v3.8.0.1

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 |
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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

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- Definition 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 + Details
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