GEOGRAPHIC AND SEGMENT INFORMATION - REPORTABLE SEGMENT (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Sales	$ 4,997	$ 5,629
Income (loss) from operations	(7,492)	(5,730)
Interest income	216	423
Interest expense	(6)	0
Other income (losses), net	426	(295)
Income tax (benefit) expense	$ (4,905)	$ 6
International sales, percent of total revenue	27.60%	30.50%
Operating Segments | Advanced Energy
Segment Reporting Information [Line Items]
Sales	$ 3,986	$ 4,371
Income (loss) from operations	(3,984)	(3,328)
Interest income	0	0
Interest expense	0
Other income (losses), net	0	0
Income tax (benefit) expense	0	0
Operating Segments | OEM
Segment Reporting Information [Line Items]
Sales	1,011	1,258
Income (loss) from operations	247	591
Interest income	0	0
Interest expense	0
Other income (losses), net	0	0
Income tax (benefit) expense	0	0
Corporate & Other
Segment Reporting Information [Line Items]
Sales	0	0
Income (loss) from operations	(3,755)	(2,993)
Interest income		423
Interest expense	$ (6)
Other income (losses), net		(295)
Income tax (benefit) expense		$ 6