Quarterly report pursuant to Section 13 or 15(d)

Marketable Securities - Additional Information (Detail)

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Marketable Securities - Additional Information (Detail) - USD ($)
$ in Thousands
 3 Months Ended
Jul. 31, 2015
Jul. 31, 2014
Apr. 30, 2015
Schedule Of Marketable Securities [Line Items]      
Proceeds from maturities of available-for-sale securities $ 3,000 $ 2,000  
Trading securities [1],[2] 127,793   $ 131,399
Gross unrealized gains 8,000   8,300
Gross unrealized losses $ 600   $ 200
Minimum      
Schedule Of Marketable Securities [Line Items]      
Available-for-sale marketable securities, remaining maturities 2 months    
Maximum      
Schedule Of Marketable Securities [Line Items]      
Available-for-sale marketable securities, remaining maturities 5 months    
[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 July 31, 2015 and April 30, 2015, the Company had no investments classified as Level 3.
[2] These investments are held in trust for settlement of the Company's vested and unvested obligations of $125.5 million and $129.1 million as of July 31, 2015 and April 30, 2015, respectively, under the ECAP (see Note 6 -Deferred Compensation and Retirement Plans). During the three months ended July 31, 2015 and 2014, the fair value of the investments increased; therefore, the Company recognized income of $0.7 million and $2.0 million, respectively, which was recorded in other (loss) income, net.