Annual report pursuant to Section 13 and 15(d)

Oil And Natural Gas Properties And Equipment (Narrative) (Details)

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Oil And Natural Gas Properties And Equipment (Narrative) (Details)
 3 Months Ended 12 Months Ended
Sep. 30, 2016
USD ($)
item
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Fair value of fields   $ 389,231,000 $ 412,593,000  
Impairment of proved properties   $ 88,000 81,322,000 $ 98,341,000
U.S. Fields [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Fair value of fields     1,200,000  
Impairment Of Oil And Gas Properties     3,200,000  
Etame Field [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Fair value of fields     12,700,000  
Impairment Of Oil And Gas Properties     78,100,000  
Etame, Ebouri, Southeast Etame and North Tchibala [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Fair value of fields       41,100,000
Impairment Of Oil And Gas Properties       $ 98,300,000
Roosevelt County, Montana [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Impairment of Leasehold     $ 1,200,000  
North Texas [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Number of wells, interest for sale | item 2      
Proceeds received from sale of property $ 830,000      
Impairment of proved properties $ 100,000