Property, Plant and Equipment (Schedule of Property, Plant and Equipment) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Gross property, plant and equipment	$ 687,284	$ 648,248
Less accumulated depreciation	421,609	391,856
Net property, plant and equipment	265,675	256,392
Depreciation	44,400	47,300	$ 41,400
Land
Property, Plant and Equipment [Line Items]
Gross property, plant and equipment	20,859	19,524
Buildings
Property, Plant and Equipment [Line Items]
Gross property, plant and equipment	107,659	102,666
Machinery and equipment
Property, Plant and Equipment [Line Items]
Gross property, plant and equipment	505,978	473,004
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Gross property, plant and equipment	15,391	14,208
Software
Property, Plant and Equipment [Line Items]
Gross property, plant and equipment	24,464	22,733
Construction in progress
Property, Plant and Equipment [Line Items]
Gross property, plant and equipment	$ 12,933	$ 16,113