GEOGRAPHIC AND SEGMENT INFORMATION - Reportable Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Segment Reporting Information [Line Items]
Sales	$ 12,493	$ 8,638
Loss from operations	(5,871)	(4,745)
Interest income	2	3
Interest expense	(8)	(4)
Other income (loss), net	(21)	(93)
Income tax (benefit) expense	70	66
Operating Segments | Advanced Energy
Segment Reporting Information [Line Items]
Sales	10,814	7,660
Loss from operations	(1,339)	(602)
Interest income	0	0
Interest expense	0	0
Other income (loss), net	0	0
Income tax (benefit) expense	0	0
Operating Segments | OEM
Segment Reporting Information [Line Items]
Sales	1,679	978
Loss from operations	317	(3)
Interest income	0	0
Interest expense	0	0
Other income (loss), net	0	0
Income tax (benefit) expense	0	0
Corporate & Other
Segment Reporting Information [Line Items]
Sales	0	0
Loss from operations	(4,849)	(4,140)
Interest income	2	3
Interest expense	(8)	(4)
Other income (loss), net	(21)	(93)
Income tax (benefit) expense	$ 70	$ 66