10. STOCK-BASED COMPENSATION - Stock options activities (Details)	3 Months Ended
	Jun. 30, 2019 USD ($) $ / shares shares
STOCK-BASED COMPENSATION
Shares available for grant, Beginning	3,426,548
Granted (in shares)	(71,610)
Forfeited (in shares)	21,650
Shares available for grant, Ending	3,376,588
Number of Shares Underlying Options Outstanding
Balance at the beginning of the period (in shares)	8,017,029
Granted (in shares)	71,610
Exercised (in shares)	(501,601)
Forfeited (in shares)	(21,950)
Balance at the end of the period (in shares)	7,565,088
Options vested and exercisable (in shares)	4,978,464
Options vested and expected to vest (in shares)	7,508,754
Weighted Average Remaining Contractual Life
Options weighted average remaining contractual life	5 years 8 months 1 day
Options vested and exercisable	4 years 3 months 18 days
Options vested and expected to vest	5 years 7 months 24 days
Weighted Average Exercise Price
Balance at the beginning of the period (in dollars per share) | $ / shares	$ 5.77
Granted (in dollars per share) | $ / shares	7.46
Exercised (in dollars per share) | $ / shares	3.94
Forfeited (in dollars per share) | $ / shares	7.90
Balance at the end of the period (in dollars per share) | $ / shares	5.90
Options vested and exercisable (in dollars per share) | $ / shares	5.64
Options vested and expected to vest (in dollars per share) | $ / shares	$ 5.89
Intrinsic Value
Exercised (in dollars) | $	$ 1,836,662
Options vested and exercisable (in dollars) | $	14,640,255
Options vested and expected to vest (in dollars) | $	$ 20,158,398