BUSINESS COMBINATIONS (Details) Share data in Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended								3 Months Ended		9 Months Ended		3 Months Ended	9 Months Ended	3 Months Ended			9 Months Ended			3 Months Ended			3 Months Ended
	Sep. 30, 2011 USD ($)	Sep. 30, 2010 USD ($)	Sep. 30, 2011 USD ($)	Sep. 30, 2010 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2009	Sep. 30, 2011 Customer lists USD ($)	Dec. 31, 2010 Customer lists USD ($)	Sep. 30, 2011 Technology USD ($)	Dec. 31, 2010 Technology USD ($)	Sep. 30, 2011 Match USD ($)	Sep. 30, 2010 Match USD ($)	Sep. 30, 2011 Match USD ($)	Sep. 30, 2010 Match USD ($)	Sep. 30, 2011 Meetic USD ($)	Sep. 30, 2011 Meetic USD ($)	Sep. 30, 2011 Meetic Match USD ($)	Sep. 30, 2011 Meetic Match EUR (€)	Sep. 30, 2010 Meetic Match USD ($)	Sep. 30, 2011 Meetic Match USD ($)	Sep. 30, 2010 Meetic Match USD ($)	Dec. 31, 2009 Meetic Match	Sep. 30, 2011 Meetic Match Customer lists USD ($) year	Sep. 30, 2011 Meetic Match Technology USD ($) year	Sep. 30, 2011 Meetic Match Indefinite-lived trade names USD ($)	Sep. 30, 2011 OkCupid Match USD ($)	Jan. 20, 2011 OkCupid Match USD ($)
Business Combination
Ownership interest acquired (as a percent)						27.00%																27.00%
Shares acquired (in shares)																	12.5	12.5		12.5
Cash paid for acquisition of shares																											$ 50,000,000
Voting interest (as a percent)																	79.00%	79.00%		79.00%
Ownership interest (as a percent)																	81.00%	81.00%		81.00%
Revenue	516,884,000	412,966,000	1,462,501,000	1,185,388,000							132,328,000	106,197,000	360,354,000	292,433,000	11,100,000	11,100,000
Write-off of deferred revenue															9,600,000	9,600,000
Net earnings (loss)	64,973,000	17,509,000	125,467,000	12,395,000											(5,900,000)	(5,900,000)
Loss on adjustment to fair value of a previously held equity method investment																	(11,700,000)
Currency translation adjustments reclassified out of accumulated other comprehensive income to earnings																	3,200,000
Percentage of interest of noncontrolling interests (as a percent)																	19.00%	19.00%		19.00%
Tender offer price (in euro per share)																		€ 15.00
Fair value at date of acquisition
Shares acquired pursuant to tender offer																	272,032,000			272,032,000
Equity method investment in Meetic																	132,652,000			132,652,000
Noncontrolling interests, including the fair value of unvested stock awards attributable to pre-acquisition services	101,487,000		101,487,000														101,487,000			101,487,000
Total																	506,171,000			506,171,000
Allocation of the purchase price
Cash and cash equivalents																	74,562,000			74,562,000
Other current assets																	22,356,000			22,356,000
Current deferred tax asset																	13,742,000			13,742,000
Property and equipment																	9,269,000			9,269,000
Goodwill																	285,809,000			285,809,000
Intangible assets																	165,250,000			165,250,000
Intangible assets with indefinite lives, net																									132,195,000
Intangible assets with definite lives, net	37,980,000		37,980,000		8,023,000		15,737,000	236,000	14,604,000	1,283,000													18,138,000	14,917,000
Other assets																	40,800,000			40,800,000
Total assets																	611,788,000			611,788,000
Current liabilities																	(49,382,000)			(49,382,000)
Other liabilities																	(2,575,000)			(2,575,000)
Non-current deferred tax liabilities																	(53,660,000)			(53,660,000)
Net assets																	506,171,000			506,171,000
Weighted-Average Amortization Life (in years)																							1	2
Increase in ownership interest (as a percent)																54.00%
Pro forma financial information
Revenue																	567,821,000		473,339,000	1,643,132,000	1,336,389,000
Net earnings (loss) attributable to IAC shareholders																	80,836,000		23,569,000	148,779,000	(5,701,000)
Basic earnings (loss) per share attributable to IAC shareholders (in dollars per share)																	$ 0.96		$ 0.23	$ 1.69	$ (0.05)
Diluted earnings (loss) per share attributable to IAC shareholders (in dollars per share)																	$ 0.86		$ 0.22	$ 1.57	$ (0.05)
Acquisition information
Purchase consideration paid in cash																											50,000,000
Maximum additional contingent payment																											40,000,000
Payment to the former owner																										30,000,000
Potential additional payment to the former owner																										10,000,000
Fair value of contingent consideration arrangement																										$ 10,000,000