INCOME TAXES - Schedule of Deferred Tax Assets and Deferred Tax Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Gross increases—prior year tax positions	$ 8,761
Deferred tax assets:
Net operating losses		$ 6,618	$ 16,391
Tax credit carryforwards		1,096	1,860
Intangibles		33,604	38,509
Stock-based compensation		2,286	1,505
Reserves and other accruals not currently deductible		10,706	12,094
Total deferred tax assets		54,310	70,359
Valuation allowance for deferred tax assets		(41,905)	(54,224)
Deferred tax assets		12,405	16,135
Deferred tax liabilities
Convertible debt		(12,213)	(16,135)
Fixed Assets		(192)	0
Net deferred tax asset (liability)		$ 0	$ 0