Property, Plant and Equipment (Schedule of Plant Property and Equipment) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 444,365	$ 428,599
Accumulated depreciation	(289,909)	(259,178)
Property, plant and equipment, net	154,456	169,421
Equipment in process	25,155	7,495
Total property, plant and equipment, net	179,611	176,916
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	14,620	15,855
Buildings and improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	135,191	138,493
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	238,000	220,238
Office equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 56,554	$ 54,013