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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Carrying amount due after one year of the balance sheet date (or one operating cycle, if longer) from tax authorities as of the balance sheet date representing refunds of overpayments or recoveries based on agreed-upon resolutions of disputes.

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The amount of the tax credit carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

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A description of the origin, nature, and characteristics of the tax credit carryforward.

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Income Tax and New Jersey Corporation Business Tax (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
	Dec. 22, 2017	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2018	Apr. 30, 2017	Sep. 30, 2017
Income Tax and New Jersey Corporation Business Tax (Textual)
Benefit from income taxes		$ 1,029	$ (2,162)	$ 931	$ (14,817)
Tax credits to be received						$ 21,100
Tax credit, description				In September 2017, the Company, IDT Domestic Telecom, Inc. (a subsidiary of the Company) and certain other affiliates, were certified by the New Jersey Economic Development Authority as having met all of the requirements of the Grow New Jersey Assistance Act Tax Credit Program. The corporation business tax credits to be received are a maximum of $21.1 million. The Company may claim a tax credit each tax year for ten years beginning in 2017. The tax credit can be applied to 100% of the Company's New Jersey tax liability each year, and the unused amount of the annual credit can be carried forward. In addition, the Company may apply for a tax credit transfer certificate to sell unused tax credits to another business. The tax credits must be sold for no less than 75% of the value of the tax credits. The tax credits are subject to reduction, forfeiture and recapture if, among other things, the number of full-time employees declines below the program or statewide minimum.
Maximum [Member]
Income Tax and New Jersey Corporation Business Tax (Textual)
U.S. federal statutory corporate tax rate				35.00%
Minimum [Member]
Income Tax and New Jersey Corporation Business Tax (Textual)
U.S. federal statutory corporate tax rate				21.00%
Elmion Netherlands B.V. [Member]
Income Tax and New Jersey Corporation Business Tax (Textual)
Benefit from income taxes					$ 16,600
AMT [Member]
Income Tax and New Jersey Corporation Business Tax (Textual)
Noncurrent receivable		$ 3,300		$ 3,300
Benefit from income taxes				$ 3,300
Tax Cuts and Jobs Act [Member]
Income Tax and New Jersey Corporation Business Tax (Textual)
U.S. federal statutory corporate tax rate	26.90%