Assets - Property, Plant, and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Property, plant, and equipment
Gross property, plant and equipment	$ 211,087		$ 211,340
Less: accumulated depreciation and amortization	138,796		135,629
Net property, plant, and equipment	72,291		75,711
Depreciation expense	3,900	$ 4,600
Land
Property, plant, and equipment
Gross property, plant and equipment	5,061		5,061
Building and improvements
Property, plant, and equipment
Gross property, plant and equipment	62,631		61,884
Machinery and equipment
Property, plant, and equipment
Gross property, plant and equipment	136,625		137,692
Leaseholds improvements
Property, plant, and equipment
Gross property, plant and equipment	$ 6,770		$ 6,703

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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The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

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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.

+ References

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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