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Deferred Compensation and Retirement Plans - Additional Information (Detail) (USD $)
 3 Months Ended
Jul. 31, 2013
Jul. 31, 2012
Apr. 30, 2013
Defined Benefit Plan Disclosure [Line Items]      
Gross CSV $ 160,900,000   $ 159,200,000
Outstanding policy loans 73,300,000   73,300,000
Increase in market value of the underlying COLI investments 1,291,000 671,000  
Executive Capital Accumulation Plan
      
Defined Benefit Plan Disclosure [Line Items]      
Company's contributions 14,200,000 17,500,000  
Deferred compensation arrangement vesting terms Participants generally vest in Company contributions over a four year period.    
Deferred compensation arrangement, expected company contribution in remainder of fiscal year 2,500,000    
Increase (decrease) in compensation expense $ 1,600,000 $ (1,000,000)