Annual report pursuant to Section 13 and 15(d)

Acquisitions And Dispositions (Narrative) (Details)

v3.6.0.2
Acquisitions And Dispositions (Narrative) (Details)
a in Millions
 1 Months Ended 12 Months Ended
Nov. 22, 2016
Mar. 14, 2016
USD ($)
Jan. 01, 2014
Oct. 31, 2014
item
Nov. 30, 2006
a
item
Dec. 31, 2016
USD ($)
item
Sep. 30, 2016
USD ($)
Dec. 31, 2015
USD ($)
Apr. 30, 2014
USD ($)
Business Acquisition [Line Items]                  
Fair value of fields           $ 389,231,000   $ 412,593,000  
Fair value of fields           10,000,000   10,000,000  
Restricted cash           918,000   15,830,000  
Allowance for accounts with partners           $ 500,000   $ 0  
Offshore Gabon [Member]                  
Business Acquisition [Line Items]                  
Production license agreement term extended by government           5 years      
Hefley Field [Member]                  
Business Acquisition [Line Items]                  
Proceeds received from sale of property           $ 830,000      
Number of wells, interest for sale | item           2      
East Poplar Dome Field [Member]                  
Business Acquisition [Line Items]                  
Property with letter of inten to sale, expected proceeds amount           $ 250,000      
Joint Operating With Republic Of Angola [Member]                  
Business Acquisition [Line Items]                  
Production license agreement term           4 years      
Production license agreement term extended by government           3 years      
Area under acquire property exploration rights agreement term (acres) | a         1.4        
Number of exploration wells | item         2        
Number Of Additional Exploration Wells | item       2          
Joint operation agreement related to third party in working interest percentage         40.00%        
Additional joint operation agreement related to third party in working interest percentage         10.00%        
Drilling commitment, net           $ 5,000,000      
Restricted cash             $ 15,000,000    
Liability for the penalty           $ 15,000,000      
Working interest ownership other, percentage     40.00%            
Allowance for accounts with partners                 $ 7,600,000
Joint Operating With Republic Of Angola [Member] | Remaining Obligation [Member]                  
Business Acquisition [Line Items]                  
Number of exploration wells | item           3      
Sojitz [Member]                  
Business Acquisition [Line Items]                  
Percentage of working interest 2.98%                
Percentage of participating interest 3.23%                
Actual impact on revenue from acquisition           $ 200,000      
Sonangol P&P [Member]                  
Business Acquisition [Line Items]                  
Payment from joint venture partners   $ 19,000,000              
Reversal of allowance   7,600,000              
Interest income   $ 3,200,000              
Sonangol P&P [Member] | Drilling or Commencing Wells By November 30, 2017 [Member]                  
Business Acquisition [Line Items]                  
Number of exploration wells | item         4