SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Patient Accounts Receivable Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) day	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Accounting Policies [Abstract]
Percentage of patient receivables outstanding	10.00%
Historical collection rate from Medicare	99.00%
Minimum days for accounts receivable outstanding to be fully reserved	365
Portion of accounts receivable derived from Medicare	59.00%	61.00%
Revenue adjustment to Medicare revenue | $	$ 14.4	$ 7.9	$ 6.1
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