Discontinued Operations and Assets Held for Sale (Results of Operations Associated with Discontinued Operations) (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018		Sep. 30, 2019	Sep. 30, 2018
Discontinued Operations and Disposal Groups [Abstract]
Revenues 1	$ 972,737	$ 201,370		$ 1,328,110	$ 640,806
Lease operating expenses	6,262	49,390		127,138	152,406
Depreciation, depletion and amortization	0	44,326		33,697	139,566
Other costs and expenses (benefits)	11,078	36,642		81,560	55,665
Income before taxes	955,397	71,012		1,085,715	293,169
Income tax expense	2,029	33,200		58,083	106,981
Income from discontinued operations	$ 953,368	$ 37,812	[1]	$ 1,027,632	$ 186,188	[1],[2]

[1] Reclassified to conform to current presentation (see Note A).

[2] Reclassified to conform to current presentation (See Note A).