Condensed Consolidated Statements of Income and Comprehensive Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Operating Revenue:
Total Operating Revenue	$ 524.1	$ 557.9	$ 1,038.0	$ 1,090.3
Costs and Expenses:
Operating costs	(426.3)	(472.8)	(874.6)	(939.9)
Income from SSAT	3.7	0.9	7.7	9.4
Selling, general and administrative	(50.3)	(55.0)	(106.9)	(111.3)
Total Costs and Expenses	(472.9)	(526.9)	(973.8)	(1,041.8)
Operating Income	51.2	31.0	64.2	48.5
Interest expense	(8.2)	(6.1)	(16.8)	(10.7)
Other income (expense), net	1.5	0.8	2.1	1.4
Income before Income Taxes	44.5	25.7	49.5	39.2
Income taxes	(11.7)	(7.3)	(12.9)	(8.3)
Net Income	32.8	18.4	36.6	30.9
Other Comprehensive Income (Loss), Net of Income Taxes:
Net Income	32.8	18.4	36.6	30.9
Other Comprehensive Income (Loss):
Amortization of prior service cost	(1.1)	(1.2)	(2.3)	(2.3)
Amortization of net loss	1.3	0.9	2.6	1.8
Other adjustments	(0.1)	(0.2)	(0.8)	(0.2)
Total Other Comprehensive Income (Loss)	0.1	(0.5)	(0.5)	(0.7)
Comprehensive Income	$ 32.9	$ 17.9	$ 36.1	$ 30.2
Basic Earnings Per-Share: (in dollars per share)	$ 0.76	$ 0.43	$ 0.85	$ 0.72
Diluted Earnings Per-Share: (in dollars per share)	$ 0.76	$ 0.43	$ 0.85	$ 0.72
Weighted Average Number of Shares Outstanding:
Basic (in shares)	43.1	42.8	43.0	42.8
Diluted (in shares)	43.3	43.2	43.3	43.2
Ocean Transportation
Operating Revenue:
Total Operating Revenue	$ 410.8	$ 415.4	$ 811.7	$ 813.3
Logistics
Operating Revenue:
Total Operating Revenue	$ 113.3	$ 142.5	$ 226.3	$ 277.0