Condensed Consolidated Statements of Income and Comprehensive Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Operating Revenue:
Ocean Transportation	$ 437.3	$ 419.2	$ 1,223.2	$ 1,181.9
Logistics	152.1	124.7	434.7	348.9
Total Operating Revenue	589.4	543.9	1,657.9	1,530.8
Costs and Expenses:
Operating costs	(485.5)	(439.9)	(1,390.7)	(1,274.1)
Equity in income of Terminal Joint Venture	9.2	7.5	28.8	19.3
Selling, general and administrative	(54.5)	(53.2)	(162.7)	(153.5)
Total Costs and Expenses	(530.8)	(485.6)	(1,524.6)	(1,408.3)
Operating Income	58.6	58.3	133.3	122.5
Interest expense	(4.4)	(6.2)	(14.4)	(18.8)
Other income (expense), net	0.7	3.5	1.9	1.6
Income before Income Taxes	54.9	55.6	120.8	105.3
Income taxes	(13.3)	(21.5)	(32.4)	(40.2)
Net Income	41.6	34.1	88.4	65.1
Other Comprehensive Income (Loss), Net of Income Taxes:
Net Income	41.6	34.1	88.4	65.1
Other Comprehensive Income (Loss):
Net gain in prior service cost		0.7		0.8
Amortization of prior service cost	(1.1)	(2.2)	(3.5)	(2.9)
Amortization of net loss	1.1	1.0	2.9	3.1
Other adjustments	0.1			0.2
Total Other Comprehensive Income (Loss)	0.1	(0.5)	(0.6)	1.2
Comprehensive Income	$ 41.7	$ 33.6	$ 87.8	$ 66.3
Basic Earnings Per-Share: (in dollars per share)	$ 0.97	$ 0.79	$ 2.07	$ 1.51
Diluted Earnings Per-Share: (in dollars per share)	$ 0.97	$ 0.79	$ 2.06	$ 1.50
Weighted Average Number of Shares Outstanding:
Basic (in shares)	42.7	42.9	42.7	43.0
Diluted (in shares)	43.1	43.2	43.0	43.3