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Fair Value Measurements (Details Textual) - USD ($) $ in Millions	Jul. 31, 2018	Jul. 31, 2017
Fair Value Measurements (Textual)
Fair value of investments in hedge funds	$ 4.8	$ 8.6
Carrying value of investments	$ 3.0	$ 10.8

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- Definition

This item represents a financial instrument (as defined) for which it is not practicable to estimate fair value. Such disclosure may be for an individual financial instrument or a class of financial instruments.

+ References

No definition available.

+ Details

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

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- References

No definition available.

+ Details

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Namespace Prefix:	idt_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

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- Definition

Investment in hedge funds.

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No definition available.

+ Details

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