Accumulated Other Comprehensive Loss (Details Textual) - Unrealized (loss) gain on available-for-sale securities [Member] $ in Thousands	12 Months Ended
	Jul. 31, 2017 USD ($)
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
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