Supplemental Oil and Natural Gas Reserve Data (unaudited) (Proved Undeveloped Reserves Narrative) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 MBoe	Dec. 31, 2013 MBoe	Dec. 31, 2012 MBoe	Dec. 31, 2011 MBoe
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserve, Net (Energy)	32,824	14,857	14,072
Proved Developed and Proved Undeveloped Reserves, Net				15,928
Proved Developed and Proved Undeveloped Reserves, Percentage Change Between Periods	121.00%	6.00%	(12.00%)
Proved Undeveloped Reserves, Percentage Change Between Periods	98.00%	1.00%	(18.00%)
Proved Undeveloped Reserves	14,623	7,387	7,337	8,925
Proved Undeveloped Reserves Extensions Discoveries And Additions	10,125	5,168	2,344
Proved Undeveloped Reserves Reclassification to Proved Developed Production	(1,757)		557
Proved Undeveloped Reserves Conversion to Proved Developed Reserves, Percentage Transferred	24.00%	51.00%	6.00%
Proved Undeveloped Reserves Conversion to Proved Developed Reserves Total Cost	$ 34,619		$ 19,000
Reclassification of Proved Undeveloped Production Reserves to Horizontal Probable	1,132	3,724
Proved Undeveloped Reserves Sales Of Minerals In Place		1,297	1,148
Proved Undeveloped Reserves Sales Of Minerals In Place, Percentage		18.00%
Proved Undeveloped Reserve Reductions No Longer Deemed To Be Economic			2,227
Permian Basin [Member]
Reserve Quantities [Line Items]
Number of wells drilled during the period	34		27
Number of wells drilled during the period, net	28.7