Derivative Instruments and Hedging Activities (Schedule of Cash Paid (Received)) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities
Cash (paid) received for commodity derivative settlements	$ 98,688	$ (1,157)	$ 101,301	$ (1,447)
Not Designated as Hedging Instrument | Gain on contingent consideration arrangements
Cash flows from investing activities
Cash paid for settlements of contingent consideration arrangements, net	0	0	(40,000)	0
Commodity - Oil | Not Designated as Hedging Instrument
Cash flows from operating activities
Cash (paid) received for commodity derivative settlements	100,470	(4,461)	98,693	(6,003)
Commodity - Natural gas | Not Designated as Hedging Instrument
Cash flows from operating activities
Cash (paid) received for commodity derivative settlements	$ (1,782)	$ 3,304	$ 2,608	$ 4,556