Reinsurance LPT Agreement (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reinsurance Agreement [Line Items]
Unpaid losses	$ 476.3	$ 496.6
Recoverables was related to the LPT agreement	$ 328.7	353.5
Reinsurance quota share, percentage	100.00%
LPT collateral held in trust account	$ 432.5	369.1
Ceded premiums written	6.6	5.2	$ 5.4
Coverage provided under LPT agreement	2,000.0
Paid losses and LAE claims related to LPT	838.8
Amortization of deferred gain	8.4	10.5	10.7
Unpaid losses and loss adjustment expenses	1,981.2	2,069.4	2,192.8	$ 2,207.9
LPT Agreement [Member]
Reinsurance Agreement [Line Items]
Liabilities for the incurred but unpaid losses and LAE related to claims prior to July 1, 1995	1,500.0
Ceded premiums written	775.0
Change Due to Estimated Reserves Ceded Under the LPT Agreement [Member]
Reinsurance Agreement [Line Items]
Amortization of deferred gain	2.6	1.2	1.8
Unpaid losses and loss adjustment expenses	(4.9)	(4.2)	(5.3)
Change to Contingent Profit Commission [Member]
Reinsurance Agreement [Line Items]
Amortization of deferred gain	$ 0.5	$ 0.2	$ 0.2