Supplemental Oil and Gas Disclosures (Unaudited) - Capitalized Cost Related to Oil and Natural Gas Producing Activities (Detail) - Consolidated Entities - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Capitalized Costs Relating To Oil And Gas Producing Activities [Line Items]
Unproved oil and gas properties	$ 0	$ 374
Proved oil and gas properties	0	5,159
Total costs	0	5,533
Less accumulated depreciation, depletion and amortization	0	(4,751)
Net capitalized costs	$ 0	$ 782

Capitalized Costs Relating To Oil And Gas Producing Activities Line Items

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Amount of accumulated depreciation, depletion, amortization and valuation allowance relating to oil and gas producing activities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 235
-Section 50
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e61901-109447

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The sum of capitalized costs relating to oil and gas producing activities before accounting for accumulated depreciation.

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Net amount of capitalized costs relating to oil and gas producing activities.

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- Definition

Capitalized costs of proved properties incurred for any combination mineral interests acquisitions; wells and related equipment; support equipment and facilities; and uncompleted wells and equipment and other costs not previously disclosed within this table.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 360
-URI http://asc.fasb.org/subtopic&trid=2145654

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
-Paragraph 13
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Capitalized costs of unproved properties incurred for any combination mineral interests acquisitions and other costs not previously disclosed within this table.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-URI http://asc.fasb.org/topic&trid=2145477

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-Name Accounting Standards Codification
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-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e61901-109447

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