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Revolving Credit Loan Payable (Details) $ in Millions		12 Months Ended
Revolving Credit Loan Payable (Details) $ in Millions	Jul. 12, 2012 USD ($) BasisPoint	Jul. 31, 2017 USD ($)	Jul. 31, 2016 USD ($)
Revolving Credit Loan Payable (Textual)
Maximum principal amount of credit agreement	$ 25.0
Unused outstanding amount	$ 25.0
Line of credit maturity date		Apr. 30, 2018
Average percentage of commitment fee per annum	0.375%
Maximum amount of investments in and advances to affiliates at fair value	$ 110.0
Aggregate loans and advances to affiliates and subsidiaries		$ 94.9	$ 91.1
Line of credit utilized for letters of credit outstanding amount
Line of credit [Member]
Revolving Credit Loan Payable (Textual)
Line of credit facility, outstanding
July 12, 2012 [Member]
Revolving Credit Loan Payable (Textual)
Interest rate description		The principal outstanding bears interest per annum, at the option of IDT Telecom, at either (a) the U.S. Prime Rate less 125 basis points, or (b) the LIBOR rate adjusted by the Regulation D maximum reserve requirement plus 150 basis points.
Prime Rate [Member]
Revolving Credit Loan Payable (Textual)
U.S. Prime rate basis points \| BasisPoint	125