Business Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Apr. 30, 2015	Apr. 30, 2014	Apr. 30, 2015	Apr. 30, 2014
Segment Reporting Information [Line Items]
Revenues	$ 383,930us-gaap_Revenues	$ 403,761us-gaap_Revenues	$ 1,190,981us-gaap_Revenues	$ 1,230,855us-gaap_Revenues
Income (loss) from operations	2,470us-gaap_OperatingIncomeLoss	9,170us-gaap_OperatingIncomeLoss	85,813us-gaap_OperatingIncomeLoss	24,027us-gaap_OperatingIncomeLoss
Gain on sale of interest in Fabrix Systems Ltd.	1,235		76,864
Other operating gains (loss), net	(1,552)idt_OtherOperatingLossGains		(1,552)idt_OtherOperatingLossGains	1,209idt_OtherOperatingLossGains
Operating Segments [Member] \| Telecom Platform Services [Member]
Segment Reporting Information [Line Items]
Revenues	379,139	394,568	1,171,897	1,205,490
Income (loss) from operations	5,602	12,378	18,142	36,676
Gain on sale of interest in Fabrix Systems Ltd.
Other operating gains (loss), net				650
Operating Segments [Member] \| Consumer Phone Services [Member]
Segment Reporting Information [Line Items]
Revenues	2,098	2,625	6,652	8,491
Income (loss) from operations	324	517	985	1,358
Gain on sale of interest in Fabrix Systems Ltd.
Operating Segments [Member] \| All Other [Member]
Segment Reporting Information [Line Items]
Revenues	2,693	6,568	12,432	16,874
Income (loss) from operations	1,584	(443)	77,520	(2,242)
Gain on sale of interest in Fabrix Systems Ltd.	1,235		76,864
Other operating gains (loss), net				638
Operating Segments [Member] \| Corporate [Member]
Segment Reporting Information [Line Items]
Revenues
Income (loss) from operations	(5,040)	(3,282)	(10,834)	(11,765)
Gain on sale of interest in Fabrix Systems Ltd.
Other operating gains (loss), net	$ (1,552)		$ (1,552)	$ (79)

Other aggregate amounts of gains or losses resulting from operating activities not otherwise defined.

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- Definition

Amount of gain (loss) on sale or disposal of equity in securities of subsidiaries.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (13)(g)

-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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- Definition

The net result for the period of deducting operating expenses from operating revenues.

+ References

No definition available.

+ Details

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- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

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