REVENUE RECOGNITION - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Total revenues	$ 141,082		$ 282,367
Total revenues, as a percent	100.00%		100.00%
Medicaid
Disaggregation of Revenue [Line Items]
Total revenues	$ 65,603		$ 129,489
Total revenues, as a percent	46.50%		45.90%
Medicare
Disaggregation of Revenue [Line Items]
Total revenues	$ 27,863		$ 57,614
Total revenues, as a percent	19.70%		20.40%
Managed Care
Disaggregation of Revenue [Line Items]
Total revenues	$ 13,303		$ 27,515
Total revenues, as a percent	9.40%		9.70%
Private Pay and other
Disaggregation of Revenue [Line Items]
Total revenues	$ 34,313		$ 67,749
Total revenues, as a percent	24.40%		24.00%
Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of Revenue [Line Items]
Total revenues	$ 144,509	$ 142,550	$ 289,001	$ 284,050
Total revenues, as a percent	100.00%	100.00%	100.00%	100.00%
Calculated under Revenue Guidance in Effect before Topic 606 | Medicaid
Disaggregation of Revenue [Line Items]
Total revenues	$ 75,216	$ 73,510	$ 148,431	$ 146,383
Total revenues, as a percent	52.00%	51.60%	51.40%	51.50%
Calculated under Revenue Guidance in Effect before Topic 606 | Medicare
Disaggregation of Revenue [Line Items]
Total revenues	$ 36,079	$ 38,900	$ 74,217	$ 76,911
Total revenues, as a percent	25.00%	27.30%	25.70%	27.10%
Calculated under Revenue Guidance in Effect before Topic 606 | Managed Care
Disaggregation of Revenue [Line Items]
Total revenues	$ 11,888	$ 9,959	$ 23,980	$ 20,764
Total revenues, as a percent	8.20%	7.00%	8.30%	7.30%
Calculated under Revenue Guidance in Effect before Topic 606 | Private Pay and other
Disaggregation of Revenue [Line Items]
Total revenues	$ 21,326	$ 20,181	$ 42,373	$ 39,992
Total revenues, as a percent	14.80%	14.10%	14.60%	14.10%