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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, 2017 bbl Mcf | Dec. 31, 2016 bbl Mcf | Dec. 31, 2015 bbl Mcf
Oil derivatives |  |  |
Proved Developed and Undeveloped Reserves [Roll Forward] |  |  |
Beginning of the period | 5,546 | 6,458 | 9,497
Purchases in oil and natural gas reserves in place | 15,132 | 0 | 0
Extensions and discoveries | 951 | 1,217 | 2,413
Revisions of prior reserve estimates | 107 | (3) | (2,553)
Current production | (2,579) | (2,126) | (2,899)
End of period | 19,157 | 5,546 | 6,458
Proved developed reserves | 10,245 | 4,882 | 6,120
Proved undeveloped reserves | 8,912 | 664 | 338
Natural gas liquids derivatives |  |  |
Proved Developed and Undeveloped Reserves [Roll Forward] |  |  |
Beginning of the period | Mcf | 2,167,068 | 1,560,145 | 719,006
Purchases in oil and natural gas reserves in place | Mcf | 1,098,644 | 0 | 371,663
Extensions and discoveries | Mcf | 1,594,734 | 1,082,220 | 997,057
Revisions of prior reserve estimates | Mcf | 314,925 | (247,703) | (371,430)
Current production | Mcf | (350,061) | (227,594) | (156,151)
End of period | Mcf | 4,825,310 | 2,167,068 | 1,560,145
Proved developed reserves | Mcf | 1,616,930 | 744,797 | 652,961
Proved undeveloped reserves | Mcf | 3,208,380 | 1,422,271 | 907,184
Natural gas liquids |  |  |
Proved Developed and Undeveloped Reserves [Roll Forward] |  |  |
Beginning of the period | 20,127 | 17,736 | 26,268
Purchases in oil and natural gas reserves in place | 53,617 | 0 | 0
Extensions and discoveries | 4,619 | 7,677 | 5,486
Revisions of prior reserve estimates | 2,737 | (1,439) | (9,594)
Current production | (5,334) | (3,847) | (4,424)
End of period | 75,766 | 20,127 | 17,736
Proved developed reserves | 36,247 | 14,299 | 12,910
Proved undeveloped reserves | 39,519 | 5,828 | 4,826
Investment in Grizzly Oil Sands ULC | Oil derivatives |  |  |
Proved Developed and Undeveloped Reserves [Roll Forward] |  |  |
Beginning of the period | 0 | 0 | 14,558
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 | (14,530)
Current production | 0 | 0 | (28)
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/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 + 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/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)) -URI http://asc.fasb.org/extlink&oid=82851474&loc=d3e511914-122862 + Details
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- Definition Production of proved reserves. + 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) -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/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 + 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/presentationRef -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 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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- 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/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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