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, 2013
Sep. 30, 2012
Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets $ 1,633   $ 664
Asset retirement obligation capitalized 1,771 1,711  
Level 1 [Member] | Diamondback Energy LLC [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Equity investment in Diamondback 242,174    
Level 1 [Member] | Fixed Price Swaps [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets 0    
Liabilities 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]      
Assets 1,760    
Liabilities 5,770    
Level 3 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Asset retirement obligation capitalized 1,800    
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]      
Assets 0    
Liabilities $ 0