INCOME TAXES - Deferred tax assets/(liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets/(liabilities)::
Acquired intangibles	$ 2,504	$ 2,682
Accrued bonus	153
Unrealized foreign exchange (gain)	(261)	(163)
Accrued royalty	415	415
Stock based compensation	2,594	981
Net operating loss carryforwards	51,649	25,285
Tax credit carryforwards	8,412	2,789
ROU asset	(625)
Lease liability	711
Other		78
Other liabilities	(63)
Total deferred tax assets/(liabilities)	65,489	32,067
Valuation allowance	$ (65,489)	$ (32,067)