Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2018	Jan. 31, 2017
Schedule of accumulated balances for each classification of other comprehensive income (loss)
Beginning balance			$ (2,343)
Net other comprehensive loss attributable to IDT Corporation	$ 210	$ 419	(188)	$ (2,466)
Ending balance	(2,531)		(2,531)
Unrealized Gain (Loss) on Available-for-Sale Securities [Member]
Schedule of accumulated balances for each classification of other comprehensive income (loss)
Beginning balance			2,134
Other comprehensive loss attributable to IDT Corporation before reclassifications			(159)
Net other comprehensive loss attributable to IDT Corporation			(150)
Ending balance	1,984		1,984
Unrealized Gain (Loss) on Available-for-Sale Securities [Member] | Other income (expense), net [Member]
Schedule of accumulated balances for each classification of other comprehensive income (loss)
Less: reclassification for loss included in net loss			9
Foreign Currency Translation [Member]
Schedule of accumulated balances for each classification of other comprehensive income (loss)
Beginning balance			(4,477)
Other comprehensive loss attributable to IDT Corporation before reclassifications			(38)
Net other comprehensive loss attributable to IDT Corporation			(38)
Ending balance	(4,515)		(4,515)
Foreign Currency Translation [Member] | Other income (expense), net [Member]
Schedule of accumulated balances for each classification of other comprehensive income (loss)
Less: reclassification for loss included in net loss
Accumulated Other Comprehensive Loss [Member]
Schedule of accumulated balances for each classification of other comprehensive income (loss)
Beginning balance			(2,343)
Other comprehensive loss attributable to IDT Corporation before reclassifications			(197)
Net other comprehensive loss attributable to IDT Corporation			(188)
Ending balance	$ (2,531)		(2,531)
Accumulated Other Comprehensive Loss [Member] | Other income (expense), net [Member]
Schedule of accumulated balances for each classification of other comprehensive income (loss)
Less: reclassification for loss included in net loss			$ 9