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Deferred Compensation and Retirement Plans - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended
Jul. 31, 2016
Jul. 31, 2015
Apr. 30, 2016
Defined Benefit Plan Disclosure [Line Items]      
Increase in market value of the underlying COLI investments $ 2,498 $ 2,494  
Recognized investment income 3,915 665  
CSV of COLI Contracts      
Defined Benefit Plan Disclosure [Line Items]      
Gross CSV 178,600   $ 175,700
Outstanding policy loans 68,400   $ 68,400
Increase in market value of the underlying COLI investments 2,500 2,500  
Executive Capital Accumulation Plan      
Defined Benefit Plan Disclosure [Line Items]      
Compensation expense recognized $ 3,200 $ 700  
Executive Capital Accumulation Plan | Minimum      
Defined Benefit Plan Disclosure [Line Items]      
Deferred compensation arrangement vesting period 4 years    
Executive Capital Accumulation Plan | Maximum      
Defined Benefit Plan Disclosure [Line Items]      
Deferred compensation arrangement vesting period 5 years