STOCKHOLDERS' DEFICIENCY - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Class of Stock [Line Items]
Common stock, authorized (in shares)	900,000,000	900,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Tax withholdings related to net share settlements of restricted stock units and awards	$ 1.7	$ 1.6
Treasury Stock
Class of Stock [Line Items]
Shares withheld for withholding taxes (in shares)	148,620	92,260
Class A Common Stock
Class of Stock [Line Items]
Common stock, authorized (in shares)	900,000,000
Common stock, par value (in dollars per share)	$ 0.01
Percentage ownership of outstanding common stock	86.70%
Class A Common Stock | Treasury Stock | Restricted Stock and Restricted Stock Units
Class of Stock [Line Items]
Share repurchase price (in dollars per share)	$ 10.98	$ 17.75
Class B Common Stock
Class of Stock [Line Items]
Common stock, authorized (in shares)	200,000,000
Common stock, par value (in dollars per share)	$ 0.01