v3.26.1
Schedule H, Line 4i – Schedule of Assets (Held at End of Year) (Details) - EBP WRPSP
12 Months Ended
Dec. 31, 2025
USD ($)
loan
shares
Dec. 31, 2024
loan
EBP, Schedule of Asset Held for Investment [Line Items]    
Participant loan, current value $ 19,471,900  
Total investments and participant loans $ 2,556,015,138  
Number of participant loans outstanding | loan 1,727 1,687
Participant loan, interest rate 3.25% 8.50%
Maximum    
EBP, Schedule of Asset Held for Investment [Line Items]    
Participant loan, interest rate 8.50%  
Participant loan, term 25 years 25 years
Minimum    
EBP, Schedule of Asset Held for Investment [Line Items]    
Participant loan, interest rate 3.25%  
Participant loan, term 1 year  
W. R. Berkley Corporation Common Stock Fund    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, current value $ 298,705,590  
Mutual Funds    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, current value 390,070,293  
Common Collective Trusts    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, current value 1,744,402,311  
Money Market Fund    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, current value 42,062,308  
Other Investments    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, current value 154,500  
Fixed Income Investments    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, current value $ 61,148,236  
Investment, Identifier [Axis]: Dodge & Cox Income Fund Class X    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 3,181,506  
Investment, current value $ 40,914,166  
Investment, Identifier [Axis]: FIAM Target Date 2010 Commingled Pool Class S    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 120,963  
Investment, current value $ 2,822,068  
Investment, Identifier [Axis]: FIAM Target Date 2015 Commingled Pool Class S    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 321,115  
Investment, current value $ 8,079,247  
Investment, Identifier [Axis]: FIAM Target Date 2020 Commingled Pool Class S    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 1,067,825  
Investment, current value $ 27,977,020  
Investment, Identifier [Axis]: FIAM Target Date 2025 Commingled Pool Class S    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 2,881,235  
Investment, current value $ 82,893,133  
Investment, Identifier [Axis]: FIAM Target Date 2030 Commingled Pool Class S    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 4,842,388  
Investment, current value $ 146,918,041  
Investment, Identifier [Axis]: FIAM Target Date 2035 Commingled Pool Class S    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 3,772,012  
Investment, current value $ 129,908,093  
Investment, Identifier [Axis]: FIAM Target Date 2040 Commingled Pool Class S    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 2,964,209  
Investment, current value $ 109,557,180  
Investment, Identifier [Axis]: FIAM Target Date 2045 Commingled Pool Class S    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 2,883,353  
Investment, current value $ 109,682,763  
Investment, Identifier [Axis]: FIAM Target Date 2050 Commingled Pool Class S    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 2,424,689  
Investment, current value $ 90,901,587  
Investment, Identifier [Axis]: FIAM Target Date 2055 Commingled Pool Class S    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 1,290,432  
Investment, current value $ 51,901,157  
Investment, Identifier [Axis]: FIAM Target Date 2060 Commingled Pool Class S    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 1,148,077  
Investment, current value $ 30,952,148  
Investment, Identifier [Axis]: FIAM Target Date 2065 Commingled Pool Class S    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 546,039  
Investment, current value $ 11,193,799  
Investment, Identifier [Axis]: FIAM Target Date Income Commingled Pool Class S    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 120,797  
Investment, current value $ 2,246,823  
Investment, Identifier [Axis]: Fidelity® Contrafund® Commingled Pool    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 5,498,345  
Investment, current value $ 306,367,794  
Investment, Identifier [Axis]: Fidelity® Growth Company Commingled Pool    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 3,594,613  
Investment, current value $ 318,806,269  
Investment, Identifier [Axis]: Fidelity® Government Income Fund    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 1,740,221  
Investment, current value $ 16,114,446  
Investment, Identifier [Axis]: Fidelity® Puritan® Fund - Class K6    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 3,588,632  
Investment, current value $ 61,939,783  
Investment, Identifier [Axis]: Fidelity® Small Cap Growth K6 Fund    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 1,857,952  
Investment, current value $ 35,895,638  
Investment, Identifier [Axis]: JPMorgan Mid Cap Value Fund Class L    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 711,128  
Investment, current value $ 22,692,110  
Investment, Identifier [Axis]: MFS International Diversification Fund Class R6    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 1,901,623  
Investment, current value $ 52,827,075  
Investment, Identifier [Axis]: Managed Income Portfolio II Class 4    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 61,148,236  
Investment, current value $ 61,148,236  
Investment, Identifier [Axis]: Neuberger Berman Mid Cap Growth Fund Class R6    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 1,359,313  
Investment, current value $ 19,941,119  
Investment, Identifier [Axis]: State Street Global All Cap Equity Ex-U.S. Index Securities Lending Series Fund Class II    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 1,605,700  
Investment, current value $ 29,813,037  
Investment, Identifier [Axis]: State Street Russell Small/Mid Cap® Index Securities Lending Series Fund Class II    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 1,504,492  
Investment, current value $ 31,227,241  
Investment, Identifier [Axis]: State Street S&P 500® Index Securities Lending Series Fund Class II    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 7,689,144  
Investment, current value $ 234,534,277  
Investment, Identifier [Axis]: State Street U.S. Bond Index Securities Lending Series Fund Class XIV    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 1,613,573  
Investment, current value $ 18,620,634  
Investment, Identifier [Axis]: T. Rowe Price Small-Cap Value Fund I Class    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 686,913  
Investment, current value $ 35,060,036  
Investment, Identifier [Axis]: Vanguard Equity-Income Fund Admiral Shares    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 959,533  
Investment, current value $ 89,150,186  
Investment, Identifier [Axis]: Vanguard Federal Money Market Fund Investor Shares    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 42,062,308  
Investment, current value $ 42,062,308  
Investment, Identifier [Axis]: Vanguard Inflation-Protected Securities Fund Institutional Shares    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 1,659,801  
Investment, current value $ 15,535,734  
Investment, Identifier [Axis]: W. R. Berkley Corporation Common Stock Fund    
EBP, Schedule of Asset Held for Investment [Line Items]    
Investment, number of shares (in shares) | shares 4,259,920  
Investment, current value $ 298,705,590