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Fair Value Measurements (Details Textual) (USD $) In Millions, unless otherwise specified | Apr. 30, 2015 | Jul. 31, 2014
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Fair Value Assets Liabilities Quantitative Information [Line Items] |  |
Fair value of investments in hedge funds | $ 9.1 idt_InvestmentInHedgeFunds | $ 9.5 idt_InvestmentInHedgeFunds
Carrying value of investments | 3.6 us-gaap_FairValueEstimateNotPracticableCostMethodInvestments | 1.8 us-gaap_FairValueEstimateNotPracticableCostMethodInvestments
Long-term Investments [Member] |  |
Fair Value Assets Liabilities Quantitative Information [Line Items] |  |
Fair value of investments in hedge funds | 9.1 idt_InvestmentInHedgeFunds / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_OtherLongTermInvestmentsMember | 9.4 idt_InvestmentInHedgeFunds / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_OtherLongTermInvestmentsMember
Other Current Assets [Member] |  |
Fair Value Assets Liabilities Quantitative Information [Line Items] |  |
Fair value of investments in hedge funds | $ 0.1 idt_InvestmentInHedgeFunds / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_OtherCurrentAssetsMember | $ 0.1 idt_InvestmentInHedgeFunds / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_OtherCurrentAssetsMember

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- Definition Investment in hedge funds. + References No definition available. + Details
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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 Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 325 -SubTopic 20 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=29638263&loc=d3e39828-111592 + Details
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