Condensed Consolidated Statements of Income and Comprehensive Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Operating Revenue:
Total Operating Revenue	$ 847.4	$ 773.4	$ 1,569.5	$ 1,478.2
Costs and Expenses:
Operating costs	(646.9)	(604.7)	(1,259.1)	(1,202.2)
Income (Loss) from SSAT	1.2	(1.4)	1.6	(3.2)
Selling, general and administrative	(77.1)	(70.6)	(150.5)	(137.4)
Total Costs and Expenses	(722.8)	(676.7)	(1,408.0)	(1,342.8)
Operating Income	124.6	96.7	161.5	135.4
Interest income	18.8	8.7	27.6	16.9
Interest expense	(2.1)	(2.9)	(4.3)	(7.4)
Other income (expense), net	1.8	1.8	3.6	3.6
Income before Taxes	143.1	104.3	188.4	148.5
Income taxes	(29.9)	(23.5)	(39.1)	(33.7)
Net Income	113.2	80.8	149.3	114.8
Other Comprehensive Income (Loss), Net of Income Taxes:
Net Income (Loss)	113.2	80.8	149.3	114.8
Other Comprehensive Income (Loss):
Net change in pension and post-retirement liabilities	(0.7)	(0.9)	(1.5)	(1.7)
Other adjustments	0.3	(0.7)	(0.5)	0.7
Total Other Comprehensive Income (Loss), Net of Income Taxes	(0.4)	(1.6)	(2.0)	(1.0)
Comprehensive Income	$ 112.8	$ 79.2	$ 147.3	$ 113.8
Basic Earnings Per Share (in dollars per share)	$ 3.34	$ 2.28	$ 4.38	$ 3.21
Diluted Earnings Per Share (in dollars per share)	$ 3.31	$ 2.26	$ 4.33	$ 3.19
Weighted Average Number of Shares Outstanding:
Basic (in shares)	33.9	35.5	34.1	35.8
Diluted (in shares)	34.2	35.7	34.5	36.0
Ocean Transportation
Operating Revenue:
Total Operating Revenue	$ 689.9	$ 616.9	$ 1,268.9	$ 1,167.9
Logistics
Operating Revenue:
Total Operating Revenue	$ 157.5	$ 156.5	$ 300.6	$ 310.3