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Related Party Transactions (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Related Party Transaction [Line Items]
Services and other revenues	$ 684,481	$ 672,291	$ 1,302,119	$ 1,238,152
Premiums ceded	2,433,351	1,580,492	4,141,713	2,798,726
Reinsurance recoverables	9,756,660		9,756,660		$ 9,235,501
Nephila Reinsurers [Member]
Related Party Transaction [Line Items]
Reinsurance recoverables	687,100		687,100		794,300
Hagerty, Inc. [Member]
Related Party Transaction [Line Items]
Gross premium volume	275,642	236,225	473,924	401,196
Premiums ceded	211,052	181,841	363,737	306,469
Reinsurance recoverables	239,400		239,400		$ 214,800
Insurance-linked Securities Operations [Member] | Unconsolidated entities managed by Nephila [Member]
Related Party Transaction [Line Items]
Services and other revenues	21,800	20,800	41,100	30,600
Program services and other fronting [Member] | Nephila Reinsurers [Member]
Related Party Transaction [Line Items]
Gross premium volume	741,700	297,400	1,100,000	534,300
Premiums ceded	741,700	$ 297,400	1,100,000	$ 534,300
Industry Loss Warranties (ILW) Program
Related Party Transaction [Line Items]
Premiums ceded	168,000		168,000
Industry Loss Warranties (ILW) Program | Nephila Reinsurers [Member]
Related Party Transaction [Line Items]
Gross premium volume	$ 168,000		$ 168,000

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Amount, after valuation allowance, recoverable under reinsurance contracts. Examples include, but are not limited to, settled and unsettled claims, incurred but not reported losses, loss adjustment expense, policy benefits and policy reserves. Excludes premiums paid under reinsurance contracts.

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