Risk Concentrations (Details) (USD $)	12 Months Ended
	Dec. 31, 2011 T	Dec. 31, 2010	Dec. 31, 2009
Concentration Risk [Line Items]
Sales to customers in foreign countries	$ 920,000,000	$ 471,500,000	$ 194,400,000
Trade accounts receivable	380,595,000	208,060,000
Receivables	469,179,000	252,320,000
Tons of coal sold	156,900,000
Percentage of tons sold	72.00%
Long-term contracts, life term, minimum (years)	one
Long term sales contract term, in years	to nine years
Electric Utilities [Member]
Concentration Risk [Line Items]
Percentage of total trade accounts receivable	69.00%	88.00%
Customer Concentration Risk [Member]
Concentration Risk [Line Items]
Sales (including spot sales)	266,800,000	301,400,000	278,800,000
Domestic And Foreign Steel Producers [Member]
Concentration Risk [Line Items]
Trade accounts receivable	117,400,000	24,900,000
Trade receivables, percentage	31.00%	12.00%
Domestic Electric Utilities [Member]
Concentration Risk [Line Items]
Receivables	261,200,000	183,100,000
Long-term Contracts [Member]
Concentration Risk [Line Items]
Percentage of total revenue	57.00%
Europe [Member]
Concentration Risk [Line Items]
Sales to customers in foreign countries	427,514,000,000
South America [Member]
Concentration Risk [Line Items]
Sales to customers in foreign countries	120,842,000,000
North America [Member]
Concentration Risk [Line Items]
Sales to customers in foreign countries	97,255,000,000
Asia [Member]
Concentration Risk [Line Items]
Sales to customers in foreign countries	61,308,000,000
Brokered sales [Member]
Concentration Risk [Line Items]
Sales to customers in foreign countries	213,087,000,000
Total [Member]
Concentration Risk [Line Items]
Sales to customers in foreign countries	$ 920,006,000,000