INCOME TAXES - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
NOL carryforwards	$ 124,877	$ 135,042
Stock-based compensation	35,991	34,408
Deferred revenue	939	10,924
Other	13,847	11,692
Total deferred tax assets	175,654	192,066
Less valuation allowance	(58,903)	(61,563)
Net deferred tax assets	116,751	130,503
Deferred tax liabilities:
Intangibles	(30,501)	(44,148)
Indefinite lived intangibles	(45,221)	(41,079)
Other	(4,000)	(179)
Total deferred tax liabilities	(79,722)	(85,406)
Net deferred tax assets	$ 37,029	$ 45,097