GOODWILL AND OTHER INTANGIBLE ASSETS - Carrying Amount and Accumulated Amortization of Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Total gross intangible assets	$ 483,059	$ 483,059
Total accumulated amortization	(132,007)	(97,149)
Total intangible assets, net	351,052	385,910
Referral sources
Finite-Lived Intangible Assets [Line Items]
Total gross intangible assets	438,121	438,121
Total accumulated amortization	(110,498)	(84,295)
Trademarks/names
Finite-Lived Intangible Assets [Line Items]
Total gross intangible assets	44,536	44,536
Total accumulated amortization	(21,146)	(12,748)
Other amortizable intangible assets
Finite-Lived Intangible Assets [Line Items]
Total gross intangible assets	402	402
Total accumulated amortization	$ (363)	$ (106)