8. STOCK- BASED COMPENSATION - Options outstanding by exercise price (Details) - $ / shares	6 Months Ended
	Sep. 30, 2017	Mar. 31, 2017
Options outstanding by exercise price
Exercise Price (in dollars per share)	$ 5.30	$ 5.09
Number of Shares Underlying Options Outstanding (in shares)	7,794,623
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 5.30
Options Outstanding, Weighted Average Remaining Contractual Life	5 years 8 months 27 days
Options Exercisable, Number Vested and Exercisable (in shares)	4,851,100
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 5.18
$2.43 - $3.43
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)	$ 3.43
Number of Shares Underlying Options Outstanding (in shares)	962,345
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 3.30
Options Outstanding, Weighted Average Remaining Contractual Life	3 years 6 months 18 days
Options Exercisable, Number Vested and Exercisable (in shares)	735,612
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 3.26
$3.60 - $4.00
Options outstanding by exercise price
Exercise Price, low end of range (in dollars per share)	3.60
Exercise Price, high end of range (in dollars per share)	$ 4.00
Number of Shares Underlying Options Outstanding (in shares)	794,446
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 3.92
Options Outstanding, Weighted Average Remaining Contractual Life	2 years 8 months 9 days
Options Exercisable, Number Vested and Exercisable (in shares)	699,352
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 3.96
$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)	902,210
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 4.53
Options Outstanding, Weighted Average Remaining Contractual Life	4 years 9 months 22 days
Options Exercisable, Number Vested and Exercisable (in shares)	847,985
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)	1,194,039
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 4.98
Options Outstanding, Weighted Average Remaining Contractual Life	8 years 1 month 10 days
Options Exercisable, Number Vested and Exercisable (in shares)	195,237
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 4.96
$5.13 - $5.34
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)	$ 5.34
Number of Shares Underlying Options Outstanding (in shares)	813,812
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 5.24
Options Outstanding, Weighted Average Remaining Contractual Life	7 years 6 months 26 days
Options Exercisable, Number Vested and Exercisable (in shares)	223,804
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 5.25
$5.59 - $6.16
Options outstanding by exercise price
Exercise Price, low end of range (in dollars per share)	5.59
Exercise Price, high end of range (in dollars per share)	$ 6.16
Number of Shares Underlying Options Outstanding (in shares)	946,052
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 5.87
Options Outstanding, Weighted Average Remaining Contractual Life	5 years 10 months 2 days
Options Exercisable, Number Vested and Exercisable (in shares)	695,542
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 5.78
$6.24 - $6.63
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)	$ 6.63
Number of Shares Underlying Options Outstanding (in shares)	827,926
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 6.46
Options Outstanding, Weighted Average Remaining Contractual Life	4 years 11 months 5 days
Options Exercisable, Number Vested and Exercisable (in shares)	755,758
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 6.47
$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)	1,161,223
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 7.07
Options Outstanding, Weighted Average Remaining Contractual Life	7 years 18 days
Options Exercisable, Number Vested and Exercisable (in shares)	589,230
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 6.89
$7.40
Options outstanding by exercise price
Exercise Price (in dollars per share)	$ 7.40
Number of Shares Underlying Options Outstanding (in shares)	83,990
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 7.40
Options Outstanding, Weighted Average Remaining Contractual Life	9 years 7 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)	108,580
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 9.20
Options Outstanding, Weighted Average Remaining Contractual Life	3 years 4 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