The cash inflow to dispose of long-lived, physical assets and mineral interests in oil and gas properties used for normal oil and gas operations.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 12

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3179-108585

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 15

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 16

-Subparagraph c

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Investing Activities

-URI http://asc.fasb.org/extlink&oid=6516133

Name:	us-gaap_ProceedsFromSaleOfOilAndGasPropertyAndEquipment
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Divestitures and Assets Held for Sale (Details) (USD $)	9 Months Ended		1 Months Ended
Divestitures and Assets Held for Sale (Details) (USD $)	Sep. 30, 2011	Sep. 30, 2010	Aug. 31, 2011 LaSalle County	Jun. 30, 2011 Rockies Mid-Continent Divestiture	Jan. 31, 2011 Rocky Mountain	Jul. 31, 2011 Marcellus shale
Divestitures and Assets Held for Sale
Cash received on divestiture of non-strategic assets	$ 325,053,000	$ 259,501,000	$ 226,900,000	$ 35,700,000	$ 45,500,000	$ 80,000,000
Estimated gain on divestiture of assets			191,400,000	28,400,000	27,200,000
Assets Held for Sale
Reasonably certain period within which sale will take place (in years)	1
Book value of assets held for sale, net of accumulated depletion, depreciation and amortization	$ 105,900,000