GOODWILL AND INTANGIBLE ASSETS - Goodwill by Reportable Segment (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Goodwill
Balance at beginning of period	$ 2,854,462	$ 2,726,859	$ 2,726,859
Additions	416,797		168,866
(Deductions)	(38)		(29,267)
Impairment	(211,973)	0	(3,318)
Foreign Exchange Translation	(17,109)		(8,678)
Balance at end of period	3,042,139		2,854,462
Match Group
Goodwill
Balance at beginning of period	1,239,840	1,245,013	1,245,013
Additions			3,553
(Deductions)	0		0
Foreign Exchange Translation	(12,108)		(8,726)
Balance at end of period	1,227,732		1,239,840
ANGI Homeservices
Goodwill
Balance at beginning of period	882,051	892,800	892,800
Additions	0		18,326
(Deductions)	0		(29,267)
Impairment	0		0
Foreign Exchange Translation	(4,867)		192
Balance at end of period	877,184		882,051
Vimeo
Goodwill
Balance at beginning of period	219,374	77,152	77,152
Additions	0		142,222
(Deductions)	(38)		0
Impairment	0		0
Foreign Exchange Translation	0		0
Balance at end of period	219,336		219,374
Applications
Goodwill
Balance at beginning of period	504,748	504,892	504,892
Additions	0		0
(Deductions)	0		0
Impairment	(211,973)		0
Foreign Exchange Translation	(134)		(144)
Balance at end of period	292,641		504,748
Applications | Desktop
Goodwill
Balance at beginning of period	265,146	265,146	265,146
Additions	0		0
(Deductions)	0		0
Impairment	(211,973)		0
Foreign Exchange Translation	0		0
Balance at end of period	53,173		265,146
Applications | Mosaic Group
Goodwill
Balance at beginning of period	239,602	239,746	239,746
Additions	0		0
(Deductions)	0		0
Impairment	0		0
Foreign Exchange Translation	(134)		(144)
Balance at end of period	239,468		239,602
Emerging & Other
Goodwill
Balance at beginning of period	8,449	$ 7,002	7,002
Additions	416,797		4,765
(Deductions)	0		0
Impairment			(3,318)
Balance at end of period	$ 425,246		$ 8,449