EARNINGS PER SHARE - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Numerator: Basic
Net earnings	$ 87,839	$ 28,463
Net earnings attributable to noncontrolling interests	(16,757)	(2,254)
Net earnings (loss) attributable to IAC shareholders	71,082	26,209
Numerator: Diluted
Net earnings	87,839	28,463
Net earnings attributable to noncontrolling interests	(16,757)	(2,254)
Impact from public subsidiaries' dilutive securities	(7,442)	(2,430)
Net earnings (loss) attributable to IAC shareholders	$ 63,640	$ 23,779
Denominator: Basic
Weighted average basic shares outstanding (shares)	82,983	78,193
Denominator: Diluted
Weighted average basic shares outstanding (shares)	82,983	78,193
Dilutive securities including stock options and RSUs and subsidiary denominated equity awards (shares)	6,086	4,311
Denominator for earnings per share - weighted average shares (shares)	89,069	82,504
Earnings (loss) per share attributable to IAC shareholders: Basic
Basic earnings per share (USD per share)	$ 0.86	$ 0.34
Earnings (loss) per share attributable to IAC shareholders: Diluted
Diluted earnings per share (USD per share)	0.71	$ 0.29
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Exchange price per share (USD per share)	$ 152.18
Subsidiary Denominated Equity, Stock Options, and RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from calculation of diluted earnings per share (less than or equal to) (shares)	6,800	2,000
Market-based awards and PSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from calculation of diluted earnings per share (less than or equal to) (shares)	200	400