NATURE OF OPERATIONS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenue Recognition, Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Advertising arrangement contract terms	The term of our advertising arrangements is generally less than one year and the timing between when an advertisement is aired and when payment is due is not significant.
Deferred revenue	$ 83,270	$ 49,522	$ 31,700
Deferred revenue, revenue recognized	$ 38,800	$ 22,300