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Property, Plant and Equipment - Additional Information (Detail) - USD ($) |  | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Mar. 05, 2014 | Sep. 30, 2015 | Sep. 30, 2014 | Sep. 30, 2015 | Sep. 30, 2014 | Dec. 31, 2014
Property, Plant and Equipment [Line Items] |  |  |  |  |  |
Impairment of oil and gas properties |  | $ 80,000 | $ 1,439,000 | $ 24,917,000 | $ 2,243,000 |
Gain on sale of properties |  | 172,000 | 43,000 | 172,000 | 187,076,000 |
Unproved property leases [Member] |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |
Impairment of oil and gas properties |  | 100,000 | 1,400,000 | 24,900,000 | 2,200,000 |
Impairment of oil and gas properties, periodic assessments |  |  |  | 16,400,000 |  |
Proved Oil And Gas Properties [Member] |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |
Impairment of oil and gas properties |  | $ 0 | $ 0 | $ 0 | $ 0 |
Non-Operated Oil and Natural Gas Properties [Member] |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |
Proceeds from sale of properties | $ 324,900,000 |  |  |  |  |
Gain on sale of properties |  |  |  |  |  | $ 187,000,000

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- Definition Amount of gain (loss) on sale or disposal of oil and gas property or timber property. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3602-108585 + Details
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- Definition The expense recorded to reduce the value of oil and gas assets consisting of proved properties and unproved properties as the estimate of future successful production from these properties is reduced. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=51719941&loc=d3e2921-110230 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 360 -Section 35 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=28370743&loc=d3e66150-109466 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3602-108585 + Details
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- Definition The cash inflow to dispose of long-lived, physical assets and mineral interests in oil and gas properties used for normal oil and gas operations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Investing Activities -URI http://asc.fasb.org/extlink&oid=6516133 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 12 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3179-108585 + Details
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