Suspended Exploratory Well Costs - Additional Information (Detail) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Extractive Industries [Abstract]
Suspended exploratory well costs	$ 0	$ 0

The amount of capitalized exploratory well costs that is pending the determination of proved reserves. This does not include amounts that were capitalized and subsequently expensed in the same annual period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 235
-Section 50
-Paragraph 1B
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=68064819&loc=SL6806780-109447

Name:	us-gaap_CapitalizedExploratoryWellCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant