FAIR VALUE MEASUREMENTS (Fair Value Hierarchy for Assets and Liabilities Measured at Fair Value on Recurring Basis) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative asset, fair value	$ 10,678	$ 26,613
Equity securities		47,082
Derivative liability, fair value		3,827
Recurring basis
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity securities		47,082
Total, Derivative asset, fair value		73,695
Recurring basis | Commodity contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative asset, fair value	10,678	26,613
Derivative liability, fair value		3,827
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity securities		47,082
Total, Derivative asset, fair value		47,082
Recurring basis | Significant Other Observable Inputs (Level 2)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total, Derivative asset, fair value		26,613
Recurring basis | Significant Other Observable Inputs (Level 2) | Commodity contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative asset, fair value	$ 10,678	26,613
Derivative liability, fair value		$ 3,827