Income Taxes - Additional Information (Detail) (USD $)	12 Months Ended					1 Months Ended	3 Months Ended
	Jul. 31, 2012	Jul. 31, 2011	Jul. 31, 2010	Jul. 31, 2012 Net Two Phone [Member]	Jul. 31, 2012 IDT Spectrum [Member]	Apr. 30, 2011 PUERTO RICO	Aug. 31, 2010 Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Reversal of portion of the valuation allowance	$ 36,900,000
Liquidated entity						Feb. 28, 2011
Tax claiming refund						4,800,000
Income tax expense reversal						3,500,000
Income tax expense	(42,756,000)	(12,484,000)	(8,674,000)				2,000,000
Federal and state net operating loss carryforwards	183,000,000
Foreign net operating losses	140,000,000
Net operating losses				98,000,000	124,000,000
Losses limited under Internal Revenue Code	7,000,000
Cumulative undistributed foreign earnings	355,000,000
Agreement on certain state tax position	3,800,000
Interest on Income Taxes		100,000	100,000
Accrued interest included in current income taxes payable		$ 200,000