Unpaid Loss and Loss Adjustment Expense - Activity (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Unpaid loss and LAE at beginning of period	$ 97.9	$ 46.3
Less: Reinsurance recoverable at beginning of period	72.7	36.3
Net unpaid loss and LAE at beginning of period	25.2	10.0
Add: Incurred loss and LAE, net of reinsurance, related to:
Current year	24.8	16.7
Prior years	(0.4)	(0.2)
Total incurred	24.4	16.5
Deduct: Paid loss and LAE, net of reinsurance, related to:
Current year	10.6	8.3
Prior years	10.8	3.9
Total paid	21.4	12.2
Unpaid loss and LAE, gross of reinsurance recoverable, at end of period	28.2	14.3
Reinsurance recoverable at end of period	79.4	47.9
Unpaid loss and LAE, gross of reinsurance recoverable, at end of period	$ 107.6	$ 62.2