LEASES - Summary of Operating Lease Costs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 8.8	$ 8.5
Operating cash flow - Operating leases	9.4	8.4
New ROU assets - Operating leases	$ 2.8	$ 5.6
Weighted average remaining lease term - Operating leases	5 years 6 months	6 years 3 months 18 days
Weighted average discount rate - Operating leases	9.50%	10.30%
Third-Party
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 8.0	$ 7.6
Related-Party
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 0.8	$ 0.9