Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ 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
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 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
Direct cost of revenues	295,353		282,791		291,178		304,693		325,133		307,165		337,229		336,510	1,174,015	1,306,037	1,275,708
Income (loss) from operations	(1,179)		449		(457)		182		10,468		(1,693)		(480)		83	(1,005)	8,378	5,549
Net (loss) income	882		2,457		(1,011)		(1,998)		8,536		(3,230)		1,690		(1,797)	330	5,199	9,641
Net (loss) income attributable to IDT Corporation	$ 1,574		$ 2,170		$ (1,311)		$ (2,299)		$ 8,242		$ (3,458)		$ 1,516		$ (2,092)	$ 134	$ 4,208	$ 8,177
Net (loss) income per share -basic	$ 0.06		$ 0.08		$ (0.05)		$ (0.10)		$ 0.33		$ (0.14)		$ 0.06		$ (0.08)	$ 0.01	$ 0.17	$ 0.35
Net (loss) income per share - diluted	$ 0.06		$ 0.08		$ (0.05)		$ (0.10)		$ 0.33		$ (0.14)		$ 0.06		$ (0.08)	$ 0.01	$ 0.17	$ 0.35

[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.