Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	Jul. 31, 2016	[1]	Apr. 30, 2016	[2]	Jan. 31, 2016	Oct. 31, 2015	Jul. 31, 2015	Apr. 30, 2015	[3]	Jan. 31, 2015	Oct. 31, 2014	[4]	Jul. 31, 2016	Jul. 31, 2015	Jul. 31, 2014
Selected Quarterly Financial Data [Abstract]
Revenues	$ 368,075		$ 355,154		$ 382,454	$ 390,578	$ 405,796	$ 383,930		$ 394,173	$ 412,878		$ 1,496,261	$ 1,596,777	$ 1,651,541
Direct cost of revenues	309,139		293,220		319,724	324,511	339,311	316,508		328,737	343,807		1,246,594	1,328,363	1,367,266
Income from operations	6,225		5,676		6,377	7,925	7,238	2,470		3,735	79,607		26,203	93,050	29,840
Net income	11,419		4,701		4,663	4,575	1,881	1,123		2,757	80,354		25,358	86,115	21,010
Net income attributable to IDT Corporation	$ 11,019		$ 4,237		$ 4,065	$ 4,193	$ 1,260	$ 565		$ 2,510	$ 80,155		$ 23,514	$ 84,490	$ 18,784
Net income per share-basic	$ 0.49		$ 0.19		$ 0.18	$ 0.18	$ 0.05	$ 0.02		$ 0.11	$ 3.52		$ 1.03	$ 3.69	$ 0.85
Net income per share-diluted	$ 0.48		$ 0.19		$ 0.18	$ 0.18	$ 0.05	$ 0.02		$ 0.11	$ 3.47		$ 1.03	$ 3.63	$ 0.82

[1] Included in income from operations was severance expense of $6.3 million and gain on sale of member interest in Visa Europe Ltd. of $7.5 million.

[2] Included in income from operations was gain on sale of interest in Fabrix Systems Ltd. of $1.1 million.

[3] Included in income from operations was severance expense of $6.2 million, gain on sale of interest in Fabrix Systems Ltd. of $1.2 million and other operating losses of $1.6 million.

[4] Included in income from operations was gain on sale of interest in Fabrix Systems Ltd. of $75.1 million.