Summary of Significant Accounting Policies - Asset Retirement Obligations (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Proceeds from insurance reimbursement	$ 7.2
Gulf of Mexico Oil and Gas Properties [Member]
Asset retirement obligation, cash paid to settle		$ 5.2

The cash inflow from the amounts received by the insured under the terms of an insurance contract settlement. This element pertains only to insurance proceeds related to operating activities. It excludes insurance settlements classified as investing cash flows, for example, insurance settlements related to fixed assets.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 16
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3337-108585

Name:	us-gaap_ProceedsFromInsuranceSettlementOperatingActivities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration