SEGMENT INFORMATION - Schedule of Reconciliation of Operating Income (Loss) to Adjusted EBITDA (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting, Other Significant Reconciling Item [Line Items]
Operating income	$ 168,437	$ 75,635	$ 258,387	$ 112,695
Stock-based compensation expense	57,561	38,915	116,643	72,890
Depreciation	18,805	18,339	38,062	38,227
Amortization of intangibles	20,188	8,624	40,141	17,785
Interest expense	(27,356)	(24,728)	(53,861)	(49,520)
Other income, net	171,141	10,230	166,522	2,516
Earnings before income taxes	312,222	61,137	371,048	65,691
Income tax benefit (provision)	(31,368)	19,420	(2,355)	43,329
Net earnings	280,854	80,557	368,693	109,020
Net earnings attributable to noncontrolling interests	(62,501)	(14,289)	(79,258)	(16,543)
Net earnings attributable to IAC shareholders	218,353	66,268	289,435	92,477
Operating segments | Match Group
Segment Reporting, Other Significant Reconciling Item [Line Items]
Operating income	150,165	82,975	262,398	141,846
Stock-based compensation expense	16,706	15,654	33,669	33,678
Depreciation	8,399	7,883	16,546	15,472
Amortization of intangibles	237	404	479	807
Acquisition-related Contingent Consideration Fair Value Adjustments	54	2,994	210	4,338
Adjusted EBITDA	175,561	109,910	313,302	196,141
Operating segments | ANGI Homeservices
Segment Reporting, Other Significant Reconciling Item [Line Items]
Operating income	23,262	(4,141)	12,506	(2,753)
Stock-based compensation expense	22,053	11,839	46,959	16,300
Depreciation	5,886	3,218	12,070	6,214
Amortization of intangibles	15,778	2,750	32,084	4,117
Acquisition-related Contingent Consideration Fair Value Adjustments	0	0	0	0
Adjusted EBITDA	66,979	13,666	103,619	23,878
Operating segments | Video
Segment Reporting, Other Significant Reconciling Item [Line Items]
Operating income	(14,982)	(7,829)	(30,857)	(23,418)
Stock-based compensation expense	1,293	133	1,424	133
Depreciation	447	552	1,122	1,096
Amortization of intangibles	2,140	312	4,269	625
Acquisition-related Contingent Consideration Fair Value Adjustments	0	0	0	0
Adjusted EBITDA	(11,102)	(6,832)	(24,042)	(21,564)
Operating segments | Applications
Segment Reporting, Other Significant Reconciling Item [Line Items]
Operating income	33,077	39,134	58,538	71,902
Stock-based compensation expense	0	0	0	0
Depreciation	773	921	1,528	1,932
Amortization of intangibles	1,554	491	2,090	1,097
Acquisition-related Contingent Consideration Fair Value Adjustments	0	0	0	548
Adjusted EBITDA	35,404	40,546	62,156	75,479
Operating segments | Publishing
Segment Reporting, Other Significant Reconciling Item [Line Items]
Operating income	12,807	(2,857)	28,618	(8,645)
Stock-based compensation expense	0	0	0	0
Depreciation	469	930	1,131	2,949
Amortization of intangibles	479	4,667	1,219	9,615
Acquisition-related Contingent Consideration Fair Value Adjustments	0	0	0	0
Adjusted EBITDA	13,755	2,740	30,968	3,919
Operating segments | Other
Segment Reporting, Other Significant Reconciling Item [Line Items]
Operating income	0	0	0	(5,621)
Stock-based compensation expense	0	0	0	1,729
Depreciation				836
Amortization of intangibles	0	0	0	1,524
Acquisition-related Contingent Consideration Fair Value Adjustments	0	0	0	0
Adjusted EBITDA	0	0	0	(1,532)
Corporate
Segment Reporting, Other Significant Reconciling Item [Line Items]
Operating income	(35,892)	(31,647)	(72,816)	(60,616)
Stock-based compensation expense	17,509	11,289	34,591	21,050
Depreciation	2,831	4,835	5,665	9,728
Amortization of intangibles	0	0	0	0
Acquisition-related Contingent Consideration Fair Value Adjustments	0	0	0	0
Adjusted EBITDA	$ (15,552)	$ (15,523)	$ (32,560)	$ (29,838)