8. STOCK- BASED COMPENSATION - Weighted average assumptions (Details) - $ / shares	3 Months Ended		6 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Stock-based compensation
Weighted average fair value per underlying share of options granted (in dollars per share)	$ 1.57	$ 1.72	$ 1.50	$ 1.74
Employee Consultants And Directors Stock Options
Stock-based compensation
Risk-free interest rate (as a percent)	1.12%	1.57%
Risk-free interest rate, low end of range (as a percent)			1.12%	1.52%
Risk-free interest rate, high end of range (as a percent)			1.26%	1.57%
Expected life	5 years	5 years	5 years	5 years
Volatility (as a percent)	33.90%	36.80%
Volatility, low end of range (as a percent)			33.90%	36.80%
Volatility, high end of range (as a percent)			34.80%	38.00%
Employee stock purchase plan
Stock-based compensation
Risk-free interest rate (as a percent)			0.38%	0.09%
Expected life			6 months	6 months
Volatility (as a percent)			39.60%	26.30%