SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Effect of Adoption of ASU 2014-09 (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
Disaggregation of Revenue [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 costs and expenses									3,697,753	3,118,773	3,172,507
Operating income (loss)	133,920	172,832	168,437	89,950	94,360	(18,589)	75,635	37,060	565,139	188,466	(32,625)
Net earnings	$ 217,477	$ 171,577	$ 280,854	$ 87,839	$ 23,349	$ 225,639	$ 80,557	$ 28,463	757,747	358,008	(16,151)
Operating segments | Match Group
Disaggregation of Revenue [Line Items]
Revenues									1,729,850	1,330,661	1,118,110
Operating costs and expenses									1,176,556
Operating income (loss)									553,294	360,517	315,549
Operating segments | ANGI Homeservices
Disaggregation of Revenue [Line Items]
Revenues									1,132,241	736,386	498,890
Operating costs and expenses									1,068,335
Operating income (loss)									63,906	(149,176)	25,363
Operating segments | Vimeo
Disaggregation of Revenue [Line Items]
Revenues									159,641	103,332	78,805
Operating costs and expenses									195,235
Operating income (loss)									(35,594)	(27,328)	(25,350)
Operating segments | Dotdash
Disaggregation of Revenue [Line Items]
Revenues									130,991	90,890	77,913
Operating costs and expenses									112,213
Operating income (loss)									18,778	(15,694)	(248,705)
Operating segments | Applications
Disaggregation of Revenue [Line Items]
Revenues									582,287	577,998	604,140
Operating costs and expenses									487,453
Operating income (loss)									94,834	130,176	109,663
Operating segments | Emerging & Other
Disaggregation of Revenue [Line Items]
Revenues									528,250	468,589	762,609
Operating costs and expenses									498,286
Operating income (loss)									29,964	17,412	(99,696)
Inter-segment eliminations
Disaggregation of Revenue [Line Items]
Revenues									(368)	(617)	(585)
Corporate
Disaggregation of Revenue [Line Items]
Operating costs and expenses									159,675
Operating income (loss)									(160,043)	$ (127,441)	$ (109,449)
Under ASC 605
Disaggregation of Revenue [Line Items]
Revenues									4,263,387
Operating costs and expenses									3,700,861
Operating income (loss)									562,526
Net earnings									755,741
Under ASC 605 | Operating segments | Match Group
Disaggregation of Revenue [Line Items]
Revenues									1,729,850
Operating costs and expenses									1,176,556
Operating income (loss)									553,294
Under ASC 605 | Operating segments | ANGI Homeservices
Disaggregation of Revenue [Line Items]
Revenues									1,132,241
Operating costs and expenses									1,073,275
Operating income (loss)									58,966
Under ASC 605 | Operating segments | Vimeo
Disaggregation of Revenue [Line Items]
Revenues									160,931
Operating costs and expenses									196,212
Operating income (loss)									(35,281)
Under ASC 605 | Operating segments | Dotdash
Disaggregation of Revenue [Line Items]
Revenues									130,991
Operating costs and expenses									112,213
Operating income (loss)									18,778
Under ASC 605 | Operating segments | Applications
Disaggregation of Revenue [Line Items]
Revenues									581,492
Operating costs and expenses									484,644
Operating income (loss)									96,848
Under ASC 605 | Operating segments | Emerging & Other
Disaggregation of Revenue [Line Items]
Revenues									528,250
Operating costs and expenses									498,286
Operating income (loss)									29,964
Under ASC 605 | Inter-segment eliminations
Disaggregation of Revenue [Line Items]
Revenues									(368)
Under ASC 605 | Corporate
Disaggregation of Revenue [Line Items]
Operating costs and expenses									159,675
Operating income (loss)									(160,043)
Accounting Standards Update 2014-09 | Effect of adoption of ASU No. 2014-09
Disaggregation of Revenue [Line Items]
Revenues									(495)
Operating costs and expenses									(3,108)
Operating income (loss)									2,613
Net earnings									2,006
Accounting Standards Update 2014-09 | Effect of adoption of ASU No. 2014-09 | Operating segments | Match Group
Disaggregation of Revenue [Line Items]
Revenues									0
Operating costs and expenses									0
Operating income (loss)									0
Accounting Standards Update 2014-09 | Effect of adoption of ASU No. 2014-09 | Operating segments | ANGI Homeservices
Disaggregation of Revenue [Line Items]
Revenues									0
Operating costs and expenses									(4,940)
Operating income (loss)									4,940
Accounting Standards Update 2014-09 | Effect of adoption of ASU No. 2014-09 | Operating segments | Vimeo
Disaggregation of Revenue [Line Items]
Revenues									(1,290)
Operating costs and expenses									(977)
Operating income (loss)									(313)
Accounting Standards Update 2014-09 | Effect of adoption of ASU No. 2014-09 | Operating segments | Dotdash
Disaggregation of Revenue [Line Items]
Revenues									0
Operating costs and expenses									0
Operating income (loss)									0
Accounting Standards Update 2014-09 | Effect of adoption of ASU No. 2014-09 | Operating segments | Applications
Disaggregation of Revenue [Line Items]
Revenues									795
Operating costs and expenses									2,809
Operating income (loss)									(2,014)
Accounting Standards Update 2014-09 | Effect of adoption of ASU No. 2014-09 | Operating segments | Emerging & Other
Disaggregation of Revenue [Line Items]
Revenues									0
Operating costs and expenses									0
Operating income (loss)									0
Accounting Standards Update 2014-09 | Effect of adoption of ASU No. 2014-09 | Inter-segment eliminations
Disaggregation of Revenue [Line Items]
Revenues									0
Accounting Standards Update 2014-09 | Effect of adoption of ASU No. 2014-09 | Corporate
Disaggregation of Revenue [Line Items]
Operating costs and expenses									0
Operating income (loss)									$ 0