SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)			12 Months Ended
	Jan. 01, 2019 USD ($)	Jan. 01, 2017 USD ($)	Dec. 31, 2019 USD ($) segment radioMarket	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) radioMarket	Nov. 17, 2017 radioMarket	Nov. 01, 2017 radioMarket	Oct. 31, 2017 radioMarket
Accounting Policies [Abstract]
Number of reportable segments | segment			1
Number of operating segments | segment			1
Number of radio markets | radioMarket			47		48	28	48	28
FDIC insured amount			$ 250,000
Restricted cash			0	$ 69,365,000
Advertising cost incurred			$ 7,100,000	3,600,000	$ 700,000
Capitalized computer software, amortization period			3 years
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income tax expense (benefit)			$ 37,206,000	$ (4,153,000)	$ (257,085,000)
Operating lease right-of-use assets			259,613,000
Operating lease liability			$ 288,681,000
Cumulative gain recognized from sale leaseback transaction,	$ 4,700,000
Tax on gain of sales lease buyback transaction	1,700,000
Accounting Standards Update 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment to accumulated deficit		$ 5,100,000
Income tax expense (benefit)		(4,600,000)
Stock-based compensation forfeitures		$ 500,000
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets	288,700,000
Operating lease liability	306,200,000
Cumulative gain recognized from sale leaseback transaction,	4,700,000
Tax on gain of sales lease buyback transaction	$ 1,700,000