Oil and Gas Operations (Unaudited) (Costs Incurred) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Property acquisition:
Proved	$ 4,661	$ 79,862	$ 214,993
Unproved	26,820	58,634	91,888
Exploration	435,636	419,284	190,854
Development	655,353	749,256	623,775
Total costs incurred	$ 1,122,470	$ 1,307,036	$ 1,121,510

Name:	us-gaap_CostsIncurredAcquisitionOfOilAndGasPropertiesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Costs incurred, including capitalized costs and costs charged to expense, associated with the acquisition of oil and gas properties that have proved reserves.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 19

-URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62038-109447

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 18

-Subparagraph (a)

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

+ Details

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

- Definition

Costs incurred, including capitalized costs and costs charged to expense, associated with the acquisition of oil and gas properties that have unproved reserves.

+ References

+ Details

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

- Definition

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

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 18

-Subparagraph (c)

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

+ Details

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

- Definition

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

+ References

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

+ Details

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

- Definition

Amount of costs incurred related to oil and gas property acquisition, exploration and development activities, including capitalized costs and costs charged to expense.

+ References

No definition available.

+ Details

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