Revenue Recognition (Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Revenues	$ 250,799	$ 241,373
Oil sales
Disaggregation of Revenue [Line Items]
Revenues	233,044	228,577
Natural gas sales
Disaggregation of Revenue [Line Items]
Revenues	2,401	1,047
CO2 sales and transportation fees
Disaggregation of Revenue [Line Items]
Revenues	9,228	8,028
Oil marketing revenues
Disaggregation of Revenue [Line Items]
Revenues	$ 6,126	$ 3,721