Noncurrent portion of the carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

Name:	us-gaap_AssetRetirementObligationsNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Asset Retirement Obligations - Additional Information (Detail) - USD ($)	3 Months Ended
	Jun. 30, 2017	Sep. 30, 2017	Dec. 31, 2016
Asset Retirement Obligations [Line Items]
Accrued liability for AROs		$ 116,000	$ 546,000
Zena Energy L.L.C [Member]
Asset Retirement Obligations [Line Items]
Extinguishment and derecognition of asset retirement obligation	$ 193,000