Annual report pursuant to Section 13 and 15(d)

Equity Investments (Grizzly and Diamondback Income Statement Disclosures) (Details)

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Equity Investments (Grizzly and Diamondback Income Statement Disclosures) (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Grizzly Oil Sands ULC [Member]
     
Schedule of Equity Method Investments [Line Items]      
Gross revenue $ 0 $ 0 $ 0
Net income (loss) (6,050) (6,605) (3,234)
Diamondback Energy LLC [Member]
     
Schedule of Equity Method Investments [Line Items]      
Gross revenue 74,962 49,366 27,253
Income from operations 17,307 15,147 9,181
Net income (loss) $ (36,521) $ (386) $ 8,231