Condensed Consolidating Financial Information (Condensed Consolidating Statement of Operations) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Operating Revenues	$ 685,848		$ 767,255		$ 1,942,045		$ 2,208,756
Gas purchases - midstream services	149,651		175,236		423,941		545,518
Operating expenses	61,906		63,911		179,478		175,763
General and administrative expenses	36,121		35,600		129,879		112,955
Depreciation, depletion and amortization	200,655		179,113		602,112		514,180
Impairment of natural gas and oil properties	441,465				1,377,364
Taxes, other than income taxes	16,252		17,677		51,154		49,429
Total operating costs and expenses	906,050		471,537		2,763,928		1,397,845
Operating income (loss)	(220,202)	[1]	295,718	[1]	(821,883)	[1]	810,911	[1]
Other Income (Loss), Net	238		(122)		2,615		321
Interest expense	10,606	[2]	5,657	[2]	26,305	[2]	19,263	[2]
Income (Loss) Before Income Taxes	(230,570)		289,939		(845,573)		791,969
Provision (benefit) for income taxes	(85,755)	[2]	114,766	[2]	(320,362)	[2]	312,733	[2]
Net income (loss)	(144,815)		175,173		(525,211)		479,236
Comprehensive income (loss)	(274,706)		296,540		(741,599)		625,011
Parent [Member]
Equity in earnings of subsidiaries	(144,815)		175,173		(525,211)		479,236
Income (Loss) Before Income Taxes	(144,815)		175,173		(525,211)		479,236
Net income (loss)	(144,815)		175,173		(525,211)		479,236
Comprehensive income (loss)	(274,706)		296,540		(741,599)		625,011
Guarantors [Member]
Operating Revenues	642,082		730,826		1,814,001		2,101,099
Gas purchases - midstream services	149,765		175,729		424,425		546,731
Operating expenses	106,293		101,645		311,165		276,974
General and administrative expenses	30,818		34,030		111,567		101,372
Depreciation, depletion and amortization	189,777		169,446		568,859		485,546
Impairment of natural gas and oil properties	441,465				1,377,364
Taxes, other than income taxes	13,513		13,731		42,159		41,206
Total operating costs and expenses	931,631		494,581		2,835,539		1,451,829
Operating income (loss)	(289,549)		236,245		(1,021,538)		649,270
Other Income (Loss), Net	216		(16)		(23)		345
Interest expense	7,200		2,376		15,460		7,769
Income (Loss) Before Income Taxes	(296,533)		233,853		(1,037,021)		641,846
Provision (benefit) for income taxes	(111,505)		92,725		(395,112)		253,738
Net income (loss)	(185,028)		141,128		(641,909)		388,108
Comprehensive income (loss)	(316,170)		263,517		(860,021)		534,124
Non-Guarantors [Member]
Operating Revenues	121,343		105,486		350,064		299,252
Operating expenses	32,277		30,034		87,461		86,811
General and administrative expenses	6,102		2,366		20,700		13,943
Depreciation, depletion and amortization	10,878		9,667		33,253		28,634
Taxes, other than income taxes	2,739		3,946		8,995		8,223
Total operating costs and expenses	51,996		46,013		150,409		137,611
Operating income (loss)	69,347		59,473		199,655		161,641
Other Income (Loss), Net	22		(106)		2,638		(24)
Interest expense	3,406		3,281		10,845		11,494
Income (Loss) Before Income Taxes	65,963		56,086		191,448		150,123
Provision (benefit) for income taxes	25,750		22,041		74,750		58,995
Net income (loss)	40,213		34,045		116,698		91,128
Comprehensive income (loss)	41,210		32,826		117,660		90,297
Eliminations [Member]
Operating Revenues	(77,577)		(69,057)		(222,020)		(191,595)
Gas purchases - midstream services	(114)		(493)		(484)		(1,213)
Operating expenses	(76,664)		(67,768)		(219,148)		(188,022)
General and administrative expenses	(799)		(796)		(2,388)		(2,360)
Total operating costs and expenses	(77,577)		(69,057)		(222,020)		(191,595)
Equity in earnings of subsidiaries	144,815		(175,173)		525,211		(479,236)
Income (Loss) Before Income Taxes	144,815		(175,173)		525,211		(479,236)
Net income (loss)	144,815		(175,173)		525,211		(479,236)
Comprehensive income (loss)	$ 274,960		$ (296,343)		$ 742,361		$ (624,421)

[1] The operating loss for the E&P segment includes a $441.5 million and $1,377.4 million non-cash ceiling test impairment of our natural gas and oil properties for the three and nine-months ended September 30, 2012 respectively.

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