Related Party Transactions (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Related Party Transaction [Line Items]
Services and other revenues	$ 735,872	$ 725,627	$ 2,037,991	$ 1,963,779
Premiums ceded	1,489,573	1,651,001	5,631,286	4,449,727
Reinsurance recoverables	10,746,213		10,746,213		$ 9,235,501
Nephila Reinsurers [Member]
Related Party Transaction [Line Items]
Reinsurance recoverables	711,500		711,500		794,300
Hagerty, Inc. [Member]
Related Party Transaction [Line Items]
Gross premium volume	253,071	227,693	726,995	628,889
Premiums ceded	193,844	174,455	557,581	480,924
Reinsurance recoverables	264,200		264,200		$ 214,800
Insurance-linked Securities Operations [Member] | Unconsolidated entities managed by Nephila [Member]
Related Party Transaction [Line Items]
Services and other revenues	25,100	43,600	66,200	74,100
Program services and other fronting [Member] | Nephila Reinsurers [Member]
Related Party Transaction [Line Items]
Gross premium volume	94,300	501,800	1,200,000	1,000,000
Premiums ceded	94,300	$ 501,800	1,200,000	$ 1,000,000
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