Quarterly report pursuant to Section 13 or 15(d)

Financial Instruments, Fair Value, Hedging Activities, and Concentrations of Credit Risk - Summary of Fair Value Measurements and Financial Statement Presentation (Detail)

v3.20.2
Financial Instruments, Fair Value, Hedging Activities, and Concentrations of Credit Risk - Summary of Fair Value Measurements and Financial Statement Presentation (Detail) - USD ($)
$ in Thousands
Jun. 30, 2020
Dec. 31, 2019
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]    
Fair Values of Assets $ 30,778 $ 62
Fair Values of Liabilities 15,364 15,651
Short Term Investments [Member]    
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]    
Fair Values of Assets 29,942  
Commodity Futures and Options [Member]    
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]    
Fair Values of Assets 836 62
Financing Lease Obligations [Member]    
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]    
Fair Values of Liabilities 15,364 15,651
Level 1 [Member]    
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]    
Fair Values of Assets 30,778 62
Level 1 [Member] | Short Term Investments [Member]    
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]    
Fair Values of Assets 29,942  
Level 1 [Member] | Commodity Futures and Options [Member]    
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]    
Fair Values of Assets 836 62
Level 2 [Member]    
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]    
Fair Values of Liabilities 15,364 15,651
Level 2 [Member] | Financing Lease Obligations [Member]    
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]    
Fair Values of Liabilities $ 15,364 $ 15,651