Debt Instrument, Variable Interest Rate, Maximum Percentage

No definition available.

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- Definition

Carrying value as of the balance sheet date of the long-term debt associated with industrial revenue bonds. For classified balance sheets, these bonds are considered current assets because they are remarketed weekly and the bonds could be required to be repaid upon demand if there is a failed remarketing.

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

Carrying value as of the balance sheet date of long-term debt (with maturities initially due after one year or beyond the operating cycle if longer) identified as Convertible Notes Payable, excluding current portion. Convertible Notes Payable is a written promise to pay a note which can be exchanged for a specified amount of another, related security, at the option of the issuer and the holder.

+ References

+ Details

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Period Type:	instant

- Definition

Amount of the fee that accompanies borrowing money under the debt instrument.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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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.

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+ Details

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- Definition

Represents the aggregate of total long-term debt, including current maturities and short-term debt.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

+ References

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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Carrying value as of the balance sheet date of the portion of long-term, collateralized debt obligations due within one year or the operating cycle, if longer. Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

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Balance Type:	credit
Period Type:	instant

- 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

+ Details

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- Details

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Period Type:

- Details

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- Details

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Balance Type:
Period Type:

- Details

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Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=cenx_VlissingenCreditFacilityMember
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Balance Type:
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- Details

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- Details

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- Details

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Balance Type:
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- Details

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- Details

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Debt - Activity (Details) - USD ($) $ in Millions	Sep. 30, 2025	Jul. 31, 2025	Dec. 31, 2024	Oct. 01, 2024	Apr. 30, 2021
Debt Instrument [Line Items]
Total debt	$ 618.5		$ 528.2
Industrial revenue bonds, variable
Debt Instrument [Line Items]
Maximum variable interest rate	12.00%
Hancock County industrial revenue bonds ("IRBs") due April 1, 2028, interest payable quarterly (variable interest rates (not to exceed 12%))	$ 7.8		7.8
Revolving credit facility \| U.S. revolving credit facility
Debt Instrument [Line Items]
Revolving credit facility	$ 0.0		20.0
Stated interest rate, percentage	7.75%
Revolving credit facility \| Foreign line of credit
Debt Instrument [Line Items]
Revolving credit facility	$ 16.5		34.0
Stated interest rate, percentage	7.66%
Casthouse Facility \| Foreign line of credit
Debt Instrument [Line Items]
Financing fees	$ 1.5
Revolving credit facility	115.0		9.0
Secured debt	$ 0.0		114.2
Stated interest rate, percentage	7.89%
Vlissingen Credit Facility \| Foreign line of credit
Debt Instrument [Line Items]
Secured debt	$ 0.0		10.0
Stated interest rate, percentage	7.83%			8.75%
Senior secured notes, 7.5% \| Senior notes
Debt Instrument [Line Items]
Stated interest rate, percentage	7.50%
Secured long-term debt	$ 0.0		248.1
Senior convertible notes, 2.75% \| Senior notes
Debt Instrument [Line Items]
Financing fees	$ 0.9
Stated interest rate, percentage	2.75%				2.75%
2.75% convertible senior notes due May 1, 2028, net of financing fees of $0.9 million at September 30, 2025, interest payable semiannually	$ 85.4		85.1
Senior Secured Notes, 6.875% \| Senior notes
Debt Instrument [Line Items]
Financing fees	$ 6.1
Stated interest rate, percentage	6.875%	6.875%
Secured long-term debt	$ 393.8		$ 0.0
Industrial Revenue Bonds Due 2028
Debt Instrument [Line Items]
Stated interest rate, percentage	3.02%