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Derivative Instruments (Schedule Of Location And Fair Value Of Outstanding Commodity Derivative Instruments) (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2012
Dec. 31, 2011
Derivatives, Fair Value [Line Items]    
Other current assets - current assets $ 80 $ 491
Derivative instruments - non-current assets 486 4,362
Derivative instruments - current liabilities (16,469) (5,907)
Derivative instruments - non-current liabilities (6,434) (3,505)
Total derivative instruments 22,345  
Crude Oil Collar [Member]
    
Derivatives, Fair Value [Line Items]    
Other current assets - current assets 72  
Derivative instruments - non-current assets 486 4,362
Derivative instruments - current liabilities (16,469) (5,907)
Derivative instruments - non-current liabilities (6,434) (3,505)
Total derivative instruments $ 22,345 $ 5,050