Summarized Financial Information Concerning Segments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014 segment business_unit		Sep. 30, 2013		Dec. 31, 2013
Segment Reporting Information
Reportable segments					3
Business units					3
Total revenues	$ 394,107		$ 493,603		$ 1,211,877		$ 1,518,280
Income (loss) from operations	256,491		(2,166)	[1]	216,240		(291,262)	[1]
Interest expense	(59,783)		(61,385)		(183,689)		(208,454)
Loss on extinguishment of debt	0		0		0		(82,005)
Other (expense) income, net	(273)		658		3,159		1,163
Income (loss) before income taxes	196,435		(62,893)	[1]	35,710		(580,558)	[1]
Capital expenditures	467,828	[2]	322,582	[2]	1,120,537	[2]	1,098,452	[2]
Depreciation, depletion, amortization, accretion and impairment	128,156		162,068		546,264		525,077
Total assets	6,978,389				6,978,389				7,684,795
Exploration and Production
Segment Reporting Information
Total revenues	359,613		462,503		1,106,857		1,402,125
Income (loss) from operations	275,191		(19,858)		288,497	[3]	(95,927)	[3]
Interest expense	0		331		138		757
Loss on extinguishment of debt							0
Other (expense) income, net	(38)		(350)		(272)		157
Income (loss) before income taxes	275,153		(19,877)		288,363		(95,013)
Capital expenditures	435,758	[2]	292,697	[2]	1,056,568	[2]	1,008,869	[2]
Depreciation, depletion, amortization, accretion and impairment	113,711		146,286		497,888		462,683
Total assets	5,685,412				5,685,412				6,157,225
Drilling and Oil Field Services
Segment Reporting Information
Total revenues	21,348		16,192		57,280		49,651
Income (loss) from operations	(1,155)		(8,276)		(6,605)	[4]	(36,684)	[4]
Interest expense	0		0		0		0
Loss on extinguishment of debt							0
Other (expense) income, net	(89)		0		(561)		0
Income (loss) before income taxes	(1,244)		(8,276)		(7,166)		(36,684)
Capital expenditures	3,603	[2]	3,142	[2]	10,877	[2]	4,657	[2]
Depreciation, depletion, amortization, accretion and impairment	6,884		8,252		25,390		36,544
Total assets	142,104				142,104				158,737
Midstream Services
Segment Reporting Information
Total revenues	11,922		14,141		44,441		64,105
Income (loss) from operations	(3,218)		(7,691)		(6,973)		(18,106)
Interest expense	0		0		0		0
Loss on extinguishment of debt							0
Other (expense) income, net	5		(41)		5		(914)
Income (loss) before income taxes	(3,213)		(7,732)		(6,968)		(19,020)
Capital expenditures	14,045	[2]	16,551	[2]	25,810	[2]	46,883	[2]
Depreciation, depletion, amortization, accretion and impairment	2,584		2,128		7,534		7,832
Total assets	193,630				193,630				188,165
All Other
Segment Reporting Information
Total revenues	1,224		767		3,299		2,399
Income (loss) from operations	(14,327)		33,659		(58,679)		(140,545)
Interest expense	(59,783)		(61,716)		(183,827)		(209,211)
Loss on extinguishment of debt							(82,005)
Other (expense) income, net	(151)		1,049		3,987		1,920
Income (loss) before income taxes	(74,261)		(27,008)		(238,519)		(429,841)
Capital expenditures	14,422	[2]	10,192	[2]	27,282	[2]	38,043	[2]
Depreciation, depletion, amortization, accretion and impairment	4,977		5,402		15,452		18,018
Total assets	957,243				957,243				1,180,668
Operating Segments
Segment Reporting Information
Total revenues	443,051		545,752		1,376,082		1,685,130
Operating Segments | Exploration and Production
Segment Reporting Information
Total revenues	359,613		462,582		1,106,883		1,402,366
Operating Segments | Drilling and Oil Field Services
Segment Reporting Information
Total revenues	51,082		44,527		150,054		141,364
Operating Segments | Midstream Services
Segment Reporting Information
Total revenues	31,132		37,876		115,846		139,001
Operating Segments | All Other
Segment Reporting Information
Total revenues	1,224		767		3,299		2,399
Intersegment Eliminations
Segment Reporting Information
Total revenues	(48,944)		(52,149)		(164,205)		(166,850)
Intersegment Eliminations | Exploration and Production
Segment Reporting Information
Total revenues	0		(79)		(26)		(241)
Intersegment Eliminations | Drilling and Oil Field Services
Segment Reporting Information
Total revenues	(29,734)		(28,335)		(92,774)		(91,713)
Intersegment Eliminations | Midstream Services
Segment Reporting Information
Total revenues	(19,210)		(23,735)		(71,405)		(74,896)
Intersegment Eliminations | All Other
Segment Reporting Information
Total revenues	$ 0		$ 0		$ 0		$ 0

[1] Guarantor and Consolidated direct operating expenses have been restated to reflect accrual of the CO2 delivery shortfall penalty. See Note 2.

[2] On an accrual basis and exclusive of acquisitions.

[3] Income (loss) from operations includes a full cost ceiling limitation impairment of $164.8 million for the nine-month period ended September 30, 2014, and a loss on the sale of the Permian Properties of $398.9 million for the nine-month period ended September 30, 2013.

[4] Income (loss) from operations includes an impairment of $3.1 million and $11.1 million on certain drilling assets held for sale for the nine-month periods ended September 30, 2014 and September 30, 2013, respectively.