Revenue Recognition (Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2020	Sep. 18, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue
Revenues	$ 215,903	$ 521,693	$ 1,260,360	$ 1,455,655
Oil sales
Disaggregation of Revenue
Revenues	199,769	489,251	1,205,083	1,412,358
Natural gas sales
Disaggregation of Revenue
Revenues	1,339	2,850	6,937	10,231
CO2 sales and transportation fees
Disaggregation of Revenue
Revenues	9,419	21,049	34,142	31,145
Oil marketing revenues
Disaggregation of Revenue
Revenues	$ 5,376	$ 8,543	$ 14,198	$ 1,921