Current report filing

Fair Value Measurements (Details)

v2.4.0.8
Fair Value Measurements (Details) (USD $)
 3 Months Ended 12 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Assets $ 343,000   $ 664,000 $ 1,601,000  
Equity investment in Diamondback 212,413,000 151,317,000 151,317,000 0  
Asset retirement obligations 670,000 598,000 2,195,000 1,390,000 1,328,000
Level 1 [Member] | Fixed Price Swaps [Member]
          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Assets 0   0 0  
Liabilities 0   0 0  
Level 2 [Member] | Fixed Price Swaps [Member]
          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Assets 343,000   664,000 1,601,000  
Liabilities 9,689,000   10,442,000 0  
Level 3 [Member]
          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Asset retirement obligations 700,000   2,195,000    
Level 3 [Member] | Fixed Price Swaps [Member]
          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Assets 0   0 0  
Liabilities 0   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 212,413,000   151,317,000    
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   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   $ 0