Discontinued Operations - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	0 Months Ended
Mar. 31, 2013 Oil and Gas Properties [Member]	Aug. 30, 2013 Murphy USA Inc [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Common stock outstanding		100.00%
After tax gain on sale of oil and natural gas production	$ 147.4

This element represents the amount of gain (loss) on sale of properties during the reporting period net of the applicable income taxes realized.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 15

-Paragraph a

-Subparagraph 1(ii)

-Article 3

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 974

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.3-15.(a)(1)(ii))

-URI http://asc.fasb.org/extlink&oid=6875705&loc=d3e641549-123027

Name:	us-gaap_GainLossOnSaleOfPropertiesNetOfApplicableIncomeTaxes
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration