8. STOCK- BASED COMPENSATION - Stock options activities (Details)	3 Months Ended
	Jun. 30, 2018 USD ($) $ / shares shares
STOCK- BASED COMPENSATION
Shares available for grant, Beginning	4,444,301
Granted (in shares)	(78,590)
Forfeited (in shares)	8,750
Shares available for grant, Ending	4,374,461
Number of Shares Underlying Options Outstanding
Balance at the beginning of the period (in shares)	7,874,267
Granted (in shares)	78,590
Exercised (in shares)	(300,528)
Forfeited (in shares)	(38,550)
Balance at the end of the period (in shares)	7,613,779
Options vested and exercisable (in shares)	5,046,534
Options vested and expected to vest (in shares)	7,556,754
Weighted Average Remaining Contractual Life
Options weighted average remaining contractual life	5 years 6 months 11 days
Options vested and exercisable	4 years 29 days
Options vested and expected to vest	5 years 6 months 4 days
Weighted Average Exercise Price
Balance at the beginning of the period (in dollars per share) | $ / shares	$ 5.45
Granted (in dollars per share) | $ / shares	7.70
Exercised (in dollars per share) | $ / shares	3.92
Forfeited (in dollars per share) | $ / shares	4.57
Balance at the end of the period (in dollars per share) | $ / shares	5.53
Options vested and exercisable (in dollars per share) | $ / shares	5.34
Options vested and expected to vest (in dollars per share) | $ / shares	$ 5.53
Intrinsic Value
Exercised (in dollars) | $	$ 1,054,096
Options vested and exercisable (in dollars) | $	11,189,643
Options vested and expected to vest (in dollars) | $	$ 15,312,078