11. STOCK-BASED COMPENSATION - Stock option activities (Details) - USD ($)	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
STOCK-BASED COMPENSATION
Shares available for grant, Beginning	3,426,548	4,444,301	5,464,185
Granted (in shares)	(1,011,708)	(1,097,893)	(1,029,684)
Forfeited (in shares)	107,474	80,140	9,800
Shares available for grant, Ending	2,522,314	3,426,548	4,444,301
Number of Shares Underlying Options Outstanding
Balance at the beginning of the period (in shares)	8,017,029	7,874,267	7,622,830
Granted (in shares)	1,011,708	1,097,893	1,029,684
Exercised (in shares)	(772,667)	(823,456)	(678,897)
Forfeited (in shares)	(120,279)	(131,675)	(99,350)
Balance at the end of the period (in shares)	8,135,791	8,017,029	7,874,267
Options vested and exercisable (in shares)	5,138,027
Options vested and expected to vest (in shares)	8,056,574
Weighted Average Remaining Contractual Life
Options weighted average remaining contractual life	5 years 5 months 19 days
Options vested and exercisable	3 years 10 months 24 days
Options vested and expected to vest	5 years 5 months 9 days
Weighted Average Exercise Price
Balance at the beginning of the period (in dollars per share)	$ 5.77	$ 5.45	$ 5.09
Granted (in dollars per share)	8.11	6.74	7.28
Exercised (in dollars per share)	4.39	4.00	4.22
Forfeited (in dollars per share)	7.03	5.60	5.06
Balance at the end of the period (in dollars per share)	6.17	$ 5.77	$ 5.45
Options vested and exercisable (in dollars per share)	5.68
Options vested and expected to vest (in dollars per share)	$ 6.16
Intrinsic Value
Exercised (in dollars)	$ 2,614,879	$ 2,782,691	$ 2,460,812
Options vested and exercisable (in dollars)	4,830,618
Options vested and expected to vest (in dollars)	$ 5,581,363