INTANGIBLE ASSETS AND GOODWILL - Goodwill (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill balance before cumulative loss on impairment as of January 1,		$ 1,024,467	$ 982,663
Accumulated loss on impairment as of January 1,		(980,547)	(443,194)
Goodwill beginning balance after cumulative loss on impairment as of January 1,		43,920	539,469
Loss on impairment (see Note 14)	$ (537,400)	0	(537,353)	$ (317,138)
Dispositions (see Note 3)		0	(4,862)
Acquisitions (see Note 3)		18,323	46,666
Measurement period adjustments to acquired goodwill		(28)	0
Ending period balance	43,920	62,215	43,920	539,469
Goodwill balance before cumulative loss on impairment as of December 31,	1,024,467	1,042,762	1,024,467	982,663
Accumulated loss on impairment as of December 31,	$ (980,547)	$ (980,547)	$ (980,547)	$ (443,194)