9. STOCK- BASED COMPENSATION - Stock-based compensation expense (Details) - USD ($)	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Stock-based compensation expense by line item
Stock-based compensation expense	$ 1,877,000	$ 1,850,000	$ 2,077,000
Other information
Income tax benefit recognized from allocation of share-based compensation expense	0	0
Windfall tax benefits realized	0	0
Unrecognized compensation costs	$ 3,400,000
Weighted average period of recognition of unrecognized compensation costs	2 years 3 months 4 days
Cost of revenues
Stock-based compensation expense by line item
Stock-based compensation expense	$ 282,000	320,000	401,000
Research and development
Stock-based compensation expense by line item
Stock-based compensation expense	980,000	858,000	941,000
Selling, general and administrative
Stock-based compensation expense by line item
Stock-based compensation expense	615,000	672,000	735,000
2007 Employee Stock Purchase Plan
Stock-based compensation expense by line item
Stock-based compensation expense	$ 150,000	$ 136,000	$ 153,000