Long-term Debt and Other Financing (Details2) (USD $)		9 Months Ended					1 Months Ended
	Sep. 30, 2012	Sep. 30, 2012 Revolving Credit Facility [Member]	Dec. 31, 2011 Revolving Credit Facility [Member]	Sep. 30, 2012 Industrial Revenue Bonds [Member]	Dec. 31, 2011 Industrial Revenue Bonds [Member]	Feb. 28, 2012 Debt After Refinancing [Member] Industrial Revenue Bonds [Member]	Mar. 31, 2012 Senior Notes Due April 2022 [Member]	Sep. 30, 2012 Senior Notes Due April 2022 [Member]	Dec. 31, 2011 Senior Notes Due April 2022 [Member]	Sep. 30, 2012 Senior Notes Due May 2020 [Member]	Dec. 31, 2011 Senior Notes Due May 2020 [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Expiration Date		Apr. 30, 2016
Line of credit facility, maximum borrowing capacity		$ 1,100,000,000
Line of Credit Facility, Current Borrowing Capacity		1,081,000,000
Credit facility borrowings outstanding		442,000,000	250,000,000
Credit facility borrowings classified as long-term debt	400,000,000	400,000,000
Letters of credit, outstanding		81,200,000
Line of credit facility, remaining borrowing capacity		557,800,000
Long-term Debt, Gross				101,000,000	101,500,000	73,300,000		300,000,000	0	550,000,000	550,000,000
Debt Instrument, Interest Rate, Stated Percentage						6.80%	8.375%			7.625%
Senior notes, outstanding debt							300,000,000
Debt Instrument, Maturity Date							Apr. 01, 2022
Proceeds from Debt, Net of Issuance Costs							$ 293,400,000