Oil and Natural Gas Activities--Costs Incurred Footnote (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Oil and Gas In Process Activities [Line Items]
Exploration costs	$ 90,146us-gaap_CostsIncurredExplorationCosts	$ 77,507us-gaap_CostsIncurredExplorationCosts	$ 54,432us-gaap_CostsIncurredExplorationCosts
Enhanced Oil Recovery [Member]
Oil and Gas In Process Activities [Line Items]
Exploration costs	$ 152	$ 37,344	$ 52,188

Exploration costs incurred, including capitalized costs and costs charged to expense, in oil and gas activities.

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Exploration

-URI http://asc.fasb.org/extlink&oid=6512329

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 18

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62014-109447

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