Supplemental Oil and Gas Reserve Information - Unaudited - Net Proved, Proved Developed and Proved Undeveloped Reserves (Detail)	1 Months Ended	12 Months Ended
Mar. 31, 2014 MBoe	Dec. 31, 2014 MMcf MBbls MBoe	Dec. 31, 2014 MBbls MBoe MMcf	Dec. 31, 2013 MBbls MMcf MBoe	Dec. 31, 2013 MMcf MBoe MBbls	Dec. 31, 2012 MMcf MBbls MBoe	Dec. 31, 2012 MBbls MBoe MMcf
Proved Developed and Undeveloped Reserve (Energy) [Roll Forward]
Proved reserves (Volume), beginning balance		198,590	198,590	91,530	91,530	57,900	57,900
Proved reserves (Energy), beginning balance		227,920	227,920	143,345	143,345	78,715	78,715
Revisions of previous estimates (Volume)		(12,290)	(23,069)	3,390	10,412	(8,495)	(567)
Proved Undeveloped Reserves, Decrease from Estimated Net Proved Reserve Balance (Energy)		21,411	21,411
Revisions of previous estimates (Energy)		(25,117)	(25,117)	5,125	5,125	(1,983)	(1,983)
Extensions, discoveries and other additions (Volume)		70,449	80,855	40,784	31,856	45,759	66,245
Extensions, discoveries and other additions (Energy)		92,596	92,596	46,094	46,094	73,871	73,871
Sales of reserves in place (Volume)		(4,850)	(7,640)	0	0	0	0
Sales of reserves in place (Energy)	(8,448)	(8,448)	(8,448)	0	0	0	0
Purchases of reserves in place (Volume)		1,523	1,546	37,459	49,631	512	881
Purchases of reserves in place (Energy)		1,799	1,799	45,731	45,731	966	966
Production (Volume)		(10,691)	(14,883)	(11,133)	(7,450)	(4,146)	(7,533)
Production (Energy)		(16,664)	(16,664)	(12,375)	(12,375)	(8,224)	(8,224)
Net proved reserves (Volume), closing balance		220,120	220,120	198,590	198,590	91,530	91,530
Net proved reserves (Energy), closing balance		272,086	272,086	227,920	227,920	143,345	143,345
Proved developed reserves (Volume)		114,016us-gaap_ProvedDevelopedReservesVolume	114,016us-gaap_ProvedDevelopedReservesVolume	106,774us-gaap_ProvedDevelopedReservesVolume	106,774us-gaap_ProvedDevelopedReservesVolume	44,695us-gaap_ProvedDevelopedReservesVolume	44,695us-gaap_ProvedDevelopedReservesVolume
Proved developed reserves (Energy)		146,343us-gaap_ProvedDevelopedReservesBOE1	146,343us-gaap_ProvedDevelopedReservesBOE1	122,136us-gaap_ProvedDevelopedReservesBOE1	122,136us-gaap_ProvedDevelopedReservesBOE1	70,051us-gaap_ProvedDevelopedReservesBOE1	70,051us-gaap_ProvedDevelopedReservesBOE1
Proved undeveloped reserve (Volume)		106,104us-gaap_ProvedUndevelopedReserveVolume	106,104us-gaap_ProvedUndevelopedReserveVolume	91,816us-gaap_ProvedUndevelopedReserveVolume	91,816us-gaap_ProvedUndevelopedReserveVolume	46,835us-gaap_ProvedUndevelopedReserveVolume	46,835us-gaap_ProvedUndevelopedReserveVolume
Proved undeveloped reserves (Energy)		125,743us-gaap_ProvedUndevelopedReserveBOE1	125,743us-gaap_ProvedUndevelopedReserveBOE1	105,784us-gaap_ProvedUndevelopedReserveBOE1	105,784us-gaap_ProvedUndevelopedReserveBOE1	73,294us-gaap_ProvedUndevelopedReserveBOE1	73,294us-gaap_ProvedUndevelopedReserveBOE1

Proved Undeveloped Reserves, Decrease from Estimated Net Proved Reserve Balance (Energy)

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Energy measure of increase in quantity of proved reserve of oil and gas resulting from the extension of the proved acreage of previously discovered reservoir or discovery of new field with proved reserve or of new reservoir of proved reserve in old field, stated in a unit of energy. For example, but not limited to, barrel of oil equivalents (BOE) or one thousand cubic feet of natural gas equivalent (Mcfe).

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Energy measure of proved reserve of oil and gas, stated in a unit of energy. For example, but not limited to, barrel of oil equivalents (BOE) or one thousand cubic feet of natural gas equivalent (Mcfe).

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Energy measure of decrease in quantity of proved reserve of oil and gas resulting from production, stated in a unit of energy. For example, but not limited to, barrel of oil equivalents (BOE) or one thousand cubic feet of natural gas equivalent (Mcfe).

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Energy measure of increase in quantity of proved reserve of oil and gas resulting from purchase of mineral in place, stated in a unit of energy. For example, but not limited to, barrel of oil equivalents (BOE) or one thousand cubic feet of natural gas equivalent (Mcfe).

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Energy measure of increase (decrease) in quantity of proved reserve of oil and gas related to revision of a previous estimate resulting from new information, except for an increase in proved acreage, or change in economic factors, stated in a unit of energy. For example, but not limited to, barrel of oil equivalents (BOE) or one thousand cubic feet of natural gas equivalent (Mcfe).

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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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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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Purchase of minerals in place.

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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 decrease in quantity of proved reserve of oil and gas resulting from sale of mineral in place, stated in a unit of energy. For example, but not limited to, barrel of oil equivalents (BOE) or one thousand cubic feet of natural gas equivalent (Mcfe).

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Sales of minerals in place.

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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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No definition available.

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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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