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ACQUISITIONS Table 3 - Navigator Pro Forma Information (Details) - Navigator Acquisition [Member] - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Business Acquisition [Line Items]    
Revenues $ 1,828,418 $ 1,782,932
Net income $ 127,433 $ 78,664
Basic net income per common unit $ 0.31 $ 0.01
Diluted net income per common unit $ 0.31 $ 0.01