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Business Segment Information (Details 1)	12 Months Ended
	Jul. 31, 2015	Jul. 31, 2014	Jul. 31, 2013
Outside of the United States
Revenue, Major Customer [Line Items]
Percentage of revenue from customers	30.00%	30.00%	23.00%
United Kingdom
Revenue, Major Customer [Line Items]
Percentage of revenue from customers	20.00%	19.00%	13.00%

X

- Definition

Percentage of revenue from external customers attributed to foreign Countries.

+ References

No definition available.

+ Details

Name:	idt_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToForeignCountriesPercentage
Namespace Prefix:	idt_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_EntityWideRevenueMajorCustomerLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_StatementGeographicalAxis=idt_OtherCountriesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementGeographicalAxis=country_GB
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: