PROPERTY, PLANT AND EQUIPMENT, INTANGIBLE ASSETS AND GOODWILL - Annual Impairment Test to Indefinite-lived Intangible Assets (Narrative) (Details) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2018 USD ($) market	Dec. 31, 2017 USD ($) market	Dec. 31, 2016 USD ($) market
Regulatory Assets [Line Items]
Period over which the Company forecasts revenue, expenses, and cash flows		10 years
Billboard permits
Regulatory Assets [Line Items]
Number of markets | market		1
FCC licenses
Regulatory Assets [Line Items]
Impairment charge			$ 6.0	$ 0.7
Number of markets | market			1	1
iHM
Regulatory Assets [Line Items]
Impairment charge		$ 33.1
Americas Outdoor Advertising | Billboard permits
Regulatory Assets [Line Items]
Impairment charge	$ 7.8