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Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited) - Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves (Details) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
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Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items] |  |  |
Future cash flows | $ 11,202,692 | $ 3,354,168 | $ 3,043,450
Future development and abandonment costs | (3,005,217) | (1,165,025) | (877,660)
Future production costs | (2,152,821) | (924,167) | (941,243)
Future production taxes | (289,944) | (69,447) | (58,169)
Future income taxes | (573,965) | (14,545) | (2,648)
Future net cash flows | 5,180,745 | 1,180,984 | 1,163,730
10% discount to reflect timing of cash flows | (2,537,181) | (492,944) | (399,399)
Standardized measure of discounted future net cash flows | 2,643,564 | 688,040 | 764,331
Investment in Grizzly Oil Sands ULC |  |  |
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items] |  |  |
Future cash flows | 0 | 0 | 0
Future development and abandonment costs | 0 | 0 | 0
Future production costs | 0 | 0 | 0
Future production taxes | 0 | 0 | 0
Future income taxes | 0 | 0 | 0
Future net cash flows | 0 | 0 | 0
10% discount to reflect timing of cash flows |  |  |
Standardized measure of discounted future net cash flows | $ 0 | $ 0 | $ 0

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- Definition Discounted Future Net Cash Flows Relating To Proved Oil And Gas Reserves Future Production Taxes + References No definition available. + Details
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- Definition 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. + References No definition available. + Details
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- Definition Amount of estimated future accumulated cash inflow from the sale of proved oil and 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 30 -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62424-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 33 -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62479-109447 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 31 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62455-109447 + Details
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- Definition Amount of estimated future accumulated cash outflow for costs to be incurred in developing proved oil and 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 30 -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62424-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 31 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62455-109447 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 33 -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62479-109447 + Details
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- Definition Amount of estimated future accumulated cash outflow for income tax, based on the future income less future expense derived from production and sale of proved oil and 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 33 -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62479-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 30 -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62424-109447 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 31 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62455-109447 + Details
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- Definition Amount, after future accumulated cash outflow for development and production costs and future income tax, of estimated future accumulated cash inflow from the sale of proved oil and 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 33 -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62479-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 30 -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62424-109447 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 31 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62455-109447 + Details
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- Definition Amount of estimated future accumulated cash outflow for costs to be incurred in producing proved oil and 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 33 -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62479-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 30 -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62424-109447 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 31 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62455-109447 + Details
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- Definition Amount of discount on future accumulated cash inflow, after deducting future accumulated cash outflow for development and production costs and future income tax, from sale of proved oil and gas reserves, using a discount rate of ten percent a year. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 31 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62455-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 33 -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62479-109447 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 30 -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62424-109447 + Details
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- Definition Amount of discounted future accumulated cash inflow relating to proved oil and 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 30 -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62424-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 55 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=34713648&loc=d3e63123-109448 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 33 -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62479-109447 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 35 -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62500-109447 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 31 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62455-109447 + Details
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