INCOME TAXES - Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income tax provision (benefit) at the federal statutory rate of 21% (35% for 2017)	$ 7,066	$ 14,705	$ (53,771)
State income taxes, net of effect of federal tax benefit	2,693	4,702	(3,678)
Stock-based compensation	(12,768)	(25,184)	(32,702)
Research credit	(3,308)	(1,169)	(784)
Unbenefited losses	1,523	2,227	5,915
Deferred tax adjustment for enacted changes in tax law and rates	502	(1,431)	33,002
Other, net	2,624	(1,333)	2,912
Income tax benefit	$ (1,668)	$ (7,483)	$ (49,106)