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Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited) - Oil and Gas Reserves (Details) bbl in Thousands, Mcf in Thousands | 12 Months Ended
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Dec. 31, 2018 bbl Mcf | Dec. 31, 2017 bbl Mcf | Dec. 31, 2016 bbl Mcf
Oil derivatives |  |  |
Proved Developed and Undeveloped Reserves [Roll Forward] |  |  |
Beginning of the period | 19,157 | 5,546 | 6,458
Purchases in oil and natural gas reserves in place | 0 | 15,132 | 0
Extensions and discoveries | 5,205 | 951 | 1,217
Sales of oil and natural gas reserves in place | (134) | 0 | 0
Revisions of prior reserve estimates | (377) | 107 | (3)
Current production | (2,801) | (2,579) | (2,126)
End of period | 21,050 | 19,157 | 5,546
Proved developed reserves | 9,570 | 10,245 | 4,882
Proved undeveloped reserves | 11,480 | 8,912 | 664
Natural gas liquids derivatives |  |  |
Proved Developed and Undeveloped Reserves [Roll Forward] |  |  |
Beginning of the period | Mcf | 4,825,310 | 2,167,068 | 1,560,145
Purchases in oil and natural gas reserves in place | Mcf | 0 | 1,098,644 | 0
Extensions and discoveries | Mcf | 622,271 | 1,594,734 | 1,082,220
Sales of oil and natural gas reserves in place | Mcf | (43,444) | 0 | 0
Revisions of prior reserve estimates | Mcf | (826,506) | 314,925 | (247,703)
Current production | Mcf | (443,742) | (350,061) | (227,594)
End of period | Mcf | 4,133,889 | 4,825,310 | 2,167,068
Proved developed reserves | Mcf | 1,813,184 | 1,616,930 | 744,797
Proved undeveloped reserves | Mcf | 2,320,705 | 3,208,380 | 1,422,271
Natural gas liquids |  |  |
Proved Developed and Undeveloped Reserves [Roll Forward] |  |  |
Beginning of the period | 75,766 | 20,127 | 17,736
Purchases in oil and natural gas reserves in place | 0 | 53,617 | 0
Extensions and discoveries | 9,631 | 4,619 | 7,677
Sales of oil and natural gas reserves in place | (112) | 0 | 0
Revisions of prior reserve estimates | 1,228 | 2,737 | (1,439)
Current production | (5,993) | (5,334) | (3,847)
End of period | 80,520 | 75,766 | 20,127
Proved developed reserves | 40,810 | 36,247 | 14,299
Proved undeveloped reserves | 39,710 | 39,519 | 5,828
Investment in Grizzly Oil Sands ULC | Oil derivatives |  |  |
Proved Developed and Undeveloped Reserves [Roll Forward] |  |  |
Beginning of the period | 0 | 0 | 0
Purchases in oil and natural gas reserves in place | 0 | 0 | 0
Extensions and discoveries | 0 | 0 | 0
Revisions of prior reserve estimates | 0 | 0 | 0
Current production | 0 | 0 | 0
End of period | 0 | 0 | 0
Proved developed reserves | 0 | 0 | 0
Proved undeveloped reserves | 0 | 0 | 0
Investment in Grizzly Oil Sands ULC | Natural gas liquids derivatives |  |  |
Proved Developed and Undeveloped Reserves [Roll Forward] |  |  |
Beginning of the period | Mcf | 0 | 0 | 0
Purchases in oil and natural gas reserves in place | Mcf | 0 | 0 | 0
Extensions and discoveries | Mcf | 0 | 0 | 0
Revisions of prior reserve estimates | Mcf | 0 | 0 | 0
Current production | Mcf | 0 | 0 | 0
End of period | Mcf | 0 | 0 | 0
Proved developed reserves | Mcf | 0 | 0 | 0
Proved undeveloped reserves | Mcf | 0 | 0 | 0
Investment in Grizzly Oil Sands ULC | Natural gas liquids |  |  |
Proved Developed and Undeveloped Reserves [Roll Forward] |  |  |
Beginning of the period | 0 | 0 | 0
Purchases in oil and natural gas reserves in place | 0 | 0 | 0
Extensions and discoveries | 0 | 0 | 0
Revisions of prior reserve estimates | 0 | 0 | 0
Current production | 0 | 0 | 0
End of period | 0 | 0 | 0
Proved developed reserves | 0 | 0 | 0
Proved undeveloped reserves | 0 | 0 | 0

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- Definition Proved Developed and Undeveloped Reserves [Roll Forward] + References No definition available. + Details
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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Form 20-F -Section Item 18 -Subsection Instruction 2 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -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 + Details
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- Definition 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/disclosureRef -Publisher SEC -Name Form 20-F -Section Item 18 -Subsection Instruction 2 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -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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- Definition Production of proved reserves. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Form 20-F -Section Item 18 -Subsection Instruction 2 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -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 + Details
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- Definition Purchase of minerals in place. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Form 20-F -Section Item 18 -Subsection Instruction 2 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -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 + Details
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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Form 20-F -Section Item 18 -Subsection Instruction 2 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 5 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e61831-109447 + Details
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- Definition Sales of minerals in place. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Form 20-F -Section Item 18 -Subsection Instruction 2 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 5 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e61831-109447 + Details
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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/disclosureRef -Publisher SEC -Name Form 20-F -Section Item 18 -Subsection Instruction 2 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -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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- Definition 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 Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Form 20-F -Section Item 18 -Subsection Instruction 2 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -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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