INCOME TAXES - Narrative (Details) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)
Operating Loss Carryforwards [Line Items]
Decrease in valuation allowance	$ 92.9
Increase to unrecognized tax benefits		$ 0.3
Federal
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	147.4	147.4
Federal | Research tax credit carryforward
Operating Loss Carryforwards [Line Items]
Research tax credit carryforwards	12.4	12.4
State
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	78.9	78.9
State | Research tax credit carryforward
Operating Loss Carryforwards [Line Items]
Research tax credit carryforwards	$ 11.3	$ 11.3