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Goodwill And Intangible Assets (Narrative) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Goodwill And Intangible Assets [Line Items]      
Impairment of goodwill $ 0 $ 0 $ 80,000
Impairment of intangible assets (excluding goodwill) 0 0 0
Goodwill, carrying value 2,735,867 [1] 2,624,749 [1] 2,638,838
Estimated amortization of intangible assets for 2025 172,700    
Estimated amortization of intangible assets for 2026 165,500    
Estimated amortization of intangible assets for 2027 154,900    
Estimated amortization of intangible assets for 2028 146,100    
Estimated amortization of intangible assets for 2029 142,000    
Indefinite-lived intangible assets $ 90,400 $ 90,400  
Nephila Holdings Limited [Member]      
Goodwill And Intangible Assets [Line Items]      
Impairment of goodwill     80,000
Goodwill, carrying value     $ 221,800
[1] As of December 31, 2024 and 2023, goodwill was net of accumulated impairment losses of $190.6 million, of which $171.9 million was in other insurance operations and $18.7 million was in Markel Ventures.