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SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)
12 Months Ended
Dec. 31, 2020
USD ($)
segment
Dec. 31, 2019
USD ($)
radioMarket
Dec. 31, 2018
USD ($)
radioMarket
Nov. 30, 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 48 28
FDIC insured amount | $ $ 250,000        
Advertising cost incurred | $ $ 1,200,000 $ 7,100,000 $ 3,600,000    
Capitalized computer software, amortization period 3 years