CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($)		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Revenues
Sales and other operating revenues		$ 2,097,695,000		$ 1,809,575,000	[1]	$ 2,787,116,000	[1]
Gain on sale of assets		127,434,000		1,663,000	[1]	154,155,000	[1]
Total revenues		2,225,129,000		1,811,238,000	[1]	2,941,271,000	[1]
Costs and Expenses
Lease operating expenses		468,323,000		559,360,000	[1]	832,306,000	[1]
Severance and ad valorem taxes		43,618,000		43,826,000	[1]	65,794,000	[1]
Exploration expenses, inlcluding undeveloped lease amortization		122,834,000		101,861,000	[1]	470,924,000	[1]
Selling and general expenses		222,766,000		265,210,000	[1]	306,663,000	[1]
Depreciation, depletion and amortization		957,719,000		1,054,081,000	[1]	1,619,824,000	[1]
Impairment of assets		0		95,088,000	[1]	2,493,156,000	[1]
Redetermination expense		15,000,000	[2]	39,100,000	[1]
Accretion of asset retirement obligations		42,590,000		46,742,000	[1]	48,665,000	[1]
Other expense		30,706,000		13,806,000	[1]	360,635,000	[1]
Total costs and expenses		1,903,556,000		2,219,074,000	[1]	6,197,967,000	[1]
Operating income (loss) from continuing operations		321,573,000		(407,836,000)	[1]	(3,256,696,000)	[1]
Other income (loss)
Interest and other income (loss)		(67,988,000)		62,891,000	[1]	91,809,000	[1]
Interest expense, net		(181,783,000)		(148,170,000)	[1]	(117,375,000)	[1]
Total other loss		(249,771,000)		(85,279,000)	[1]	(25,566,000)	[1]
Income (loss) from continuing operations before income taxes		71,802,000		(493,115,000)	[1]	(3,282,262,000)	[1]
Income tax expense (benefit)		382,738,000		(219,172,000)	[1]	(1,026,490,000)	[1]
Loss from continuing operations		(310,936,000)		(273,943,000)	[1]	(2,255,772,000)	[1]
Loss from discontinued operations, net of income taxes		(853,000)		(2,027,000)	[1]	(15,061,000)	[1]
NET LOSS		$ (311,789,000)		$ (275,970,000)	[1]	$ (2,270,833,000)	[1]
LOSS PER COMMON SHARE - BASIC
Continuing operations		$ (1.81)		$ (1.59)	[1]	$ (12.94)	[1]
Discontinued operations	[1]			(0.01)		(0.09)
Net loss		(1.81)		(1.60)	[1]	(13.03)	[1]
LOSS PER COMMON SHARE - DILUTED
Continuing operations		(1.81)		(1.59)	[1]	(12.94)	[1]
Discontinued operations	[1]			(0.01)		(0.09)
Net loss		(1.81)		(1.60)	[1]	(13.03)	[1]
Cash dividends per Common share		$ 1.00		$ 1.20	[1]	$ 1.40	[1]
Average Common shares outstanding
Basic		172,524,061		172,173,012	[1]	174,351,227	[1]
Diluted		172,524,061		172,173,012	[1]	174,351,227	[1]

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

[2] Results exclude corporate overhead, interest and discontinued operations.