Statutory Capital and Surplus (Details) - USD ($)	Dec. 31, 2024	Dec. 31, 2023
Statutory Accounting Practices [Line Items]
Assets held-in-trust	$ 950,100,000	$ 948,500,000
P&C Insurance and Reinsurance (Ark/WM Outrigger) | WM Outrigger Re - Segment
Statutory Accounting Practices [Line Items]
Statutory capital and surplus	196,300,000
Minimum regulatory capital requirement	$ 1
P&C Insurance and Reinsurance (Ark/WM Outrigger) | Ark Insurance Holdings Limited - Segment
Statutory Accounting Practices [Line Items]
Percent of statutory capital balance	15.00%
Percent of statutory capital and surplus balance	25.00%
Maximum dividend payable	$ 336,700,000
Financial Guarantee (HG Global) | HG Global
Statutory Accounting Practices [Line Items]
Statutory capital and surplus	718,300,000
Minimum regulatory capital requirement	1
Net unrestricted cash	6,500,000
Accrued interest	157,500,000
Bamboo Captive
Statutory Accounting Practices [Line Items]
Statutory capital and surplus	6,800,000
Minimum regulatory capital requirement	500,000
Net unrestricted cash and short-term investments	11,400,000
Ark
Statutory Accounting Practices [Line Items]
Funds provided	361,500,000
Statutory capital and surplus	1,346,700,000
Minimum regulatory capital requirement	$ 577,700,000