Derivative Financial Instruments and Related Hedging Programs, Notional Quantity Table (Details)	Sep. 30, 2015 EUR (€) MMBTU mmlbs MWH
Remainder of 2015
Derivative [Line Items]
Percentage of natural gas purchases for which the Company's exposure to fluctuations in gas prices had been substantially reduced	76.00%
Percentage of Electricity Purchases For Which Company Exposure To Fluctuations In Electricity Prices Have Been Reduced	54.00%
2016
Derivative [Line Items]
Percentage of natural gas purchases for which the Company's exposure to fluctuations in gas prices had been substantially reduced	75.00%
Percentage of Electricity Purchases For Which Company Exposure To Fluctuations In Electricity Prices Have Been Reduced	54.00%
2017
Derivative [Line Items]
Percentage of natural gas purchases for which the Company's exposure to fluctuations in gas prices had been substantially reduced	57.00%
Percentage of Electricity Purchases For Which Company Exposure To Fluctuations In Electricity Prices Have Been Reduced	54.00%
2018
Derivative [Line Items]
Percentage of natural gas purchases for which the Company's exposure to fluctuations in gas prices had been substantially reduced	11.00%
Not Designated as Hedging Instrument \| Electricity Member \| Fixed priced contracts \| Purchase
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount \| MWH	44,180
Not Designated as Hedging Instrument \| Aluminum \| Fixed priced contracts \| Purchase
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	148.9
Not Designated as Hedging Instrument \| Aluminum \| Fixed priced contracts \| Sales
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	2.4
Not Designated as Hedging Instrument \| Aluminum \| Midwest premium swap contracts \| Purchase
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	87.8
Not Designated as Hedging Instrument \| Natural Gas \| Fixed priced contracts \| Purchase
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount \| MMBTU	6,820,000
Designated as Hedging Instrument [Member] \| Foreign Currency Member \| Fixed priced contracts \| Purchase
Derivative [Line Items]
Notional amount of contracts \| €	€ 7,315,000

Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

-Section 13

-Sentence Column B

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+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 1B

-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5580258-113959

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

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-Name Accounting Standards Codification

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

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-Topic 815

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-Section 50

-Paragraph 1A

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