8. STOCK- BASED COMPENSATION - Weighted average assumptions (Details) - $ / shares	3 Months Ended		9 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015
Stock-based compensation
Weighted average fair value per underlying share of options granted (in dollars per share)	$ 1.75	$ 1.48	$ 1.56	$ 1.70
Employee Consultants And Directors Stock Options
Stock-based compensation
Risk-free interest rate (as a percent)	1.62%	1.56%
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)			1.62%	1.57%
Expected life	5 years	5 years	5 years	5 years
Volatility (as a percent)	33.30%	36.30%
Volatility, low end of range (as a percent)			33.30%	36.30%
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)	0.45%	0.15%
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	6 months
Volatility (as a percent)	30.80%	27.90%
Volatility, low end of range (as a percent)			30.80%	26.30%
Volatility, high end of range (as a percent)			39.60%	27.90%