XML 11 R39.htm IDEA: XBRL DOCUMENT v2.4.1.9
Amortized Cost and Fair Values of Marketable Securities Classified as Available-For-Sale Investments (Parenthetical) (Detail) (USD $)
Jan. 31, 2015
Apr. 30, 2014
Schedule of Available-for-sale Securities [Line Items]    
Marketable securities that have been in a continuous unrealized loss position for 12 months or more $ 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue $ 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue