Acquisitions and Divestitures Acquisitions and Divestitures (Components of Discontinued Operations) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Oil and gas	$ 557,000	$ 967,000	$ 1,670,000	$ 2,795,000
Interest and other	(17,000)	2,000	0	9,000
Gain on disposition of assets, net	(779,000)	(1,000)	(782,000)	(11,000)
Oil and gas production	189,000	168,000	532,000	493,000
Production and ad valorem taxes	36,000	58,000	112,000	169,000
Depletion, depreciation and amortization	364,000	274,000	1,003,000	734,000
Impairment of oil and gas properties	72,000	0	210,000	0
Exploration and abandonment	25,000	22,000	79,000	80,000
General and administrative	81,000	81,000	246,000	244,000
Asset Retirement Obligation, Accretion Expense	3,000	3,000	9,000	9,000
Other Nonoperating Expense	60,000	20,000	170,000	55,000
Costs and Expenses	(1,215,000)	(866,000)	(3,183,000)	(2,457,000)
Current tax provision	(48,000)	14,000	(49,000)	(4,000)
Deferred tax benefit	(307,000)	(250,000)	(146,000)	(315,000)
Income (Loss) from Discontinued Operations, Net of Tax	(2,000)	(37,000)	(6,000)	(113,000)
Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total Revenues And Other Income From Discontinued Operations	0	50,000	1,000	234,000
Costs and Expenses	(2,000)	(108,000)	(10,000)	(408,000)
Loss from discontinued operations before income taxes	(2,000)	(58,000)	(9,000)	(174,000)
Current tax provision	0	0	0	(1,000)
Deferred tax benefit	0	21,000	3,000	62,000
Income (Loss) from Discontinued Operations, Net of Tax	$ (2,000)	$ (37,000)	$ (6,000)	$ (113,000)