Acquired Sales Contracts (Schedule of Acquired Sales Contracts) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2014
Acquired Finite-Lived Intangible Assets And Liabilities By Major Class [Line Items]
Impairment of Intangible Assets, Finite-lived	$ 15,700,000
Acquired fair value, Assets	131,819,000	131,299,000
Acquired fair value, Liabilities	166,697,000	166,697,000
Accumulated amortization, Asset	(129,449,000)	(130,363,000)
Accumulated amortization, Liabilities	(120,367,000)	(134,988,000)
Total, Assets	2,370,000	936,000
Total, Liabilities	46,330,000	31,709,000
Net total, Liabilites		(30,773,000)
Coal Supply Agreement, Liabilities	14,373,000	12,453,000
Other Current Assets [Member]
Acquired Finite-Lived Intangible Assets And Liabilities By Major Class [Line Items]
Coal supply agreement, Assets	1,324,000	462,000
Accrued Liabilities [Member]
Acquired Finite-Lived Intangible Assets And Liabilities By Major Class [Line Items]
Coal Supply Agreement, Liabilities	14,373,000	12,453,000
Other Assets [Member]
Acquired Finite-Lived Intangible Assets And Liabilities By Major Class [Line Items]
Coal supply agreement, Assets	1,046,000	474,000
Other Noncurrent Liabilities [Member]
Acquired Finite-Lived Intangible Assets And Liabilities By Major Class [Line Items]
Coal Supply Agreement, Liabilities	$ 31,957,000	$ 19,256,000