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Amortized Cost and Fair Values of Marketable Securities Classified as Available-For-Sale Investments (Detail) (USD $)
In Thousands, unless otherwise specified
Jan. 31, 2015
Apr. 30, 2014
Schedule of Available-for-sale Securities [Line Items]    
Estimated Fair Value $ 15,214us-gaap_AvailableForSaleSecuritiesDebtSecurities [1] $ 18,352us-gaap_AvailableForSaleSecuritiesDebtSecurities [1]
Corporate Bonds    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 15,198us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
18,325us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
Gross Unrealized Gains 17us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
31us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
Gross Unrealized Losses (1)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
[2] (4)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
[2]
Estimated Fair Value $ 15,214us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
[1] $ 18,352us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
[1]
[1] The Company's financial assets measured at fair value on a recurring basis include trading securities classified as Level 1 and available-for-sale securities classified as Level 2. As of January 31, 2015 and April 30, 2014, the Company had no investments classified as Level 3.
[2] There are no marketable securities that have been in a continuous unrealized loss position for 12 months or more.