Asset Retirement Obligation (Narrative) (Details) (USD $)	9 Months Ended
Sep. 30, 2013
Asset Retirement Obligations [Abstract]
Asset Retirement Obligation Revision Shallow Water Assets	$ 31,000,000
Asset Retirement Obligation, Revision of Estimate	63,462,000
Loss on abandonment activities of non-operated interests	$ 21,800,000

Amount of the Increase or Decrease in the amount of the asset retirement obligation during the current period for changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation.

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)(4)

-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

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