Liability for Unpaid Losses and Loss Adjustment Expenses Reconciliation of Claims Development to Aggregate Carrying Amount of the Liability for Unpaid Losses and LAE (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid losses and LAE, net of reinsurance	$ 1,441.3
Reinsurance recoverable on unpaid losses	476.9	$ 497.0	$ 532.5	$ 504.4
Unallocated LAE	63.0
Unpaid losses and loss adjustment expenses	$ 1,981.2	$ 2,069.4	$ 2,192.8	$ 2,207.9