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Third-Party Reinsurance - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2021	Sep. 30, 2022	Sep. 30, 2021
Reinsurance [Line Items]
Reinsurance recoverables on unpaid losses		$ 521.4	$ 457.5
Reinsurance recoverables on paid losses		29.5	8.1
TPC Providers
Reinsurance [Line Items]
Reinsurance recoverables			299.9
Ark
Reinsurance [Line Items]
Reinsurance recoverables	$ 448.4	550.9	465.6
Ark \| TPC Providers
Reinsurance [Line Items]
Reinsurance recoverables		168.0	$ 299.9
Ark \| Third Point Re
Reinsurance [Line Items]
Annual crediting rate	3.00%
Decrease in investment	$ 31.7
Carrying value of investment		$ 20.3