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
Mar. 31, 2020
Mar. 31, 2019
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative instruments gain (loss), net $ 7,339 $ (1,912)
Realized Gain - Contract Settlements [Member]    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative instruments gain (loss), net 718 1,131
Unrealized (Gain) Loss [Member]    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative instruments gain (loss), net $ 6,621 $ (3,043)