Annual report pursuant to Section 13 and 15(d)

Equity Investments (Grizzly and Diamondback Balance Sheet Disclosures) (Details)

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Equity Investments (Grizzly and Diamondback Balance Sheet Disclosures) (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2012
Dec. 31, 2011
Grizzly Oil Sands ULC [Member]
    
Schedule of Equity Method Investments [Line Items]    
Current assets $ 30,098 $ 21,247
Noncurrent assets 720,550 284,361
Current liabilities 42,547 25,984
Noncurrent liabilities 14,515 1,780
Diamondback Energy LLC [Member]
    
Schedule of Equity Method Investments [Line Items]    
Current assets 50,275 30,812
Noncurrent assets 556,426 232,766
Current liabilities 79,232 42,298
Noncurrent liabilities $ 65,401 $ 92,243