Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Jul. 31, 2017		Jul. 31, 2016	Jul. 31, 2015
Schedule of accumulated balances for each classification of other comprehensive income (loss)
Beginning balance	$ (3,744)
Sale of interest in Fabrix Systems Ltd.				$ 640
Net other comprehensive income (loss) attributable to IDT Corporation	1,401		$ (5,544)	(2,999)
Ending balance	(2,343)		(3,744)
Unrealized gain (loss) on available-for-sale securities [Member]
Schedule of accumulated balances for each classification of other comprehensive income (loss)
Beginning balance	8		(575)	(8)
Sale of interest in Fabrix Systems Ltd.
Zedge Spin-Off
Other comprehensive income (loss) attributable to IDT Corporation before reclassification	2,449		1,126	(567)
Net other comprehensive income (loss) attributable to IDT Corporation	2,126	[1]	583
Ending balance	2,134		8	(575)
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 gain included in net income	(323)		(543)
Foreign currency translation [Member]
Schedule of accumulated balances for each classification of other comprehensive income (loss)
Beginning balance	(3,752)		1,346	3,676
Sale of interest in Fabrix Systems Ltd.				102
Zedge Spin-Off			1,029
Other comprehensive income (loss) attributable to IDT Corporation before reclassification	(725)		(6,127)	(2,432)
Net other comprehensive income (loss) attributable to IDT Corporation	(725)	[1]	(6,127)
Ending balance	(4,477)		(3,752)	1,346
Foreign currency translation [Member] | Other income (expense), net [Member]
Schedule of accumulated balances for each classification of other comprehensive income (loss)
Less: reclassification for gain included in net income
Accumulated other comprehensive income (loss) [Member]
Schedule of accumulated balances for each classification of other comprehensive income (loss)
Beginning balance	(3,744)		771	3,668
Sale of interest in Fabrix Systems Ltd.				102
Zedge Spin-Off			1,029
Other comprehensive income (loss) attributable to IDT Corporation before reclassification	1,724		(5,001)
Net other comprehensive income (loss) attributable to IDT Corporation	1,401	[1]	(5,544)	(2,999)
Ending balance	(2,343)		(3,744)	$ 771
Accumulated other comprehensive income (loss) [Member] | Other income (expense), net [Member]
Schedule of accumulated balances for each classification of other comprehensive income (loss)
Less: reclassification for gain included in net income	$ (323)		$ (543)

[1] In fiscal 2017, net other comprehensive income attributable to IDT Corporation from unrealized gains on available-for-sale securities included unrealized gains on the Rafael convertible promissory notes of $2.1 million and unrealized gains, net on marketable securities of $26,000.