Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Oct. 31, 2018	Oct. 31, 2017
Schedule of accumulated balances for each classification of other comprehensive income (loss)
Beginning balance	$ (4,972)
Other comprehensive (loss) income attributable to IDT Corporation	522	$ (398)
Ending balance	(4,417)
Unrealized (loss) gain on available-for-sale securities [Member]
Schedule of accumulated balances for each classification of other comprehensive income (loss)
Beginning balance	(34)
Adjustment from the adoption of change in accounting for equity investments (see Note 8)	33
Adjusted balance, August 1, 2018	(1)
Other comprehensive (loss) income attributable to IDT Corporation	(2)
Ending balance	(3)
Foreign currency translation [Member]
Schedule of accumulated balances for each classification of other comprehensive income (loss)
Beginning balance	(4,938)
Adjustment from the adoption of change in accounting for equity investments (see Note 8)
Adjusted balance, August 1, 2018	(4,938)
Other comprehensive (loss) income attributable to IDT Corporation	524
Ending balance	(4,414)
Accumulated other comprehensive income (loss) [Member]
Schedule of accumulated balances for each classification of other comprehensive income (loss)
Beginning balance	(4,972)
Adjustment from the adoption of change in accounting for equity investments (see Note 8)	33
Adjusted balance, August 1, 2018	(4,939)
Other comprehensive (loss) income attributable to IDT Corporation	522
Ending balance	$ (4,417)