INCOME TAXES - Net Operating Losses and Credit Carryforwards (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Reduction of income tax provision due to tax holidays	$ 1,900	$ 1,300	$ 1,000
Federal
Operating Loss Carryforwards [Line Items]
Net operating losses	120,722
Credit carryforwards	8,202
Net operating losses expected to expire unused	60,200
Tax credits expected to expire unused	100
Carryforwards with unlimited carryforward period	43,900
State
Operating Loss Carryforwards [Line Items]
Net operating losses	3,337
Credit carryforwards	1,958
Net operating losses expected to expire unused	800
Tax credits expected to expire unused	8,300
Carryforwards with unlimited carryforward period	1,000
OpenSpan, Inc. | Federal
Operating Loss Carryforwards [Line Items]
Net operating losses	76,827
Credit carryforwards	640
OpenSpan, Inc. | State
Operating Loss Carryforwards [Line Items]
Net operating losses	778
Credit carryforwards	$ 227