Related Party Transactions (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Dec. 31, 2024
Related Party Transaction [Line Items]
Services and other revenues	$ 803,918	$ 684,481	$ 1,464,501	$ 1,302,119
Premiums ceded	2,901,140	2,433,351	4,809,079	4,141,713
Reinsurance recoverables	12,789,658		12,789,658		$ 11,604,844
Nephila Reinsurers [Member]
Related Party Transaction [Line Items]
Reinsurance recoverables	986,200		986,200		968,900
Hagerty, Inc. [Member]
Related Party Transaction [Line Items]
Gross premium volume	304,106	275,642	524,033	473,924
Premiums ceded	234,459	211,052	404,144	363,737
Reinsurance recoverables	314,700		314,700		$ 308,800
Industry Loss Warranties (ILW) Program \| Nephila Reinsurers [Member]
Related Party Transaction [Line Items]
Gross premium volume	60,500	168,000	74,200	168,000
Premiums ceded	60,500	168,000	74,200	168,000
Fronting \| Nephila Reinsurers [Member]
Related Party Transaction [Line Items]
Gross premium volume	1,300,000	741,700	1,700,000	1,100,000
Premiums ceded	1,300,000	741,700	1,700,000	1,100,000
Fund Management \| Unconsolidated entities managed by Nephila [Member]
Related Party Transaction [Line Items]
Services and other revenues	$ 29,100	$ 21,800	$ 54,600	$ 41,100