Annual report pursuant to Section 13 and 15(d)

Fair Value Measurements (Details)

v2.4.0.6
Fair Value Measurements (Details) (USD $)
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets $ 1,601,000    
Liabilities   4,720,000  
Asset retirement obligations incurred 1,390,000 1,328,000 361,000
Level 1 [Member] | Fixed Price Swaps [Member]
     
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets        
Liabilities        
Level 2 [Member] | Fixed Price Swaps [Member]
     
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets 1,601,000    
Liabilities   4,720,000  
Level 3 [Member] | Fixed Price Swaps [Member]
     
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets        
Liabilities