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Fair Value Measurements - Significant Unobservable Inputs (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Significant Unobservable Inputs        
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis $ 0 $ (512) $ (4,252) $ (222,554)
Oil basis swaps | Fair Value Measurements Level 3
        
Significant Unobservable Inputs        
Derivative, weighted average forward price (in dollars per barrel)   14.74    
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis $ 0 $ (512)    
Minimum | Oil basis swaps | Fair Value Measurements Level 3
        
Significant Unobservable Inputs        
Derivative, forward price (in dollars per barrel)   10.00    
Maximum | Oil basis swaps | Fair Value Measurements Level 3
        
Significant Unobservable Inputs        
Derivative, forward price (in dollars per barrel)   21.98