Supplemental Oil and Natural Gas Disclosures (Unaudited) (Estimated Quantities of Proved Reserves) (Details 2)	12 Months Ended
	Dec. 31, 2012 bbl	Dec. 31, 2011 bbl	Dec. 31, 2010 bbl
Estimated Quantities of Reserves
Extensions and discoveries	114.2
Improved recovery			39.4
Sales of minerals in place	123.9
Oil Reserves (MBbl) [Member]
Estimated Quantities of Reserves
Balance at beginning of year	357,733	338,276	192,879
Revisions of previous estimates	(7,099)	(4,478)	3,538
Revisions due to price changes	(401)	2,558	2,780
Extensions and discoveries	14,910	42,936	26,313
Improved recovery	69,543	264	30,173
Production	(24,462)	(22,169)	(21,870)
Acquisition of minerals in place	24,677	346	155,021
Sales of minerals in place	(105,777)	0	(50,558)
Balance at end of year	329,124	357,733	338,276
Proved Developed Reserves:
Balance at beginning of year	239,741	219,077	116,192
Balance at end of year	236,009	239,741	219,077
Gas Reserves (Mmcf) [Member]
Estimated Quantities of Reserves
Balance at beginning of year	625,208	357,893	87,975
Revisions of previous estimates	(16,720)	(14,058)	16,171
Revisions due to price changes	(37,969)	485	811
Extensions and discoveries	10,005	52,339	130,245
Improved recovery	0	0	0
Production	(10,654)	(10,783)	(28,491)
Acquisition of minerals in place	20,598	239,332	622,984
Sales of minerals in place	(108,827)	0	(471,802)
Balance at end of year	481,641	625,208	357,893
Proved Developed Reserves:
Balance at beginning of year	125,970	110,516	69,513
Balance at end of year	64,191	125,970	110,516
Total Reserves (MBOE) [Member]
Estimated Quantities of Reserves
Balance at beginning of year	461,934	397,925	207,542
Revisions of previous estimates	(9,886)	(6,821)	6,233
Revisions due to price changes	(6,729)	2,639	2,915
Extensions and discoveries	16,579	51,658	48,021
Improved recovery	69,543	264	30,173
Production	(26,238)	(23,966)	(26,619)
Acquisition of minerals in place	28,110	40,235	258,852
Sales of minerals in place	(123,915)	0	(129,192)
Balance at end of year	409,398	461,934	397,925
Proved Developed Reserves:
Balance at beginning of year (mBOE)	260,736	237,496	127,778
Balance at end of year (mBOE)	246,708	260,736	237,496