Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Property, Plant and Equipment
Gross property, plant and equipment	$ 1,850,243	$ 1,696,729
Less: Accumulated depreciation	(1,299,572)	(1,263,936)
Property, plant and equipment, net	550,671	432,793
Land
Property, Plant and Equipment
Gross property, plant and equipment	30,427	10,143
Land improvements
Property, Plant and Equipment
Gross property, plant and equipment	18,713	15,961
Buildings and improvements
Property, Plant and Equipment
Gross property, plant and equipment	180,640	163,037
Machinery and equipment
Property, Plant and Equipment
Gross property, plant and equipment	1,558,713	1,470,620
Construction in progress
Property, Plant and Equipment
Gross property, plant and equipment	$ 61,750	$ 36,968

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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