Summary of Significant Accounting Policies (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Property Plant And Equipment [Line Items]
Depreciation Expense			$ 11,600,000	$ 9,000,000
Summary of Significant Accounting Policies Additional (Textuals) [Abstract]
Carrying amount of the Company's investment in Anglesey	0		0		0
Non-cash LIFO charges (benefits)	5,000,000	(1,000,000)	19,900,000	8,200,000
Interest Expense capitalized	200,000	1,000,000	400,000	1,900,000
Margin deposits with or from Counterparties	0		0		0
Anglesey Aluminum Limited [Member]
Noncontrolling Interest [Line Items]
Non-controlling ownership interest in Anglesey Aluminum Limited	49.00%		49.00%
Fabricated Products [Member]
Property Plant And Equipment [Line Items]
Depreciation Expense	5,700,000	4,900,000	11,400,000	8,900,000
Summary of Significant Accounting Policies Additional (Textuals) [Abstract]
Non-cash LIFO charges (benefits)	$ 5,000,000	$ (1,000,000)	$ 19,900,000	$ 8,200,000