Disclosures about Oil and Natural Gas Activities (Unaudited)--Summary of Changes in Quantities of Proved Reserves (Details)	12 Months Ended
Dec. 31, 2014 MBoe	Dec. 31, 2013 MBoe	Dec. 31, 2012 MBoe	Jan. 01, 2012 MBoe
Reserve Quantities [Line Items]
Balance at beginning of period (MBoe)	158,475	146,095	156,000
Purchase of minerals in place (MBoe)	474	4,945	0
Sales of minerals in place (MBoe)	(23,761)	(7,116)	(4,000)
Extensions and discoveries (MBoe)	25,541	25,085	13,000
Revisions (MBoe)	(3,608)	(4,671)	(11,000)
Improved recoveries (MBoe)	13,254	3,879	1,000
Production (MBoe)	(10,982)	(9,742)	(9,000)
Balance at end of period (MBoe)	159,393	158,475	146,095
Proved developed reserves (MBoe)	93,027us-gaap_ProvedDevelopedReservesBOE1	100,664us-gaap_ProvedDevelopedReservesBOE1	95,000us-gaap_ProvedDevelopedReservesBOE1	100,000us-gaap_ProvedDevelopedReservesBOE1
Proved undeveloped reserves (MBoe)	66,366us-gaap_ProvedUndevelopedReserveBOE1	57,811us-gaap_ProvedUndevelopedReserveBOE1	51,000us-gaap_ProvedUndevelopedReserveBOE1	56,000us-gaap_ProvedUndevelopedReserveBOE1
Oil (including natural gas liquids) [Member]
Reserve Quantities [Line Items]
Balance at beginning of period			100,000
Purchase of minerals in place			0
Sales of minerals in place			(3,000)
Extensions and discoveries			7,000
Revisions			3,000
Improved recoveries			1,000
Production			(6,000)
Balance at end of the period			103,000
Proved developed reserves			64,000	62,000
Proved undeveloped reserves			39,000	38,000
Oil [Member]
Reserve Quantities [Line Items]
Balance at beginning of period	92,813	92,047
Purchase of minerals in place	276	3,283
Sales of minerals in place	(8,539)	(5,174)
Extensions and discoveries	12,776	11,556
Revisions	(3,356)	(7,772)
Improved recoveries	13,254	3,879
Production	(5,977)	(5,006)
Balance at end of the period	101,247	92,813
Proved developed reserves	54,862	56,360
Proved undeveloped reserves	46,385	36,453
Natural Gas [Member]
Reserve Quantities [Line Items]
Balance at beginning of period	302,922	257,115	335,000
Purchase of minerals in place	859	3,618	0
Sales of minerals in place	(79,579)	(9,708)	(7,000)
Extensions and discoveries	56,159	62,412	37,000
Revisions	(11,957)	9,735	(89,000)
Improved recoveries	0	0	0
Production	(20,648)	(20,250)	(20,000)
Balance at end of the period	247,756	302,922	257,115
Proved developed reserves	158,265	196,920	186,000	226,000
Proved undeveloped reserves	89,491	106,002	71,000	109,000
Natural Gas Liquids [Member]
Reserve Quantities [Line Items]
Balance at beginning of period	15,175	11,195
Purchase of minerals in place	55	1,059
Sales of minerals in place	(1,959)	(324)
Extensions and discoveries	3,405	3,127
Revisions	1,741	1,479
Improved recoveries	0	0
Production	(1,564)	(1,361)
Balance at end of the period	16,853	15,175
Proved developed reserves	11,787	11,484
Proved undeveloped reserves	5,066	3,691

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Additions to proved reserves that result from (1) extension of the proved acreage of previously discovered (old) reservoirs through additional drilling in periods after discovery and (2) discovery of new fields with proved reserves or of new reservoirs of proved reserves in old fields.

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Changes in proved reserve estimates resulting from application of improved recovery techniques.

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The net quantity of proved reserves as of the balance sheet date. Proved oil reserves are the estimated quantities of crude oil and natural gas liquids which geological and engineering data demonstrate with reasonable certainty to be recoverable.

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Production of proved reserves.

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Revisions represent changes in previous estimates of proved reserves, either upward or downward, resulting from new information (except for an increase in proved acreage) normally obtained from development drilling and production history or resulting from change in economic factors.

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Energy measure of interests in proved developed reserves of crude oil, including condensate and natural gas liquids, natural gas, synthetic oil and gas, or other nonrenewable natural resource that is intended to be upgraded into synthetic oil and gas.

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Net quantities of an enterprise's interests in proved developed reserves of either crude oil (including condensate and natural gas liquids), natural gas, synthetic oil and gas, or other nonrenewable natural resource that is intended to be upgraded into synthetic oil and gas as of the beginning and the end of the year. "Net" quantities of reserves include those relating to the enterprise's operating and nonoperating interests in properties. Quantities of reserves relating to royalty interests owned are included in "net" quantities if the necessary information is available to the enterprise. "Net" quantities does not include reserves relating to interests of others in properties owned by the enterprise. The unit of measure for reserve quantities is defined as "barrels" for oil and synthetic oil reserves or "cubic feet" or "cubic meters" for natural gas and synthetic gas reserves.

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Energy measure of proved undeveloped reserves of crude oil, including condensate and natural gas liquids, natural gas, synthetic oil and gas, or other nonrenewable natural resource that is intended to be upgraded into synthetic oil and gas.

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Net quantities of an enterprise's interests in proved undeveloped reserves of either crude oil (including condensate and natural gas liquids), natural gas, synthetic oil and gas, or other renewable natural resource that is intended to be upgraded into synthetic oil and gas as of the beginning and the end of the year. "Net" quantities of reserves include those relating to the enterprise's operating and nonoperating interests in properties. Quantities of reserves relating to royalty interests owned are included in "net" quantities if the necessary information is available to the enterprise. "Net" quantities does not include reserves relating to interests of others in properties owned by the enterprise. The unit of measure for reserve quantities is defined as "barrels" for oil and synthetic oil reserves or "cubic feet" or "cubic meters" for natural gas and synthetic gas reserves.

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