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Investment Funds (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended		18 Months Ended
Investment Funds (Details) - USD ($) $ in Thousands	Jul. 01, 2022	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Jun. 30, 2022	Dec. 31, 2023
Schedule of Equity Method Investments [Line Items]
Unfunded commitments		$ 248,000		$ 248,000
Investment funds		1,607,381		1,607,381			$ 1,621,655
Income (Loss) from Investment Funds				868	$ 5,444
Written premiums ceded		576,002	$ 504,746	1,678,460	1,504,497
Fair Value
Schedule of Equity Method Investments [Line Items]
Trading account receivables from brokers and clearing organizations		410,756		410,756			303,614
Lifson Re
Schedule of Equity Method Investments [Line Items]
Percentage of reinsurance placements of share placed amounts	30.00%					22.50%
Written premiums ceded				315,000	348,000
Financial services
Schedule of Equity Method Investments [Line Items]
Investment funds		190,318		190,318			201,625
Income (Loss) from Investment Funds				11,471	(5,062)
Transportation
Schedule of Equity Method Investments [Line Items]
Investment funds		460,264		460,264			433,407
Income (Loss) from Investment Funds				(16,908)	(15,606)
Real Estate
Schedule of Equity Method Investments [Line Items]
Investment funds		300,937		300,937			344,278
Income (Loss) from Investment Funds				962	37,894
Energy
Schedule of Equity Method Investments [Line Items]
Investment funds		131,113		131,113			114,794
Income (Loss) from Investment Funds				9,473	3,921
Infrastructure
Schedule of Equity Method Investments [Line Items]
Investment funds		146,936		146,936			130,589
Income (Loss) from Investment Funds				12,730	7,813
Other funds
Schedule of Equity Method Investments [Line Items]
Investment funds		377,813		377,813			396,962
Income (Loss) from Investment Funds				(16,860)	$ (23,516)
Deferred compensation trust assets		$ 38,000		$ 38,000			$ 36,000