INVESTMENT IN TERMINAL JOINT VENTURE (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investments in affiliates
Investment in related party Terminal Joint Venture	$ 93.2	$ 82.4
Financial information for equity method investment
Equity in income of Terminal Joint Venture	28.2	15.8	$ 16.5
Distributions Received	17.5		14.0
Current assets	181.0	147.7
Noncurrent assets	161.8	138.5
Total assets	342.8	286.2
Current liabilities	65.3	48.9
Noncurrent liabilities	23.8	14.8
Equity	253.7	222.5
Total Liabilities and Equity	342.8	286.2
Operating revenue	933.5	740.9	621.0
Operating costs and expenses	850.2	706.5	610.2
Operating Income (loss)	83.3	34.4	10.8
Net Income	$ 80.9	45.1	44.9
SSAT | Ocean Transportation
Investments in affiliates
Ownership interest accounted in the related party terminal joint venture (as a percent)	35.00%
Cost of services from transactions with unconsolidated affiliate	$ 181.3	177.8	$ 174.1
Accounts payable and accrued liabilities	$ 22.8	$ 16.7