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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
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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

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