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Property, Plant and Equipment - Additional Information (Detail) (USD $) | 3 Months Ended | 9 Months Ended |  | 3 Months Ended | 9 Months Ended | 0 Months Ended | 1 Months Ended
--- | --- | --- | --- | --- | --- | --- | ---
Sep. 30, 2013 | Sep. 30, 2012 | Sep. 30, 2013 | Sep. 30, 2012 | Sep. 26, 2013 | Sep. 30, 2013 Unproved property leases [Member] | Sep. 30, 2012 Unproved property leases [Member] | Sep. 30, 2013 Unproved property leases [Member] | Sep. 30, 2012 Unproved property leases [Member] | Sep. 26, 2013 East Nesson [Member] acre | Sep. 30, 2013 West Williston Acquisition [Member]
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |  |  |
Impairment of oil and gas properties | $ 56,000 | $ 36,000 | $ 762,000 | $ 2,607,000 |  | $ 56,000 | $ 36,000 | $ 762,000 | $ 2,607,000 |  |
Acres acquired |  |  |  |  |  |  |  |  |  | 25,000 |
Payments to acquire productive assets |  |  |  |  |  |  |  |  |  | 54,800,000 |
Investment commitment | 7,200,000 |  | 7,200,000 |  | 8,200,000 |  |  |  |  |  |
Acquisition, consideration transferred, deposit |  |  |  |  |  |  |  |  |  |  | $ 72,500,000

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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 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 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 360 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6391110&loc=d3e2921-110230 + Details
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