11. STOCK-BASED COMPENSATION - Weighted average assumptions (Details) - USD ($)	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Stock-based compensation
Expected life	5 years
Dividend yield (as a percent)	0.00%
Other information
Income tax benefit recognized from allocation of share-based compensation expense	$ 0	$ 0
Windfall tax benefits realized	0	$ 0
Unrecognized compensation costs	$ 4,800,000
Weighted average period of recognition of unrecognized compensation costs	1 year 10 months 24 days
Weighted average fair value per underlying share of options granted (in dollars per share)	$ 2.86	$ 2.44	$ 2.54
Employee stock options
Stock-based compensation
Risk-free interest rate, low end of range (as a percent)	1.35%	2.53%	1.84%
Risk-free interest rate, high end of range (as a percent)	2.30%	2.91%	2.49%
Expected life	5 years	5 years	5 years
Volatility, low end of range (as a percent)	36.50%	35.60%	35.50%
Volatility, high end of range (as a percent)	39.70%	37.30%	36.50%
Employee stock purchase plan options
Stock-based compensation
Risk-free interest rate, low end of range (as a percent)	1.58%	2.09%	1.04%
Risk-free interest rate, high end of range (as a percent)	2.43%	2.50%	1.42%
Expected life	6 months	6 months	6 months
Volatility, low end of range (as a percent)	33.50%	32.60%	38.80%
Volatility, high end of range (as a percent)	43.10%	37.70%	51.10%