Net Quantities of Proved Reserves, Including Changes therein and Proved Developed and Proved Undeveloped Reserves (Detail)	12 Months Ended
	Dec. 31, 2012 MBoe		Dec. 31, 2011 MBoe		Dec. 31, 2010 MBoe
Proved Developed and Undeveloped Reserves (BOE) [Roll Forward]
Beginning Balance	147,223,000		156,959,000		155,831,000
Revisions of previous estimates	(28,662,000)	[1]	(15,608,000)	[2]	(6,702,000)	[3]
Extensions, discoveries and other additions	18,255,000	[4]	19,792,000	[5]	19,142,000	[6]
Production	(6,513,000)		(7,758,000)		(7,867,000)
Purchase of reserves	41,000		20,000		557,000
Sale of reserves in place	(16,882,000)		(6,182,000)		(4,002,000)
Ending Balance	113,462,000		147,223,000		156,959,000
Proved Developed Reserves:	46,980,000		71,562,000		83,587,000
Proved Undeveloped Reserves:	66,482,000		75,661,000		73,372,000
Oil
Proved Developed and Undeveloped Reserves
Beginning Balance	14,079,000		8,082,000		11,517,000
Revisions of previous estimates	(439,000)	[1]	(2,367,000)	[2]	(2,410,000)	[3]
Extensions, discoveries and other additions	13,444,000	[4]	9,669,000	[5]	513,000	[6]
Production	(2,252,000)		(1,283,000)		(710,000)
Purchase of reserves	39,000		20,000		9,000
Sale of reserves in place	(20,000)		(42,000)		(837,000)
Ending Balance	24,851,000		14,079,000		8,082,000
Proved Developed Reserves:	10,472,000		7,075,000		4,035,000
Proved Undeveloped Reserves:	14,379,000		7,004,000		4,047,000
NGLs
Proved Developed and Undeveloped Reserves
Beginning Balance	21,491,000		24,713,000		14,870,000
Revisions of previous estimates	(2,495,000)		(3,047,000)		7,611,000
Extensions, discoveries and other additions	2,578,000		732,000		3,556,000
Production	884,000		907,000		671,000
Purchase of reserves	1,000		0		0
Sale of reserves in place	0		0		653,000
Ending Balance	20,691,000		21,491,000		24,713,000
Proved Developed Reserves:	8,266,000		9,395,000		10,778,000
Proved Undeveloped Reserves:	12,425,000		12,096,000		13,935,000
Natural Gas
Proved Developed and Undeveloped Reserves
Beginning Balance	669,913		744,982		776,665
Revisions of previous estimates	(154,372)	[1]	(61,165)	[2]	(71,421)	[3]
Extensions, discoveries and other additions	13,405	[4]	56,345	[5]	90,439	[6]
Production	(20,261)		(33,410)		(38,919)
Purchase of reserves	6		1		3,288
Sale of reserves in place	(101,172)		(36,840)		(15,070)
Ending Balance	407,519		669,913		744,982
Proved Developed Reserves:	169,449		330,552		412,644
Proved Undeveloped Reserves:	238,070		339,361		332,338

[1] We had downward revisions of 28.7 MMBOE primarily as a result of the following: 1) downward revisions of 5.0 MMBOE due to well performance issues, interest changes and economic limits due to operating conditions, including lease operating expense and basis differentials, primarily in the Selma Chalk, the Granite Wash, the Cotton Valley, and the Haynesville and Marcellus Shales

[2] We had downward revisions of 15.6 MMBOE primarily as a result of the following: 1) downward revisions of 12.0 MMBOE 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 1.7 MMBOE due to lower condensate yield in the Granite Wash, 3) downward revisions of 1.5 MMBOE attributable to the elimination of proved undeveloped locations particularly in the Haynesville Shale in East Texas, 4) downward revisions of 0.8 MMBOE due to lower natural gas prices and 5) upward revisions of 0.5 MMBOE due to higher gas processing yields in the Haynesville Shale and Granite Wash .

[3] We had downward revisions of 6.7 MMBOE primarily as a result of the following: 1) downward revisions of 7.5 MMBOE due to the removal of 200 proved undeveloped locations that would not be developed within five years, 2) upward revisions of 5.7 MMBOE as a result of processing the gas in the Mid-Continent Granite Wash for NGLs, 3) upward revisions of 2.0 MMBOE due to higher prices and 4) various downward revisions for 6.5 MMBOE across our assets as a result of well performance, lease expirations and interest changes.

[4] We added 18.3 MMBOE due primarily to the drilling of 18 wells and the addition of 48 proved undeveloped locations in the Eagle Ford Shale.

[5] We added 19.8 MMBOE due primarily to an increase of 9.0 MMBOE 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 10.8 MMBOE .

[6] We added 19.1 MMBOE due to the drilling of 16 wells on locations not classified as proved undeveloped locations in our 2010 year-end reserve report and the addition of 51 new proved undeveloped locations, primarily in East Texas, as a result of our 2011 drilling activities .