GOODWILL AND DEFINITE-LIVED INTANGIBLE ASSETS - Definite-lived intangible assets (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
DEFINITE-LIVED INTANGIBLE ASSETS
Gross Carrying Amount	$ 307,779			$ 307,779		$ 384,039
Accumulated Amortization	(151,981)			(151,981)		(143,229)
Net Carrying Amount	155,798			155,798		$ 240,810
Amortization expense	11,962		$ 17,190	39,520	$ 51,360
Impairment	34,173	$ 17,979		$ 52,152
Customer relationships
DEFINITE-LIVED INTANGIBLE ASSETS
Weighted Average Amortization Period (in years)				9 years 3 months 18 days		9 years 9 months 18 days
Gross Carrying Amount	52,000			$ 52,000		$ 100,200
Accumulated Amortization						(1,238)
Net Carrying Amount	52,000			$ 52,000		$ 98,962
Patient relationships
DEFINITE-LIVED INTANGIBLE ASSETS
Weighted Average Amortization Period (in years)				5 years 3 months 18 days		5 years 10 months 24 days
Gross Carrying Amount	174,500			$ 174,500		$ 170,100
Accumulated Amortization	(81,535)			(81,535)		(67,964)
Net Carrying Amount	92,965			$ 92,965		$ 102,136
Trade names and trademarks
DEFINITE-LIVED INTANGIBLE ASSETS
Weighted Average Amortization Period (in years)				2 years 8 months 12 days		1 year 9 months 18 days
Gross Carrying Amount	29,620			$ 29,620		$ 30,650
Accumulated Amortization	(25,171)			(25,171)		(20,270)
Net Carrying Amount	4,449			$ 4,449		$ 10,380
Non-compete employment agreements
DEFINITE-LIVED INTANGIBLE ASSETS
Weighted Average Amortization Period (in years)				1 year 3 months 18 days		1 year 7 months 6 days
Gross Carrying Amount	51,659			$ 51,659		$ 61,389
Accumulated Amortization	(45,275)			(45,275)		(44,100)
Net Carrying Amount	$ 6,384			$ 6,384		$ 17,289
Physician relationships
DEFINITE-LIVED INTANGIBLE ASSETS
Weighted Average Amortization Period (in years)						4 years 9 months 18 days
Gross Carrying Amount						$ 21,700
Accumulated Amortization						(9,657)
Net Carrying Amount						$ 12,043