LEASES - Lease Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Leases [Abstract]
Cost of goods sold before depreciation, depletion and amortization	$ 4.8	$ 6.1	$ 10.3	$ 12.0
Selling, general and administrative expenses	0.7	0.5	1.4	1.0
Total operating lease cost	5.5	6.6	11.7	13.0
Depreciation, depletion and amortization	3.9	2.9	7.6	5.6
Interest expense, net	0.7	0.7	1.5	1.3
Total finance lease cost	4.6	3.6	9.1	6.9
Total lease cost	10.1	10.2	20.8	19.9
Short-term lease and variable lease costs	$ 1.0	$ 1.8	$ 2.7	$ 3.3