10. STOCKHOLDERS' EQUITY, COMPREHENSIVE INCOME AND STOCK-BASED COMPENSATION (Details 3) - Employee Stock Purchase Plan - $ / shares	12 Months Ended
May 31, 2019	May 31, 2018	May 31, 2017
Weighted-average grant date fair value	$ 1.14	$ 1.01	$ 1.65
Minimum
Expected term (in years)	6 months	6 months	6 months
Volatility	48.00%	56.00%	79.00%
Risk-free interest rates	2.33%	1.92%	0.48%
Maximum
Expected term (in years)	2 years	2 years	2 years
Volatility	78.00%	81.00%	108.00%
Risk-free interest rates	2.82%	2.25%	0.80%

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

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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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- Definition

Expected term of award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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-Publisher FASB
-Name Accounting Standards Codification
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-Section S99
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

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