Investment Funds (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended		12 Months Ended
	Jan. 01, 2025	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Dec. 31, 2024
Schedule of Equity Method Investments [Line Items]
Unfunded commitments		$ 272,000		$ 272,000
Investment funds		1,492,258		1,492,258		$ 1,468,246
Income (Loss) from Investment Funds				54,291	$ (3,873)
Written premiums ceded		626,330	$ 590,993	1,176,966	1,102,458
Fair Value
Schedule of Equity Method Investments [Line Items]
Trading account receivables from brokers and clearing organizations		138,891		138,891		$ 60,327
Lifson Re
Schedule of Equity Method Investments [Line Items]
Percentage of reinsurance placements of share placed amounts	32.50%					30.00%
Written premiums ceded				362,000	206,000
Financial services
Schedule of Equity Method Investments [Line Items]
Investment funds		181,509		181,509		$ 178,685
Income (Loss) from Investment Funds				5,614	12,880
Transportation
Schedule of Equity Method Investments [Line Items]
Investment funds		434,518		434,518		430,163
Income (Loss) from Investment Funds				12,277	(18,231)
Real Estate
Schedule of Equity Method Investments [Line Items]
Investment funds		276,904		276,904		286,426
Income (Loss) from Investment Funds				20,714	(3,732)
Energy
Schedule of Equity Method Investments [Line Items]
Investment funds		42,193		42,193		42,776
Income (Loss) from Investment Funds				(1,234)	8,505
Infrastructure
Schedule of Equity Method Investments [Line Items]
Investment funds		161,019		161,019		151,560
Income (Loss) from Investment Funds				9,064	7,828
Other funds
Schedule of Equity Method Investments [Line Items]
Investment funds		396,115		396,115		378,636
Income (Loss) from Investment Funds				7,856	$ (11,123)
Deferred compensation trust assets		$ 42,000		$ 42,000		$ 38,000