Condensed Consolidated Statements of Income and Comprehensive Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Operating Revenue:
Ocean Transportation	$ 392.7	$ 370.9	$ 762.7	$ 737.0
Logistics	119.8	96.8	224.2	184.9
Total Operating Revenue	512.5	467.7	986.9	921.9
Costs and Expenses:
Operating costs	(422.9)	(389.9)	(835.1)	(766.3)
Equity in income of related party Terminal Joint Venture	6.9	3.0	11.8	5.6
Selling, general and administrative	(50.6)	(44.7)	(101.3)	(90.5)
Total Costs and Expenses	(466.6)	(431.6)	(924.6)	(851.2)
Operating Income	45.9	36.1	62.3	70.7
Interest expense	(6.3)	(6.5)	(12.6)	(11.4)
Income before Income Taxes	39.6	29.6	49.7	59.3
Income tax expense	(15.6)	(11.6)	(18.7)	(23.2)
Net Income	24.0	18.0	31.0	36.1
Other Comprehensive Income (Loss), Net of Income Taxes:
Net Income	24.0	18.0	31.0	36.1
Other Comprehensive Income (Loss):
Net gain in prior service cost	0.1		0.1	0.7
Amortization of prior service cost included in net periodic pension cost	(0.3)	(0.2)	(0.7)	(0.6)
Amortization of net loss included in net periodic pension cost	1.2	1.0	2.1	2.1
Other adjustments			0.2	(0.1)
Total Other Comprehensive Income	1.0	0.8	1.7	2.1
Comprehensive Income	$ 25.0	$ 18.8	$ 32.7	$ 38.2
Basic Earnings Per-Share: (in dollars per share)	$ 0.56	$ 0.42	$ 0.72	$ 0.83
Diluted Earnings Per-Share: (in dollars per share)	$ 0.55	$ 0.42	$ 0.72	$ 0.83
Weighted Average Number of Shares Outstanding:
Basic (in shares)	43.1	43.1	43.1	43.3
Diluted (in shares)	43.3	43.4	43.3	43.7
Dividends
Cash Dividends Per-Share	$ 0.19	$ 0.18	$ 0.38	$ 0.36