SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Allowance for Doubtful Accounts (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) accounts_receivable	Dec. 31, 2016 USD ($)
Accounting Policies [Abstract]
Number of primary overall types of accounts receivable | accounts_receivable	3
Change in Estimate of the Collectability of Accounts Receivable
Gross accounts receivable	$ 123,434	$ 153,816
Allowance for doubtful accounts	(37,912)	(44,730)
Net accounts receivable	$ 85,522	$ 109,086
Allowance for doubtful accounts, percentage of accounts receivable	30.70%	29.10%
Decrease in allowance, due to change in estimate	$ 3,000
0 - 180 days
Change in Estimate of the Collectability of Accounts Receivable
Gross accounts receivable	86,946	$ 118,864
Over 180 days
Change in Estimate of the Collectability of Accounts Receivable
Gross accounts receivable	36,488	34,952
Government
Change in Estimate of the Collectability of Accounts Receivable
Gross accounts receivable	30,684	28,169
Government | 0 - 180 days
Change in Estimate of the Collectability of Accounts Receivable
Gross accounts receivable	20,602	19,891
Government | Over 180 days
Change in Estimate of the Collectability of Accounts Receivable
Gross accounts receivable	10,082	8,278
Commercial
Change in Estimate of the Collectability of Accounts Receivable
Gross accounts receivable	82,546	114,867
Commercial | 0 - 180 days
Change in Estimate of the Collectability of Accounts Receivable
Gross accounts receivable	63,767	95,018
Commercial | Over 180 days
Change in Estimate of the Collectability of Accounts Receivable
Gross accounts receivable	18,779	19,849
Patient
Change in Estimate of the Collectability of Accounts Receivable
Gross accounts receivable	10,204	10,780
Patient | 0 - 180 days
Change in Estimate of the Collectability of Accounts Receivable
Gross accounts receivable	2,577	3,955
Patient | Over 180 days
Change in Estimate of the Collectability of Accounts Receivable
Gross accounts receivable	$ 7,627	$ 6,825