SEGMENT INFORMATION - Reconciliation of Operating Income (Loss) to Adjusted EBITDA (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting, Other Significant Reconciling Item [Line Items]
Operating income	$ 154,310	$ 168,437	$ 234,183	$ 258,387
Stock-based compensation expense	62,425	57,561	129,869	116,643
Depreciation	21,091	18,805	40,062	38,062
Amortization of intangibles	19,638	20,188	42,390	40,141
Interest expense	(37,206)	(27,356)	(68,349)	(53,861)
Other income, net	45,972	171,141	46,623	166,522
Earnings before income taxes	163,076	312,222	212,457	371,048
Income tax benefit (provision)	(16,285)	(31,368)	47,319	(2,355)
Net earnings	146,791	280,854	259,776	368,693
Net earnings attributable to noncontrolling interests	(33,324)	(62,501)	(57,614)	(79,258)
Net earnings attributable to IAC shareholders	113,467	218,353	202,162	289,435
Operating segments | Match Group
Segment Reporting, Other Significant Reconciling Item [Line Items]
Operating income	172,898	150,165	291,726	262,398
Stock-based compensation expense	22,015	16,706	50,012	33,669
Depreciation	8,197	8,399	16,028	16,546
Amortization of intangibles	412	237	823	479
Acquisition-related Contingent Consideration Fair Value Adjustments	0	54	0	210
Adjusted EBITDA	203,522	175,561	358,589	313,302
Operating segments | ANGI Homeservices
Segment Reporting, Other Significant Reconciling Item [Line Items]
Operating income	11,403	23,262	7,762	12,506
Stock-based compensation expense	17,520	22,053	36,802	46,959
Depreciation	8,796	5,886	15,795	12,070
Amortization of intangibles	13,713	15,778	28,252	32,084
Acquisition-related Contingent Consideration Fair Value Adjustments	0	0	0	0
Adjusted EBITDA	51,432	66,979	88,611	103,619
Operating segments | Vimeo
Segment Reporting, Other Significant Reconciling Item [Line Items]
Operating income	(11,616)	(9,593)	(29,400)	(19,341)
Stock-based compensation expense	0	0	0	0
Depreciation	132	321	325	656
Amortization of intangibles	2,020	1,641	3,411	3,270
Acquisition-related Contingent Consideration Fair Value Adjustments	0	0	0	0
Adjusted EBITDA	(9,464)	(7,631)	(25,664)	(15,415)
Operating segments | Dotdash
Segment Reporting, Other Significant Reconciling Item [Line Items]
Operating income	7,010	1,339	10,057	4,530
Stock-based compensation expense	0	0	0	0
Depreciation	218	246	444	495
Amortization of intangibles	1,147	409	5,024	818
Acquisition-related Contingent Consideration Fair Value Adjustments	0	0	0	0
Adjusted EBITDA	8,375	1,994	15,525	5,843
Operating segments | Applications
Segment Reporting, Other Significant Reconciling Item [Line Items]
Operating income	20,967	33,077	46,323	58,538
Stock-based compensation expense	0	0	0	0
Depreciation	389	773	808	1,528
Amortization of intangibles	2,346	1,554	4,730	2,090
Acquisition-related Contingent Consideration Fair Value Adjustments	1,617	0	3,146	0
Adjusted EBITDA	25,319	35,404	55,007	62,156
Operating segments | Emerging & Other
Segment Reporting, Other Significant Reconciling Item [Line Items]
Operating income	(1,789)	6,079	(4,309)	12,572
Stock-based compensation expense	0	1,293	0	1,424
Depreciation	272	349	547	1,102
Amortization of intangibles	0	569	150	1,400
Acquisition-related Contingent Consideration Fair Value Adjustments	0	0	0	0
Adjusted EBITDA	(1,517)	8,290	(3,612)	16,498
Corporate
Segment Reporting, Other Significant Reconciling Item [Line Items]
Operating income	(44,563)	(35,892)	(87,976)	(72,816)
Stock-based compensation expense	22,890	17,509	43,055	34,591
Depreciation	3,087	2,831	6,115	5,665
Amortization of intangibles	0	0	0	0
Acquisition-related Contingent Consideration Fair Value Adjustments	0	0	0	0
Adjusted EBITDA	$ (18,586)	$ (15,552)	$ (38,806)	$ (32,560)