10. STOCK-BASED COMPENSATION - Options outstanding by exercise price (Details) - $ / shares	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Options outstanding by exercise price
Exercise Price (in dollars per share)	$ 5.77	$ 5.45	$ 5.09	$ 5.08
Number of Shares Underlying Options Outstanding (in shares)	8,017,029
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 5.77
Options Outstanding, Weighted Average Remaining Contractual Life	5 years 6 months 26 days
Options Exercisable, Number Vested and Exercisable (in shares)	4,905,367
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 5.50
$3.38 - $4.00
Options outstanding by exercise price
Exercise Price, low end of range (in dollars per share)	3.38
Exercise Price, high end of range (in dollars per share)	$ 4.00
Number of Shares Underlying Options Outstanding (in shares)	864,046
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 3.63
Options Outstanding, Weighted Average Remaining Contractual Life	3 years 15 days
Options Exercisable, Number Vested and Exercisable (in shares)	771,339
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 3.66
$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)	806,788
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 4.55
Options Outstanding, Weighted Average Remaining Contractual Life	3 years 6 months 11 days
Options Exercisable, Number Vested and Exercisable (in shares)	789,463
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 4.55
$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)	1,181,766
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 4.98
Options Outstanding, Weighted Average Remaining Contractual Life	6 years 7 months 21 days
Options Exercisable, Number Vested and Exercisable (in shares)	273,940
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 4.97
$5.13 - $5.59
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)	$ 5.59
Number of Shares Underlying Options Outstanding (in shares)	992,004
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 5.31
Options Outstanding, Weighted Average Remaining Contractual Life	5 years 6 months 22 days
Options Exercisable, Number Vested and Exercisable (in shares)	906,254
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 5.32
$5.69 - $6.16
Options outstanding by exercise price
Exercise Price, low end of range (in dollars per share)	5.69
Exercise Price, high end of range (in dollars per share)	$ 6.16
Number of Shares Underlying Options Outstanding (in shares)	882,372
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 5.93
Options Outstanding, Weighted Average Remaining Contractual Life	5 years 7 months 24 days
Options Exercisable, Number Vested and Exercisable (in shares)	543,016
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 5.89
$6.24 - $6.70
Options outstanding by exercise price
Exercise Price, low end of range (in dollars per share)	6.24
Exercise Price, high end of range (in dollars per share)	$ 6.70
Number of Shares Underlying Options Outstanding (in shares)	1,422,638
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 6.58
Options Outstanding, Weighted Average Remaining Contractual Life	6 years 29 days
Options Exercisable, Number Vested and Exercisable (in shares)	732,745
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 6.48
$6.82 - $7.26
Options outstanding by exercise price
Exercise Price, low end of range (in dollars per share)	6.82
Exercise Price, high end of range (in dollars per share)	$ 7.26
Number of Shares Underlying Options Outstanding (in shares)	1,362,255
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 7.04
Options Outstanding, Weighted Average Remaining Contractual Life	6 years 1 month 28 days
Options Exercisable, Number Vested and Exercisable (in shares)	692,985
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 6.91
$7.40 - $7.88
Options outstanding by exercise price
Exercise Price, low end of range (in dollars per share)	7.40
Exercise Price, high end of range (in dollars per share)	$ 7.88
Number of Shares Underlying Options Outstanding (in shares)	269,720
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 7.70
Options Outstanding, Weighted Average Remaining Contractual Life	9 years 1 month 24 days
Options Exercisable, Number Vested and Exercisable (in shares)	55,518
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 7.50
$8.09
Options outstanding by exercise price
Exercise Price (in dollars per share)	$ 8.09
Number of Shares Underlying Options Outstanding (in shares)	126,860
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 8.09
Options Outstanding, Weighted Average Remaining Contractual Life	8 years 9 months 29 days
Options Exercisable, Number Vested and Exercisable (in shares)	31,527
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 8.09
$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	1 year 9 months 22 days
Options Exercisable, Number Vested and Exercisable (in shares)	108,580
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 9.20