GOODWILL AND OTHER INTANGIBLE ASSETS - Carrying Amount and Accumulated Amortization of Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Total gross intangible assets	$ 483,059		$ 483,059		$ 483,059
Total accumulated amortization	(123,293)		(123,293)		(97,149)
Total intangible assets, net	359,766		359,766		385,910
Amortization expense for intangible assets	8,800	$ 7,500	26,300	$ 17,300
Referral sources
Finite-Lived Intangible Assets [Line Items]
Total gross intangible assets	438,121		438,121		438,121
Total accumulated amortization	(103,947)		(103,947)		(84,295)
Trademarks/names
Finite-Lived Intangible Assets [Line Items]
Total gross intangible assets	44,536		44,536		44,536
Total accumulated amortization	(19,046)		(19,046)		(12,748)
Other amortizable intangible assets
Finite-Lived Intangible Assets [Line Items]
Total gross intangible assets	402		402		402
Total accumulated amortization	$ (300)		$ (300)		$ (106)