REPORTABLE SEGMENTS (Details) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2022 USD ($)	Jun. 30, 2022 USD ($)	Mar. 31, 2022 USD ($)	Sep. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Sep. 30, 2022 USD ($) segment	Sep. 30, 2021 USD ($)	Dec. 31, 2021 USD ($)
Segment results
Number of segments | segment							2
Total Operating Revenue	$ 1,114.8			$ 1,071.6			$ 3,541.4	$ 2,658.3
Operating Income	335.3			377.9			1,261.0	712.0
Interest income	1.3						1.3
Interest expense	(5.0)			(5.1)			(14.3)	(17.9)
Other income (expense), net	2.5			1.8			6.3	4.7
Income before Taxes	334.1			374.6			1,254.3	698.8
Income taxes	(68.1)			(91.4)			(268.4)	(165.9)
Net Income	266.0	$ 380.7	$ 339.2	283.2	$ 162.5	$ 87.2	985.9	532.9
Deferred dry-docking amortization							18.6	18.0
Assets	4,459.0						4,459.0		$ 3,693.1
Income from SSAT	23.4			13.0			82.1	35.0
Intersegment Eliminations
Segment results
Total Operating Revenue	78.2			57.8			220.6	140.5
Ocean Transportation
Segment results
Total Operating Revenue	918.5			863.5			2,911.6	2,106.9
Operating Income	315.2			361.9			1,201.4	677.0
Income from SSAT	23.4			13.0			82.1	35.0
Ocean Transportation | Intersegment Eliminations
Segment results
Total Operating Revenue	28.0			21.8			73.8	55.6
Logistics
Segment results
Total Operating Revenue	196.3			208.1			629.8	551.4
Operating Income	20.1			16.0			59.6	35.0
Logistics | Intersegment Eliminations
Segment results
Total Operating Revenue	$ 50.2			$ 36.0			$ 146.8	$ 84.9