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Deferred Compensation and Retirement Plans - Additional Information (Detail) (USD $)
 3 Months Ended 6 Months Ended
Oct. 31, 2014
Oct. 31, 2013
Oct. 31, 2014
Oct. 31, 2013
Apr. 30, 2014
Defined Benefit Plan Disclosure [Line Items]          
Increase in market value of the underlying COLI investments     $ 5,494,000 $ 4,587,000  
Recognized investment income 2,500,000 4,400,000 4,527,000 6,369,000  
Csv Of Coli Contracts
          
Defined Benefit Plan Disclosure [Line Items]          
Gross CSV 171,200,000   171,200,000   167,200,000
Outstanding policy loans 72,200,000   72,200,000   72,900,000
Increase in market value of the underlying COLI investments 2,200,000 3,300,000 5,494,000 4,587,000  
Executive Capital Accumulation Plan
          
Defined Benefit Plan Disclosure [Line Items]          
Company contributions 17,400,000 2,500,000 18,600,000 16,700,000  
Deferred compensation arrangement vesting period     4 years    
Gain on investment $ 1,000,000 $ 3,400,000 $ 2,700,000 $ 5,000,000