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Business Segment Information (Details Textual) | 6 Months Ended
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Jan. 31, 2018 Segment
Business Segment Information (Textual) |
Number of reportable segments | 2

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- References No definition available. + Details
Name: | idt_BusinessSegmentInformationTextualAbstract
Namespace Prefix: | idt_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements. + References No definition available. + Details
Name: | us-gaap_NumberOfReportableSegments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration