Revolving Credit Loan Payable - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended		1 Months Ended			12 Months Ended
	Jul. 12, 2012	Jul. 31, 2014	Jul. 31, 2013	Aug. 31, 2014 Subsequent Event [Member]	Jul. 31, 2014 Line of Credit [Member]	Jul. 31, 2013 Line of Credit [Member]	Jul. 31, 2014 July 30, 2012 [Member]	Jul. 12, 2012 Prime Rate [Member] BasisPoint
Debt Instrument [Line Items]
Maximum principal amount of credit agreement	$ 25,000,000
Interest rate description							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
U.S Prime Rate basis points								125
Revolving credit loan payable		13,000,000	21,062,000		13,000,000	21,100,000
Interest rate of credit agreement		1.65%	1.69%
Average percentage of commitment fee per annum	0.375%
Line of credit facility, convenant compliance		IDT Telecom is required to comply with various affirmative and negative covenants as well as maintain certain financial targets and ratios during the term of the line of credit, including IDT Telecom may not pay any dividend on its capital stock and IDT Telecom's aggregate loans and advances to affiliates or subsidiaries may not exceed $90.0 million.
Maximum amount of investments in and advances to affiliates, at fair value	90,000,000
Repayments of credit agreement				13,000,000
Aggregate loans and advances to affiliates and subsidiaries		$ 73,700,000	$ 46,400,000