v3.26.1
Fair Value Measurements of Investments (Details) - EBP WRPSP - USD ($)
Dec. 31, 2025
Dec. 31, 2024
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value $ 2,536,543,238 $ 2,197,627,805
W. R. Berkley Corporation Common Stock Fund    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value 298,705,590 254,610,103
Mutual Funds    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value 390,070,293 365,920,928
Common Collective Trusts    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value 1,744,402,311 1,478,011,673
Money Market Fund    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value 42,062,308 29,422,425
Other Investments    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value 154,500 156,331
Fair Value, Inputs, Level 1, Level 2, and Level 3 | W. R. Berkley Corporation Common Stock Fund    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value 298,705,590 254,610,103
Fair Value, Inputs, Level 1, Level 2, and Level 3 | Mutual Funds    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value 390,070,293 365,920,928
Fair Value, Inputs, Level 1, Level 2, and Level 3 | Common Collective Trusts    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value 1,744,402,311 1,478,011,673
Fair Value, Inputs, Level 1, Level 2, and Level 3 | Money Market Fund    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value 42,062,308 29,422,425
Fair Value, Inputs, Level 1, Level 2, and Level 3 | Other Investments    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value 154,500 156,331
Fair Value, Inputs, Level 1    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value 2,475,395,002 2,128,121,460
Fair Value, Inputs, Level 1 | W. R. Berkley Corporation Common Stock Fund    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value 298,705,590 254,610,103
Fair Value, Inputs, Level 1 | Mutual Funds    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value 390,070,293 365,920,928
Fair Value, Inputs, Level 1 | Common Collective Trusts    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value 1,744,402,311 1,478,011,673
Fair Value, Inputs, Level 1 | Money Market Fund    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value 42,062,308 29,422,425
Fair Value, Inputs, Level 1 | Other Investments    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value 154,500 156,331
Fair Value, Inputs, Level 2    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value 0 0
Fair Value, Inputs, Level 2 | W. R. Berkley Corporation Common Stock Fund    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value 0 0
Fair Value, Inputs, Level 2 | Mutual Funds    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value 0 0
Fair Value, Inputs, Level 2 | Common Collective Trusts    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value 0 0
Fair Value, Inputs, Level 2 | Money Market Fund    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value 0 0
Fair Value, Inputs, Level 2 | Other Investments    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value 0 0
Fair Value, Inputs, Level 3    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value 0 0
Fair Value, Inputs, Level 3 | W. R. Berkley Corporation Common Stock Fund    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value 0 0
Fair Value, Inputs, Level 3 | Mutual Funds    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value 0 0
Fair Value, Inputs, Level 3 | Common Collective Trusts    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value 0 0
Fair Value, Inputs, Level 3 | Money Market Fund    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value 0 0
Fair Value, Inputs, Level 3 | Other Investments    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value 0 0
Fair Value Measured at Net Asset Value Per Share    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Investments, at fair value $ 61,148,236 $ 69,506,345