10. STOCK-BASED COMPENSATION - Stock option activities (Details)	3 Months Ended
	Jun. 30, 2020 USD ($) $ / shares shares
STOCK-BASED COMPENSATION
Shares available for grant, Beginning	2,522,314
Granted (in shares)	(114,110)
Forfeited (in shares)	9,250
Shares available for grant, Ending	2,417,454
Number of Shares Underlying Options Outstanding
Balance at the beginning of the period (in shares)	8,135,791
Granted (in shares)	114,110
Exercised (in shares)	(321,188)
Forfeited (in shares)	(9,500)
Balance at the end of the period (in shares)	7,919,213
Options vested and exercisable (in shares)	5,407,382
Options vested and expected to vest (in shares)	7,859,438
Weighted Average Remaining Contractual Life
Options weighted average remaining contractual life	5 years 5 months 23 days
Options vested and exercisable	4 years 2 months 5 days
Options vested and expected to vest	5 years 5 months 16 days
Weighted Average Exercise Price
Balance at the beginning of the period (in dollars per share) | $ / shares	$ 6.17
Granted (in dollars per share) | $ / shares	7.65
Exercised (in dollars per share) | $ / shares	6.21
Forfeited (in dollars per share) | $ / shares	7.92
Balance at the end of the period (in dollars per share) | $ / shares	6.19
Options vested and exercisable (in dollars per share) | $ / shares	5.64
Options vested and expected to vest (in dollars per share) | $ / shares	$ 6.18
Intrinsic Value
Exercised (in dollars) | $	$ 428,272
Options vested and exercisable (in dollars) | $	8,712,915
Options vested and expected to vest (in dollars) | $	$ 9,282,831