Condensed Consolidated Statements of Income and Comprehensive Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Operating Revenue:
Ocean Transportation	$ 406.6	$ 392.7	$ 785.9	$ 762.7
Logistics	150.5	119.8	282.6	224.2
Total Operating Revenue	557.1	512.5	1,068.5	986.9
Costs and Expenses:
Operating costs	(465.9)	(422.4)	(905.2)	(834.2)
Equity in income of Terminal Joint Venture	9.1	6.9	19.6	11.8
Selling, general and administrative	(54.3)	(50.0)	(108.2)	(100.3)
Total Costs and Expenses	(511.1)	(465.5)	(993.8)	(922.7)
Operating Income	46.0	47.0	74.7	64.2
Interest expense	(5.0)	(6.3)	(10.0)	(12.6)
Other income (expense), net	0.4	(1.1)	1.2	(1.9)
Income before Income Taxes	41.4	39.6	65.9	49.7
Income taxes	(8.8)	(15.6)	(19.1)	(18.7)
Net Income	32.6	24.0	46.8	31.0
Other Comprehensive Income (Loss), Net of Income Taxes:
Net Income	32.6	24.0	46.8	31.0
Other Comprehensive Income (Loss):
Net gain in prior service cost		0.1		0.1
Amortization of prior service cost	(1.1)	(0.3)	(2.4)	(0.7)
Amortization of net loss	0.5	1.2	1.8	2.1
Other adjustments	(0.3)		(0.1)	0.2
Total Other Comprehensive (Loss) Income	(0.9)	1.0	(0.7)	1.7
Comprehensive Income	$ 31.7	$ 25.0	$ 46.1	$ 32.7
Basic Earnings Per-Share: (in dollars per share)	$ 0.76	$ 0.56	$ 1.10	$ 0.72
Diluted Earnings Per-Share: (in dollars per share)	$ 0.76	$ 0.55	$ 1.09	$ 0.72
Weighted Average Number of Shares Outstanding:
Basic (in shares)	42.7	43.1	42.6	43.1
Diluted (in shares)	43.0	43.3	42.9	43.3
Dividends
Cash Dividends Per-Share	$ 0.20	$ 0.19	$ 0.40	$ 0.38