Other Operating Expense, Net (Details 2) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Jul. 31, 2019	[1],[2]	Apr. 30, 2019		Jan. 31, 2019		Jan. 31, 2019	Oct. 31, 2018		Jul. 31, 2018	[4]	Apr. 30, 2018	[5]	Jan. 31, 2018		Oct. 31, 2017	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2017
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Other operating expense																	$ (7,726)	$ (2,398)	$ (10,475)
Provision for Benefit from income taxes								$ (1,200)						$ 3,300			123	2,902	(2,021)
Net income (loss)	$ 882		$ 2,457	[1]	$ (1,011)	[1]		(1,998)	[1],[3]	$ 8,536		$ (3,230)		1,690	[6]	$ (1,797)	330	5,199	9,641
Net loss attributable to IDT Corporation	$ 1,574		$ 2,170	[1]	$ (1,311)	[1]		$ (2,299)	[1],[3]	$ 8,242		$ (3,458)		$ 1,516	[6]	$ (2,092)	$ 134	$ 4,208	$ 8,177
Earnings per share attributable to IDT Corporation common stockholders:
Basic	$ 0.06		$ 0.08	[1]	$ (0.05)	[1]		$ (0.10)	[1],[3]	$ 0.33		$ (0.14)		$ 0.06	[6]	$ (0.08)	$ 0.01	$ 0.17	$ 0.35
Diluted	$ 0.06		$ 0.08	[1]	$ (0.05)	[1]		$ (0.10)	[1],[3]	$ 0.33		$ (0.14)		$ 0.06	[6]	$ (0.08)	$ 0.01	$ 0.17	$ 0.35
Error Correction [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Other operating expense			$ (2,300)		$ (2,000)			$ (1,100)
Provision for Benefit from income taxes			600		500			250
Net income (loss)			(1,700)		(1,500)			(850)
Net loss attributable to IDT Corporation			$ (1,700)		$ (1,500)			$ (850)
Earnings per share attributable to IDT Corporation common stockholders:
Basic			$ (0.07)		$ (0.06)			$ (0.04)
Diluted			$ (0.07)		$ (0.06)			$ (0.04)
Previously Reported [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Other operating expense			$ (120)		$ (90)			$ (195)
Provision for Benefit from income taxes			871		(1,736)			(1,189)
Net income (loss)			4,157		489			(1,148)
Net loss attributable to IDT Corporation			$ 3,870		$ 189			$ (1,449)
Earnings per share attributable to IDT Corporation common stockholders:
Basic			$ 0.15		$ 0.01			$ (0.06)
Diluted			$ 0.15		$ 0.01			$ (0.06)
As Adjusted [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Other operating expense			$ (2,420)				$ (2,090)	$ (1,295)
Provision for Benefit from income taxes			1,471				(1,236)	(939)
Net income (loss)			2,457				(1,011)	(1,998)
Net loss attributable to IDT Corporation			$ 2,170				$ (1,311)	$ (2,299)
Earnings per share attributable to IDT Corporation common stockholders:
Basic			$ 0.08				$ (0.05)	$ (0.10)
Diluted			$ 0.08				$ (0.05)	$ (0.10)

[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.