Financial Statement Restatement (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Loss Per Share:
Basic	$ (0.16)	$ 0.50	$ (1.01)	$ 1.38
Diluted	$ (0.16)	$ 0.50	$ (1.01)	$ 1.37
Depreciation, depletion and amortization	$ 203,935	$ 179,113	$ 605,392	$ 514,180
Impairment of natural gas and oil properties	289,821		1,090,473
Deferred benefit for income taxes	(28,254)	111,275	(210,850)	309,042
Net loss	(54,053)	175,173	(351,481)	479,236
CONDENSED CONSOLIDATED BALANCE SHEETS
Less: Accumulated depreciation, depletion and amortization	(6,131,344)		(6,131,344)		(4,415,339)
Deferred income taxes	1,313,584		1,313,584		1,586,798
Retained earnings	2,304,733		2,304,733		2,656,214
Cash Flows From Operating Activities
Net loss	(54,053)	175,173	(351,481)	479,236
Impairment of natural gas and oil properties	289,821		1,090,473
Deferred benefit for income taxes	(28,254)	111,275	(210,850)	309,042
Parent [Member]
Loss Per Share:
Net loss	(54,053)	175,173	(351,481)	479,236
CONDENSED CONSOLIDATED BALANCE SHEETS
Less: Accumulated depreciation, depletion and amortization	(73,829)		(73,829)		(57,254)
Deferred income taxes	(96,550)		(96,550)		(97,045)
Cash Flows From Operating Activities
Net loss	(54,053)	175,173	(351,481)	479,236
Scenario, Previously Reported [Member]
Loss Per Share:
Basic	$ (0.42)		$ (1.51)
Diluted	$ (0.42)		$ (1.51)
Depreciation, depletion and amortization	200,655		602,112
Impairment of natural gas and oil properties	441,465		1,377,364
Deferred benefit for income taxes	(85,856)		(320,731)
Net loss	(144,815)		(525,211)
CONDENSED CONSOLIDATED BALANCE SHEETS
Less: Accumulated depreciation, depletion and amortization	(6,414,955)		(6,414,955)
Deferred income taxes	1,203,703		1,203,703
Retained earnings	2,131,003		2,131,003
Cash Flows From Operating Activities
Net loss	(144,815)		(525,211)
Impairment of natural gas and oil properties	441,465		1,377,364
Deferred benefit for income taxes	$ (85,856)		$ (320,731)