XML 61 R47.htm IDEA: XBRL DOCUMENT
v3.19.3

Commitments and Contingencies (Details) |  | 1 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Aug. 18, 2017 USD ($) | Sep. 30, 2017 USD ($) | Sep. 30, 2019 USD ($) Labor_Union MW | Sep. 30, 2018 USD ($) | Dec. 31, 2013 USD ($)
Labor Commitments [Abstract] |  |  |  |  |
Percentage of total work force in union |  |  | 65.00% |  |
Percentage of Grundartangi work force represented by the labor unions (in hundredths) |  |  | 87.00% |  |
Number of labor unions Grundartangi subsidiary entered into a new labor agreement with | Labor_Union |  |  | 5 |  |
Percentage of U.S. based work force represented by a union (in hundredths) |  |  | 56.00% |  |
Ravenswood Retiree Medical Benefits Changes [Member] |  |  |  |  |
Ravenswood litigation [Abstract] |  |  |  |  |
Gain (loss) related to litigation settlement |  | $ 5,500,000 |  |  |
Loss contingency accrual |  | 12,500,000 |  |  |
PBGC Agreement [Member] |  |  |  |  |
PBGC Settlement [Abstract] |  |  |  |  |
Required pension contributions above minimum |  |  |  |  | $ 17,400,000
Payment for pension benefits |  |  | $ 0 | $ 0 |
Pension contributions above minimum remaining |  |  | $ 9,600,000 |  |
Hawesville [Member] |  |  |  |  |
Power Contingencies [Abstract] |  |  |  |  |
Power supply agreement, termination notice period |  |  | 1 year |  |
Sebree [Member] |  |  |  |  |
Power Contingencies [Abstract] |  |  |  |  |
Power supply agreement, termination notice period |  |  | 1 year |  |
South Carolina Public Service Authority [Member] |  |  |  |  |
Power Contingencies [Abstract] |  |  |  |  |
Power supply agreement, termination notice period |  |  | 120 days |  |
Power agreement, power supply from source one, percentage |  |  | 25.00% |  |
Power agreement, power supply from source two, percentage |  |  | 75.00% |  |
Other Power Suppliers [Member] |  |  |  |  |
Power Contingencies [Abstract] |  |  |  |  |
Power supply agreement, termination notice period |  |  | 60 days |  |
Grundartangi - HS, Landsvirkjun and OR [Member] |  |  |  |  |
Power Contingencies [Abstract] |  |  |  |  |
Power currently available under the power purchase agreement (in megawatts) | MW |  |  | 525 |  |
Grundartangi - Landsvirkjun [Member] |  |  |  |  |
Power Contingencies [Abstract] |  |  |  |  |
Power currently available under the power purchase agreement (in megawatts) | MW |  |  | 161 |  |
Helguvik [Member] |  |  |  |  |
Power Contingencies [Abstract] |  |  |  |  |
Power currently available under the power purchase agreement (in megawatts) | MW |  |  | 47.5 |  |
NETHERLANDS |  |  |  |  |
Labor Commitments [Abstract] |  |  |  |  |
Percentage of Vlissingen work force represented by the labor union (in hundredths) |  |  | 100.00% |  |
Ravenswood Retiree Medical Benefits Changes [Member] |  |  |  |  |
Ravenswood litigation [Abstract] |  |  |  |  |
Ravenswood litigation settlement amount | $ 23,000,000.0 |  |  |  |
Ravenswood litigation settlement installment period | 10 years |  | 9 years |  |
Litigation payment to trust |  | $ 5,000,000.0 |  |  |
Litigation settlement, amount awarded to other party, annual payments |  |  | $ 2,000,000.0 |  |
Other Current Liabilities [Member] | Ravenswood Retiree Medical Benefits Changes [Member] |  |  |  |  |
Ravenswood litigation [Abstract] |  |  |  |  |
Litigation settlement, amount awarded to other party, annual payments |  |  | 2,000,000.0 |  |
Other Liabilities [Member] | Ravenswood Retiree Medical Benefits Changes [Member] |  |  |  |  |
Ravenswood litigation [Abstract] |  |  |  |  |
Litigation settlement, amount awarded to other party, annual payments |  |  | $ 8,500,000 |  |

X
- References No definition available. + Details
Name: | cenx_LaborCommitmentsAbstract
Namespace Prefix: | cenx_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Legal Contingencies [Abstract] + References No definition available. + Details
Name: | cenx_LegalContingenciesAbstract
Namespace Prefix: | cenx_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Litigation Settlement, Amount Awarded to Other Party, Annual Payments + References No definition available. + Details
Name: | cenx_LitigationSettlementAmountAwardedtoOtherPartyAnnualPayments
Namespace Prefix: | cenx_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Litigation Settlement Payment Period + References No definition available. + Details
Name: | cenx_LitigationSettlementPeriod
Namespace Prefix: | cenx_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition The number of labor unions representing a group of employees. + References No definition available. + Details
Name: | cenx_NumberOfLaborUnionsUnderNewLaborAgreement
Namespace Prefix: | cenx_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition PBGC Settlement [Abstract] + References No definition available. + Details
Name: | cenx_PBGCSettlementAbstract
Namespace Prefix: | cenx_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- 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
Name: | cenx_PensionContributionsAboveRequiredMinimumRemaining
Namespace Prefix: | cenx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- 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
Name: | cenx_PensionContributionsAboveRequiredMinimumTotal
Namespace Prefix: | cenx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The percentage of a Company's work force, based in the country of domicile, that are subject to collective bargaining agreements. + References No definition available. + Details
Name: | cenx_PercentageOfDomesticWorkForceInUnion
Namespace Prefix: | cenx_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Percentage Of Foreign Netherlands Work Force Represented By The Labor Union + References No definition available. + Details
Name: | cenx_PercentageOfForeignNetherlandsWorkForceRepresentedByTheLaborUnion
Namespace Prefix: | cenx_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The percentage of a Company's Icelandic work force that are subject to collective bargaining agreements. + References No definition available. + Details
Name: | cenx_PercentageOfForeignWorkForceCoveredUnderNewLaborAgreement
Namespace Prefix: | cenx_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The percentage of a Company's work force that are subject to collective bargaining agreements. + References No definition available. + Details
Name: | cenx_PercentageofWorkForceinUnion
Namespace Prefix: | cenx_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Power Supply Agreement, Termination Notice Period + References No definition available. + Details
Name: | cenx_PowerSupplyAgreementTerminationNoticePeriod
Namespace Prefix: | cenx_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Ravenswood litigation [Abstract] + References No definition available. + Details
Name: | cenx_RavenswoodlitigationAbstract
Namespace Prefix: | cenx_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Short-term Power Agreement, Supply from Source One, Percentage + References No definition available. + Details
Name: | cenx_ShorttermPowerAgreementSupplyfromSourceOnePercentage
Namespace Prefix: | cenx_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Short-term Power Agreement, Supply from Source Two, Percentage + References No definition available. + Details
Name: | cenx_ShorttermPowerAgreementSupplyfromSourceTwoPercentage
Namespace Prefix: | cenx_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The power currently available under the power purchase agreement. + References No definition available. + Details
Name: | cenx_UnderlyingDerivativePowerAvailable
Namespace Prefix: | cenx_
Data Type: | num:powerItemType
Balance Type: | na
Period Type: | instant

X
- 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=118942415&loc=d3e14326-108349 + Details
Name: | us-gaap_GainLossRelatedToLitigationSettlement
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount awarded to other party in judgment or settlement of litigation. + References No definition available. + Details
Name: | us-gaap_LitigationSettlementAmountAwardedToOtherParty
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- 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=118942415&loc=d3e14326-108349 + Details
Name: | us-gaap_LossContingencyAccrualAtCarryingValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- 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=118932676&loc=d3e3536-108585 + Details
Name: | us-gaap_PaymentsForLegalSettlements
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- 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=118932676&loc=d3e3536-108585 + Details
Name: | us-gaap_PensionContributions
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | srt_CounterpartyNameAxis=cenx_RavenswoodRetireeMedicalBenefitsChangesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=cenx_PBGCAgreementMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=cenx_HawesvilleMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=cenx_SebreeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=cenx_SouthCarolinaPublicServiceAuthorityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=cenx_OtherPowerSuppliersMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=cenx_GrundartangiHSLandsvirkjunandORMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=cenx_GrundartangiLandsvirkjunMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=cenx_HelguvikMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementGeographicalAxis=country_NL
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LossContingenciesByNatureOfContingencyAxis=cenx_RavenswoodRetireeMedicalBenefitsChangesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BalanceSheetLocationAxis=us-gaap_OtherCurrentLiabilitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BalanceSheetLocationAxis=us-gaap_OtherLiabilitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |