Derivative Instruments and Hedging Activities (Schedule of Derivative Instruments in Statement of Financial Position, Fair Value) (Details) - Not Designated as Hedging Instrument - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair value of derivatives - Current
Offsetting Assets and Liabilities [Line Items]
Presented without Effects of Netting	$ 21,156	$ 43,567
Effects of Netting	(20,235)	(17,511)
As Presented with Effects of Netting	921	26,056
Fair value of derivatives - Current | Contingent consideration arrangements
Offsetting Assets and Liabilities [Line Items]
Presented without Effects of Netting	0	16,718
Effects of Netting	0	0
As Presented with Effects of Netting	0	16,718
Fair value of derivatives - Current | Commodity derivative instruments
Offsetting Assets and Liabilities [Line Items]
Presented without Effects of Netting	21,156	26,849
Effects of Netting	(20,235)	(17,511)
As Presented with Effects of Netting	921	9,338
Fair value of derivatives - Non-current
Offsetting Assets and Liabilities [Line Items]
Presented without Effects of Netting	1,816	9,216
Effects of Netting	0	0
As Presented with Effects of Netting	1,816	9,216
Fair value of derivatives - Non-current | Contingent consideration arrangements
Offsetting Assets and Liabilities [Line Items]
Presented without Effects of Netting	1,816	9,216
Effects of Netting	0	0
As Presented with Effects of Netting	1,816	9,216
Fair value of derivatives - Non-current | Commodity derivative instruments
Offsetting Assets and Liabilities [Line Items]
Presented without Effects of Netting	0	0
Effects of Netting	0	0
As Presented with Effects of Netting	0	0
Fair value of derivatives - Current
Offsetting Assets and Liabilities [Line Items]
Presented without Effects of Netting	(117,295)	(88,708)
Effects of Netting	20,235	17,511
As Presented with Effects of Netting	(97,060)	(71,197)
Fair value of derivatives - Current | Contingent consideration arrangements
Offsetting Assets and Liabilities [Line Items]
Presented without Effects of Netting	0	(50,000)
Effects of Netting	0	0
As Presented with Effects of Netting	0	(50,000)
Fair value of derivatives - Current | Commodity derivative instruments
Offsetting Assets and Liabilities [Line Items]
Presented without Effects of Netting	(117,295)	(38,708)
Effects of Netting	20,235	17,511
As Presented with Effects of Netting	(97,060)	(21,197)
Fair value of derivatives - Non-current
Offsetting Assets and Liabilities [Line Items]
Presented without Effects of Netting	(88,046)	(32,695)
Effects of Netting	0	0
As Presented with Effects of Netting	(88,046)	(32,695)
Fair value of derivatives - Non-current | Contingent consideration arrangements
Offsetting Assets and Liabilities [Line Items]
Presented without Effects of Netting	(8,618)	(19,760)
Effects of Netting	0	0
As Presented with Effects of Netting	(8,618)	(19,760)
Fair value of derivatives - Non-current | Commodity derivative instruments
Offsetting Assets and Liabilities [Line Items]
Presented without Effects of Netting	0	(12,935)
Effects of Netting	0	0
As Presented with Effects of Netting	0	$ (12,935)
Fair value of derivatives - Non-current | Warrant liability
Offsetting Assets and Liabilities [Line Items]
Presented without Effects of Netting	(79,428)
Effects of Netting	0
As Presented with Effects of Netting	$ (79,428)