FAIR VALUE MEASUREMENTS (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carbon option contracts	$ 4,870	$ 2,433
Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	146,259	112,653
Restricted cash	45,418	59,703
Current maturities of long-term debt	0	(3,375)
Long-term debt	(972,426)	(1,022,004)
Carrying Amount | Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swaps	41,900	15,440
Carrying Amount | Foreign currency exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign currency contracts, liabilities	(1,808)
Foreign currency contracts, assets		2,807
Carrying Amount | Foreign currency option contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign currency contracts, liabilities	(64)
Foreign currency contracts, assets		352
Carrying Amount | Carbon options
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carbon option contracts	(664)	0
Fair Value | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	146,259	112,653
Restricted cash	45,418	59,703
Current maturities of long-term debt	0	0
Long-term debt	0	0
Fair Value | Level 1 | Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swaps	0	0
Fair Value | Level 1 | Foreign currency exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign currency contracts, liabilities	0
Foreign currency contracts, assets		0
Fair Value | Level 1 | Foreign currency option contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign currency contracts, liabilities	0
Foreign currency contracts, assets		0
Fair Value | Level 1 | Carbon options
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carbon option contracts	0	0
Fair Value | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
Restricted cash	0	0
Current maturities of long-term debt	0	(3,375)
Long-term debt	(970,970)	(1,030,135)
Fair Value | Level 2 | Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swaps	41,900	15,440
Fair Value | Level 2 | Foreign currency exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign currency contracts, liabilities	(1,808)
Foreign currency contracts, assets		2,807
Fair Value | Level 2 | Foreign currency option contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign currency contracts, liabilities	(64)
Foreign currency contracts, assets		352
Fair Value | Level 2 | Carbon options
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carbon option contracts	$ (664)	$ 0