EARNINGS PER SHARE - Summary (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator: Basic
Net earnings	$ 280,854	$ 80,557	$ 368,693	$ 109,020
Net earnings attributable to noncontrolling interests	(62,501)	(14,289)	(79,258)	(16,543)
Net earnings (loss) attributable to IAC shareholders	218,353	66,268	289,435	92,477
Numerator: Diluted
Net earnings	280,854	80,557	368,693	109,020
Net earnings attributable to noncontrolling interests	(62,501)	(14,289)	(79,258)	(16,543)
Impact from public subsidiaries' dilutive securities	(6,994)	(7,925)	(12,569)	(10,355)
Net earnings (loss) attributable to IAC shareholders	$ 211,359	$ 58,343	$ 276,866	$ 82,122
Denominator: Basic
Weighted average basic shares outstanding (shares)	83,604	79,067	83,296	78,633
Denominator: Diluted
Weighted average basic shares outstanding (shares)	83,604	79,067	83,296	78,633
Dilutive securities including stock options and RSUs and subsidiary denominated equity awards (shares)	7,330	4,711	7,438	4,510
Denominator for earnings per share - weighted average shares (shares)	90,934	83,778	90,734	83,143
Earnings (loss) per share attributable to IAC shareholders: Basic
Basic earnings per share (USD per share)	$ 2.61	$ 0.84	$ 3.47	$ 1.18
Earnings (loss) per share attributable to IAC shareholders: Diluted
Diluted earnings per share (USD per share)	2.32	$ 0.70	$ 3.05	$ 0.99
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)	3,400	100	6,900	500
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	200	400

Debt Instrument, Exchange Price Per Share

No definition available.

Name:	iac_DebtInstrumentExchangePricePerShare
Namespace Prefix:	iac_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.