NET REVENUE AND ACCOUNTS RECEIVABLE - Aging of Accounts Receivable (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net	$ 120,824	$ 114,864
Government
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net	26,742	23,947
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net	83,426	82,028
Patient
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net	10,656	8,889
0 - 180 days
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net	88,664	87,229
0 - 180 days | Government
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net	19,202	17,849
0 - 180 days | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net	65,746	67,288
0 - 180 days | Patient
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net	3,716	2,092
Over 180 days
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net	32,160	27,635
Over 180 days | Government
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net	7,540	6,098
Over 180 days | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net	17,680	14,740
Over 180 days | Patient
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net	$ 6,940	$ 6,797