Discontinued Operations and Assets Held for Sale (Results of Operations Associated with Discontinued Operations) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income from discontinued operations	$ 49,846	$ 77,672	[1]
Discontinued Operations, Held-for-sale or Disposed of by Sale [Member]
Revenues	195,412	210,815
Lease operating expenses	62,716	47,610
Depreciation, depletion and amortization	31,353	47,991
Other costs and expenses (benefits)	13,080	(2,451)
Total costs and expenses	88,263	117,665
Income tax expense	38,417	39,993
Income from discontinued operations	$ 49,846	$ 77,672

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