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Accumulated Other Comprehensive Loss (Details Textual) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | ---
Jan. 31, 2018 | Jan. 31, 2017 | Jan. 31, 2018 | Jan. 31, 2017 | Jul. 31, 2017
Accumulated Other Comprehensive Loss (Textual) |  |  |  |  |
Net other comprehensive income (loss) attributable to IDT Corporation | $ 210 | $ 419 | $ (188) | $ (2,466) |
Unrealized gain (loss) on available-for-sale securities [Member] |  |  |  |  |
Accumulated Other Comprehensive Loss (Textual) |  |  |  |  |
Net other comprehensive income (loss) attributable to IDT Corporation |  |  | (150) |  |
Unrealized gain (loss) on available-for-sale securities [Member] | Rafael Pharmaceuticals, Inc. Series D Note [Member] |  |  |  |  |
Accumulated Other Comprehensive Loss (Textual) |  |  |  |  |
Net other comprehensive income (loss) attributable to IDT Corporation |  |  | $ 2,100 |  | $ 2,100

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