GEOGRAPHIC AND SEGMENT INFORMATION - Reportable Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Sales	$ 48,517	$ 27,711
Income (loss) from operations	(14,448)	(20,083)
Interest income	11	241
Interest expense	(10)	(46)
Other (losses) income, net	(373)	479
Income tax expense (benefit)	380	(7,503)
Operating Segments | Advanced Energy
Segment Reporting Information [Line Items]
Sales	42,985	22,214
Income (loss) from operations	2,784	(7,128)
Interest expense	0
Income tax expense (benefit)	0	0
Operating Segments | OEM
Segment Reporting Information [Line Items]
Sales	5,532	5,497
Income (loss) from operations	1,033	1,838
Income tax expense (benefit)	0	0
Corporate (Other)
Segment Reporting Information [Line Items]
Income (loss) from operations	(18,265)	(14,793)
Interest income	11	241
Interest expense	(10)	(46)
Other (losses) income, net	(373)	479
Income tax expense (benefit)	$ 380	$ (7,503)