Accumulated Other Comprehensive (Loss) Income (Details) $ in Thousands	9 Months Ended
	Apr. 30, 2016 USD ($)
Accumulated Other Comprehensive (Loss) Income [Line Items]
Beginning balance	$ 771
Ending balance	(782)
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	992
Less: reclassification for gain included in net income	(543)
Net other comprehensive income (loss) attributable to IDT Corporation	449
Ending balance	(126)
Unrealized Gain (Loss) on Available-for-Sale Securities [Member] | Other income (expense), 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	$ (2,002)
Less: reclassification for gain included in net income
Net other comprehensive income (loss) attributable to IDT Corporation	$ (2,002)
Ending balance	$ (656)
Foreign Currency Translation [Member] | Other income (expense), 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	(1,010)
Less: reclassification for gain included in net income	(543)
Net other comprehensive income (loss) attributable to IDT Corporation	(1,553)
Ending balance	(782)
Accumulated Other Comprehensive Income (Loss) [Member] | Other income (expense), net [Member]
Accumulated Other Comprehensive (Loss) Income [Line Items]
Less: reclassification for gain included in net income	$ (543)