Net Quantities of Proved Reserves, Including Changes therein and Proved Developed and Proved Undeveloped Reserves (Detail)	12 Months Ended
	Dec. 31, 2011 MMcfe		Dec. 31, 2010 MMcfe		Dec. 31, 2009 MMcfe
Proved Developed and Undeveloped Reserves
Beginning Balance	941,755		934,987		915,975
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]
Production	(46,553)		(47,201)		(51,000)
Purchase of reserves	124		3,342
Sale of reserves in place	(37,092)		(24,014)		(4,659)
Ending Balance	883,331		941,755		934,987
Proved Developed Reserves	429,370		501,521		438,524
Proved Undeveloped Reserves	453,961		440,234		496,463
Natural Gas
Proved Developed and Undeveloped Reserves
Beginning Balance	744,982		776,665		754,132
Revisions of previous estimates	(61,165)	[1]	(71,421)	[2]	(110,349)	[3]
Extensions, discoveries and other additions	56,345	[4]	90,439	[5]	180,448	[6]
Production	(33,410)		(38,919)		(43,337)
Purchase of reserves	1		3,288
Sale of reserves in place	(36,840)		(15,070)		(4,229)
Ending Balance	669,913		744,982		776,665
Proved Developed Reserves	330,552		412,644		388,382
Proved Undeveloped Reserves	339,361		332,338		388,283
Oil and Condensate
Proved Developed and Undeveloped Reserves
Beginning Balance	32,797		26,387		26,974
Revisions of previous estimates	(5,414)	[1]	5,202	[2]	(8,442)	[3]
Extensions, discoveries and other additions	10,399	[4]	4,069	[5]	9,203	[6]
Production	(2,190)		(1,380)		(1,277)
Purchase of reserves	20		9
Sale of reserves in place	(42)		(1,490)		(71)
Ending Balance	35,570		32,797		26,387
Proved Developed Reserves	16,470		14,813		8,357
Proved Undeveloped Reserves	19,100		17,984		18,030

[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.