SEGMENT INFORMATION - Revenue Disaggregated by Service (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Revenues	$ 1,104,103	$ 1,104,592	$ 1,059,122	$ 995,075	$ 950,585	$ 828,434	$ 767,387	$ 760,833	$ 4,262,892	$ 3,307,239	$ 3,139,882
Operating Segments | Match Group
Segment Reporting Information [Line Items]
Revenues									1,729,850	1,330,661	1,118,110
Operating Segments | ANGI Homeservices
Segment Reporting Information [Line Items]
Revenues									1,132,241	736,386	498,890
Operating Segments | Vimeo
Segment Reporting Information [Line Items]
Revenues									159,641	103,332	78,805
Operating Segments | Dotdash
Segment Reporting Information [Line Items]
Revenues									130,991	90,890	77,913
Operating Segments | Applications
Segment Reporting Information [Line Items]
Revenues									582,287	577,998	604,140
Operating Segments | Applications | Mosaic Group
Segment Reporting Information [Line Items]
Revenues									123,516	55,849	40,825
Operating Segments | Emerging & Other
Segment Reporting Information [Line Items]
Revenues									528,250	468,589	762,609
North America | Operating Segments | ANGI Homeservices
Segment Reporting Information [Line Items]
Revenues									1,062,171	678,897	461,847
Europe | Operating Segments | ANGI Homeservices
Segment Reporting Information [Line Items]
Revenues									70,070	57,489	37,043
Direct | Operating Segments | Match Group
Segment Reporting Information [Line Items]
Revenues									1,677,171	1,281,249	1,067,364
Direct | Operating Segments | Match Group | Tinder
Segment Reporting Information [Line Items]
Revenues									805,316	403,216	168,522
Direct | Operating Segments | Match Group | Other brands
Segment Reporting Information [Line Items]
Revenues									871,855	878,033	898,842
Direct | North America | Operating Segments | Match Group
Segment Reporting Information [Line Items]
Revenues									902,478	741,334	673,944
Direct | All Other Countries | Operating Segments | Match Group
Segment Reporting Information [Line Items]
Revenues									774,693	539,915	393,420
Indirect | Operating Segments | Match Group
Segment Reporting Information [Line Items]
Revenues									52,679	49,412	50,746
Marketplace | North America | Operating Segments | ANGI Homeservices
Segment Reporting Information [Line Items]
Revenues									774,495	581,414	428,866
Consumer Connection | North America | Operating Segments | ANGI Homeservices
Segment Reporting Information [Line Items]
Revenues									704,341	521,481	382,466
Membership Subscription | North America | Operating Segments | ANGI Homeservices
Segment Reporting Information [Line Items]
Revenues									66,214	56,135	43,573
Other | North America | Operating Segments | ANGI Homeservices
Segment Reporting Information [Line Items]
Revenues									3,940	3,798	2,827
Advertising and Other | North America | Operating Segments | ANGI Homeservices
Segment Reporting Information [Line Items]
Revenues									287,676	97,483	32,981
Advertising and Other | Europe | Operating Segments | ANGI Homeservices
Segment Reporting Information [Line Items]
Revenues									1,795	884	983
Consumer Connection | Europe | Operating Segments | ANGI Homeservices
Segment Reporting Information [Line Items]
Revenues									50,913	40,009	28,124
Membership Subscription | Europe | Operating Segments | ANGI Homeservices
Segment Reporting Information [Line Items]
Revenues									17,362	16,596	7,936
Platform | Operating Segments | Vimeo
Segment Reporting Information [Line Items]
Revenues									146,665	99,650	78,805
Hardware | Operating Segments | Vimeo
Segment Reporting Information [Line Items]
Revenues									12,976	3,682	0
Advertising | Operating Segments | Dotdash
Segment Reporting Information [Line Items]
Revenues									113,014	81,948	76,099
Advertising | Operating Segments | Applications | Mosaic Group
Segment Reporting Information [Line Items]
Revenues									18,541	27,869	19,038
Advertising | Operating Segments | Emerging & Other
Segment Reporting Information [Line Items]
Revenues									424,485	279,487	344,200
Google Advertising | Operating Segments | Emerging & Other
Segment Reporting Information [Line Items]
Revenues									357,752	225,576	269,192
Other | Operating Segments | Emerging & Other
Segment Reporting Information [Line Items]
Revenues									66,733	53,911	75,008
Affiliate Commerce Commission | Operating Segments | Dotdash
Segment Reporting Information [Line Items]
Revenues									14,458	7,372	1,685
Other | Operating Segments | Dotdash
Segment Reporting Information [Line Items]
Revenues									3,519	1,570	129
Other | Operating Segments | Emerging & Other
Segment Reporting Information [Line Items]
Revenues									103,765	169,497	160,329
Desktop | Operating Segments | Applications
Segment Reporting Information [Line Items]
Revenues									458,771	522,149	563,315
Advertising | Operating Segments | Applications
Segment Reporting Information [Line Items]
Revenues									437,956	487,536	533,372
Google Advertising | Operating Segments | Applications
Segment Reporting Information [Line Items]
Revenues									426,964	480,774	523,335
Other | Operating Segments | Applications
Segment Reporting Information [Line Items]
Revenues									10,992	6,762	10,037
Subscription and Other | Operating Segments | Applications
Segment Reporting Information [Line Items]
Revenues									20,815	34,613	29,943
Subscription and Other | Operating Segments | Applications | Mosaic Group
Segment Reporting Information [Line Items]
Revenues									104,975	27,980	21,787
Test Preparation | Operating Segments | Emerging & Other
Segment Reporting Information [Line Items]
Revenues									0	19,605	86,517
Product
Segment Reporting Information [Line Items]
Revenues									13,665	4,302	172,408
Product | Operating Segments | Emerging & Other
Segment Reporting Information [Line Items]
Revenues									$ 0	$ 0	$ 171,563