8. STOCK- BASED COMPENSATION - Stock-based compensation expense (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Stock-based compensation expense by line item
Stock-based compensation expense	$ 508	$ 487	$ 986	$ 930
Other information
Income tax benefit recognized from allocation of share-based compensation expense	0	0	0	0
Windfall tax benefits realized	0	0	0	0
Unrecognized compensation costs	4,100		$ 4,100
Weighted average period of recognition of unrecognized compensation costs			2 years 3 months 29 days
Cost of revenues
Stock-based compensation expense by line item
Stock-based compensation expense	66	79	$ 113	131
Research and development
Stock-based compensation expense by line item
Stock-based compensation expense	284	238	551	461
Selling, general and administrative
Stock-based compensation expense by line item
Stock-based compensation expense	$ 158	$ 170	$ 322	$ 338

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.F)
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Amount of deferred tax expense from write-off of the deferred tax asset related to deductible stock options at exercise.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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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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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Unrecognized cost of unvested options awarded to employees as compensation.

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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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