GOODWILL AND OTHER INTANGIBLE ASSETS - Other intangible assets - (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Other intangible assets:
Cost	$ 10,831,000	$ 10,840,000
Accumulated amortization	5,082,000	4,614,000
Net book value	5,749,000	6,226,000
Customer relationships [Member]
Other intangible assets:
Cost	6,498,000	6,502,000
Accumulated amortization	3,416,000	3,034,000
Net book value	$ 3,082,000	$ 3,468,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	6 years 10 months 24 days	7 years 7 months 6 days
Trademarks and trade names one [Member]
Other intangible assets:
Cost	$ 2,184,000	$ 2,187,000
Accumulated amortization	0	0
Net book value	$ 2,184,000	$ 2,187,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	9 years 9 months 18 days	10 years 6 months
Trademarks and Trade Names Two [Member]
Other intangible assets:
Cost	$ 200,000	$ 200,000
Accumulated amortization	69,000	59,000
Net book value	131,000	141,000
Engineering drawings [Member]
Other intangible assets:
Cost	330,000	330,000
Accumulated amortization	250,000	239,000
Net book value	$ 80,000	$ 91,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	5 years 4 months 24 days	6 years 1 month 6 days
Non-compete agreements [Member]
Other intangible assets:
Cost	$ 333,000	$ 335,000
Accumulated amortization	284,000	266,000
Net book value	$ 49,000	$ 69,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	2 years 3 months 18 days	3 years
Patents [Member]
Other intangible assets:
Cost	$ 1,286,000	$ 1,286,000
Accumulated amortization	1,063,000	1,016,000
Net book value	$ 223,000	$ 270,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	4 years 8 months 12 days	5 years 2 months 12 days