Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenues	$ 134,057	$ 89,007	$ 254,954	$ 211,383
General and administrative	5,751	25,814	12,920	37,367
Decrease in operating costs	(74,623)	(115,103)	(145,306)	(198,826)
Intersegment Eliminations
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenues	(10,103)	(4,871)	(19,514)	(10,331)
General and administrative	880	0	1,760	0
Decrease in operating costs	10,983	4,871	21,274	10,331
Oil and natural gas
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenues	41,970	26,956	96,994	75,478
Decrease in operating costs	(15,487)	(71,540)	(34,636)	(102,203)
Oil and natural gas | Intersegment Eliminations
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenues	(17,806)	(1)	(17,807)	(3)
Decrease in operating costs	863	$ 814	$ 1,707	$ 1,566
Revision of Prior Period, Adjustment [Member] | Intersegment Eliminations | Error Correction, Inter-Segment Eliminations Between Oil and Natural Gas
Error Corrections and Prior Period Adjustments Restatement [Line Items]
General and administrative	900
Revision of Prior Period, Adjustment [Member] | Oil and natural gas | Error Correction, Separate Errors Between Oil and Natural Gas
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenues	3,900
Decrease in operating costs	3,400
Revision of Prior Period, Adjustment [Member] | Oil and natural gas | Intersegment Eliminations | Error Correction, Inter-Segment Eliminations Between Oil and Natural Gas
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenues	$ (8,600)