NATURE OF OPERATIONS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenue Recognition, Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Revenue	$ 893,325	$ 766,261	$ 730,143	$ 665,352	$ 712,512	$ 644,532	$ 652,235	$ 626,936	$ 3,055,081	$ 2,636,215	$ 2,622,510
Broadcast
Disaggregation of Revenue [Line Items]
Revenue									2,714,663	2,393,641	2,416,985
Other
Disaggregation of Revenue [Line Items]
Revenue									340,418	242,574	205,525
Advertising revenue
Disaggregation of Revenue [Line Items]
Revenue									1,559,727	1,369,401	1,508,333
Advertising revenue | Broadcast
Disaggregation of Revenue [Line Items]
Revenue									1,484,188	1,314,999	1,480,157
Advertising revenue | Other
Disaggregation of Revenue [Line Items]
Revenue									75,539	54,402	28,176
Distribution revenue
Disaggregation of Revenue [Line Items]
Revenue									1,298,627	1,139,850	955,936
Distribution revenue | Broadcast
Disaggregation of Revenue [Line Items]
Revenue									1,185,800	1,032,838	890,554
Distribution revenue | Other
Disaggregation of Revenue [Line Items]
Revenue									112,827	107,012	65,382
Other media and non-media revenues
Disaggregation of Revenue [Line Items]
Revenue									196,727	126,964	158,241
Other media and non-media revenues | Broadcast
Disaggregation of Revenue [Line Items]
Revenue									44,675	45,804	46,274
Other media and non-media revenues | Other
Disaggregation of Revenue [Line Items]
Revenue									$ 152,052	$ 81,160	$ 111,967