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FAIR VALUE MEASUREMENTS Table 2 - Estimated Fair Values and Carrying Amounts of Long-Term Debt (Details) - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 31, 2017
Fair Value Disclosures [Abstract]    
Fair value, long-term debt $ 3,665,335 $ 3,677,622
Carrying amount, long-term debt $ 3,656,066 $ 3,613,059