REPORTABLE SEGMENTS (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($) segment	Mar. 31, 2018 USD ($)
Segment results
Number of reportable segments | segment	2
Total Operating Revenue	$ 532.4	$ 511.4
Total Operating Income	17.5	28.7
Interest expense, net	(4.6)	(5.0)
Other income (expense), net	0.6	0.8
Income before Income Taxes	13.5	24.5
Income tax expense	(1.0)	(10.3)
Net Income	12.5	14.2
Equity in income of Terminal Joint Venture	8.5	10.5
Operating segments
Segment results
Total Operating Revenue	532.4	511.4
Total Operating Income	17.5	28.7
Intersegment Eliminations
Segment results
Total Operating Revenue	21.8	18.3
Ocean Transportation
Segment results
Total Operating Revenue	397.9	379.3
Ocean Transportation | Operating segments
Segment results
Total Operating Revenue	397.9	379.3
Total Operating Income	9.4	24.5
Logistics
Segment results
Total Operating Revenue	134.5	132.1
Logistics | Operating segments
Segment results
Total Operating Revenue	134.5	132.1
Total Operating Income	$ 8.1	$ 4.2