INCOME TAXES - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Income tax benefit	$ (92)	$ 0	$ 0
Valuation allowance	96,301	50,524
Increase in valuation allowance		10,500
Reduction in the value of net deferred assets		10,500
Unrecognized tax benefits	2,543	$ 1,297	819	$ 574
Real Estate Owned, Valuation Allowance, Period Increase (Decrease)	45,800
Domestic Tax Authority
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	272,800
Operating losses subject to expiration			$ 89,100
Research tax credit carryforward	8,000
Domestic Tax Authority | Internal Revenue Service (IRS)
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	361,900
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	89,600
Research tax credit carryforward	$ 4,200