Basis of Presentation and Significant Accounting Policies (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) segment	Oct. 25, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 20, 2022 account	May 26, 2022	May 25, 2022
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of reportable segments | segment	3
Other long-term investments	$ 1,998.2		$ 1,488.0
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Other assets		Other assets
Operating lease, right-of-use asset	$ 20.3		$ 25.2
Operating Lease, Liability, Statement of Financial Position [Extensible List]	Other liabilities		Other liabilities
Lease liabilities	$ 22.0		$ 27.1
Net unrealized foreign currency translation gain (losses)	$ (1.6)		(3.5)
Third Point Re | Ark
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Annual crediting rate	3.00%
Level 2
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Variance threshold for outliers	$ 0.5
Variance threshold for outliers (as a percent)	5.00%
Level 2 | Fair value measured on a recurring basis | Other long-term investments
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Other long-term investments	$ 26.2		14.8
Level 3 | Fair value measured on a recurring basis | Other long-term investments
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Other long-term investments	1,138.2		911.6
NAV | Fair value measured on a recurring basis | Other long-term investments
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Other long-term investments	$ 833.8		$ 561.6
Redeemable Preferred Stock | Outrigger Re Ltd
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of segregated accounts | account				4
Ark
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Percent of shares outstanding	12.50%
Subsidiary - HG Global | Preferred stocks
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Basic ownership	96.90%		96.90%
Subsidiary - HG Global | Common Stock
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Basic ownership	88.40%		88.40%
Subsidiary - Ark Insurance Holdings Limited
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Basic ownership	72.00%		72.00%
Ownership percentage, after equity incentives	61.90%		63.00%
Subsidiary - WM Outrigger Re | Preferred stocks
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Basic ownership	100.00%		100.00%
Subsidiary - Kudu Investment Management, LLC
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Basic ownership			89.60%
Ownership percentage basic units outstanding			89.30%		89.30%	99.10%
Ownership percentage, fully diluted	76.30%
Ownership percentage, fully converted			76.10%
Subsidiary - HG Global
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Purchase of surplus notes	$ 503.0
Subsidiary - HG Global | Maximum
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Percentage of par value of policy reinsured	15.00%
Subsidiary - WTM Partners
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Expected capital contribution		$ 500.0