Annual report pursuant to Section 13 and 15(d)

Income Taxes (Narrative) (Details)

v3.10.0.1
Income Taxes (Narrative) (Details)
$ in Thousands
12 Months Ended
Dec. 31, 2018
USD ($)
item
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Income Taxes [Line Items]      
Interest or penalties accrued $ 0 $ 0  
Deferred tax assets 40,077 1,260  
Alternative minimum tax credit 674 1,349  
Valuation allowance $ 90,935 $ 153,205 $ 211,800
U.S. corporate income tax rate 21.00% 35.00%  
Cost account associated with interest in profit, remaining portion   $ 97,600  
Change in valuation allowance $ (16,500) $ 57,600  
Prior Production Sharing Contract, Through September 17, 2018 [Member]      
Income Taxes [Line Items]      
Entitled percent for consortium after initial royalty percentage 70.00%    
Production Sharing Contract, September 17, 2018 Through September 16, 2028 [Member]      
Income Taxes [Line Items]      
Entitled percent for consortium after initial royalty percentage 80.00%    
Production Sharing Contract, After September 16, 2028 [Member]      
Income Taxes [Line Items]      
Entitled percent for consortium after initial royalty percentage 70.00%    
Expected Refunded Between 2018 And 2021 [Member]      
Income Taxes [Line Items]      
Alternative minimum tax credit $ 1,400    
Minimum      
Income Taxes [Line Items]      
Allocation of remaining profit production, government payments, percentage 50.00%    
Planned wells in the next fiscal year | item 2    
Maximum      
Income Taxes [Line Items]      
Allocation of remaining profit production, government payments, percentage 60.00%    
Planned wells in the next fiscal year | item 3