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Amortized Cost and Fair Values of Marketable Securities Classified as Available-For-Sale Investments (Detail) - USD ($)
$ in Thousands
Apr. 30, 2015
Apr. 30, 2014
Schedule of Available-for-sale Securities [Line Items]    
Estimated Fair Value [1] $ 13,177 $ 18,352
Corporate Bonds    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 13,167 18,325
Gross Unrealized Gains 11 31
Gross Unrealized Losses [2] (1) (4)
Estimated Fair Value [1] $ 13,177 $ 18,352
[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 April 30, 2015 and 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.