BACKGROUND AND ORGANIZATION (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Net loss	$ 25,261	$ 30,976	$ 26,743	$ 28,125	$ 26,152	$ 27,532	$ 82,980	$ 81,809
Net cash used in operating activities							56,389	$ 59,680
Cash and cash equivalents	$ 149,900						$ 149,900		$ 156,720