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Deferred Compensation and Retirement Plans - Additional Information (Detail) (USD $)
 3 Months Ended 6 Months Ended
Oct. 31, 2013
Oct. 31, 2012
Oct. 31, 2013
Oct. 31, 2012
Apr. 30, 2013
Defined Benefit Plan Disclosure [Line Items]          
Gross CSV $ 164,200,000   $ 164,200,000   $ 159,200,000
Outstanding policy loans 73,300,000   73,300,000   73,300,000
Increase in market value of the underlying COLI investments 3,300,000 1,500,000 4,587,000 2,178,000  
Increase in fair value trading securities 4,400,000 1,900,000 6,369,000 1,129,000  
Executive Capital Accumulation Plan
          
Defined Benefit Plan Disclosure [Line Items]          
Company's contributions 2,500,000 1,800,000 16,700,000 19,300,000  
Deferred compensation arrangement vesting terms Participants generally vest in Company contributions over a four year period.        
Increase (decrease) in compensation expense $ 3,400,000 $ 1,500,000 $ 5,000,000 $ 500,000