Related Party Transactions (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025	Dec. 31, 2025
Related Party Transaction [Line Items]
Services and other revenues	$ 957,831	$ 875,608	$ 2,462,310	$ 2,340,109
Premiums ceded	1,750,297	1,620,697	6,138,791	6,429,776
Reinsurance recoverables	17,300,376		17,300,376		$ 14,616,279
Retroactive reinsurance transaction with Hagerty Re, net losses and loss adjustment expenses			(62,202)	0
Fronting
Related Party Transaction [Line Items]
Premiums ceded	1,417,202	1,057,016	5,017,932	4,667,803
Unconsolidated entities managed by Nephila [Member] \| Fund Management
Related Party Transaction [Line Items]
Services and other revenues	42,200	30,300	120,300	85,000
Nephila Reinsurers [Member]
Related Party Transaction [Line Items]
Reinsurance recoverables	187,200		187,200		496,000
Nephila Reinsurers [Member] \| Fronting
Related Party Transaction [Line Items]
Gross premiums volume	58,500	162,900	1,100,000	1,800,000
Premiums ceded	58,500	162,900	1,100,000	1,800,000
Nephila Reinsurers [Member] \| Industry Loss Warranties (ILW) Program
Related Party Transaction [Line Items]
Gross premiums volume	18,800	7,000	36,800	81,500
Premiums ceded	18,800	7,000	36,800	81,500
Hagerty, Inc. [Member]
Related Party Transaction [Line Items]
Gross premiums volume	319,988	284,630	918,125	808,663
Premiums ceded	308,242	$ 219,309	880,483	$ 623,453
Reinsurance recoverables	$ 298,700		298,700		317,100
Hagerty, Inc. [Member] \| Retroactive reinsurance transaction with Hagerty Re
Related Party Transaction [Line Items]
Retroactive reinsurance transaction with Hagerty Re, net losses and loss adjustment expenses			$ 62,200
Retroactive reinsurance transaction with Hagerty Re, unearned premiums					$ 92,500