Supplemental Information about Oil & Gas Producing Activities (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2011

Oil and Gas Exploration and Production Industries Disclosures [Abstract]

Schedule of Proved Developed and Undeveloped Oil and Gas Reserve Quantities

	2011						2010						2009
	Oil MBOE		Natural Gas MMcf		MBOE		Oil MBOE		Natural Gas MMcf		MBOE		Oil MBOE		Natural Gas MMcf		MBOE
Proved developed  and undeveloped reserves:
Beginning of year	166,181		630,192		271,213		129,940		632,178		235,303		125,251		724,135		245,940
Revision of previous estimates	(4,054	)	(146,349	)	(28,446	)	4,288		(46,860	)	(3,522	)	2,786		(34,564	)	(2,975	)
Improved recovery	—		—		—		1,700		—		1,700		—		—		—
Extensions and  discoveries	19,601		65,992		30,600		12,774		43,469		20,019		8,989		54,664		18,100
Property sales	—		—		—		—		—		—		—		(126,600	)	(21,100	)
Production	(9,041	)	(23,907	)	(13,025	)	(7,925	)	(23,989	)	(11,923	)	(7,186	)	(22,657	)	(10,962	)
Purchase of reserves in place	13,193		8,351		14,584		25,404		25,394		29,636		100		37,200		6,300
End of year	185,880		534,279		274,926		166,181		630,192		271,213		129,940		632,178		235,303
Proved developed  reserves:
Beginning of year	88,917		268,566		133,678		82,870		255,520		125,456		74,616		361,575		134,879
End of year	107,849		221,606		144,783		88,917		268,566		133,678		82,870		255,520		125,456

Schedule of Standardized Measure of Discounted Future Cash Flows Relating to Proved Reserves

	Year Ended December 31,
	2011			2010			2009
	(in thousands)
Future cash inflows	$	19,568,628		$	14,354,627		$	9,028,991
Future production costs	(5,226,044		)	(4,446,183		)	(3,826,832		)
Future development costs	(1,975,429		)	(1,789,001		)	(1,159,465		)
Future income tax expense	(3,770,512		)	(2,272,184		)	(969,771		)
Future net cash flows	8,596,643			5,847,259			3,072,923
10% annual discount for estimated timing of cash flows	(4,561,364		)	(3,048,103		)	(1,627,176		)
Standardized measure of discounted future net cash flows	$	4,035,279		$	2,799,156		$	1,445,747
Average price during the 12-month period: (1)
Oil ($/BOE)	$	93.72		$	69.04		$	52.06
Natural gas ($/Mcf)	4.02			4.57			3.58
BOE ($/BOE)	$	71.18		$	52.93		$	38.37

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(1) Differences between the average benchmark prices and the average prices used in the calculation of the standardized measure are attributable to adjustments made for transportation, quality and basis differentials.

Schedule of Changes in Standardized Measure of Discounted Future Net Cash Flows

	Year ended December 31,
	2011			2010			2009
	(in thousands)
Standardized measure—beginning of year	$	2,799,156		$	1,445,747		$	1,135,581
Sales of oil and natural gas produced, net of production costs	(599,679		)	(406,390		)	(353,052		)
Revisions to estimates of proved reserves:
Net changes in sales prices and production costs	1,473,454			1,724,212			637,882
Revisions of previous quantity estimates	(281,765		)	(49,784		)	(33,943		)
Improved recovery	—			24,033			—
Extensions and discoveries	601,313			283,011			206,542
Change in estimated future development costs	(274,122		)	(152,096		)	(52,824		)
Purchases of reserves in place	164,383			307,205			29,348
Sales of reserves in place	—			—			(138,265		)
Development costs incurred during the period	433,660			144,086			110,200
Accretion of discount	383,418			184,917			131,745
Income taxes	(634,747		)	(593,272		)	(190,727		)
Other	(29,792		)	(112,513		)	(36,740		)
Net increase	1,236,123			1,353,409			310,166
Standardized measure—end of year	$	4,035,279		$	2,799,156		$	1,445,747

Schedule of Cost Incurred in Oil and Gas Property Acquisition, Exploration, and Development Activities

The following table presents costs incurred in oil and natural gas property acquisition, exploration, and development activities:

	Year ended December 31,
	2011		2010		2009
	(in thousands)
Property acquisitions
Proved properties	$	149,158	$	334,409	$	13,497
Unproved properties	6,632		—		—
Development	544,114		320,927		138,168
Exploration	627		2,310		209
Total(1)	$	700,531	$	657,646	$	151,874

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(1)The total above does not reflect $29.1 million, $28.3 million, and $30.1 million of capitalized interest incurred in 2011, 2010, and 2009, respectively.