Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements (Details)

v2.4.0.6
Fair Value Measurements (Details) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets $ 343   $ 664
Asset retirement obligation capitalized 670 598  
Level 1 [Member] | Diamondback Energy LLC [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Equity investment in Diamondback 212,413    
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 343    
Liabilities 9,689    
Level 3 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Asset retirement obligation capitalized 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]      
Assets 0    
Liabilities $ 0