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Acquisitions (Fair Value of Net Assets Acquired ) (Details) - Casselman-Bohannon Fields [Member]
$ in Thousands
Jan. 18, 2016
USD ($)
Business Acquisition [Line Items]  
Net assets acquired $ 10,183
Oil and Gas Properties [Member]  
Business Acquisition [Line Items]  
Oil and natural gas properties 5,527
Unevaluated Oil and Gas Properties [Member]  
Business Acquisition [Line Items]  
Oil and natural gas properties $ 4,656