CONSOLIDATED STATEMENT OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Total IAC Shareholders' Equity	Redeemable Noncontrolling Interests	Common Stock Common Stock	Common Stock Class B Convertible Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive (Loss) Income	Treasury Stock	Noncontrolling Interests	Match Group	Match Group Total IAC Shareholders' Equity	Match Group Additional Paid-in Capital	Match Group Accumulated Other Comprehensive (Loss) Income	Match Group Noncontrolling Interests	ANGI Homeservices	ANGI Homeservices Total IAC Shareholders' Equity	ANGI Homeservices Additional Paid-in Capital	ANGI Homeservices Accumulated Other Comprehensive (Loss) Income	ANGI Homeservices Noncontrolling Interests
Balance at beginning of period at Dec. 31, 2015				$ 30,391
Increase (Decrease) in Temporary Equity [Roll Forward]
Net (loss) earnings				(3,849)
Other comprehensive income (loss), net of tax				385
Stock-based compensation expense				1,632
Purchase of redeemable noncontrolling interests				(2,529)
Adjustment of redeemable noncontrolling interests to fair value				7,921
Noncontrolling interests created in acquisitions	$ 22,033		$ 12,222				$ 12,222				$ 9,811
Other				(1,124)
Balance at end of period at Dec. 31, 2016				32,827
Balance at beginning of period at Dec. 31, 2015	2,215,825		1,804,526		$ 254	$ 16	11,486,315	$ 331,394	$ (152,103)	$ (9,861,350)	411,299
Balance at beginning of period (shares) at Dec. 31, 2015					254,015,000	16,157,000
Increase (Decrease) in Shareholders' Equity
Net (loss) earnings	(12,302)		(41,280)					(41,280)			28,978
Other comprehensive income (loss), net of tax	(42,027)		(35,151)						(35,151)		(6,876)
Stock-based compensation expense	94,724		50,201				50,201				44,523
Issuance of common stock pursuant to stock-based awards, net of withholding taxes	(770)		(770)		$ 2		(772)
Issuance of common stock pursuant to stock-based awards, net of withholding taxes (shares)					1,657,000
Income tax benefit related to stock-based awards	49,406		49,406				49,406
Purchase of treasury stock	(315,250)	$ (315,300)	(315,250)							(315,250)
Adjustment of redeemable noncontrolling interests to fair value	(7,560)		(7,560)				(7,560)
Purchase of noncontrolling interests	(211)										(211)
Issuance of Match Group common stock pursuant to stock-based awards, net of withholding taxes	10,224										10,224
Reallocation of shareholders' equity balances related to the noncontrolling interests created in the Match Group IPO	0		363,638				342,507		21,131		(363,638)
Changes in noncontrolling interests of Match Group due to the issuance of its common stock	0		(7,691)				(7,691)				7,691
Noncontrolling interests created in an acquisition	22,033		12,222				12,222				9,811
Other	(3,422)		(3,069)				(3,069)				(353)
Balance at end of period at Dec. 31, 2016	2,010,670		1,869,222		$ 256	$ 16	11,921,559	290,114	(166,123)	(10,176,600)	141,448
Balance at end of period (shares) at Dec. 31, 2016					255,672,000	16,157,000
Increase (Decrease) in Temporary Equity [Roll Forward]
Net (loss) earnings				3,620
Other comprehensive income (loss), net of tax				1,291
Stock-based compensation expense				2,017
Purchase of redeemable noncontrolling interests				(14,641)
Adjustment of redeemable noncontrolling interests to fair value				6,341
Noncontrolling interests created in acquisitions				17,758
Other				(6,346)
Balance at end of period at Dec. 31, 2017	42,867			42,867
Increase (Decrease) in Shareholders' Equity
Net (loss) earnings	354,388		304,924					304,924			49,464
Other comprehensive income (loss), net of tax	74,952		62,446						62,446		12,506
Stock-based compensation expense	246,388		66,333				66,333				180,055
Issuance of common stock pursuant to stock-based awards, net of withholding taxes	(10,504)		(10,504)		$ 5		(10,509)
Issuance of common stock pursuant to stock-based awards, net of withholding taxes (shares)					4,952,000
Purchase of treasury stock	(50,121)	(50,100)	(50,121)							(50,121)
Adjustment of redeemable noncontrolling interests to fair value	(6,341)		(6,341)				(6,341)
Purchase of noncontrolling interests	(848)										(848)
Issuance of common stock pursuant to stock-based awards, net of withholding taxes, and impact to noncontrolling interests												$ (464,209)	$ (460,774)	$ (460,890)	$ 116	$ (3,435)	$ (8,493)	$ (11,223)	$ (11,216)	$ (7)	$ 2,730
Purchase of exchangeable note hedge	(74,365)		(74,365)				(74,365)
Equity component of exchangeable debt issuance, net of deferred financing costs and deferred tax asset	71,158		71,158				71,158
Acquisition of Angie's List and creation of noncontrolling interests in ANGI Homeservices	779,471		645,475				645,475				133,996
Noncontrolling interests created in an acquisition				17,758
Issuance of warrants	23,650		23,650				23,650
Other	1,027		148				148				879
Balance at end of period at Dec. 31, 2017	2,946,823		2,430,028		$ 261	$ 16	12,165,002	595,038	(103,568)	(10,226,721)	516,795
Balance at end of period (shares) at Dec. 31, 2017					260,624,000	16,157,000
Increase (Decrease) in Temporary Equity [Roll Forward]
Net (loss) earnings				33,897
Other comprehensive income (loss), net of tax				(702)
Stock-based compensation expense				1,138
Purchase of redeemable noncontrolling interests				(8,350)
Adjustment of redeemable noncontrolling interests to fair value				4,098
Noncontrolling interests created in acquisitions	14,307			2,261							14,307
Other				(9,522)
Balance at end of period at Dec. 31, 2018	65,687			65,687
Increase (Decrease) in Shareholders' Equity
Net (loss) earnings	723,850		626,961					626,961			96,889
Other comprehensive income (loss), net of tax	(30,704)		(25,278)						(25,278)		(5,426)
Stock-based compensation expense	237,282		75,311				75,311				161,971
Issuance of common stock pursuant to stock-based awards, net of withholding taxes	21,786		21,786		$ 1		21,785
Issuance of common stock pursuant to stock-based awards, net of withholding taxes (shares)					1,679,000
Purchase of treasury stock	(82,891)	$ (82,900)	(82,891)							(82,891)
Adjustment of redeemable noncontrolling interests to fair value	(4,098)		(4,098)				(4,098)
Purchase of noncontrolling interests	(9,364)										(9,364)
Issuance of common stock pursuant to stock-based awards, net of withholding taxes, and impact to noncontrolling interests												$ (341,400)	$ (342,457)	$ (342,592)	$ 135	$ 1,057	140,706	$ 106,204	$ 106,215	$ (11)	34,502
Dividends paid to Match Group noncontrolling interests																	$ (105,126)				$ (105,126)
Noncontrolling interests created in an acquisition	14,307			$ 2,261							14,307
Other	425		764				764				(339)
Balance at end of period at Dec. 31, 2018	$ 3,551,801		$ 2,843,125		$ 262	$ 16	$ 12,022,387	$ 1,258,794	$ (128,722)	$ (10,309,612)	$ 708,676
Balance at end of period (shares) at Dec. 31, 2018					262,303,000	16,157,000