Annual report pursuant to Section 13 and 15(d)

Marketable Securities - Additional Information (Detail)

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Marketable Securities - Additional Information (Detail) (USD $)
 12 Months Ended
Apr. 30, 2013
Apr. 30, 2012
Schedule Of Marketable Securities [Line Items]    
Trading securities $ 98,001,000 [1],[2] $ 82,176,000 [1],[2]
Minimum
    
Schedule Of Marketable Securities [Line Items]    
Available for sale marketable securities, remaining maturities 1 month  
Maximum
    
Schedule Of Marketable Securities [Line Items]    
Available for sale marketable securities, remaining maturities 3 years  
Debt Securities
    
Schedule Of Marketable Securities [Line Items]    
Gross unrealized gains 3,100,000 3,500,000
Gross unrealized losses   $ 400,000
[1] These investments are held in trust for settlement of the Company's obligations of $99.2 million and $82.6 million as of April 30, 2013 and 2012, respectively, under the Executive Capital Accumulation Plan (see Note 6 - Deferred Compensation and Retirement Plans).
[2] 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, 2013 and 2012, the Company had cash equivalents of $93.6 million and $60.5 million, and restricted cash of $2.9 million and $10.0 million, respectively, classified as Level 1. As of April 30, 2013 and 2012, the Company had no investments classified as Level 3.