurance recoverable, at end of period	164.0	154.2	164.0	154.2
Reinsurance recoverable at end of period	148.1	140.0	148.1	140.0
Unpaid loss and LAE, gross of reinsurance recoverable, at end of period	$ 312.1	$ 294.2	$ 312.1	$ 294.2