Selected Quarterly Financial Data (Unaudited) (Details Textual) - USD ($) $ in Thousands	3 Months Ended															12 Months Ended
	Jul. 31, 2019		Apr. 30, 2019	[1]	Jan. 31, 2019	[1]	Oct. 31, 2018		Jul. 31, 2018		Apr. 30, 2018		Jan. 31, 2018		Oct. 31, 2017	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2017
Selected Quarterly Financial Data (Unaudited) (Textual)
(Provision for) benefit from income taxes							$ (1,200)						$ 3,300			$ 123	$ 2,902	$ (2,021)
Severance expense									$ 300		$ 3,700					1,438	4,630
Other operating losses, net									400
Revenues	$ 356,128	[1],[2]	$ 341,255		$ 349,473		362,316	[1],[3]	392,647	[4]	$ 365,410	[5]	$ 395,883	[6]	$ 393,555	1,409,172	1,547,495	1,501,729
Foreign currency transaction losses							$ 1,200
Net loss attributable to noncontrolling interests	700															196	991	1,464
Accrual for non-income related taxes	8,000															8,000
Foreign currency transaction gains	$ 1,100															$ 1,779	$ (6)	$ 355
Breakage Revenue [Member]
Selected Quarterly Financial Data (Unaudited) (Textual)
Revenues									$ 9,500

[1] In fiscal 2019, the Company recorded an $8.0 million accrual for non-income related taxes related to one of its foreign subsidiaries. A portion of the accrual related to each of the fiscal quarters in fiscal 2019 (see Note 13). Accordingly, the Company corrected its consolidated financial statements for its fiscal quarters ended October 31, 2018, January 31, 2019, and April 30, 2019 to include the accrued expense and the related income tax benefit. The Company has determined that the adjustments were not material to its previously issued quarterly financial statements.

[2] Included in net income was gain on investments of $1.1 million and included in net income attributable to IDT Corporation was net loss attributable to noncontrolling interests of $0.7 million.

[3] Included in net loss was foreign currency transaction losses of $1.2 million and provision for income taxes of $1.2 million.

[4] Included in revenues was $9.5 million related to a change in estimate for recognizing certain breakage revenue. The Company recorded breakage revenue when the likelihood of the customer exercising its remaining rights became remote. In the fourth quarter of 2018, the Company changed when it generally deemed the likelihood remote from 24 or 36 months of no activity to 12 or 24 months of no activity. Included in income from operations was severance expense of $0.3 million and other operating losses, net of $0.4 million.

[5] Included in loss from operations was severance expense of $3.7 million.

[6] Included in net income was a benefit from income taxes of $3.3 million for an anticipated AMT credit refund.