INVESTMENT IN SSAT (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Investments in affiliates
Investment in Terminal Joint Venture	$ 48.7	$ 76.2
Financial information for equity method investment
Company's share of net income	26.3	20.8	$ 36.8
Distributions Received	55.4	25.2	42.0
Current assets	305.9	289.6
Non-current assets	2,594.7	2,555.8
Total Assets	2,900.6	2,845.4
Current liabilities	511.5	436.7
Non-current liabilities	1,427.9	1,603.0
Total Liabilities and Equity	2,900.6	2,845.4
SSAT
Investments in affiliates
Increase in investment in SSAT	$ 2.2
Ocean Transportation | SSAT
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	$ 251.6	218.7	213.4
Accounts payable and accrued liabilities	29.8	63.6
Financial information for equity method investment
Company's share of net income	26.3	20.8	36.8
Current assets	294.3	300.8
Non-current assets	1,249.5	1,283.0
Total Assets	1,543.8	1,583.8
Current liabilities	238.2	201.9
Non-current liabilities	1,179.9	1,179.2
Equity	125.7	202.7
Total Liabilities and Equity	1,543.8	1,583.8
Operating revenue	1,091.6	1,098.3	1,074.2
Operating costs and expenses	1,003.2	1,035.3	963.7
Operating Income	88.4	63.0	110.5
Net Income	$ 76.6	$ 57.2	$ 104.9