Derivative Instruments and Hedging Activities (Schedule of Gain or Loss on Derivative Contracts) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) loss on derivative contracts	$ (27,038)	$ 21,809	$ 97,966	$ (31,415)
Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) loss on derivative contracts	27,038	(21,809)	(97,966)	31,415
Not Designated as Hedging Instrument | (Gain) loss on contingent consideration arrangements
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) loss on derivative contracts	715	4,236	(855)	923
Not Designated as Hedging Instrument | Commodity - Oil
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) loss on derivative contracts	16,606	(24,722)	(118,348)	34,798
Not Designated as Hedging Instrument | Commodity - Natural gas
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) loss on derivative contracts	7,296	(1,323)	18,819	(4,306)
Not Designated as Hedging Instrument | Commodity - Natural gas liquids
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) loss on derivative contracts	$ 2,421	$ 0	$ 2,418	$ 0