Disclosures about Oil and Natural Gas Activities (Unaudited)--Summary of Changes in Quantities of Proved Reserves (Details)	12 Months Ended
	Dec. 31, 2013 MBoe		Dec. 31, 2012 MBoe	Dec. 31, 2011 MBoe	Dec. 31, 2010 MBoe
Reserve Quantities [Line Items]
Balance at beginning of period (MBoe)	146,095		156,260	149,282
Purchase of minerals in place (MBoe)	4,945		9	378
Sales of minerals in place (MBoe)	(7,116)		(3,795)	(3,544)
Extensions and discoveries (MBoe)	25,085		13,326	13,178
Revisions (MBoe)	(4,671)		(11,429)	4,564
Improved recoveries (MBoe)	3,879		842	1,057
Production (MBoe)	(9,742)		(9,118)	(8,655)
Balance at end of period (MBoe)	158,475		146,095	156,260
Proved developed reserves (MBoe)	100,664		94,927	100,118	98,566
Proved undeveloped reserves (MBoe)	57,811		51,169	56,142	50,716
Oil (including natural gas liquids)
Reserve Quantities [Line Items]
Balance at beginning of period			100,380	93,412
Purchase of minerals in place			0	241
Sales of minerals in place			(2,694)	(2,355)
Extensions and discoveries			7,117	6,362
Revisions			(3,410)	(6,711)
Improved recoveries			842	1,057
Production			(5,812)	(5,048)
Balance at end of the period			103,243	100,380
Proved developed reserves			62,450	55,607
Proved undeveloped reserves			39,287	37,930	37,805
Natural Gas
Reserve Quantities [Line Items]
Balance at beginning of period	257,115		335,280	335,220
Purchase of minerals in place	3,618		57	822
Sales of minerals in place	(9,708)		(6,608)	(7,134)
Extensions and discoveries	62,412		37,256	40,896
Revisions	(9,735)	[1]	89,036	12,882
Improved recoveries	0		0	0
Production	(20,250)		(19,834)	(21,642)
Balance at end of the period	302,922		257,115	335,280
Proved developed reserves	185,826		226,008	257,754
Proved undeveloped reserves	106,002		71,289	109,272	77,466
Oil
Reserve Quantities [Line Items]
Balance at beginning of period	92,047
Purchase of minerals in place	3,283
Sales of minerals in place	(5,174)
Extensions and discoveries	11,556
Revisions	7,772	[1]
Improved recoveries	3,879
Production	(5,006)
Balance at end of the period	92,813
Proved undeveloped reserves	36,453
Natural Gas Liquids
Reserve Quantities [Line Items]
Balance at beginning of period	11,195	[2]
Purchase of minerals in place	1,059	[2]
Sales of minerals in place	(324)	[2]
Extensions and discoveries	3,127	[2]
Revisions	(1,479)	[1],[2]
Improved recoveries	0	[2]
Production	(1,361)	[2]
Balance at end of the period	15,175	[2]
Proved undeveloped reserves	3,691	[2]

[1] Includes natural gas liquids.

[2] The downward revision in our oil reserves during 2013 was primarily due to removing proved undeveloped reserves that are not expected to be developed within the five-year time frame mandated by the SEC and to negative technical revisions. These downward revisions were partially offset by positive revisions due to improved pricing of oil and natural gas.