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Deferred Compensation and Retirement Plans - Additional Information (Detail) | 12 Months Ended |
--- | --- | ---
Apr. 30, 2018 USD ($) Person | Apr. 30, 2017 USD ($) Person | Apr. 30, 2016 USD ($) | Dec. 01, 2015 Person
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Recognized investment income(expense) | $ 10,278,000 | $ 10,842,000 | $ (3,333,000) |
Increase in market value of the underlying COLI investments | 7,776,000 | 4,918,000 | 3,984,000 |
Net CSV | 120,087,000 | 113,067,000 |  |
Long Term Performance Unit Plan |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Value per unit award | 50,000 |  |  |
Annual Benefit Payments per vested unit after anniversary period | $ 25,000 |  |  |
Number of payments after the seventh anniversary of the grant date | 5 years |  |  |
Vesting percentage on each anniversary date | 25.00% |  |  |
CSV of COLI Contracts |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Gross CSV | $ 186,800,000 | 180,300,000 |  |
Outstanding policy loans | 66,700,000 | 67,200,000 |  |
Total death benefits payable, net of loans | 226,000,000 | 220,600,000 |  |
Increase in market value of the underlying COLI investments | $ 7,800,000 | 4,900,000 | 4,000,000 |
Equity Securities | Minimum |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Target allocation range | 40.00% |  |  |
Equity Securities | Maximum |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Target allocation range | 50.00% |  |  |
Debt Securities | Minimum |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Target allocation range | 45.00% |  |  |
Debt Securities | Maximum |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Target allocation range | 55.00% |  |  |
Other Assets | Minimum |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Target allocation range | 5.00% |  |  |
Other Assets | Maximum |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Target allocation range | 10.00% |  |  |
Enhanced Wealth Accumulation Plan |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Participant contribution period towards deferred compensation plans (in years) | 8 years |  |  |
Participant after tax contribution period towards deferred compensation plans (in years) | 15 years |  |  |
Additional deferred units to acquire (in years) | 5 years |  |  |
Senior Executive Incentive Plan |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Participant contribution period towards deferred compensation plans (in years) | 4 years |  |  |
Participant after tax contribution period towards deferred compensation plans (in years) | 15 years |  |  |
Pension Plans, Defined Benefit |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Participant employment term, maximum years | 20 years |  |  |
Deferred Compensation Plan |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Deferred compensation and pension plans in periodic benefit expense cost expected to be recognized | $ 1,800,000 |  |  |
Total benefit obligation | 126,494,000 | 121,042,000 | 124,566,000 |
Deferred Compensation Plan | CSV of COLI Contracts |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Gross CSV | 186,800,000 | 180,300,000 |  |
Outstanding policy loans | 66,700,000 | 67,200,000 |  |
Medical and Life Insurance plan |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Net periodic benefit income expected to be recognized | (300,000) |  |  |
Medical and Life Insurance plan | Legacy Hay |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Benefit plan, number of participants | Person |  |  |  | 128
Reduction in benefit obligation | $ (4,008,000) |  |  |
Defined benefit plan ultimate health care cost trend rate | 5.00% |  |  |
Defined benefit plan year that rate reaches ultimate trend rate | 2022 |  |  |
Defined benefit plan effect of one percentage point increase on accumulated postretirement benefit obligation | $ 100,000 |  |  |
Defined benefit plan effect of one percentage point decrease on accumulated postretirement benefit obligation | 100,000 |  |  |
Total benefit obligation | 7,157,000 | 12,147,000 | 13,006,000 |
International Retirement Plans |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total benefit obligation | $ 13,700,000 | $ 12,000,000 |  |
Long-term benefit obligation accrued, number of participants | Person | 1,999 | 1,710 |  |
Company's contributions | $ 10,700,000 | $ 9,300,000 |  |
Executive Capital Accumulation Plan |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total benefit obligation | 128,430,000 | 111,584,000 | 105,676,000 |
Company's contributions | 6,200,000 | 6,200,000 | 23,200,000 |
Gain (loss) on deferred compensation plan | 11,100,000 | 10,600,000 | $ (1,700,000) |
Company's contributions, unamortized portion | $ 19,200,000 | 25,500,000 |  |
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 Contribution Plan |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Company's matching contributions | $ 2,300,000 | $ 1,800,000 |  |
Percentage contribution by the participants to defined contribution plan | 50.00% |  |  |
Company Owned Life Insurance Held In Trust | CSV of COLI Contracts |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Net CSV | $ 81,500,000 |  |  |
Total death benefits, net of loans held in trust | $ 150,400,000 |  |  |

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