LEASES - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Lessee, Lease, Description [Line Items]
Rent expense	$ 2,828	$ 2,835
Rental income under subleases, before ASU 2016-02	462	438
Future rental receipts due from related party	4,137
Finance lease not yet commenced, liability	$ 992
Lease not yet commenced coverage periods	10 years
Operating Lease Of One Dialysis Clinic To Noncontrolling Interest Member
Lessee, Lease, Description [Line Items]
Rental income under subleases, before ASU 2016-02		257
Facility Space to Noncontrolling Interest Members
Lessee, Lease, Description [Line Items]
Rental income under subleases, before ASU 2016-02	$ 233
Facility Space to Nephrologist Partners
Lessee, Lease, Description [Line Items]
Rental income under subleases, before ASU 2016-02	$ 462	$ 438
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