NOTES PAYABLE, REVOLVING CREDIT FACILITY AND CAPITAL LEASES - Schedule of Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Equipment notes payable at interest rates ranging from 3.3% to 5.6%, due through 2020, collateralized by medical equipment	$ 632	$ 195
Obligations under capital leases at interest rates ranging from 4.3% to 11.2%, due through 2022, collateralized by medical and office equipment	12,119	6,538
Total debt obligations	672,279	609,127
Less current portion	(39,267)	(34,090)
Long-term portion debt obligations	633,012	575,037
Promissory note
Debt Instrument [Line Items]
Promissory note payable to the former owner of a practice acquired at an interest rate of 1.5% due through 2019	199	592
Term Loan \| First Lien Term Loans
Debt Instrument [Line Items]
Debt	587,191	620,272
Discount on First Lien Term Loans	(15,112)	(18,470)
Term Loan \| Term Loan Agreement collateralized by NJIN's tangible and intangible assets
Debt Instrument [Line Items]
Debt	59,250	0
Line of Credit \| Revolving Credit Facility
Debt Instrument [Line Items]
Debt	$ 28,000	$ 0

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