Quarterly report pursuant to Section 13 or 15(d)

Property and Equipment (Summary of Non-producing Properties Excluded from Amortization by Area) (Details)

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Property and Equipment (Summary of Non-producing Properties Excluded from Amortization by Area) (Details) - USD ($)
$ in Thousands
Sep. 30, 2017
Dec. 31, 2016
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]    
Total non-producing properties not subject to amortization $ 2,956,732 $ 1,580,305
Utica    
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]    
Total non-producing properties not subject to amortization 1,517,555  
MidContinent    
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]    
Total non-producing properties not subject to amortization 1,435,992  
Niobrara    
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]    
Total non-producing properties not subject to amortization 2,182  
Southern Louisiana    
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]    
Total non-producing properties not subject to amortization 536  
Bakken    
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]    
Total non-producing properties not subject to amortization 99  
Other    
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]    
Total non-producing properties not subject to amortization $ 368