| Document and Entity Information - USD ($) | Sep. 30, 2020 | Dec. 09, 2020 | Mar. 31, 2020 |
| Cover [Abstract] | |||
| Document Type | 10-K/A | ||
| Amendment Flag | true | ||
| Amendment Description | Amendment No. 1 | ||
| Document Period End Date | Sep. 30, 2020 | ||
| Current Fiscal Year End Date | --09-30 | ||
| Document Transition Report | false | ||
| Entity Registrant Name | BARNWELL INDUSTRIES, INC. | ||
| Entity Incorporation, State or Country Code | DE | ||
| Entity File Number | 001-05103 | ||
| Entity Tax Identification Number | 72-0496921 | ||
| Entity Address, Address Line One | 1100 Alakea Street | ||
| Entity Address, Address Line Two | Suite 2900 | ||
| Entity Address, City or Town | Honolulu | ||
| Entity Address, State or Province | HI | ||
| Entity Address, Postal Zip Code | 96813-2840 | ||
| City Area Code | 808 | ||
| Local Phone Number | 531-8400 | ||
| Entity Well-known Seasoned Issuer | No | ||
| Entity Voluntary Filers | No | ||
| Entity Filer Category | Non-accelerated Filer | ||
| Entity Current Reporting Status | Yes | ||
| Entity Interactive Data Current | Yes | ||
| Entity Emerging Growth Company | false | ||
| Entity Shell Company | false | ||
| Entity Small Business | true | ||
| Entity Public Float | $ 1,990,000 | ||
| Entity Common Stock, Shares Outstanding | 8,277,160 | ||
| Document Fiscal Year Focus | 2020 | ||
| Document Fiscal Period Focus | FY | ||
| Entity Central Index Key | 0000010048 | ||
| Document Annual Report | true | ||
| Title of 12(b) Security | Common Stock, $0.50 par value | ||
| Trading Symbol | BRN | ||
| Security Exchange Name | NYSEAMER |
