INTANGIBLE ASSETS AND GOODWILL (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Changes in Intangible assets [Line Items]
Goodwill	$ 534,607	$ 539,469
Radio Broadcasting Licences [Member]
Changes in Intangible assets [Line Items]
Beginning of period balance	2,516,625	2,649,959
Assets held for sale	(17,135)	0
Acquisition of radio stations - Emmis Acquisition	0	12,785
Acquisition Of Radio Station - Jerry Lee Acquisition	0	27,346
Impairment loss	0	(148,564)
Disposition Of Radio Stations -WXTU Transaction	0	(24,901)
Ending period balance	2,499,490	2,516,625
Goodwill [Member]
Changes in Intangible assets [Line Items]
Goodwill before cumulative loss on impairment		982,663	$ 988,056
Accumulated loss on impairment		(443,194)	(126,056)
Goodwill	534,607	539,469	$ 862,000
Assets held for sale	(4,862)	0
Acquisition of radio stations - Emmis Acquisition	0	332
Acquisition Of Radio Station - Jerry Lee Acquisition	0	24,396
Disposition Of Radio Stations -WXTU Transaction	0	(8,623)
Goodwill, Impairment Loss	0	(317,138)
Adjustments to Acquired Goodwill	$ 0	$ (21,498)