Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2017	Apr. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, July 31, 2016			$ (3,744)
Net other comprehensive loss attributable to IDT Corporation	$ 1,159	$ 1,962	(1,307)	$ (1,553)
Balance, April 30, 2017	(5,051)		(5,051)
Unrealized Gain (Loss) on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, July 31, 2016			8
Other comprehensive income (loss) attributable to IDT Corporation before reclassifications			370
Net other comprehensive loss attributable to IDT Corporation			39
Balance, April 30, 2017	47		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			(331)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, July 31, 2016			(3,752)
Other comprehensive income (loss) attributable to IDT Corporation before reclassifications			(1,346)
Net other comprehensive loss attributable to IDT Corporation			(1,346)
Balance, April 30, 2017	(5,098)		(5,098)
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 Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, July 31, 2016			(3,744)
Other comprehensive income (loss) attributable to IDT Corporation before reclassifications			(976)
Net other comprehensive loss attributable to IDT Corporation			(1,307)
Balance, April 30, 2017	$ (5,051)		(5,051)
Accumulated Other Comprehensive Loss [Member] | Other (expense) income, net [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Less: reclassification for gain included in net income			$ (331)