GENERAL AND SIGNIFICANT ACCOUNTING POLICIES (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2015	May. 29, 2015	Dec. 31, 2014
Accumulated depreciation of property and equipment	$ 1,153.8	$ 1,153.8		$ 1,107.0
Accumulated amortization of intangible assets	14.2	14.2		11.8
Goodwill	248.3	248.3		27.4
Long-term Assets
Qualified withdrawals from CCF	(91.5)	(93.7)
Long-term Assets | Horizon vessels
Qualified withdrawals from CCF	(91.5)	(91.5)
Long-term Assets | Eligible Accounts Receivable Assigned to CCF
CCF Balance	176.4	176.4		150.7
Long-term Assets | CCF Cash Deposits and Withdrawals
Cash Deposits Into CCF	75.7	77.9
CCF Balance	11.7	11.7		27.5
Other Long-term Assets
Other long term assets
Deferred dry-docking costs	52.9	52.9		47.5
Vessel and crane spare parts	11.5	11.5		7.7
Other assets	15.0	15.0		$ 14.1
Horizon
Intangibles - Customer relationships			$ 140.0
Goodwill	220.9	220.9	$ 220.9
Customer relationships | Horizon
Intangibles - Customer relationships	$ 140.0	$ 140.0