INTANGIBLE ASSETS AND GOODWILL (Details) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017 USD ($) number	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Changes in broadcasting licenses [Line Items]
Beginning of period balance	$ 823,195	$ 807,381
Consolidation of a VIE	(15,738)	15,738
Acquisition of radio stations	17,174	0
Assets held for sale	(54,518)	0
Deconsolidation of a subsidiary	0	(36)
Acquisition - other	0	112
Dispositions	(13,500)	0
Indefinitelived Intangible Assets Acquired Through Exchange	0	0
Ending period balance	$ 756,613	823,195
Market approach for step one goodwill analysis [Abstract]
Income model years used for the discounted cash flow approach | number	10
Changes in goodwill [Roll Forward]
Goodwill before cumulative loss on impairment		158,333	$ 158,244
Accumulated loss on impairment		(125,615)	$ (125,615)
Beginning balance after cumulative loss on impairment	$ 32,718	32,629
Loss on impairment during the year	(441)	0
Acquisition	43	0
Dispositions	0	(3)
Assets held for sale	(266)	0
Deconsolidation of a subsidiary	0	0
Goodwill Acquired Through Exchange	0	0
Adjustments to acquired goodwill	0	92
Ending balance	$ 32,054	$ 32,718