ACCRUED LIABILITIES - Schedule of Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounts Payable and Accrued Liabilities, Current [Abstract]
Accrued compensation	$ 5,498	$ 6,188
Accrued consent fees	4,500	0
Accrued restructuring and one-time termination costs	8,744	3,763	$ 1,578
Other accrued liabilities	12,829	8,997
Total accrued liabilities	$ 31,571	$ 18,948