Disclosures About Oil and Gas Producing Activities - Summary of Changes in Quantities of Proved Oil, NGL and Natural Gas Reserves (Detail)	12 Months Ended
Dec. 31, 2017 MBoe MBbls MMcf	Dec. 31, 2016 MBoe MBbls MMcf	Dec. 31, 2015 MBoe MBbls MMcf
Reserve Quantities [Line Items]
Production \| MMcf	(1,319)	(1,330)	(1,530)
Proved Developed and Proved Undeveloped Reserves, Beginning Balance \| MBoe	156,377	166,646	146,248
Extensions and discoveries \| MBoe	33,307	16,651	34,895
Acquisition of minerals in place \| MBoe	1,572
Production \| MBoe	(4,452)	(4,759)	(5,787)
Revisions to previous estimates \| MBoe	(5,259)	(22,161)	(8,710)
Proved Developed and Proved Undeveloped Reserves, Ending Balance \| MBoe	181,545	156,377	166,646
Oil (MBbls) [Member]
Reserve Quantities [Line Items]
Proved Developed and Proved Undeveloped Reserves, Beginning Balance	50,031	54,496	55,338
Extensions and discoveries	10,546	6,529	11,054
Acquisition of minerals in place	710
Production	(1,107)	(1,275)	(1,882)
Revisions to previous estimates	(10,120)	(9,719)	(10,014)
Proved Developed and Proved Undeveloped Reserves, Ending Balance	50,060	50,031	54,496
NGLs (MBbls) [Member]
Reserve Quantities [Line Items]
Proved Developed and Proved Undeveloped Reserves, Beginning Balance	47,634	49,486	40,907
Extensions and discoveries	9,975	4,564	10,630
Acquisition of minerals in place	394
Production	(1,486)	(1,529)	(1,694)
Revisions to previous estimates	1,431	(4,887)	(357)
Proved Developed and Proved Undeveloped Reserves, Ending Balance	57,948	47,634	49,486
Natural Gas (MMcf) [Member]
Reserve Quantities [Line Items]
Proved Developed and Proved Undeveloped Reserves, Beginning Balance \| MMcf	352,277	375,988	300,020
Extensions and discoveries \| MMcf	76,710	33,347	79,268
Acquisition of minerals in place \| MMcf	2,808
Production \| MMcf	(11,148)	(11,734)	(13,262)
Revisions to previous estimates \| MMcf	20,581	(45,324)	9,962
Proved Developed and Proved Undeveloped Reserves, Ending Balance \| MMcf	441,228	352,277	375,988

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).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 235
-Section 50
-Paragraph 5
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e61831-109447

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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).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 235
-Section 50
-Paragraph 5
-Subparagraph (e)
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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).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 235
-Section 50
-Paragraph 5
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e61831-109447

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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).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
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-Paragraph 5
-Subparagraph (a)
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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 235
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e61831-109447

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-10.(a)(2))
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Production of proved reserves.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Purchase of minerals in place.

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-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e61831-109447

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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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