Retirement Benefits - Summary of Change in Projected Benefit Obligations and Change in Fair Value of Plan Assets (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Apr. 30, 2014	Apr. 30, 2013	Apr. 30, 2012
Compensation And Retirement Disclosure [Abstract]
Accumulated Benefit Obligation, April 30	$ 19,857	$ 20,683
Change in Projected Benefit Obligations
Projected benefit obligations, beginning of year	20,683	19,061
Interest cost	857	906	942
Actuarial (gain) loss	(737)	1,610
Actual benefits paid	(946)	(894)
Projected benefit obligations, end of year	19,857	20,683	19,061
Change in Plan Assets
Fair value of plan assets, beginning of year	15,415	14,007
Actual return on plan assets	1,519	1,302
Employer contributions	300	1,000
Actual benefits paid	(946)	(894)
Fair value of plan assets, end of year	16,288	15,415	14,007
Funded status - under	(3,569)	(5,268)
Amounts Recognized in the Consolidated Balance Sheets consist of:
Noncurrent assets	0	0
Noncurrent liabilities	(3,569)	(5,268)
Net amount recognized	(3,569)	(5,268)
Amounts recognized in accumulated other comprehensive income (loss) consist of:
Net actual loss	8,962	11,078
Deferred tax benefit	(3,486)	(4,309)
After-tax actuarial loss	$ 5,476	$ 6,768
Weighted-Average Assumptions Used to Determine Benefit Obligations at April 30
Discount rate	4.60%	4.25%
Rate of compensation increase	0.00%	0.00%
Weighted-Average Assumptions Used to Determine Net Periodic Benefit Cost for Years Ended April 30
Discount rate	4.25%	4.75%
Expected long-term return on plan assets	8.50%	8.50%
Rate of compensation increase	0.00%	0.00%

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from postretirement benefits.

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This represents the noncurrent liability recognized in the balance sheet that is associated with the defined benefit pension plans.

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For defined benefit pension plans, the actuarial present value of benefits (whether vested or nonvested) attributed by the pension benefit formula to employee service rendered before a specified date and based on employee service and compensation (if applicable) before that date. The accumulated benefit obligation differs from the projected benefit obligation in that it includes no assumption about future compensation levels. For plans with flat-benefit or nonpay-related pension benefit formulas, the accumulated benefit obligation and the projected benefit obligation are the same.

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After tax total of net gain (loss), prior service cost (credit), and transition assets (obligations), as well as minimum pension liability if still remaining, included in accumulated other comprehensive income associated with a defined benefit pension or other postretirement plan(s).

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After tax net amount of gain (loss) that are not yet recognized as a component of net periodic benefit cost, and that are recognized as increases (decreases) in other comprehensive income as they arise.

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The difference between fair value of plan assets at the end of the period and the fair value at the beginning of the period, adjusted for contributions and payments of benefits during the period, and after adjusting for taxes and other expenses, as applicable.

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Amount of gain (loss) related to change in benefit obligation resulting from changes in actuarial assumptions, for example, but not limited to, interest, mortality, employee turnover, salary, and temporary deviation from the substantive plan.

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The aggregate net amount recognized in the balance sheet associated with the defined benefit plan(s). Will normally be the same as the Defined Benefit Plan, Funded Status of Plan, Total.

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The amount for overfunded plans recognized in the balance sheet as a noncurrent asset associated with a defined benefit pension plan or other postretirement defined benefit plan.

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The interest rate used to adjust for the time value of money for the plan.

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Expected rate of compensation increases (for pay-related plans).

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The interest rate used to adjust for the time value of money.

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An assumption as to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation.

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Expected rate of compensation increases (for pay-related plans).

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1) For defined benefit pension plans, the benefit obligation is the projected benefit obligation, which is the actuarial present value as of a date of all benefits attributed by the pension benefit formula to employee service rendered prior to that date. 2) For other postretirement defined benefit plans, the benefit obligation is the accumulated postretirement benefit obligation, which is the actuarial present value of benefits attributed to employee service rendered to a particular date.

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The amount of payments made for which participants are entitled under a pension plan, including pension benefits, death benefits, and benefits due on termination of employment. Also includes payments made under a postretirement benefit plan, including prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services. This item represents a periodic decrease to the plan obligations and a decrease to plan assets.

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The increase in the fair value of plan assets from contributions made by the employer.

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Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets.

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The funded status is measured as the difference between the fair value of plan assets and the benefit obligation. Will normally be the same as the net Defined Benefit Plan, Amounts Recognized in Balance Sheet, Total.

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The increase in a defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation due to the passage of time.

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