Condensed Consolidated Statements of Income and Comprehensive Income - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Revenue:
Ocean Transportation	$ 1,571.8	$ 1,541.1	$ 1,498.0
Logistics	475.1	400.5	386.9
Total Operating Revenue	2,046.9	1,941.6	1,884.9
Costs and Expenses:
Operating costs	(1,717.2)	(1,617.7)	(1,510.1)
Equity in income of Terminal Joint Venture	28.2	15.8	16.5
Selling, general and administrative	(208.5)	(185.1)	(195.0)
Total Costs and Expenses	(1,897.5)	(1,787.0)	(1,688.6)
Operating Income	149.4	154.6	196.3
Interest expense	(24.2)	(24.1)	(18.5)
Income before Income Taxes	125.2	130.5	177.8
Income taxes	106.8	(49.1)	(74.8)
Net Income	232.0	81.4	103.0
Other Comprehensive (Loss) Income, Net of Income Taxes:
Net Income	232.0	81.4	103.0
Other Comprehensive Income (Loss):
Net gain in prior service cost	0.8	24.1	5.1
Amortization of prior service cost included in net periodic pension cost	(4.0)	(2.2)	(1.3)
Amortization of net loss included in net periodic pension cost	1.7	1.2	1.8
Other adjustments	0.2	0.2	0.8
Total Other Comprehensive (Loss) Income	(1.3)	23.3	6.4
Comprehensive Income	$ 230.7	$ 104.7	$ 109.4
Basic Earnings Per-Share: (in dollars per share)	$ 5.41	$ 1.89	$ 2.37
Diluted Earnings Per-Share: (in dollars per share)	$ 5.37	$ 1.87	$ 2.34
Weighted Average Number of Shares Outstanding:
Basic (in shares)	42.9	43.1	43.5
Diluted (in shares)	43.2	43.5	44.0