GOODWILL AND OTHER INTANGIBLE ASSETS - Carrying Amount and Accumulated Amortization of Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Finite-Lived Intangible Assets [Line Items]
Total gross intangible assets	$ 530,955		$ 530,955
Total accumulated amortization	(172,404)		(164,935)
Total intangible assets, net	358,551		366,020
Amortization expense for intangible assets	7,500	$ 8,700
Referral sources
Finite-Lived Intangible Assets [Line Items]
Total gross intangible assets	482,407		482,200
Total accumulated amortization	(144,525)		(137,613)
Trademarks/names
Finite-Lived Intangible Assets [Line Items]
Total gross intangible assets	47,718		47,718
Total accumulated amortization	(27,476)		(26,936)
Other amortizable intangible assets
Finite-Lived Intangible Assets [Line Items]
Total gross intangible assets	830		1,037
Total accumulated amortization	$ (403)		$ (386)