STOCKHOLDER'S EQUITY - Common Stock Issued, Net of Issuance Costs (Details) - USD ($) $ / shares in Units, $ in Thousands						1 Months Ended	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 04, 2020	Oct. 02, 2020	Jun. 26, 2020	May 21, 2020	Apr. 14, 2017	Oct. 31, 2020	Sep. 30, 2020	Sep. 30, 2020	Dec. 31, 2021	Dec. 31, 2020
Net proceeds from common stock									$ 84,142	$ 63,614
ATM Offering Agreement
Amount available for future sales									$ 47,700
Common Stock
Number of common stock issued									16,050,518	15,681,968
Cantor Fitzgerald & Co | ATM Offering Agreement
Number of common stock issued									10,000,000.0
Net proceeds from common stock									$ 49,500
2020 Lincoln Park PA
Maximum aggregate offering price	$ 100,000
Period for financing from common stock	36 months
Percentage of common stock issuable	19.99%
Threshold average sale price per share of common stock	$ 6.15
2020 Lincoln Park PA | Lincoln Park
Number of common stock issued									6,100,000
Net proceeds from common stock									$ 34,600
Amount available for future sales									$ 47,700
May 2020 Purchase Agreement with Lincoln Park
Maximum aggregate offering price		$ 3,200		$ 12,000		$ 12,000
Period for financing from common stock				24 months
Number of common stock issued		1,100,000	1,970,000	156,250			1,600,000	1,800,000
Net proceeds from common stock		$ 8,200					$ 3,500	$ 3,800
Number of warrants issued for common stock				250,000
Warrant purchase price per share				$ 1.2989
2019 Purchase Agreement with Lincoln Park | Lincoln Park
Minimum percentage considered for not to sale common stock	9.99%
ATM Offering Agreement | Cantor Fitzgerald & Co
Net proceeds from common stock										$ 49,900
Number of common stock sold										11,000,000.0
ATM Offering Agreement | Cantor Fitzgerald & Co | Maximum
Sales commission percentage					2.50%