Annual report pursuant to Section 13 and 15(d)

Derivative Instruments and Hedging Activities (Schedule of Gain or Loss on Derivative Contracts) (Details)

v3.19.3.a.u2
Derivative Instruments and Hedging Activities (Schedule of Gain or Loss on Derivative Contracts) (Details) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2019
Sep. 30, 2019
Jun. 30, 2019
Mar. 31, 2019
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]                    
Net gain (loss) on fair value adjustments $ (30,700) $ 21,800 $ 14,000 $ (67,300) $ 103,900 $ (34,300) $ (16,600) $ (62,109) $ 48,544 $ (18,901)
Total gain (loss) on derivative contracts               (62,109) 48,544 (18,901)
Not Designated as Hedging Instrument                    
Derivative Instruments, Gain (Loss) [Line Items]                    
Total gain (loss) on derivative contracts               (62,109) 48,544 (18,901)
Not Designated as Hedging Instrument | Credit Risk Contract                    
Derivative Instruments, Gain (Loss) [Line Items]                    
Net gain (loss) on fair value adjustments               2,315 0 0
Not Designated as Hedging Instrument | Commodity - Oil                    
Derivative Instruments, Gain (Loss) [Line Items]                    
Net gain (loss) on settlements               (11,188) (27,510) (9,067)
Net gain (loss) on fair value adjustments               (62,125) 72,973 (11,426)
Total gain (loss) on derivative contracts               (73,313) 45,463 (20,493)
Not Designated as Hedging Instrument | Commodity - Natural gas                    
Derivative Instruments, Gain (Loss) [Line Items]                    
Net gain (loss) on settlements               7,399 238 594
Net gain (loss) on fair value adjustments               1,490 2,843 998
Total gain (loss) on derivative contracts               $ 8,889 $ 3,081 $ 1,592