SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Concentration of Risk and Taxes (Details) $ in Thousands	12 Months Ended
Dec. 31, 2016 USD ($) item	Dec. 31, 2015 USD ($)
Valuation allowance
Deferred tax asset valuation allowance	$ 277,912	$ 215,100
Change in valuation allowance	62,800	53,200
Future minimum operating lease payments	6,882
Excess tax benefit arising from stock option deductions credited to additional paid in capital	$ 62,700	$ 45,500
Revenue \| Customer Concentration Risk \| Medicare
Concentration Risk [Line Items]
Number of payors which provided greater than 10% of revenue \| item	1
Concentration risk (as a percent)	60.00%	71.00%
Accounts Receivable \| Customer Concentration Risk \| Medicare
Concentration Risk [Line Items]
Concentration risk (as a percent)	63.00%	64.00%

The number of payors which provided greater than 10% of revenue.

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Amount of increase in additional paid in capital (APIC) resulting from a tax benefit associated with share-based compensation plan other than an employee stock ownership plan (ESOP). Includes, but is not limited to, excess tax benefit.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 740
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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- Definition

Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

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Amount of required minimum rental payments for leases having an initial or remaining non-cancelable letter-terms in excess of one year.

+ References

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Amount of increase (decrease) in the valuation allowance for a specified deferred tax asset.

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