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REVENUE - Narrative (Details) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]        
Trade and barter revenues $ 927,747 $ 743,829 $ 2,495,188 $ 2,011,248
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-10-01        
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]        
Revenue, remaining performance obligation $ 220,500   $ 220,500  
Revenue, remaining performance obligation, period 5 years   5 years  
Advertising Trade and Barter Transactions        
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]        
Trade and barter revenues $ 4,900 $ 2,300 $ 9,400 $ 7,500