PUBLIC OFFERING AND PRIVATE PLACEMENT - Fair Value of Derivative Liability (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Derivative Liability Rollforward [Roll Forward]
Change in fair value	$ (4,264)	$ (12,131)	$ (7,506)	$ (14,256)
Level 3
Derivative Liability Rollforward [Roll Forward]
Balance, December 31, 2020			18,148
Change in fair value			(7,506)
Balance, September 30, 2021	10,642		10,642
Warrant Derivative Liability |  Level 3
Derivative Liability Rollforward [Roll Forward]
Balance, December 31, 2020			10,345
Change in fair value			(2,503)
Balance, September 30, 2021	7,842		7,842
Private Placement Option Liability |  Level 3
Derivative Liability Rollforward [Roll Forward]
Balance, December 31, 2020			7,803
Change in fair value			(5,003)
Balance, September 30, 2021	$ 2,800		$ 2,800