PROPERTY, PLANT AND EQUIPMENT (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, plant and equipment
Property, plant and equipment, gross	$ 174,015	$ 179,231
Accumulated depreciation	(123,225)	(122,270)
Property, plant and equipment, net	50,790	56,961
Depreciation expense	6,300	6,600	$ 7,000
Land, buildings, and improvements
Property, plant and equipment
Property, plant and equipment, gross	71,914	81,311
Machinery, equipment and fixtures
Property, plant and equipment
Property, plant and equipment, gross	78,168	75,177
Office furniture, equipment and vehicles
Property, plant and equipment
Property, plant and equipment, gross	23,633	22,471
Construction in progress
Property, plant and equipment
Property, plant and equipment, gross	$ 300	$ 272