THE COMPANY AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) Service_Professional in Thousands, $ in Thousands, marketplace_service_request in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018 USD ($) Service_Professional operating_segment marketplace_service_request consumer_review	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($)	Jan. 01, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Entity Operations Information [Abstract]
Number of consumer reviews | consumer_review	15,000,000
Period of consumer reviews collected	20 years
Number of marketplace service requests | marketplace_service_request	5.0
Number of operating segments | operating_segment	2
Retained earnings (accumulated deficit)	$ (105,000)				$ (121,764)
Operating income (loss)	$ (10,756)	$ 1,388
Restricted cash included in Other assets						$ 10,600
Class B Common Stock | IAC
Entity Operations Information [Abstract]
Ownership interest (as a percent)	86.80%
Voting interest (as a percent)	98.50%
Marketplace
Entity Operations Information [Abstract]
Number of employees | Service_Professional	194
Advertising
Entity Operations Information [Abstract]
Number of employees | Service_Professional	41
Accounting Standards Update 2014-09
Entity Operations Information [Abstract]
Retained earnings (accumulated deficit)				$ 25,600
Current asset for capitalized sales commissions				29,700
Noncurrent asset for capitalized sales commissions				4,200
Deferred tax liability				$ (8,300)
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Entity Operations Information [Abstract]
Operating income (loss)	$ 6,093
Minimum | Scenario, Forecast [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Entity Operations Information [Abstract]
Operating income (loss)			$ 13,000
Maximum | Scenario, Forecast [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Entity Operations Information [Abstract]
Operating income (loss)			$ 17,000