Sale of Oil and Natural Gas Property Interests - Additional Information (Detail) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018 USD ($) a	Jun. 30, 2018 USD ($) a
Asset Sale 1,000 Acres [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sale of oil and gas property	$ 1.5	$ 1.5
Proceeds from sale of oil and gas property	$ 6.0	$ 6.0
Area of land \| a	1,000	1,000
Asset Sale 400 Acres [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sale of oil and gas property		$ 0.0
Proceeds from sale of oil and gas property		$ 3.8
Area of land \| a	400	400
Asset Sale 50 Acres [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sale of oil and gas property		$ 0.3
Proceeds from sale of oil and gas property		$ 0.3
Area of land \| a	50	50

Area of land held.

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- Definition

Amount of gain (loss) on sale or disposal of proven and unproven oil and gas properties.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

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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.

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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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3179-108585

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