Stock Option Plans and Equity Incentive Plan - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
May. 31, 2015	May. 31, 2014	May. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
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	$ 1,292	$ 1,356	$ 1,330
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units granted	87,000	65,000	73,000
Unrecognized share based compensation cost	$ 1,205
Expected period to recognize the unrecognized share based compensation cost	1 year 8 months 6 days
Vested restricted stock units	274,000	329,000	246,000
Exercise Of Conversion Right, Period	5 years
Fair value of shares vested	$ 807	$ 1,414	$ 1,439
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total tax benefit realized	$ 358	$ 183	$ 251
2005 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares authorized	1,000,000

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

+ References

No definition available.

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section S99

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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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Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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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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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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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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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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