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Deferred Compensation and Retirement Plans - Additional Information (Detail) - USD ($)
$ in Thousands
 3 Months Ended
Jul. 31, 2017
Jul. 31, 2016
Apr. 30, 2017
Defined Benefit Plan Disclosure [Line Items]      
Increase in market value of the underlying COLI investments $ 2,485 $ 2,498  
Recognized investment income(expense) 3,429 3,915  
CSV of COLI Contracts      
Defined Benefit Plan Disclosure [Line Items]      
Gross CSV 180,700   $ 180,300
Outstanding policy loans 66,800   $ 67,200
Increase in market value of the underlying COLI investments 2,500 2,500  
Executive Capital Accumulation Plan      
Defined Benefit Plan Disclosure [Line Items]      
Gain (loss) on deferred compensation plan $ 3,700 $ 3,200  
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    
Defined Benefit Plan      
Defined Benefit Plan Disclosure [Line Items]      
Defined benefit plan, expected future employer contributions, current fiscal year $ 200