GOODWILL AND INTANGIBLE ASSETS - INTANGIBLE ASSETS (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Feb. 28, 2023	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Intangible assets
Gross Amount		$ 274.1	$ 278.3
Total Intangible Assets, net		159.4	176.4
Aggregate intangible asset amortization		12.8	13.6	$ 11.4
Less: Accumulated Amortization		(114.7)	(101.9)
Total Customer Relationships, net		132.1
Estimated amortization expenses related to intangibles
2025		13.0
2026		12.5
2027		12.6
2028		12.5
2029		12.5
Thereafter		69.0
Total Customer Relationships, net		$ 132.1
Customer Relationships | Maximum
Intangible assets
Expected useful life		21 years
Ocean Transportation | Customer Relationships
Intangible assets
Gross Amount		$ 140.6	140.6
Total Intangible Assets, net		76.2	82.7
Less: Accumulated Amortization		$ (64.4)	(57.9)
Ocean Transportation | Customer Relationships | Horizon
Intangible assets
Expected useful life		21 years
Finite-Lived intangible assets acquired		$ 140.6
Logistics
Intangible assets
Gross Amount		133.5	137.7
Total Intangible Assets, net		83.2	93.7
Less: Accumulated Amortization		(50.3)	(44.0)
Logistics | Trade Names
Intangible assets
Indefinite-Lived intangible asset		27.3	27.3
Logistics | Span Alaska | Trade Names
Intangible assets
Indefinite-Lived intangible asset acquired		27.3
Logistics | Customer Relationships
Intangible assets
Gross Amount		106.2	110.4
Total Intangible Assets, net		55.9	66.4
Expected useful life	7 years
Finite-Lived intangible assets acquired	$ 16.5
Less: Accumulated Amortization		$ (50.3)	$ (44.0)
Logistics | Customer Relationships | Minimum
Intangible assets
Expected useful life		3 years
Logistics | Customer Relationships | Maximum
Intangible assets
Expected useful life		13 years
Logistics | Customer Relationships | Span Alaska
Intangible assets
Total Intangible Assets, net		$ 79.3
Expected useful life		20 years