OIL AND GAS RESERVE INFORMATION - UNAUDITED (Tables)

12 Months Ended

Dec. 31, 2013

Extractive Industries [Abstract]

Summary of Estimated Proved Oil and Natural Gas Reserve

Reserve volumes for the year ended December 31, 2010 have not been reclassified to conform to the current presentation given the immateriality of NGL volumes in such period.

	Oil (MBbls)			NGLs (MBbls)			Natural Gas (MMcf)			Oil, Natural Gas and NGLs (MMcfe)
Estimated proved reserves as of December 31, 2010		33,203			—			274,705			473,923
Revisions of previous estimates		2,889			4,911			(26,725	)		20,075
Extensions, discoveries and other additions		3,544			—			93,520			114,784
Purchase of producing properties		14,396			—			24,595			110,971
Sale of reserves		(1,950	)		—			(2,150	)		(13,850	)
Production		(6,427	)		(506	)		(38,466	)		(80,064	)
Estimated proved reserves as of December 31, 2011		45,655			4,405			325,479			625,839
Revisions of previous estimates		(1,559	)		9,349			(26,694	)		20,050
Extensions, discoveries and other additions		3,681			4,856			131,408			182,633
Purchase of producing properties		4,336			619			8,168			37,895
Sale of reserves		(60	)		—			(418	)		(775	)
Production		(7,135	)		(1,163	)		(42,569	)		(92,357	)
Estimated proved reserves as of December 31, 2012		44,918			18,066			395,374			773,285
Revisions of previous estimates		3,606			2,439			36,006			72,275
Extensions, discoveries and other additions		2,367			4,395			79,729			120,299
Sale of reserves		(170	)		—			(214	)		(1,235	)
Production		(6,894	)		(1,603	)		(50,129	)		(101,111	)
Estimated proved reserves as of December 31, 2013		43,827			23,297			460,766			863,513
Estimated proved developed reserves:
as of December 31, 2011		30,914			3,195			171,871			376,528
as of December 31, 2012		29,005			8,593			210,956			436,540
as of December 31, 2013		27,920			11,569			246,946			483,885

Summary of Standardized Measure of Discounted Future Net Cash Flows

	Standardized Measure Year Ended December 31,
	2013			2012			2011
Future cash inflows	$	7,040,928		$	6,295,455		$	6,171,279
Future production costs		(2,062,657	)		(1,946,426	)		(1,747,806	)
Future development costs		(1,431,101	)		(1,241,531	)		(1,219,214	)
Future income taxes		(884,637	)		(799,007	)		(852,364	)
Future net cash flows		2,662,533			2,308,491			2,351,895
10% annual discount		(977,531	)		(794,632	)		(808,933	)
Standardized measure of discounted future net cash flows	$	1,685,002		$	1,513,859		$	1,542,962
	Changes in Standardized Measure Year Ended December 31,
	2013			2012			2011
Standardized measure at beginning of year	$	1,513,859		$	1,542,962		$	957,629
Sales and transfers of oil, gas and NGLs produced, net of production costs		(708,017	)		(697,741	)		(670,347	)
Changes in price, net of future production costs		229,425			(380,841	)		502,324
Extensions and discoveries, net of future production and development costs		155,592			178,272			293,168
Changes in estimated future development costs, net of development costs incurred during the period		28,684			212,329			97,852
Revisions of quantity estimates		281,558			76,450			(27,854	)
Accretion of discount		202,087			207,292			118,722
Net change in income taxes		(28,084	)		22,947			(300,363	)
Purchases of reserves in-place		—			276,389			567,286
Sales of reserves in-place		15,531			2,480			(36,278	)
Changes in production rates due to timing and other		(5,633	)		73,320			40,823
Net increase (decrease) in standardized measure		171,143			(29,103	)		585,333
Standardized measure at end of year	$	1,685,002		$	1,513,859		$	1,542,962