REVENUE RECOGNITION - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Total revenues	$ 141,431		$ 423,798
Total revenues, as a percent	100.00%		100.00%
Medicaid
Disaggregation of Revenue [Line Items]
Total revenues	$ 68,929		$ 198,418
Total revenues, as a percent	48.70%		46.80%
Medicare
Disaggregation of Revenue [Line Items]
Total revenues	$ 26,997		$ 84,611
Total revenues, as a percent	19.10%		20.00%
Managed Care
Disaggregation of Revenue [Line Items]
Total revenues	$ 12,404		$ 39,919
Total revenues, as a percent	8.80%		9.40%
Private Pay and other
Disaggregation of Revenue [Line Items]
Total revenues	$ 33,101		$ 100,850
Total revenues, as a percent	23.40%		23.80%
Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of Revenue [Line Items]
Total revenues	$ 145,065	$ 146,377	$ 434,066	$ 430,427
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	$ 78,200	$ 77,027	$ 226,631	$ 223,410
Total revenues, as a percent	53.90%	52.60%	52.20%	51.90%
Calculated under Revenue Guidance in Effect before Topic 606 | Medicare
Disaggregation of Revenue [Line Items]
Total revenues	$ 34,933	$ 36,449	$ 109,150	$ 113,360
Total revenues, as a percent	24.10%	24.90%	25.10%	26.30%
Calculated under Revenue Guidance in Effect before Topic 606 | Managed Care
Disaggregation of Revenue [Line Items]
Total revenues	$ 10,874	$ 10,992	$ 34,854	$ 31,756
Total revenues, as a percent	7.50%	7.50%	8.00%	7.40%
Calculated under Revenue Guidance in Effect before Topic 606 | Private Pay and other
Disaggregation of Revenue [Line Items]
Total revenues	$ 21,058	$ 21,909	$ 63,431	$ 61,901
Total revenues, as a percent	14.50%	15.00%	14.70%	14.40%