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

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- 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

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

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