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
6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets $ 9,714   $ 1,601
Asset retirement obligations incurred 1,176 449  
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 9,714    
Liabilities       
Level 3 [Member]
     
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Asset retirement obligations incurred 1,176    
Level 3 [Member] | Fixed Price Swaps [Member]
     
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets       
Liabilities