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Commitments and Contingencies - Legal Contingencies (Details) - USD ($) |  | 1 Months Ended | 12 Months Ended
--- | --- | --- | ---
Aug. 18, 2017 | Sep. 30, 2017 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2013
Ravenswood Retiree Medical Benefits Changes [Member] |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |
Litigation settlement amount | $ 23,000,000.0 |  |  |  |  |
Litigation settlement period |  |  | 10 years |  |  |
Ravenswood retiree legal settlement |  | $ 5,000,000.0 |  |  |  |
Gain recognized |  | 5,500,000 |  |  |  |
Loss contingency accrual |  | $ 12,500,000 |  |  |  |
Other liabilities, current |  |  | $ 2,000,000.0 |  |  |
Other liabilities |  |  | 7,500,000 |  |  |
Litigation settlement, annual installment |  |  | $ 2,000,000.0 |  |  |
Litigation settlement installment period |  |  | 9 years |  |  |
PBGC Agreement [Member] |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |
Required pension contributions above minimum |  |  |  |  |  | $ 17,400,000
Pension contributions |  |  | $ 0 | $ 0 | $ 0 |
Pension contributions above minimum remaining |  |  | $ 9,600,000 |  |  |

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- Definition Litigation Settlement Installment Period + References No definition available. + Details
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- Definition Litigation Settlement Payment Period + References No definition available. + Details
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- Definition Pursuant to the terms of the settlement agreement with the Pension Benefit Guaranty Corporation, this amount represents the remaining additional contributions (above any minimum required contributions) to our defined benefit pension plans. + References No definition available. + Details
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- Definition Pursuant to the terms of the settlement agreement with the Pension Benefit Guaranty Corporation, we will make additional contributions (above any minimum required contributions) to our defined benefit pension plans. + References No definition available. + Details
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- Definition Amount of gain (loss) recognized in settlement of litigation and insurance claims. Excludes claims within an insurance entity's normal claims settlement process. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=121557415&loc=d3e14326-108349 + Details
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- Definition Amount awarded to other party in judgment or settlement of litigation. + References No definition available. + Details
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- Definition 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. + References No definition available. + Details
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- Definition Amount of loss contingency liability. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=121557415&loc=d3e14326-108349 + Details
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- Definition Amount of liabilities classified as other, due within one year or the normal operating cycle, if longer. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=121566466&loc=d3e6904-107765 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 45 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=121566466&loc=d3e6911-107765 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.20) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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- Definition The amount of cash paid for the settlement of litigation or for other legal issues during the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 25 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3536-108585 + Details
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- Definition Amount of cash outflow for pension benefit. Includes, but is not limited to, employer contribution to fund plan asset and payment to retiree. Excludes other postretirement benefit. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 25 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3536-108585 + Details
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