Annual report pursuant to Section 13 and 15(d)

Derivative Instruments and Hedging Activities (Schedule of Derivative Instruments in Statement of Financial Position, Fair Value) (Details)

v3.20.4
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)