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Financial Instruments, Fair Value, and Concentrations of Credit Risk - Summary of Fair Value Measurements and Financial Statement Presentation (Detail) - USD ($)
$ in Thousands
Dec. 31, 2020
Dec. 31, 2019
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]    
Fair Values of Assets $ 12,165 $ 62
Short Term Investments [Member]    
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]    
Fair Values of Assets 11,698  
Level 1 [Member]    
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]    
Fair Values of Assets 12,165 62
Level 1 [Member] | Short Term Investments [Member]    
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]    
Fair Values of Assets 11,698  
Commodity Derivative Contracts [Member]    
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]    
Fair Values of Assets 467 62
Commodity Derivative Contracts [Member] | Level 1 [Member]    
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]    
Fair Values of Assets $ 467 $ 62