STOCKHOLDERS' EQUITY - Warrants (Details) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares
Outstanding at ending balance	708
Warrant
Outstanding at beginning balance	100
Number of Warrants, Granted	0
Number of Shares, Exercised	(10)
Number of Warrants, Forfeited	0
Outstanding at ending balance	90	100
Weighted Average Exercise Price, Outstanding at beginning balance | $ / shares	$ 2.63
Weighted Average Exercise Price, Granted | $ / shares	0
Weighted Average Exercise Price, Exercised | $ / shares	2.50
Weighted Average Exercise Price, Forfeited | $ / shares	0
Weighted Average Exercise Price, Outstanding at ending balance | $ / shares	$ 2.64	$ 2.63
Weighted Average Remaining Contractual Life (Years)	3 years 7 days	3 years 9 months 3 days
Weighted Average Remaining Contractual Life, Exercised (Years)	3 years 7 days
Aggregate Intrinsic Value | $	$ 788	$ 1,084
Aggregate Intrinsic Value, Exercised | $	$ 192
Employee Stock Option [Member]
Outstanding at beginning balance	1,006
Number of Shares, Exercised	(100)
Number of Warrants, Forfeited	(198)
Outstanding at ending balance	708	1,006
Weighted Average Exercise Price, Outstanding at beginning balance | $ / shares	$ 3.04
Weighted Average Exercise Price, Exercised | $ / shares	5.31
Weighted Average Exercise Price, Forfeited | $ / shares	7.22
Weighted Average Exercise Price, Outstanding at ending balance | $ / shares	$ 1.55	$ 3.04
Weighted Average Remaining Contractual Life (Years)	4 years 11 months 19 days	6 years 5 months 19 days
Weighted Average Remaining Contractual Life, Exercised (Years)	4 years 6 months 7 days
Aggregate Intrinsic Value | $	$ 6,963	$ 10,483