Property, Plant And Equipment (Schedule Of Property, Plant And Equipment) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Property, plant and equipment, gross	$ 572,523	$ 557,258
Less accumulated depreciation	(406,375)	(379,088)
Property, plant and equipment, Net	166,148	178,170
Land [Member]
Property, plant and equipment, gross	6,169	6,169
Buildings And Building Improvements [Member]
Property, plant and equipment, gross	90,330	89,720
Machinery And Equipment [Member]
Property, plant and equipment, gross	445,537	432,582
Furniture And Fixtures [Member]
Property, plant and equipment, gross	8,089	8,049
Vehicles [Member]
Property, plant and equipment, gross	1,231	1,009
Leasehold Improvements [Member]
Property, plant and equipment, gross	$ 21,167	$ 19,729