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, 2020
Jun. 30, 2019
Jun. 30, 2020
Jun. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative instruments gain (loss), net $ (756) $ 1,911 $ 6,583 $ (1)
Realized Gain - Contract Settlements [Member]        
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative instruments gain (loss), net 6,498 432 7,216 1,563
Unrealized (Gain) Loss [Member]        
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative instruments gain (loss), net $ (7,254) $ 1,479 $ (633) $ (1,564)