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-Number 210
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-Subsection 15
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-Name Accounting Standards Codification
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-SubTopic 10
-Topic 230
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SCHEDULE I - SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Summary of investments other than investments in related parties
Cost	$ 5,878.3
Carrying Value	6,477.6
Fair Value	6,477.6
Dividend and income distributions from equity method eligible investments	71.4	$ 67.0	$ 68.9
Fixed maturity investments
Summary of investments other than investments in related parties
Cost	2,569.2
Carrying Value	2,511.6
Fair Value	2,511.6
U.S. Government and agency obligations
Summary of investments other than investments in related parties
Cost	461.8
Carrying Value	462.1
Fair Value	462.1
Debt securities issued by corporations
Summary of investments other than investments in related parties
Cost	1,444.5
Carrying Value	1,414.2
Fair Value	1,414.2
Municipal obligations
Summary of investments other than investments in related parties
Cost	3.2
Carrying Value	3.2
Fair Value	3.2
Mortgage and asset-backed securities
Summary of investments other than investments in related parties
Cost	400.2
Carrying Value	373.9
Fair Value	373.9
Collateralized loan obligations
Summary of investments other than investments in related parties
Cost	237.3
Carrying Value	236.7
Fair Value	236.7
Foreign government and agency obligations
Summary of investments other than investments in related parties
Cost	22.2
Carrying Value	21.5
Fair Value	21.5
Short-term investments
Summary of investments other than investments in related parties
Cost	964.2
Carrying Value	964.2
Fair Value	964.2
Equity Method Investments
Summary of investments other than investments in related parties
Cost	1,083.8
Carrying Value	1,423.3
Equity Method Investments \| Investment in MediaAlpha
Summary of investments other than investments in related parties
Cost	59.2
Carrying Value	201.6
Fair Value	201.6
Common equity securities - Industrial, Miscellaneous and Other
Summary of investments other than investments in related parties
Cost	373.7
Carrying Value	425.4
Fair Value	425.4
Exchange-traded funds
Summary of investments other than investments in related parties
Cost	163.3
Carrying Value	224.6
Fair Value	224.6
Total common equity securities
Summary of investments other than investments in related parties
Cost	537.0
Carrying Value	650.0
Fair Value	650.0
Other long-term investments
Summary of investments other than investments in related parties
Cost	1,748.7
Carrying Value	2,150.2
Fair Value	$ 2,150.2