REPORTABLE SEGMENTS (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014 segment	Dec. 31, 2013	Dec. 31, 2012
Segment results
Number of segments									2us-gaap_NumberOfReportableSegments
Revenue	$ 443.5us-gaap_SalesRevenueNet	$ 441.8us-gaap_SalesRevenueNet	$ 436.4us-gaap_SalesRevenueNet	$ 392.5us-gaap_SalesRevenueNet	$ 410.9us-gaap_SalesRevenueNet	$ 415.0us-gaap_SalesRevenueNet	$ 416.6us-gaap_SalesRevenueNet	$ 394.7us-gaap_SalesRevenueNet	$ 1,714.2us-gaap_SalesRevenueNet	$ 1,637.2us-gaap_SalesRevenueNet	$ 1,560.0us-gaap_SalesRevenueNet
Operating income	49.4us-gaap_OperatingIncomeLoss	45.0us-gaap_OperatingIncomeLoss	35.7us-gaap_OperatingIncomeLoss	9.9us-gaap_OperatingIncomeLoss	17.9us-gaap_OperatingIncomeLoss	27.2us-gaap_OperatingIncomeLoss	36.5us-gaap_OperatingIncomeLoss	18.7us-gaap_OperatingIncomeLoss	140.0us-gaap_OperatingIncomeLoss	100.3us-gaap_OperatingIncomeLoss	96.7us-gaap_OperatingIncomeLoss
Interest expense, net	(4.3)us-gaap_InterestExpense	(4.4)us-gaap_InterestExpense	(4.5)us-gaap_InterestExpense	(4.1)us-gaap_InterestExpense	(3.5)us-gaap_InterestExpense	(3.6)us-gaap_InterestExpense	(3.6)us-gaap_InterestExpense	(3.7)us-gaap_InterestExpense	(17.3)us-gaap_InterestExpense	(14.4)us-gaap_InterestExpense	(11.7)us-gaap_InterestExpense
Income before income taxes	45.1	40.6	31.2	5.8	14.4	23.6	32.9	15.0	122.7	85.9	85.0
Income taxes	(17.3)us-gaap_IncomeTaxExpenseBenefit	(19.1)us-gaap_IncomeTaxExpenseBenefit	(13.1)us-gaap_IncomeTaxExpenseBenefit	(2.4)us-gaap_IncomeTaxExpenseBenefit	(7.1)us-gaap_IncomeTaxExpenseBenefit	(6.4)us-gaap_IncomeTaxExpenseBenefit	(12.8)us-gaap_IncomeTaxExpenseBenefit	(5.9)us-gaap_IncomeTaxExpenseBenefit	(51.9)us-gaap_IncomeTaxExpenseBenefit	(32.2)us-gaap_IncomeTaxExpenseBenefit	(33.0)us-gaap_IncomeTaxExpenseBenefit
Income (Loss) from Continuing Operations Attributable to Parent, Total									70.8	53.7	52.0
Loss from discontinued operations									0	0	(6.1)
Net Income	27.8us-gaap_NetIncomeLoss	21.5us-gaap_NetIncomeLoss	18.1us-gaap_NetIncomeLoss	3.4us-gaap_NetIncomeLoss	7.3us-gaap_NetIncomeLoss	17.2us-gaap_NetIncomeLoss	20.1us-gaap_NetIncomeLoss	9.1us-gaap_NetIncomeLoss	70.8us-gaap_NetIncomeLoss	53.7us-gaap_NetIncomeLoss	45.9us-gaap_NetIncomeLoss
Assets	1,401.8us-gaap_Assets				1,248.3us-gaap_Assets				1,401.8us-gaap_Assets	1,248.3us-gaap_Assets	1,174.3us-gaap_Assets
Capital expenditures									27.9	35.2	38.1
Depreciation and amortization									69.7	69.7	72.5
Ocean Transportation
Segment results
Revenue	333.2	329.5	321.1	294.6	309.4	310.1	310.0	299.9	1,278.4	1,229.4	1,189.8
Operating income	46.3	42.6	32.8	9.4	16.0	25.5	34.3	18.5	131.1	94.3	96.6
Assets	1,313.9				1,168.6				1,313.9	1,168.6	1,097.2
Capital expenditures									27.8	33.8	37.0
Depreciation and amortization									66.6	66.4	69.1
Ocean Transportation \| SSAT
Segment results
Equity in earnings from affiliates	6.6				(2.0)				6.6	(2.0)	3.2
Equity method investments	64.4				57.6				64.4	57.6	59.6
Logistics
Segment results
Revenue	110.3	112.3	115.3	97.9	101.5	104.9	106.6	94.8	435.8	407.8	370.2
Operating income	3.1	2.4	2.9	0.5	1.9	1.7	2.2	0.2	8.9	6.0	0.1
Assets	87.9				79.7				87.9	79.7	77.1
Capital expenditures									0.1	1.4	1.1
Depreciation and amortization									$ 3.1	$ 3.3	$ 3.4

Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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