Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies (Narrative) (Details)

v3.20.4
Summary of Significant Accounting Policies (Narrative) (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2020
USD ($)
/ $
Dec. 31, 2019
USD ($)
/ $
Dec. 31, 2018
USD ($)
Jun. 20, 2026
Organization And Accounting Policies [Line Items]        
Receivable balance, gross, noncurrent $ 13.4      
Value added tax receivable, net $ 4.5      
Exchange rate | / $ 534.8 585.7    
Interest costs capitalized $ 0.0 $ 0.0 $ 0.0  
Gain (loss) on foreign currency transaction $ (0.2) $ (0.2) $ 0.1  
Office and Miscellaneous Equipment [Member]        
Organization And Accounting Policies [Line Items]        
Estimated useful life of assets 5 years      
Leasehold Improvements [Member] | Minimum [Member]        
Organization And Accounting Policies [Line Items]        
Estimated useful life of assets 5 years      
Leasehold Improvements [Member] | Maximum [Member]        
Organization And Accounting Policies [Line Items]        
Estimated useful life of assets 7 years      
Prior Production Sharing Contract, Through September 17, 2018 [Member] | Government Of Gabon [Member]        
Organization And Accounting Policies [Line Items]        
Monthly royalty rate, based on production at the published price 13.00%      
Production Sharing Contract, September 17, 2018 Through September 16, 2028 [Member] | Consortium [Member]        
Organization And Accounting Policies [Line Items]        
Monthly royalty rate, based on production at the published price 13.00%      
Etame Marine Block [Member] | Government Of Gabon [Member]        
Organization And Accounting Policies [Line Items]        
Monthly royalty rate, based on production at the published price 13.00%      
Working interest ownership, percentage 7.50%      
Etame Marine Block [Member] | Prior Production Sharing Contract, Through September 17, 2018 [Member] | Consortium [Member]        
Organization And Accounting Policies [Line Items]        
Working interest ownership, percentage 7.50%      
Etame Marine Block [Member] | Prior Production Sharing Contract, Through September 17, 2018 [Member] | Government Of Gabon [Member]        
Organization And Accounting Policies [Line Items]        
Working interest ownership, percentage     7.50%  
Etame Marine Block [Member] | Scenario, Forecast [Member] | Government Of Gabon [Member]        
Organization And Accounting Policies [Line Items]        
Working interest ownership, percentage       10.00%
Etame Marine Block [Member] | Scenario, Forecast [Member] | Production Sharing Contract, September 17, 2018 Through September 16, 2028 [Member] | Government Of Gabon [Member]        
Organization And Accounting Policies [Line Items]        
Working interest ownership, percentage       10.00%