Acquisitions and Divestitures Acquisitions and Divestitures (Components of Discontinued Operations) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Oil and gas	$ 596,000	$ 938,000	$ 1,113,000	$ 1,828,000
Interest and other	11,000	3,000	17,000	7,000
Gain on disposition of assets, net	(2,000)	(4,000)	(3,000)	(10,000)
Oil and gas production	163,000	167,000	343,000	325,000
Production and ad valorem taxes	37,000	56,000	76,000	111,000
Depletion, depreciation and amortization	329,000	243,000	639,000	460,000
Impairment of oil and gas properties	0	0	138,000	0
Exploration and abandonment	28,000	28,000	54,000	59,000
General and administrative	83,000	82,000	165,000	163,000
Asset Retirement Obligation, Accretion Expense	3,000	3,000	6,000	6,000
Other Nonoperating Expense	62,000	21,000	110,000	36,000
Costs and Expenses	(988,000)	(845,000)	(1,968,000)	(1,593,000)
Current tax provision	(1,000)	(6,000)	(1,000)	(18,000)
Deferred tax benefit	124,000	(26,000)	161,000	(65,000)
Income (Loss) from Discontinued Operations, Net of Tax	(1,000)	(54,000)	(4,000)	(76,000)
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	66,000	0	184,000
Costs and Expenses	(1,000)	(148,000)	(6,000)	(300,000)
Loss from discontinued operations before income taxes	(1,000)	(82,000)	(6,000)	(116,000)
Current tax provision	0	0	0	(1,000)
Deferred tax benefit	0	28,000	2,000	41,000
Income (Loss) from Discontinued Operations, Net of Tax	$ (1,000)	$ (54,000)	$ (4,000)	$ (76,000)