Property, Plant and Equipment (Schedule of Property, Plant and Equipment) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 631,925	$ 622,641
Accumulated depreciation	(440,756)	(423,729)
Property, plant and equipment, net	191,169	198,912
Land and land improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	8,103	8,080
Building and building improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	78,191	77,021
Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	521,434	517,782
Furniture and fixtures [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	8,729	9,124
Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 15,468	$ 10,634