FAIR VALUE MEASUREMENTS - Fair Value Measurements and Fair Value Hierarchy for Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Life-insurance contracts	$ 18,254	$ 16,930
Mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mutual funds	7,608	5,331
Commodity swap contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity swap contracts	21,914	13,384
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Life-insurance contracts	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mutual funds	7,608	5,331
Quoted Prices in Active Markets for Identical Assets (Level 1) | Commodity swap contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity swap contracts	0	0
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Life-insurance contracts	18,254	16,930
Significant Other Observable Inputs (Level 2) | Mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mutual funds	0	0
Significant Other Observable Inputs (Level 2) | Commodity swap contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity swap contracts	21,914	13,384
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Life-insurance contracts	0	0
Significant Unobservable Inputs (Level 3) | Mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mutual funds	0	0
Significant Unobservable Inputs (Level 3) | Commodity swap contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity swap contracts	$ 0	$ 0