Disclosures About Fair Value Measurements (Fair Value Measurements Using Significant Unobservable Inputs) (Details) (NGL Swap Contracts [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011
NGL Swap Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning liability balance	$ (9,556)
Net unrealized gains included in earnings	188	[1]
Net realized losses included in earnings	(11,803)	[1]
Settlement payments	11,803
Transfers out of Level 3	9,368	[2]
Ending liability balance

[1] Changes in fair value are included in derivative gains (losses), net in the accompanying consolidated statements of operations.

[2] The values related to NGL swap and collar contracts were transferred from Level 3 to Level 2 as a result of the Company's ability to obtain independent market-quoted NGL data. The Company recognized the transfer between Level 3 and Level 2 at the end of the reporting period of transfer.