Derivative Instruments and Hedging Activities (Schedule of Gain or Loss on Derivative Contracts) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) loss on derivative contracts	$ (126,965)	$ 14,036	$ 125,004	$ (53,224)
Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) loss on derivative contracts	126,965	(14,036)	(125,004)	53,224
Not Designated as Hedging Instrument | Gain on contingent consideration arrangements
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) loss on derivative contracts	(95)	(3,313)	(1,570)	(3,313)
Not Designated as Hedging Instrument | Commodity - Oil
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) loss on derivative contracts	122,369	(8,849)	(134,954)	59,520
Not Designated as Hedging Instrument | Commodity - Natural gas
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) loss on derivative contracts	4,695	(1,874)	11,524	(2,983)
Not Designated as Hedging Instrument | Commodity - Natural gas liquids
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) loss on derivative contracts	$ (4)	$ 0	$ (4)	$ 0