Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements (Details)

v2.4.0.8
Fair Value Measurements (Details) (USD $)
In Thousands, unless otherwise specified
9 Months Ended
Sep. 30, 2014
Sep. 30, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Asset retirement obligation capitalized $ 5,713 $ 1,771
Level 1 [Member] | Diamondback Energy LLC [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Equity investment in Diamondback 70,443  
Level 1 [Member] | Fixed Price Swaps [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fixed price swaps 0  
Fixed price swaps and swaptions 0  
Level 2 [Member] | Diamondback Energy LLC [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Equity investment in Diamondback 0  
Level 2 [Member] | Fixed Price Swaps [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fixed price swaps 6,909  
Fixed price swaps and swaptions 6,662  
Level 3 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Asset retirement obligation capitalized 5,700  
Level 3 [Member] | Diamondback Energy LLC [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Equity investment in Diamondback 0  
Level 3 [Member] | Fixed Price Swaps [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fixed price swaps 0  
Fixed price swaps and swaptions $ 0