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Quarterly information (Unaudited) - 2015 Financial Results Overview (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended					12 Months Ended
	Jun. 30, 2015	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Effect of Fourth Quarter Events [Line Items]
Lower cost or market inventory adjustment		$ 23,474	$ 5,324				$ 7,539	$ (1,247)	$ 1,247
Pension charges		3,400				$ 4,964
Depreciation							80,117	70,827	66,570
Impairment							11,584	0	0
Labor disruption costs			1,400	$ 11,700
Impairment charge							30,850	0	0
Gain on fair value of contingent consideration					$ 6,527	$ 7,943	18,337	$ 7,943	$ 0
Severance charge					1,000
Hawesville and Mt. Holly [Member]
Effect of Fourth Quarter Events [Line Items]
Curtailment expenses		3,500
Hawesville [Member]
Effect of Fourth Quarter Events [Line Items]
Curtailment expenses			$ 2,900
Ravenswood Aluminum Smelter [Member]
Effect of Fourth Quarter Events [Line Items]
Lower cost or market inventory adjustment				25,689
Impairment charge	$ 30,850			30,850
Grundartangi, Iceland [Member]
Effect of Fourth Quarter Events [Line Items]
Signing bonuses, amount					$ 1,570
Mt. Holly Smelter [Member]
Effect of Fourth Quarter Events [Line Items]
Depreciation		5,000
Gain on fair value of contingent consideration				$ 10,287			18,337
BHH [Member]
Effect of Fourth Quarter Events [Line Items]
Impairment		$ 11,584					$ 11,584

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