GOODWILL AND OTHER INTANGIBLE ASSETS - Carrying Amount and Accumulated Amortization of Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Total gross intangible assets	$ 483,059		$ 483,059		$ 483,059
Total accumulated amortization	(114,578)		(114,578)		(97,149)
Total intangible assets, net	368,481		368,481		385,910
Amortization expense for intangible assets	8,800	$ 4,900	17,600	$ 9,800
Referral sources
Finite-Lived Intangible Assets [Line Items]
Total gross intangible assets	438,121		438,121		438,121
Total accumulated amortization	(97,396)		(97,396)		(84,295)
Trademarks/names
Finite-Lived Intangible Assets [Line Items]
Total gross intangible assets	44,536		44,536		44,536
Total accumulated amortization	(16,946)		(16,946)		(12,748)
Other amortizable intangible assets
Finite-Lived Intangible Assets [Line Items]
Total gross intangible assets	402		402		402
Total accumulated amortization	$ (236)		$ (236)		$ (106)