Derivatives and Fair Value (Effect of Derivative Instruments on the Condensed Consolidated Statements of Operations) (Details) - Crude Oil Swaps [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments gain (loss), net	$ 6,577	$ (446)	$ 4,264
Realized Gain - Contract Settlements [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments gain (loss), net	7,216	2,439	744
Unrealized Gain (Loss) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments gain (loss), net	$ (639)	$ (2,885)	$ 3,520