Capitalization of Exploratory Well Costs (Detail) $ in Millions	Jun. 30, 2015 USD ($)
Mutamba Iroru \| Aging of Capitalized Exploratory Well Costs, Period Two [Member]
Capitalized Costs Relating To Oil And Gas Producing Activities By Geographic Area [Line Items]
Capitalized exploratory well costs that have been capitalized for a period greater than one year	$ 8.9

The amount of exploratory well costs that have been capitalized for a period of greater than one year after the completion of drilling.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 1B

-Subparagraph b

-URI http://asc.fasb.org/extlink&oid=51678428&loc=SL6806780-109447

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