BUSINESS COMBINATION - CONSIDERATION PAID (Details) $ / shares in Units, $ in Millions		12 Months Ended
	May. 29, 2015 USD ($) item $ / shares	Dec. 31, 2015 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Assets acquired and liabilities assumed
Multi-employer withdrawal liabilities		$ (56.2)
Goodwill		241.6		$ 27.4	$ 27.4
Horizon
Business acquisition
Business Combination, Ownership Percentage	100.00%
Cash price (in dollars per share) | $ / shares	$ 0.72
Number of Jones Act qualified containerships | item	7
Assets acquired and liabilities assumed
Cash and cash equivalent		0.8
Accounts receivable		31.7
Other current assets		7.2
Deferred tax assets, net		45.6
Property and equipment	$ 170.4	170.4
Intangibles - Customer relationships		140.0
Other long-term assets		4.1
Accounts payable		(22.8)
Accruals and other current liabilities		(32.1)
Multi-employer withdrawal liabilities		(60.6)
Capital lease obligations		(1.6)
Horizon's debt and warrants		(467.5)
Total identifiable assets less liabilities		(184.8)
Total cash paid for common shares		(29.4)
Goodwill		$ 214.2
Horizon | Vessels
Assets acquired and liabilities assumed
Property and equipment	130.7
Horizon | Containers and equipment
Assets acquired and liabilities assumed
Property and equipment	17.9
Horizon | Terminal facilities and other property
Assets acquired and liabilities assumed
Property and equipment	9.7
Horizon | Construction in progress
Assets acquired and liabilities assumed
Property and equipment	12.1
Horizon | Customer relationships
Assets acquired and liabilities assumed
Intangibles - Customer relationships	$ 140.0
Expected useful lives	21 years
Horizon | As previously Reported
Total cash consideration
Common shares	$ 29.4
Warrants	37.1
Horizon's debt (including accrued interest and breakage fees)	428.9
Total	$ 495.4
Horizon | Adjustments
Assets acquired and liabilities assumed
Total identifiable assets less liabilities			$ (5.5)