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FAIR VALUE MEASUREMENTS Table 2 - Fair Value and Carrying Amounts of Long-Term Debt and Axeon Term Loan (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Fair Value and Carrying Value of Debt and Note Receivable from Counterparty [Line Items]    
Fair value, long-term debt $ 3,677,622 $ 3,084,762
Carrying amount, long-term debt 3,613,059 3,014,364
Axeon [Member]    
Fair Value and Carrying Value of Debt and Note Receivable from Counterparty [Line Items]    
Fair value, Axeon Term Loan   110,000
Carrying amount, Axeon Term Loan $ 0 $ 110,000