PROPERTY, PLANT AND EQUIPMENT (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Property, plant and equipment
Property, plant and equipment, gross	$ 181,651	$ 179,231
Accumulated depreciation	(124,788)	(122,270)
Property, plant and equipment, net	56,863	56,961
Land, buildings and improvements
Property, plant and equipment
Property, plant and equipment, gross	82,606	81,311
Machinery, equipment and fixtures
Property, plant and equipment
Property, plant and equipment, gross	75,933	75,177
Office furniture, equipment and vehicles
Property, plant and equipment
Property, plant and equipment, gross	22,736	22,471
Construction in progress
Property, plant and equipment
Property, plant and equipment, gross	$ 376	$ 272