v3.8.0.1

Disclosures About Oil and Gas Producing Activities - Summary of Changes in Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Natural Gas Reserves (Detail) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Extractive Industries [Abstract] |  |  |
Standardized measure of discounted future net cash flows, Beginning balance | $ 297,755 | $ 460,395 | $ 1,055,815
Net change in sales and transfer prices and in production (lifting) costs related to future production | 229,139 | (191,841) | (1,405,864)
Changes in estimated future development costs | (72,439) | 17,405 | 231,900
Sales and transfers of oil and gas produced during the period | (78,803) | (62,835) | (91,278)
Net change due to acquisition of minerals in place | 17,331 |  |
Net change due to extensions, discoveries and improved recovery | 49,377 | 13,988 | 156,783
Net change due to revisions in quantity estimates | (3,817) | (25,236) | (59,305)
Previously estimated development costs incurred during the period | 43,202 | 15,884 | 146,237
Accretion of discount | 30,789 | 46,040 | 105,582
Other | (1,677) | (9,500) | 6,915
Net change in income taxes | (49,826) | 33,455 | 313,610
Standardized Measure of discounted future net cash flows | $ 461,031 | $ 297,755 | $ 460,395

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- Definition Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of extensions, discoveries and improved recovery 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 35 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62500-109447 + Details
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- Definition Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of change in estimated future development costs. + 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 (b) -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 35 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62500-109447 + Details
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- Definition Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of change in the estimated future income tax on future pretax net cash flows related to the entity's 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 35 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62500-109447 + Details
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- Definition Amount of increase in standardized measure of discounted future net cash flow as a result of purchases 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 35 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62500-109447 + Details
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- Definition Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of change in sales and transfer prices and in production (lifting) costs related to future production. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 35 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62500-109447 + Details
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- Definition Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of revisions of estimated quantity of oil and gas in 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 35 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62500-109447 + Details
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- Definition Amount of (increase) decrease in standardized measure of discounted future net cash flow as a result of sales and transfers of oil and gas produced. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 35 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62500-109447 + Details
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- Definition Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of changes from other sources. + References Reference 1: 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 + Details
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- Definition Amount of accretion of discount for the standardized measure of discounted future net cash flow related 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 35 -Subparagraph (h) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62500-109447 + 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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