| Cover Page | Oct. 20, 2020 |
| Entity Information [Line Items] | |
| Document Type | 8-K |
| Document Period End Date | Oct. 20, 2020 |
| Entity Registrant Name | W. R. BERKLEY CORP |
| Entity File Number | 1-15202 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 22-1867895 |
| Entity Address, Address Line One | 475 Steamboat Road |
| Entity Address, City or Town | Greenwich |
| Entity Address, State or Province | CT |
| Entity Address, Postal Zip Code | 06830 |
| City Area Code | (203) |
| Local Phone Number | 629-3000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $.20 per share |
| Trading Symbol | WRB |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0000011544 |
| Amendment Flag | false |
| 5.625% Subordinated Debentures due 2053 | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | 5.625% Subordinated Debentures due 2053 |
| Trading Symbol | WRB-PB |
| Security Exchange Name | NYSE |
| 5.90% Subordinated Debentures due 2056 | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | 5.90% Subordinated Debentures due 2056 |
| Trading Symbol | WRB-PC |
| Security Exchange Name | NYSE |
| 5.75% Subordinated Debentures due 2056 | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | 5.75% Subordinated Debentures due 2056 |
| Trading Symbol | WRB-PD |
| Security Exchange Name | NYSE |
| 5.70% Subordinated Debentures due 2058 | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | 5.70% Subordinated Debentures due 2058 |
| Trading Symbol | WRB-PE |
| Security Exchange Name | NYSE |
| 5.10% Subordinated Debentures due 2059 | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | 5.10% Subordinated Debentures due 2059 |
| Trading Symbol | WRB-PF |
| Security Exchange Name | NYSE |
| 4.25% Subordinated Debentures due 2060 | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | 4.25% Subordinated Debentures due 2060 |
| Trading Symbol | WRB-PG |
| Security Exchange Name | NYSE |
