Selected Quarterly Financial Data - Summary of Selected Quarterly Financial Data (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended										12 Months Ended
	Jul. 31, 2014	Apr. 30, 2014	Jan. 31, 2014	Oct. 31, 2013	Jul. 31, 2013		Apr. 30, 2013		Jan. 31, 2013	Oct. 31, 2012	Jul. 31, 2014	Jul. 31, 2013	Jul. 31, 2012
Selected Quarterly Financial Data [Abstract]
REVENUES	$ 420,687	$ 403,761	$ 406,423	$ 420,670	$ 412,109	[1]	$ 396,935	[2]	$ 411,456	$ 400,117	$ 1,651,541	$ 1,620,617	$ 1,506,283
Direct cost of revenues	349,313	332,376	335,258	350,319	344,673	[1]	331,163	[2]	344,486	335,251	1,367,266	1,355,573	1,269,386
Income from operations	5,813	9,170	7,574	7,283	1,365	[1]	15,687	[2]	5,655	6,684	29,840	29,391	(7,096)
Income (loss) from continuing operations	8,388	5,599	2,973	4,050	(1,532)	[1]	10,082	[2]	3,908	5,620	21,010	18,078	30,934
Net income (loss) attributable to IDT corporation	$ 7,709	$ 5,017	$ 2,535	$ 3,523	$ (3,651)	[1]	$ 8,691	[2]	$ 2,953	$ 3,614	$ 18,784	$ 11,607	$ 38,648
Income (loss) per share-basic, From continuing operations	$ 0.34	$ 0.22	$ 0.12	$ 0.17	$ (0.09)	[1]	$ 0.46	[2]	$ 0.16	$ 0.24	$ 0.85	$ 0.85	$ 1.45
Income (loss) per share-basic, Net income (loss)	$ 0.34	$ 0.22	$ 0.12	$ 0.17	$ (0.17)	[1]	$ 0.42	[2]	$ 0.14	$ 0.17	$ 0.85	$ 0.85	$ 1.87
Income (loss) per share-diluted, From continuing operations	$ 0.33	$ 0.22	$ 0.11	$ 0.15	$ (0.09)	[1]	$ 0.43	[2]	$ 0.15	$ 0.23	$ 0.82	$ 0.82	$ 1.36
Income (loss) per share-diluted, Net income (loss)	$ 0.33	$ 0.22	$ 0.11	$ 0.15	$ (0.17)	[1]	$ 0.39	[2]	$ 0.13	$ 0.16	$ 0.82	$ 0.82	$ 1.75

[1] Included in income from operations was a charge for impairment of building and improvements of $4.4 million.

[2] Included in income from operations was other operating gains of $9.6 million related to legal matters