THE COMPANY AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	3 Months Ended
	Mar. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Operations	Nature of Operations IAC operates Vimeo, Dotdash and Care.com, among many other online businesses, and 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.
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 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 carrying value of right-of-use assets ("ROU assets"); the useful lives and recoverability of definite-lived intangible assets and property, capitalized software 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.
Accounting for Investments and Equity Securities	Accounting for Investments in Equity Securities Investments in equity securities, other than those of the Company's consolidated subsidiaries and those accounted for under the equity method, if applicable, are accounted for at fair value or under the measurement alternative of Financial Accounting Standards Board ("FASB") 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 the Company considers 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 the its investments in equity securities, which require judgment and the use of estimates. When the Company's 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. See "Note 4—Financial Instruments and Fair Value Measurements" for additional information on the impairments of certain equity securities without readily determinable fair values recorded in the quarter ended March 31, 2020. In the event the Company has 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. At March 31, 2020 and December 31, 2019, the Company did not have any investments accounted for using the equity method.
General Revenue Recognition	General Revenue Recognition Revenue is recognized when control of the promised services or goods is transferred to the Company's customers and in the 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." Prior to January 1, 2020, ANGI's Handy business recorded revenue on a net basis. Effective January 1, 2020, the Company modified the Handy terms and conditions so that Handy, rather than the service professional, has the contractual relationship with the consumer to deliver the service and Handy, rather than the consumer, has the contractual relationship with the service professional. Consumers request services and pay for such services directly through the Handy platform and then Handy fulfills the request with independently established home services providers engaged in a trade, occupation and/or business that customarily provides such services. This change in contractual terms requires gross revenue accounting treatment effective January 1, 2020. Also, in the case of certain tasks, HomeAdvisor provides a pre-priced product offering, pursuant to which consumers can request services through a HomeAdvisor platform and pay HomeAdvisor for the services directly. HomeAdvisor then fulfills the request with independently established home services providers engaged in a trade, occupation and/or business that customarily provides such services. Revenue from HomeAdvisor’s pre-priced product offering is also recorded on a gross basis effective January 1, 2020. In addition to changing the presentation of revenue to gross from net, the timing of revenue recognition will change for pre-priced jobs and will be later than the timing of existing consumer connection revenue for HomeAdvisor because the Company will not be able to record revenue, generally, until the service professional completes the job on the Company's behalf. The change to gross revenue reporting for Handy and HomeAdvisor’s pre-priced product offering, effective January 1, 2020, resulted in an increase in revenue of $15.2 million during the three months ended March 31, 2020. 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 the Company's performance obligation is one year or less. The current and non-current deferred revenue balances at December 31, 2019 are $397.5 million and $1.3 million, respectively. During the three months ended March 31, 2020, the Company recognized $258.2 million of revenue that was included in the deferred revenue balance as of December 31, 2019. During the three months ended March 31, 2019, the Company recognized $234.8 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 March 31, 2020 are $433.7 million and $1.3 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 the Company has 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"). In addition, the Company earns certain other advertising revenue from Google that is not attributable to the Services Agreement.
Adoption of ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes	Adoption of ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes The Company adopted ASU No. 2019-12 effective January 1, 2020, which simplifies the accounting for income taxes, eliminates certain exceptions within ASC 740, Income Taxes, and clarifies certain aspects of the current guidance to promote consistency among reporting entities. Most amendments within ASU No. 2019-12 are required to be applied on a prospective basis, while certain amendments must be applied on a retrospective or modified retrospective basis. The Company adopted ASU No. 2019-12 on January 1, 2020 using the modified retrospective basis for those amendments that are not applied on a prospective basis. The adoption of ASU No. 2019-12 did not have a material impact on the Company’s consolidated financial statements.
Reclassifications	Reclassifications Certain prior year amounts have been reclassified to conform to the current year presentation.