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Summary of significant accounting policies Long-term Debt Instruments (Details) (USD $) In Thousands, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
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Debt Instrument [Line Items] |  |  |
Carrying amount of current portion of long term debt | $ 0 us-gaap_UnsecuredDebtCurrent |  | $ 2,603 us-gaap_UnsecuredDebtCurrent
Senior secured notes due June 01, 2021 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate (as a percent) | 7.50%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = cenx_SeniorsecurednotesdueJune012021Member |  |
Senior unsecured notes due August 15, 2014 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate (as a percent) | 7.50%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = cenx_SeniorUnsecuredNotesDueAugust152014Member |  |
Long-term Debt [Member] | Senior secured notes due June 01, 2021 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Carrying amount of secured long term debt | 246,888 us-gaap_SecuredLongTermDebt / us-gaap_DebtInstrumentAxis = cenx_SeniorsecurednotesdueJune012021Member / us-gaap_LongtermDebtTypeAxis = us-gaap_LongTermDebtMember |  | 246,528 us-gaap_SecuredLongTermDebt / us-gaap_DebtInstrumentAxis = cenx_SeniorsecurednotesdueJune012021Member / us-gaap_LongtermDebtTypeAxis = us-gaap_LongTermDebtMember
Fair value of long term debt | 256,408 us-gaap_LongTermDebtFairValue / us-gaap_DebtInstrumentAxis = cenx_SeniorsecurednotesdueJune012021Member / us-gaap_LongtermDebtTypeAxis = us-gaap_LongTermDebtMember |  | 244,375 us-gaap_LongTermDebtFairValue / us-gaap_DebtInstrumentAxis = cenx_SeniorsecurednotesdueJune012021Member / us-gaap_LongtermDebtTypeAxis = us-gaap_LongTermDebtMember
Interest rate (as a percent) | 7.50%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = cenx_SeniorsecurednotesdueJune012021Member / us-gaap_LongtermDebtTypeAxis = us-gaap_LongTermDebtMember |  | 7.50%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = cenx_SeniorsecurednotesdueJune012021Member / us-gaap_LongtermDebtTypeAxis = us-gaap_LongTermDebtMember
Short-term Debt [Member] | Senior unsecured notes due August 15, 2014 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Carrying amount of current portion of long term debt | 0 us-gaap_UnsecuredDebtCurrent / us-gaap_DebtInstrumentAxis = cenx_SeniorUnsecuredNotesDueAugust152014Member / us-gaap_ShortTermDebtTypeAxis = us-gaap_ShortTermDebtMember | [1],[2] | 2,603 us-gaap_UnsecuredDebtCurrent / us-gaap_DebtInstrumentAxis = cenx_SeniorUnsecuredNotesDueAugust152014Member / us-gaap_ShortTermDebtTypeAxis = us-gaap_ShortTermDebtMember
Fair value of current portion of long term debt | $ 0 us-gaap_ShorttermDebtFairValue / us-gaap_DebtInstrumentAxis = cenx_SeniorUnsecuredNotesDueAugust152014Member / us-gaap_ShortTermDebtTypeAxis = us-gaap_ShortTermDebtMember |  | $ 2,487 us-gaap_ShorttermDebtFairValue / us-gaap_DebtInstrumentAxis = cenx_SeniorUnsecuredNotesDueAugust152014Member / us-gaap_ShortTermDebtTypeAxis = us-gaap_ShortTermDebtMember
Interest rate (as a percent) | 7.50%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = cenx_SeniorUnsecuredNotesDueAugust152014Member / us-gaap_ShortTermDebtTypeAxis = us-gaap_ShortTermDebtMember |  | 7.50%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = cenx_SeniorUnsecuredNotesDueAugust152014Member / us-gaap_ShortTermDebtTypeAxis = us-gaap_ShortTermDebtMember
[1] | The amount outstanding was repaid upon maturity.
[2] | These items are recorded in accrued and other current liabilities based on the repayment terms and expected maturity.

X
- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | us-gaap_DebtInstrumentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. + References No definition available. + Details
Name: | us-gaap_LongTermDebtFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Carrying amount of collateralized debt obligations with maturities initially due after one year or beyond the operating cycle, if longer, excluding the current portion. Obligations include, but not limited to, mortgage loans, chattel loans, and other borrowings secured by assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 + Details
Name: | us-gaap_SecuredLongTermDebt
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents the amount of short-term debt existing as of the balance sheet date. + References No definition available. + Details
Name: | us-gaap_ShorttermDebtFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Carrying value as of the balance sheet date of the portion of long-term, uncollateralized debt obligations due within one year or the normal operating cycle, if longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -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=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 20 -Article 5 + Details
Name: | us-gaap_UnsecuredDebtCurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | us-gaap_DebtInstrumentAxis=cenx_SeniorsecurednotesdueJune012021Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=cenx_SeniorUnsecuredNotesDueAugust152014Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=us-gaap_LongTermDebtMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ShortTermDebtTypeAxis=us-gaap_ShortTermDebtMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |