Third-Party Reinsurance - Remaining Gross and Net Reinsurance Recoverables (Details) - All Entities Except TCP Providers $ in Millions	Sep. 30, 2022 USD ($)
Reinsurance [Line Items]
Reinsurance recoverables	$ 382.9
Reinsurance Recoverables, Collateral	119.4
Net Reinsurance Recoverables	$ 263.5
Percent of reinsurance recoverables from insurers that are collateralized	100.00%
A+ or better
Reinsurance [Line Items]
Reinsurance recoverables	$ 178.3
Reinsurance Recoverables, Collateral	0.0
Net Reinsurance Recoverables	$ 178.3
Percent of reinsurance recoverables from insurers that are collateralized	67.70%
A- to A
Reinsurance [Line Items]
Reinsurance recoverables	$ 78.9
Reinsurance Recoverables, Collateral	0.0
Net Reinsurance Recoverables	$ 78.9
Percent of reinsurance recoverables from insurers that are collateralized	29.90%
B++ or lower and not rated
Reinsurance [Line Items]
Reinsurance recoverables	$ 125.7
Reinsurance Recoverables, Collateral	119.4
Net Reinsurance Recoverables	$ 6.3
Percent of reinsurance recoverables from insurers that are collateralized	2.40%