Condensed Consolidating Financial Information (Condensed Consolidating Statement of Operations) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Operating revenues	$ 868,366		$ 691,727		$ 2,464,056		$ 1,952,638
Gas purchases - midstream services	195,271		149,651		575,337		423,941
Operating expenses	90,269		61,906		236,648		179,478
General and administrative expenses	50,969		36,121		135,754		129,879
Depreciation, depletion and amortization	204,934		203,935		571,268		605,392
Impairment of natural gas and oil properties			289,821				1,090,473	[1]
Taxes, other than income taxes	17,694		16,252		58,543		51,154
Total operating costs and expenses	559,137		757,686		1,577,550		2,480,317
Operating Income (loss)	309,229		(65,959)		886,506		(527,679)	[2]
Other income (loss), net	(319)		238	[2]	(498)	[1]	2,615	[1]
Gain (Loss) on Derivatives	12,124	[1]	(5,879)	[1]	75,779		(10,593)
Interest expense	11,018		10,606		29,317	[1]	26,305	[1]
Income (Loss) before income taxes	310,016		(82,206)		932,470		(561,962)
Provision (benefit) for income taxes	124,149	[1]	(28,153)	[1]	373,457	[1]	(210,481)	[1]
Net income (loss)	185,867		(54,053)		559,013		(351,481)
Comprehensive income (loss)	139,179		(183,944)		457,967		(567,869)
Parent [Member]
Equity in earnings of subsidiaries	185,867		(54,053)		559,013		(351,481)
Income (Loss) before income taxes	185,867		(54,053)		559,013		(351,481)
Net income (loss)	185,867		(54,053)		559,013		(351,481)
Comprehensive income (loss)	139,179		(183,944)		457,967		(567,869)
Guarantors [Member]
Operating revenues	823,112		647,961		2,331,343		1,824,594
Gas purchases - midstream services	195,437		149,765		576,185		424,425
Operating expenses	140,400		106,293		375,721		311,165
General and administrative expenses	43,836		30,818		116,648		111,567
Depreciation, depletion and amortization	191,972		193,057		533,876		572,139
Impairment of natural gas and oil properties			289,821				1,090,473
Taxes, other than income taxes	15,348		13,513		50,053		42,159
Total operating costs and expenses	586,993		783,267		1,652,483		2,551,928
Operating Income (loss)	236,119		(135,306)		678,860		(727,334)
Other income (loss), net	145		216		67		(23)
Gain (Loss) on Derivatives	10,251		(5,879)		73,906		(10,593)
Interest expense	9,359		7,200		23,884		15,460
Income (Loss) before income taxes	237,156		(148,169)		728,949		(753,410)
Provision (benefit) for income taxes	91,466		(53,903)		291,795		(285,231)
Net income (loss)	145,690		(94,266)		437,154		(468,179)
Comprehensive income (loss)	98,102		(225,408)		337,122		(686,291)
Non-Guarantors [Member]
Operating revenues	130,998		121,343		379,212		350,064
Operating expenses	35,425		32,277		106,520		87,461
General and administrative expenses	7,155		6,102		19,164		20,700
Depreciation, depletion and amortization	12,962		10,878		37,392		33,253
Taxes, other than income taxes	2,346		2,739		8,490		8,995
Total operating costs and expenses	57,888		51,996		171,566		150,409
Operating Income (loss)	73,110		69,347		207,646		199,655
Other income (loss), net	(464)		22		(565)		2,638
Gain (Loss) on Derivatives	1,873				1,873
Interest expense	1,659		3,406		5,433		10,845
Income (Loss) before income taxes	72,860		65,963		203,521		191,448
Provision (benefit) for income taxes	32,683		25,750		81,662		74,750
Net income (loss)	40,177		40,213		121,859		116,698
Comprehensive income (loss)	40,811		41,210		120,045		117,660
Eliminations [Member]
Operating revenues	(85,744)		(77,577)		(246,499)		(222,020)
Gas purchases - midstream services	(166)		(114)		(848)		(484)
Operating expenses	(85,556)		(76,664)		(245,593)		(219,148)
General and administrative expenses	(22)		(799)		(58)		(2,388)
Total operating costs and expenses	(85,744)		(77,577)		(246,499)		(222,020)
Equity in earnings of subsidiaries	(185,867)		54,053		(559,013)		351,481
Income (Loss) before income taxes	(185,867)		54,053		(559,013)		351,481
Net income (loss)	(185,867)		54,053		(559,013)		351,481
Comprehensive income (loss)	$ (138,913)		$ 184,198		$ (457,167)		$ 568,631

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

[2] The operating loss for the E&P segment for the three and nine months ended September 30, 2012 includes a $289.8 million and $1,090.5 million non-cash ceiling test impairment of our natural gas and oil properties respectively.