Net Quantities of Proved Reserves, Including Changes therein and Proved Developed and Proved Undeveloped Reserves (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2011 MMcfe		Dec. 31, 2010 MMcfe Location Well		Dec. 31, 2009 Location Well MMcfe
Reserve Quantities [Line Items]
Revisions of previous estimates	(93,649)	[1]	(40,210)	[2]	(160,995)	[3]
Extensions, discoveries and other additions	118,746	[4]	114,851	[5]	235,666	[6]
Wells drilled on locations not classified as proved undeveloped			16		13
Added Proved undeveloped locations			51		105
Proved undeveloped Locations removed			200
Downward revisions due to price
Reserve Quantities [Line Items]
Revisions of previous estimates					(63.1)
Downward revision in Appalachia for removal of proved undeveloped reserves
Reserve Quantities [Line Items]
Revisions of previous estimates					(27.1)
Downward revisions as result of lower plant yields
Reserve Quantities [Line Items]
Revisions of previous estimates					(20.1)
Downward revisions as result of well performance and application of revised oil and gas reserve calculation methodology
Reserve Quantities [Line Items]
Revisions of previous estimates					(50.7)
Downward revisions due to removal of proved undeveloped locations that would not be developed within five years
Reserve Quantities [Line Items]
Revisions of previous estimates			(45)
Upward revisions as result of processing gas in Mid-Continent Granite Wash for NGLs
Reserve Quantities [Line Items]
Revisions of previous estimates			34
Upward revisions due to higher prices
Reserve Quantities [Line Items]
Revisions of previous estimates			12
Downward revisions as result of well performance, lease expirations and interest changes
Reserve Quantities [Line Items]
Revisions of previous estimates			(39)
Downward revisions due to well performance issues, interest changes and economic limits
Reserve Quantities [Line Items]
Revisions of previous estimates	(72)
Downward revisions due to lower condensate yield in Granite Wash
Reserve Quantities [Line Items]
Revisions of previous estimates	(10)
Downward revisions due to elimination of proved undeveloped locations
Reserve Quantities [Line Items]
Revisions of previous estimates	(9)
Downward revisions due to lower natural gas prices
Reserve Quantities [Line Items]
Revisions of previous estimates	(5)
Upward revisions due to higher gas processing yields
Reserve Quantities [Line Items]
Revisions of previous estimates	3
Increase due to drilling of additional wells and added proved undeveloped locations
Reserve Quantities [Line Items]
Extensions, discoveries and other additions	54
Increase due to drilling of additional wells and added proved undeveloped locations
Reserve Quantities [Line Items]
Extensions, discoveries and other additions	65
Marcellus Shale and Selma Chalk
Reserve Quantities [Line Items]
Added Proved undeveloped locations	25
Other proved undeveloped locations
Reserve Quantities [Line Items]
Added Proved undeveloped locations	26
Marcellus Shale
Reserve Quantities [Line Items]
Added drilling wells	3
Granite Wash
Reserve Quantities [Line Items]
Added drilling wells	2
Eagle Ford Shale
Reserve Quantities [Line Items]
Added drilling wells	28

[1] We had downward revisions of 93.6 Bcfe primarily as a result of the following: 1) downward revisions of 72 Bcfe due to well performance issues, interest changes and economic limits attributable to operating conditions particularly in the Granite Wash, Cotton Valley and Selma Chalk, 2) downward revisions of 10 Bcfe due to lower condensate yield in the Granite Wash, 3) downward revisions of 9 Bcfe attributable to the elimination of proved undeveloped locations particularly in the Haynesville Shale in East Texas, 4) downward revisions of 5 Bcfe due to lower natural gas prices and 5) upward revisions of 3 Bcfe due to higher gas processing yields in the Haynesville Shale and Granite Wash.

[2] We had downward revisions of 40.2 Bcfe primarily as a result of the following: 1) downward revisions of 45 Bcfe due to the removal of 200 proved undeveloped locations that would not be developed within five years, 2) upward revisions of 34 Bcfe as a result of processing the gas in the Mid-Continent Granite Wash for NGLs, 3) upward revisions of 12 Bcfe due to higher prices and 4) various downward revisions for 39 Bcfe across our assets as a result of well performance, lease expirations and interest changes.

[3] We had downward revisions of 161 Bcfe which were primarily the result of the following: 1) downward revisions of 63.1 Bcfe due to price, 2) a downward revision of 27.1 Bcfe in Appalachia for the removal of proved undeveloped reserves, which resulted from wells that no longer met the reasonable certainty threshold, 3) downward revisions of 20.1 Bcfe for NGLs that we received in East Texas as a result of lower plant yields and 4) various downward revisions amounting to 50.7 Bcfe across our assets as a result of well performance and the application of the revised oil and gas reserve calculation methodology required by the SEC in 2009.

[4] We added 118.7 Bcfe due primarily to an increase of 54 Bcfe due to the drilling of three Marcellus Shale wells and two Granite Wash wells as well as the addition of 25 proved undeveloped locations in the Marcellus Shale and Selma Chalk. We also drilled 28 Eagle Ford Shale wells and added 26 proved undeveloped locations which resulted in an increase of 65 Bcfe.

[5] We added 114.9 Bcfe due to the drilling of 16 wells on locations not classified as proved undeveloped locations in our 2009 year-end reserve report and the addition of 51 new proved undeveloped locations, primarily in East Texas, as a result of our 2010 drilling activities.

[6] We added 235.7 Bcfe due to the drilling of 13 wells on locations that were not classified as proved undeveloped locations in our 2008 year-end reserve report and the addition of 105 new proved undeveloped locations, primarily in the Gulf Coast and Mid-Continent regions, as a result of our 2009 drilling activities.