REVENUE RECOGNITION - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Total revenues	$ 141,285
Total revenues, as a percent	100.00%
Medicaid
Disaggregation of Revenue [Line Items]
Total revenues	$ 63,886
Total revenues, as a percent	45.20%
Medicare
Disaggregation of Revenue [Line Items]
Total revenues	$ 29,751
Total revenues, as a percent	21.10%
Managed Care
Disaggregation of Revenue [Line Items]
Total revenues	$ 14,212
Total revenues, as a percent	10.10%
Private Pay and other
Disaggregation of Revenue [Line Items]
Total revenues	$ 33,436
Total revenues, as a percent	23.60%
Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of Revenue [Line Items]
Total revenues	$ 144,492	$ 141,500
Total revenues, as a percent	100.00%	100.00%
Calculated under Revenue Guidance in Effect before Topic 606 | Medicaid
Disaggregation of Revenue [Line Items]
Total revenues	$ 73,214	$ 72,873
Total revenues, as a percent	50.70%	51.50%
Calculated under Revenue Guidance in Effect before Topic 606 | Medicare
Disaggregation of Revenue [Line Items]
Total revenues	$ 38,139	$ 38,011
Total revenues, as a percent	26.40%	26.90%
Calculated under Revenue Guidance in Effect before Topic 606 | Managed Care
Disaggregation of Revenue [Line Items]
Total revenues	$ 12,092	$ 10,806
Total revenues, as a percent	8.40%	7.60%
Calculated under Revenue Guidance in Effect before Topic 606 | Private Pay and other
Disaggregation of Revenue [Line Items]
Total revenues	$ 21,047	$ 19,810
Total revenues, as a percent	14.50%	14.00%