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Subsequent events Increase in letters of credit to Big Rivers (Details) (Subsequent Event [Member], USD $) In Thousands, unless otherwise specified	Jul. 01, 2012	Jun. 30, 2012
Subsequent Event [Member]
Subsequent Event [Line Items]
Outstanding letters of credit issued under the revolving credit facility	$ 34,000	$ 30,000
increase in letters of credit	$ 4,000

X

- Definition

Increase in obligations to Big Rivers Electric Corporation secured by letters of credit outstanding

+ References

No definition available.

+ Details

Name:	cenx_IncreaseInLettersOfCredit
Namespace Prefix:	cenx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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

X

- Details

Name:	us-gaap_SubsequentEventLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration