FAIR VALUE MEASUREMENTS - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended					3 Months Ended
	Feb. 28, 2018	Jun. 30, 2017	May 31, 2017	Jul. 31, 2016	May 31, 2013	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Shares issued (in shares)						20,226,000		3,439,000
Class of warrant, numerator input value (in usd per share)			$ 68.9516
Number of trading days			30 days
Class of warrant (in shares)					644,365	0		110,000
Exercise price of warrants (in usd per share)		$ 27.68		$ 20.00	$ 23.64
Volatility					50.00%		53.00%
Warrant, term		10 years		10 years	10 years
Common Stock Warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liability value						$ 17,666	$ 0	$ 7,945	$ 0
Changes in fair value, loss						9,721	0
Accrued interest on convertible promissory notes							0
Convertible promissory notes (converted into Series G' Stock in May 2017)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liability value						0	76,184	$ 0	$ 72,332
Changes in fair value, loss						$ 0	2,606
Accrued interest on convertible promissory notes							$ 1,246
Series G Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Shares issued (in shares)			346,334
Class of warrant, numerator input value (in usd per share)			$ 68.9516
Number of trading days			30 days
Number of days following prospectus			180 days
Number of days prior to sale of company			10 days
Exercise price of warrants (in usd per share)			$ 0.0004
Volatility			59.00%
Discount for lack of marketability			11.00%
Liability value			$ 7,500
Series B-R Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value per share (in usd per share)						$ 20.18		$ 26.8
Series D-R Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value per share (in usd per share)						$ 10.57		$ 13.63
Common Stock Warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Stock option expense	$ 2,500