ORGANIZATION - NARRATIVE (Details) - Dec. 31, 2017 Service_Professional in Thousands, Professional_Under_Contract_For_Adverstising in Thousands, customer in Millions	customer	Professional_Under_Contract_For_Adverstising	Service_Professional	Total
Customer Information [Abstract]
Number of Customers		45	181
Number of Marketplace Service Requests	18.1
Class B Common Stock | IAC
Customer Information [Abstract]
Ownership interest (as a percent)				86.90%
Voting interest (as a percent)				98.50%