Supplemental Oil and Natural Gas Disclosures (Unaudited) (Details 2)	12 Months Ended
	Dec. 31, 2011 MBbls	Dec. 31, 2010 MBbls	Dec. 31, 2009 MBbls
Estimated Quantities of Reserves
Improved recovery		39.4
Oil Reserves [Member]
Estimated Quantities of Reserves
Balance at beginning of year	338,276	192,879	179,126
Revisions of previous estimates	(4,478)	3,538	(69)
Revisions due to price changes	2,558	2,780	4,557
Extensions and discoveries	42,936	26,313	334
Improved recovery	264	30,173	13,875
Production	(22,169)	(21,870)	(13,495)
Acquisition of minerals in place	346	155,021	28,379
Sales of minerals in place	0	(50,558)	(19,828)
Balance at end of year	357,733	338,276	192,879
Proved Developed Reserves:
Balance at beginning of year	219,077	116,192	96,746
Balance at end of year	239,741	219,077	116,192
Gas Reserves [Member]
Estimated Quantities of Reserves
Balance at beginning of year	357,893	87,975	427,955
Revisions of previous estimates	(14,058)	16,171	(1,298)
Revisions due to price changes	485	811	(2,079)
Extensions and discoveries	52,339	130,245	11,785
Improved recovery	0	0	0
Production	(10,783)	(28,491)	(24,764)
Acquisition of minerals in place	239,332	622,984	2,317
Sales of minerals in place	0	(471,802)	(325,941)
Balance at end of year	625,208	357,893	87,975
Proved Developed Reserves:
Balance at beginning of year	110,516	69,513	298,114
Balance at end of year	125,970	110,516	69,513
Total Reserves [Member]
Estimated Quantities of Reserves
Balance at beginning of year	397,925	207,542	250,452
Revisions of previous estimates	(6,821)	6,233	(285)
Revisions due to price changes	2,639	2,915	4,211
Extensions and discoveries	51,658	48,021	2,298
Improved recovery	264	30,173	13,875
Production	(23,966)	(26,619)	(17,622)
Acquisition of minerals in place	40,235	258,852	28,765
Sales of minerals in place	0	(129,192)	(74,152)
Balance at end of year	461,934	397,925	207,542
Proved Developed Reserves:
Balance at beginning of year (BOE)	237,496	127,778	146,432
Balance at end of year (BOE)	260,736	237,496	127,778