Discontinued Operations (Details Textual) (USD $) In Millions, unless otherwise specified	1 Months Ended		3 Months Ended		9 Months Ended							1 Months Ended	3 Months Ended
	Oct. 31, 2011	Aug. 31, 2011	Apr. 30, 2013 Genie Energy [Member]	Apr. 30, 2012 Genie Energy [Member]	Apr. 30, 2013 Genie Energy [Member]	Apr. 30, 2012 Genie Energy [Member]	Jul. 31, 2012 Genie Energy [Member]	Oct. 28, 2011 Genie Energy [Member]	Oct. 28, 2011 IDT Energy [Member]	Oct. 28, 2011 Genie Oil and Gas [Member]	Oct. 31, 2011 Genie Spin-off [Member]	Sep. 30, 2011 IDT Entertainment [Member]	Aug. 31, 2007 IDT Entertainment [Member]
Discontinued Operations (Textual)
Ownership percentage at the time of spin-off								99.30%	100.00%	92.00%
Description of shares issued in spin-off transaction	Each of the Company's stockholders received one share of Genie Class A common stock for every share of the Company's Class A common stock and one share of Genie Class B common stock for every share of the Company's Class B common stock held of record as of the close of business on October 21, 2011.
Discontinued operations amount committed to fund prior to spin-off											$ 106.0
Reduction of selling, general and administrative expense			1.0	0.8	3.2	1.8
Receivable from subsidiaries included in other current assets			0.7		0.7		0.7
Period to receive additional consideration from Liberty Media Corporation													5 years
Payment to Liberty Media in connection with IDT Entertainment		3.5
Gain on sale of discontinued operations												$ 2.0