Equity Compensation Plans - Additional Information (Detail) (USD $)	12 Months Ended
May 31, 2013	May 31, 2012	May 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant	818,000	1,108,000	397,000
Options Exercisable, Weighted Average Exercise Price	$ 21.31	$ 16.59
Weighted-Average Grant-Date Fair Value of Options Granted	$ 13.81	$ 10.41	$ 8.66
Aggregate intrinsic value of options outstanding	$ 35,778,000	$ 25,617,000	$ 42,607,000
Aggregate intrinsic value of options exercisable	16,557,000	12,855,000	16,040,000
Aggregate intrinsic value of options exercised	12,519,000	8,226,000	15,262,000
Remaining compensation cost to be expensed in future periods for non-vested options	$ 4,096,000
Weighted average expense recognition period	3 years 2 months 12 days
Number of shares purchased by employees	14,925	14,144	18,252
2002 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	43,539
Number of shares authorized for grant	225,000
2002 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	250,000
Annual maximum limit percentage of compensation to purchase shares	5.00%
Employee stock purchase plan stock price percentage	10.00%
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

Employee Purchase Plan Purchase Price Percentage of Fair Market Value

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- Definition

Employee Stock Purchase Plan, Maximum Percentage of Compensation to Purchase Shares By Eligible Participants

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- Definition

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

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

-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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-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

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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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-Topic 718

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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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-Publisher FASB

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-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

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- Definition

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

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.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)(iii)

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- Definition

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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-Publisher FASB

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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-Publisher FASB

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- Definition

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

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- Definition

The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

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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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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

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