SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Accounts Receivable Aging (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	$ 136,035	$ 156,541
Allowance for doubtful accounts	(46,820)	(44,730)
Net accounts receivable	89,215	111,811
Government
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	26,463	28,169
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	95,347	117,592
Patient
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	14,225	10,780
Receivables 0 to 180 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	94,750	121,590
Receivables 0 to 180 Days Past Due | Government
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	18,566	19,891
Receivables 0 to 180 Days Past Due | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	72,744	97,744
Receivables 0 to 180 Days Past Due | Patient
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	3,440	3,955
Receivables Over 180 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	41,285	34,951
Receivables Over 180 Days Past Due | Government
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	7,897	8,278
Receivables Over 180 Days Past Due | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	22,603	19,848
Receivables Over 180 Days Past Due | Patient
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	$ 10,785	$ 6,825