Derivative and hedging instruments (Details) (Not Designated as Hedging Instrument [Member], USD $) In Thousands, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Fair value of derivative assets and liabilities by balance sheet location [Abstract]
DERIVATIVE ASSETS	$ 0		$ 140
DERIVATIVE LIABILITIES	0		140
Midwest Premium Contracts [Member]
Outstanding forward contracts not designated as hedging instruments [Abstract]
Midwest premium contracts (tonnes)	0		6,000
Midwest Premium Contracts [Member] | Prepaid and Other Current Assets [Member]
Fair value of derivative assets and liabilities by balance sheet location [Abstract]
DERIVATIVE ASSETS	0		140
Primary Aluminum Sales Contracts [Member] | Accrued and Other Current Liabilities [Member]
Fair value of derivative assets and liabilities by balance sheet location [Abstract]
DERIVATIVE LIABILITIES	0		140
E.ON Contingent Obligation - Net [Member] | Other Liabilities [Member]
Fair value of derivative assets and liabilities by balance sheet location [Abstract]
DERIVATIVE LIABILITIES	$ 0	[1]	$ 0	[1]
Primary Aluminum Sales Contract Premium [Member]
Outstanding forward contracts not designated as hedging instruments [Abstract]
Primary aluminum sales contract premium (tonnes) (1)	0	[2]	1,782	[2]

[1] See Note 9 Debt for additional information about the E.ON contingent obligation.

[2] Represents the remaining physical deliveries under the Glencore Metal Agreement.