8. STOCK- BASED COMPENSATION - Stock options activities (Details)	3 Months Ended
	Jun. 30, 2017 USD ($) $ / shares shares
STOCK- BASED COMPENSATION
Shares available for grant, Beginning	5,464,185
Granted (in shares)	(86,990)
Forfeited (in shares)	6,800
Shares available for grant, Ending	5,383,995
Number of Shares Underlying Options Outstanding
Balance at the beginning of the period (in shares)	7,622,830
Granted (in shares)	86,990
Exercised (in shares)	(330,321)
Forfeited (in shares)	(47,675)
Balance at the end of the period (in shares)	7,331,824
Options vested and exercisable (in shares)	4,753,789
Options vested and expected to vest (in shares)	7,276,640
Weighted Average Remaining Contractual Life
Options vested and exercisable	4 years 1 month 2 days
Options vested and expected to vest	5 years 7 months 17 days
Weighted Average Exercise Price
Balance at the beginning of the period (in dollars per share) | $ / shares	$ 5.09
Granted (in dollars per share) | $ / shares	7.40
Exercised (in dollars per share) | $ / shares	4.59
Forfeited (in dollars per share) | $ / shares	4.99
Balance at the end of the period (in dollars per share) | $ / shares	5.14
Options vested and exercisable (in dollars per share) | $ / shares	5.16
Options vested and expected to vest (in dollars per share) | $ / shares	$ 5.14
Intrinsic Value
Exercised (in dollars) | $	$ 1,110,705
Options vested and exercisable (in dollars) | $	12,980,279
Options vested and expected to vest (in dollars) | $	$ 19,975,008