Obligation and Asset Data for Defined Benefit Pension Plan and Postretirement Health Benefit Plan (Detail) (Riverside Defined Benefit Plans, USD $) In Thousands, unless otherwise specified	12 Months Ended
May 31, 2012	May 31, 2011	May 31, 2010
Change in plan assets
Fair value of plan assets at end of year	$ 40,028	$ 39,752
Pension Plans, Defined Benefit
Change in projected benefit obligation
Benefit obligation at beginning of year	57,756	53,567
Service cost	537	502	457
Interest cost	3,040	2,951	3,166
Benefits paid	(3,102)	(2,924)
Actuarial loss (gain)	7,890	3,660
Benefit obligation at end of year	66,121	57,756	53,567
Change in plan assets
Fair value of plan assets at beginning of year	39,752	33,080
Actual return on plan assets	(864)	6,526
Employer contributions	4,242	3,070
Benefits paid	(3,102)	(2,924)
Fair value of plan assets at end of year	40,028	39,752	33,080
Funded status at end of year	(26,093)	(18,004)
Weighted average assumptions used to determine benefit obligations
Assumed discount rate	4.35%	5.35%
Average long-term pay progression	3.00%	3.00%
Defined Benefit Postretirement Health Coverage
Change in projected benefit obligation
Benefit obligation at beginning of year	7,857	7,654
Service cost	98	114	106
Interest cost	415	425	466
Participant contributions	184	196
Benefits paid	(405)	(377)
Actuarial loss (gain)	19	(155)
Benefit obligation at end of year	8,168	7,857	7,654
Change in plan assets
Employer contributions	221	181
Benefits paid	(221)	(181)
Funded status at end of year	$ (8,168)	$ (7,857)
Weighted average assumptions used to determine benefit obligations
Assumed discount rate	4.35%	5.35%

Defined Benefit Plan, Benefit Obligation, Benefits Paid

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- Definition

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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- Definition

Amount of gain (loss) from a decision to temporarily deviate from the substantive plan, or from a change in benefit obligation or plan asset value from changes in actuarial assumptions, for example, but not limited to, interest, mortality, employee turnover or salary scale.

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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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- Definition

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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-Glossary Postretirement Benefits

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

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The amount of contributions made by plan participants. This item represents a periodic increase to the plan obligation and an increase to plan assets.

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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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The actuarial present value of benefits attributed by the pension benefit formula to services rendered by employees during the period. The portion of the expected postretirement benefit obligation attributed to employee service during the period. The service cost component is a portion of the benefit obligation and is unaffected by the funded status of the plan.

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