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Fair Value Measurements - Hierarchy of Fair Value, Assets and Liabilities Measured on Recurring Basis (Detail) (Fair Value, Measurements, Recurring [Member], USD $)
In Thousands, unless otherwise specified
Jun. 30, 2014
Dec. 31, 2013
Assets:    
Total assets $ 742 $ 4,339
Liabilities:    
Total liabilities 74,259 8,327
Money market funds [Member]
    
Assets:    
Total assets 742 742
Commodity derivative instruments [Member]
    
Assets:    
Total assets   3,597
Liabilities:    
Total liabilities 74,259 8,327
Level 1 [Member]
    
Assets:    
Total assets 742 742
Liabilities:    
Total liabilities      
Level 1 [Member] | Money market funds [Member]
    
Assets:    
Total assets 742 742
Level 1 [Member] | Commodity derivative instruments [Member]
    
Assets:    
Total assets     
Liabilities:    
Total liabilities      
Level 2 [Member]
    
Assets:    
Total assets 0 3,597
Liabilities:    
Total liabilities 74,259 8,327
Level 2 [Member] | Money market funds [Member]
    
Assets:    
Total assets      
Level 2 [Member] | Commodity derivative instruments [Member]
    
Assets:    
Total assets   3,597
Liabilities:    
Total liabilities 74,259 8,327
Fair Value, Inputs, Level 3 [Member]
    
Assets:    
Total assets      
Liabilities:    
Total liabilities      
Fair Value, Inputs, Level 3 [Member] | Money market funds [Member]
    
Assets:    
Total assets      
Fair Value, Inputs, Level 3 [Member] | Commodity derivative instruments [Member]
    
Assets:    
Total assets     
Liabilities:    
Total liabilities