GOODWILL, RADIO BROADCASTING LICENSES AND OTHER INTANGIBLE ASSETS - Radio Market Reporting Units (Details) - USD ($) $ in Millions	Dec. 31, 2020	Oct. 01, 2020	Sep. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Oct. 01, 2019
Schedule of Goodwill, Radio Broadcasting Licenses And Other Intangible Assets [Line Items]
Impairment charge (in millions)	$ 84.4				$ 10.6
Radio Market Reporting Units [Member]
Schedule of Goodwill, Radio Broadcasting Licenses And Other Intangible Assets [Line Items]
Impairment charge (in millions)		$ 0.0	$ 10.0	$ 5.9		$ 0.0
Discount Rate		9.00%	9.00%	9.50%		9.00%
Radio Market Reporting Units [Member] | Minimum [Member]
Schedule of Goodwill, Radio Broadcasting Licenses And Other Intangible Assets [Line Items]
Year 1 Market Revenue Growth Rate Range		(12.90%)	(26.60%)	(14.50%)		(7.60%)
Long-term Market Revenue Growth Rate Range (Years 6 - 10)		0.70%	0.90%	0.90%		0.70%
Mature Market Share Range		6.80%	8.40%	11.10%		7.10%
Mature Operating Profit Margin Range		27.70%	27.70%	29.40%		26.80%
Radio Market Reporting Units [Member] | Maximum [Member]
Schedule of Goodwill, Radio Broadcasting Licenses And Other Intangible Assets [Line Items]
Year 1 Market Revenue Growth Rate Range		25.90%	34.70%	(12.90%)		49.30%
Long-term Market Revenue Growth Rate Range (Years 6 - 10)		1.10%	1.10%	1.10%		1.10%
Mature Market Share Range		16.80%	12.70%	13.00%		17.00%
Mature Operating Profit Margin Range		49.10%	48.10%	39.00%		47.60%