Equity Compensation Plans - Additional Information (Detail) - USD ($)	12 Months Ended
May. 31, 2015	May. 31, 2014	May. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant	306,000	805,000	1,227,000
Options Exercisable, Weighted Average Exercise Price	$ 24.50	$ 18.91
Aggregate intrinsic value of options outstanding	$ 31,204,000	$ 22,751,000	$ 35,778,000
Aggregate intrinsic value of options exercisable	14,201,000	10,984,000	16,557,000
Aggregate intrinsic value of options exercised	10,690,000	$ 17,669,000	$ 12,519,000
Remaining compensation cost to be expensed in future periods for non-vested options	$ 13,567,000
Weighted average expense recognition period	2 years 10 months 24 days
Number of shares purchased by employees	19,592	18,466	22,388
Employee Stock Purchase Plan \| 2011 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of additional shares authorized	375,000
Annual maximum limit percentage of compensation to purchase shares	5.00%
Employee stock purchase plan stock price percentage	10.00%
Employee Stock Purchase Plan \| 2002 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant	45,717
Number of shares authorized for grant	337,500
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option vesting period	3 years
Stock option contractual terms	5 years
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option vesting period	5 years
Stock option contractual terms	10 years

Employee Purchase Plan Purchase Price Percentage of Fair Market Value

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Share Based Compensation Arrangement by Share Based Payment Award, Options, Contractual Term One

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- Definition

Unrecognized cost of unvested share-based compensation awards.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (i)

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- Definition

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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- Definition

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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- Definition

Discount rate from fair value on purchase date that participants pay for shares.

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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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- Definition

Number of additional shares authorized for issuance under an established share-based compensation plan.

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- Definition

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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- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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- Definition

Number of shares issued during the period as a result of an employee stock purchase plan.

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-Number 210

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