SIGNIFICANT ACCOUNTING POLICIES - ACCRUED AND OTHER LIABILITIES (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Intangible assets
Impairment charges related to finite-lived intangible assets	$ 0.0	$ 0.0	$ 0.0
Impairment charges related to indefinite-lived intangible assets and goodwill for impairment	0.0	0.0	$ 0.0
Accrued and other liabilities
Payroll and vacation	29.2	28.5
Employee incentives and other	25.9	14.7
Uninsured risks and related liabilities - short term	7.0	12.6
Multi-employer withdrawal liability - short-term (see Note 12)	10.6	10.8
Income tax liabilities	11.7	2.3
Deferred revenues	4.2	6.9
Interest on debt	3.4	4.9
Pension and post-retirement liabilities - short term (see Note 11)	2.7	3.1
Other short-term liabilities	2.1	2.2
Total	96.8	86.0
Other long-term liabilities
Pension and post-retirement liabilities (see Note 11)	82.0	73.4
Multi-employer withdrawal liability (see Note 12)	52.8	54.8
Uninsured risks and related liabilities	25.4	26.6
Other long-term liabilities	5.6	2.6
Total	$ 165.8	$ 157.4
Customer Relationships. | Maximum
Intangible assets
Expected useful lives	21 years