SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Patient Accounts Receivable Narrative (Details) - day	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Concentration Risk [Line Items]
Percentage of patient receivables outstanding	10.00%
Accounts receivable derived from Medicare	55.00%	59.00%
Historical collection rate from Medicare	99.00%
Rate of request for anticipated payment submitted for the initial episode of care	60.00%
Rate of request for anticipated payment submitted for subsequent episodes of care	50.00%
Maximum days to submit final bill from the start of episode	120
Maximum days to submit final bill from the date the request for anticipated payment was paid	60
Customer Concentration Risk | Accounts Receivable | Single Payor
Concentration Risk [Line Items]
Concentration risk (percent)	11.00%