PROPERTY, PLANT AND EQUIPMENT (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 2,010,644	$ 1,955,953
Accumulated depreciation	(1,167,269)	(1,109,665)
Total property, plant and equipment, net	843,375	846,288
Land and land improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	15,411	13,456
Buildings [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	180,304	173,554
Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,777,299	1,749,410
Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 37,630	$ 19,533