FAIR VALUE MEASUREMENTS - Preferred Stock Warrants (Details) - $ / shares	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Jul. 31, 2016	May 31, 2013
Class of Stock [Line Items]
Exercise price of warrants (in usd per share)			$ 27.68	$ 20.00	$ 23.64
Class of warrant (in shares)	0	110,000			644,365
Series B-R Stock | Grant One
Class of Stock [Line Items]
Exercise price of warrants (in usd per share)	$ 2.36
Class of warrant (in shares)	0	59,000
Series D-R Stock | Grant One
Class of Stock [Line Items]
Exercise price of warrants (in usd per share)	$ 23.64
Class of warrant (in shares)	0	38,000
Series D-R Stock | Grant Two
Class of Stock [Line Items]
Exercise price of warrants (in usd per share)	$ 23.64
Class of warrant (in shares)	0	13,000