INTANGIBLE ASSETS - Intangible Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Definite-lived intangible assets
Gross value of definite-lived intangible assets	$ 64,724	$ 65,567
Accumulated amortization	(43,820)	(42,964)
Net definite-lived intangible assets	20,904	22,603
Indefinite-lived intangible assets
Total intangible assets, net	22,209	23,908	$ 24,332	$ 25,300
Trademarks and trade names
Indefinite-lived intangible assets
Trademarks and trade names	1,305	1,305
Customer relationships
Definite-lived intangible assets
Gross value of definite-lived intangible assets	24,102	24,862
Accumulated amortization	(19,762)	(19,537)
Unpatented technology
Definite-lived intangible assets
Gross value of definite-lived intangible assets	15,321	15,713
Accumulated amortization	(7,149)	(6,751)
Patented technology
Definite-lived intangible assets
Gross value of definite-lived intangible assets	3,114	2,642
Accumulated amortization	(2,616)	(2,593)
Tradename
Definite-lived intangible assets
Gross value of definite-lived intangible assets	12,769	13,088
Accumulated amortization	(4,978)	(4,831)
All other
Definite-lived intangible assets
Gross value of definite-lived intangible assets	9,418	9,262
Accumulated amortization	$ (9,315)	$ (9,252)