Related Party Transactions (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025
Related Party Transaction [Line Items]
Services and other revenues	$ 673,408	$ 660,583
Premiums ceded	1,939,976	1,907,939
Reinsurance recoverables	15,195,825		$ 14,616,279
Retroactive reinsurance transaction with Hagerty Re, net losses and loss adjustment expenses	(62,202)	0
Nephila Reinsurers [Member]
Related Party Transaction [Line Items]
Reinsurance recoverables	267,600		496,000
Hagerty, Inc. [Member]
Related Party Transaction [Line Items]
Reinsurance recoverables	298,000		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
Fronting
Related Party Transaction [Line Items]
Premiums ceded	1,495,631	1,353,214
Fronting \| Nephila Reinsurers [Member]
Related Party Transaction [Line Items]
Gross premium volume	267,400	389,300
Premiums ceded	267,400	389,300
Fronting \| Hagerty, Inc. [Member]
Related Party Transaction [Line Items]
Gross premium volume	253,300
Premiums ceded	242,100
Fund Management \| Unconsolidated entities managed by Nephila [Member]
Related Party Transaction [Line Items]
Services and other revenues	40,500	25,500
Underwriting [Member]
Related Party Transaction [Line Items]
Premiums ceded	$ 444,345	554,725
Underwriting [Member] \| Hagerty, Inc. [Member]
Related Party Transaction [Line Items]
Gross premium volume		219,900
Premiums ceded		$ 169,700