LONG-TERM DEBT - Narrative (Details)				3 Months Ended	12 Months Ended
	Dec. 31, 2018 USD ($) $ / shares shares	Nov. 05, 2018 USD ($)	Oct. 02, 2017 USD ($) $ / shares shares	Sep. 30, 2018	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($)	Dec. 04, 2017	Nov. 01, 2017 USD ($)	Jun. 01, 2016 USD ($)
Debt Instrument
Long-term debt	$ 2,348,239,000				$ 2,348,239,000
Exchange price (USD per share) | $ / shares					$ 152.18
Proceeds from issuance of warrants			$ 23,600,000		$ 0	$ 23,650,000	$ 0
Unamortized discount	$ 61,377,000				$ 61,377,000
Purchase of exchangeable note hedge						$ 74,365,000
Senior Notes | 4.875% Senior Notes due November 30, 2018 (the 4.875% Senior Notes); interest payable each May 30 and November 30
Debt Instrument
Stated interest rate (as a percent)	4.75%				4.75%	4.875%	4.875%
Revolving Credit Facility | IAC Credit Facility
Debt Instrument
Maximum borrowing capacity		$ 250,000,000				$ 300,000,000
Credit facility, borrowings outstanding	$ 0				$ 0	$ 0
Commitment fee rate (as a percent)					0.20%	0.25%
Revolving Credit Facility | IAC Credit Facility | Maximum
Debt Instrument
Maximum leverage ratio (not more than)	2.75				3.25
IAC
Debt Instrument
Long-term debt	$ 551,989,000				$ 551,989,000	$ 552,359,000
Unamortized discount	54,025,000				54,025,000	67,158,000
IAC | Senior Notes
Debt Instrument
Long-term debt	$ 463,500,000		$ 517,500,000.0		$ 463,500,000	$ 450,300,000
Exchangeable shares (shares) | shares			6.5713
Exchange price (USD per share) | $ / shares			$ 152.18		$ 152.18
Period of reported sale price of common stock			20 days	5 days
Period of consecutive reported sale price of common stock			30 days	5 days
Percentage of exchange price on applicable trading day			130.00%
Percentage of product of last reported price			98.00%
Proceeds from issuance of debt			$ 499,500,000
Repayment of net premium on exchangeable note hedge and warrants			50,700,000
Amount of debt discount and increase to additional paid in capital			70,400,000
Transaction costs allocated to liability and equity			18,000,000
Class of warrant outstanding (shares) | shares	3,400,000				3,400,000	3,400,000
Exercise price of warrants (USD per share) | $ / shares	$ 229.70				$ 229.70	$ 229.70
Proceeds from issuance of warrants			23,600,000
Unamortized discount	$ 54,000,000				$ 54,000,000	$ 67,200,000
If-converted value in excess of principal					105,000,000
Purchase of exchangeable note hedge			$ 74,400,000
Debt interest expense					21,200,000	5,200,000
Amortization of debt discount (premium)					13,100,000	3,200,000
Amortization of debt issuance costs					$ 3,500,000	$ 900,000
IAC | Senior Notes | 0.875% Exchangeable Senior Notes due October 1, 2022 (the Exchangeable Notes); interest payable each April 1 and October 1
Debt Instrument
Stated interest rate (as a percent)	0.875%		0.875%		0.875%	0.875%
Long-term debt	$ 517,500,000				$ 517,500,000	$ 517,500,000
IAC | Senior Notes | 0.875% Exchangeable Senior Notes due October 1, 2022 (the Exchangeable Notes); interest payable each April 1 and October 1 | Minimum
Debt Instrument
Stated interest rate (as a percent)	0.875%				0.875%
IAC | Senior Notes | 0.875% Exchangeable Senior Notes due October 1, 2022 (the Exchangeable Notes); interest payable each April 1 and October 1 | Maximum
Debt Instrument
Stated interest rate (as a percent)	3.88%				3.88%
IAC | Senior Notes | 4.75% Senior Notes due December 15, 2022 (the 4.75% Senior Notes); interest payable each June 15 and December 15
Debt Instrument
Stated interest rate (as a percent)	4.75%				4.75%	4.75%
Long-term debt	$ 34,489,000				$ 34,489,000	$ 34,859,000
Match Group
Debt Instrument
Long-term debt	1,535,000,000				1,535,000,000	1,275,000,000
Proceeds from issuance of IAC debt					260,000,000	525,000,000	$ 400,000,000
Unamortized discount	$ 7,352,000				$ 7,352,000	$ 8,668,000
Match Group | Senior Notes | 6.75% Senior Notes due December 15, 2022 (the Match Group 6.75% Senior Notes); interest payable each June 15 and December 15
Debt Instrument
Stated interest rate (as a percent)						6.75%		6.75%
Long-term debt							445,200,000
Match Group | Senior Notes | 5.00% Senior Notes due December 15, 2027 (the 5.00% MTCH Senior Notes); interest payable each June 15 and December 15
Debt Instrument
Stated interest rate (as a percent)	5.00%				5.00%	5.00%		5.00%
Long-term debt	$ 450,000,000				$ 450,000,000	$ 450,000,000
Match Group | Senior Notes | 6.375% Senior Notes due June 1, 2024 (the 6.375% MTCH Senior Notes); interest payable each June 1 and December 1
Debt Instrument
Stated interest rate (as a percent)	6.375%				6.375%	6.375%				6.375%
Long-term debt	$ 400,000,000				$ 400,000,000	$ 400,000,000
Face amount of debt instrument										$ 400,000,000.0
Match Group | Senior Notes | 6.375% Senior Notes due June 1, 2024 (the 6.375% MTCH Senior Notes); interest payable each June 1 and December 1 | Maximum
Debt Instrument
Maximum leverage ratio (not more than)						5.0
Match Group | Term Loan | MTCH Term Loan due November 16, 2022
Debt Instrument
Long-term debt	$ 425,000,000				$ 425,000,000	$ 425,000,000
Match Group | Term Loan | Match Group Term Loan due November 16, 2022
Debt Instrument
Repayment of debt							$ 440,000,000
Effective interest rate (as a percent)	5.09%				5.09%	3.85%
Match Group | Term Loan | Match Group Term Loan due November 16, 2022 | LIBOR
Debt Instrument
Basis spread on variable rate (as a percent)					2.50%
Match Group | Revolving Credit Facility | MTCH Term Loan due November 16, 2022 | Maximum
Debt Instrument
Net leverage ratio affecting ability to pay dividends, make distributions, or repurchase stock					4.0
Match Group | Revolving Credit Facility | Match Group Credit Agreement
Debt Instrument
Effective interest rate (as a percent)	4.00%				4.00%
Maximum borrowing capacity	$ 500,000,000.0				$ 500,000,000.0
Credit facility, borrowings outstanding	260,000,000.0				$ 260,000,000.0	$ 0
Commitment fee rate (as a percent)					0.25%	0.30%
Match Group | Revolving Credit Facility | Match Group Credit Agreement | Minimum
Debt Instrument
Minimum interest coverage ratio (not less than)					2.0
Match Group | Revolving Credit Facility | Match Group Credit Agreement | Maximum
Debt Instrument
Maximum leverage ratio (not more than)					5.0
Net leverage ratio affecting ability to pay dividends, make distributions, or repurchase stock					2.0
Match Group | Revolving Credit Facility | Match Group Credit Agreement | LIBOR
Debt Instrument
Basis spread on variable rate (as a percent)					1.50%
ANGI Homeservices | Term Loan
Debt Instrument
Face amount of debt instrument									$ 275,000,000
ANGI Homeservices | Term Loan | Quarterly Payments for First Three Years
Debt Instrument
Stated interest rate (as a percent)									1.25%
ANGI Homeservices | Term Loan | Quarterly Payments in Fourth Year
Debt Instrument
Stated interest rate (as a percent)									2.50%
ANGI Homeservices | Term Loan | Quarterly Payments in Fifth Year
Debt Instrument
Stated interest rate (as a percent)									3.75%
ANGI Homeservices | Term Loan | ANGI Term Loan due November 5, 2023
Debt Instrument
Long-term debt	261,250,000				$ 261,250,000	$ 275,000,000
Basis spread on variable rate (as a percent)					4.00%	3.38%
ANGI Homeservices | Term Loan | ANGI Term Loan due November 5, 2023 | Minimum
Debt Instrument
Minimum interest coverage ratio (not less than)					2.0
ANGI Homeservices | Term Loan | ANGI Term Loan due November 5, 2023 | Maximum
Debt Instrument
Maximum leverage ratio (not more than)					4.5
Net leverage ratio affecting ability to pay dividends, make distributions, or repurchase stock					4.25
ANGI Homeservices | Term Loan | ANGI Term Loan due November 5, 2023 | LIBOR
Debt Instrument
Basis spread on variable rate (as a percent)					1.50%	2.00%
ANGI Homeservices | Revolving Credit Facility | ANGI Homeservices Credit Facility
Debt Instrument
Maximum borrowing capacity		$ 250,000,000
Credit facility, borrowings outstanding	$ 0				$ 0
Term of debt instrument		5 years
Commitment fee rate (as a percent)					0.25%