Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2017
Schedule of accumulated balances for each classification of other comprehensive income (loss)
Beginning balance	$ (4,972)
Net other comprehensive income (loss) attributable to IDT Corporation	81	$ (359)	$ 1,401
Ending balance	(4,858)	(4,972)
Unrealized (loss) gain on available-for-sale securities [Member]
Schedule of accumulated balances for each classification of other comprehensive income (loss)
Beginning balance	(34)	2,134	8
Other comprehensive income (loss) attributable to IDT Corporation before reclassification		(193)	2,449
Net other comprehensive income (loss) attributable to IDT Corporation	1	(177)	2,126	[1]
Rafael Spin-Off		(1,991)
Adjustment from the adoption of change in accounting for equity investments (see Note 8)	33
Adjusted balance at August 1, 2018	(1)
Ending balance		(34)	2,134
Unrealized (loss) gain on available-for-sale securities [Member] | Other (expense) income, net [Member]
Schedule of accumulated balances for each classification of other comprehensive income (loss)
Less: reclassification for gain included in net income		16	(323)
Foreign currency translation [Member]
Schedule of accumulated balances for each classification of other comprehensive income (loss)
Beginning balance	(4,938)	(4,477)	(3,752)
Other comprehensive income (loss) attributable to IDT Corporation before reclassification		(182)	(725)
Net other comprehensive income (loss) attributable to IDT Corporation	80	(182)	(725)	[1]
Rafael Spin-Off		(279)
Adjustment from the adoption of change in accounting for equity investments (see Note 8)
Adjusted balance at August 1, 2018	(4,938)
Ending balance	(4,858)	(4,938)	(4,477)
Foreign currency translation [Member] | Other (expense) income, 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	(4,972)	(2,343)	(3,744)
Other comprehensive income (loss) attributable to IDT Corporation before reclassification		(375)	1,724
Net other comprehensive income (loss) attributable to IDT Corporation	81	(359)	1,401	[1]
Rafael Spin-Off		(2,270)
Adjustment from the adoption of change in accounting for equity investments (see Note 8)	33
Adjusted balance at August 1, 2018	(4,939)
Ending balance	$ (4,858)	(4,972)	(2,343)
Accumulated other comprehensive income (loss) [Member] | Other (expense) income, net [Member]
Schedule of accumulated balances for each classification of other comprehensive income (loss)
Less: reclassification for gain included in net income		$ 16	$ (323)

[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.