STOCKHOLDERS' EQUITY - Warrant activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Shares Under Warrants
Outstanding, ending balance	9,494,712
Weighted Average Exercise Price
Outstanding, ending balance	$ 12.00
Weighted Average Remaining Contractual Life
Options outstanding, remaining term	8 years 18 days
Warrant
Shares Under Warrants
Outstanding, beginning balance	0	6,301,216	6,566,216
Issued		0	0
Exercised		(6,301,216)	(265,000)
Expired/Cancelled		0	0
Outstanding, ending balance	0	0	6,301,216
Weighted Average Exercise Price
Outstanding, beginning balance	$ 0	$ 2.51	$ 2.51
Exercise price (in dollars per share)		0	0
Exercised		2.51	2.50
Expired/Cancelled		0	0
Outstanding, ending balance	$ 0	$ 0	$ 2.51
Weighted Average Remaining Contractual Life
Options outstanding, remaining term	0 years	0 years
Aggregate Intrinsic Value
Outstanding, ending balance	$ 0	$ 0