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Acquisitions (Details) (USD $)
6 Months Ended
Jun. 30, 2011
Dec. 31, 2010
Jun. 30, 2011
Appalachian Natural Gas Trust
Dec. 31, 2000
Appalachian Natural Gas Trust
May 31, 2011
Class A interest
Jun. 30, 2011
7.76% notes, due 2011 thru 2016
Acquisitions            
Proceeds from sale of net profits interest (NPI) in certain producing properties       $ 298,000,000    
Ownership percentage (as a percent)         100.00%  
Percentage of net profits received by ANGT (as a percent)       100.00%    
Debt instrument, stated interest rate percentage (as a percent)           7.76%
Aggregate principal amount           57,141,000
Fair value of notes 2,000,000,000 2,000,000,000       64,200,000
Gain on revaluation of existing equity investment in aquiree     10,100,000      
Derecognition of post revaluation of equity investment in ANGT     48,000,000      
Derecognition of post revaluation of oil and gas properties     140,600,000      
Recognition of a derivative liability for swap     12,700,000      
Liability for discounted sales     16,400,000      
Net increase in liabilities     $ 92,600,000