SIGNIFICANT ACCOUNTING POLICIES - CASH AND ACCOUNTS RECEIVABLE (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash and Cash Equivalents
Outstanding checks in excess of funds on deposits	$ 13.8	$ 16.4
Restricted cash	7.2	4.9
Allowance for doubtful accounts
Balance at Beginning of year	4.8	4.6	$ 4.2
Expense	0.6	0.8	1.0
Write-offs and Other	(1.1)	(0.6)	(0.6)
Balance at End of Year	4.3	4.8	$ 4.6
Prepaid and Other Assets:
Prepaid fuel	13.7	16.3
Prepaid insurance and insurance related receivables	13.4	12.6
Income tax receivables	12.8	26.8
Restricted cash - vessel construction obligations	7.2	4.9
Prepaid operating expenses	5.7	6.8
Other	9.7	7.7
Total	62.5	75.1
Other Long-term Assets
Vessel and equipment spare parts	12.4	13.1
Income tax receivables	11.5	21.5
Insurance related receivables	10.6	11.2
Deferred charges and other	3.3	3.7
Total	$ 37.8	$ 49.5