Condensed Consolidating Financial Information (Condensed Consolidating Statement of Operations) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011
Operating Revenues	$ 599,728		$ 765,166		$ 1,256,197		$ 1,441,501
Gas purchases - midstream services	127,614		200,052		274,290		370,282
Operating expenses	56,614		55,054		117,572		111,852
General and administrative expenses	44,932		40,238		93,758		77,355
Depreciation, depletion and amortization	207,830		171,620		401,457		335,067
Impairment of natural gas and oil properties	800,652				800,652
Taxes, other than income taxes	14,480		15,660		34,902		31,752
Total operating costs and expenses	1,252,122		482,624		1,722,631		926,308
Operating Income (loss)	(652,394)	[1]	282,542		(466,434)	[1]	515,193
Other income (loss), net	2,577		69		2,377		443
Interest expense	8,361	[2]	6,170	[2]	15,699	[2]	13,606	[2]
Income (loss) before income taxes	(658,178)		276,441		(479,756)		502,030
Provision for income taxes	(253,046)	[2]	108,987	[2]	(182,328)	[2]	197,967	[2]
Net income (loss)	(405,132)		167,454		(297,428)		304,063
Comprehensive income (loss)	(558,199)		216,395		(383,925)		328,471
Parent [Member]
Equity in earnings of subsidiaries	(405,132)		167,454		(297,428)		304,063
Income (loss) before income taxes	(405,132)		167,454		(297,428)		304,063
Net income (loss)	(405,132)		167,454		(297,428)		304,063
Comprehensive income (loss)	(558,199)		216,395		(383,925)		328,471
Guarantors [Member]
Operating Revenues	557,474		728,430		1,171,919		1,370,273
Gas purchases - midstream services	127,757		200,420		274,660		371,002
Operating expenses	101,816		88,477		204,872		175,329
General and administrative expenses	39,041		35,298		80,749		67,342
Depreciation, depletion and amortization	196,245		161,699		379,082		316,100
Impairment of natural gas and oil properties	800,652				800,652
Taxes, other than income taxes	11,648		13,568		28,646		27,475
Total operating costs and expenses	1,277,159		499,462		1,768,661		957,248
Operating Income (loss)	(719,685)		228,968		(596,742)		413,025
Other income (loss), net	(65)		16		(239)		361
Interest expense	4,505		1,748		8,260		5,393
Income (loss) before income taxes	(724,255)		227,236		(605,241)		407,993
Provision for income taxes	(278,220)		89,651		(231,328)		161,013
Net income (loss)	(446,035)		137,585		(373,913)		246,980
Comprehensive income (loss)	(598,840)		186,204		(460,883)		270,607
Non-Guarantors [Member]
Operating Revenues	115,596		100,108		228,721		193,766
Operating expenses	27,203		28,793		55,184		56,777
General and administrative expenses	6,685		5,728		14,598		11,577
Depreciation, depletion and amortization	11,585		9,921		22,375		18,967
Taxes, other than income taxes	2,832		2,092		6,256		4,277
Total operating costs and expenses	48,305		46,534		98,413		91,598
Operating Income (loss)	67,291		53,574		130,308		102,168
Other income (loss), net	2,642		53		2,616		82
Interest expense	3,856		4,422		7,439		8,213
Income (loss) before income taxes	66,077		49,205		125,485		94,037
Provision for income taxes	25,174		19,336		49,000		36,954
Net income (loss)	40,903		29,869		76,485		57,083
Comprehensive income (loss)	40,387		29,995		76,450		57,471
Eliminations [Member]
Operating Revenues	(73,342)		(63,372)		(144,443)		(122,538)
Gas purchases - midstream services	(143)		(368)		(370)		(720)
Operating expenses	(72,405)		(62,216)		(142,484)		(120,254)
General and administrative expenses	(794)		(788)		(1,589)		(1,564)
Total operating costs and expenses	(73,342)		(63,372)		(144,443)		(122,538)
Equity in earnings of subsidiaries	405,132		(167,454)		297,428		(304,063)
Income (loss) before income taxes	405,132		(167,454)		297,428		(304,063)
Net income (loss)	405,132		(167,454)		297,428		(304,063)
Comprehensive income (loss)	$ 558,453		$ (216,199)		$ 384,433		$ (328,078)

[1] The operating loss for the E&P segment for the three and six- months ended June 30, 2012 includes a $800.7 million non-cash ceiling test impairment of our natural gas and oil properties.

[2] Interest income, interest expense and the provision for income taxes by segment are allocated as they are incurred at the corporate level.