Stock Option Plans and Equity Incentive Plan - Additional Information (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
May 31, 2013	May 31, 2012	May 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Right of restricted stock unit to receive common stock	1
Expected period to recognize the unrecognized share based compensation cost	3 years
Selling, general and administrative expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share based compensation	$ 1,330	$ 1,438	$ 956
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units granted	73,000	101,000	107,000
Unrecognized share based compensation cost	1,270
Expected period to recognize the unrecognized share based compensation cost	1 year 7 months 6 days
Vested restricted stock units	246,000	145,000	64,000
Exercise Of Conversion Right, Period	5
Fair value of shares vested	1,439
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total tax benefit realized	251	102	37
Cash received from stock option exercises	$ 0	$ 0	$ 197
2005 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares authorized	1,000,000
Minimum percentage for fair market value of grant	100.00%
Expiration date	Oct. 31, 2011
Prior stock option plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding options in prior stock option plans	0

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Minimum percentage for fair market value of grant.

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Restricted Stock Units Vested and not Issued at the End of the Period receiving dividends.

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Right of restricted stock units on shares.

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Aggregate proceeds received by the entity during the annual period from exercises of stock or unit options and conversion of similar instruments granted under equity-based payment arrangements.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Aggregate unrecognized cost of share-based awards, other than options, made to employees under an equity-based compensation plan, that have yet to vest.

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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Date the equity-based award expires, in CCYY-MM-DD format.

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The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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The number of shares reserved for issuance under stock option agreements awarded under the plan that validly exist and are outstanding as of the balance sheet date, including vested options.

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Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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