Accumulated Other Comprehensive Income (Details) $ in Thousands	3 Months Ended
	Oct. 31, 2015 USD ($)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 771
Ending balance	1,410
Unrealized Gain (Loss) on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(575)
Other comprehensive income attributable to IDT Corporation before reclassifications	1,071
Net other comprehensive income attributable to IDT Corporation	528
Ending balance	(47)
Unrealized Gain (Loss) on Available-for-Sale Securities [Member] | Other (expense) income, net [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Less: reclassification for gain included in net income	(543)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	1,346
Other comprehensive income attributable to IDT Corporation before reclassifications	111
Net other comprehensive income attributable to IDT Corporation	111
Ending balance	$ 1,457
Foreign Currency Translation [Member] | Other (expense) income, net [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Less: reclassification for gain included in net income
Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 771
Other comprehensive income attributable to IDT Corporation before reclassifications	1,182
Net other comprehensive income attributable to IDT Corporation	639
Ending balance	1,410
Accumulated Other Comprehensive Income [Member] | Other (expense) income, net [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Less: reclassification for gain included in net income	$ (543)