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Marketable Securities (Details 2) (USD $)
In Thousands, unless otherwise specified
Jul. 31, 2014
Apr. 30, 2015
Equity Securities [Member]    
Schedule Of Available For Sale Securities [Line Items]    
Fair Value $ 22us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		  
Unrealized Losses 9idt_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInAccumulatedOtherComprehensiveIncome
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		  
Municipal Bonds [Member]    
Schedule Of Available For Sale Securities [Line Items]    
Fair Value   2,993us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MunicipalBondsMember
Unrealized Losses   $ 3idt_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInAccumulatedOtherComprehensiveIncome
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MunicipalBondsMember