Oil and Gas Reserve Information Unaudited (Tables)

12 Months Ended

Dec. 31, 2011

Oil and Gas Reserve Information - Unaudited [Abstract]

Estimated quantities of net proved and proved developed oil and natural gas reserves

	Oil (MBbls)			Natural Gas (MMcf)			Oil and Natural Gas (MMcfe)
Estimated proved reserves as of December 31, 2008		36,564			299,554			518,935
Revisions of previous estimates		1,964			(53,423	)		(41,636	)
Extensions, discoveries and other additions		417			12,198			14,703
Sale of reserves		(402	)		(300	)		(2,714	)
Production		(6,207	)		(41,335	)		(78,577	)
Estimated proved reserves as of December 31, 2009		32,336			216,694			410,711
Revisions of previous estimates		3,299			13,439			33,231
Extensions, discoveries and other additions		2,668			82,846			98,854
Purchase of producing properties		637			3,816			7,637
Sale of reserves		(23	)		(153	)		(289	)
Production		(5,714	)		(41,937	)		(76,221	)
Estimated proved reserves as of December 31, 2010		33,203			274,705			473,923
Revisions of previous estimates		2,988			(23,801	)		(5,869	)
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	)		(39,517	)		(78,079	)
Estimated proved reserves as of December 31, 2011		45,754			327,352			601,880
Estimated proved developed reserves:
as of December 31, 2009		24,380			172,452			318,729
as of December 31, 2010		25,000			174,876			324,876
as of December 31, 2011		31,026			174,067			360,224

Standardized measure of future net cash flows related to estimated proved oil and gas reserves

	Standardized Measure Year Ended December 31,
	2011			2010			2009
Future cash inflows	$	6,171,279		$	3,803,004		$	2,663,285
Future production costs		(1,747,806	)		(1,191,718	)		(950,434	)
Future development costs		(1,219,214	)		(907,956	)		(912,500	)
Future income taxes		(852,364	)		(330,651	)		(38,845	)
Future net cash flows		2,351,895			1,372,679			761,506
10% annual discount		(808,933	)		(415,050	)		(146,519	)
Standardized measure of discounted future net cash flows	$	1,542,962		$	957,629		$	614,987

	Changes in Standardized Measure Year Ended December 31,
	2011			2010			2009
Standardized measure at beginning of year	$	957,629		$	614,987		$	793,104
Sales and transfers of oil and gas produced, net of production costs		(670,347	)		(487,418	)		(546,737	)
Changes in price, net of future production costs		502,324			485,272			284,504
Extensions and discoveries, net of future production and development costs		293,168			270,629			21,249
Changes in estimated future development costs, net of development costs incurred during the period		97,852			119,986			183,058
Revisions of quantity estimates		(27,854	)		147,509			(150,609	)
Accretion of discount		118,722			64,836			79,904
Net change in income taxes		(300,363	)		(196,219	)		(27,436	)
Purchases of reserves in-place		567,286			21,264			—
Sales of reserves in-place		(36,278	)		1,424			3,152
Changes in production rates due to timing and other		40,823			(84,641	)		(25,202	)
Net increase (decrease) in standardized measure		585,333			342,642			(178,117	)
Standardized measure at end of year	$	1,542,962		$	957,629		$	614,987