Oil and Gas Operations (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2012

Oil and Gas Exploration and Production Industries Disclosures [Abstract]

Schedule of capitalized costs

The following table sets forth capitalized costs:

(in thousands)	December 31, 2012		December 31, 2011
Proved	$	6,241,148	$	4,927,576
Unproved	197,979		238,792
Total capitalized costs	6,439,127		5,166,368
Accumulated depreciation, depletion and amortization	1,765,241		1,382,526
Capitalized costs, net	$	4,673,886	$	3,783,842

Schedule of cost incurred in property acquisition, exploration and development activities

The following table sets forth costs incurred in property acquisition, exploration and development activities and includes both capitalized costs and costs charged to expense during the year:

Years ended December 31, (in thousands)	2012		2011		2010
Property acquisition:
Proved	$	79,862	$	214,993	$	207,161
Unproved	58,634		91,888		201,881
Exploration	419,284		190,854		37,371
Development	749,256		623,775		332,541
Total costs incurred	$	1,307,036	$	1,121,510	$	778,954

Schedule of results of operations from producing activities

The following table sets forth results of the Company's oil and gas operations from producing activities:

Years ended December 31, (in thousands)	2012		2011		2010
Gross revenues*	$	1,167,183	$	944,908	$	957,371
Production (lifting costs)	306,375		257,045		224,901
Exploration expense	19,363		13,110		64,584
Depreciation, depletion and amortization	394,668		240,232		200,179
Accretion expense	7,534		6,837		6,178
Income tax expense	157,670		154,180		166,750
Results of operations from producing activities	$	281,573	$	273,504	$	294,779

*The years ended December 31, 2012, 2011 and 2010 gross revenues includes a pre-tax non cash mark-to-market gain on derivatives of $58.8 million, a pre-tax non-cash mark-to-market loss on derivatives of $37.6 million and a pre-tax non-cash mark-to-market loss on derivatives of $3,000, respectively.

Schedule of proved developed and undeveloped oil and gas reserves

The independent reservoir engineers have issued reports covering approximately 99 percent of the Company's ending proved reserves indicating that in their judgment the estimates are reasonable in the aggregate.

Year ended December 31, 2012	Gas MMcf		Oil MBbl		NGL MBbl		Total MMBOE
Proved reserves at beginning of period	957,368		129,578		53,957		343.1
Revisions of previous estimates	(143,704	)	(8,546	)	(9,557	)	(42.1	)
Purchases	10,656		7,950		2,569		12.4
Extensions and discoveries	61,170		35,132		11,759		57.1
Production	(76,362	)	(8,766	)	(2,573	)	(24.1	)
Proved reserves at end of period	809,128		155,348		56,155		346.4
Proved developed reserves at end of period	708,657		105,976		36,440		260.5
Proved undeveloped reserves at end of period	100,471		49,372		19,715		85.9

Year ended December 31, 2011	Gas MMcf		Oil MBbl		NGL MBbl		Total MMBOE
Proved reserves at beginning of period	954,387		103,262		40,601		302.9
Revisions of previous estimates	(12,823	)	(4,513	)	841		(5.8	)
Purchases	19,362		12,583		5,055		20.8
Extensions and discoveries	68,160		24,564		9,637		45.6
Production	(71,718	)	(6,318	)	(2,177	)	(20.4	)
Proved reserves at end of period	957,368		129,578		53,957		343.1
Proved developed reserves at end of period	788,812		83,899		33,154		248.5
Proved undeveloped reserves at end of period	168,556		45,679		20,803		94.6

Year ended December 31, 2010	Gas MMcf		Oil MBbl		NGL MBbl		Total MMBOE
Proved reserves at beginning of period	897,546		77,963		30,257		257.8
Revisions of previous estimates	66,679		(2,243	)	2,434		11.3
Purchases	21,700		16,443		5,730		25.8
Extensions and discoveries	39,570		16,234		4,058		26.8
Production	(70,924	)	(5,131	)	(1,880	)	(18.8	)
Sales	(184	)	(4	)	2		—
Proved reserves at end of period	954,387		103,262		40,601		302.9
Proved developed reserves at end of period	786,292		72,030		28,809		231.9
Proved undeveloped reserves at end of period	168,095		31,232		11,792		71.0

Schedule of standardized measure of discounted future net cash flows relating to proved oil and gas reserves

Years ended December 31, (in thousands)	2012		2011		2010
Future gross revenues	$	17,735,363	$	18,196,229	$	13,210,211
Future production costs	5,715,248		5,823,395		4,959,403
Future development costs	1,892,600		1,539,072		1,026,903
Future income tax expense	2,809,411		3,326,382		2,201,742
Future net cash flows	7,318,104		7,507,380		5,022,163
Discount at 10% per annum	3,618,785		3,878,217		2,555,027
Standardized measure of discounted future net cash flows relating to proved oil and gas reserves	$	3,699,319	$	3,629,163	$	2,467,136
Discounted future net cash flows before income taxes	$	4,411,399	$	4,691,086	$	3,155,746

Schedule of principal sources of changes in standardized measure of discounted future net cash flows

The following are the principal sources of changes in the standardized measure of discounted future net cash flows:

Years ended December 31, (in thousands)	2012			2011			2010
Balance at beginning of year	$	3,629,163		$	2,467,136		$	1,563,190
Revisions to reserves proved in prior years:
Net changes in prices, production costs and future development costs	(922,792		)	707,411			945,179
Net changes due to revisions in quantity estimates	(383,755		)	(80,004		)	36,349
Development costs incurred, previously estimated	472,603			392,720			195,269
Accretion of discount	362,916			246,714			156,319
Changes in timing and other	(317,244		)	(25,937		)	15,815
Total revisions	(788,272		)	1,240,904			1,348,931
New field discoveries and extensions, net of future production and development costs	1,025,419			755,977			319,223
Sales of oil and gas produced, net of production costs	(812,781		)	(763,171		)	(576,755		)
Purchases	189,755			232,768			278,384
Sales	—			—			87
Net change in income taxes	456,035			(304,451		)	(465,924		)
Net change in standardized measure of discounted future net cash flows	70,156			1,162,027			903,946
Balance at end of year	$	3,699,319		$	3,629,163		$	2,467,136