Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Property, Plant and Equipment
Gross property, plant and equipment	$ 1,974,824	$ 1,985,456
Less: Accumulated depreciation	(1,302,686)	(1,317,247)
Property, plant and equipment, net	672,138	668,209
Land
Property, Plant and Equipment
Gross property, plant and equipment	75,669	75,559
Land improvements
Property, Plant and Equipment
Gross property, plant and equipment	19,784	20,166
Buildings and improvements
Property, Plant and Equipment
Gross property, plant and equipment	253,410	249,954
Machinery and equipment
Property, Plant and Equipment
Gross property, plant and equipment	1,566,448	1,597,592
Construction in progress
Property, Plant and Equipment
Gross property, plant and equipment	$ 59,513	$ 42,185

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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