CONSOLIDATED STATEMENT OF COMPREHENSIVE OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net earnings (loss)	$ 757,747	$ 358,008	$ (16,151)
Other comprehensive (loss) income, net of tax:
Change in foreign currency translation adjustment	(31,411)	80,269	(43,126)
Change in unrealized gains and losses on available-for-sale securities (net of tax benefit of $3,846 and $884 in 2017 and 2016, respectively)	5	(4,026)	1,484
Total other comprehensive (loss) income	(31,406)	76,243	(41,642)
Comprehensive income (loss), net of tax	726,341	434,251	(57,793)
Components of comprehensive (income) loss attributable to noncontrolling interests:
Net earnings attributable to noncontrolling interests	(130,786)	(53,084)	(25,129)
Change in foreign currency translation adjustment attributable to noncontrolling interests	6,129	(13,797)	6,033
Change in unrealized gain and losses of available-for-sale securities attributable to noncontrolling interests	(1)	0	458
Comprehensive income attributable to noncontrolling interests	(124,658)	(66,881)	(18,638)
Comprehensive income (loss) attributable to IAC shareholders	$ 601,683	$ 367,370	$ (76,431)