| Cover | Sep. 30, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K/A |
| Amendment Flag | true |
| Amendment Description | Amendment |
| Document Period End Date | Sep. 30, 2020 |
| Entity File Number | 1-16371 |
| Entity Registrant Name | IDT CORPORATION |
| Entity Central Index Key | 0001005731 |
| Entity Tax Identification Number | 22-3415036 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, Address Line One | 520 Broad Street |
| Entity Address, City or Town | Newark |
| Entity Address, State or Province | NJ |
| Entity Address, Postal Zip Code | 07102 |
| City Area Code | (973) |
| Local Phone Number | 438-1000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Class B common stock, par value $.01 per share |
| Trading Symbol | IDT |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
