SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Accounts Receivable Aging (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	$ 113,628	$ 123,434
Allowance for doubtful accounts	0	(37,912)
Net accounts receivable	113,628	85,522
Government
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	15,583	30,684
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	91,333	82,546
Patient
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	6,712	10,204
Receivables 0 to 180 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	94,985	86,946
Receivables 0 to 180 Days Past Due | Government
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	12,555	20,602
Receivables 0 to 180 Days Past Due | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	80,508	63,767
Receivables 0 to 180 Days Past Due | Patient
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	1,922	2,577
Receivables Over 180 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	18,643	36,488
Receivables Over 180 Days Past Due | Government
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	3,028	10,082
Receivables Over 180 Days Past Due | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	10,825	18,779
Receivables Over 180 Days Past Due | Patient
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	$ 4,790	$ 7,627