GOODWILL AND OTHER INTANGIBLE ASSETS - Other intangible assets - (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Other intangible assets:
Cost	$ 10,844,000	$ 10,840,000
Accumulated amortization	4,774,000	4,614,000
Net book value	6,070,000	6,226,000
Customer relationships [Member]
Other intangible assets:
Cost	6,504,000	6,502,000
Accumulated amortization	3,163,000	3,034,000
Net book value	$ 3,341,000	$ 3,468,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	7 years 4 months 24 days	7 years 7 months 6 days
Trademarks and trade names one [Member]
Other intangible assets:
Cost	$ 2,188,000	$ 2,187,000
Accumulated amortization	0	0
Net book value	$ 2,188,000	$ 2,187,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	10 years 3 months 18 days	10 years 6 months
Trademarks and Trade Names Two [Member]
Other intangible assets:
Cost	$ 200,000	$ 200,000
Accumulated amortization	62,000	59,000
Net book value	138,000	141,000
Engineering drawings [Member]
Other intangible assets:
Cost	330,000	330,000
Accumulated amortization	243,000	239,000
Net book value	$ 87,000	$ 91,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	5 years 10 months 24 days	6 years 1 month 6 days
Non-compete agreements [Member]
Other intangible assets:
Cost	$ 336,000	$ 335,000
Accumulated amortization	274,000	266,000
Net book value	$ 62,000	$ 69,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	2 years 9 months 18 days	3 years
Patents [Member]
Other intangible assets:
Cost	$ 1,286,000	$ 1,286,000
Accumulated amortization	1,032,000	1,016,000
Net book value	$ 254,000	$ 270,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	5 years	5 years 2 months 12 days