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Summary of Significant Accounting Policies - Goodwill (Narrative) (Details) - USD ($) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2019 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Goodwill [Line Items] |  |  |  |
Goodwill impairment |  | $ 0 | $ 4,100,000 | $ 2,403,000
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount |  |  | 23.00% |
Horizon Plastics reporting unit |  |  |  |
Goodwill [Line Items] |  |  |  |
Goodwill impairment | $ 4,100,000 |  |  |
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount | 19.00% |  |  |

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- Definition Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121556970&loc=d3e13854-109267 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=121556970&loc=d3e13816-109267 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=99380562&loc=d3e13777-109266 + Details
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