10. STOCK-BASED COMPENSATION - Options outstanding by exercise price (Details) - $ / shares	3 Months Ended
	Jun. 30, 2020	Mar. 31, 2020
Options outstanding by exercise price
Exercise Price (in dollars per share)	$ 6.19	$ 6.17
Number of Shares Underlying Options Outstanding (in shares)	7,919,213
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 6.19
Options Outstanding, Weighted Average Remaining Contractual Life	5 years 5 months 23 days
Options Exercisable, Number Vested and Exercisable (in shares)	5,407,382
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 5.64
$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)	902,585
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 4.06
Options Outstanding, Weighted Average Remaining Contractual Life	3 years 9 months 26 days
Options Exercisable, Number Vested and Exercisable (in shares)	902,585
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 4.06
$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)	1,316,046
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 4.97
Options Outstanding, Weighted Average Remaining Contractual Life	4 years 11 months 12 days
Options Exercisable, Number Vested and Exercisable (in shares)	1,316,046
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)	926,721
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 5.32
Options Outstanding, Weighted Average Remaining Contractual Life	4 years 1 month 21 days
Options Exercisable, Number Vested and Exercisable (in shares)	891,496
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 5.32
$5.69 - $6.28
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)	$ 6.28
Number of Shares Underlying Options Outstanding (in shares)	838,702
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 5.99
Options Outstanding, Weighted Average Remaining Contractual Life	4 years 6 months 18 days
Options Exercisable, Number Vested and Exercisable (in shares)	650,263
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 5.98
$6.45 - $6.70
Options outstanding by exercise price
Exercise Price, low end of range (in dollars per share)	6.45
Exercise Price, high end of range (in dollars per share)	$ 6.70
Number of Shares Underlying Options Outstanding (in shares)	1,197,400
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 6.63
Options Outstanding, Weighted Average Remaining Contractual Life	5 years 4 months 28 days
Options Exercisable, Number Vested and Exercisable (in shares)	652,453
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 6.58
$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)	1,192,855
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 7.06
Options Outstanding, Weighted Average Remaining Contractual Life	5 years 5 months 19 days
Options Exercisable, Number Vested and Exercisable (in shares)	661,556
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 6.95
$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)	737,571
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 7.75
Options Outstanding, Weighted Average Remaining Contractual Life	8 years 9 months 26 days
Options Exercisable, Number Vested and Exercisable (in shares)	135,626
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)	83,860
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 8.09
Options Outstanding, Weighted Average Remaining Contractual Life	7 years 6 months 29 days
Options Exercisable, Number Vested and Exercisable (in shares)	41,804
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)	614,893
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 8.30
Options Outstanding, Weighted Average Remaining Contractual Life	9 years 26 days
Options Exercisable, Number Vested and Exercisable (in shares)	46,973
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 8.30
$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	7 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