Fair Value Measurements (Recurring Fair Value Measurements) (Details) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Commodity Derivatives [Member]
Financial assets (liabilities)	$ 64,694	$ (9,086)
Commodity Derivatives [Member] \| Level 2 [Member]
Financial assets (liabilities)	39,565	(19,954)
Commodity Derivatives [Member] \| Level 3 [Member]
Financial assets (liabilities)	25,129	10,868
Interest Rate Swaps [Member] \| Swap [Member]
Financial assets (liabilities)		(1,614)
Interest Rate Swaps [Member] \| Swap [Member] \| Level 2 [Member]
Financial assets (liabilities)		0
Interest Rate Swaps [Member] \| Swap [Member] \| Level 3 [Member]
Financial assets (liabilities)		$ (1,614)

Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 107

-Paragraph 10

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 4, 17

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

Name:	us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant