2. STOCK-BASED COMPENSATION - Options outstanding and exercisable (Details 4) (USD $) In Thousands, except Share data, unless otherwise specified	9 Months Ended
Feb. 28, 2015
Range Exercise Prices Options Outstanding Minimum	$ 0.59
Range Exercise Prices Options Outstanding Maximum	$ 2.71
Number of Options Outstanding, Ending (in thousands)	3,402
Weighted Average Remaining Contractual Life (Years) Options Outstanding	4 years 6 months 3 days
Weighted Average Exercise Price Outstanding, Ending	$ 1.61
Options exercisable shares, ending (in thousands)	2,098
Weighted Average Remaining Contractual Life (Years) Options Exercisable	3 years 10 months 2 days
Weighted Average Exercise Price for Options exercisable, ending	$ 1.43
Aggregate Intrinsic Value for Options exercisable, ending	$ 2,551
Options Price Range A
Range Exercise Prices Options Outstanding Minimum	$ 0.59
Range Exercise Prices Options Outstanding Maximum	$ 0.97
Number of Options Outstanding, Ending (in thousands)	680
Weighted Average Remaining Contractual Life (Years) Options Outstanding	4 years 1 month 6 days
Weighted Average Exercise Price Outstanding, Ending	$ 0.70
Options exercisable shares, ending (in thousands)	586
Weighted Average Remaining Contractual Life (Years) Options Exercisable	4 years 1 month 20 days
Weighted Average Exercise Price for Options exercisable, ending	$ 0.72
Options Price Range B
Range Exercise Prices Options Outstanding Minimum	$ 1.09
Range Exercise Prices Options Outstanding Maximum	$ 1.40
Number of Options Outstanding, Ending (in thousands)	1,311
Weighted Average Remaining Contractual Life (Years) Options Outstanding	4 years 2 months 23 days
Weighted Average Exercise Price Outstanding, Ending	$ 1.28
Options exercisable shares, ending (in thousands)	807
Weighted Average Remaining Contractual Life (Years) Options Exercisable	3 years 10 months 10 days
Weighted Average Exercise Price for Options exercisable, ending	$ 1.28
Options Price Range C
Range Exercise Prices Options Outstanding Minimum	$ 1.73
Range Exercise Prices Options Outstanding Maximum	$ 2.06
Number of Options Outstanding, Ending (in thousands)	512
Weighted Average Remaining Contractual Life (Years) Options Outstanding	3 years 3 months
Weighted Average Exercise Price Outstanding, Ending	$ 1.91
Options exercisable shares, ending (in thousands)	409
Weighted Average Remaining Contractual Life (Years) Options Exercisable	2 years 6 months 18 days
Weighted Average Exercise Price for Options exercisable, ending	$ 1.92
Options Price Range D
Range Exercise Prices Options Outstanding Minimum	$ 2.15
Range Exercise Prices Options Outstanding Maximum	$ 2.71
Number of Options Outstanding, Ending (in thousands)	899
Weighted Average Remaining Contractual Life (Years) Options Outstanding	5 years 11 months 16 days
Weighted Average Exercise Price Outstanding, Ending	$ 2.62
Options exercisable shares, ending (in thousands)	296
Weighted Average Remaining Contractual Life (Years) Options Exercisable	4 years 11 months 16 days
Weighted Average Exercise Price for Options exercisable, ending	$ 2.56

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 number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

+ 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)(iii)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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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.

+ References

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- Definition

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

+ References

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- Definition

Number of options outstanding, including both vested and non-vested options.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Reference 2: 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)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

+ 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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-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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Weighted average remaining contractual term for option awards outstanding, 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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- 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.

+ 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 (g)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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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

-Paragraph 2

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