Acquired Sales Contracts (Schedule Of Acquired Sales Contracts) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Acquired Finite-Lived Intangible Assets And Liabilities By Major Class [Line Items]
Acquired fair value, Assets	$ 149,457	$ 114,453
Acquired fair value, Liabilities	166,697	40,654
Accumulated amortization, Asset	(115,322)	(82,376)
Accumulated amortization, Liabilities	(69,699)	(14,613)
Total, Assets	34,135	32,077
Total, Liabilities	96,998	26,041
Net total, Assets		6,036
Net total, Liabilities	(62,863)
Coal supply agreement, Liabilities	38,441	5,615
Accrued Expenses and Other Current Liabilities [Member]
Acquired Finite-Lived Intangible Assets And Liabilities By Major Class [Line Items]
Coal supply agreement, Liabilities	38,441	5,615
Other Current Assets [Member]
Acquired Finite-Lived Intangible Assets And Liabilities By Major Class [Line Items]
Coal supply agreement, Assets	18,929	25,063
Other Noncurrent Liabilities [Member]
Acquired Finite-Lived Intangible Assets And Liabilities By Major Class [Line Items]
Coal supply agreement, Liabilities	58,557	20,426
Other Assets [Member]
Acquired Finite-Lived Intangible Assets And Liabilities By Major Class [Line Items]
Coal supply agreement, Assets	$ 15,206	$ 7,014