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Investment Funds (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
	Jan. 01, 2025	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Schedule of Equity Method Investments [Line Items]
Unfunded commitments		$ 252,000		$ 252,000
Investment funds		1,430,991		1,430,991		$ 1,468,246
Income (Loss) from Investment Funds				59,713	$ 868
Written premiums ceded		609,326	$ 576,002	1,786,292	1,678,460
Fair Value
Schedule of Equity Method Investments [Line Items]
Trading account receivables from brokers and clearing organizations		113,330		113,330		$ 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				482,000	315,000
Financial services
Schedule of Equity Method Investments [Line Items]
Investment funds		177,082		177,082		$ 178,685
Income (Loss) from Investment Funds				2,054	11,471
Transportation
Schedule of Equity Method Investments [Line Items]
Investment funds		374,134		374,134		430,163
Income (Loss) from Investment Funds				9,917	(16,908)
Real Estate
Schedule of Equity Method Investments [Line Items]
Investment funds		272,874		272,874		286,426
Income (Loss) from Investment Funds				29,325	962
Energy
Schedule of Equity Method Investments [Line Items]
Investment funds		42,429		42,429		42,776
Income (Loss) from Investment Funds				667	9,473
Infrastructure
Schedule of Equity Method Investments [Line Items]
Investment funds		164,911		164,911		151,560
Income (Loss) from Investment Funds				10,279	12,730
Other funds
Schedule of Equity Method Investments [Line Items]
Investment funds		399,561		399,561		378,636
Income (Loss) from Investment Funds				7,471	$ (16,860)
Deferred compensation trust assets		$ 42,000		$ 42,000		$ 38,000

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