Property, Plant and Equipment - Summary of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Property, plant and equipment
Less: Accumulated depreciation	$ (202,128)	$ (202,128)	$ (200,734)
Property, plant and equipment, net	93,630	93,630	88,247
Depreciation	3,774	7,537
Land
Property, plant and equipment
Property, plant and equipment gross	1,137	1,137	1,130
Buildings and improvements
Property, plant and equipment
Property, plant and equipment gross	68,778	68,778	64,201
Machinery and equipment
Property, plant and equipment
Property, plant and equipment gross	$ 225,843	$ 225,843	$ 223,650

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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-SubTopic 10
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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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-Publisher FASB
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