LEASES - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Lessee, Lease, Description [Line Items]
Rent expense	$ 2,944	$ 2,818	$ 5,772	$ 5,653
Rental income under subleases	473	465	936	903
Future rental receipts due from related party	3,905		3,905
Operating lease not yet commenced, liability	1,028		1,028
Finance lease not yet commenced, liability	$ 992		$ 992
Finance lease not yet commenced lease term	10 years		10 years
Operating lease not yet commenced lease term	10 years		10 years
Facility Space to Noncontrolling Interest Members
Lessee, Lease, Description [Line Items]
Rental income under subleases	$ 233	257	$ 465	514
Facility Space to Nephrologist Partners
Lessee, Lease, Description [Line Items]
Rental income under subleases	$ 473	$ 465	$ 936	$ 903
Minimum
Lessee, Lease, Description [Line Items]
Lease agreements cover periods			5 years
Lease agreements renewal option period			5 years
Maximum
Lessee, Lease, Description [Line Items]
Lease agreements cover periods			15 years
Lease agreements renewal option period			10 years