Disclosures About Oil and Gas Producing Activities - Summary of Changes in Quantities of Proved Oil, NGL and Natural Gas Reserves (Parenthetical) (Detail)	12 Months Ended
Dec. 31, 2017 MBoe MBbls MMcf	Dec. 31, 2016 MBoe MBbls MMcf	Dec. 31, 2015 MBoe MBbls MMcf	Dec. 31, 2014 MBoe MBbls MMcf
Reserve Quantities [Line Items]
Field fuel \| MMcf	1,319	1,330	1,530
Proved Developed Reserves \| MBoe	66,399	58,875	61,856	60,220
Proved Undeveloped Reserves \| MBoe	115,146	97,502	104,790	86,028
Oil (MBbls) [Member]
Reserve Quantities [Line Items]
Field fuel	1,107	1,275	1,882
Proved Developed Oil Reserves	13,853	13,466	15,667	17,978
Proved Undeveloped Oil Reserves	36,207	36,565	38,829	37,360
NGLs (MBbls) [Member]
Reserve Quantities [Line Items]
Field fuel	1,486	1,529	1,694
Proved Developed Oil Reserves	23,180	20,375	20,414	19,082
Proved Undeveloped Oil Reserves	34,768	27,259	29,072	21,825
Natural Gas (MMcf) [Member]
Reserve Quantities [Line Items]
Field fuel \| MMcf	11,148	11,734	13,262
Proved Developed Oil Reserves \| MMcf	176,201	150,208	154,652	138,961
Proved Undeveloped Oil Reserves \| MMcf	265,028	202,069	221,335	161,059

Production of proved reserves.

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)
-URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e61831-109447

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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.

+ References

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 235
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e61884-109447

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 235
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e61797-109447

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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.

+ References

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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.

+ References

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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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