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Fair Value Measurements (Recurring Narrative) (Detail)
3 Months Ended
Mar. 31, 2021
USD ($)
$ / gal
Embedded derivatives in commodity contracts  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Term of contract 5 years
Level 3  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Average forward price | $ / gal 0.62
Level 3 | Commodity derivatives | Minimum  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Forward commodity price 0.48
Level 3 | Commodity derivatives | Maximum  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Forward commodity price 1.36
Level 3 | Embedded derivatives in commodity contracts  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Probability of renewal first term 100.00%
Probability of renewal second term 100.00%