Annual report pursuant to Section 13 and 15(d)

Acquisitions and Dispositions (Narrative) (Details)

v3.20.4
Acquisitions and Dispositions (Narrative) (Details)
 1 Months Ended 3 Months Ended 12 Months Ended
Feb. 25, 2021
USD ($)
$ / bbl
Nov. 17, 2020
USD ($)
Jul. 31, 2019
USD ($)
Nov. 30, 2006
Mar. 31, 2019
USD ($)
Dec. 31, 2020
USD ($)
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Feb. 24, 2021
Business Acquisition [Line Items]                  
Income (loss) from discontinued operations, net of tax           $ (98,000) $ 5,411,000 $ (496,000)  
Cash paid           20,008,000 10,348,000 14,127,000  
Joint Operating With Republic Of Angola [Member]                  
Business Acquisition [Line Items]                  
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%          
Discontinued Operations [Member] | Joint Operating With Republic Of Angola [Member]                  
Business Acquisition [Line Items]                  
Liability for the potential payment         $ 4,500,000        
Write off of receivable         3,300,000        
Income (loss) from discontinued operations, net of tax         $ 5,700,000 (98,000) $ 5,411,000 $ (496,000)  
Payment for settlement     $ 4,500,000            
Etame Marine Block [Member]                  
Business Acquisition [Line Items]                  
Liability for the potential payment     $ 4,400,000     $ 4,400,000      
Etame Marine Block [Member] | Sasol Gabon S.A. [Member]                  
Business Acquisition [Line Items]                  
Cash paid   $ 4,300,000              
Etame Marine Block [Member] | Subsequent Event [Member]                  
Business Acquisition [Line Items]                  
Working interest ownership, percentage 58.80%               31.10%
Etame Marine Block [Member] | Subsequent Event [Member] | Sasol Gabon S.A. [Member]                  
Business Acquisition [Line Items]                  
Increase (decrease) in working interest ownership percentage 27.80%                
Effective date of acquisition Jul. 01, 2020                
Total consideration $ 44,000,000.0                
Cash paid 29,600,000                
Contingent consideration $ 5,000,000.0                
Contingent consideration, oil price threshold | $ / bbl 60.00                
Contingent consideration, oil price threshold measurement period 90 days