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Business Segment Information (Details Textual)	12 Months Ended
	Jul. 31, 2018 Segment
Business Segment Information (Textual)
Number of reportable segments	2

X

- 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