INCOME TAXES - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Total tax benefit related to federal and state research and development	$ (16,878,000)	$ (2,324,000)	$ (480,000)
Benefit for uncertain tax positions	5,057,000	$ 0	$ 0	$ 0
Tax expense for interest and penalties related to uncertain tax positions	$ 0