Unpaid Loss and Loss Adjustment Expense - Activity (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 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	72.4	57.9
Prior years	(6.5)	5.7
Total incurred	65.9	63.6
Deduct: Paid loss and LAE, net of reinsurance, related to:
Current year	33.7	26.9
Prior years	35.1	39.5
Total paid	68.8	66.4
Unpaid loss and LAE, net of reinsurance recoverable, at end of period	139.2	128.8
Reinsurance recoverable at end of period	124.8	116.4
Unpaid loss and LAE, gross of reinsurance recoverable, at end of period	$ 264.0	$ 245.2