REPORTABLE SEGMENTS (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) segment	Jun. 30, 2015 USD ($)
Segment results
Number of segments | segment			2
Operating Revenue	$ 467.7	$ 447.6	$ 921.9	$ 845.8
Operating Income	36.1	33.7	70.7	78.6
Interest expense	(6.5)	(4.6)	(11.4)	(8.9)
Income before Income Taxes	29.6	29.1	59.3	69.7
Income taxes	(11.6)	(19.2)	(23.2)	(34.8)
Net Income	18.0	9.9	36.1	34.9
Operating segments
Segment results
Operating Income	36.1	33.7	70.7	78.6
Ocean Transportation | Operating segments
Segment results
Operating Revenue	370.9	346.7	737.0	652.2
Operating Income	33.9	31.4	66.9	75.3
Logistics | Operating segments
Segment results
Operating Revenue	96.8	100.9	184.9	193.6
Operating Income	$ 2.2	$ 2.3	$ 3.8	$ 3.3