STOCK-BASED COMPENSATION PLANS - Summary of stock option activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Summary of stock option activity under the option Plan
Outstanding at ending balance	708
Exercisable Number of Options	588
Employee Stock Option [Member]
Summary of stock option activity under the option Plan
Outstanding at beginning balance	1,006
Number of Shares, Forfeited	(198)
Number of Shares, Exercised	(100)
Outstanding at ending balance	708	1,006
Exercisable Number of Options	588
Weighted Average Exercise Price, Outstanding at beginning balance	$ 3.04
Weighted Average Exercise Price, Forfeited	7.22
Weighted Average Exercise Price, Exercised	5.31
Weighted Average Exercise Price, Outstanding at ending balance	1.55	$ 3.04
Weighted Average Exercise Price, Exercisable at ending balance	$ 1.04
Weighted Average Remaining Contractual Life, Outstanding	4 years 11 months 19 days	6 years 5 months 19 days
Weighted Average Remaining Contractual Life, Exercisable (Years)	4 years 6 months 7 days
Aggregate Intrinsic Value, Outstanding	$ 6,963	$ 10,483
Aggregate Intrinsic Value, Exercisable	$ 6,088