10. STOCK-BASED COMPENSATION - Stock options activities (Details) - USD ($)	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
STOCK-BASED COMPENSATION
Shares available for grant, Beginning	4,444,301	5,464,185	6,432,063
Options reserved (in shares)			1,085,818
Terminated plan (in shares)			(705,699)
Granted (in shares)	(1,097,893)	(1,029,684)	(1,362,798)
Forfeited (in shares)	80,140	9,800	14,801
Shares available for grant, Ending	3,426,548	4,444,301	5,464,185
Number of Shares Underlying Options Outstanding
Balance at the beginning of the period (in shares)	7,874,267	7,622,830	7,625,705
Granted (in shares)	1,097,893	1,029,684	1,362,798
Exercised (in shares)	(823,456)	(678,897)	(391,039)
Forfeited (in shares)	(131,675)	(99,350)	(974,634)
Balance at the end of the period (in shares)	8,017,029	7,874,267	7,622,830
Options vested and exercisable (in shares)	4,905,367
Options vested and expected to vest (in shares)	7,943,690
Weighted Average Remaining Contractual Life
Options weighted average remaining contractual life	5 years 6 months 26 days
Options vested and exercisable	3 years 10 months 21 days
Options vested and expected to vest	5 years 6 months 15 days
Weighted Average Exercise Price
Balance at the beginning of the period (in dollars per share)	$ 5.45	$ 5.09	$ 5.08
Granted (in dollars per share)	6.74	7.28	5.14
Exercised (in dollars per share)	4.00	4.22	3.96
Forfeited (in dollars per share)	5.60	5.06	5.53
Balance at the end of the period (in dollars per share)	5.77	$ 5.45	$ 5.09
Options vested and exercisable (in dollars per share)	5.50
Options vested and expected to vest (in dollars per share)	$ 5.76
Intrinsic Value
Exercised (in dollars)	$ 2,782,691	$ 2,460,812	$ 855,160
Options vested and exercisable (in dollars)	11,281,978
Options vested and expected to vest (in dollars)	$ 16,165,270