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Derivative and hedging instruments (Details) (USD $)
In Thousands, unless otherwise specified

12 Months Ended

Dec. 31, 2011

Dec. 31, 2010

Fair value of derivative assets and liabilities by balance sheet location [Abstract]

ASSETS

$ 9,437

$ 4,842

LIABILITIES

15,147

13,874

Outstanding forward contracts not designated as hedging instruments [Abstract]

Accumulated other comprehensive loss to be reclassified to earnings over the next 12-month period

196

Primary Aluminum Put Option Contracts [Member] | Not Designated as Hedging Instrument [Member] | Related Party [Member]

Outstanding forward contracts not designated as hedging instruments [Abstract]

Aluminum forward contract outstanding (in metric tons)

18,000

46,800

Primary Aluminum Put Option Contracts [Member] | Prepaid and Other Current Assets [Member]

Fair value of derivative assets and liabilities by balance sheet location [Abstract]

ASSETS

3,892

2,712

Primary Aluminum Put Option Contracts [Member] | Due From Affiliates [Member]

Fair value of derivative assets and liabilities by balance sheet location [Abstract]

ASSETS

5,439

1,979

Natural Gas Forward Contracts [Member] | Prepaid and Other Current Assets [Member] | Designated as Hedging Instrument [Member]

Fair value of derivative assets and liabilities by balance sheet location [Abstract]

ASSETS

0

79

Natural Gas Forward Contracts [Member] | Accrued and Other Liabilities [Member]

Fair value of derivative assets and liabilities by balance sheet location [Abstract]

LIABILITIES

281

0

Power Contracts [Member] | Not Designated as Hedging Instrument [Member]

Outstanding forward contracts not designated as hedging instruments [Abstract]

Power contracts (in megawatt hours (MWH))

3,772

^[1]

4,379

^[1]

Power Contracts [Member] | Prepaid and Other Current Assets [Member]

Fair value of derivative assets and liabilities by balance sheet location [Abstract]

ASSETS

106

72

E.ON Contingent Obligation [Member] | Other Liabilities [Member]

Fair value of derivative assets and liabilities by balance sheet location [Abstract]

LIABILITIES

13,958

13,091

Aluminum Sales Premium Contract [Member] | Other Liabilities [Member]

Fair value of derivative assets and liabilities by balance sheet location [Abstract]

LIABILITIES

301

347

Aluminum Sales Premium Contract [Member] | Accrued and Other Liabilities [Member]

Fair value of derivative assets and liabilities by balance sheet location [Abstract]

LIABILITIES

607

436

Calcined Petroleum Coke Contract [Member] | Accrued and Other Liabilities [Member]

Fair value of derivative assets and liabilities by balance sheet location [Abstract]

LIABILITIES

$ 0

$ 0

Primary Aluminum Sales Contract Premium [Member] | Not Designated as Hedging Instrument [Member]

Outstanding forward contracts not designated as hedging instruments [Abstract]

Aluminum forward contract outstanding (in metric tons)

40,870

^[2]

62,252

^[2]

Primary Aluminum Put Option Contracts [Member] | Not Designated as Hedging Instrument [Member]

Outstanding forward contracts not designated as hedging instruments [Abstract]

Aluminum forward contract outstanding (in metric tons)

15,000

61,800

[1]	Represents our expected usage during the remaining term of the Ravenswood power contract. In June 2011, the West Virginia PSC extended the term of this contract for an additional year.
[2]	Represents the remaining physical deliveries under our 2013 Glencore Metal Agreement.

X

- Definition

The metric tons of aluminum covered by forward contracts outstanding for sales, put options and call options at the end of the period.

+ References

No definition available.

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X

- Definition

The estimated number of megawatt hours expected to be used through the remaining term of forward power contracts with embedded derivatives at date of balance sheet.

+ References

No definition available.

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X

- Definition

Fair values as of the balance sheet date of all assets resulting from contracts that meet the criteria of being accounted for as derivative instruments, net of the effects of master netting arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 15

-URI http://asc.fasb.org/extlink&oid=6947722&loc=d3e13495-108611



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 6

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958



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-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FIN39-1

-Paragraph 10A, 10B

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.



Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958



Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 4, 17

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.



Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6947722&loc=d3e13433-108611

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- Definition

The estimated value of gains (losses), net anticipated to be transferred in the future from accumulated other comprehensive income into earnings.

+ References

No definition available.

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- Definition

Fair values as of the balance sheet date of all liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments, net of the effects of master netting arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 15

-URI http://asc.fasb.org/extlink&oid=6947722&loc=d3e13495-108611



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 6

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FIN39-1

-Paragraph 10A, 10B

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.



Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958



Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 4, 17

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.



Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6947722&loc=d3e13433-108611

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