9. STOCK- BASED COMPENSATION - Weighted average assumptions (Details) - $ / shares	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Stock-based compensation
Expected life	5 years
Dividend yield (as a percent)	0.00%
Weighted average fair value per underlying share of options granted (in dollars per share)	$ 1.66	$ 1.52	$ 2.08
Employee Consultants And Directors Stock Options
Stock-based compensation
Risk-free interest rate, low end of range (as a percent)	1.12%	1.41%	1.47%
Risk-free interest rate, high end of range (as a percent)	1.95%	1.57%	1.70%
Expected life	5 years	5 years	5 years
Volatility, low end of range (as a percent)	33.30%	36.30%	40.40%
Volatility, high end of range (as a percent)	35.40%	38.00%	44.80%
Employee stock purchase plan
Stock-based compensation
Risk-free interest rate (as a percent)			0.05%
Risk-free interest rate, low end of range (as a percent)	0.38%	0.09%
Risk-free interest rate, high end of range (as a percent)	0.45%	0.15%
Expected life	6 months	6 months	6 months
Volatility, low end of range (as a percent)	30.80%	26.30%	30.80%
Volatility, high end of range (as a percent)	39.60%	27.90%	38.00%