Annual report pursuant to Section 13 and 15(d)

Fair Value Measurements (Details)

v2.4.0.6
Fair Value Measurements (Details) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets $ 664 $ 1,601  
Asset retirement obligations 2,195 1,390 1,328
Level 1 [Member] | Fixed Price Swaps [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets 0 0  
Liabilities 0 0  
Level 2 [Member] | Fixed Price Swaps [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets 664 1,601  
Liabilities 10,442 0  
Level 3 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Asset retirement obligations 2,195    
Level 3 [Member] | Fixed Price Swaps [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets 0 0  
Liabilities 0 0  
Diamondback Energy LLC [Member] | Level 1 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Equity investment in Diamondback 151,317    
Diamondback Energy LLC [Member] | Level 2 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Equity investment in Diamondback 0    
Diamondback Energy LLC [Member] | Level 3 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Equity investment in Diamondback $ 0