Unpaid Loss and Loss Adjustment Expense - Activity (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
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 losses and LAE, net of reinsurance, related to:
Current year	170.5	73.2
Prior years	(3.2)	(1.3)
Total incurred	167.3	71.9	$ 54.7
Deduct: Paid losses and LAE, net of reinsurance, related to:
Current year	106.9	49.2
Prior years	30.1	7.5
Total paid	137.0	56.7
Unpaid loss and LAE, net of reinsurance recoverable, at end of period	131.6	25.2	10.0
Reinsurance recoverable at end of period	124.6	72.7	36.3
Unpaid loss and LAE, gross of reinsurance recoverable, at end of period	256.2	97.9	$ 46.3
Metromile
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Net unpaid loss and LAE at beginning of period	0.0
Deduct: Paid losses and LAE, net of reinsurance, related to:
Unpaid loss and LAE, net of reinsurance recoverable, at end of period	$ 76.2	$ 0.0