9. STOCK- BASED COMPENSATION - Options outstanding by exercise price (Details) - $ / shares	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Options outstanding by exercise price
Exercise Price (in dollars per share)	$ 5.45	$ 5.09	$ 5.08	$ 5.16
Number of Shares Underlying Options Outstanding (in shares)	7,874,267
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 5.45
Options Outstanding, Weighted Average Remaining Contractual Life	5 years 7 months 2 days
Options Exercisable, Number Vested and Exercisable (in shares)	4,813,339
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 5.25
$2.43 - $3.60
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)	$ 3.60
Number of Shares Underlying Options Outstanding (in shares)	903,633
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 3.37
Options Outstanding, Weighted Average Remaining Contractual Life	4 years 3 months 4 days
Options Exercisable, Number Vested and Exercisable (in shares)	689,079
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 3.34
$3.75 - $4.17
Options outstanding by exercise price
Exercise Price, low end of range (in dollars per share)	3.75
Exercise Price, high end of range (in dollars per share)	$ 4.17
Number of Shares Underlying Options Outstanding (in shares)	905,706
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 4.03
Options Outstanding, Weighted Average Remaining Contractual Life	1 year 11 months 12 days
Options Exercisable, Number Vested and Exercisable (in shares)	905,706
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 4.03
$4.30 - $4.98
Options outstanding by exercise price
Exercise Price, low end of range (in dollars per share)	4.30
Exercise Price, high end of range (in dollars per share)	$ 4.98
Number of Shares Underlying Options Outstanding (in shares)	1,180,166
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 4.83
Options Outstanding, Weighted Average Remaining Contractual Life	5 years 7 months 21 days
Options Exercisable, Number Vested and Exercisable (in shares)	692,684
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 4.76
$4.99 - $5.23
Options outstanding by exercise price
Exercise Price, low end of range (in dollars per share)	4.99
Exercise Price, high end of range (in dollars per share)	$ 5.23
Number of Shares Underlying Options Outstanding (in shares)	1,158,816
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 5.10
Options Outstanding, Weighted Average Remaining Contractual Life	7 years 5 months 12 days
Options Exercisable, Number Vested and Exercisable (in shares)	177,739
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 5.12
$5.28 - $6.00
Options outstanding by exercise price
Exercise Price, low end of range (in dollars per share)	5.28
Exercise Price, high end of range (in dollars per share)	$ 6.00
Number of Shares Underlying Options Outstanding (in shares)	975,486
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 5.64
Options Outstanding, Weighted Average Remaining Contractual Life	5 years 4 months 17 days
Options Exercisable, Number Vested and Exercisable (in shares)	830,592
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 5.70
$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)	849,678
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 6.35
Options Outstanding, Weighted Average Remaining Contractual Life	5 years 3 months 18 days
Options Exercisable, Number Vested and Exercisable (in shares)	622,445
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 6.41
$6.61 - $6.86
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)	$ 6.86
Number of Shares Underlying Options Outstanding (in shares)	843,896
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 6.80
Options Outstanding, Weighted Average Remaining Contractual Life	6 years 2 months 23 days
Options Exercisable, Number Vested and Exercisable (in shares)	604,005
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 6.78
$7.00 - $7.40
Options outstanding by exercise price
Exercise Price, low end of range (in dollars per share)	7.00
Exercise Price, high end of range (in dollars per share)	$ 7.40
Number of Shares Underlying Options Outstanding (in shares)	817,496
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 7.22
Options Outstanding, Weighted Average Remaining Contractual Life	7 years 11 months 1 day
Options Exercisable, Number Vested and Exercisable (in shares)	182,509
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 7.05
$8.09
Options outstanding by exercise price
Exercise Price (in dollars per share)	$ 8.09
Number of Shares Underlying Options Outstanding (in shares)	130,810
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 8.09
Options Outstanding, Weighted Average Remaining Contractual Life	9 years 9 months 29 days
$9.20
Options outstanding by exercise price
Exercise Price (in dollars per share)	$ 9.20
Number of Shares Underlying Options Outstanding (in shares)	108,580
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 9.20
Options Outstanding, Weighted Average Remaining Contractual Life	2 years 10 months 2 days
Options Exercisable, Number Vested and Exercisable (in shares)	108,580
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 9.20