STOCKHOLDERS' EQUITY - Warrant (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended			6 Months Ended
	Jun. 19, 2017	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Jul. 25, 2017
Class of Warrant or Right [Line Items]
Common stock, par value (in dollars per share)		$ 0.0001			$ 0.0001		$ 0.0001
Common stock, shares issued (in shares)		27,172,924			27,172,924		27,707,328
Series A-1 warrant liability		$ 0		$ 3,313	$ 0	$ 3,313
Change in fair value of warrant liability		293		$ 0	$ 2,399	$ 0
Common Stock Warrant
Class of Warrant or Right [Line Items]
Common stock, par value (in dollars per share)	$ 0.0001
Right to acquire variable amount of common stock, term	15 months
Common Stock Warrant | Soryn HLDR
Class of Warrant or Right [Line Items]
Exercise price (in dollars per share)	$ 3.18
Term of warrant	3 years				2 years
Series A-1 warrant liability	$ 3,300
Aggregate intrinsic value of the warrant		$ 500			$ 500
Common stock | Common Stock Warrant | Soryn HLDR
Class of Warrant or Right [Line Items]
Common stock warrant purchased (in shares)	2,000,000	2,355,506			2,355,506
Common stock, shares issued (in shares)	2,000,000			309,136		309,136		46,370
Series A-1 warrant liability		$ 3,500	$ 3,200		$ 3,500		$ 1,100
Change in fair value of warrant liability		$ 300	$ 2,100