BASIS OF PRESENTATION (Policies)	3 Months Ended
BASIS OF PRESENTATION (Policies)	Mar. 31, 2018
Accounting Policies [Abstract]
Principles of Consolidation	The accompanying consolidated financial statements were prepared by the Company pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”) and, in the opinion of management, include all normal and recurring adjustments necessary to present fairly the results of the interim periods shown. Certain information and footnote disclosures normally included in financial statements prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) have been condensed or omitted pursuant to such SEC rules and regulations. Management believes that the disclosures made are adequate to make the information presented not misleading. Due to seasonality and other factors, the results for the interim periods may not be indicative of results for the full year. The financial statements contained herein should be read in conjunction with the consolidated financial statements and notes thereto included in the Company’s 2017 Annual Report on Form 10-K. The consolidated financial statements include the accounts of the Company and its subsidiaries. Also included in the consolidated financial statements are entities for which the Company has a controlling financial interest or is the primary beneficiary. Investments in companies in which the Company owns 20% to 50% of the voting common stock or otherwise exercises significant influence over operating and financial policies of the company are accounted for under the equity method. All significant intercompany transactions are eliminated in the consolidation process.
New Accounting Pronouncements Recently Adopted and Not Yet Adopted	New Accounting Pronouncements Recently Adopted As of January 1, 2018, the Company adopted the new accounting standard, ASC 606, Revenue from Contracts with Customers. This standard provides guidance for the recognition, measurement and disclosure of revenue from contracts with customers and supersedes previous revenue recognition guidance under U.S. GAAP. The Company has applied this standard using the full retrospective method and concluded that its adoption did not have a material impact on the Company’s balance sheets, statements of comprehensive loss, or statements of cash flows for prior periods. Please refer to Note 2, “Revenue from Contracts with Customers,” for more information. New Accounting Pronouncements Not Yet Adopted During the first quarter of 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). The new leasing standard presents significant changes to the balance sheets of lessees. Lessor accounting is updated to align with certain changes in the lessee model and the new revenue recognition standard which was issued in the third quarter of 2015. The standard is effective for annual periods, and for interim periods within those annual periods, beginning after December 15, 2018. The Company is currently evaluating the impact of the provisions of this new standard on its consolidated financial statements. During the first quarter of 2017, the FASB issued ASU 2017-04, Intangibles - Goodwill and Other (Topic 350). This update eliminates the requirement to calculate the implied fair value of goodwill to measure a goodwill impairment charge. Entities will record an impairment charge based on the excess of a reporting unit's carrying amount over its fair value. The standard is effective for annual and any interim impairment tests performed for periods beginning after December 15, 2019. The Company is currently evaluating the impact of the provisions of this new standard on its consolidated financial statements.
Accounts Receivable	Accounts Receivable Accounts receivable are recorded when the Company has an unconditional right to payment, either because it has satisfied a performance obligation prior to receiving payment from the customer or has a non-cancelable contract that has been billed in advance in accordance with the Company’s normal billing terms. Accounts receivable are recorded at the invoiced amount, net of reserves for sales returns and allowances and allowances for doubtful accounts. The Company evaluates the collectability of its accounts receivable based on a combination of factors. In circumstances where it is aware of a specific customer’s inability to meet its financial obligations, it records a specific reserve to reduce the amounts recorded to what it believes will be collected. For all other customers, it recognizes reserves for bad debt based on historical experience of bad debts as a percent of revenue for each business unit, adjusted for relative improvements or deteriorations in the agings and changes in current economic conditions. The Company believes its concentration of credit risk is limited due to the large number and the geographic diversification of its customers.
Revenue Recognition	Revenue Recognition The Company recognizes revenue in amounts that reflect the consideration it expects to receive in exchange for transferring goods or services to customers, excluding sales taxes and other similar taxes collected on behalf of governmental authorities (the "transaction price”). When this consideration includes a variable amount, the Company estimates the amount of consideration it expects to receive and only recognizes revenue to the extent that it is probable it will not be reversed in a future reporting period. For revenue arrangements that contain multiple distinct goods or services, the Company allocates the transaction price to these performance obligations in proportion to their relative standalone selling prices. The Company recognizes revenue when or as it satisfies a performance obligation by transferring a promised good or service to a customer. Revenues from the Company’s iHM segment are recognized at the point in time when advertisements or programs are broadcast or other contracted services are provided. Revenues from the Company’s Americas and International outdoor advertising segments’ contracts, which typically cover periods of a few weeks to one year, are generally recognized ratably over the term of the contract as the advertisement is displayed and the performance obligation is satisfied. Revenues from the Company’s Other segment’s full-service media representation contracts, which typically have terms of up to ten years in length, consist of contractual commissions realized from the sale of advertising on behalf of clients and are recognized at the point in time when these advertisements are broadcast. Advertising revenue is reported net of agency commissions. The Company receives payments from customers based on billing schedules that are established in its contracts. Revenues from the Company’s iHM and Other segments are generally billed monthly upon satisfaction of the performance obligations. Outdoor advertising contracts are also generally billed monthly. Americas outdoor is generally billed in advance, and International outdoor includes a combination of advance billings and billings upon completion of service. Deferred income is recorded when payment is received from a customer before the Company has satisfied the performance obligation or a non-cancelable contract has been billed in advance in accordance with the Company’s normal billing terms. Trade and barter transactions represent the exchange of advertising spots or display space for merchandise, services or other assets in the ordinary course of business. The transaction price for these contracts is calculated based on the estimated fair value of the non-cash consideration received unless this is not reasonably estimable, in which case the consideration is measured based on the standalone selling price of the advertising spots or display space promised to the customer. Revenue is recognized on trade and barter transactions when the advertisements are broadcasted or displayed, and expenses are recorded ratably over a period that estimates when the merchandise, services or other assets received are utilized, or when the event occurs. Trade and barter revenues and expenses from continuing operations are included in consolidated revenue and selling, general and administrative expenses, respectively.