Income Taxes (Details Textual) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Aug. 31, 2016	Jul. 31, 2016	Jul. 31, 2015	Jul. 31, 2014
Income Tax Contingency [Line Items]
Benefit from income taxes		$ 4,110	$ 6,088	$ 3,982
Federal and state net operating loss carryforwards		$ 175,000
Net operating loss carryforwards expiration date		2017
Net operating losses expiration date		Jul. 31, 2037
Foreign net operating losses		$ 183,000
Foreign net operating loss, no expiration		114,000
Foreign net operating loss, expiration in two to nine years		69,000
Losses limited under Internal Revenue Code		7,000
Cumulative undistributed foreign earnings		324,000
Accrued interest included in current income taxes payable
Net2Phone [Member]
Income Tax Contingency [Line Items]
Net operating losses expiration description		Expire through fiscal 2027.
Net operating losses, Federal		$ 77,000
IDT Global [Member]
Income Tax Contingency [Line Items]
Benefit from income taxes				$ 4,100
Subsequent Event [Member]
Income Tax Contingency [Line Items]
Tax credit, description	In August 2016, the Company and the New Jersey Economic Development Authority entered into an incentive agreement pursuant to which the Company may receive corporation business tax credits in exchange for investment in a qualified business facility and employment of the required number of full-time employees. The corporation business tax credits to be received are a maximum of $24.3 million. The Company is required to invest $5.3 million in its building located at 520 Broad Street, Newark, New Jersey, as well as retain 528 full-time jobs and create 40 new full-time jobs in New Jersey. The Company may claim a tax credit each tax year for ten years beginning when the Economic Development Authority accepts the Company's project completion certification. The Company must submit the project completion certification on or before December 9, 2016. 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.
Tax credits to be received	$ 24,300
Payments for investment in building	$ 5,300