XML 25 R48.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
Dec. 31, 2012
Dec. 31, 2011
Assets:    
Total assets $ 90,384 $ 254,781
Liabilities:    
Total liabilities 1,428 9,412
Money market funds [Member]
    
Assets:    
Total assets 66,387 250,419
Commodity derivative instruments [Member]
    
Assets:    
Total assets 23,997 4,362
Liabilities:    
Total liabilities 1,428 9,412
Level 1 [Member]
    
Assets:    
Total assets 66,387 250,419
Level 1 [Member] | Money market funds [Member]
    
Assets:    
Total assets 66,387 250,419
Level 2 [Member]
    
Assets:    
Total assets 23,997  
Liabilities:    
Total liabilities 1,428  
Level 2 [Member] | Commodity derivative instruments [Member]
    
Assets:    
Total assets 23,997  
Liabilities:    
Total liabilities 1,428  
Level 3 [Member]
    
Assets:    
Total assets   4,362
Liabilities:    
Total liabilities   9,412
Level 3 [Member] | Commodity derivative instruments [Member]
    
Assets:    
Total assets   4,362
Liabilities:    
Total liabilities   $ 9,412