DESCRIPTION OF BUSINESS AND ACCOUNTING POLICIES - Impairment of Long-Lived Assets (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Finite-Lived Intangible Assets [Line Items]
Impairment of long-lived assets held-for-use	$ 0.9	$ 1.8	$ 3.5	$ 1.8
Technology and development
Finite-Lived Intangible Assets [Line Items]
Impairment of long-lived assets held-for-use	0.6	0.9	2.5	0.9
General and administrative
Finite-Lived Intangible Assets [Line Items]
Impairment of long-lived assets held-for-use	$ 0.3	$ 0.9	$ 1.0	$ 0.9