Third-Party Reinsurance - Effects of Reinsurance (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Earned premiums:
Net earned premiums	$ 1,076.7	$ 664.2	$ 22.8
Ark
Written premiums:
Direct	1,452.0	1,058.7
Ceded	(256.8)	(199.6)
Net written premiums	1,195.2	859.1
Earned premiums:
Direct	1,324.2	886.4
Ceded	(280.8)	(249.1)
Net earned premiums	1,043.4	637.3
Losses and LAE:
Gross	814.9	442.9
Ceded	(278.5)	(128.1)
Net Losses and LAE	$ 536.4	$ 314.8

Amount of earned premiums ceded to other entities.

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