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Derivatives Hedges and Financial Instruments - Liabilities Measured at Fair Value on Recurring Basis (Detail) - Fair Value, Recurring - USD ($)
$ in Thousands
Jun. 30, 2020
Dec. 31, 2019
Liabilities - Current and noncurrent accrued and other liabilities:    
Natural gas contracts $ 131  
Embedded derivative 327 $ 1,084
Total 458 $ 1,084
Significant Other Observable Inputs (Level 2) [Member]    
Liabilities - Current and noncurrent accrued and other liabilities:    
Natural gas contracts 131  
Total 131  
Significant Unobservable Inputs (Level 3) [Member]    
Liabilities - Current and noncurrent accrued and other liabilities:    
Embedded derivative 327  
Total $ 327