Annual report pursuant to Section 13 and 15(d)

Deferred Compensation And Retirement Plans (Weighted-Average Assumptions Used In Calculating The Benefit Obligations) (Detail)

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Deferred Compensation And Retirement Plans (Weighted-Average Assumptions Used In Calculating The Benefit Obligations) (Detail)
12 Months Ended
Apr. 30, 2017
Apr. 30, 2016
Apr. 30, 2015
Pension Plans, Defined Benefit      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate, beginning of period 3.18% 3.28% 3.60%
Discount rate, end of year 3.57% 3.18% 3.28%
Rate of compensation increase 0.00% 0.00% 0.00%
Expected long-term rates of return on plan assets 6.50% 6.50%
Medical and Life Insurance | Hay Group      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate, beginning of period 3.36% 4.10%  
Discount rate, end of year 3.75% 3.36% 4.10%
Healthcare care cost trend rate 7.00% 7.00%