GOODWILL AND OTHER INTANGIBLE ASSETS - Carrying Amount and Accumulated Amortization of Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Total gross intangible assets	$ 530,955	$ 483,059
Total accumulated amortization	(164,935)	(132,007)
Total intangible assets, net	366,020	351,052
Referral sources
Finite-Lived Intangible Assets [Line Items]
Total gross intangible assets	482,200	438,121
Total accumulated amortization	(137,613)	(110,498)
Trademarks/names
Finite-Lived Intangible Assets [Line Items]
Total gross intangible assets	47,718	44,536
Total accumulated amortization	(26,936)	(21,146)
Other amortizable intangible assets
Finite-Lived Intangible Assets [Line Items]
Total gross intangible assets	1,037	402
Total accumulated amortization	$ (386)	$ (363)