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Property And Equipment (Summary Of Oil And Gas Properties Not Subject To Amortization) (Details)

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Property And Equipment (Summary Of Oil And Gas Properties Not Subject To Amortization) (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended 130 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Mar. 31, 2013
Mar. 31, 2012
Property, Plant and Equipment [Abstract]            
Acquisition costs $ 512,636 $ 112,591 $ 661 $ 407    
Exploration costs 0 0 0 0    
Development costs 0 0 0 0    
Total oil and gas properties not subject to amortization 512,636 112,591 661 407    
Acquisition costs, Total 626,295          
Exploration costs, Total 0          
Development costs, Total 0          
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]            
Total oil and gas properties not subject to amortization 626,295 138,623     869,879 626,295
Colorado [Member]
           
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]            
Total oil and gas properties not subject to amortization 5,998       6,088  
Bakken [Member]
           
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]            
Total oil and gas properties not subject to amortization 295       301  
Southern Louisiana [Member]
           
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]            
Total oil and gas properties not subject to amortization 774       789  
Ohio [Member]
           
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]            
Total oil and gas properties not subject to amortization 619,182       862,655  
Other [Member]
           
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]            
Total oil and gas properties not subject to amortization $ 46       $ 46