Quarterly report pursuant to Section 13 or 15(d)

Derivatives and Fair Value (Effect of Derivative Instruments on the Condensed Consolidated Statements of Operations) (Details)

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Derivatives and Fair Value (Effect of Derivative Instruments on the Condensed Consolidated Statements of Operations) (Details) - Crude Oil Swaps [Member] - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative instruments gain (loss), net $ (9,969) $ (756) $ (15,923) $ 6,583
Realized Gain (Loss) - Contract Settlements [Member]        
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative instruments gain (loss), net (4,293) 6,498 (6,003) 7,216
Unrealized Loss [Member]        
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative instruments gain (loss), net $ (5,676) $ (7,254) $ (9,920) $ (633)