11. STOCK-BASED COMPENSATION - Options outstanding by exercise price (Details) - $ / shares	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Options outstanding by exercise price
Exercise Price (in dollars per share)	$ 6.17	$ 5.77	$ 5.45	$ 5.09
Number of Shares Underlying Options Outstanding (in shares)	8,135,791
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 6.17
Options Outstanding, Weighted Average Remaining Contractual Life	5 years 5 months 19 days
Options Exercisable, Number Vested and Exercisable (in shares)	5,138,027
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 5.68
$3.40 - $4.81
Options outstanding by exercise price
Exercise Price, low end of range (in dollars per share)	3.40
Exercise Price, high end of range (in dollars per share)	$ 4.81
Number of Shares Underlying Options Outstanding (in shares)	910,273
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 4.07
Options Outstanding, Weighted Average Remaining Contractual Life	4 years 29 days
Options Exercisable, Number Vested and Exercisable (in shares)	910,273
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 4.07
$4.90 - $4.99
Options outstanding by exercise price
Exercise Price, low end of range (in dollars per share)	4.90
Exercise Price, high end of range (in dollars per share)	$ 4.99
Number of Shares Underlying Options Outstanding (in shares)	1,336,396
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 4.97
Options Outstanding, Weighted Average Remaining Contractual Life	5 years 1 month 24 days
Options Exercisable, Number Vested and Exercisable (in shares)	897,047
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 4.96
$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)	926,921
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 5.32
Options Outstanding, Weighted Average Remaining Contractual Life	4 years 4 months 21 days
Options Exercisable, Number Vested and Exercisable (in shares)	891,696
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)	825,827
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 5.92
Options Outstanding, Weighted Average Remaining Contractual Life	4 years 5 months 12 days
Options Exercisable, Number Vested and Exercisable (in shares)	644,888
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 5.90
$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)	1,399,575
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 6.58
Options Outstanding, Weighted Average Remaining Contractual Life	5 years 1 month 10 days
Options Exercisable, Number Vested and Exercisable (in shares)	784,655
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 6.49
$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)	1,296,755
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 7.05
Options Outstanding, Weighted Average Remaining Contractual Life	5 years 3 months 18 days
Options Exercisable, Number Vested and Exercisable (in shares)	721,208
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 6.93
$7.40 - $8.06
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)	$ 8.06
Number of Shares Underlying Options Outstanding (in shares)	628,211
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 7.77
Options Outstanding, Weighted Average Remaining Contractual Life	8 years 11 months 27 days
Options Exercisable, Number Vested and Exercisable (in shares)	136,376
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 7.59
$8.09
Options outstanding by exercise price
Exercise Price (in dollars per share)	$ 8.09
Number of Shares Underlying Options Outstanding (in shares)	85,360
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 8.09
Options Outstanding, Weighted Average Remaining Contractual Life	7 years 8 months 9 days
Options Exercisable, Number Vested and Exercisable (in shares)	43,304
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 8.09
$8.30
Options outstanding by exercise price
Exercise Price (in dollars per share)	$ 8.30
Number of Shares Underlying Options Outstanding (in shares)	617,893
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 8.30
Options Outstanding, Weighted Average Remaining Contractual Life	9 years 3 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	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