Stockholders' Equity (Details 3) (USD $)	12 Months Ended
May 31, 2014
Options outstanding
Number outstanding	2,673,751
Weighted-average remaining life in years	4 years 6 months 22 days
Weighted -average exercise price	$ 14.84
Number Exercisable	1,675,790
Weighted-average exercise price	$ 16.12
Range One [Member]
Options outstanding
Range of exercise prices, Lower limit	$ 6.52
Range of exercise prices, Upper limit	$ 11.93
Number outstanding	463,965
Weighted-average remaining life in years	5 years 7 months 21 days
Weighted -average exercise price	$ 11.37
Number Exercisable	65,832
Weighted-average exercise price	$ 10.61
Range Two [Member]
Options outstanding
Range of exercise prices, Lower limit	$ 12.06
Range of exercise prices, Upper limit	$ 12.97
Number outstanding	343,161
Weighted-average remaining life in years	4 years 10 months 10 days
Weighted -average exercise price	$ 12.41
Number Exercisable	155,661
Weighted-average exercise price	$ 12.44
Range Three [Member]
Options outstanding
Range of exercise prices, Lower limit	$ 13.18
Range of exercise prices, Upper limit	$ 13.85
Number outstanding	432,426
Weighted-average remaining life in years	3 years 4 months 17 days
Weighted -average exercise price	$ 13.35
Number Exercisable	321,348
Weighted-average exercise price	$ 13.36
Range Four [Member]
Options outstanding
Range of exercise prices, Lower limit	$ 13.92
Range of exercise prices, Upper limit	$ 14.31
Number outstanding	430,000
Weighted-average remaining life in years	4 years 2 months 16 days
Weighted -average exercise price	$ 13.95
Number Exercisable	228,750
Weighted-average exercise price	$ 13.97
Range Five [Member]
Options outstanding
Range of exercise prices, Lower limit	$ 14.48
Range of exercise prices, Upper limit	$ 15.57
Number outstanding	202,880
Weighted-average remaining life in years	1 year 1 month 2 days
Weighted -average exercise price	$ 15.25
Number Exercisable	202,880
Weighted-average exercise price	$ 15.25
Range Six [Member]
Options outstanding
Range of exercise prices, Lower limit	$ 15.75
Range of exercise prices, Upper limit	$ 16.58
Number outstanding	376,196
Weighted-average remaining life in years	3 years 4 months 21 days
Weighted -average exercise price	$ 16.06
Number Exercisable	276,196
Weighted-average exercise price	$ 16.03
Range Seven [Member]
Options outstanding
Range of exercise prices, Lower limit	$ 16.75
Range of exercise prices, Upper limit	$ 19.94
Number outstanding	267,522
Weighted-average remaining life in years	1 year 0 months 22 days
Weighted -average exercise price	$ 18.19
Number Exercisable	267,522
Weighted-average exercise price	$ 18.16
Range Eight [Member]
Options outstanding
Range of exercise prices, Lower limit	$ 20.06
Range of exercise prices, Upper limit	$ 31.33
Number outstanding	157,601
Weighted-average remaining life in years	1 year 3 months 4 days
Weighted -average exercise price	$ 23.05
Number Exercisable	157,601
Weighted-average exercise price	$ 13.81

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Weighted average exercise price as of the balance sheet date for those equity-based payment arrangements exercisable and outstanding.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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-SubTopic 10

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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.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

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The number of shares reserved for issuance pertaining to the outstanding exercisable stock options as of the balance sheet date in the customized range of exercise prices for which the market and performance vesting condition has been satisfied.

+ 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 (c)(iii)

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The number of shares reserved for issuance pertaining to the outstanding stock options as of the balance sheet date for all option plans in the customized range of exercise prices.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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The weighted average price as of the balance sheet date at which grantees could acquire the underlying shares with respect to all outstanding stock options which are in the customized range of exercise prices.

+ 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 (c)(1)(i)-(ii)

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Weighted average remaining contractual term of outstanding stock options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

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The ceiling 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.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

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