AUGUST 2019 PUBLIC OFFERING AND PRIVATE PLACEMENT - Fair Value of Derivative Liability (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Change in fair value of warrant and private placement option liabilities	$ 30,701	$ 0	$ (2,125)	$ 0
Level 3
Derivatives, Fair Value [Line Items]
Derivative liability, fair value at date of issuance	62,153		62,153		$ 64,278
Change in fair value of warrant and private placement option liabilities			(2,125)
Warrant Derivative Liability |  Level 3
Derivatives, Fair Value [Line Items]
Derivative liability, fair value at date of issuance	28,183		28,183		52,184
Change in fair value of warrant and private placement option liabilities			(24,001)
Private Placement Option Liability |  Level 3
Derivatives, Fair Value [Line Items]
Derivative liability, fair value at date of issuance	$ 33,970		33,970		$ 12,094
Change in fair value of warrant and private placement option liabilities			$ 21,876