Derivative Instruments and Hedging Activities (Schedule of Cash Paid (Received)) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities
Cash (paid) received for commodity derivative settlements	$ 453	$ 1,011	$ 101,754	$ (436)
Not Designated as Hedging Instrument | (Gain) loss 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	2,130	(1,045)	100,823	(7,048)
Commodity - Natural gas | Not Designated as Hedging Instrument
Cash flows from operating activities
Cash (paid) received for commodity derivative settlements	$ (1,677)	$ 2,056	$ 931	$ 6,612