Escrow deposit disbursement.

No definition available.

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Namespace Prefix:	idt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Minority interest combined ownership percentage by parent and non controlling interests.

+ References

No definition available.

+ Details

Name:	idt_MinorityInterestCombinedOwnershipPercentageByParentAndNonControllingInterests
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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash inflow associated with divestiture of interest in consolidated subsidiaries parent only portion.

+ References

No definition available.

+ Details

Name:	idt_ProceedsFromDivestitureOfInterestInConsolidatedSubsidiariesParentOnlyPortion
Namespace Prefix:	idt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- References

No definition available.

+ Details

Name:	idt_SaleOfInterestFabrixSystemsLtdTextualAbstract
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- Definition

The designation of funds furnished by a borrower to a lender to assure future payments of the borrower's real estate taxes and insurance obligations with respect to a mortgaged property. Escrow deposits may be made for a variety of other purposes such as earnest money and contingent payments. This element excludes replacement reserves which are an escrow separately provided for within the US GAAP taxonomy.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.10)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_EscrowDeposit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- 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

+ Details

Name:	us-gaap_GainOrLossOnSaleOfStockInSubsidiary
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The cash inflow associated with the deconsolidation of a previously consolidated subsidiary or the sale of investment in consolidated subsidiaries (generally greater than 50 percent).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3179-108585

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Percentage of subsidiary's or equity investee's stock owned by parent company before stock transaction.

+ References

No definition available.

+ Details

Name:	us-gaap_SaleOfStockPercentageOfOwnershipBeforeTransaction
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=idt_FabrixMember
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Period Type:

Sale of Interest in Fabrix Systems Ltd. (Details Textual) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
	Oct. 08, 2014	Apr. 30, 2016	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2015	Oct. 31, 2015
Sale of Interest in Fabrix Systems Ltd. (Textual)
Gain on sale of interest in Fabrix Systems, Ltd.		$ 1,100		$ 1,086	$ 76,864
Fabrix Subsidiary [Member]
Sale of Interest in Fabrix Systems Ltd. (Textual)
Sale of stock to Ericsson in percentage	100.00%
Common stock sold to Ericsson	$ 95,000
Company owns in Fabrix in percentage	78.00%
Proceeds from divestiture of interest in consolidated subsidiaries	$ 69,200
Escrow deposit	$ 13,000
Escrow deposit disbursement		$ 6,500				$ 6,500
Gain on sale of interest in Fabrix Systems, Ltd.				$ 1,100	$ 76,900