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Equity Investments (Details) - Schedule of carrying value of equity investments - USD ($) $ in Thousands | 3 Months Ended
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Oct. 31, 2020 | Oct. 31, 2019
Schedule of carrying value of equity investments [Abstract] |  |
Balance, beginning of period | $ 4,109 | $ 3,919
Redemption for Visa mandatory release assessment | (1,870) |
Adjustment for observable transactions involving a similar investment from the same issuer | (130) | 18
Impairments |  |
Balance, end of the period | $ 2,109 | $ 3,937

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- Definition Amount of gain from upward price adjustment on investment in equity security without readily determinable fair value. + References No definition available. + Details
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Namespace Prefix: | idt_
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Period Type: | duration

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- Definition Redemption for Visa mandatory release assessment + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- References No definition available. + Details
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Namespace Prefix: | idt_
Data Type: | xbrli:stringItemType
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- Definition Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 45 -Paragraph 1A -URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740 + Details
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- Definition Amount of impairment loss on investment in equity security without readily determinable fair value. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 321 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=120269885&loc=SL75117539-209714 + Details
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