GOODWILL AND OTHER INTANGIBLE ASSETS - Carrying Amount and Accumulated Amortization of Intangible Assets (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Goodwill impairment	$ 0	$ 0	$ 0
Total gross intangible assets	483,059,000	293,943,000
Total accumulated amortization	(97,149,000)	(74,230,000)
Total intangible assets, net	385,910,000	219,713,000
Amortization expense for intangible assets	$ 26,100,000	19,600,000	$ 19,800,000
Weighted average amortization period of intangibles	15 years 11 months
Referral sources
Finite-Lived Intangible Assets [Line Items]
Total gross intangible assets	$ 438,121,000	257,792,000
Total accumulated amortization	$ (84,295,000)	(63,353,000)
Weighted average amortization period of intangibles	17 years 1 month
Trademarks/names
Finite-Lived Intangible Assets [Line Items]
Total gross intangible assets	$ 44,536,000	32,000,000
Total accumulated amortization	$ (12,748,000)	(8,000,000)
Weighted average amortization period of intangibles	4 years 2 months
Other amortizable intangible assets
Finite-Lived Intangible Assets [Line Items]
Total gross intangible assets	$ 402,000	4,151,000
Total accumulated amortization	$ (106,000)	$ (2,877,000)
Weighted average amortization period of intangibles	1 year 6 months