INCOME TAXES - Deferred Tax Assets (Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Compensation	$ 57,666	$ 52,538
Accrued expenses	27,683	3,155
Receivables	8,093	8,819
Other	6,004	4,737
Deferred tax liabilities:
Intangible assets	(77,059)	(81,932)
Accrued revenue	(19,571)	0
Prepaid assets	(5,798)	(8,247)
Long-lived assets	(15,615)	(15,465)
Other	(7,167)	(2,090)
Net deferred tax liabilities	$ (25,764)	$ (38,485)