XML 60 R34.htm IDEA: XBRL DOCUMENT v2.4.0.6
Fair Value Measurements (Hierarchy of Fair Value, Assets and Liabilities Measured on Recurring Basis) (Detail) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Assets:    
Total assets $ 193,104 $ 254,781
Liabilities:    
Total liabilities 1,633 9,412
Money Market Funds [Member]
    
Assets:    
Total assets 165,737 250,419
Commodity Derivative Instruments [Member]
    
Assets:    
Total assets 27,367 4,362
Liabilities:    
Total liabilities 1,633 9,412
Fair Value, Inputs, Level 1 [Member]
    
Assets:    
Total assets 165,737 250,419
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
    
Assets:    
Total assets 165,737 250,419
Fair Value, Inputs, Level 2 [Member]
    
Assets:    
Total assets 27,367  
Liabilities:    
Total liabilities 1,633  
Fair Value, Inputs, Level 2 [Member] | Commodity Derivative Instruments [Member]
    
Assets:    
Total assets 27,367  
Liabilities:    
Total liabilities 1,633  
Fair Value, Inputs, Level 3 [Member]
    
Assets:    
Total assets   4,362
Liabilities:    
Total liabilities   9,412
Fair Value, Inputs, Level 3 [Member] | Commodity Derivative Instruments [Member]
    
Assets:    
Total assets   4,362
Liabilities:    
Total liabilities   $ 9,412