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Deferred Compensation and Retirement Plans - Additional Information (Detail) (USD $)
 3 Months Ended
Jul. 31, 2014
Jul. 31, 2013
Apr. 30, 2014
Defined Benefit Plan Disclosure [Line Items]      
Increase in market value of the underlying COLI investments $ 3,263,000 $ 1,291,000  
Recognized investment income 2,018,000 1,941,000  
Csv Of Coli Contracts
      
Defined Benefit Plan Disclosure [Line Items]      
Gross CSV 168,900,000   167,200,000
Outstanding policy loans 72,200,000   72,900,000
Increase in market value of the underlying COLI investments 3,263,000 1,291,000  
Executive Capital Accumulation Plan
      
Defined Benefit Plan Disclosure [Line Items]      
Company contributions 1,200,000 14,200,000  
Deferred compensation arrangement, expected company contribution in remainder of fiscal year 17,100,000    
Deferred compensation arrangement vesting period 4 years    
Gain on investment $ 1,700,000 $ 1,600,000