SIGNIFICANT ACCOUNTING POLICIES - INVESTMENT IN TERMINAL JOINT VENTURE (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Investments in affiliates
Investment in Terminal Joint Venture	$ 86.7		$ 86.7		$ 87.0
Financial information for equity method investment
Company Share of Net Income	0.9	$ 9.1	9.4	$ 19.6
SSAT
Financial information for equity method investment
Operating revenue	268.8	266.1	536.9	517.0
Operating costs and expenses	(265.0)	(240.4)	(509.2)	(460.1)
Operating Income	3.8	25.7	27.7	56.9
Net Income	$ 4.2	$ 24.3	$ 26.8	$ 55.0

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