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Third-Party Reinsurance - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2021	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2020
Reinsurance [Line Items]
Reinsurance recoverables on unpaid losses		$ 396.0
Reinsurance recoverables on paid losses		16.7
Loss and loss adjustment expense reserves	$ 428.9	396.0	$ 447.5	$ 433.4
TPC Providers
Reinsurance [Line Items]
Loss and loss adjustment expense reserves	276.8	207.3	$ 331.0	$ 319.2
Ark
Reinsurance [Line Items]
Reinsurance recoverables	$ 448.4	412.7
Ark \| Third Point Re
Reinsurance [Line Items]
Annual crediting rate	3.00%
Decrease in investment	$ 31.7
Carrying value of investment		$ 20.6