Revenue Recognition (Details 1) - USD ($) $ in Thousands	3 Months Ended															12 Months Ended
	Jul. 31, 2019	[1],[2]	Apr. 30, 2019	[1]	Jan. 31, 2019	[1]	Oct. 31, 2018	[1],[3]	Jul. 31, 2018	[4]	Apr. 30, 2018	[5]	Jan. 31, 2018	[6]	Oct. 31, 2017	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2017
Outside the United States:
Total outside the United States																$ 473,318	$ 498,165	$ 467,934
Revenues, Total	$ 356,128		$ 341,255		$ 349,473		$ 362,316		$ 392,647		$ 365,410		$ 395,883		$ 393,555	1,409,172	1,547,495	1,501,729
United States [Member]
Outside the United States:
Revenues, Total																935,854	1,049,330	1,033,795
United Kingdom [Member]
Outside the United States:
Total outside the United States																195,682	220,260	211,249
Netherlands [Member]
Outside the United States:
Total outside the United States																192,284	191,076	175,869
Other [Member]
Outside the United States:
Total outside the United States																85,352	86,829	80,816
Telecom & Payment Services [Member]
Outside the United States:
Total outside the United States																459,911	490,469	460,793
Revenues, Total																1,361,908	1,511,473	1,469,987
Telecom & Payment Services [Member] | United States [Member]
Outside the United States:
Revenues, Total																901,997	1,021,004	1,009,194
Telecom & Payment Services [Member] | United Kingdom [Member]
Outside the United States:
Total outside the United States																195,661	220,257	211,249
Telecom & Payment Services [Member] | Netherlands [Member]
Outside the United States:
Total outside the United States																192,284	191,076	175,869
Telecom & Payment Services [Member] | Other [Member]
Outside the United States:
Total outside the United States																71,966	79,136	73,675
Total net2phone [Member]
Outside the United States:
Total outside the United States																13,407	7,696	7,141
Revenues, Total																47,264	34,857	29,450
Total net2phone [Member] | United States [Member]
Outside the United States:
Revenues, Total																33,857	27,161	22,309
Total net2phone [Member] | United Kingdom [Member]
Outside the United States:
Total outside the United States																21	3
Total net2phone [Member] | Netherlands [Member]
Outside the United States:
Total outside the United States
Total net2phone [Member] | Other [Member]
Outside the United States:
Total outside the United States																13,386	7,693	7,141
All Other [Member]
Outside the United States:
Total outside the United States
Revenues, Total																	1,165	2,292
All Other [Member] | United States [Member]
Outside the United States:
Revenues, Total																	1,165	2,292
All Other [Member] | United Kingdom [Member]
Outside the United States:
Total outside the United States
All Other [Member] | Netherlands [Member]
Outside the United States:
Total outside the United States
All Other [Member] | Other [Member]
Outside the United States:
Total outside the United States

[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.