Derivative Instruments and Hedging Activities (Schedule of Cash Paid (Received)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities
Cash received (paid) for commodity derivative settlements, net	$ 98,870	$ (3,789)	$ (27,272)
Not Designated as Hedging Instrument | Contingent consideration arrangements
Cash flows from investing activities
Cash paid for settlements of contingent consideration arrangements, net	(40,000)	0	0
Commodity - Oil | Not Designated as Hedging Instrument
Cash flows from operating activities
Cash received (paid) for commodity derivative settlements, net	98,723	(11,188)	(27,510)
Commodity - Natural gas | Not Designated as Hedging Instrument
Cash flows from operating activities
Cash received (paid) for commodity derivative settlements, net	$ 147	$ 7,399	$ 238