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Related Party Transactions (Tables) | 12 Months Ended
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Jul. 31, 2018
Related Party Transactions [Abstract] |
Summary of changes in estimated liability to straight path included in other current liabilities |
Year ended July 31 |  |  |  |  |  |
(in thousands) |  | 2018 |  |  | 2017 |
Balance at beginning of year |  | $ | 81 |  |  | $ | 133 |
Additional liability |  |  | — |  |  |  | 104 |
Adjustments |  |  | (46 | ) |  |  | (51 | )
Payments |  |  | (35 | ) |  |  | (105 | )
Balance at end of year |  | $ | — |  |  | $ | 81 |

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- Definition Tabular disclosure of changes in company's estimated liability. + References No definition available. + Details
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Namespace Prefix: | idt_
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Balance Type: | na
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- References No definition available. + Details
Name: | us-gaap_RelatedPartyTransactionsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration