Yelp (YELP) 10-Q 9 Nov 18 2018 Q3 Quarterly report Financial data

DOCUMENT AND ENTITY INFORMATION

DOCUMENT AND ENTITY INFORMATION - shares	9 Months Ended
	Sep. 30, 2018	Oct. 31, 2018
Document and Entity Information [Abstract]
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Amendment Flag	false
Entity Registrant Name	YELP INC
Entity Central Index Key	1,345,016
Trading Symbol	YELP
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding		83,083,501

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	[1]
Current assets:
Cash and cash equivalents	$ 423,495	$ 547,850
Short-term marketable securities	414,002	273,366
Accounts receivable (net of allowance for doubtful accounts of $8,885 and $8,602 at September 30, 2018 and December 31, 2017, respectively)	81,835	76,173
Prepaid expenses and other current assets	17,567	15,700
Total current assets	936,899	913,089
Long-term marketable securities	0	25,032
Property, equipment and software, net	110,899	103,651
Goodwill	106,323	107,954
Intangibles, net	14,242	16,893
Restricted cash	22,121	18,554
Other non-current assets	42,773	40,428
Total assets	1,233,257	1,225,601
Current liabilities:
Accounts payable	6,829	9,033
Accrued liabilities	58,564	73,665
Deferred revenue	3,392	3,469
Total current liabilities	68,785	86,167
Long-term liabilities	34,978	30,737
Total liabilities	103,763	116,904
Commitments and contingencies (Note 12)
Stockholders' equity:
Common stock, $0.000001 par value, 200,000,000 shares authorized – 84,375,021 shares issued and outstanding at September 30, 2018 and 83,724,916 shares issued and outstanding at December 31, 2017	0	0
Additional paid-in capital	1,109,199	1,038,017
Treasury stock	0	(46)
Accumulated other comprehensive loss	(10,225)	(8,444)
Retained earnings	30,520	79,170
Total stockholders' equity	1,129,494	1,108,697
Total liabilities and stockholders' equity	$ 1,233,257	$ 1,225,601
[1]	As of January 1, 2018, the Company adopted Accounting Standards Update 2014-09, "Revenue from Contracts with Customers (Topic 606)" ("ASC 606"), using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior period presented. See Note 1 below for additional discussion.

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	[1]
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 8,885	$ 8,602
Common stock, par value (in USD per share)	$ 0.000001	$ 0.000001
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	84,375,021	83,724,916
Common stock, shares outstanding (in shares)	84,375,021	83,724,916
[1]	As of January 1, 2018, the Company adopted Accounting Standards Update 2014-09, "Revenue from Contracts with Customers (Topic 606)" ("ASC 606"), using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior period presented. See Note 1 below for additional discussion.

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	[1]	Sep. 30, 2018	Sep. 30, 2017	[1]
Income Statement [Abstract]
Net revenue	$ 241,096	$ 223,287		$ 699,033	$ 631,406
Costs and expenses:
Cost of revenue (exclusive of depreciation and amortization shown separately below)	14,177	19,312		43,618	54,282
Sales and marketing	121,759	112,958		362,054	326,409
Product development	53,764	45,834		158,046	127,793
General and administrative	30,302	27,601		90,892	81,808
Depreciation and amortization	10,713	10,656		31,250	31,470	[2]
Restructuring and integration	0	35		0	286
Total costs and expenses	230,715	216,396		685,860	622,048
Income from operations	10,381	6,891		13,173	9,358
Other income, net	3,921	1,371		9,950	2,933
Income before income taxes	14,302	8,262		23,123	12,291
Benefit from (provision for) income taxes	684	(232)		281	(417)
Net income attributable to common stockholders	$ 14,986	$ 8,030		$ 23,404	$ 11,874	[2]
Net income per share attributable to common stockholders
Basic (in USD per share)	$ 0.18	$ 0.10		$ 0.28	$ 0.15
Diluted (in USD per share)	$ 0.17	$ 0.09		$ 0.26	$ 0.14
Weighted-average shares used to compute net income per share attributable to common stockholders
Basic (in shares)	84,008	82,259		83,865	81,041
Diluted (in shares)	88,724	87,433		89,271	86,097
[1]	As of January 1, 2018, the Company adopted ASC 606 using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior periods presented. See Note 1 below for additional discussion.
[2]	As of January 1, 2018, the Company adopted ASC 606 using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior period presented. Also as of January 1, 2018, the Company adopted Accounting Standards Update No. 2016-18, "Statement of Cash Flows (Subtopic 230): Restricted Cash," and recast the prior period presented. See Note 1 below for additional discussion.

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	[1]	Sep. 30, 2018	Sep. 30, 2017	[1]
Statement of Comprehensive Income [Abstract]
Net income attributable to common stockholders	$ 14,986	$ 8,030		$ 23,404	$ 11,874	[2]
Other comprehensive (loss) income:
Foreign currency translation adjustments	(193)	2,041		(1,811)	6,673
Foreign currency adjustments to net income upon liquidation of investment in foreign entities	0	(175)		30	(204)
Other comprehensive (loss) income	(193)	1,866		(1,781)	6,469
Comprehensive income	$ 14,793	$ 9,896		$ 21,623	$ 18,343
[1]	As of January 1, 2018, the Company adopted ASC 606 using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior periods presented. See Note 1 below for additional discussion.
[2]	As of January 1, 2018, the Company adopted ASC 606 using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior period presented. Also as of January 1, 2018, the Company adopted Accounting Standards Update No. 2016-18, "Statement of Cash Flows (Subtopic 230): Restricted Cash," and recast the prior period presented. See Note 1 below for additional discussion.

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	[1]
OPERATING ACTIVITIES:
Net income attributable to common stockholders	$ 23,404	$ 11,874	[2]
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	31,250	31,470	[2]
Bad debt expense	19,285	15,239
Stock-based compensation	85,732	75,007
Other adjustments	(2,793)	280
Changes in operating assets and liabilities:
Accounts receivable	(24,956)	(19,810)
Prepaid expenses and other assets	(2,085)	(2,077)
Accounts payable, accrued expenses and other liabilities	(13,647)	15,628
Deferred revenue	(75)	350
Net cash provided by operating activities	116,115	127,961
INVESTING ACTIVITIES:
Purchases of marketable securities	(572,788)	(179,557)
Maturities of marketable securities	460,800	191,000
Acquisition of a business, net of cash received	0	(50,544)
Purchases of property, equipment and software	(18,699)	(7,892)
Capitalized website and software development costs	(15,238)	(12,236)
Other investing activities	64	69
Net cash used in investing activities	(145,861)	(59,160)
FINANCING ACTIVITIES:
Proceeds from issuance of common stock for employee stock-based plans	21,835	29,556
Repurchases of common stock	(71,993)	(7,743)
Taxes paid related to the net share settlement of equity awards	(41,081)	0
Net cash (used in) provided by financing activities	(91,239)	21,813
Effect of exchange rate changes on cash, cash equivalents and restricted cash	197	864
CHANGE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	(120,788)	91,478
CASH, CASH EQUIVALENTS AND RESTRICTED CASH—Beginning of period	566,404	289,518
CASH, CASH EQUIVALENTS AND RESTRICTED CASH—End of period	445,616	380,996
SUPPLEMENTAL DISCLOSURES OF OTHER CASH FLOW INFORMATION:
Cash paid for income taxes, net	28,820	82
SUPPLEMENTAL DISCLOSURES OF NONCASH INVESTING AND FINANCING ACTIVITIES:
Purchases of property, equipment and software recorded in accounts payable, accrued expenses and other liabilities	2,393	3,555
Tax liability related to net share settlement of equity awards included in accrued liabilities	$ 1,679	$ 0
[1]	As of January 1, 2018, the Company adopted ASC 606 using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior period presented. Also as of January 1, 2018, the Company adopted Accounting Standards Update No. 2016-18, "Statement of Cash Flows (Subtopic 230): Restricted Cash," and recast the prior period presented. See Note 1 below for additional discussion.
[2]	As of January 1, 2018, the Company adopted ASC 606 using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior periods presented. See Note 1 below for additional discussion.

DESCRIPTION OF BUSINESS AND BAS

DESCRIPTION OF BUSINESS AND BASIS FOR PRESENTATION	9 Months Ended
	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business and Basis for Presentation	DESCRIPTION OF BUSINESS AND BASIS FOR PRESENTATION Yelp Inc. was incorporated in Delaware on September 3, 2004. Except where specifically noted or the context otherwise requires, the use of terms such as the "Company" and "Yelp" in these Notes to Condensed Consolidated Financial Statements refers to Yelp Inc. and its subsidiaries. Yelp connects people with great local businesses by bringing "word of mouth" online and providing a platform for businesses and consumers to engage and transact. Yelp’s platform is transforming the way people discover local businesses; every day, millions of consumers visit its website or use its mobile app to find great local businesses to meet their everyday needs. Businesses of all sizes use the Yelp platform to engage with consumers at the critical moment when they are deciding where to spend their money. Basis of Presentation The accompanying interim condensed consolidated financial statements are unaudited. These unaudited interim condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America ("GAAP") and the applicable rules and regulations of the U.S. Securities and Exchange Commission ("SEC") regarding interim financial reporting. Certain information and note disclosures normally included in the financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. Accordingly, these unaudited interim condensed consolidated financial statements should be read in conjunction with the consolidated financial statements contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017 , filed with the SEC on February 28, 2018 (the "Annual Report"). The unaudited condensed consolidated balance sheet as of December 31, 2017 included herein was derived from the audited consolidated financial statements as of that date, but does not include all disclosures required by GAAP, including certain notes to the financial statements and certain balances that have been recast as a result of the adoption of new accounting pronouncements. The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited consolidated financial statements, except as follows: Revenue from Contracts with Customers —In May 2014, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update No. 2014-09, "Revenue from Contracts with Customers (Topic 606)" ("ASC 606"), which supersedes the revenue recognition requirements in Revenue Recognition (Topic 605) and requires entities to recognize revenue when they transfer promised goods or services to customers in an amount that reflects the consideration that the entity expects to be entitled to receive in exchange for such goods or services. ASC 606 also modified Subtopic Accounting Standards Codification 340-40, "Other Assets and Deferred Costs—Contracts with Customers," which required the Company to recognize a deferred cost asset for the incremental costs of obtaining a contract with a customer. The Company adopted ASC 606 effective January 1, 2018 using the full retrospective method and, accordingly, has recast each prior reporting period presented. The Company's adoption of ASC 606 resulted in the following adjustments to its previously reported results (in thousands): As Previously Reported Impact of ASC 606 Adoption As Currently Reported Condensed Consolidated Statement of Operations—Three Months Ended September 30, 2017 Net revenue $ 222,380 $ 907 $ 223,287 Costs and Expenses: Sales and marketing 113,041 (83 ) 112,958 General and administrative 26,694 907 27,601 Net income attributable to common stockholders 7,947 83 8,030 Condensed Consolidated Statement of Operations—Nine Months Ended September 30, 2017 Net revenue $ 628,567 $ 2,839 $ 631,406 Costs and Expenses: Sales and marketing 327,559 (1,150 ) 326,409 General and administrative 78,969 2,839 81,808 Net income attributable to common stockholders 10,724 1,150 11,874 Basic net income per share 0.13 0.02 0.15 Diluted net income per share 0.12 0.02 0.14 Condensed Consolidated Balance Sheet—As of December 31, 2017 Allowance for doubtful accounts 7,352 1,250 8,602 Other non-current assets 31,339 9,089 40,428 Retained earnings 70,081 9,089 79,170 Condensed Consolidated Statement of Cash Flows—Nine Months Ended September 30, 2017 Bad debt expense 12,400 2,839 15,239 Change in accounts receivable (16,971 ) (2,839 ) (19,810 ) Other adjustments to reconcile net income to net cash provided by operating activities (927 ) (1,150 ) (2,077 ) Statement of Cash Flows —In November 2016, FASB issued Accounting Standards Update No. 2016-18, "Statement of Cash Flows (Subtopic 230): Restricted Cash" ("ASU 2016-18"), which requires amounts generally described as restricted cash and restricted cash equivalents to be included with cash and cash equivalents when reconciling the total beginning and ending amounts for the periods shown on the statement of cash flows. The Company adopted the standard effective January 1, 2018 and recast the prior reported periods presented. The impact to the change in cash and cash equivalents balance previously reported on the consolidated statement of cash flows is presentation only; changes in restricted cash were previously included within investing activities and are now included in changes to the total cash balance within the condensed consolidated statements of cash flows. In the opinion of management, the accompanying unaudited condensed consolidated financial statements include all adjustments of a normally recurring nature necessary for the fair presentation of the interim periods presented. Significant Accounting Policies Except as set forth below, there have been no material changes to the Company's significant accounting policies from those described in the Annual Report. Revenue Recognition— The Company generates revenue from the sale of of advertising products, transactions and other services, which correspond to the Company's major product lines. The Company recognizes revenue when all of the following criteria are met: the contract with the customer is identified; the performance obligations in the contract are identified; the transaction price is determined; the transaction price is allocated to the performance obligations in the contract; and revenue is recognized when (or as) the Company satisfies these performance obligations. The Company applies the portfolio practical expedient to account for contracts with customers in each category of revenue. Revenue is recognized net of any taxes collected from customers, which are remitted to governmental authorities. The Company does not typically refund customers for services once it determines the performance obligations of the contract have been satisfied, but will assess any refund requests from customers and partners on a case by case basis. The Company records an allowance for potential future refunds, which is estimated based on historical trends and recorded as a reduction of net revenue. Advertising. The Company generates advertising revenue primarily through the display of advertising products on its website and mobile app. These arrangements are evidenced by either written or electronic acceptance of a contract that stipulates the types of advertising to be delivered, the timing and pricing. Performance-based advertising placements are priced on a cost-per-click basis, while impression-based advertising placements are priced on a cost per thousand impressions basis. The Company recognizes revenue from the delivery of performance-based ads and impression-based ads in the period of delivery, in each case net of customer discounts, assuming all other revenue recognition criteria are met. The Company also offers businesses premium features in connection with their business listing pages pursuant to fixed monthly fees, and recognizes revenue from such offerings over the service period, assuming all other revenue recognition criteria are met. The Company also generates advertising revenue through indirect sales of advertising products, such as through reseller contracts that allow partners to sell Yelp Branded Profiles to their clients and the monetization of remnant advertising inventory through third-party ad networks, and recognizes revenue in the period of delivery, assuming all other revenue recognition criteria are met. Transactions. The Company generates transactions revenue from revenue-sharing partner contracts, the sale of vouchers through the Company's "Yelp Deals" and "Yelp Gift Certificates" products, and, through October 10, 2017, Yelp Eat24 as a standalone product. The Company's transactions platform provides consumers with the ability to complete food delivery and other transactions through third parties directly on Yelp. The Company earns a per-transaction commission fee pursuant to partnership contracts for acting as an agent for these transactions, which it recognizes on a net basis and includes in revenue upon completion of a transaction, assuming all other revenue recognition criteria are met. Other Services. The Company generates other services revenue through subscription services contracts, such as sales of monthly subscriptions to its Yelp Reservations, Yelp Nowait and Yelp WiFi Marketing products, licensing contracts for access to Yelp data and other non-advertising, non-transaction partnerships. Subscription revenues are recognized ratably over the contract terms beginning on the commencement date of each contract, which is the date the service is made available to customers, assuming all other revenue recognition criteria are met. Contracts with Multiple Performance Obligations. Contracts with customers can include multiple performance obligations, where revenue is allocated to each performance obligation based on its relative standalone selling price ("SSP"). The Company determines SSP based on the prices of the promised goods or services charged when sold separately to customers, which are determined using contractually stated prices. The various products and services comprising contracts with multiple performance obligations are typically capable of being distinguished and accounted for as separate performance obligations. Estimates and assumptions include determining variable consideration, identifying the nature and timing of satisfaction of performance obligations, and calculating the SSP of performance obligations. The Company allocates revenue to each of the performance obligations included in a contract with multiple performance obligations at the inception of the contract. The Company applies the invoice practical expedient to depict the value transferred to the customer and measure of progress towards completion of its obligations. The Company considers the right to receive consideration from a customer to correspond directly with the value to the customer of its performance completed to date. Because the Company considers contracts month-to-month, variable consideration is resolved at the time of invoicing, which eliminates the use of estimates in determining the transaction price. The Company does not consider the effects of the time value of money as the majority of the Company’s contracts are invoiced on a monthly basis, one month in arrears. Accounts Receivable, Net, and Payment Terms— The timing of revenue recognition may differ from the timing of invoicing to customers. The Company records an accounts receivable balance when revenue is recognized prior to or at the time of invoicing the customer. Payment terms and conditions vary by contract type and the service being provided. For advertising services, the Company typically invoices customers on a monthly basis, one month in arrears, and payment is collected either at the end of each billing period or up to 30 days after the end of the billing period. For transaction services, the Company's commission fee on each transaction is collected either at the time of the transaction, or up to 30 days after the end of the billing period. For subscription services, the Company typically invoices one month in advance, and payment is collected at the beginning of each billing period. Allowance for Doubtful Accounts— The Company maintains an allowance for doubtful accounts receivable. The allowance reflects the Company's best estimate of probable losses inherent in the accounts receivable balance. It is based upon historical experience and loss patterns, the number of days that billings are past due, an evaluation of the potential risk of loss associated with delinquent accounts and known delinquent accounts. When new information becomes available that allows the Company to more accurately estimate the allowance, it makes an adjustment, which is considered a change in accounting estimate. The carrying value of accounts receivable approximates their fair value. Deferred Contract Costs —The Company classifies certain sales incentive compensation costs as incremental to obtaining the related contract. These costs are capitalized in the period in which they are incurred and amortized on a straight-line basis over the expected customer life of the associated contract. The Company uses a straight line basis as it expects the benefit of these costs to be realized uniformly over the amortization period. The amortization periods for contract costs, which extend up to 41 months, were determined based on both qualitative and quantitative factors, including product lifecycle attributes and customer retention historical data. For contract costs with amortization periods of less than 12 months, the Company applies a practical expedient to expense such costs as incurred. The Company assesses deferred contract costs for impairment on a quarterly basis. Amortized contract costs are recorded within sales and marketing expense on the consolidated statements of operations. Deferred contract costs are included within other non-current assets on the Company's consolidated balance sheets (see Note 8). Deferred Revenue —The Company records deferred revenue when it has received consideration, or has the right to receive consideration, in advance of the transfer of the performance obligations of the contract to the customer. Recent Accounting Pronouncements Not Yet Effective Lease Accounting In February 2016, FASB issued Accounting Standards Update No. 2016-02, "Leases (Topic 842)" ("ASC 842"). ASC 842 supersedes the previous accounting guidance for leases included within Accounting Standards Codification 840, "Leases" ("ASC 840"). The new guidance generally requires an entity to recognize on its balance sheet operating and financing lease liabilities and corresponding right-of-use assets, as well as to recognize the associated lease expenses on its statements of operations in a manner similar to that required under current accounting rules. The standard will be effective for the first interim period within annual reporting periods beginning after December 15, 2018 and early adoption is permitted. The new standard initially required a modified retrospective transition for existing leases to each prior reporting period presented. However, in July 2018, FASB issued Accounting Standards Update No. 2018-11, "Targeted Improvements to ASC 842" ("ASU 2018-11"), which provides entities with the option to begin applying ASC 842 at the adoption date rather than at the beginning of the earliest period presented (the "Effective Date Method"). Entities using the Effective Date Method recognize a cumulative-effect adjustment to the opening balance of retained earnings (or accumulated deficit) in the period of adoption. The Company plans to adopt ASC 842 on January 1, 2019 using the Effective Date Method by recording a cumulative-effect adjustment to retained earnings (or accumulated deficit) as of January 1, 2019. As a result, the Company will continue to disclose comparative reporting periods under the previous accounting guidance, ASC 840. The Company continues to evaluate the impact of ASC 842 on its consolidated financial statements and accounting processes. Based on these ongoing evaluations, the Company currently expects the most significant changes will be related to the recognition of operating lease right-of-use assets and operating lease liabilities on its consolidated balance sheet in the amounts of approximately $240 million to $260 million and approximately $270 million to $290 million , respectively. The Company does not expect the impact on its consolidated statement of operations to be material. These estimates are based on the Company's office lease portfolio and, to a much lesser extent, its lease portfolio of computer equipment, each as of September 30, 2018. The ultimate impact of the Company's adoption of ASC 842 on its financial statements may change for reasons including, but not limited to: • finalization of the impact analysis of the new standard; • new lease contracts entered into during the three months ending December 31, 2018 that result in additional lease assets and lease liabilities; • changes in discount rates used to calculate the initial lease liability; • significant changes in foreign exchange rates applied to lease liabilities and right-of-use assets denominated in currencies other than U.S. dollars; and • changes in the Company's expectations for renewal options of existing leases. Other Pronouncements In January 2017, FASB issued Accounting Standards Update No. 2017-04, "Intangibles—Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment" ("ASU 2017-04"). This new guidance simplifies the subsequent measurement of goodwill by eliminating Step 2 from the goodwill impairment test. Under the new standard, entities will perform goodwill impairment tests by comparing fair value of a reporting unit with its carrying amount and recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value. The standard will be effective for the first interim period within annual reporting periods beginning after December 15, 2019 and early adoption is permitted. The Company does not expect the adoption of ASU 2017-04 to have a material impact on its consolidated financial statements. In March 2017, FASB issued Accounting Standards Update No. 2017-08, "Receivables—Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities" ("ASU 2017-08"). This new guidance requires entities to amortize purchased callable debt securities held at a premium to the earliest call date. The standard will be effective for the first interim period within annual reporting periods beginning after December 15, 2018 and early adoption is permitted. The Company does not expect the adoption of ASU 2017-08 to have a material impact on its consolidated financial statements. In June 2018, FASB issued Accounting Standards Update No. 2018-07, "Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting" ("ASU 2018-07"). This new guidance changes the accounting for non-employee share-based payments to align with the accounting for employee stock compensation. The standard will be effective for the first interim period within annual reporting periods beginning after December 15, 2018 and early adoption is permitted. The Company does not expect the adoption of ASU 2018-07 to have a material impact on its consolidated financial statements. In August 2018, FASB issued Accounting Standards Update No. 2018-13, "Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement" (“ASU 2018-13”), which amends Accounting Standards Codification 820, "Fair Value Measurement." ASU 2018-13 modifies the disclosure requirements for fair value measurements by removing, modifying and adding certain disclosures. The standard will be effective for the first interim period within annual reporting periods beginning after December 15, 2019 and early adoption is permitted. The Company is currently evaluating the impact of ASU 2018-13 on its consolidated financial statements. In August 2018, FASB issued Accounting Standards Update No. 2018-15, "Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That is a Service Contract" ("ASU 2018-15"). This new guidance requires a customer in a cloud computing arrangement that is a service contract to follow the internal-use software guidance in Accounting Standards Codification 350-40 to determine which implementation costs to defer and recognize as an asset. ASU 2018-15 generally aligns the guidance on recognizing implementation costs incurred in a cloud computing arrangement that is a service contract with that for implementation costs incurred to develop or obtain internal-use software, including hosting arrangements that include an internal-use software license. ASU 2018-15 is effective for the first interim period within annual reporting periods beginning after December 15, 2019 and early adoption is permitted. The Company is currently assessing the impact of ASU 2018-15 on its consolidated financial statements and related disclosures. Principles of Consolidation These unaudited interim condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany accounts and transactions have been eliminated upon consolidation. Use of Estimates The preparation of the Company’s unaudited interim condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of income and expenses during the reporting period. These estimates are based on information available as of the date of the condensed consolidated financial statements; therefore, actual results could differ from management’s estimates.

CASH, CASH EQUIVALENTS AND REST

CASH, CASH EQUIVALENTS AND RESTRICTED CASH	9 Months Ended
	Sep. 30, 2018
Cash and Cash Equivalents [Abstract]
Cash, Cash Equivalents and Restricted Cash	CASH, CASH EQUIVALENTS AND RESTRICTED CASH Cash, cash equivalents and restricted cash as of September 30, 2018 and December 31, 2017 consisted of the following (in thousands): September 30, 2018 December 31, 2017 Cash $ 166,336 $ 283,085 Cash equivalents 257,159 264,765 Total cash and cash equivalents $ 423,495 $ 547,850 Restricted cash 22,121 18,554 Total cash, cash equivalents and restricted cash $ 445,616 $ 566,404 As of September 30, 2018 and December 31, 2017 , the Company had letters of credit collateralized fully by bank deposits which totaled $22.1 million and $18.6 million , respectively. These letters of credit primarily relate to lease agreements for certain of the Company’s offices, which are required to be maintained and issued to the landlords of each facility. Each letter of credit is subject to renewal annually until the applicable lease expires. As the bank deposits have restrictions on their use, they are classified as restricted cash on the Company's condensed consolidated balance sheets.

FAIR VALUE OF FINANCIAL INSTRUM

FAIR VALUE OF FINANCIAL INSTRUMENTS	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	FAIR VALUE OF FINANCIAL INSTRUMENTS The Company’s investments in money market accounts are recorded as cash equivalents at fair value in the condensed consolidated balance sheets. All other financial instruments are classified as held-to-maturity investments and, accordingly, are recorded at amortized cost; however, the Company is required to determine the fair value of these investments on a recurring basis to identify any potential impairment. The accounting guidance for fair value measurements prioritizes the inputs used in measuring fair value in the following hierarchy: Level 1 —Observable inputs, such as quoted prices in active markets, Level 2 —Inputs other than quoted prices in active markets that are observable either directly or indirectly, or Level 3 —Unobservable inputs in which there are little or no market data, which require the Company to develop its own assumptions. This hierarchy requires the Company to use observable market data, when available, to minimize the use of unobservable inputs when determining fair value. The Company’s money market funds are classified within Level 1 of the fair value hierarchy because they are valued using quoted prices in active markets. The Company’s commercial paper, corporate bonds, U.S. government bonds, agency bonds and agency discount notes are classified within Level 2 of the fair value hierarchy because they have been valued using inputs other than quoted prices in active markets that are observable directly or indirectly. The following table represents the Company’s financial instruments measured at fair value as of September 30, 2018 and December 31, 2017 (in thousands): September 30, 2018 December 31, 2017 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Cash Equivalents: Money market funds $ 219,742 $ — $ — $ 219,742 $ 217,838 $ — $ — $ 217,838 Commercial paper — 37,417 — 37,417 — 46,927 — 46,927 Marketable Securities: Commercial paper — 158,506 — 158,506 — 138,412 — 138,412 Corporate bonds — 137,967 — 137,967 — 69,926 — 69,926 U.S. government bonds — 69,208 — 69,208 — — — — Agency bonds — 48,047 — 48,047 — 78,913 — 78,913 Agency discount notes — — — — — 10,989 — 10,989 Total cash equivalents and marketable securities $ 219,742 $ 451,145 $ — $ 670,887 $ 217,838 $ 345,167 $ — $ 563,005

MARKETABLE SECURITIES

MARKETABLE SECURITIES	9 Months Ended
	Sep. 30, 2018
Investments, Debt and Equity Securities [Abstract]
Marketable Securities	MARKETABLE SECURITIES The amortized cost, gross unrealized gains and losses, and fair value of securities held-to-maturity as of September 30, 2018 and December 31, 2017 were as follows (in thousands): September 30, 2018 Short-term marketable securities: Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Commercial paper $ 158,506 $ — $ — $ 158,506 Corporate bonds 138,141 — (174 ) 137,967 U.S. government bonds 69,241 — (33 ) 69,208 Agency bonds 48,114 — (67 ) 48,047 Total short-term marketable securities 414,002 — (274 ) 413,728 Total marketable securities $ 414,002 $ — $ (274 ) $ 413,728 December 31, 2017 Short-term marketable securities: Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Commercial paper $ 138,412 $ 1 $ (1 ) $ 138,412 Corporate bonds 45,006 — (41 ) 44,965 Agency bonds 78,958 — (45 ) 78,913 Agency discount bonds $ 10,990 $ — $ (1 ) $ 10,989 Total short-term marketable securities $ 273,366 $ 1 $ (88 ) $ 273,279 Long-term marketable securities: Corporate bonds $ 25,032 $ — $ (71 ) $ 24,961 Total long-term marketable securities $ 25,032 $ — $ (71 ) $ 24,961 Total marketable securities $ 298,398 $ 1 $ (159 ) $ 298,240 The following tables present gross unrealized losses and fair values for those securities that were in an unrealized loss position as of September 30, 2018 and December 31, 2017 , aggregated by investment category and the length of time that the individual securities have been in a continuous loss position (in thousands): September 30, 2018 Less Than 12 Months 12 Months or Greater Total Fair Value Unrealized Loss Fair Value Unrealized Loss Fair Value Unrealized Loss Corporate bonds $ 132,992 $ (174 ) $ — $ — $ 132,992 $ (174 ) Agency bonds 48,047 (67 ) — — 48,047 (67 ) U.S. government bonds 69,208 (33 ) — — 69,208 (33 ) Commercial paper — — — — — — Total $ 250,247 $ (274 ) $ — $ — $ 250,247 $ (274 ) December 31, 2017 Less Than 12 Months 12 Months or Greater Total Fair Value Unrealized Loss Fair Value Unrealized Loss Fair Value Unrealized Loss Agency bonds $ 78,913 $ (45 ) $ — $ — $ 78,913 $ (45 ) Corporate bonds 62,927 (112 ) — — 62,927 (112 ) Agency discount notes 10,989 (1 ) — — 10,989 (1 ) Commercial paper 3,975 (1 ) — — 3,975 (1 ) Total $ 156,804 $ (159 ) $ — $ — $ 156,804 $ (159 ) The Company periodically reviews its investment portfolio for other-than-temporary impairment. The Company considers such factors as the duration, severity and reason for the decline in value, and the potential recovery period. The Company also considers whether it is more likely than not that it will be required to sell the securities before the recovery of their amortized cost basis, and whether the amortized cost basis cannot be recovered as a result of credit losses. During the three and nine months ended September 30, 2018 and 2017 , the Company did not recognize any other-than-temporary impairment loss.

PROPERTY, EQUIPMENT AND SOFTWAR

PROPERTY, EQUIPMENT AND SOFTWARE, NET	9 Months Ended
	Sep. 30, 2018
Property, Plant and Equipment [Abstract]
Property, Equipment and Software, Net	PROPERTY, EQUIPMENT AND SOFTWARE, NET Property, equipment and software, net as of September 30, 2018 and December 31, 2017 consisted of the following (in thousands): September 30, 2018 December 31, 2017 Capitalized website and internal-use software development costs $ 102,004 $ 81,710 Leasehold improvements 79,589 74,236 Computer equipment 40,129 32,450 Furniture and fixtures 17,351 16,435 Telecommunication 4,554 3,996 Software 1,515 1,212 Total 245,142 210,039 Less accumulated depreciation (134,243 ) (106,388 ) Property, equipment and software, net $ 110,899 $ 103,651 Depreciation expense was approximately $9.8 million and $9.2 million for the three months ended September 30, 2018 and 2017 , respectively, and approximately $ 28.6 million and $25.8 million for the nine months ended September 30, 2018 and 2017 , respectively.

GOODWILL AND INTANGIBLE ASSETS

GOODWILL AND INTANGIBLE ASSETS	9 Months Ended
	Sep. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	GOODWILL AND INTANGIBLE ASSETS The Company’s goodwill is the result of its acquisitions of other businesses, and represents the excess of purchase consideration over the fair value of assets and liabilities acquired. The Company performed its annual goodwill impairment analysis during the three months ended September 30, 2018 and concluded that goodwill was not impaired, as the fair value of each reporting unit exceeded its carrying value. The changes in carrying amount of goodwill during the nine months ended September 30, 2018 were as follows (in thousands): Balance as of December 31, 2017 $ 107,954 Effect of foreign currency translation (1,631 ) Balance as of September 30, 2018 $ 106,323 Intangible assets at September 30, 2018 and December 31, 2017 consisted of the following (dollars in thousands): September 30, 2018 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Weighted Average Remaining Life Business relationships $ 9,918 $ (1,625 ) $ 8,293 9.7 years Developed technology 7,832 (3,189 ) 4,643 3.4 years Content 3,912 (3,681 ) 231 1.0 years Domains and data licenses 2,869 (2,231 ) 638 1.6 years Trademarks 877 (506 ) 371 1.4 years User relationships 146 (80 ) 66 1.5 years Total $ 25,554 $ (11,312 ) $ 14,242 December 31, 2017 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Weighted Average Remaining Life Business relationships $ 9,918 $ (896 ) $ 9,022 10.3 years Developed technology 7,832 (2,071 ) 5,761 4.1 years Content 4,005 (3,610 ) 395 1.8 years Domain and data licenses 2,869 (1,847 ) 1,022 2.2 years Trademarks 877 (287 ) 590 2.2 years User relationships 146 (43 ) 103 2.2 years Total $ 25,647 $ (8,754 ) $ 16,893 Amortization expense was $0.9 million and $1.4 million for the three months ended September 30, 2018 and 2017 , respectively, and $2.7 million and $5.7 million for the nine months ended September 30, 2018 and 2017 , respectively. As of September 30, 2018 , the estimated future amortization of purchased intangible assets for (i) the remaining three months of 2018 , (ii) each of the succeeding four years, and (iii) thereafter is as follows (in thousands): Year Ending December 31, Amount 2018 (from October 1, 2018) $ 882 2019 3,277 2020 2,402 2021 2,262 2022 1,045 Thereafter 4,374 Total amortization $ 14,242

ACQUISITIONS AND DISPOSALS

ACQUISITIONS AND DISPOSALS	9 Months Ended
	Sep. 30, 2018
Business Combinations [Abstract]
Acquisitions and Disposals	ACQUISITIONS AND DISPOSALS Nowait, Inc. On February 28, 2017, the Company acquired Nowait, Inc. ("Nowait"). In connection with the acquisition, all outstanding capital stock and options and warrants to purchase capital stock of Nowait — including the 20% equity investment in Nowait the Company acquired in July 2016 — were converted into the right to receive an aggregate of $39.8 million in cash. Of the total amount of consideration paid in connection with the acquisition, $7.9 million is being held in escrow for a two -year period after the closing to secure the Company’s indemnification rights. The key purpose underlying the acquisition was to secure waitlist system and seating tool technology. The Company utilized an income approach to determine the valuation of the Company’s existing equity investment in Nowait as of the acquisition date. The carrying value of the Company’s investment approximated its fair value. The acquisition was accounted for as a business combination in accordance with Accounting Standards Codification Topic 805, "Business Combinations" ("ASC 805"), with the results of Nowait’s operations included in the Company’s condensed consolidated financial statements from February 28, 2017. The final purchase price allocation is as follows (in thousands): February 28, 2017 Fair value of purchase consideration Cash: Distributed to Nowait stockholders $ 31,892 Held in escrow account 7,945 Total purchase consideration $ 39,837 Fair value of net assets acquired: Cash and cash equivalents $ 1,004 Intangible assets 12,670 Goodwill 25,959 Other assets 1,065 Total assets acquired 40,698 Liabilities assumed (861 ) Total liabilities assumed (861 ) Net assets acquired $ 39,837 Estimated useful lives and the amount assigned to each class of intangible assets acquired are as follows (dollars in thousands): Intangible Asset Type Amount Assigned Useful Life Enterprise restaurant relationships $ 8,500 12.0 years Acquired technology 2,900 5.0 years Trademarks 610 3.0 years Local restaurant relationships 600 5.0 years User relationships 60 3.0 years Weighted average 9.6 years The intangible assets are being amortized on a straight-line basis, which reflects the pattern in which the economic benefits of the intangible assets are being utilized. The goodwill results from the Company’s opportunity to drive daily engagement in its key restaurant vertical by allowing consumers to move more quickly from search and discovery to transacting at a local business. None of the goodwill is deductible for tax purposes. The Company recorded no acquisition-related transaction costs for the three months ended September 30, 2018 and 2017, and zero and $0.1 million for the nine months ended September 30, 2018 and 2017, respectively, which were included in general and administrative expenses in the accompanying condensed consolidated statements of operations. The condensed consolidated statements of operations for the three and nine months ended September 30, 2018 include $1.3 million and $3.9 million of revenue attributable to the Nowait product, respectively. The Company completed its integration of Nowait's operations into those of the Company during the three months ended December 31, 2017 and, as such, determining Nowait's contribution to the net income of the Company for the three and nine months ended September 30, 2018 is impracticable. The condensed consolidated statements of operations for the three and nine months ended September 30, 2017 include $1.3 million and $2.6 million of revenue, respectively, and $1.9 million and $5.1 million of net loss, respectively, attributable to Nowait. Turnstyle Analytics Inc. On April 3, 2017, the Company acquired all of the equity interests in Turnstyle Analytics Inc. ("Turnstyle") for $20.6 million , approximately $1.0 million of which represents compensation cost due to a continuous service requirement, and the remainder of which represents purchase consideration. Of the total consideration paid in connection with the acquisition, $3.1 million was initially held in escrow for an 18 -month period after the closing to secure the Company’s indemnification rights. The balance remaining in the escrow fund was $3.0 million as of September 30, 2018, and the remaining escrow funds were released in October 2018. The key factor underlying the acquisition was to obtain a customer retention and loyalty product in the form of a location-based marketing and analytics platform that provides Wi-Fi as a digital marketing tool to expand its product offerings for local businesses. The acquisition was accounted for as a business combination in accordance with ASC 805, with the results of Turnstyle’s operations included in the Company’s condensed consolidated financial statements from April 3, 2017. The final purchase price allocation is as follows (in thousands): April 3, 2017 Fair value of purchase consideration Cash: Distributed to Turnstyle stockholders $ 16,648 Held in escrow account 3,093 Total purchase consideration $ 19,741 Fair value of net assets acquired: Cash and cash equivalents $ 30 Intangible assets 4,252 Goodwill 16,048 Other assets 250 Total assets acquired 20,580 Deferred tax liability (450 ) Liabilities assumed (389 ) Total liabilities assumed (839 ) Net assets acquired $ 19,741 Estimated useful lives and the amount assigned to each class of intangible assets acquired are as follows (dollars in thousands): Intangible Asset Type Amount Assigned Useful Life Acquired technology $ 3,250 5.0 years Business relationships 672 5.0 years Trademarks 250 3.0 years User relationships 80 3.0 years Weighted average 4.9 years The intangible assets are being amortized on a straight-line basis, which reflects the pattern in which the economic benefits of the intangible assets are being utilized. The goodwill results from the Company’s opportunity to expand its product offerings to local businesses through the Turnstyle marketing and analytics platform, which the Company renamed Yelp WiFi Marketing. None of the goodwill is deductible for tax purposes. The Company recorded no acquisition-related transaction costs for the three and nine months ended September 30, 2018, and zero and $0.3 million for the three and nine months ended September 30, 2017, respectively, which were included in general and administrative expenses in the accompanying condensed consolidated statements of operations. The condensed consolidated statements of operations for the three and nine months ended September 30, 2018 include $0.9 million and $2.4 million of revenue attributable to Yelp WiFi Marketing, respectively. The Company completed its integration of Turnstyle's operations into those of the Company during the three months ended December 31, 2017 and, as such, determining Turnstyle's contribution to the net income of the Company for the three and nine months ended September 30, 2018 is impracticable. The condensed consolidated statements of operations for the three and nine months ended September 30, 2017 include $0.4 million and $0.8 million of revenue, respectively, and $4.0 million and $4.6 million of net loss, respectively, attributable to Turnstyle. Eat24, LLC On October 10, 2017, pursuant to the terms of a Unit Purchase Agreement, dated as of August 3, 2017 (the "Purchase Agreement"), by and among the Company, Eat24, LLC, a wholly-owned subsidiary of the Company ("Eat24"), Grubhub Inc. ("Grubhub") and Grubhub Holdings Inc. ("Purchaser"), a wholly-owned subsidiary of Grubhub, the Company completed the sale of all of the outstanding equity interests in Eat24 to the Purchaser (the "Disposal"). Immediately prior to the closing of the Disposal, the Company transferred certain assets to Eat24, which consisted of assets that were material to or necessary for the operation of the Eat24 business that were not then owned by Eat24. The Company entered into a Marketing Partnership Agreement ("Partnership Agreement") with the Purchaser concurrently with the Purchase Agreement. The purpose of the Disposal was to further capitalize on the Company's strong market position of connecting people with local businesses by selling Eat24 to the Purchaser, which has a strong presence in online and mobile food ordering, and entering into the Partnership Agreement, pursuant to which the Company earns a fee on all food orders placed through the Grubhub restaurant network, including Eat24 restaurants, that originate on the Company's Platform. The Company received $251.7 million in cash at closing; the Purchaser paid the remaining $28.8 million of the purchase price into an escrow account, which will be held for an 18 -month period after closing to secure the Purchaser's rights of indemnification under the Purchase Agreement and is presented on the Company's consolidated balance sheets as an other non-current asset (see Note 8). The Company received $1.0 million in additional purchase consideration on December 14, 2017 as a net working capital adjustment. As a result of the sale, the Company recognized a pre-tax gain of $164.8 million during the three months ended December 31, 2017, which is included in gain on disposal of a business unit in the Company's consolidated statement of operations, and which is net of $0.3 million in Disposal-related costs. Prior to the Disposal, Eat24 was its own reporting unit and $110.8 million of goodwill associated with the Eat24 reporting unit was derecognized and included with the net assets disposed. The gain recognized on the sale of Eat24 decreased by $1.1 million to $163.7 million as a result of an increase in the net assets of Eat24 as of the closing date due to the Company's adoption of ASC 606 on January 1, 2018 (see Note 1), which related to the recognition of capitalized contract costs. The Disposal was accounted for as an asset group disposal in accordance with Accounting Standards Codification 360, "Property, Plant, and Equipment." The results of Eat24's operations are included in the Company's consolidated financial statements through October 10, 2017. The loss before provision for income taxes attributable to Eat24 for the three and nine months ended September 30, 2017 was $2.7 million and $11.0 million , respectively. The Company acquired Eat24 on February 9, 2015. The final disbursement from the escrow account created to secure indemnification obligations related to the Company's acquisition of Eat24 was completed in the three months ended March 31, 2018.

OTHER NON-CURRENT ASSETS

OTHER NON-CURRENT ASSETS	9 Months Ended
	Sep. 30, 2018
Other Assets, Noncurrent Disclosure [Abstract]
Other Non-Current Assets	OTHER NON-CURRENT ASSETS Other non-current assets as of September 30, 2018 and December 31, 2017 consisted of the following (in thousands): September 30, 2018 December 31, 2017 Escrow deposit $ 28,750 $ 28,750 Deferred contract costs 11,367 9,089 Other 2,656 2,589 Total other non-current assets $ 42,773 $ 40,428 The escrow deposit consists of the funds held in escrow in connection with the Disposal of Eat24 (see Note 7), which are being held for an 18 -month period after closing (provided, however, that any amounts subject to unresolved claims as of the end of the escrow period will remain in escrow until such claims are resolved) to secure the Purchaser's rights of indemnification under the Purchase Agreement. Deferred contract costs as of September 30, 2018 and December 31, 2017 , and changes in deferred contract costs during the nine months ended September 30, 2018 , were as follows (in thousands): Nine Months Ended September 30, 2018 Balance, beginning of period $ 9,089 Add: costs deferred on new contracts 10,629 Less: amortization recorded in sales and marketing expenses (8,351 ) Balance, end of period $ 11,367

CONTRACT BALANCES

CONTRACT BALANCES	9 Months Ended
	Sep. 30, 2018
Revenue from Contract with Customer [Abstract]
Contract Balances	CONTRACT BALANCES The allowance for doubtful accounts as of September 30, 2018 , and changes in the allowance for doubtful accounts during the nine months ended September 30, 2018 , were as follows (in thousands): Nine Months Ended September 30, 2018 Balance, beginning of period $ 8,602 Add: bad debt expense 19,285 Less: write-offs, net of recoveries (19,002 ) Balance, end of period $ 8,885 Contract liabilities consist of deferred revenue, which is recorded on the consolidated balance sheets when the Company has received consideration, or has the right to receive consideration, in advance of the transfer of the performance obligations of the contract to the customer. As of September 30, 2018 , deferred revenue was $3.4 million , the majority of which is expected to be recognized as revenue in the subsequent three-month period ending December 31, 2018. Changes in deferred revenue during the nine months ended September 30, 2018 were as follows (in thousands): Nine Months Ended September 30, 2018 Balance, beginning of period $ 3,469 Less: Recognition of deferred revenue from beginning balance (3,132 ) Add: Net increase in current period contract liabilities 3,055 Balance, end of period $ 3,392 No other contract assets or liabilities are recorded on the Company's condensed consolidated balance sheets as of September 30, 2018 and December 31, 2017.

ACCRUED LIABILITIES

ACCRUED LIABILITIES	9 Months Ended
	Sep. 30, 2018
Payables and Accruals [Abstract]
Accrued Liabilities	ACCRUED LIABILITIES Accrued liabilities as of September 30, 2018 and December 31, 2017 consisted of the following (in thousands): September 30, 2018 December 31, 2017 Accrued compensation $ 27,652 $ 17,725 Accrued sales and marketing 6,057 3,458 Accrued tax liabilities 4,785 32,617 Accrued cost of revenue 5,397 3,022 Other accrued expenses 14,673 16,843 Total accrued liabilities $ 58,564 $ 73,665

LONG-TERM LIABILITIES

LONG-TERM LIABILITIES	9 Months Ended
	Sep. 30, 2018
Payables and Accruals [Abstract]
Long-Term Liabilities	LONG-TERM LIABILITIES Long-term liabilities as of September 30, 2018 and December 31, 2017 consisted of the following (in thousands): September 30, 2018 December 31, 2017 Deferred rent $ 30,446 $ 26,904 Other long-term liabilities 4,532 3,833 Total long-term liabilities $ 34,978 $ 30,737

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	9 Months Ended
	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	COMMITMENTS AND CONTINGENCIES Office Facility Leases —The Company leases its office facilities under operating lease agreements that expire from 2018 to 2029. Certain lease agreements provide for rental payments on a graduated basis. The Company recognizes rent expense on a straight-line basis over the lease period. Rental expense was $13.7 million and $11.4 million for the three months ended September 30, 2018 and 2017 , respectively, and $37.7 million and $31.0 million for the nine months ended September 30, 2018 and 2017 , respectively. The Company has subleased certain office facilities under operating lease agreements that expire in 2021. The Company recognizes sublease rentals as a reduction in rental expense on a straight-line basis over the lease period. Sublease rental income was $0.5 million and $0.5 million for the three months ended September 30, 2018 and 2017 , respectively, and $ 1.7 million and $1.5 million for the nine months ended September 30, 2018 and 2017 , respectively. Legal Proceedings —In January 2018, a putative class action lawsuit alleging violations of the federal securities laws was filed in the U.S. District Court for the Northern District of California, naming as defendants the Company and certain of its officers. The complaint, which the plaintiff amended on June 25, 2018, alleges violations of the Exchange Act by the Company and its officers for allegedly making materially false and misleading statements regarding its business and operations on February 9, 2017. The plaintiff seeks unspecified monetary damages and other relief. On August 2, 2018, the Company and the other defendants filed a motion to dismiss the amended complaint. The court held a hearing on the motion on September 20, 2018 and has not yet issued a ruling. Due to the preliminary nature of this lawsuit, the Company is unable to reasonably estimate either the probability of incurring a loss or an estimated range of such loss, if any, from the lawsuit. The Company is subject to other legal proceedings arising in the ordinary course of business. Although the results of litigation and claims cannot be predicted with certainty, the Company currently does not believe that the final outcome of any of these other matters will have a material adverse effect on the Company’s business, financial position, results of operations or cash flows. Indemnification Agreements —In the ordinary course of business, the Company may provide indemnifications of varying scope and terms to customers, vendors, lessors, business partners and other parties with respect to certain matters, including, but not limited to, losses arising out of breach of such agreements, services to be provided by the Company or from intellectual property infringement claims made by third parties. Under the Purchase Agreement (see Note 7), the Company agreed to indemnify the Purchaser and certain related parties against certain losses arising out of Purchaser's acquisition of Eat24, including, but not limited to, any breach or inaccuracy of any representation or warranty made by the Company or Eat24 in the Purchase Agreement. The Company's indemnification obligations are subject to the terms and conditions set forth in the Purchase Agreement, and are capped at the purchase price received by the Company in the Disposal. In addition, the Company has entered into indemnification agreements with directors and certain officers and employees that will require the Company to, among other things, indemnify them against certain liabilities that may arise by reason of their status or service as directors, officers or employees. While the outcome of claims cannot be predicted with certainty, the Company does not believe that the outcome of any claims under the indemnification arrangements will have a material effect on the Company’s financial position, results of operations or cash flows.

STOCKHOLDERS' EQUITY

STOCKHOLDERS' EQUITY	9 Months Ended
	Sep. 30, 2018
Stockholders' Equity Note [Abstract]
Stockholders' Equity	STOCKHOLDERS’ EQUITY The following table presents the number of shares authorized and issued as of the dates indicated: September 30, 2018 December 31, 2017 Shares Authorized Shares Issued Shares Authorized Shares Issued Stockholders’ equity: Common stock, $0.000001 par value 200,000,000 84,375,021 200,000,000 83,724,916 Undesignated Preferred Stock 10,000,000 — 10,000,000 — Stock Repurchase Program On July 31, 2017 , the Company’s board of directors authorized a stock repurchase program under which the Company may repurchase up to $200.0 million of its outstanding common stock. The Company may purchase shares at management’s discretion in the open market, in privately negotiated transactions, in transactions structured through investment banking institutions, or a combination of the foregoing. The Company repurchased on the open market and retired 1,752,895 shares for an aggregate purchase price of $72.0 million during the nine months ended September 30, 2018. Equity Incentive Plans The Company has outstanding awards under three equity incentive plans: the Amended and Restated 2005 Equity Incentive Plan (the "2005 Plan"), the 2011 Equity Incentive Plan (the "2011 Plan") and the 2012 Equity Incentive Plan, as amended (the "2012 Plan"). In July 2011, the Company adopted the 2011 Plan, terminated the 2005 Plan and provided that no further stock awards were to be granted under the 2005 Plan. All outstanding stock awards under the 2005 Plan continue to be governed by their existing terms. Upon the effectiveness of the underwriting agreement in connection with the Company’s initial public offering ("IPO"), the Company terminated the 2011 Plan and all shares that were reserved under the 2011 Plan but not issued were assumed by the 2012 Plan. No further awards will be granted pursuant to the 2011 Plan. All outstanding stock awards under the 2011 Plan continue to be governed by their existing terms. Under the 2012 Plan, the Company has the ability to issue incentive stock options, non-statutory stock options, stock appreciation rights, restricted stock units ("RSUs"), restricted stock awards ("RSAs"), performance units and performance shares. Additionally, the 2012 Plan provides for the grant of performance cash awards to employees, directors and consultants. Stock Options Stock options granted under the 2012 Plan are granted at a price per share not less than the fair value of a share of the Company’s common stock at date of grant. Options granted to date generally vest over a three - or four -year period, on one of four schedules: (a) 25% vesting at the end of one year and the remaining shares vesting monthly thereafter; (b) 10% vesting over the first year, 20% vesting over the second year, 30% vesting over the third year and 40% vesting over the fourth year; (c) ratably on a monthly basis; or (d) 35% vesting over the first year, 40% vesting over the second year and 25% vesting over the third year. Options granted are generally exercisable for up to 10 years . The Company issues new shares when stock options are exercised. A summary of stock option activity for the nine months ended September 30, 2018 is as follows: Options Outstanding Number of Shares Weighted-Average Exercise Price Weighted-Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding - December 31, 2017 7,078,932 $ 22.70 5.56 $ 145,613 Granted 685,850 43.52 Exercised (737,986 ) 19.91 Canceled (109,361 ) 48.85 Outstanding - September 30, 2018 6,917,435 $ 24.65 5.38 $ 174,842 Options vested and exercisable as of September 30, 2018 5,543,179 $ 21.71 4.60 $ 157,306 Aggregate intrinsic value represents the difference between the closing price of the Company’s common stock as quoted on the New York Stock Exchange on a given date and the exercise price of outstanding, in-the-money options. The total intrinsic value of options exercised was approximately $5.3 million and $9.8 million for the three months ended September 30, 2018 and 2017 , respectively, and $18.1 million and $20.2 million for the nine months ended September 30, 2018 and 2017, respectively. The weighted-average grant date fair value of options granted was $23.41 and $13.31 per share for the three months ended September 30, 2018 and 2017 , respectively, and $18.89 and $15.35 per share for the nine months ended September 30, 2018 and 2017, respectively. As of September 30, 2018 , total unrecognized compensation costs related to unvested stock options was approximately $21.0 million , which is expected to be recognized over a weighted-average time period of 2.5 years . RSUs The cost of RSUs is determined using the fair value of the Company’s common stock on the date of grant. RSUs generally vest over a four -year period, on one of three schedules: (a) 25% vesting at the end of one year and the remaining vesting quarterly or annually thereafter; (b) 10% vesting over the first year, 20% vesting over the second year, 30% vesting over the third year and 40% vesting over the fourth year; or (c) ratably on a quarterly basis. A summary of RSU activity for the nine months ended September 30, 2018 is as follows: Restricted Stock Units Number of Shares Weighted-Average Grant Date Fair Value Unvested - December 31, 2017 7,249,205 $ 34.57 Granted 3,029,151 42.59 Released (2,393,407 ) 36.06 Canceled (1,087,920 ) 36.02 Unvested - September 30, 2018 6,797,029 $ 37.39 As of September 30, 2018 , the Company had approximately $242.0 million of unrecognized stock-based compensation expense related to RSUs, which is expected to be recognized over the remaining weighted-average vesting period of approximately 2.6 years . Employee Stock Purchase Plan The 2012 Employee Stock Purchase Plan, as amended ("ESPP"), allows eligible employees to purchase shares of the Company’s common stock at a discount through payroll deductions of up to 15% of their eligible compensation, subject to any plan limitations, during designated offering periods. At the end of each offering period, employees are able to purchase shares at 85% of the fair market value of the Company’s common stock on the last day of the offering period, based on the closing sales price of the Company's common stock as quoted on the New York Stock Exchange on such date. There were no shares purchased by employees under the ESPP in the three months ended September 30, 2018 or 2017. Employees purchased 195,987 shares and 228,299 shares under the ESPP in the nine months ended September 30, 2018 and 2017, respectively, at weighted-average purchase prices of $36.42 per share and $23.73 per share, respectively. The Company recognized $0.7 million and $0.5 million of stock-based compensation expense related to the discounted share price provided to employees under the ESPP in the three months ended September 30, 2018 and 2017 , respectively, and $2.0 million and $1.5 million in the nine months ended September 30, 2018 and 2017, respectively. Stock-Based Compensation The following table summarizes the effects of stock-based compensation expense related to stock-based awards in the condensed consolidated statements of operations during the periods presented (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Cost of revenue $ 1,162 $ 993 $ 3,345 $ 2,931 Sales and marketing 7,941 7,305 23,514 21,434 Product development 14,536 11,976 41,878 34,428 General and administrative 5,555 5,035 16,995 16,214 Total stock-based compensation $ 29,194 $ 25,309 $ 85,732 $ 75,007 The Company capitalized $1.9 million and $1.5 million of stock-based compensation expense as website development costs in the three months ended September 30, 2018 and 2017 , respectively, and $5.9 million and $4.6 million in the nine months ended September 30, 2018 and 2017, respectively.

OTHER INCOME, NET

OTHER INCOME, NET	9 Months Ended
	Sep. 30, 2018
Other Income and Expenses [Abstract]
Other Income, Net	OTHER INCOME, NET Other income, net for the three and nine months ended September 30, 2018 and 2017 consisted of the following (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Interest income, net $ 3,705 $ 991 $ 9,606 $ 2,431 Transaction gain on foreign exchange 75 323 89 377 Other non-operating income, net 141 57 255 125 Other income, net $ 3,921 $ 1,371 $ 9,950 $ 2,933

INCOME TAXES

INCOME TAXES	9 Months Ended
	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES Benefit from (provision for) income taxes for the three and nine months ended September 30, 2018 and 2017 consisted of the following (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Benefit from (provision for) income taxes $ 684 $ (232 ) $ 281 $ (417 ) The Company is subject to income tax in the United States as well as other tax jurisdictions in which it conducts business. Earnings from non-U.S. activities are subject to local country income tax. The tax benefit for the nine months ended September 30, 2018 is $0.3 million , which is due to $ 1.2 million in U.S. federal, state and foreign income tax expense, offset by $ 1.5 million of net discrete tax benefit related to a change in the valuation allowance from return to provision true-ups and excess stock option benefits. The tax provision for the nine months ended September 30, 2017 is due to $ 0.4 million in U.S. state and foreign income tax expense. Accounting for income taxes for interim periods generally requires the provision for income taxes to be determined by applying an estimate of the annual effective tax rate for the full fiscal year to income or loss before income taxes, excluding unusual or infrequently occurring discrete items ("Ordinary" income), for the reporting period. For the three and nine months ended September 30, 2018 , a discrete effective tax rate method was used in jurisdictions where a small change in estimated Ordinary income has a significant impact on the annual effective tax rate. The primary difference between the effective tax rate and the federal statutory tax rate relates to the valuation allowances on certain of the Company’s net operating losses, foreign tax rate differences and stock-based compensation expense. Jurisdictions where no benefit is recorded on forecasted losses were excluded from the consolidated effective tax rate. As of September 30, 2018 , the total amount of gross unrecognized tax benefits was $24.4 million , $23.5 million of which is subject to a full valuation allowance and would not affect the Company’s effective tax rate if recognized. As of September 30, 2018 , amounts related to the accrual of interest and penalties were immaterial. During the three months ended September 30, 2018 , the Company’s gross unrecognized tax benefits increased by $2.0 million , an immaterial amount of which would affect the Company’s effective tax rate if recognized. On December 22, 2017, the U.S. Tax Cuts and Jobs Act (the "Tax Act") was signed into law. The Tax Act makes broad and complex changes to the U.S. tax code that impact the Company's provision for income taxes, including, but not limited to, reducing the U.S. federal corporate tax rate from 35.0% to 21.0% (the "Tax Rate Reduction"), and requiring a one-time Deemed Repatriation Tax (the "Transition Tax") on certain un-repatriated earnings of foreign subsidiaries. However, because the Company has a net cumulative deficit on the earnings and profits of its foreign subsidiaries, it is not subject to the Transition Tax. Prior to the effectiveness of the Tax Act, the Company did not recognize a deferred tax liability related to un-remitted foreign earnings because such earnings were expected to be reinvested indefinitely. Although the Company is not subject to the Transition Tax, an actual repatriation from its non-U.S. subsidiaries could still be subject to additional foreign withholding taxes and U.S. state taxes. However, it remains the Company’s intention to reinvest the earnings from its non-U.S. subsidiaries. As of September 30, 2018 , the Company estimates that it had $3.3 million of cumulative earnings upon which U.S. income taxes had not been provided. Determination of the amount of unrecognized deferred tax liability with respect to un-remitted foreign earnings, if any, is not practicable. In March 2018, FASB issued Accounting Standards Update No. 2018-05, "Income Taxes Topic (740): Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 118" ("ASU 2018-05") to address the application of GAAP in situations when a registrant does not have the necessary information available, prepared or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the Tax Act. As of September 30, 2018, the Company's analysis for the Transition Tax was final; the Company considered its accounting for this area of the Tax Act to be complete as of such date and did not make any measurement-period adjustments related to it. However, the Company's accounting for other areas of the Tax Act was incomplete as of September 30, 2018 . For the nine months ended September 30, 2018 , the Company made measurement-period adjustments related to the re-measurement of deferred taxes and valuation allowance due to the Tax Rate Reduction previously estimated, but the adjustment had no material impact on the Company's income tax benefit. Since ongoing guidance and accounting interpretation for the Tax Act are expected over the next three months, the Company considers the accounting for areas of the Tax Act other than the Transition Tax to be incomplete as the Company continues to gather additional information and evaluate the provisions of the Tax Act and the application of ASU 2018-05. The Company expects to finalize the analysis and record any adjustments to provisional estimates no later than one year beyond the enactment date in accordance with ASU 2018-05. Any subsequent adjustment to these amounts will be recorded to current tax expense in the quarter of 2018 when the analysis is complete. In addition, the Company is subject to the continuous examination of its income tax returns by the Internal Revenue Service and other tax authorities. The Company’s federal and state income tax returns for fiscal years subsequent to 2003 remain open to examination. In the Company’s most significant foreign jurisdictions — Canada, Ireland, the United Kingdom and Germany — the tax years subsequent to 2010 remain open to examination. The Company regularly assesses the likelihood of adverse outcomes resulting from examinations to determine the adequacy of its provision for income taxes, and monitors the progress of ongoing discussions with tax authorities and the impact, if any, of the expected expiration of the statute of limitations in various taxing jurisdictions. The Company believes that an adequate provision has been made for any adjustments that may result from tax examinations. However, the outcome of tax audits cannot be predicted with certainty. If any issues addressed in the Company’s tax audits are resolved in a manner not consistent with management’s expectations, the Company could be required to adjust its provision for income taxes in the period such resolution occurs. Although the timing of the resolution or closure of audits is not certain, the Company believes it is reasonably possible that its unrecognized tax benefits could be reduced by an immaterial amount over the 12 months following December 31, 2017 .

NET INCOME PER SHARE

NET INCOME PER SHARE	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Net Income Per Share	NET INCOME PER SHARE Basic net income per share is computed using the weighted-average number of outstanding shares of common stock during the period. Diluted net income per share is computed using the weighted-average number of outstanding shares of common stock and, when dilutive, potential shares of common stock outstanding during the period. Potential common shares consist of the incremental shares of common stock issuable upon the exercise of stock options, shares issuable upon the vesting of RSUs and, to a lesser extent, purchase rights related to the ESPP. The following table presents the calculation of basic and diluted net income per share (in thousands, except per share data): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Basic net income per share: Net income $ 14,986 $ 8,030 $ 23,404 $ 11,874 Shares used in computation: Weighted-average common shares outstanding 84,008 82,259 83,865 81,041 Basic net income per share attributable to common stockholders $ 0.18 $ 0.10 $ 0.28 $ 0.15 Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Diluted net income per share Net income 14,986 8,030 23,404 11,874 Shares used in computation: Weighted-average common shares outstanding 84,008 82,259 83,865 81,041 Stock options 3,011 3,253 3,096 3,179 Restricted stock units 1,656 1,921 2,240 1,877 Employee stock purchase program 49 — 70 — Number of shares used in diluted calculation 88,724 87,433 89,271 86,097 Diluted net income per share attributable to common stockholders $ 0.17 $ 0.09 $ 0.26 $ 0.14 The following weighted-average stock-based instruments were excluded from the calculation of diluted net income per share because their effect would have been anti-dilutive for the periods presented (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Stock options 1,694 1,793 1,681 1,911 Restricted stock units 591 871 106 978

INFORMATION ABOUT REVENUE AND G

INFORMATION ABOUT REVENUE AND GEOGRAPHIC AREAS	9 Months Ended
	Sep. 30, 2018
Segment Reporting [Abstract]
Information About Revenue and Geographic Areas	INFORMATION ABOUT REVENUE AND GEOGRAPHIC AREAS The Company considers operating segments to be components of the Company in which separate financial information is available that is evaluated regularly by the Company’s chief operating decision maker in deciding how to allocate resources and in assessing performance. The chief operating decision maker for the Company is the chief executive officer. The chief executive officer reviews financial information presented on a consolidated basis, accompanied by information about revenue by product line and geographic region for purposes of allocating resources and evaluating financial performance. The Company has one business activity and there are no segment managers who are held accountable for operations, operating results or plans for levels or components below the consolidated unit level. Accordingly, the Company has determined that it has a single operating and reporting segment. When the Company communicates results externally, it disaggregates net revenue into major product lines and primary geographical markets (which is based on the billing address of the customer). The disaggregation of revenue by major product lines is based on the type of service provided and also aligns with the timing of revenue recognition. Net Revenue The following table presents the Company’s net revenue disaggregated by major product line for the periods presented (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Net revenue by product: Advertising $ 232,502 $ 200,502 $ 672,712 $ 566,085 Transactions 3,042 18,524 10,402 55,024 Other services 5,552 4,261 15,919 10,297 Total net revenue $ 241,096 $ 223,287 $ 699,033 $ 631,406 During the three and nine months ended September 30, 2018 and 2017 , no individual customer accounted for 10% or more of consolidated net revenue. The following table presents the Company’s net revenue disaggregated by major geographic region for the periods indicated (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 United States $ 237,597 $ 219,642 $ 689,096 $ 620,925 All other countries 3,499 3,645 9,937 10,481 Total net revenue $ 241,096 $ 223,287 $ 699,033 $ 631,406 Long-Lived Assets The following table presents the Company’s long-lived assets by geographic region for the periods indicated (in thousands): September 30, 2018 December 31, 2017 United States $ 108,900 $ 100,990 All other countries 1,999 2,661 Total long-lived assets $ 110,899 $ 103,651

RESTRUCTURING AND INTEGRATION

RESTRUCTURING AND INTEGRATION	9 Months Ended
	Sep. 30, 2018
Restructuring and Related Activities [Abstract]
Restructuring and Integration	RESTRUCTURING AND INTEGRATION The following table presents the Company’s restructuring and integration costs for the periods indicated (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Restructuring and integration $ — $ 35 $ — $ 286 On November 2, 2016, the Company announced plans to significantly reduce sales and marketing activities in markets outside of the United States and Canada. The restructuring plan was completed by December 31, 2017 . No additional expense related to this restructuring plan is expected. No goodwill, intangible assets or other long-lived assets were impaired as a result of the restructuring plan. There were no remaining unpaid amounts related to this plan as of December 31, 2017 .

DESCRIPTION OF BUSINESS AND B_2

DESCRIPTION OF BUSINESS AND BASIS FOR PRESENTATION (Policies)	9 Months Ended
	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying interim condensed consolidated financial statements are unaudited. These unaudited interim condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America ("GAAP") and the applicable rules and regulations of the U.S. Securities and Exchange Commission ("SEC") regarding interim financial reporting. Certain information and note disclosures normally included in the financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. Accordingly, these unaudited interim condensed consolidated financial statements should be read in conjunction with the consolidated financial statements contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017 , filed with the SEC on February 28, 2018 (the "Annual Report"). The unaudited condensed consolidated balance sheet as of December 31, 2017 included herein was derived from the audited consolidated financial statements as of that date, but does not include all disclosures required by GAAP, including certain notes to the financial statements and certain balances that have been recast as a result of the adoption of new accounting pronouncements.
Revenue Recognition	Revenue Recognition— The Company generates revenue from the sale of of advertising products, transactions and other services, which correspond to the Company's major product lines. The Company recognizes revenue when all of the following criteria are met: the contract with the customer is identified; the performance obligations in the contract are identified; the transaction price is determined; the transaction price is allocated to the performance obligations in the contract; and revenue is recognized when (or as) the Company satisfies these performance obligations. The Company applies the portfolio practical expedient to account for contracts with customers in each category of revenue. Revenue is recognized net of any taxes collected from customers, which are remitted to governmental authorities. The Company does not typically refund customers for services once it determines the performance obligations of the contract have been satisfied, but will assess any refund requests from customers and partners on a case by case basis. The Company records an allowance for potential future refunds, which is estimated based on historical trends and recorded as a reduction of net revenue. Advertising. The Company generates advertising revenue primarily through the display of advertising products on its website and mobile app. These arrangements are evidenced by either written or electronic acceptance of a contract that stipulates the types of advertising to be delivered, the timing and pricing. Performance-based advertising placements are priced on a cost-per-click basis, while impression-based advertising placements are priced on a cost per thousand impressions basis. The Company recognizes revenue from the delivery of performance-based ads and impression-based ads in the period of delivery, in each case net of customer discounts, assuming all other revenue recognition criteria are met. The Company also offers businesses premium features in connection with their business listing pages pursuant to fixed monthly fees, and recognizes revenue from such offerings over the service period, assuming all other revenue recognition criteria are met. The Company also generates advertising revenue through indirect sales of advertising products, such as through reseller contracts that allow partners to sell Yelp Branded Profiles to their clients and the monetization of remnant advertising inventory through third-party ad networks, and recognizes revenue in the period of delivery, assuming all other revenue recognition criteria are met. Transactions. The Company generates transactions revenue from revenue-sharing partner contracts, the sale of vouchers through the Company's "Yelp Deals" and "Yelp Gift Certificates" products, and, through October 10, 2017, Yelp Eat24 as a standalone product. The Company's transactions platform provides consumers with the ability to complete food delivery and other transactions through third parties directly on Yelp. The Company earns a per-transaction commission fee pursuant to partnership contracts for acting as an agent for these transactions, which it recognizes on a net basis and includes in revenue upon completion of a transaction, assuming all other revenue recognition criteria are met. Other Services. The Company generates other services revenue through subscription services contracts, such as sales of monthly subscriptions to its Yelp Reservations, Yelp Nowait and Yelp WiFi Marketing products, licensing contracts for access to Yelp data and other non-advertising, non-transaction partnerships. Subscription revenues are recognized ratably over the contract terms beginning on the commencement date of each contract, which is the date the service is made available to customers, assuming all other revenue recognition criteria are met. Contracts with Multiple Performance Obligations. Contracts with customers can include multiple performance obligations, where revenue is allocated to each performance obligation based on its relative standalone selling price ("SSP"). The Company determines SSP based on the prices of the promised goods or services charged when sold separately to customers, which are determined using contractually stated prices. The various products and services comprising contracts with multiple performance obligations are typically capable of being distinguished and accounted for as separate performance obligations. Estimates and assumptions include determining variable consideration, identifying the nature and timing of satisfaction of performance obligations, and calculating the SSP of performance obligations. The Company allocates revenue to each of the performance obligations included in a contract with multiple performance obligations at the inception of the contract. The Company applies the invoice practical expedient to depict the value transferred to the customer and measure of progress towards completion of its obligations. The Company considers the right to receive consideration from a customer to correspond directly with the value to the customer of its performance completed to date. Because the Company considers contracts month-to-month, variable consideration is resolved at the time of invoicing, which eliminates the use of estimates in determining the transaction price. The Company does not consider the effects of the time value of money as the majority of the Company’s contracts are invoiced on a monthly basis, one month in arrears. Accounts Receivable, Net, and Payment Terms— The timing of revenue recognition may differ from the timing of invoicing to customers. The Company records an accounts receivable balance when revenue is recognized prior to or at the time of invoicing the customer. Payment terms and conditions vary by contract type and the service being provided. For advertising services, the Company typically invoices customers on a monthly basis, one month in arrears, and payment is collected either at the end of each billing period or up to 30 days after the end of the billing period. For transaction services, the Company's commission fee on each transaction is collected either at the time of the transaction, or up to 30 days after the end of the billing period. For subscription services, the Company typically invoices one month in advance, and payment is collected at the beginning of each billing period. Allowance for Doubtful Accounts— The Company maintains an allowance for doubtful accounts receivable. The allowance reflects the Company's best estimate of probable losses inherent in the accounts receivable balance. It is based upon historical experience and loss patterns, the number of days that billings are past due, an evaluation of the potential risk of loss associated with delinquent accounts and known delinquent accounts. When new information becomes available that allows the Company to more accurately estimate the allowance, it makes an adjustment, which is considered a change in accounting estimate. The carrying value of accounts receivable approximates their fair value. Deferred Contract Costs —The Company classifies certain sales incentive compensation costs as incremental to obtaining the related contract. These costs are capitalized in the period in which they are incurred and amortized on a straight-line basis over the expected customer life of the associated contract. The Company uses a straight line basis as it expects the benefit of these costs to be realized uniformly over the amortization period. The amortization periods for contract costs, which extend up to 41 months, were determined based on both qualitative and quantitative factors, including product lifecycle attributes and customer retention historical data. For contract costs with amortization periods of less than 12 months, the Company applies a practical expedient to expense such costs as incurred. The Company assesses deferred contract costs for impairment on a quarterly basis. Amortized contract costs are recorded within sales and marketing expense on the consolidated statements of operations. Deferred contract costs are included within other non-current assets on the Company's consolidated balance sheets (see Note 8). Deferred Revenue —The Company records deferred revenue when it has received consideration, or has the right to receive consideration, in advance of the transfer of the performance obligations of the contract to the customer.
Recent Accounting Pronouncements Not Yet Effective	Recent Accounting Pronouncements Not Yet Effective Lease Accounting In February 2016, FASB issued Accounting Standards Update No. 2016-02, "Leases (Topic 842)" ("ASC 842"). ASC 842 supersedes the previous accounting guidance for leases included within Accounting Standards Codification 840, "Leases" ("ASC 840"). The new guidance generally requires an entity to recognize on its balance sheet operating and financing lease liabilities and corresponding right-of-use assets, as well as to recognize the associated lease expenses on its statements of operations in a manner similar to that required under current accounting rules. The standard will be effective for the first interim period within annual reporting periods beginning after December 15, 2018 and early adoption is permitted. The new standard initially required a modified retrospective transition for existing leases to each prior reporting period presented. However, in July 2018, FASB issued Accounting Standards Update No. 2018-11, "Targeted Improvements to ASC 842" ("ASU 2018-11"), which provides entities with the option to begin applying ASC 842 at the adoption date rather than at the beginning of the earliest period presented (the "Effective Date Method"). Entities using the Effective Date Method recognize a cumulative-effect adjustment to the opening balance of retained earnings (or accumulated deficit) in the period of adoption. The Company plans to adopt ASC 842 on January 1, 2019 using the Effective Date Method by recording a cumulative-effect adjustment to retained earnings (or accumulated deficit) as of January 1, 2019. As a result, the Company will continue to disclose comparative reporting periods under the previous accounting guidance, ASC 840. The Company continues to evaluate the impact of ASC 842 on its consolidated financial statements and accounting processes. Based on these ongoing evaluations, the Company currently expects the most significant changes will be related to the recognition of operating lease right-of-use assets and operating lease liabilities on its consolidated balance sheet in the amounts of approximately $240 million to $260 million and approximately $270 million to $290 million , respectively. The Company does not expect the impact on its consolidated statement of operations to be material. These estimates are based on the Company's office lease portfolio and, to a much lesser extent, its lease portfolio of computer equipment, each as of September 30, 2018. The ultimate impact of the Company's adoption of ASC 842 on its financial statements may change for reasons including, but not limited to: • finalization of the impact analysis of the new standard; • new lease contracts entered into during the three months ending December 31, 2018 that result in additional lease assets and lease liabilities; • changes in discount rates used to calculate the initial lease liability; • significant changes in foreign exchange rates applied to lease liabilities and right-of-use assets denominated in currencies other than U.S. dollars; and • changes in the Company's expectations for renewal options of existing leases. Other Pronouncements In January 2017, FASB issued Accounting Standards Update No. 2017-04, "Intangibles—Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment" ("ASU 2017-04"). This new guidance simplifies the subsequent measurement of goodwill by eliminating Step 2 from the goodwill impairment test. Under the new standard, entities will perform goodwill impairment tests by comparing fair value of a reporting unit with its carrying amount and recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value. The standard will be effective for the first interim period within annual reporting periods beginning after December 15, 2019 and early adoption is permitted. The Company does not expect the adoption of ASU 2017-04 to have a material impact on its consolidated financial statements. In March 2017, FASB issued Accounting Standards Update No. 2017-08, "Receivables—Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities" ("ASU 2017-08"). This new guidance requires entities to amortize purchased callable debt securities held at a premium to the earliest call date. The standard will be effective for the first interim period within annual reporting periods beginning after December 15, 2018 and early adoption is permitted. The Company does not expect the adoption of ASU 2017-08 to have a material impact on its consolidated financial statements. In June 2018, FASB issued Accounting Standards Update No. 2018-07, "Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting" ("ASU 2018-07"). This new guidance changes the accounting for non-employee share-based payments to align with the accounting for employee stock compensation. The standard will be effective for the first interim period within annual reporting periods beginning after December 15, 2018 and early adoption is permitted. The Company does not expect the adoption of ASU 2018-07 to have a material impact on its consolidated financial statements. In August 2018, FASB issued Accounting Standards Update No. 2018-13, "Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement" (“ASU 2018-13”), which amends Accounting Standards Codification 820, "Fair Value Measurement." ASU 2018-13 modifies the disclosure requirements for fair value measurements by removing, modifying and adding certain disclosures. The standard will be effective for the first interim period within annual reporting periods beginning after December 15, 2019 and early adoption is permitted. The Company is currently evaluating the impact of ASU 2018-13 on its consolidated financial statements. In August 2018, FASB issued Accounting Standards Update No. 2018-15, "Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That is a Service Contract" ("ASU 2018-15"). This new guidance requires a customer in a cloud computing arrangement that is a service contract to follow the internal-use software guidance in Accounting Standards Codification 350-40 to determine which implementation costs to defer and recognize as an asset. ASU 2018-15 generally aligns the guidance on recognizing implementation costs incurred in a cloud computing arrangement that is a service contract with that for implementation costs incurred to develop or obtain internal-use software, including hosting arrangements that include an internal-use software license. ASU 2018-15 is effective for the first interim period within annual reporting periods beginning after December 15, 2019 and early adoption is permitted. The Company is currently assessing the impact of ASU 2018-15 on its consolidated financial statements and related disclosures.
Principles of Consolidation	Principles of Consolidation These unaudited interim condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany accounts and transactions have been eliminated upon consolidation.
Use of Estimates	Use of Estimates The preparation of the Company’s unaudited interim condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of income and expenses during the reporting period. These estimates are based on information available as of the date of the condensed consolidated financial statements; therefore, actual results could differ from management’s estimates.

DESCRIPTION OF BUSINESS AND B_3

DESCRIPTION OF BUSINESS AND BASIS FOR PRESENTATION (Tables)	9 Months Ended
	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of New Accounting Pronouncements and Changes in Accounting Principles	The Company's adoption of ASC 606 resulted in the following adjustments to its previously reported results (in thousands): As Previously Reported Impact of ASC 606 Adoption As Currently Reported Condensed Consolidated Statement of Operations—Three Months Ended September 30, 2017 Net revenue $ 222,380 $ 907 $ 223,287 Costs and Expenses: Sales and marketing 113,041 (83 ) 112,958 General and administrative 26,694 907 27,601 Net income attributable to common stockholders 7,947 83 8,030 Condensed Consolidated Statement of Operations—Nine Months Ended September 30, 2017 Net revenue $ 628,567 $ 2,839 $ 631,406 Costs and Expenses: Sales and marketing 327,559 (1,150 ) 326,409 General and administrative 78,969 2,839 81,808 Net income attributable to common stockholders 10,724 1,150 11,874 Basic net income per share 0.13 0.02 0.15 Diluted net income per share 0.12 0.02 0.14 Condensed Consolidated Balance Sheet—As of December 31, 2017 Allowance for doubtful accounts 7,352 1,250 8,602 Other non-current assets 31,339 9,089 40,428 Retained earnings 70,081 9,089 79,170 Condensed Consolidated Statement of Cash Flows—Nine Months Ended September 30, 2017 Bad debt expense 12,400 2,839 15,239 Change in accounts receivable (16,971 ) (2,839 ) (19,810 ) Other adjustments to reconcile net income to net cash provided by operating activities (927 ) (1,150 ) (2,077 )

CASH, CASH EQUIVALENTS AND RE_2

CASH, CASH EQUIVALENTS AND RESTRICTED CASH (Tables)	9 Months Ended
	Sep. 30, 2018
Cash and Cash Equivalents [Abstract]
Schedule of Cash and Cash Equivalents	Cash, cash equivalents and restricted cash as of September 30, 2018 and December 31, 2017 consisted of the following (in thousands): September 30, 2018 December 31, 2017 Cash $ 166,336 $ 283,085 Cash equivalents 257,159 264,765 Total cash and cash equivalents $ 423,495 $ 547,850 Restricted cash 22,121 18,554 Total cash, cash equivalents and restricted cash $ 445,616 $ 566,404
Restrictions on Cash and Cash Equivalents	Cash, cash equivalents and restricted cash as of September 30, 2018 and December 31, 2017 consisted of the following (in thousands): September 30, 2018 December 31, 2017 Cash $ 166,336 $ 283,085 Cash equivalents 257,159 264,765 Total cash and cash equivalents $ 423,495 $ 547,850 Restricted cash 22,121 18,554 Total cash, cash equivalents and restricted cash $ 445,616 $ 566,404

FAIR VALUE OF FINANCIAL INSTR_2

FAIR VALUE OF FINANCIAL INSTRUMENTS (Tables)	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Schedule of Financial Instruments Measured at Fair Value	The following table represents the Company’s financial instruments measured at fair value as of September 30, 2018 and December 31, 2017 (in thousands): September 30, 2018 December 31, 2017 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Cash Equivalents: Money market funds $ 219,742 $ — $ — $ 219,742 $ 217,838 $ — $ — $ 217,838 Commercial paper — 37,417 — 37,417 — 46,927 — 46,927 Marketable Securities: Commercial paper — 158,506 — 158,506 — 138,412 — 138,412 Corporate bonds — 137,967 — 137,967 — 69,926 — 69,926 U.S. government bonds — 69,208 — 69,208 — — — — Agency bonds — 48,047 — 48,047 — 78,913 — 78,913 Agency discount notes — — — — — 10,989 — 10,989 Total cash equivalents and marketable securities $ 219,742 $ 451,145 $ — $ 670,887 $ 217,838 $ 345,167 $ — $ 563,005

MARKETABLE SECURITIES (Tables)

MARKETABLE SECURITIES (Tables)	9 Months Ended
	Sep. 30, 2018
Investments, Debt and Equity Securities [Abstract]
Schedule of the Fair Value to Amortized Cost Basis of Securities Held-to-Maturity	The amortized cost, gross unrealized gains and losses, and fair value of securities held-to-maturity as of September 30, 2018 and December 31, 2017 were as follows (in thousands): September 30, 2018 Short-term marketable securities: Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Commercial paper $ 158,506 $ — $ — $ 158,506 Corporate bonds 138,141 — (174 ) 137,967 U.S. government bonds 69,241 — (33 ) 69,208 Agency bonds 48,114 — (67 ) 48,047 Total short-term marketable securities 414,002 — (274 ) 413,728 Total marketable securities $ 414,002 $ — $ (274 ) $ 413,728 December 31, 2017 Short-term marketable securities: Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Commercial paper $ 138,412 $ 1 $ (1 ) $ 138,412 Corporate bonds 45,006 — (41 ) 44,965 Agency bonds 78,958 — (45 ) 78,913 Agency discount bonds $ 10,990 $ — $ (1 ) $ 10,989 Total short-term marketable securities $ 273,366 $ 1 $ (88 ) $ 273,279 Long-term marketable securities: Corporate bonds $ 25,032 $ — $ (71 ) $ 24,961 Total long-term marketable securities $ 25,032 $ — $ (71 ) $ 24,961 Total marketable securities $ 298,398 $ 1 $ (159 ) $ 298,240
Schedule of Securities in an Unrealized Loss Position	The following tables present gross unrealized losses and fair values for those securities that were in an unrealized loss position as of September 30, 2018 and December 31, 2017 , aggregated by investment category and the length of time that the individual securities have been in a continuous loss position (in thousands): September 30, 2018 Less Than 12 Months 12 Months or Greater Total Fair Value Unrealized Loss Fair Value Unrealized Loss Fair Value Unrealized Loss Corporate bonds $ 132,992 $ (174 ) $ — $ — $ 132,992 $ (174 ) Agency bonds 48,047 (67 ) — — 48,047 (67 ) U.S. government bonds 69,208 (33 ) — — 69,208 (33 ) Commercial paper — — — — — — Total $ 250,247 $ (274 ) $ — $ — $ 250,247 $ (274 ) December 31, 2017 Less Than 12 Months 12 Months or Greater Total Fair Value Unrealized Loss Fair Value Unrealized Loss Fair Value Unrealized Loss Agency bonds $ 78,913 $ (45 ) $ — $ — $ 78,913 $ (45 ) Corporate bonds 62,927 (112 ) — — 62,927 (112 ) Agency discount notes 10,989 (1 ) — — 10,989 (1 ) Commercial paper 3,975 (1 ) — — 3,975 (1 ) Total $ 156,804 $ (159 ) $ — $ — $ 156,804 $ (159 )

PROPERTY, EQUIPMENT, AND SOFTWA

PROPERTY, EQUIPMENT, AND SOFTWARE, NET (Tables)	9 Months Ended
	Sep. 30, 2018
Property, Plant and Equipment [Abstract]
Schedule of Property, Equipment and Software, Net	Property, equipment and software, net as of September 30, 2018 and December 31, 2017 consisted of the following (in thousands): September 30, 2018 December 31, 2017 Capitalized website and internal-use software development costs $ 102,004 $ 81,710 Leasehold improvements 79,589 74,236 Computer equipment 40,129 32,450 Furniture and fixtures 17,351 16,435 Telecommunication 4,554 3,996 Software 1,515 1,212 Total 245,142 210,039 Less accumulated depreciation (134,243 ) (106,388 ) Property, equipment and software, net $ 110,899 $ 103,651

GOODWILL AND INTANGIBLE ASSETS

GOODWILL AND INTANGIBLE ASSETS (Tables)	9 Months Ended
	Sep. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	The changes in carrying amount of goodwill during the nine months ended September 30, 2018 were as follows (in thousands): Balance as of December 31, 2017 $ 107,954 Effect of foreign currency translation (1,631 ) Balance as of September 30, 2018 $ 106,323
Schedule of Intangible Assets	Intangible assets at September 30, 2018 and December 31, 2017 consisted of the following (dollars in thousands): September 30, 2018 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Weighted Average Remaining Life Business relationships $ 9,918 $ (1,625 ) $ 8,293 9.7 years Developed technology 7,832 (3,189 ) 4,643 3.4 years Content 3,912 (3,681 ) 231 1.0 years Domains and data licenses 2,869 (2,231 ) 638 1.6 years Trademarks 877 (506 ) 371 1.4 years User relationships 146 (80 ) 66 1.5 years Total $ 25,554 $ (11,312 ) $ 14,242 December 31, 2017 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Weighted Average Remaining Life Business relationships $ 9,918 $ (896 ) $ 9,022 10.3 years Developed technology 7,832 (2,071 ) 5,761 4.1 years Content 4,005 (3,610 ) 395 1.8 years Domain and data licenses 2,869 (1,847 ) 1,022 2.2 years Trademarks 877 (287 ) 590 2.2 years User relationships 146 (43 ) 103 2.2 years Total $ 25,647 $ (8,754 ) $ 16,893
Schedule of Future Amortization Expense	As of September 30, 2018 , the estimated future amortization of purchased intangible assets for (i) the remaining three months of 2018 , (ii) each of the succeeding four years, and (iii) thereafter is as follows (in thousands): Year Ending December 31, Amount 2018 (from October 1, 2018) $ 882 2019 3,277 2020 2,402 2021 2,262 2022 1,045 Thereafter 4,374 Total amortization $ 14,242

ACQUISITIONS AND DISPOSALS (Tab

ACQUISITIONS AND DISPOSALS (Tables)	9 Months Ended
	Sep. 30, 2018
Business Combinations [Abstract]
Schedule of Purchase Price, Assets Acquired and Liabilities Assumed	The final purchase price allocation is as follows (in thousands): February 28, 2017 Fair value of purchase consideration Cash: Distributed to Nowait stockholders $ 31,892 Held in escrow account 7,945 Total purchase consideration $ 39,837 Fair value of net assets acquired: Cash and cash equivalents $ 1,004 Intangible assets 12,670 Goodwill 25,959 Other assets 1,065 Total assets acquired 40,698 Liabilities assumed (861 ) Total liabilities assumed (861 ) Net assets acquired $ 39,837 Estimated useful lives and the amount assigned to each class of intangible assets acquired are as follows (dollars in thousands): Intangible Asset Type Amount Assigned Useful Life Enterprise restaurant relationships $ 8,500 12.0 years Acquired technology 2,900 5.0 years Trademarks 610 3.0 years Local restaurant relationships 600 5.0 years User relationships 60 3.0 years Weighted average 9.6 years The final purchase price allocation is as follows (in thousands): April 3, 2017 Fair value of purchase consideration Cash: Distributed to Turnstyle stockholders $ 16,648 Held in escrow account 3,093 Total purchase consideration $ 19,741 Fair value of net assets acquired: Cash and cash equivalents $ 30 Intangible assets 4,252 Goodwill 16,048 Other assets 250 Total assets acquired 20,580 Deferred tax liability (450 ) Liabilities assumed (389 ) Total liabilities assumed (839 ) Net assets acquired $ 19,741 Estimated useful lives and the amount assigned to each class of intangible assets acquired are as follows (dollars in thousands): Intangible Asset Type Amount Assigned Useful Life Acquired technology $ 3,250 5.0 years Business relationships 672 5.0 years Trademarks 250 3.0 years User relationships 80 3.0 years Weighted average 4.9 years

OTHER NON-CURRENT ASSETS (Table

OTHER NON-CURRENT ASSETS (Tables)	9 Months Ended
	Sep. 30, 2018
Other Assets, Noncurrent Disclosure [Abstract]
Schedule of Other Non-Current Assets	Other non-current assets as of September 30, 2018 and December 31, 2017 consisted of the following (in thousands): September 30, 2018 December 31, 2017 Escrow deposit $ 28,750 $ 28,750 Deferred contract costs 11,367 9,089 Other 2,656 2,589 Total other non-current assets $ 42,773 $ 40,428
Capitalized Contract Cost	Deferred contract costs as of September 30, 2018 and December 31, 2017 , and changes in deferred contract costs during the nine months ended September 30, 2018 , were as follows (in thousands): Nine Months Ended September 30, 2018 Balance, beginning of period $ 9,089 Add: costs deferred on new contracts 10,629 Less: amortization recorded in sales and marketing expenses (8,351 ) Balance, end of period $ 11,367

CONTRACT BALANCES (Tables)

CONTRACT BALANCES (Tables)	9 Months Ended
	Sep. 30, 2018
Revenue from Contract with Customer [Abstract]
Schedule of Allowance for Doubtful Accounts Receivable	The allowance for doubtful accounts as of September 30, 2018 , and changes in the allowance for doubtful accounts during the nine months ended September 30, 2018 , were as follows (in thousands): Nine Months Ended September 30, 2018 Balance, beginning of period $ 8,602 Add: bad debt expense 19,285 Less: write-offs, net of recoveries (19,002 ) Balance, end of period $ 8,885
Contract with Customer, Liability	Changes in deferred revenue during the nine months ended September 30, 2018 were as follows (in thousands): Nine Months Ended September 30, 2018 Balance, beginning of period $ 3,469 Less: Recognition of deferred revenue from beginning balance (3,132 ) Add: Net increase in current period contract liabilities 3,055 Balance, end of period $ 3,392

ACCRUED LIABILITIES (Tables)

ACCRUED LIABILITIES (Tables)	9 Months Ended
	Sep. 30, 2018
Payables and Accruals [Abstract]
Schedule of Accrued Liabilities	Accrued liabilities as of September 30, 2018 and December 31, 2017 consisted of the following (in thousands): September 30, 2018 December 31, 2017 Accrued compensation $ 27,652 $ 17,725 Accrued sales and marketing 6,057 3,458 Accrued tax liabilities 4,785 32,617 Accrued cost of revenue 5,397 3,022 Other accrued expenses 14,673 16,843 Total accrued liabilities $ 58,564 $ 73,665

LONG-TERM LIABILITIES (Tables)

LONG-TERM LIABILITIES (Tables)	9 Months Ended
	Sep. 30, 2018
Payables and Accruals [Abstract]
Schedule of Long-Term Liabilities	Long-term liabilities as of September 30, 2018 and December 31, 2017 consisted of the following (in thousands): September 30, 2018 December 31, 2017 Deferred rent $ 30,446 $ 26,904 Other long-term liabilities 4,532 3,833 Total long-term liabilities $ 34,978 $ 30,737

STOCKHOLDERS' EQUITY (Tables)

STOCKHOLDERS' EQUITY (Tables)	9 Months Ended
	Sep. 30, 2018
Stockholders' Equity Note [Abstract]
Schedule of Stock by Class	The following table presents the number of shares authorized and issued as of the dates indicated: September 30, 2018 December 31, 2017 Shares Authorized Shares Issued Shares Authorized Shares Issued Stockholders’ equity: Common stock, $0.000001 par value 200,000,000 84,375,021 200,000,000 83,724,916 Undesignated Preferred Stock 10,000,000 — 10,000,000 —
Schedule of Stock Option Activity	A summary of stock option activity for the nine months ended September 30, 2018 is as follows: Options Outstanding Number of Shares Weighted-Average Exercise Price Weighted-Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding - December 31, 2017 7,078,932 $ 22.70 5.56 $ 145,613 Granted 685,850 43.52 Exercised (737,986 ) 19.91 Canceled (109,361 ) 48.85 Outstanding - September 30, 2018 6,917,435 $ 24.65 5.38 $ 174,842 Options vested and exercisable as of September 30, 2018 5,543,179 $ 21.71 4.60 $ 157,306
Schedule of RSU Activity	A summary of RSU activity for the nine months ended September 30, 2018 is as follows: Restricted Stock Units Number of Shares Weighted-Average Grant Date Fair Value Unvested - December 31, 2017 7,249,205 $ 34.57 Granted 3,029,151 42.59 Released (2,393,407 ) 36.06 Canceled (1,087,920 ) 36.02 Unvested - September 30, 2018 6,797,029 $ 37.39
Schedule of Stock-Based Compensation Expense	The following table summarizes the effects of stock-based compensation expense related to stock-based awards in the condensed consolidated statements of operations during the periods presented (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Cost of revenue $ 1,162 $ 993 $ 3,345 $ 2,931 Sales and marketing 7,941 7,305 23,514 21,434 Product development 14,536 11,976 41,878 34,428 General and administrative 5,555 5,035 16,995 16,214 Total stock-based compensation $ 29,194 $ 25,309 $ 85,732 $ 75,007

OTHER INCOME, NET (Tables)

OTHER INCOME, NET (Tables)	9 Months Ended
	Sep. 30, 2018
Other Income and Expenses [Abstract]
Schedule of Other Income, Net	Other income, net for the three and nine months ended September 30, 2018 and 2017 consisted of the following (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Interest income, net $ 3,705 $ 991 $ 9,606 $ 2,431 Transaction gain on foreign exchange 75 323 89 377 Other non-operating income, net 141 57 255 125 Other income, net $ 3,921 $ 1,371 $ 9,950 $ 2,933

INCOME TAXES (Tables)

INCOME TAXES (Tables)	9 Months Ended
	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Summary of Provision for Income Taxes	Benefit from (provision for) income taxes for the three and nine months ended September 30, 2018 and 2017 consisted of the following (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Benefit from (provision for) income taxes $ 684 $ (232 ) $ 281 $ (417 )

NET INCOME PER SHARE (Tables)

NET INCOME PER SHARE (Tables)	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Schedule of Calculation of Basic and Diluted Net Income (Loss) Per Share	The following table presents the calculation of basic and diluted net income per share (in thousands, except per share data): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Basic net income per share: Net income $ 14,986 $ 8,030 $ 23,404 $ 11,874 Shares used in computation: Weighted-average common shares outstanding 84,008 82,259 83,865 81,041 Basic net income per share attributable to common stockholders $ 0.18 $ 0.10 $ 0.28 $ 0.15 Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Diluted net income per share Net income 14,986 8,030 23,404 11,874 Shares used in computation: Weighted-average common shares outstanding 84,008 82,259 83,865 81,041 Stock options 3,011 3,253 3,096 3,179 Restricted stock units 1,656 1,921 2,240 1,877 Employee stock purchase program 49 — 70 — Number of shares used in diluted calculation 88,724 87,433 89,271 86,097 Diluted net income per share attributable to common stockholders $ 0.17 $ 0.09 $ 0.26 $ 0.14
Schedule of Anti-dilutive Securities	The following weighted-average stock-based instruments were excluded from the calculation of diluted net income per share because their effect would have been anti-dilutive for the periods presented (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Stock options 1,694 1,793 1,681 1,911 Restricted stock units 591 871 106 978

INFORMATION ABOUT REVENUE AND_2

INFORMATION ABOUT REVENUE AND GEOGRAPHIC AREAS (Tables)	9 Months Ended
	Sep. 30, 2018
Segment Reporting [Abstract]
Schedule of Revenue by Product Line	The following table presents the Company’s net revenue disaggregated by major product line for the periods presented (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Net revenue by product: Advertising $ 232,502 $ 200,502 $ 672,712 $ 566,085 Transactions 3,042 18,524 10,402 55,024 Other services 5,552 4,261 15,919 10,297 Total net revenue $ 241,096 $ 223,287 $ 699,033 $ 631,406
Schedule of Net Revenue by Geographic Region	The following table presents the Company’s net revenue disaggregated by major geographic region for the periods indicated (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 United States $ 237,597 $ 219,642 $ 689,096 $ 620,925 All other countries 3,499 3,645 9,937 10,481 Total net revenue $ 241,096 $ 223,287 $ 699,033 $ 631,406
Schedule of Long-Lived Assets by Geographic Location	The following table presents the Company’s long-lived assets by geographic region for the periods indicated (in thousands): September 30, 2018 December 31, 2017 United States $ 108,900 $ 100,990 All other countries 1,999 2,661 Total long-lived assets $ 110,899 $ 103,651

RESTRUCTURING AND INTEGRATION (

RESTRUCTURING AND INTEGRATION (Tables)	9 Months Ended
	Sep. 30, 2018
Restructuring and Related Activities [Abstract]
Schedule of Restructuring and Integration Costs	The following table presents the Company’s restructuring and integration costs for the periods indicated (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Restructuring and integration $ — $ 35 $ — $ 286

DESCRIPTION OF BUSINESS AND B_4

DESCRIPTION OF BUSINESS AND BASIS FOR PRESENTATION (Revenue Recognition) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017		Dec. 31, 2017
Condensed Consolidated Statement of Operations
Net revenue	$ 241,096	$ 223,287	[1]	$ 699,033	$ 631,406	[1]
Costs and Expenses:
Sales and marketing	121,759	112,958	[1]	362,054	326,409	[1]
General and administrative	30,302	27,601	[1]	90,892	81,808	[1]
Net income attributable to common stockholders	$ 14,986	$ 8,030	[1]	$ 23,404	$ 11,874	[1],[2]
Basic net income per share (in USD per share)	$ 0.18	$ 0.10	[1]	$ 0.28	$ 0.15	[1]
Diluted net income per share (in USD per share)	$ 0.17	$ 0.09	[1]	$ 0.26	$ 0.14	[1]
Condensed Consolidated Balance Sheet
Allowance for doubtful accounts	$ 8,885			$ 8,885			$ 8,602	[3]
Other non-current assets	42,773			42,773			40,428	[3]
Retained earnings	$ 30,520			30,520			79,170	[3]
Condensed Consolidated Statement of Cash Flows
Bad debt expense				19,285	$ 15,239	[2]
Change in accounts receivable				(24,956)	(19,810)	[2]
Other adjustments to reconcile net income to net cash provided by operating activities				$ (2,085)	(2,077)	[2]
As Previously Reported
Condensed Consolidated Statement of Operations
Net revenue		$ 222,380			628,567
Costs and Expenses:
Sales and marketing		113,041			327,559
General and administrative		26,694			78,969
Net income attributable to common stockholders		7,947			$ 10,724
Basic net income per share (in USD per share)					$ 0.13
Diluted net income per share (in USD per share)					$ 0.12
Condensed Consolidated Balance Sheet
Allowance for doubtful accounts							7,352
Other non-current assets							31,339
Retained earnings							70,081
Condensed Consolidated Statement of Cash Flows
Bad debt expense					$ 12,400
Change in accounts receivable					(16,971)
Other adjustments to reconcile net income to net cash provided by operating activities					(927)
Accounting Standards Update 2014-09 | Impact of ASC 606 Adoption
Condensed Consolidated Statement of Operations
Net revenue		907			2,839
Costs and Expenses:
Sales and marketing		(83)			(1,150)
General and administrative		907			2,839
Net income attributable to common stockholders		$ 83			$ 1,150
Basic net income per share (in USD per share)					$ 0.02
Diluted net income per share (in USD per share)					$ 0.02
Condensed Consolidated Balance Sheet
Allowance for doubtful accounts							1,250
Other non-current assets							9,089
Retained earnings							$ 9,089
Condensed Consolidated Statement of Cash Flows
Bad debt expense					$ 2,839
Change in accounts receivable					(2,839)
Other adjustments to reconcile net income to net cash provided by operating activities					$ (1,150)
[1]	As of January 1, 2018, the Company adopted ASC 606 using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior periods presented. See Note 1 below for additional discussion.
[2]	As of January 1, 2018, the Company adopted ASC 606 using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior period presented. Also as of January 1, 2018, the Company adopted Accounting Standards Update No. 2016-18, "Statement of Cash Flows (Subtopic 230): Restricted Cash," and recast the prior period presented. See Note 1 below for additional discussion.
[3]	As of January 1, 2018, the Company adopted Accounting Standards Update 2014-09, "Revenue from Contracts with Customers (Topic 606)" ("ASC 606"), using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior period presented. See Note 1 below for additional discussion.

DESCRIPTION OF BUSINESS AND B_5

DESCRIPTION OF BUSINESS AND BASIS FOR PRESENTATION (Narrative) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Jan. 01, 2019
Capitalized Contract Cost [Line Items]
Contracts invoiced in arrears, duration	1 month
Capitalized contract cost, amortization period threshold for practical expedient	12 months
Minimum | Scenario, Forecast | Accounting Standards Update 2018-11
Capitalized Contract Cost [Line Items]
Operating lease right-of-use asset		$ 240
Operating lease liability		270
Maximum
Capitalized Contract Cost [Line Items]
Capitalized contract cost, amortization period	41 months
Maximum | Scenario, Forecast | Accounting Standards Update 2018-11
Capitalized Contract Cost [Line Items]
Operating lease right-of-use asset		260
Operating lease liability		$ 290
Advertising services
Capitalized Contract Cost [Line Items]
Contracts invoiced in arrears, duration	1 month
Payment collection after billing period, duration	30 days
Transaction services
Capitalized Contract Cost [Line Items]
Payment collection after billing period, duration	30 days
Subscription services
Capitalized Contract Cost [Line Items]
Contracts invoiced in advance, duration	1 month

CASH, CASH EQUIVALENTS AND RE_3

CASH, CASH EQUIVALENTS AND RESTRICTED CASH (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017		Sep. 30, 2017	[2]	Dec. 31, 2016	[2]
Cash and Cash Equivalents [Abstract]
Cash	$ 166,336	$ 283,085
Cash equivalents	257,159	264,765
Total cash and cash equivalents	423,495	547,850	[1]
Restricted cash	22,121	18,554	[1]
Total cash, cash equivalents and restricted cash	$ 445,616	$ 566,404		$ 380,996		$ 289,518
[1]	As of January 1, 2018, the Company adopted Accounting Standards Update 2014-09, "Revenue from Contracts with Customers (Topic 606)" ("ASC 606"), using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior period presented. See Note 1 below for additional discussion.
[2]	As of January 1, 2018, the Company adopted ASC 606 using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior period presented. Also as of January 1, 2018, the Company adopted Accounting Standards Update No. 2016-18, "Statement of Cash Flows (Subtopic 230): Restricted Cash," and recast the prior period presented. See Note 1 below for additional discussion.

FAIR VALUE OF FINANCIAL INSTR_3

FAIR VALUE OF FINANCIAL INSTRUMENTS (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	$ 413,728	$ 298,240
Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	670,887	563,005
Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	219,742	217,838
Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	451,145	345,167
Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	0	0
Recurring | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	158,506	138,412
Recurring | Commercial paper | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	0	0
Recurring | Commercial paper | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	158,506	138,412
Recurring | Commercial paper | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	0	0
Recurring | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	137,967	69,926
Recurring | Corporate bonds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	0	0
Recurring | Corporate bonds | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	137,967	69,926
Recurring | Corporate bonds | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	0	0
Recurring | U.S. government bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	69,208	0
Recurring | U.S. government bonds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	0	0
Recurring | U.S. government bonds | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	69,208	0
Recurring | U.S. government bonds | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	0	0
Recurring | Agency bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	48,047	78,913
Recurring | Agency bonds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	0	0
Recurring | Agency bonds | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	48,047	78,913
Recurring | Agency bonds | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	0	0
Recurring | Agency discount notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	0	10,989
Recurring | Agency discount notes | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	0	0
Recurring | Agency discount notes | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	0	10,989
Recurring | Agency discount notes | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	0	0
Recurring | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents	219,742	217,838
Recurring | Money market funds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents	219,742	217,838
Recurring | Money market funds | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents	0	0
Recurring | Money market funds | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents	0	0
Recurring | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents	37,417	46,927
Recurring | Commercial paper | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents	0	0
Recurring | Commercial paper | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents	37,417	46,927
Recurring | Commercial paper | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents	$ 0	$ 0

MARKETABLE SECURITIES (Schedule

MARKETABLE SECURITIES (Schedule of the Fair Value to Amortized Cost Basis of Securities Held-to-Maturity) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Short-term marketable securities:
Amortized Cost	$ 414,002	$ 273,366
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(274)	(88)
Fair Value	413,728	273,279
Long-term marketable securities:
Amortized Cost		25,032
Gross Unrealized Gains		0
Gross Unrealized Losses		(71)
Fair Value		24,961
Amortized Cost	414,002	298,398
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(274)	(159)
Fair Value	413,728	298,240
Commercial paper
Short-term marketable securities:
Amortized Cost	158,506	138,412
Gross Unrealized Gains	0	1
Gross Unrealized Losses	0	(1)
Fair Value	158,506	138,412
Corporate bonds
Short-term marketable securities:
Amortized Cost	138,141	45,006
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(174)	(41)
Fair Value	137,967	44,965
Long-term marketable securities:
Amortized Cost		25,032
Gross Unrealized Gains		0
Gross Unrealized Losses		(71)
Fair Value		24,961
U.S. government bonds
Short-term marketable securities:
Amortized Cost	69,241
Gross Unrealized Gains	0
Gross Unrealized Losses	(33)
Fair Value	69,208
Agency bonds
Short-term marketable securities:
Amortized Cost	48,114	78,958
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(67)	(45)
Fair Value	$ 48,047	78,913
Agency discount bonds
Short-term marketable securities:
Amortized Cost		10,990
Gross Unrealized Gains		0
Gross Unrealized Losses		(1)
Fair Value		$ 10,989

MARKETABLE SECURITIES (Schedu_2

MARKETABLE SECURITIES (Schedule of Securities in an Unrealized Loss Position) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair Value
Less Than 12 Months	$ 250,247	$ 156,804
12 Months or Greater	0	0
Total	250,247	156,804
Unrealized Loss
Less Than 12 Months	(274)	(159)
12 Months or Greater	0	0
Total	(274)	(159)
Corporate bonds
Fair Value
Less Than 12 Months	132,992	62,927
12 Months or Greater	0	0
Total	132,992	62,927
Unrealized Loss
Less Than 12 Months	(174)	(112)
12 Months or Greater	0	0
Total	(174)	(112)
Agency bonds
Fair Value
Less Than 12 Months	48,047	78,913
12 Months or Greater	0	0
Total	48,047	78,913
Unrealized Loss
Less Than 12 Months	(67)	(45)
12 Months or Greater	0	0
Total	(67)	(45)
U.S. government bonds
Fair Value
Less Than 12 Months	69,208
12 Months or Greater	0
Total	69,208
Unrealized Loss
Less Than 12 Months	(33)
12 Months or Greater	0
Total	(33)
Agency discount notes
Fair Value
Less Than 12 Months		10,989
12 Months or Greater		0
Total		10,989
Unrealized Loss
Less Than 12 Months		(1)
12 Months or Greater		0
Total		(1)
Commercial paper
Fair Value
Less Than 12 Months	0	3,975
12 Months or Greater	0	0
Total	0	3,975
Unrealized Loss
Less Than 12 Months	0	(1)
12 Months or Greater	0	0
Total	$ 0	$ (1)

PROPERTY, EQUIPMENT AND SOFTW_2

PROPERTY, EQUIPMENT AND SOFTWARE, NET (Schedule of Property, Equipment and Software) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	$ 245,142	$ 210,039
Less accumulated depreciation	(134,243)	(106,388)
Property, equipment and software, net	110,899	103,651	[1]
Capitalized website and internal-use software development costs
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	102,004	81,710
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	79,589	74,236
Computer equipment
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	40,129	32,450
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	17,351	16,435
Telecommunication
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	4,554	3,996
Software
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	$ 1,515	$ 1,212
[1]	As of January 1, 2018, the Company adopted Accounting Standards Update 2014-09, "Revenue from Contracts with Customers (Topic 606)" ("ASC 606"), using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior period presented. See Note 1 below for additional discussion.

PROPERTY, EQUIPMENT, AND SOFT_2

PROPERTY, EQUIPMENT, AND SOFTWARE, NET (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 9.8	$ 9.2	$ 28.6	$ 25.8

GOODWILL AND INTANGIBLE ASSET_2

GOODWILL AND INTANGIBLE ASSETS (Schedule of Goodwill) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018USD ($)
Goodwill [Roll Forward]
Balance as of December 31, 2017	$ 107,954	[1]
Effect of foreign currency translation	(1,631)
Balance as of September 30, 2018	$ 106,323
[1]	As of January 1, 2018, the Company adopted Accounting Standards Update 2014-09, "Revenue from Contracts with Customers (Topic 606)" ("ASC 606"), using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior period presented. See Note 1 below for additional discussion.

GOODWILL AND INTANGIBLE ASSET_3

GOODWILL AND INTANGIBLE ASSETS (Schedule of Intangible Assets) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 25,554	$ 25,647
Accumulated Amortization	(11,312)	(8,754)
Total amortization	14,242	16,893
Business relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	9,918	9,918
Accumulated Amortization	(1,625)	(896)
Total amortization	$ 8,293	$ 9,022
Weighted Average Remaining Life (in years)	9 years 8 months 12 days	10 years 3 months 19 days
Developed technology
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 7,832	$ 7,832
Accumulated Amortization	(3,189)	(2,071)
Total amortization	$ 4,643	$ 5,761
Weighted Average Remaining Life (in years)	3 years 4 months 24 days	4 years 1 month 6 days
Content
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 3,912	$ 4,005
Accumulated Amortization	(3,681)	(3,610)
Total amortization	$ 231	$ 395
Weighted Average Remaining Life (in years)	1 year	1 year 9 months 18 days
Domains and data licenses
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 2,869	$ 2,869
Accumulated Amortization	(2,231)	(1,847)
Total amortization	$ 638	$ 1,022
Weighted Average Remaining Life (in years)	1 year 7 months 6 days	2 years 2 months 12 days
Trademarks
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 877	$ 877
Accumulated Amortization	(506)	(287)
Total amortization	$ 371	$ 590
Weighted Average Remaining Life (in years)	1 year 4 months 24 days	2 years 2 months 12 days
User relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 146	$ 146
Accumulated Amortization	(80)	(43)
Total amortization	$ 66	$ 103
Weighted Average Remaining Life (in years)	1 year 6 months	2 years 2 months 12 days

GOODWILL AND INTANGIBLE ASSET_4

GOODWILL AND INTANGIBLE ASSETS (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense	$ 0.9	$ 1.4	$ 2.7	$ 5.7

GOODWILL AND INTANGIBLE ASSET_5

GOODWILL AND INTANGIBLE ASSETS (Schedule of Future Amortization Expense) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Year Ending December 31,
2018 (from October 1, 2018)	$ 882
2,019	3,277
2,020	2,402
2,021	2,262
2,022	1,045
Thereafter	4,374
Total amortization	$ 14,242	$ 16,893

ACQUISITIONS AND DISPOSALS (Nar

ACQUISITIONS AND DISPOSALS (Narrative) (Details) - USD ($)	Oct. 10, 2017	Apr. 03, 2017	Feb. 28, 2017	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 14, 2017
Business Acquisition [Line Items]
Held in escrow account				$ 28,750,000	$ 28,750,000		$ 28,750,000
Eat 24 Inc
Business Acquisition [Line Items]
Escrow deposit duration							18 months
Eat 24 Inc | Disposed of by Sale
Business Acquisition [Line Items]
Held in escrow account	$ 28,800,000
Escrow deposit duration	18 months
Purchase price consideration for sale of subsidiary	$ 251,700,000
Additional purchase consideration received									$ 1,000,000
Gain on disposal of business unit					163,700,000
Disposal related costs					300,000
Goodwill related to disposed asset group					110,800,000
Loss before provision for income taxes						$ 2,700,000		$ 11,000,000
Eat 24 Inc | Disposed of by Sale | Previously Reported
Business Acquisition [Line Items]
Gain on disposal of business unit					164,800,000
Eat 24 Inc | Disposed of by Sale | New Revenue Standard Adjustment | Accounting Standards Update 2014-09
Business Acquisition [Line Items]
Gain on disposal of business unit					$ (1,100,000)
Nowait, Inc
Business Acquisition [Line Items]
Equity interest in acquiree, percentage			20.00%
Total purchase consideration			$ 39,837,000
Held in escrow account			$ 7,945,000
Escrow deposit duration			2 years
Acquisition-related transaction costs				0		0	$ 0	100,000
Revenue of acquiree since acquisition date				1,300,000		1,300,000	3,900,000	2,600,000
Net loss of acquiree since acquisition date						1,900,000		5,100,000
Turnstyle Analytics Inc
Business Acquisition [Line Items]
Total purchase consideration		$ 19,741,000
Held in escrow account		$ 3,093,000		3,000,000			3,000,000
Escrow deposit duration		18 months
Acquisition-related transaction costs				0		0	0	300,000
Revenue of acquiree since acquisition date				$ 900,000		400,000	$ 2,400,000	800,000
Net loss of acquiree since acquisition date						$ 4,000,000		$ 4,600,000
Purchase consideration including acquisition compensation cost		$ 20,600,000
Acquisition compensation cost		$ 1,000,000

ACQUISITIONS AND DISPOSALS (Sum

ACQUISITIONS AND DISPOSALS (Summary of Purchase Price and Net Assets Acquired) (Details) - USD ($) $ in Thousands	Apr. 03, 2017	Feb. 28, 2017	Sep. 30, 2018	Dec. 31, 2017
Cash:
Held in escrow account			$ 28,750	$ 28,750
Fair value of net assets acquired:
Goodwill			106,323	$ 107,954	[1]
Nowait, Inc
Cash:
Distributed to stockholders		$ 31,892
Held in escrow account		7,945
Total purchase consideration		39,837
Fair value of net assets acquired:
Cash and cash equivalents		1,004
Intangible assets		12,670
Goodwill		25,959
Other assets		1,065
Total assets acquired		40,698
Liabilities assumed		(861)
Total liabilities assumed		(861)
Net assets acquired		$ 39,837
Turnstyle Analytics Inc
Cash:
Distributed to stockholders	$ 16,648
Held in escrow account	3,093		$ 3,000
Total purchase consideration	19,741
Fair value of net assets acquired:
Cash and cash equivalents	30
Intangible assets	4,252
Goodwill	16,048
Other assets	250
Total assets acquired	20,580
Deferred tax liability	(450)
Liabilities assumed	(389)
Total liabilities assumed	(839)
Net assets acquired	$ 19,741
[1]	As of January 1, 2018, the Company adopted Accounting Standards Update 2014-09, "Revenue from Contracts with Customers (Topic 606)" ("ASC 606"), using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior period presented. See Note 1 below for additional discussion.

ACQUISITIONS AND DISPOSALS (S_2

ACQUISITIONS AND DISPOSALS (Summary of Estimated Useful lives of Intangible Assets Acquired ) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Apr. 03, 2017	Feb. 28, 2017
Nowait, Inc
Acquired Finite-Lived Intangible Assets [Line Items]
Amount Assigned			$ 12,670
Useful Life	9 years 7 months 6 days
Nowait, Inc | Enterprise restaurant relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Amount Assigned			8,500
Useful Life	12 years
Nowait, Inc | Acquired technology
Acquired Finite-Lived Intangible Assets [Line Items]
Amount Assigned			2,900
Useful Life	5 years
Nowait, Inc | Trademarks
Acquired Finite-Lived Intangible Assets [Line Items]
Amount Assigned			610
Useful Life	3 years
Nowait, Inc | Local restaurant relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Amount Assigned			600
Useful Life	5 years
Nowait, Inc | User relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Amount Assigned			$ 60
Useful Life	3 years
Turnstyle Analytics Inc
Acquired Finite-Lived Intangible Assets [Line Items]
Amount Assigned		$ 4,252
Useful Life	4 years 10 months 24 days
Turnstyle Analytics Inc | Acquired technology
Acquired Finite-Lived Intangible Assets [Line Items]
Amount Assigned		3,250
Useful Life	5 years
Turnstyle Analytics Inc | Business relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Amount Assigned		672
Useful Life	5 years
Turnstyle Analytics Inc | Trademarks
Acquired Finite-Lived Intangible Assets [Line Items]
Amount Assigned		250
Useful Life	3 years
Turnstyle Analytics Inc | User relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Amount Assigned		$ 80
Useful Life	3 years

OTHER NON-CURRENT ASSETS (Detai

OTHER NON-CURRENT ASSETS (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Other Assets, Noncurrent Disclosure [Abstract]
Escrow deposit	$ 28,750	$ 28,750
Deferred contract costs	11,367	9,089
Other	2,656	2,589
Total other non-current assets	$ 42,773	$ 40,428	[1]
[1]	As of January 1, 2018, the Company adopted Accounting Standards Update 2014-09, "Revenue from Contracts with Customers (Topic 606)" ("ASC 606"), using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior period presented. See Note 1 below for additional discussion.

OTHER NON-CURRENT ASSETS (Narra

OTHER NON-CURRENT ASSETS (Narrative) (Details)	9 Months Ended
	Sep. 30, 2018
Eat 24 Inc
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Escrow deposit duration	18 months

OTHER NON-CURRENT ASSETS (Chang

OTHER NON-CURRENT ASSETS (Changes in Deferred Contract Costs) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018USD ($)
Changes In Capitalized Contract Costs [Roll Forward]
Balance, beginning of period	$ 9,089
Add: costs deferred on new contracts	10,629
Less: amortization recorded in sales and marketing expenses	(8,351)
Balance, end of period	$ 11,367

CONTRACT BALANCES (Schedule of

CONTRACT BALANCES (Schedule of Changes in Allowance for Doubtful Accounts) (Details) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	[2]
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance, beginning of period	[1]	$ 8,602
Add: bad debt expense		19,285	$ 15,239
Less: write-offs, net of recoveries		(19,002)
Balance, end of period		$ 8,885
[1]	As of January 1, 2018, the Company adopted Accounting Standards Update 2014-09, "Revenue from Contracts with Customers (Topic 606)" ("ASC 606"), using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior period presented. See Note 1 below for additional discussion.
[2]	As of January 1, 2018, the Company adopted ASC 606 using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior period presented. Also as of January 1, 2018, the Company adopted Accounting Standards Update No. 2016-18, "Statement of Cash Flows (Subtopic 230): Restricted Cash," and recast the prior period presented. See Note 1 below for additional discussion.

CONTRACT BALANCES (Narrative) (

CONTRACT BALANCES (Narrative) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Revenue from Contract with Customer [Abstract]
Deferred revenue	$ 3,392	$ 3,469	[1]
[1]	As of January 1, 2018, the Company adopted Accounting Standards Update 2014-09, "Revenue from Contracts with Customers (Topic 606)" ("ASC 606"), using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior period presented. See Note 1 below for additional discussion.

CONTRACT BALANCES (Changes in D

CONTRACT BALANCES (Changes in Deferred Revenue) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018USD ($)
Change in Contract with Customer, Liability [Roll Forward]
Balance, beginning of period	$ 3,469	[1]
Less: Recognition of deferred revenue from beginning balance	(3,132)
Add: Net increase in current period contract liabilities	3,055
Balance, end of period	$ 3,392
[1]	As of January 1, 2018, the Company adopted Accounting Standards Update 2014-09, "Revenue from Contracts with Customers (Topic 606)" ("ASC 606"), using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior period presented. See Note 1 below for additional discussion.

ACCRUED LIABILITIES (Details)

ACCRUED LIABILITIES (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Accrued compensation	$ 27,652	$ 17,725
Accrued sales and marketing	6,057	3,458
Accrued tax liabilities	4,785	32,617
Accrued cost of revenue	5,397	3,022
Other accrued expenses	14,673	16,843
Total accrued liabilities	$ 58,564	$ 73,665	[1]
[1]	As of January 1, 2018, the Company adopted Accounting Standards Update 2014-09, "Revenue from Contracts with Customers (Topic 606)" ("ASC 606"), using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior period presented. See Note 1 below for additional discussion.

LONG-TERM LIABILITIES (Schedule

LONG-TERM LIABILITIES (Schedule of Long-Term Liabilities) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Deferred rent	$ 30,446	$ 26,904
Other long-term liabilities	4,532	3,833
Total long-term liabilities	$ 34,978	$ 30,737	[1]
[1]	As of January 1, 2018, the Company adopted Accounting Standards Update 2014-09, "Revenue from Contracts with Customers (Topic 606)" ("ASC 606"), using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior period presented. See Note 1 below for additional discussion.

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Rental expense	$ 13.7	$ 11.4	$ 37.7	$ 31
Sublease rentals	$ 0.5	$ 0.5	$ 1.7	$ 1.5

STOCKHOLDERS' EQUITY (Schedule

STOCKHOLDERS' EQUITY (Schedule of Stock by Class) (Details) - $ / shares	Sep. 30, 2018	Dec. 31, 2017
Stockholders’ equity:
Common stock, shares authorized (in shares)	200,000,000	200,000,000	[1]
Common stock, shares issued (in shares)	84,375,021	83,724,916	[1]
Undesignated preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Undesignated preferred stock, shares issued (in shares)	0	0
Common stock, par value (in USD per share)	$ 0.000001	$ 0.000001	[1]
[1]	As of January 1, 2018, the Company adopted Accounting Standards Update 2014-09, "Revenue from Contracts with Customers (Topic 606)" ("ASC 606"), using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior period presented. See Note 1 below for additional discussion.

STOCKHOLDERS' EQUITY (Award Com

STOCKHOLDERS' EQUITY (Award Compensation Narrative) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2018USD ($)$ / sharesshares	Sep. 30, 2017USD ($)$ / sharesshares	Sep. 30, 2018USD ($)scheduleplan$ / sharesshares	Sep. 30, 2017USD ($)$ / sharesshares		Jul. 31, 2017USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock repurchase program, authorized amount						$ 200,000,000
Stock repurchased and retired during period (in shares) | shares			1,752,895
Repurchase of common stock			$ 71,993,000	$ 7,743,000	[1]
Number of equity incentive plans | plan			3
Stock-based compensation	$ 29,194,000	$ 25,309,000	$ 85,732,000	75,007,000
Capitalized stock-based compensation expense	1,900,000	1,500,000	$ 5,900,000	4,600,000
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of vesting schedules | schedule			4
Exercisable period			10 years
Intrinsic value of options exercised	$ 5,300,000	$ 9,800,000	$ 18,100,000	$ 20,200,000
Weighted average grant date fair value (in USD per share) | $ / shares	$ 23.41	$ 13.31	$ 18.89	$ 15.35
Unrecognized compensation costs	$ 21,000,000		$ 21,000,000
Unrecognized compensation costs, period for recognition			2 years 6 months 1 day
Employee Stock Option | End of year one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate			25.00%
Employee Stock Option | First year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate			10.00%
Employee Stock Option | Second year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate			20.00%
Employee Stock Option | Third year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate			30.00%
Employee Stock Option | Fourth year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate			40.00%
Employee Stock Option | Monthly Basis First Year Member
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate			35.00%
Employee Stock Option | Monthly Basis Second Year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate			40.00%
Employee Stock Option | Monthly Basis Third Year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate			25.00%
Employee Stock Option | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			3 years
Employee Stock Option | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			4 years
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			4 years
Number of vesting schedules | schedule			3
Unrecognized compensation costs	$ 242,000,000		$ 242,000,000
Unrecognized compensation costs, period for recognition			2 years 7 months
RSUs | End of year one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate			25.00%
RSUs | First year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate			10.00%
RSUs | Second year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate			20.00%
RSUs | Third year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate			30.00%
RSUs | Fourth year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate			40.00%
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Subscription rate of eligible compensation	15.00%		15.00%
Purchase price, percentage of fair market value			85.00%
Number of shares purchased (in shares) | shares	0	0	195,987	228,299
Weighted-average purchase price (in dollars per share) | $ / shares	$ 36.42	$ 23.73	$ 36.42	$ 23.73
Stock-based compensation	$ 700,000	$ 500,000	$ 2,000,000	$ 1,500,000
[1]	As of January 1, 2018, the Company adopted ASC 606 using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior period presented. Also as of January 1, 2018, the Company adopted Accounting Standards Update No. 2016-18, "Statement of Cash Flows (Subtopic 230): Restricted Cash," and recast the prior period presented. See Note 1 below for additional discussion.

STOCKHOLDERS' EQUITY (Schedul_2

STOCKHOLDERS' EQUITY (Schedule of Stock Option Activity) (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Number of Shares
Outstanding, beginning balance (in shares)	7,078,932
Granted (in shares)	685,850
Exercised (in shares)	(737,986)
Canceled (in shares)	(109,361)
Outstanding, ending balance (in shares)	6,917,435	7,078,932
Options vested and exercisable (in shares)	5,543,179
Weighted-Average Exercise Price
Outstanding, beginning balance (in USD per share)	$ 22.70
Granted (in USD per share)	43.52
Exercised (in USD per share)	19.91
Canceled (in USD per share)	48.85
Outstanding, ending balance (in USD per share)	24.65	$ 22.70
Options vested and exercisable (in USD per share)	$ 21.71
Weighted- Average Remaining Contractual Term
Outstanding, Weighted-Average Remaining Contractual Term (in years)	5 years 4 months 17 days	5 years 6 months 21 days
Options vested and exercisable, Weighted-Average Remaining Contractual Term (in years)	4 years 7 months 6 days
Aggregate Intrinsic Value
Outstanding, Aggregate Intrinsic Value	$ 174,842	$ 145,613
Options vested and exercisable, Aggregate Intrinsic Value	$ 157,306

STOCKHOLDERS' EQUITY (Schedul_3

STOCKHOLDERS' EQUITY (Schedule of Restricted Stock Units Activity) (Details) - Restricted Stock Units	9 Months Ended
	Sep. 30, 2018$ / sharesshares
Number of Shares
Unvested, beginning balance (in shares) | shares	7,249,205
Granted (in shares) | shares	3,029,151
Released (in shares) | shares	(2,393,407)
Canceled (in shares) | shares	(1,087,920)
Unvested, ending balance (in shares) | shares	6,797,029
Weighted-Average Grant Date Fair Value
Unvested, beginning balance (in USD per share) | $ / shares	$ 34.57
Granted (in USD per share) | $ / shares	42.59
Released (in USD per share) | $ / shares	36.06
Canceled (in USD per share) | $ / shares	36.02
Unvested, ending balance (in USD per share) | $ / shares	$ 37.39

STOCKHOLDERS' EQUITY (Schedul_4

STOCKHOLDERS' EQUITY (Schedule of Stock-Based Compensation Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation	$ 29,194	$ 25,309	$ 85,732	$ 75,007
Cost of revenue
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation	1,162	993	3,345	2,931
Sales and marketing
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation	7,941	7,305	23,514	21,434
Product development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation	14,536	11,976	41,878	34,428
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation	$ 5,555	$ 5,035	$ 16,995	$ 16,214

OTHER INCOME, NET (Details)

OTHER INCOME, NET (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017
Other Income and Expenses [Abstract]
Interest income, net	$ 3,705	$ 991		$ 9,606	$ 2,431
Transaction gain on foreign exchange	75	323		89	377
Other non-operating income, net	141	57		255	125
Other income, net	$ 3,921	$ 1,371	[1]	$ 9,950	$ 2,933	[1]
[1]	As of January 1, 2018, the Company adopted ASC 606 using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior periods presented. See Note 1 below for additional discussion.

INCOME TAXES - Summary of Provi

INCOME TAXES - Summary of Provision for Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Benefit from (provision for) income taxes	$ 684	$ (232)	[1]	$ 281	$ (417)	[1]
[1]	As of January 1, 2018, the Company adopted ASC 606 using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior periods presented. See Note 1 below for additional discussion.

INCOME TAXES - Narrative (Detai

INCOME TAXES - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	[1]	Sep. 30, 2018	Sep. 30, 2017
Income Tax Contingency [Line Items]
Income Tax Expense (Benefit)	$ (684)	$ 232		$ (281)	$ 417	[1]
Income tax provision due to U.S. federal and state income taxes and foreign income taxes				1,200	$ 400
Net discrete tax expense (benefit)				(1,500)
Unrecognized tax benefits	24,400			24,400
Unrecognized tax benefits that would not impact the effective tax rate	23,500			23,500
Unrecognized tax benefits increase	2,000
Earnings of foreign subsidiaries to be reinvested indefinitely	$ 3,300			$ 3,300
Federal and State Tax Jurisdictions
Income Tax Contingency [Line Items]
Open tax year				2,003
Canada, Ireland, United Kingdom and Germany Tax Jurisdictions
Income Tax Contingency [Line Items]
Open tax year				2,010
[1]	As of January 1, 2018, the Company adopted ASC 606 using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior periods presented. See Note 1 below for additional discussion.

NET INCOME PER SHARE (Schedule

NET INCOME PER SHARE (Schedule of Basic and Diluted Net Income Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share Reconciliation [Line Items]
Net income	$ 14,986	$ 8,030	[1]	$ 23,404	$ 11,874	[1],[2]
Basic net income per share:
Weighted-average common shares outstanding (in shares)	84,008	82,259	[1]	83,865	81,041	[1]
Basic net income per share attributable to common stockholders	$ 0.18	$ 0.10	[1]	$ 0.28	$ 0.15	[1]
Diluted net income per share
Weighted-average common shares outstanding (in shares)	84,008	82,259	[1]	83,865	81,041	[1]
Number of shares used in diluted calculation (in shares)	88,724	87,433	[1]	89,271	86,097	[1]
Diluted net income per share attributable to common stockholders (in USD per share)	$ 0.17	$ 0.09	[1]	$ 0.26	$ 0.14	[1]
Stock options
Diluted net income per share
Incremental common shares (in shares)	3,011	3,253		3,096	3,179
Restricted stock units
Diluted net income per share
Incremental common shares (in shares)	1,656	1,921		2,240	1,877
Employee stock purchase program
Diluted net income per share
Incremental common shares (in shares)	49	0		70	0
[1]	As of January 1, 2018, the Company adopted ASC 606 using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior periods presented. See Note 1 below for additional discussion.
[2]	As of January 1, 2018, the Company adopted ASC 606 using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior period presented. Also as of January 1, 2018, the Company adopted Accounting Standards Update No. 2016-18, "Statement of Cash Flows (Subtopic 230): Restricted Cash," and recast the prior period presented. See Note 1 below for additional discussion.

NET INCOME PER SHARE (Schedul_2

NET INCOME PER SHARE (Schedule of Anti-Dilutive Employee Stock Awards) (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive awards (in shares)	1,694	1,793	1,681	1,911
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive awards (in shares)	591	871	106	978

INFORMATION ABOUT REVENUE AND_3

INFORMATION ABOUT REVENUE AND GEOGRAPHIC AREAS (Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue	$ 241,096	$ 223,287	[1]	$ 699,033	$ 631,406	[1]
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue	237,597	219,642		689,096	620,925
All other countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue	3,499	3,645		9,937	10,481
Advertising
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue	232,502	200,502		672,712	566,085
Transactions
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue	3,042	18,524		10,402	55,024
Other services
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue	$ 5,552	$ 4,261		$ 15,919	$ 10,297
[1]	As of January 1, 2018, the Company adopted ASC 606 using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior periods presented. See Note 1 below for additional discussion.

INFORMATION ABOUT REVENUE AND_4

INFORMATION ABOUT REVENUE AND GEOGRAPHIC AREAS (Long-Lived Assets) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 110,899	$ 103,651
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	108,900	100,990
All other countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 1,999	$ 2,661

RESTRUCTURING AND INTEGRATION_2

RESTRUCTURING AND INTEGRATION (Details) - USD ($)	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	[1]	Sep. 30, 2018	Sep. 30, 2017	[1]	Dec. 31, 2017
Restructuring and Related Activities [Abstract]
Restructuring and integration	$ 0	$ 35,000		$ 0	$ 286,000
Expected restructuring costs remaining							$ 0
[1]	As of January 1, 2018, the Company adopted ASC 606 using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior periods presented. See Note 1 below for additional discussion.