GENERAL AND SIGNIFICANT ACCOUNTING POLICIES - INVESTMENT IN SSAT (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	Sep. 16, 2022	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Investments in affiliates
Investment in SSAT		$ 87.2		$ 87.2		$ 58.7
Financial information for equity method investment
Company Share of Net Income		23.4	$ 13.0	82.1	$ 35.0
SSAT
Financial information for equity method investment
Company Share of Net Income		23.4	13.0	82.1	35.0
SSAT
Investments in affiliates
Adjustment to investment in SSAT	$ 15.5
Investment in SSAT		87.2		87.2		$ 58.7
Financial information for equity method investment
Operating revenue		369.8	316.3	1,191.3	944.6
Operating costs and expenses		(286.9)	(274.2)	(894.3)	(831.3)
Operating Income		82.9	42.1	297.0	113.3
Net Income		$ 68.9	$ 37.3	$ 247.0	$ 100.5
SSAT | SSAT Terminals Oakland
Investments in affiliates
Investment in SSAT, interest acquired (as a percent)	20.00%