Accumulated Other Comprehensive (Loss) Income (Details) $ in Thousands	6 Months Ended
	Jan. 31, 2016 USD ($)
Accumulated Other Comprehensive (Loss) Income [Line Items]
Beginning balance	$ 771
Ending balance	(2,744)
Unrealized Gain (Loss) on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive (Loss) Income [Line Items]
Beginning balance	(575)
Other comprehensive income (loss) attributable to IDT Corporation before reclassifications	928
Less: reclassification for gain included in net income	(543)
Net other comprehensive income (loss) attributable to IDT Corporation	385
Ending balance	(190)
Unrealized Gain (Loss) on Available-for-Sale Securities [Member] | Other (expense) income, net [Member]
Accumulated Other Comprehensive (Loss) Income [Line Items]
Less: reclassification for gain included in net income	(543)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive (Loss) Income [Line Items]
Beginning balance	1,346
Other comprehensive income (loss) attributable to IDT Corporation before reclassifications	(3,900)
Net other comprehensive income (loss) attributable to IDT Corporation	(3,900)
Ending balance	$ (2,554)
Foreign Currency Translation [Member] | Other (expense) income, net [Member]
Accumulated Other Comprehensive (Loss) Income [Line Items]
Less: reclassification for gain included in net income
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive (Loss) Income [Line Items]
Beginning balance	$ 771
Other comprehensive income (loss) attributable to IDT Corporation before reclassifications	(2,972)
Less: reclassification for gain included in net income	(543)
Net other comprehensive income (loss) attributable to IDT Corporation	(3,515)
Ending balance	(2,744)
Accumulated Other Comprehensive Income (Loss) [Member] | Other (expense) income, net [Member]
Accumulated Other Comprehensive (Loss) Income [Line Items]
Less: reclassification for gain included in net income	$ (543)