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FAIR VALUE (Details) - USD ($)
$ in Thousands
Dec. 31, 2015
Dec. 31, 2014
Carrying Amount    
Fair value:    
Long-term debt $ 3,371,679 $ 3,242,470
Carrying Amount | Recurring | Level 1    
Fair value:    
Marketable securities 1,022 1,095
Estimated Fair Value | Level 2    
Fair value:    
Long-term debt 3,616,946 3,716,513
Estimated Fair Value | Recurring | Level 1    
Fair value:    
Marketable securities $ 1,151 $ 1,349