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

12 Months Ended

Dec. 31, 2012

Oil and Gas Exploration and Production Industries Disclosures [Abstract]

Schedule of Proved Developed and Undeveloped Oil and Gas Reserve Quantities

	2012						2011						2010
	Oil MBOE		Natural Gas MMcf		MBOE		Oil MBOE		Natural Gas MMcf		MBOE		Oil MBOE		Natural Gas MMcf		MBOE
Total proved reserves:
Beginning of year	185,880		534,279		274,926		166,181		630,192		271,213		129,940		632,178		235,303
Revision of previous estimates	12,145		(205,845	)	(22,162	)	(4,054	)	(146,349	)	(28,446	)	4,288		(46,860	)	(3,522	)
Improved recovery	—		—		—		—		—		—		1,700		—		1,700
Extensions and  discoveries	8,459		100,129		25,148		19,601		65,992		30,600		12,774		43,469		20,019
Property sales	(556	)	—		(556	)	—		—		—		—		—		—
Production	(10,024	)	(19,784	)	(13,321	)	(9,041	)	(23,907	)	(13,025	)	(7,925	)	(23,989	)	(11,923	)
Purchase of reserves in place	8,304		16,740		11,094		13,193		8,351		14,584		25,404		25,394		29,636
End of year	204,208		425,519		275,129		185,880		534,279		274,926		166,181		630,192		271,213
Proved developed reserves	118,937		187,668		150,216		107,849		221,606		144,783		88,917		268,566		133,678
Proved undeveloped reserves	85,271		237,851		124,913		78,031		312,673		130,143		77,264		361,626		137,535
Total proved reserves	204,208		425,519		275,129		185,880		534,279		274,926		166,181		630,192		271,213

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

	Year Ended December 31,
(in thousands)	2012			2011			2010
Future cash inflows	$	19,738,729		$	19,568,628		$	14,354,627
Future production costs	(5,884,891		)	(5,226,044		)	(4,446,183		)
Future development costs	(2,164,780		)	(1,975,429		)	(1,789,001		)
Future income tax expense	(3,344,024		)	(3,770,512		)	(2,272,184		)
Future net cash flows	8,345,034			8,596,643			5,847,259
10% annual discount for estimated timing of cash flows	(4,511,619		)	(4,561,364		)	(3,048,103		)
Standardized measure of discounted future net cash flows	$	3,833,415		$	4,035,279		$	2,799,156
Average price during the 12-month period:(1)
Oil ($/BOE)	$	90.66		$	93.72		$	69.04
Natural gas ($/Mcf)	2.88			4.02			4.57
BOE ($/BOE)	$	71.74		$	71.18		$	52.93

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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,
(in thousands)	2012			2011			2010
Standardized measure—beginning of year	$	4,035,279		$	2,799,156		$	1,445,747
Sales of oil and natural gas produced, net of production costs	(625,707		)	(599,679		)	(406,390		)
Revisions to estimates of proved reserves:
Net changes in sales prices and production costs	(786,022		)	1,473,454			1,724,212
Revisions of previous quantity estimates	743			(281,765		)	(49,784		)
Improved recovery	—			—			24,033
Extensions and discoveries	124,466			601,313			283,011
Change in estimated future development costs	(331,498		)	(274,122		)	(152,096		)
Purchases of reserves in place	114,094			164,383			307,205
Sales of reserves in place	(15,283		)	—			—
Development costs incurred during the period	497,036			433,660			144,086
Accretion of discount	570,505			383,418			184,917
Income taxes	323,128			(634,747		)	(593,272		)
Other	(73,326		)	(29,792		)	(112,513		)
Net (decrease) increase	(201,864		)	1,236,123			1,353,409
Standardized measure—end of year	$	3,833,415		$	4,035,279		$	2,799,156

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

	Year ended December 31,
(in thousands)	2012		2011		2010
Property acquisitions
Proved properties	$	70,700	$	149,158	$	334,409
Unproved properties	10,686		6,632		—
Development	714,343		544,114		320,927
Exploration	16,405		627		2,310
Total(1)	$	812,134	$	700,531	$	657,646

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(1)The total above does not reflect $17.9 million, $29.1 million and $28.3 million of capitalized interest incurred in 2012, 2011 and 2010, respectively.