INFORMATION ABOUT REVENUE AND GEOGRAPHIC AREAS (Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue	$ 241,096	$ 223,287	[1]	$ 699,033	$ 631,406	[1]
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue	237,597	219,642		689,096	620,925
All other countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue	3,499	3,645		9,937	10,481
Advertising
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue	232,502	200,502		672,712	566,085
Transactions
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue	3,042	18,524		10,402	55,024
Other services
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue	$ 5,552	$ 4,261		$ 15,919	$ 10,297

[1] As of January 1, 2018, the Company adopted ASC 606 using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior periods presented. See Note 1 below for additional discussion.