SIGNIFICANT ACCOUNTING POLICIES - INVESTMENT IN SSAT (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Investments in affiliates
Investment in Terminal Joint Venture	$ 47.5		$ 48.7
Financial information for equity method investment
Company Share of Net Income	9.2	$ 4.0
Ocean Transportation
Financial information for equity method investment
Company Share of Net Income	9.2	4.0
SSAT
Investments in affiliates
Investment in Terminal Joint Venture	47.5		$ 48.7
Financial information for equity method investment
Operating revenue	306.1	278.9
Operating costs and expenses	(273.1)	(265.4)
Operating Income	33.0	13.5
Net Income	28.9	13.0
Company Share of Net Income	$ 9.2	$ 4.0