8. STOCK- BASED COMPENSATION - Options outstanding by exercise price (Details) - $ / shares	3 Months Ended
	Jun. 30, 2017	Mar. 31, 2017
Options outstanding by exercise price
Exercise Price (in dollars per share)	$ 5.14	$ 5.09
Number of Shares Underlying Options Outstanding (in shares)	7,331,824
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 5.14
Options Outstanding, Weighted Average Remaining Contractual Life	5 years 7 months 24 days
Options Exercisable, Number Vested and Exercisable (in shares)	4,753,789
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 5.16
$2.43 - $3.40
Options outstanding by exercise price
Exercise Price, low end of range (in dollars per share)	2.43
Exercise Price, high end of range (in dollars per share)	$ 3.40
Number of Shares Underlying Options Outstanding (in shares)	757,620
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 3.24
Options Outstanding, Weighted Average Remaining Contractual Life	4 years 2 months 12 days
Options Exercisable, Number Vested and Exercisable (in shares)	530,887
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 3.17
$3.43 - $4.00
Options outstanding by exercise price
Exercise Price, low end of range (in dollars per share)	3.43
Exercise Price, high end of range (in dollars per share)	$ 4.00
Number of Shares Underlying Options Outstanding (in shares)	1,064,296
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 3.81
Options Outstanding, Weighted Average Remaining Contractual Life	2 years 11 months 5 days
Options Exercisable, Number Vested and Exercisable (in shares)	946,702
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 3.83
$4.17 - $4.90
Options outstanding by exercise price
Exercise Price, low end of range (in dollars per share)	4.17
Exercise Price, high end of range (in dollars per share)	$ 4.90
Number of Shares Underlying Options Outstanding (in shares)	905,287
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 4.53
Options Outstanding, Weighted Average Remaining Contractual Life	5 years 26 days
Options Exercisable, Number Vested and Exercisable (in shares)	817,862
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 4.54
$4.92 - $4.99
Options outstanding by exercise price
Exercise Price, low end of range (in dollars per share)	4.92
Exercise Price, high end of range (in dollars per share)	$ 4.99
Number of Shares Underlying Options Outstanding (in shares)	1,211,981
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 4.98
Options Outstanding, Weighted Average Remaining Contractual Life	8 years 3 months 29 days
Options Exercisable, Number Vested and Exercisable (in shares)	205,454
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 4.96
$5.13 - $5.28
Options outstanding by exercise price
Exercise Price, low end of range (in dollars per share)	5.13
Exercise Price, high end of range (in dollars per share)	$ 5.28
Number of Shares Underlying Options Outstanding (in shares)	776,973
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 5.24
Options Outstanding, Weighted Average Remaining Contractual Life	7 years 9 months 11 days
Options Exercisable, Number Vested and Exercisable (in shares)	108,258
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 5.20
$5.34 - $6.00
Options outstanding by exercise price
Exercise Price, low end of range (in dollars per share)	5.34
Exercise Price, high end of range (in dollars per share)	$ 6.00
Number of Shares Underlying Options Outstanding (in shares)	761,081
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 5.75
Options Outstanding, Weighted Average Remaining Contractual Life	5 years 1 month 21 days
Options Exercisable, Number Vested and Exercisable (in shares)	718,483
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 5.77
$6.16 - $6.54
Options outstanding by exercise price
Exercise Price, low end of range (in dollars per share)	6.16
Exercise Price, high end of range (in dollars per share)	$ 6.54
Number of Shares Underlying Options Outstanding (in shares)	866,963
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 6.35
Options Outstanding, Weighted Average Remaining Contractual Life	6 years 26 days
Options Exercisable, Number Vested and Exercisable (in shares)	570,653
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 6.43
$6.61 - $7.00
Options outstanding by exercise price
Exercise Price, low end of range (in dollars per share)	6.61
Exercise Price, high end of range (in dollars per share)	$ 7.00
Number of Shares Underlying Options Outstanding (in shares)	787,253
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 6.82
Options Outstanding, Weighted Average Remaining Contractual Life	5 years 1 month 2 days
Options Exercisable, Number Vested and Exercisable (in shares)	742,110
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 6.84
$7.40
Options outstanding by exercise price
Exercise Price (in dollars per share)	$ 7.40
Number of Shares Underlying Options Outstanding (in shares)	86,990
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 7.40
Options Outstanding, Weighted Average Remaining Contractual Life	9 years 10 months 6 days
$9.20
Options outstanding by exercise price
Exercise Price (in dollars per share)	$ 9.20
Number of Shares Underlying Options Outstanding (in shares)	113,380
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 9.20
Options Outstanding, Weighted Average Remaining Contractual Life	3 years 5 months 9 days
Options Exercisable, Number Vested and Exercisable (in shares)	113,380
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 9.20