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Accumulated Other Comprehensive Loss (Details Textual) - USD ($) $ in Thousands | 12 Months Ended
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Jul. 31, 2018 | Jul. 31, 2017 | Jul. 31, 2016
Schedule of accumulated balances for each classification of other comprehensive income (loss) |  |  |  |
Net other comprehensive income (loss) attributable to IDT Corporation | $ (359) | $ 1,401 |  | $ (5,544)
Unrealized (loss) gain on available-for-sale securities [Member] |  |  |  |
Schedule of accumulated balances for each classification of other comprehensive income (loss) |  |  |  |
Net other comprehensive income (loss) attributable to IDT Corporation | $ (177) | 2,126 | [1] | $ 583
Unrealized (loss) gain on available-for-sale securities [Member] | Marketable Securities [Member] |  |  |  |
Schedule of accumulated balances for each classification of other comprehensive income (loss) |  |  |  |
Net other comprehensive income (loss) attributable to IDT Corporation |  | 26 |  |
Unrealized (loss) gain on available-for-sale securities [Member] | Rafael Pharmaceuticals, Inc. [Member] |  |  |  |
Schedule of accumulated balances for each classification of other comprehensive income (loss) |  |  |  |
Net other comprehensive income (loss) attributable to IDT Corporation |  | $ 2,100 |  |
[1] | In fiscal 2017, net other comprehensive income attributable to IDT Corporation from unrealized gains on available-for-sale securities included unrealized gains on the Rafael convertible promissory notes of $2.1 million and unrealized gains, net on marketable securities of $26,000.

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