FAIR VALUE MEASUREMENTS - Fair Value Assumptions (Details)	1 Months Ended	3 Months Ended
May 31, 2013	Mar. 31, 2018	Mar. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cost of debt applicable to convertible promissory notes			10.00%
Cost of equity applicable to convertible promissory notes			22.00%
Weighted-average cost of capital applicable to preferred stock warrants			23.00%
Volatility	50.00%		53.00%
Risk-free interest rate	2.00%
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount for lack of marketability		7.00%	7.00%
Risk-free interest rate		1.20%	0.70%
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount for lack of marketability		13.00%	11.00%
Risk-free interest rate		1.40%	1.20%

Fair Value Assumptions, Cost Of Debt Applicable To Convertible Promissory Notes

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- Definition

Fair Value Assumptions, Cost Of Equity Applicable To Convertible Promissory Notes

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No definition available.

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- Definition

Fair Value Assumptions, Weighted Average Cost Of Capital

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No definition available.

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- Definition

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.

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No definition available.

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- Definition

Measure of dispersion, in percentage terms (for instance, the standard deviation or variance), for a given stock price.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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Risk-free interest rate assumption used in valuing an instrument.

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- Definition

Adjustment to the discount rate used to measure fair value for lack of ability to convert business interests into cash quickly.

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