COMMON STOCK - Common Stock Issued, Net of Issuance Costs (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended		9 Months Ended
	Dec. 04, 2020	Apr. 14, 2017	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Common stock outstanding after the effect of reverse stock spilt conversion			34,636,063		34,636,063		19,171,859
Common stock, par value			$ 0.001		$ 0.001		$ 0.001
Net proceeds from common stock					$ 81,865	$ 13,530
ATM Offering Agreement
Number of common stock sold			0
Amount available for future sales			$ 50,000		$ 50,000
Common Stock
Number of common stock issued			1,099,748	3,769,036	15,407,018	7,093,960
Cantor Fitzgerald & Co | ATM Offering Agreement
Number of common stock issued					9,300,000
Net proceeds from common stock					$ 47,300
Cantor Fitzgerald & Co | Maximum | ATM Offering Agreement
Sales commission percentage		2.50%
December 2020 PA
Maximum aggregate offering price	$ 100,000
Period for financing from common stock	36 months
Threshold average sale price per share of common stock	$ 6.15
December 2020 PA | Lincoln Park
Number of common stock issued			1,100,000		6,100,000
Net proceeds from common stock			$ 4,000		$ 34,600
Amount available for future sales			$ 50,000		$ 50,000
2019 Purchase Agreement with Lincoln Park | Maximum
Percentage of common stock issuable	19.99%
2019 Purchase Agreement with Lincoln Park | Lincoln Park
Minimum percentage considered for not to sale common stock	9.99%