Quarterly report pursuant to Section 13 or 15(d)

Deferred Compensation and Retirement Plans - Additional Information (Detail)

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Deferred Compensation and Retirement Plans - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended
Jul. 31, 2015
Jul. 31, 2014
Apr. 30, 2015
Defined Benefit Plan Disclosure [Line Items]      
Increase in market value of the underlying COLI investments $ 2,494 $ 3,263  
Gain on marketable securities 665 2,018  
Csv Of Coli Contracts      
Defined Benefit Plan Disclosure [Line Items]      
Gross CSV 173,600   $ 172,300
Outstanding policy loans 68,500   $ 69,600
Increase in market value of the underlying COLI investments 2,494 3,263  
Executive Capital Accumulation Plan      
Defined Benefit Plan Disclosure [Line Items]      
Company's contributions 2,000 $ 1,200  
Deferred compensation arrangement vesting period   4 years  
Deferred compensation arrangement, expected company contribution in remainder of fiscal year 20,000    
Gain on investment $ 700 $ 1,700