FAIR VALUE MEASUREMENTS - Fair Value Measurements and Fair Value Hierarchy for Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Life-insurance contracts	$ 15,864	$ 15,072
Mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mutual funds	5,085	7,367
Commodity swap contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity swap contracts	(691)	(1,926)
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	5,085	7,367
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	15,864	15,072
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	(691)	(1,926)
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