THE COMPANY AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	6 Months Ended
	Jun. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Operations	Nature of Operations IAC has majority ownership of both Match Group, which includes Tinder, Match, PlentyOfFish, OkCupid and Hinge, and ANGI Homeservices, which includes HomeAdvisor, Angie’s List and Handy, and also operates Vimeo and Dotdash, among many other online businesses.
Basis of Presentation and Consolidation	Basis of Presentation and Consolidation The Company prepares its consolidated financial statements in accordance with U.S. generally accepted accounting principles ("GAAP"). The consolidated financial statements include the accounts of the Company, all entities that are wholly-owned by the Company and all entities in which the Company has a controlling financial interest. Intercompany transactions and accounts have been eliminated.
Accounting for Investments and Equity Securities	Accounting for Investments and Equity Securities Investments in equity securities, other than those of our consolidated subsidiaries and those accounted for under the equity method, are accounted for at fair value or under the measurement alternative of the Financial Accounting Standards Board's ("FASB") issued Accounting Standards Update ("ASU") No. 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities, following its adoption on January 1, 2018, with any changes to fair value recognized within other income (expense), net each reporting period. Under the measurement alternative, equity investments without readily determinable fair values are carried at cost minus impairment, if any, plus or minus changes resulting from observable price changes in orderly transactions for identical or similar securities of the same issuer; value is generally determined based on a market approach as of the transaction date. A security will be considered identical or similar if it has identical or similar rights to the equity securities held by the Company. The Company reviews its investments in equity securities without readily determinable fair values for impairment each reporting period when there are qualitative factors or events that indicate possible impairment. Factors we consider in making this determination include negative changes in industry and market conditions, financial performance, business prospects, and other relevant events and factors. When indicators of impairment exist, the Company prepares quantitative assessments of the fair value of our investments in equity securities, which require judgment and the use of estimates. When our assessment indicates that the fair value of the investment is below its carrying value, the Company writes down the investment to its fair value and records the corresponding charge within other income (expense), net. Investments in the common stock or in-substance common stock of entities in which the Company has the ability to exercise significant influence over the operating and financial matters of the investee, but does not have a controlling financial interest, are accounted for using the equity method and are included in "Long-term investments" in the accompanying consolidated balance sheet.
Accounting Estimates	Accounting Estimates Management of the Company is required to make certain estimates, judgments and assumptions during the preparation of its consolidated financial statements in accordance with GAAP. These estimates, judgments and assumptions impact the reported amounts of assets, liabilities, revenue and expenses and the related disclosure of contingent assets and liabilities. Actual results could differ from these estimates. On an ongoing basis, the Company evaluates its estimates and judgments, including those related to: the fair values of cash equivalents and marketable debt securities; the carrying value of accounts receivable, including the determination of the allowance for doubtful accounts; the determination of revenue reserves; the useful lives and recoverability of definite-lived intangible assets and property and equipment; the recoverability of goodwill and indefinite-lived intangible assets; the fair value of equity securities without readily determinable fair values; contingencies; the fair value of acquisition-related contingent consideration arrangements; unrecognized tax benefits; the valuation allowance for deferred income tax assets; and the fair value of and forfeiture rates for stock-based awards, among others. The Company bases its estimates and judgments on historical experience, its forecasts and budgets and other factors that the Company considers relevant.
General Revenue Recognition	General Revenue Recognition Revenue is recognized when control of the promised services or goods is transferred to our customers, and in an amount that reflects the consideration the Company expects to be entitled to in exchange for those services or goods. The Company's disaggregated revenue disclosures are presented in "Note 8—Segment Information." Deferred Revenue Deferred revenue consists of advance payments that are received or are contractually due in advance of the Company's performance. The Company’s deferred revenue is reported on a contract by contract basis at the end of each reporting period. The Company classifies deferred revenue as current when the term of the applicable subscription period or expected completion of our performance obligation is one year or less. The current and non-current deferred revenue balances at December 31, 2018 are $360.0 million and $1.7 million, respectively. During the six months ended June 30, 2019, the Company recognized $315.0 million of revenue that was included in the deferred revenue balance as of December 31, 2018. The current and non-current deferred revenue balances at June 30, 2019 are $402.2 million and $1.4 million, respectively. Non-current deferred revenue is included in “Other long-term liabilities” in the accompanying consolidated balance sheet. Practical Expedients and Exemptions As permitted under the practical expedient available under ASU No. 2014-09, Revenue from Contracts with Customers, the Company does not disclose the value of unsatisfied performance obligations for (i) contracts with an original expected length of one year or less, (ii) contracts with variable consideration that is allocated entirely to unsatisfied performance obligations or to a wholly unsatisfied promise accounted for under the series guidance, and (iii) contracts for which the Company recognizes revenue at the amount which we have the right to invoice for services performed. For sales incentive programs where the customer relationship period is one year or less, the Company has elected the practical expedient to expense the costs as incurred.
Certain Risks and Concentrations - Services Agreement with Google	Certain Risks and Concentrations—Services Agreement with Google A meaningful portion of the Company's revenue is attributable to a services agreement with Google (the "Services Agreement").
Adoption of ASU No. 2016-02, Leases (Topic 842)	Adoption of ASU No. 2016-02, Leases (Topic 842) The Company adopted ASU No. 2016-02, Leases (Topic 842) ("ASC 842") effective January 1, 2019. ASC 842 superseded previously existing guidance on accounting for leases and generally requires all leases to be recognized in the statement of financial position. The adoption of ASC 842 resulted in the recognition of $154.7 million of right-of-use assets ("ROU assets") and related lease liabilities as of January 1, 2019, with no cumulative effect adjustment. The adoption of ASC 842 had no impact on the Company’s consolidated statement of operations and consolidated statement of cash flows. The Company adopted ASC 842 prospectively and, therefore, did not revise comparative period information or disclosure. In addition, the Company elected the package of practical expedients permitted under ASC 842. See "Note 2—Leases" for additional information on the adoption of ASC 842.
Reclassifications	Reclassifications Certain prior year amounts have been reclassified to conform to the current year presentation.