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Financial Instruments - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)
$ in Thousands
Jun. 30, 2019
Dec. 31, 2018
Assets    
Derivative assets $ 1,081 $ 2,394
Liabilities    
Derivative liabilities (1,675) (98)
Fair Value, Measurements, Recurring [Member]    
Assets    
Derivative assets 1,081 2,394
Liabilities    
Derivative liabilities (1,675) (98)
Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member]    
Assets    
Derivative assets 1,081 2,394
Liabilities    
Derivative liabilities (1,675) (98)
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member]    
Assets    
Derivative assets 1,081 2,394
Liabilities    
Derivative liabilities (1,675) (98)
Significant Unobservable Inputs (Level 3) [Member] | Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member]    
Assets    
Derivative assets 1,081 2,394
Liabilities    
Derivative liabilities $ (1,675) $ (98)