Quarterly report pursuant to Section 13 or 15(d)

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

v3.19.1
Oil And Natural Gas Properties And Equipment (Narrative) (Details)
$ in Thousands
 3 Months Ended 12 Months Ended
Sep. 26, 2018
USD ($)
Sep. 17, 2018
USD ($)
item
Mar. 31, 2019
USD ($)
item
Mar. 31, 2018
USD ($)
Dec. 31, 2017
Dec. 31, 2018
USD ($)
Sep. 30, 2018
USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]              
Reduction in VAT receivable     $ 738 $ 83      
VAT receivable, net of valuation allowance     4,200        
Allocated to proved leasehold cost     22,500        
Allocated to unproved leasehold cost     $ 13,700        
Number of drilled wells required by agreement | item     2        
Number of appraisal wells required by agreement | item     2        
Estimated costs of wells, gross amount     $ 61,200        
Estimated costs of wells     20,500        
Estimated costs of technical studies     1,300        
Estimated costs of technical studies, net     400        
Deferred tax assets, basis difference in fixed assets     18,600        
Deferred tax liabilities, basis difference in fixed assets     18,600        
Undeveloped Acreage     $ 23,771     $ 23,771  
Period of development     25 years        
Additional increase to working interest ownership, percent     0.80%        
Etame Field [Member]              
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]              
Percent of participating interest     33.575%        
Number of exploitation areas | item   3          
Period of agreement for exploitation areas   10 years          
Number of contract extension periods | item   2          
Production license agreement term extended by government   5 years          
Gabon              
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]              
Contractual commitment, gross   $ 65,000          
Contractual obligation   $ 21,800          
Cash paid for signing bonus, gross amount $ 35,000            
Payment of signing bonus, allocated to proved and unproved property 11,800            
Reduction in VAT receivable, gross amount 25,000            
Reduction in VAT receivable 8,400            
Accrued liabilities, end of drilling activities, gross amount $ 5,000            
Accrued liabilities, end of drilling activities             $ 1,700
Working interest ownership, percentage         7.50%    
Additional increase to working interest ownership, percent     2.50%        
Block P Offshore Equatorial Guinea [Member]              
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]              
Working interest ownership, percentage     31.00%        
Undeveloped Acreage     $ 10,000        
Prior Production Sharing Contract, Through September 17, 2018 [Member]              
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]              
Entitled percent for consortium after initial royalty percentage     70.00%