GOODWILL AND INTANGIBLE ASSETS (Details2) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Balance of goodwill by reporting unit, including the changes in the carrying value of goodwill
Balance at the beginning of the period	$ 989,493,000	$ 967,735,000
Additions	397,423,000	44,698,000
(Deductions)	(409,000)	(923,000)
Impairment		(28,032,000)	(916,868,000)
Foreign Exchange Translation	(27,983,000)	6,015,000
Balance at the end of the period	1,358,524,000	989,493,000	967,735,000
Search
Balance of goodwill by reporting unit, including the changes in the carrying value of goodwill
Balance at the beginning of the period	551,454,000	545,054,000
Additions	301,000	7,323,000
(Deductions)	(237,000)	(923,000)
Impairment			(916,868,000)
Balance at the end of the period	551,518,000	551,454,000	545,054,000
IAC Search & Media
Balance of goodwill by reporting unit, including the changes in the carrying value of goodwill
Balance at the beginning of the period	534,004,000	527,604,000
Additions		7,323,000
(Deductions)	(237,000)	(923,000)
Impairment			(916,900,000)
Balance at the end of the period	533,767,000	534,004,000	527,604,000
Goodwill accumulated impairment losses	916,900,000	916,900,000	916,900,000
CityGrid Media
Balance of goodwill by reporting unit, including the changes in the carrying value of goodwill
Balance at the beginning of the period	17,450,000
Additions	301,000
Balance at the end of the period	17,751,000		17,450,000
Match
Balance of goodwill by reporting unit, including the changes in the carrying value of goodwill
Balance at the beginning of the period	297,974,000	253,812,000
Additions	397,115,000	37,375,000
Foreign Exchange Translation	(28,016,000)	6,787,000
Balance at the end of the period	667,073,000	297,974,000
Service Magic
Balance of goodwill by reporting unit, including the changes in the carrying value of goodwill
Balance at the beginning of the period	109,917,000	110,689,000
(Deductions)	(3,000)
Foreign Exchange Translation	33,000	(772,000)
Balance at the end of the period	109,947,000	109,917,000
Media & Other
Balance of goodwill by reporting unit, including the changes in the carrying value of goodwill
Balance at the beginning of the period	30,148,000	58,180,000
Additions	7,000
(Deductions)	(169,000)
Impairment		(28,032,000)
Balance at the end of the period	29,986,000	30,148,000
Shoebuy
Balance of goodwill by reporting unit, including the changes in the carrying value of goodwill
Balance at the beginning of the period	21,712,000	49,744,000
Additions	7,000
Impairment		(28,032,000)
Balance at the end of the period	21,719,000	21,712,000
Goodwill accumulated impairment losses	28,000,000	28,000,000
Connected Ventures
Balance of goodwill by reporting unit, including the changes in the carrying value of goodwill
Balance at the beginning of the period	8,436,000
(Deductions)	(169,000)
Balance at the end of the period	8,267,000		8,436,000
Goodwill accumulated impairment losses	$ 11,600,000	$ 11,600,000	$ 11,600,000