Third-Party Reinsurance - Remaining Gross and Net Reinsurance Recoverables (Details) - All Entities Except TCP Providers $ in Millions	Jun. 30, 2022 USD ($)
Reinsurance [Line Items]
Reinsurance recoverables	$ 216.3
Reinsurance Recoverables, Collateral	6.6
Net Reinsurance Recoverables	$ 209.7
Percent of reinsurance recoverables from insurers that are collateralized	100.00%
A+ or better
Reinsurance [Line Items]
Reinsurance recoverables	$ 126.8
Reinsurance Recoverables, Collateral	0.7
Net Reinsurance Recoverables	$ 126.1
Percent of reinsurance recoverables from insurers that are collateralized	60.20%
A- to A
Reinsurance [Line Items]
Reinsurance recoverables	$ 51.9
Reinsurance Recoverables, Collateral	0.0
Net Reinsurance Recoverables	$ 51.9
Percent of reinsurance recoverables from insurers that are collateralized	24.70%
B++ or lower and not rated
Reinsurance [Line Items]
Reinsurance recoverables	$ 37.6
Reinsurance Recoverables, Collateral	5.9
Net Reinsurance Recoverables	$ 31.7
Percent of reinsurance recoverables from insurers that are collateralized	15.10%