v3.25.2
Investments (Narrative) (Details)
£ in Millions
1 Months Ended 3 Months Ended 6 Months Ended
May 31, 2024
USD ($)
Apr. 30, 2023
USD ($)
Jun. 30, 2025
USD ($)
shares
Jun. 30, 2024
USD ($)
Jun. 30, 2025
USD ($)
shares
Jun. 30, 2024
USD ($)
Jun. 30, 2025
GBP (£)
shares
Dec. 31, 2024
USD ($)
shares
Schedule of Investments [Line Items]                
Money Market Investments     $ 6,000,000.0   $ 6,000,000.0     $ 3,900,000
Marketable equity securities     889,515,000   889,515,000     852,434,000
Payments to Acquire Marketable Securities         4,823,000 $ 0    
Proceeds from sales of marketable equity securities         0 0    
Cumulative realized gain (loss) on marketable securities           400,000    
Payments for Advance to Affiliate         0 2,000,000    
Cumulative undistributed income in investments in affiliates     30,600,000   30,600,000     38,000,000.0
Cost method investments     62,400,000   62,400,000     $ 74,800,000
Impairment of cost method investments     12,679,000 $ 338,000 $ 12,679,000 744,000    
Concentration in single marketable equity security [Member] | Assets, Total [Member]                
Schedule of Investments [Line Items]                
Minimum percentage of total assets considered as significant concentrations         5.00%      
Related Party [Member] | Graham Healthcare Group [Member]                
Schedule of Investments [Line Items]                
Operating Revenues     $ 4,100,000 $ 4,400,000 $ 7,900,000 $ 8,500,000    
Markel Corporation [Member]                
Schedule of Investments [Line Items]                
Number of Shares Held in Investment | shares     55,430   55,430   55,430 55,430
Marketable equity securities     $ 110,700,000   $ 110,700,000     $ 95,700,000
Berkshire Hathaway [Member]                
Schedule of Investments [Line Items]                
Marketable equity securities     $ 542,200,000   $ 542,200,000      
Berkshire Hathaway [Member] | Common Class A [Member]                
Schedule of Investments [Line Items]                
Number of Shares Held in Investment | shares     422   422   422  
Berkshire Hathaway [Member] | Common Class B [Member]                
Schedule of Investments [Line Items]                
Number of Shares Held in Investment | shares     482,945   482,945   482,945  
Residential Home Health Illinois [Member] | Graham Healthcare Group [Member]                
Schedule of Investments [Line Items]                
Equity Method Investment, Ownership Percentage     40.00%   40.00%   40.00%  
Residential Hospice Illinois [Member] | Graham Healthcare Group [Member]                
Schedule of Investments [Line Items]                
Equity Method Investment, Ownership Percentage     40.00%   40.00%   40.00%  
Mary Free Bed at Home [Member] | Graham Healthcare Group [Member]                
Schedule of Investments [Line Items]                
Equity Method Investment, Ownership Percentage     40.00%   40.00%   40.00%  
Allegheny Health Network (AHN) Healthcare at Home [Member] | Graham Healthcare Group [Member]                
Schedule of Investments [Line Items]                
Equity Method Investment, Ownership Percentage     40.00%   40.00%   40.00%  
Intersection Holdings [Member]                
Schedule of Investments [Line Items]                
Equity Method Investment, Ownership Percentage     18.00%   18.00%   18.00%  
Payments for Advance to Affiliate   $ 30,000,000.0            
Loan Receivable, Payment Terms         5 years      
Loan Receivable Fixed Interest Rate         9.00%      
Advances to Affiliate     $ 24,300,000   $ 24,300,000      
N2K Networks [Member]                
Schedule of Investments [Line Items]                
Payments for Advance to Affiliate $ 2,000,000.0              
Loan Receivable Fixed Interest Rate 12.00%              
Equity Method Investment, Diluted Ownership Percentage     50.40%   50.40%   50.40%  
Realm [Member]                
Schedule of Investments [Line Items]                
Equity Method Investment, Diluted Ownership Percentage     41.40%   41.40%   41.40%  
York Joint Venture [Member] | KIHL [Member]                
Schedule of Investments [Line Items]                
Equity Method Investment, Ownership Percentage     45.00%   45.00%   45.00%  
Loan Receivable, Payment Terms         25 years      
Loan Receivable Fixed Interest Rate         7.00%      
Advances to Affiliate | £             £ 19.3  
Cumulative payments for advance to affiliate | £             £ 22.0