Unpaid Loss and Loss Adjustment Expense - Activity (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Unpaid loss and LAE as of January 1	$ 262.3	$ 256.2	$ 97.9
Less: Reinsurance recoverable	120.2	124.6	72.7
Net unpaid loss and LAE as of January 1	142.1	131.6	25.2
Add: Incurred losses and LAE, net of reinsurance, related to:
Current year	287.0	286.2	170.5
Prior years	(10.0)	(5.8)	(3.2)
Total incurred	277.0	280.4	167.3
Deduct: Paid losses and LAE, net of reinsurance, related to:
Current year	195.4	189.4	106.9
Prior years	74.9	80.5	30.1
Total paid	270.3	269.9	137.0
Unpaid loss and LAE, net of reinsurance recoverable, as of December 31	148.6	142.1	131.6
Reinsurance recoverable at December 31	149.5	120.2	124.6
Unpaid loss and LAE, gross of reinsurance recoverable, as of December 31	298.1	262.3	256.2
Metromile
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Net unpaid loss and LAE as of January 1	0.0	76.2
Deduct: Paid losses and LAE, net of reinsurance, related to:
Unpaid loss and LAE, net of reinsurance recoverable, as of December 31	$ 0.0	$ 0.0	$ 76.2