SEGMENT INFORMATION - SCHEDULE OF REVENUE DISAGGREGATED BY SERVICE (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information
Consumer connection revenue									$ 521,481	$ 382,466	$ 269,309
Membership subscription revenue									56,135	43,573	24,164
Advertising and other revenue									3,798	2,827	3,423
Marketplace revenue									581,414	428,866	296,896
Revenue	$ 223,213	$ 181,717	$ 180,711	$ 150,745	$ 123,668	$ 133,560	$ 130,173	$ 111,489	736,386	498,890	361,201
North America
Segment Reporting Information
Advertising and other revenue									97,483	32,981	32,971
Revenue									678,897	461,847	329,867
Europe
Segment Reporting Information
Consumer connection revenue									40,009	28,124	23,298
Membership subscription revenue									16,596	7,936	6,921
Advertising and other revenue									884	983	1,115
Revenue									$ 57,489	$ 37,043	$ 31,334