INCOME TAXES - Reconciliation of Statutory Federal Income Tax Rate to Company's Effective Tax Rate (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Tax at federal statutory rate	21.00%	21.00%	34.00%
State taxes, net of federal benefit	0.10%	(1.10%)	(0.40%)
Foreign rate differential	1.40%	(14.70%)	(14.90%)
Non-deductible meals	0.30%	(3.40%)	(0.30%)
Other non-deductible expenses	1.50%	(1.70%)	(0.70%)
Credits	(13.90%)	164.80%	41.50%
Other items	(0.50%)	2.30%	(1.20%)
Change in valuation allowance	34.90%	(718.50%)	(119.50%)
Impact of U.S. tax reform	0	0	(2.091)
Share-based compensation	(45.80%)	549.00%	243.50%
Change in uncertain tax positions	0.50%	(4.10%)	(2.40%)
Termination of warrant	0.00%	0.00%	29.30%
Sale of Caviar business line	1.20%	0.00%	0.00%
Total	0.70%	(6.40%)	(0.20%)