SEGMENT DATA Long Lived Assets (Details) - USD ($) $ in Thousands		Mar. 31, 2019		Dec. 31, 2018		Dec. 31, 2017	Sep. 30, 2017
Segment Reporting Information [Line Items]
Long-lived assets		$ 110,347	[1]	$ 117,604	[1]	$ 119,349	$ 121,490
Operating Segments
Segment Reporting Information [Line Items]
Long-lived assets	[1]	108,634		115,640
Operating Segments | Bulgaria
Segment Reporting Information [Line Items]
Long-lived assets		10,838		10,627
Operating Segments | Czech Republic
Segment Reporting Information [Line Items]
Long-lived assets		37,292		39,314
Operating Segments | Romania
Segment Reporting Information [Line Items]
Long-lived assets		30,116		33,368
Operating Segments | Slovak Republic
Segment Reporting Information [Line Items]
Long-lived assets		15,469		16,376
Operating Segments | SLOVENIA
Segment Reporting Information [Line Items]
Long-lived assets		14,919		15,955
Corporate
Segment Reporting Information [Line Items]
Long-lived assets		$ 1,713		$ 1,964

[1] (1) Reflects property, plant and equipment, net