SEGMENT INFORMATION - Revenue Disaggregated by Service (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information
Revenue from contracts with customers	$ 255,311	$ 150,745
North America
Segment Reporting Information
Revenue from contracts with customers	236,026	138,072
Europe
Segment Reporting Information
Revenue from contracts with customers	19,285	12,673
Marketplace revenue | North America
Segment Reporting Information
Revenue from contracts with customers	165,608	129,644
Consumer connection revenue | North America
Segment Reporting Information
Revenue from contracts with customers	149,060	116,000
Membership subscription revenue | North America
Segment Reporting Information
Revenue from contracts with customers	15,627	12,752
Other revenue | North America
Segment Reporting Information
Revenue from contracts with customers	921	892
Advertising & Other revenue | North America
Segment Reporting Information
Revenue from contracts with customers	70,418	8,428
Advertising & Other revenue | Europe
Segment Reporting Information
Revenue from contracts with customers	247	202
Consumer connection revenue | Europe
Segment Reporting Information
Revenue from contracts with customers	14,367	8,465
Membership subscription revenue | Europe
Segment Reporting Information
Revenue from contracts with customers	$ 4,671	$ 4,006