Yelp (YELP) 10-Q 6 Nov 20 2020 Q3 Quarterly report Financial data

Cover page

Cover page - shares	9 Months Ended
	Sep. 30, 2020	Oct. 30, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2020
Document Transition Report	false
Entity File Number	001-35444
Entity Registrant Name	YELP INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	20-1854266
Entity Address, Address Line One	140 New Montgomery Street, 9th Floor
Entity Address, City or Town	San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94105
City Area Code	(415)
Local Phone Number	908-3801
Title of 12(b) Security	Common Stock, par value $0.000001 per share
Trading Symbol	YELP
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		73,996,090
Amendment Flag	false
Entity Central Index Key	0001345016
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 590,789	$ 170,281
Short-term marketable securities	0	242,000
Accounts receivable (net of allowance for doubtful accounts of $11,316 and $7,686 at September 30, 2020 and December 31, 2019, respectively)	84,813	106,832
Prepaid expenses and other current assets	18,590	14,196
Total current assets	694,192	533,309
Long-term marketable securities	0	53,499
Property, equipment and software, net	105,488	110,949
Operating lease right-of-use assets	176,603	197,866
Goodwill	106,772	104,589
Intangibles, net	14,240	10,082
Restricted cash	826	22,037
Other non-current assets	40,829	38,369
Total assets	1,138,950	1,070,700
Current liabilities:
Accounts payable and accrued liabilities	103,378	72,333
Operating lease liabilities — current	54,396	57,507
Deferred revenue	4,731	4,315
Total current liabilities	162,505	134,155
Operating lease liabilities — long-term	155,297	174,756
Other long-term liabilities	5,520	6,798
Total liabilities	323,322	315,709
Commitments and contingencies (Note 12)
Stockholders' equity:
Common stock, $0.000001 par value, 200,000,000 shares authorized – 73,976,487 and 71,185,468 shares issued and outstanding at September 30, 2020 and December 31, 2019, respectively	0	0
Additional paid-in capital	1,358,804	1,259,803
Accumulated other comprehensive loss	(9,576)	(11,759)
Accumulated deficit	(533,600)	(493,053)
Total stockholders' equity	815,628	754,991
Total liabilities and stockholders' equity	$ 1,138,950	$ 1,070,700

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Allowance for credit loss	$ 11,316	$ 7,686	$ 7,779	$ 8,685
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)	73,976,487	71,185,468
Common stock, shares outstanding (in shares)	73,976,487	71,185,468

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Net revenue	$ 220,807	$ 262,474	$ 639,738	$ 745,371
Costs and expenses:
Cost of revenue (exclusive of depreciation and amortization shown separately below)	13,193	16,514	41,865	45,754
Sales and marketing	101,301	127,655	334,887	374,016
Product development	53,022	56,661	174,104	169,302
General and administrative	30,887	39,703	100,825	101,927
Depreciation and amortization	12,544	12,391	37,484	36,507
Restructuring	535	0	3,847	0
Total costs and expenses	211,482	252,924	693,012	727,506
Income (loss) from operations	9,325	9,550	(53,274)	17,865
Other income, net	399	3,063	3,277	11,645
Income (loss) before income taxes	9,724	12,613	(49,997)	29,510
Provision for (benefit from) income taxes	10,744	2,552	(9,484)	5,781
Net (loss) income attributable to common stockholders	$ (1,020)	$ 10,061	$ (40,513)	$ 23,729
Net (loss) income per share attributable to common stockholders
Basic (in USD per share)	$ (0.01)	$ 0.14	$ (0.56)	$ 0.31
Diluted (in USD per share)	$ (0.01)	$ 0.14	$ (0.56)	$ 0.30
Weighted-average shares used to compute net (loss) income per share attributable to common stockholders
Basic (in shares)	73,514	70,773	72,495	75,975
Diluted (in shares)	73,514	73,712	72,495	79,315

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement of Comprehensive Income [Abstract]
Net (loss) income	$ (1,020)	$ 10,061	$ (40,513)	$ 23,729
Other comprehensive income (loss):
Foreign currency translation adjustments	2,269	(2,134)	2,183	(2,276)
Other comprehensive income (loss)	2,269	(2,134)	2,183	(2,276)
Comprehensive income (loss)	$ 1,249	$ 7,927	$ (38,330)	$ 21,453

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Additional Paid-In Capital	Treasury Stock	Accumulated Other Comprehensive Loss	Accumulated Deficit
Balance (in shares) at Dec. 31, 2018			81,996,839
Balance at beginning at Dec. 31, 2018	$ 1,075,518		$ 0	$ 1,139,462	$ 0	$ (11,021)	$ (52,923)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercises of employee stock options (in shares)			399,320
Issuance of common stock upon exercises of employee stock options	8,276			8,276
Issuance of common stock upon vesting of RSUs (in shares)			1,510,144
Issuance of common stock for employee stock purchase plan (in shares)			288,529
Issuance of common stock for employee stock purchase plan	7,537			7,537
Stock-based compensation (inclusive of capitalized stock-based compensation)	97,810			97,810
Shares withheld related to net share settlement of equity awards	(33,037)			(33,037)
Repurchases of common stock	(474,993)				(474,993)
Retirement of common stock (in shares)			(13,994,909)
Retirement of common stock					474,993		(474,993)
Foreign currency adjustments	(2,276)					(2,276)
Net (loss) income	23,729						23,729
Balance (in shares) at Sep. 30, 2019			70,199,923
Balance at end at Sep. 30, 2019	702,564		$ 0	1,220,048	0	(13,297)	(504,187)
Balance (in shares) at Jun. 30, 2019			71,931,789
Balance at beginning at Jun. 30, 2019	746,455		$ 0	1,194,486	(5,952)	(11,163)	(430,916)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercises of employee stock options (in shares)			225,364
Issuance of common stock upon exercises of employee stock options	4,615			4,615
Issuance of common stock upon vesting of RSUs (in shares)			527,233
Stock-based compensation (inclusive of capitalized stock-based compensation)	31,140			31,140
Shares withheld related to net share settlement of equity awards	(10,193)			(10,193)
Repurchases of common stock	(77,380)				(77,380)
Retirement of common stock (in shares)			(2,484,463)
Retirement of common stock					83,332		(83,332)
Foreign currency adjustments	(2,134)					(2,134)
Net (loss) income	10,061						10,061
Balance (in shares) at Sep. 30, 2019			70,199,923
Balance at end at Sep. 30, 2019	$ 702,564		$ 0	1,220,048	0	(13,297)	(504,187)
Balance (in shares) at Dec. 31, 2019	71,185,468		71,185,468
Balance at beginning at Dec. 31, 2019	$ 754,991	$ (34)	$ 0	1,259,803	0	(11,759)	(493,053)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercises of employee stock options (in shares)	285,388		285,388
Issuance of common stock upon exercises of employee stock options	$ 3,606			3,606
Issuance of common stock upon vesting of RSUs (in shares)			2,071,934
Issuance of common stock for employee stock purchase plan (in shares)			433,697
Issuance of common stock for employee stock purchase plan	8,014			8,014
Stock-based compensation (inclusive of capitalized stock-based compensation)	99,133			99,133
Shares withheld related to net share settlement of equity awards	(11,752)			(11,752)
Foreign currency adjustments	2,183					2,183
Net (loss) income	$ (40,513)						(40,513)
Balance (in shares) at Sep. 30, 2020	73,976,487		73,976,487
Balance at end at Sep. 30, 2020	$ 815,628		$ 0	1,358,804	0	(9,576)	(533,600)
Balance (in shares) at Jun. 30, 2020			73,121,229
Balance at beginning at Jun. 30, 2020	781,320		$ 0	1,325,745	0	(11,845)	(532,580)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercises of employee stock options (in shares)			63,031
Issuance of common stock upon exercises of employee stock options	812			812
Issuance of common stock upon vesting of RSUs (in shares)			792,227
Stock-based compensation (inclusive of capitalized stock-based compensation)	32,247			32,247
Foreign currency adjustments	2,269					2,269
Net (loss) income	$ (1,020)						(1,020)
Balance (in shares) at Sep. 30, 2020	73,976,487		73,976,487
Balance at end at Sep. 30, 2020	$ 815,628		$ 0	$ 1,358,804	$ 0	$ (9,576)	$ (533,600)

CONDENSED CONSOLIDATED STATEM_4

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Operating Activities
Net (loss) income attributable to common stockholders	$ (40,513)	$ 23,729
Adjustments to reconcile net (loss) income to net cash provided by operating activities:
Depreciation and amortization	37,484	36,507
Provision for doubtful accounts	26,802	15,259
Stock-based compensation	92,590	91,006
Noncash lease cost	31,545	31,379
Deferred income taxes	(6,505)	(673)
Other adjustments, net	1,316	(2,559)
Changes in operating assets and liabilities:
Accounts receivable	(4,783)	(29,395)
Prepaid expenses and other assets	1,552	(2,312)
Operating lease liabilities	(34,284)	(31,002)
Accounts payable, accrued liabilities and other liabilities	23,181	17,329
Net cash provided by operating activities	128,385	149,268
Investing Activities
Sales and maturities of marketable securities — available-for-sale	290,395	0
Purchases of marketable securities — held-to-maturity	(87,438)	(396,648)
Maturities of marketable securities — held-to-maturity	93,200	530,597
Release of escrow deposit	0	28,750
Purchases of property, equipment and software	(24,072)	(29,950)
Other investing activities	329	383
Net cash provided by investing activities	272,414	133,132
Financing Activities
Proceeds from issuance of common stock for employee stock-based plans	11,620	15,813
Repurchases of common stock	0	(474,993)
Taxes paid related to the net share settlement of equity awards	(12,557)	(32,784)
Other financing activities	(433)	0
Net cash used in financing activities	(1,370)	(491,964)
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(132)	258
Change in cash, cash equivalents and restricted cash	399,297	(209,306)
Cash, cash equivalents and restricted cash — Beginning of period	192,318	354,835
Cash, cash equivalents and restricted cash — End of period	591,615	145,529
Supplemental Disclosures of Other Cash Flow Information
Cash paid for income taxes, net	109	5,702
Supplemental Disclosures of Noncash Investing and Financing Activities
Purchases of property, equipment and software recorded in accounts payable and accrued liabilities	2,168	1,856
Tax liability related to net share settlement of equity awards included in accounts payable and accrued liabilities	0	896
Operating lease right-of-use assets obtained in exchange for new operating lease liabilities	$ 11,833	$ 6,325

DESCRIPTION OF BUSINESS AND BAS

DESCRIPTION OF BUSINESS AND BASIS FOR PRESENTATION	9 Months Ended
	Sep. 30, 2020
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 consumers with great local businesses. Yelp's trusted local platform delivers significant value to both consumers and businesses by helping each discover and interact with the other: its content and transaction capabilities help consumers save time and money, while its advertising and other products help businesses gain visibility and engage with its large audience of purchase-oriented consumers. 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, 2019, filed with the SEC on February 28, 2020 and amended on April 29, 2020 (the "Annual Report"). The unaudited condensed consolidated balance sheet as of December 31, 2019 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. The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited consolidated financial statements, except as set forth under "Recently Adopted Accounting Pronouncements" below. 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. 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. In early March 2020, COVID-19 — the disease caused by a novel strain of the coronavirus — was declared a global pandemic by the World Health Organization. Governments and municipalities around the world, including in the United States, have implemented extensive measures in an effort to control the spread of COVID-19, including travel restrictions, limitations on business activity, quarantines and shelter-in-place orders. Due to the COVID-19 pandemic and the uncertainty of the extent of the impacts, many of the estimates and assumptions required increased judgment and carry a higher degree of variability and volatility than they did prior to the pandemic. As events continue to evolve and additional information becomes available, these estimates may materially change in future periods. 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. Marketable Securities —The Company considers highly liquid treasury notes, U.S. agency securities, corporate debt securities, money market funds and other funds with maturities of more than three months to be marketable securities. Securities with less than one year to maturity are included in short-term marketable securities, and all other securities are classified as long-term marketable securities. The Company has a policy that generally requires its securities to be investment grade (i.e. rated ‘A+’ or higher by bond rating firms) with the objective of minimizing the potential risk of principal loss. The Company determines the classification of its marketable securities based on its investment strategy. Marketable securities are classified as held-to-maturity when the Company has the positive intent and ability to hold the securities to maturity, and it has an established history of holding investments to maturity. Held-to-maturity securities are stated at amortized cost and are periodically assessed for impairment. Amortized costs of debt securities are adjusted for amortization of premiums and accretion of discounts to maturity, and these adjustments are included in interest income. Marketable securities are classified as available-for-sale when the Company has established a practice of selling investments prior to maturity, or if the Company does not have the intent to hold securities to maturity to allow flexibility in response to liquidity needs. In the event that the Company classifies its investments as available-for-sale, it will only return to classifying investments as held-to-maturity once it has reestablished a practice and intent of holding investments to maturity. Available-for-sale securities are stated at fair value as of each balance sheet date and are periodically assessed for impairment. For the Company's available-for-sale securities, an investment is impaired if the fair value of the investment is less than its amortized cost basis. In assessing whether a credit loss exists, the Company compares the present value of cash flows expected to be collected from the security with the amortized cost basis of the security. If the present value of expected cash flows is less than the amortized cost basis of the security, an allowance for credit loss is recorded as a component of other income (expense), net. Any remaining unrealized losses are recorded to other comprehensive income (loss). The Company determines any realized gains or losses on the sale of marketable securities on a specific identification method and records such gains and losses as a component of other income (expense), net. Amortization of premiums and accretion of discounts are included in interest income. If the Company has the intent to sell an available-for-sale security in an unrealized loss position or it is more likely than not that it will be required to sell the security prior to recovery of its amortized cost basis, any previously recorded allowance is reversed and the entire difference between the amortized cost basis of the security and its fair value is recognized in the condensed consolidated statements of operations. Allowance for Doubtful Accounts —The Company maintains an allowance for doubtful accounts receivable. The allowance reflects the Company's best estimate of probable losses associated with 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 based on the credit risk of those accounts, known delinquent accounts, as well as current conditions and reasonable and supportable economic forecasts. 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. Goodwill —Goodwill represents the excess of the purchase price in a business combination over the fair value of net tangible and intangible assets acquired. The carrying amount of goodwill is reviewed at least annually, or more frequently if events or changes in circumstances indicate that the carrying value of goodwill may not be recoverable. The Company has the option to first assess qualitative factors to determine whether it is more likely than not that the fair value of a reporting unit is less than its carrying amount. If the Company determines that it is more likely than not that its fair value is less than the carrying amount, or opts not to perform a qualitative assessment, then the Company will compare the 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 carrying value of goodwill will be written down to fair value. No impairment charges associated with goodwill have been recorded by the Company to date. Stock-Based Compensation —The Company accounts for stock-based employee compensation plans under the fair value recognition and measurement provisions, which require all stock-based payments to employees, including grants of stock options, restricted stock awards, restricted stock units ("RSUs"), performance-based restricted stock units ("PRSUs") and issuances under its 2012 Employee Stock Purchase Plan, as amended ("ESPP"), to be measured based on the grant-date fair value of the awards. The Company accounts for forfeitures as they occur. The fair value of options granted to employees is estimated on the grant date using the Black-Scholes-Merton option valuation model. This valuation model for stock-based compensation expense requires the Company to make assumptions and judgments about the variables used in the calculation, including the expected term (weighted-average period of time that the options granted are expected to be outstanding), the expected volatility in the fair market value of the Company’s common stock, a risk-free interest rate and expected dividends. No compensation cost is recorded for options that do not vest. The Company uses the simplified calculation of expected life as the contractual term for options of 10 years is longer than the Company has been publicly traded. Expected volatility is based on an average of the historical volatilities of the common stock of several entities with characteristics similar to those of the Company. The risk-free rate is based on the U.S. Treasury yield curve in effect at the time of grant for periods corresponding with the expected life of the option. The Company uses the straight-line method for expense attribution. The fair value of RSUs is measured using the closing price of the Company's common stock on the New York Stock Exchange on the grant date. The Company uses the straight-line method for expense attribution. No compensation cost is recorded for RSUs that do not vest. In May 2020, the Company changed its method of settling the employee tax liabilities associated with the vesting of RSUs from withholding a portion of the vested shares and covering such taxes with cash from its balance sheet ("Net Share Withholding"), to selling a portion of the vested shares to cover taxes ("Sell-to-Cover"). The Company has two types of PRSUs outstanding — awards for which the vesting is subject to both a time-based vesting schedule and either (a) a market condition or (b) the achievement of performance goals. For the awards subject to a market condition, the Company uses a Monte Carlo model to determine the fair value of the PRSUs. The Company uses the accelerated method for expense attribution. Compensation costs are recorded if the service condition is met regardless of whether the market performance condition is satisfied. No compensation cost is recorded if the service condition is not met. For the awards subject to performance goals, compensation costs are recorded when the Company concludes that it is probable that the performance conditions will be achieved. The Company performs an analysis in each reporting period to determine the probability that the performance goals will be met, and recognizes a cumulative catch-up adjustment to compensation cost for changes in its probability assessment in subsequent reporting periods, if required, until the performance period has expired. The fair value of the PRSUs is measured using the closing price of the Company's common stock on the New York Stock Exchange on the grant date. The Company uses the accelerated method for expense attribution. No compensation cost is recorded if the service condition is not met. Recently Adopted Accounting Pronouncements In June 2016, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update No. 2016-13, "Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments" ("ASU 2016-13"). ASU 2016-13 requires certain types of financial instruments, including trade receivables and held-to-maturity investments measured at amortized cost, to be presented as the net amount expected to be collected based on historical events, current conditions and forecast information. The Company adopted and began applying ASU 2016-13 on January 1, 2020 by recording a cumulative-effect adjustment to retained earnings. This adjustment recorded an allowance related to expected credit losses on the Company's held-to-maturity debt securities, which was subsequently reversed upon its change in investment strategy in March 2020. This allowance took into consideration the composition and credit quality of the financial instruments, their respective historical credit loss activity, and reasonable and supportable economic forecasts and conditions at the time of adoption. The adoption did not have a material impact on the Company's consolidated financial statements. In January 2017, the FASB issued Accounting Standards Update No. 2017-04, "Intangibles—Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment" ("ASU 2017-04"). ASU 2017-04 simplified the subsequent measurement of goodwill by eliminating Step 2 from the goodwill impairment test. Under the new standard, entities perform goodwill impairment tests by comparing the 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 Company adopted ASU 2017-04 on January 1, 2020 and the adoption did not have a material impact on its consolidated financial statements. In August 2018, the FASB issued Accounting Standards Update No. 2018-13, "Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement" ("ASU 2018-13"), which amended Accounting Standards Codification 820, "Fair Value Measurement." ASU 2018-13 modified the disclosure requirements for fair value measurements by removing, modifying and adding certain disclosures. The Company adopted ASU 2018-13 on January 1, 2020 and the adoption did not have a material impact on its consolidated financial statements. In August 2018, the 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"). ASU 2018-15 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 which to recognize as assets. 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. The Company adopted ASU 2018-15 prospectively and began applying it on January 1, 2020. The adoption did not have a material impact on the Company's financial statements. Recent Accounting Pronouncements Not Yet Effective In December 2019, the FASB issued Accounting Standards Update No. 2019-12, Income Taxes (Topic 740): "Simplifying the Accounting for Income Taxes" ("ASU 2019-12"), which simplifies the accounting for income taxes by removing certain exceptions to the general principles for recording income taxes, while also simplifying certain recognition and allocation approaches to accounting for income taxes. ASU 2019-12 will be effective for the first interim period within annual periods beginning after December 15, 2020 on a prospective basis, and early adoption is permitted. The Company is currently evaluating the impact of ASU 2019-12 on its consolidated financial statements and related disclosures.

CASH, CASH EQUIVALENTS AND REST

CASH, CASH EQUIVALENTS AND RESTRICTED CASH	9 Months Ended
	Sep. 30, 2020
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, 2020 and December 31, 2019 consisted of the following (in thousands): September 30, December 31, Cash $ 80,698 $ 43,581 Cash equivalents 510,091 126,700 Total cash and cash equivalents $ 590,789 $ 170,281 Restricted cash 826 22,037 Total cash, cash equivalents and restricted cash $ 591,615 $ 192,318 The increase in cash equivalents during the nine months ended September 30, 2020 was primarily driven by the Company's change in its investment strategy to preserve liquidity as a result of COVID-19. During the six months ended June 30, 2020, the Company sold securities prior to maturity for proceeds of $253.4 million and reinvested these funds along with $73.0 million from maturities and redemptions into money market funds, which are recorded as cash equivalents. See Note 4, " Marketable Securities " for further details. As of December 31, 2019, the Company had letters of credit collateralized fully by bank deposits that totaled $22.0 million. These letters of credit primarily related to lease agreements for certain of the Company’s offices, which were required to be maintained and issued to the landlords of each facility. Each letter of credit was subject to renewal annually until the applicable lease expires. As the bank deposits had restrictions on their use, they were classified as restricted cash on the Company's condensed consolidated balance sheet. In May 2020, the Company moved approximately $21.5 million of these letters of credit under a sub-limit included in its credit agreement with Wells Fargo Bank, National Association, which it entered into on May 5, 2020 (the "Credit Agreement"). Following this transfer, the restrictions on the Company's use of the bank deposits previously used to collateralize its letters of credit were lifted and, as a result, such funds are no longer classified as restricted cash. See Note 12, " Commitments and Contingencies " for further details on the Credit Agreement.

FAIR VALUE OF FINANCIAL INSTRUM

FAIR VALUE OF FINANCIAL INSTRUMENTS	9 Months Ended
	Sep. 30, 2020
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 on the condensed consolidated balance sheets. 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. Prior to their sale during the six months ended June 30, 2020, the Company's commercial paper, corporate bonds, U.S. government bonds and agency bonds were classified within Level 2 of the fair value hierarchy because they were valued using inputs other than quoted prices in active markets that are observable directly or indirectly. See Note 4, " Marketable Securities " for further details. The Company's long-lived and indefinite-lived assets such as property, equipment and software, goodwill and other intangible assets are measured at fair value on a non-recurring basis if the assets are determined to be impaired. The Company recognized an immaterial impairment charge related to its intangible assets during the three months ended March 31, 2020. See Note 7, " Goodwill and Intangible Assets " for further details. The Company estimated the fair value of these intangible assets using an income approach that relied on assumptions made by management using both internal and external data; as a result, these intangible assets are classified within Level 3 of the fair value hierarchy. The following table represents the fair value of the Company’s financial instruments, including those measured at fair value on a recurring basis, as of September 30, 2020 and December 31, 2019 as well as those held-to-maturity as of December 31, 2019 (in thousands): September 30, 2020 December 31, 2019 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 510,091 $ — $ — $ 510,091 $ 126,700 $ — $ — $ 126,700 Marketable securities: Commercial paper — — — — — 130,472 — 130,472 Corporate bonds — — — — — 85,611 — 85,611 Agency bonds — — — — — 79,750 — 79,750 Total cash equivalents and marketable securities $ 510,091 $ — $ — $ 510,091 $ 126,700 $ 295,833 $ — $ 422,533

MARKETABLE SECURITIES

MARKETABLE SECURITIES	9 Months Ended
	Sep. 30, 2020
Investments, Debt and Equity Securities [Abstract]
Marketable Securities	MARKETABLE SECURITIES In March 2020, the Company changed its investment strategy in response to uncertainties resulting from the COVID-19 pandemic to allow for more flexibility in preserving liquidity. As a result of this change, the classification of the Company's investments changed from held-to-maturity to available-for-sale. The amortized cost of marketable securities transferred from held-to-maturity to available-for-sale was $300.2 million. As a result of the transfer, the Company reversed the allowance for credit loss that had been previously recorded upon adoption of ASU 2016-13 and measured the securities at fair value as of the transfer date by recording an immaterial allowance for credit loss to other income, net and the remaining adjustment as an immaterial unrealized loss recorded to other comprehensive income. As a result of its change in investment strategy, the Company liquidated its investment portfolio, which consisted of available-for-sale short- and long-term marketable securities, for proceeds of $253.4 million during the six months ended June 30, 2020. The Company recorded an immaterial amount of net realized gains to other income, net and reinvested the proceeds from the sales, along with $73.0 million from maturities and redemptions of marketable securities, into money market funds. The amortized cost, gross unrealized gains and losses, and fair value of marketable securities classified as held-to-maturity as of December 31, 2019 were as follows (in thousands): December 31, 2019 Amortized Gross Gross Fair Short-term marketable securities: Commercial paper $ 130,464 $ 17 $ (9) $ 130,472 Corporate bonds 85,396 225 (10) 85,611 Agency bonds 26,140 90 — 26,230 Total short-term marketable securities 242,000 332 (19) 242,313 Long-term marketable securities: Agency bonds 53,499 21 — 53,520 Total long-term marketable securities 53,499 21 — 53,520 Total marketable securities $ 295,499 $ 353 $ (19) $ 295,833 The Company did not have any securities that were in an unrealized loss position as of September 30, 2020 due to the liquidation of its investment portfolio. The following table presents gross unrealized losses and fair values for those securities that were in an unrealized loss position as of December 31, 2019, aggregated by investment category and the length of time that the individual securities had been in a continuous loss position (in thousands): December 31, 2019 Less Than 12 Months 12 Months or Greater Total Fair Unrealized Loss Fair Unrealized Loss Fair Unrealized Loss Commercial paper $ 63,639 $ (9) $ — $ — $ 63,639 $ (9) Corporate bonds 20,979 (10) — — 20,979 (10) Total $ 84,618 $ (19) $ — $ — $ 84,618 $ (19) Prior to the adoption of ASU 2016-13, the Company periodically reviewed its investment portfolio for other-than-temporary impairment. The Company considered such factors as the duration, severity and reason for the decline in value, and the potential recovery period. The Company also considered whether it was more likely than not that it would be required to sell the securities before the recovery of their amortized cost basis, and whether the amortized cost basis could not be recovered as a result of credit losses. During the three and nine months ended September 30, 2019, the Company did not recognize any other-than-temporary impairment loss.

PREPAID EXPENSES AND OTHER CURR

PREPAID EXPENSES AND OTHER CURRENT ASSETS	9 Months Ended
	Sep. 30, 2020
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid Expenses and Other Current Assets	PREPAID EXPENSES AND OTHER CURRENT ASSETS Prepaid expenses and other current assets as of September 30, 2020 and December 31, 2019 consisted of the following (in thousands): September 30, 2020 December 31, 2019 Prepaid expenses $ 9,612 $ 10,188 Other current assets 8,978 4,008 Total prepaid expenses and other current assets $ 18,590 $ 14,196 As of September 30, 2020, other current assets consisted primarily of $4.7 million of income tax and payroll tax receivables.

PROPERTY, EQUIPMENT AND SOFTWAR

PROPERTY, EQUIPMENT AND SOFTWARE, NET	9 Months Ended
	Sep. 30, 2020
Property, Plant and Equipment [Abstract]
Property, Equipment and Software, Net	PROPERTY, EQUIPMENT AND SOFTWARE, NET Property, equipment and software, net as of September 30, 2020 and December 31, 2019 consisted of the following (in thousands): September 30, December 31, Capitalized website and internal-use software development costs $ 164,488 $ 140,886 Leasehold improvements 88,436 86,089 Computer equipment 46,049 43,626 Furniture and fixtures 18,271 18,403 Telecommunication 4,956 5,154 Software 1,687 1,687 Total 323,887 295,845 Less accumulated depreciation (218,399) (184,896) Property, equipment and software, net $ 105,488 $ 110,949

GOODWILL AND INTANGIBLE ASSETS

GOODWILL AND INTANGIBLE ASSETS	9 Months Ended
	Sep. 30, 2020
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 acquired and liabilities assumed. The Company performed its annual goodwill impairment analysis as of August 31, 2020 and concluded that goodwill was not impaired, as the fair value of the reporting unit exceeded its carrying value. The changes in carrying amount of goodwill during the nine months ended September 30, 2020 were as follows (in thousands): Balance as of December 31, 2019 $ 104,589 Effect of currency translation 2,183 Balance as of September 30, 2020 $ 106,772 Intangible assets at September 30, 2020 and December 31, 2019 consisted of the following (dollars in thousands): September 30, 2020 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Weighted Average Remaining Life Business relationships $ 9,918 $ (3,571) $ 6,347 8.0 years Developed technology 7,709 (5,934) 1,775 1.5 years Licensing agreements 6,129 (54) 6,075 9.4 years Content 3,938 (3,938) — 0.0 years Domains and data licenses 2,869 (2,826) 43 2.0 years Trademarks 877 (877) — 0.0 years User relationships 146 (146) — 0.0 years Total $ 31,586 $ (17,346) $ 14,240 December 31, 2019 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Weighted Average Remaining Life Business relationships $ 9,918 $ (2,841) $ 7,077 8.6 years Developed technology 7,832 (4,959) 2,873 2.2 years Content 3,814 (3,814) — 0.0 years Domain and data licenses 2,869 (2,748) 121 1.7 years Trademarks 877 (872) 5 0.2 years User relationships 146 (140) 6 0.2 years Total $ 25,456 $ (15,374) $ 10,082 During the three months ended September 30, 2020, the Company recorded an intangible asset of $6.1 million related to a licensing agreement that was entered into with a third party. The Company accounted for this transaction as an asset acquisition of an intangible asset and will amortize the licensing agreement on a straight-line basis over its estimated useful life of 9.5 years. Amortization expense was $0.6 million and $0.8 million for the three months ended September 30, 2020 and 2019, respectively, and $1.8 million and $2.6 million for the nine months ended September 30, 2020 and 2019, respectively. No impairment charge was recorded during the three months ended September 30, 2020. The Company recorded an immaterial impairment charge related to developed technology during the three months ended March 31, 2020. No changes to the useful lives of any intangible assets were made. As of September 30, 2020, the estimated future amortization of purchased intangible assets for (i) the remaining three months of 2020, (ii) each of the succeeding five years, and (iii) thereafter was as follows (in thousands): Year Ending December 31, Amount 2020 (from October 1, 2020) $ 719 2021 2,848 2022 1,676 2023 1,359 2024 1,353 2025 1,353 Thereafter 4,932 Total amortization $ 14,240

LEASES

LEASES	9 Months Ended
	Sep. 30, 2020
Leases [Abstract]
Leases	LEASES The components of lease cost, net for the three and nine months ended September 30, 2020 and 2019 were as follows (in thousands): Three Months Ended Nine Months Ended 2020 2019 2020 2019 Operating lease cost $ 13,714 $ 13,544 $ 41,512 $ 40,878 Short-term lease cost (12 months or less) 369 291 1,070 938 Sublease income (1,954) (1,475) (5,868) (2,764) Total lease cost, net $ 12,129 $ 12,360 $ 36,714 $ 39,052 The Company's leases and subleases do not include any variable lease payments, residual value guarantees, related-party leases, or restrictions or covenants that would limit or prevent the Company's right to obtain substantially all of the economic benefits from use of the respective assets during the lease term. The Company has subleased certain office facilities under operating lease agreements that expire in 2025. The sublease agreements do not contain any options to renew. The Company recognizes a majority of the sublease rental income as a reduction in rent expense on a straight-line basis over the lease period, with any sublease income in excess of the original lease cost recorded to other income, net. Supplemental cash flow information related to leases for the nine months ended September 30, 2020 and 2019 was as follows (in thousands): September 30, 2020 September 30, 2019 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ 44,181 $ 42,323 As of September 30, 2020, maturities of lease liabilities for (i) the remaining three months of 2020, (ii) each of the succeeding five years, and (iii) thereafter were as follows (in thousands): Year Ending December 31, Operating 2020 (from October 1, 2020) $ 14,858 2021 52,067 2022 46,400 2023 43,495 2024 41,263 2025 22,316 Thereafter 24,009 Total minimum lease payments 244,408 Less imputed interest (34,715) Present value of lease liabilities $ 209,693 As of September 30, 2020 and December 31, 2019, the weighted-average remaining lease terms and weighted-average discount rates were as follows: September 30, 2020 December 31, Weighted-average remaining lease term (years) — operating leases 5.2 5.5 Weighted-average discount rate — operating leases 6.0 % 6.1 % In October 2020, the Company entered into a lease agreement for an office facility in Toronto, Canada for which the lease term is expected to commence in 2021 and expire in 2031. The Company expects to classify this as an operating lease and, as of September 30, 2020, expected to recognize operating lease cost of approximately $9.0 million over the life of the lease.

OTHER NON-CURRENT ASSETS

OTHER NON-CURRENT ASSETS	9 Months Ended
	Sep. 30, 2020
Other Assets, Noncurrent Disclosure [Abstract]
Other Non-Current Assets	OTHER NON-CURRENT ASSETS Other non-current assets as of September 30, 2020 and December 31, 2019 consisted of the following (in thousands): September 30, December 31, Deferred tax assets $ 26,590 $ 20,054 Deferred contract costs 11,250 15,138 Other non-current assets 2,989 3,177 Total other non-current assets $ 40,829 $ 38,369 Deferred contract costs as of September 30, 2020 and December 31, 2019, and changes in deferred contract costs during the nine months ended September 30, 2020, were as follows (in thousands): Nine Months Ended Balance, beginning of period $ 15,138 Add: costs deferred on new contracts 8,960 Less: amortization recorded in sales and marketing expenses (12,848) Balance, end of period $ 11,250 In accordance with its deferred contract costs accounting policy, the Company performs a quantitative update of the expected customer lives at least annually and reviews for any significant change on a quarterly basis based on both qualitative and quantitative factors, including product life cycle attributes and customer retention historical data. Due to the impact of the COVID-19 pandemic, the Company concluded that the useful lives of deferred contract costs had a range of up to 26 months as of March 31, 2020, down from 32 months as of December 31, 2019. As a result, additional amortized commission expense of $3.4 million was recorded in sales and marketing expenses during the three months ended March 31, 2020.

CONTRACT BALANCES

CONTRACT BALANCES	9 Months Ended
	Sep. 30, 2020
Revenue from Contract with Customer [Abstract]
Contract Balances	CONTRACT BALANCES The allowance for doubtful accounts as of September 30, 2020 and 2019 and changes in the allowance for doubtful accounts during the nine months ended September 30, 2020 and 2019 were as follows (in thousands): Nine Months Ended 2020 2019 Balance, beginning of period $ 7,686 $ 8,685 Add: provision for doubtful accounts 26,802 15,259 Less: write-offs, net of recoveries (23,172) (16,165) Balance, end of period $ 11,316 $ 7,779 The net increase in the allowance for doubtful accounts in the nine months ended September 30, 2020 was primarily related to an anticipated increase in customer delinquencies due to the COVID-19 pandemic. In calculating the allowance for doubtful accounts as of September 30, 2020, the Company considered expectations of probable credit losses associated with the COVID-19 pandemic based on observed trends to date in cancellations, observed changes to date in the credit risk of specific customers, the impact of anticipated closures and bankruptcies using forecasted economic indicators in addition to historical experience and loss patterns during periods of macroeconomic uncertainty. Contract liabilities consist of deferred revenue, which is recorded on the condensed consolidated balance sheets when the Company has received consideration, or has the right to receive consideration, in advance of transferring the performance obligations under the contract to the customer. As of September 30, 2020, deferred revenue was $4.7 million, the majority of which is expected to be recognized as revenue in the subsequent three-month period ending December 31, 2020. Changes in deferred revenue during the nine months ended September 30, 2020 were as follows (in thousands): Nine Months Ended Balance, beginning of period $ 4,315 Less: recognition of deferred revenue from beginning balance (3,713) Add: net increase in current period contract liabilities 4,129 Balance, end of period $ 4,731 No other contract assets or liabilities are recorded on the Company's condensed consolidated balance sheets as of September 30, 2020 and December 31, 2019.

ACCRUED LIABILITIES AND ACCRUED

ACCRUED LIABILITIES AND ACCRUED LIABILITIES	9 Months Ended
	Sep. 30, 2020
Payables and Accruals [Abstract]
Accrued Liabilities and Accrued Liabilities	ACCOUNTS PAYABLE AND ACCRUED LIABILITIES Accounts payable and accrued liabilities as of September 30, 2020 and December 31, 2019 consisted of the following (in thousands): September 30, December 31, Accounts payable $ 10,614 $ 6,002 Employee related liabilities 60,986 41,488 Accrued sales and marketing expenses 3,601 2,982 Taxes payable 4,988 3,695 Accrued cost of revenue 5,640 7,208 Other accrued liabilities 17,549 10,958 Total accounts payable and accrued liabilities $ 103,378 $ 72,333

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	9 Months Ended
	Sep. 30, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	COMMITMENTS AND CONTINGENCIES 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, which the court granted in part and denied in part on November 27, 2018. On October 22, 2019, the Court approved a stipulation to certify a class in this action. The case remains pending. 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 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. 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 business, financial position, results of operations or cash flows. Revolving Credit Facility —In May 2020, the Company entered into the Credit Agreement with Wells Fargo Bank, National Association, which provides for a three-year, $75.0 million senior unsecured revolving credit facility including a letter of credit sub-limit of $25.0 million. The commitments under the Credit Agreement expire on May 5, 2023. Interest on any borrowings under the revolving credit facility will accrue at either LIBOR plus 1.25% or at an alternative base rate plus 0.25%, at the Company's election. Interest is payable monthly in arrears for base rate loans and at the end of the applicable interest period (or, if the interest period extends over three months, at the end of each three-month interval during the interest period) for LIBOR loans. The Company is also required to pay an annual commitment fee that accrues at 0.25% per annum on the unused portion of the aggregate commitments under the revolving credit facility, payable quarterly in arrears. Debt issuance-related costs were $0.4 million and will be amortized to interest expense on a straight-line basis over the life of the Credit Agreement. The Company is required to pay a fee that accrues at 0.70% per annum on the undrawn portion of any letter of credit, payable quarterly in arrears. In May 2020, the Company moved letters of credit in an aggregate amount of approximately $21.5 million under the letter of credit sub-limit, which reduced the amount it can borrow under the revolving credit facility. Approximately $53.5 million remained available under the revolving credit facility as of September 30, 2020. The Company was in compliance with all covenants associated with the credit facility and there were no loans outstanding under the Credit Agreement as of September 30, 2020. See " Liquidity and Capital Resources " included under Part II, Item 2 in this Quarterly Report for additional information on the covenants included in the Credit Agreement.

STOCKHOLDERS' EQUITY

STOCKHOLDERS' EQUITY	9 Months Ended
	Sep. 30, 2020
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, 2020 December 31, 2019 Shares Authorized Shares Issued Shares Authorized Shares Issued Stockholders’ equity: Common stock, $0.000001 par value 200,000,000 73,976,487 200,000,000 71,185,468 Undesignated preferred stock 10,000,000 — 10,000,000 — Stock Repurchase Program In July 2017, the Company’s board of directors authorized a stock repurchase program under which the Company was authorized to repurchase up to $200.0 million of its outstanding common stock. The Company's board of directors authorized the Company to repurchase up to an additional $250.0 million of its outstanding common stock in each of November 2018, February 2019 and January 2020, bringing the total amount of authorized repurchases to $950.0 million as of September 30, 2020, $269.0 million of which remains available. 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 did not repurchase any shares during the nine months ended September 30, 2020. Pursuant to the restructuring plan announced on April 9, 2020 (the "Restructuring Plan"), the Company suspended share repurchases under the stock repurchase program. On November 5, 2020, the Company announced its plans to resume repurchases as early as the fourth quarter of 2020, depending on market and economic conditions. See Note 18, " Restructuring " for further details on the Restructuring Plan. During the nine months ended September 30, 2019, the Company repurchased on the open market and retired 13,994,909 shares for an aggregate purchase price of $475.0 million. The Company had no treasury stock balance as of September 30, 2019. 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 have been or 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, RSUs, restricted stock awards, 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 on the grant date. Options granted to date generally vest over a three A summary of stock option activity for the nine months ended September 30, 2020 is as follows: Number of Shares Weighted-Average Exercise Price Weighted-Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2019 6,210,385 $ 25.10 4.3 $ 75,805 Granted 146,500 31.42 Exercised (285,388) 12.64 Canceled (182,616) 47.34 Outstanding at September 30, 2020 5,888,881 $ 25.17 3.9 $ 21,260 Options vested and exercisable at September 30, 2020 5,199,107 $ 23.63 3.4 $ 21,260 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 $0.7 million and $3.4 million for the three months ended September 30, 2020 and 2019, respectively, and $5.1 million and $6.2 million for the nine months ended September 30, 2020 and 2019, respectively. The weighted-average grant date fair value of options granted was $7.61 per share for the three months ended September 30, 2020. There were no options granted in the three months ended September 30, 2019. The weighted-average grant date fair value of options granted was $9.69 and $17.64 per share for the nine months ended September 30, 2020 and 2019, respectively. As of September 30, 2020, total unrecognized compensation costs related to nonvested stock options were approximately $10.6 million, which the Company expects to recognize over a weighted-average time period of 2.1 years. RSUs 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. RSUs also include PRSUs, which are subject to both a time-based vesting schedule and either (a) a market condition or (b) the achievement of performance goals. For PRSUs subject to a market condition, the Company recognizes expense from the date of grant. For PRSUs subject to performance goals, the Company recognizes expense when it is probable that the performance condition will be achieved. For PRSUs subject to a market condition, the shares underlying each PRSU award will be eligible to vest only if the average closing price of the Company's common stock equals or exceeds $45.3125 over any 60-day trading period during the four years following the grant date of February 7, 2019. If this market condition is met, the shares underlying each PRSU award will vest quarterly over four years from the grant date ("Time-Based Vesting Schedule"). Any shares subject to the PRSUs that have met the Time-Based Vesting Schedule at the time the market condition is achieved will fully vest as of such date; thereafter, any remaining nonvested shares subject to the PRSUs will continue vesting solely according to the Time-Based Vesting Schedule, subject to the applicable employee's continued service as of each such vesting date. For PRSUs subject to performance goals, a percentage of the target number of shares, ranging from zero to 200%, will become eligible to vest based on the Company's level of achievement of certain financial targets, subject to a four-year, quarterly vesting schedule ("2020 Time-Based Vesting Schedule"). The shares subject to performance goals become eligible to vest once the achievement against the financial targets is known, which will be no later than March 15, 2021. On the quarterly vest date immediately following such determination, the eligible shares, if any, will vest to the extent that the employee has met the 2020 Time-Based Vesting Schedule as of such date. Thereafter, the eligible shares will continue to vest in accordance with the 2020 Time-Based Vesting Schedule, subject to the applicable employee's continued service as of each such vesting date. The Company performed an analysis as of September 30, 2020 to assess the probability of achievement of the PRSU financial targets and, as a result, recorded compensation costs in the three and nine months ended September 30, 2020 for the PRSUs that it expected to vest. As the PRSU activity during the nine months ended September 30, 2020 was not material, it is presented together with the RSU activity in the table below. A summary of RSU and PRSU activity for the nine months ended September 30, 2020 is as follows: Number of Shares Weighted-Average Grant Date Fair Value Nonvested at December 31, 2019 7,625,584 $ 36.51 Granted 3,424,706 32.69 Vested (1) (2,411,208) 36.80 Canceled (1,391,090) 36.56 Nonvested at September 30, 2020 7,247,992 $ 34.60 (1) Includes 339,274 shares that vested but were not issued due to net share settlement for payment of employee taxes. The aggregate fair value as of the vest date of RSUs that vested during the nine months ended September 30, 2020 and 2019 was $64.1 million and $84.9 million, respectively. As of September 30, 2020, the Company had approximately $229.3 million of unrecognized stock-based compensation expense related to RSUs, which it expects to recognize over the remaining weighted-average vesting period of approximately 2.5 years. In May 2020, the Company changed its method of settling the employee tax liabilities associated with the vesting of RSUs from Net Share Withholding to the Sell-to-Cover method. As a result of this change, the Company no longer has cash outflows relating to the settlement of tax liabilities associated with employee stock awards. The change does not impact the Company's condensed consolidated statements of operations. Employee Stock Purchase Plan The 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, 2020 and 2019. There were 433,697 shares purchased by employees under the ESPP at a weighted-average price of $18.48 in the nine months ended September 30, 2020. There were 288,529 shares purchased by employees under the ESPP at a weighted-average price of $26.12 in the nine months ended September 30, 2019. The Company recognized stock-based compensation expense related to the ESPP of $0.6 million and $0.7 million in the three months ended September 30, 2020 and 2019, respectively, and $1.9 million and $2.0 million for the nine months ended September 30, 2020 and 2019, 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, 2020 2019 2020 2019 Cost of revenue $ 849 $ 1,054 $ 2,835 $ 3,415 Sales and marketing 7,196 7,683 22,194 23,143 Product development 15,551 15,250 50,133 46,572 General and administrative 6,659 5,249 17,428 17,876 Total stock-based compensation recorded to income (loss) before income taxes 30,255 29,236 92,590 91,006 Provision for (benefit from) income taxes 378 (7,661) (23,831) (23,766) Total stock-based compensation recorded to net (loss) income $ 30,633 $ 21,575 $ 68,759 $ 67,240

OTHER INCOME, NET

OTHER INCOME, NET	9 Months Ended
	Sep. 30, 2020
Other Income and Expenses [Abstract]
Other Income, Net	OTHER INCOME, NET Other income, net for the three and nine months ended September 30, 2020 and 2019 consisted of the following (in thousands): Three Months Ended Nine Months Ended 2020 2019 2020 2019 Interest income, net $ 7 $ 2,830 $ 2,304 $ 10,946 Transaction gain (loss) on foreign exchange 28 (20) (32) 93 Other non-operating income, net 364 253 1,005 606 Other income, net $ 399 $ 3,063 $ 3,277 $ 11,645

INCOME TAXES

INCOME TAXES	9 Months Ended
	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES 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 benefit from income taxes for the nine months ended September 30, 2020 was $9.5 million, which was due to $17.1 million of U.S. federal, state and foreign income tax benefit, offset by $7.6 million of net discrete tax expense primarily related to stock-based compensation. The provision for income taxes for the nine months ended September 30, 2019 was $5.8 million, which was due to $5.5 million of U.S. federal, state and foreign income tax expense and $0.3 million of net discrete tax expense. On March 27, 2020, the CARES Act was signed into law. The CARES Act includes, among other items, provisions relating to refundable payroll tax credits, deferment of the employer portion of certain payroll taxes, net operating loss carryback periods, alternative minimum tax credit refunds, modifications to the net interest deduction limitations and technical corrections to tax depreciation methods for qualified improvement property. The CARES Act allows losses incurred in 2018, 2019 and 2020 to be carried back to each of the five preceding tax years and to offset 100% of regular taxable income. Additionally, the CARES Act accelerates the Company’s ability to receive refunds of alternative minimum tax credits generated in prior tax years. 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, 2020, the difference between the effective tax rate and the federal statutory tax rate primarily related to tax credits, offset by non-deductible expenses. For the three and nine months ended September 30, 2019, the difference between the effective tax rate and the federal statutory tax rate primarily related to tax credits and non-deductible expenses. As of September 30, 2020, the total amount of gross unrecognized tax benefits was $46.8 million, $20.0 million of which was subject to a full valuation allowance and would not affect the Company’s effective tax rate if recognized. In the three and nine months ended September 30, 2020, the Company recorded an immaterial amount of interest and penalties. As of September 30, 2020, the Company estimated that it had accumulated undistributed earnings generated by its foreign subsidiaries of approximately $5.7 million. Any taxes due with respect to such earnings or the excess of the amount for financial reporting over the tax basis of the Company's foreign investments would generally be limited to foreign and state taxes. The Company has not recognized a deferred tax liability related to un-remitted foreign earnings, as it intends to indefinitely reinvest these earnings, and expects future U.S. cash generation to be sufficient to meet future U.S. cash needs. 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 tax years subsequent to 2003 remain open to examination. In the Company’s foreign jurisdictions — Canada, Germany, Ireland and the United Kingdom — the tax years subsequent to 2014 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

NET (LOSS) INCOME PER SHARE

NET (LOSS) INCOME PER SHARE	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Net (Loss) Income Per Share	NET (LOSS) INCOME PER SHARE Basic net (loss) income per share is computed using the weighted-average number of outstanding shares of common stock during the period. Diluted net (loss) 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 (loss) income per share for the periods presented (in thousands, except per share data): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Basic net (loss) income per share: Net (loss) income $ (1,020) $ 10,061 $ (40,513) $ 23,729 Shares used in computation: Weighted-average common shares outstanding 73,514 70,773 72,495 75,975 Basic net (loss) income per share attributable to common stockholders $ (0.01) $ 0.14 $ (0.56) $ 0.31 Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Diluted net (loss) income per share: Net (loss) income $ (1,020) $ 10,061 $ (40,513) $ 23,729 Shares used in computation: Weighted-average common shares outstanding 73,514 70,773 72,495 75,975 Stock options — 2,345 — 2,429 Restricted stock units — 478 — 870 Employee stock purchase program — 116 — 41 Number of shares used in diluted calculation 73,514 73,712 72,495 79,315 Diluted net (loss) income per share attributable to common stockholders $ (0.01) $ 0.14 $ (0.56) $ 0.30 The following stock-based instruments were excluded from the calculation of diluted net (loss) 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, 2020 2019 2020 2019 Stock options 5,889 2,718 5,889 2,629 Restricted stock units 7,248 2,718 7,248 2,530 ESPP 228 — 228 —

INFORMATION ABOUT REVENUE AND G

INFORMATION ABOUT REVENUE AND GEOGRAPHIC AREAS	9 Months Ended
	Sep. 30, 2020
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 for which separate financial information is available and 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 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 by major product line for the periods presented (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Net revenue by product: Advertising $ 211,167 $ 253,098 $ 613,493 $ 717,973 Transactions 4,412 3,074 11,019 9,528 Other services 5,228 6,302 15,226 17,870 Total net revenue $ 220,807 $ 262,474 $ 639,738 $ 745,371 During the three and nine months ended September 30, 2020 and 2019, no individual customer accounted for 10% or more of consolidated net revenue. As a result of the COVID-19 pandemic, the Company considered whether there was any impact to the manner in which revenue is recognized, in particular with respect to the collectability criteria for recognizing revenue from contracts with customers. The Company did not change the manner in which it recognizes revenue as a result of that assessment. During the three and nine months ended September 30, 2020, the Company offered a number of relief incentives totaling $2.9 million and $20.8 million, respectively, to advertising and other services customers most impacted by the COVID-19 pandemic. These incentives were primarily in the form of waived advertising fees and waived subscription fees. The Company accounted for these incentives as price concessions and reduced net revenue recognized in the three and nine months ended September 30, 2020 accordingly. During the nine months ended September 30, 2020, the Company also paused certain advertising campaigns that were scheduled to run from April to May 2020 and offered certain free advertising products during those months with a total value of $14.5 million. All paused advertising campaigns that were not cancelled by customers resumed by the end of May 2020. The following table presents the Company’s net revenue by major geographic region for the periods presented (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 United States $ 218,563 $ 258,820 $ 632,360 $ 735,169 All other countries 2,244 3,654 7,378 10,202 Total net revenue $ 220,807 $ 262,474 $ 639,738 $ 745,371 Long-Lived Assets The following table presents the Company’s long-lived assets by major geographic region for the periods presented (in thousands): September 30, December 31, United States $ 101,335 $ 109,849 All other countries 4,153 1,100 Total long-lived assets $ 105,488 $ 110,949

RESTRUCTURING

RESTRUCTURING	9 Months Ended
	Sep. 30, 2020
Restructuring and Related Activities [Abstract]
Restructuring	RESTRUCTURING On April 9, 2020, the Company announced the Restructuring Plan to help manage the near-term financial impacts of the COVID-19 pandemic. In addition to reductions and deferrals in spending, the Restructuring Plan’s cost-cutting measures included workforce reductions affecting approximately 1,000 employees and furloughs affecting approximately 1,100 additional employees, as well as salary reductions and reduced-hour work weeks. For further details on the Restructuring Plan, refer to the Company's Current Report on Form 8-K filed with the SEC on April 9, 2020. On July 13, 2020, the Company announced an additional workforce reduction (separate from the Restructuring Plan) affecting approximately 60 employees. During the three months ended September 30, 2020, the Company restored reduced salaries and returned many of its furloughed employees. The Company incurred $0.5 million and $3.8 million in restructuring costs during the three and nine months ended September 30, 2020, respectively, in connection with terminations under the Restructuring Plan and additional workforce reduction, which represent expenditures for severance, payroll taxes and related benefits costs. These costs were recorded as restructuring expenses on the Company's condensed consolidated statements of operations. Additional costs related to supporting furloughed employees incurred during the three and nine months ended September 30, 2020 were excluded from restructuring expenses and recorded in operating expenses. The Company paid substantially all the costs incurred in connection with the terminations under the Restructuring Plan and additional workforce reduction as of September 30, 2020 and does not expect to incur any material additional costs in connection with these terminations.

DESCRIPTION OF BUSINESS AND B_2

DESCRIPTION OF BUSINESS AND BASIS FOR PRESENTATION (Policies)	9 Months Ended
	Sep. 30, 2020
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, 2019, filed with the SEC on February 28, 2020 and amended on April 29, 2020 (the "Annual Report"). The unaudited condensed consolidated balance sheet as of December 31, 2019 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. The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited consolidated financial statements, except as set forth under "Recently Adopted Accounting Pronouncements" below. 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.
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. In early March 2020, COVID-19 — the disease caused by a novel strain of the coronavirus — was declared a global pandemic by the World Health Organization. Governments and municipalities around the world, including in the United States, have implemented extensive measures in an effort to control the spread of COVID-19, including travel restrictions, limitations on business activity, quarantines and shelter-in-place orders. Due to the COVID-19 pandemic and the uncertainty of the extent of the impacts, many of the estimates and assumptions required increased judgment and carry a higher degree of variability and volatility than they did prior to the pandemic. As events continue to evolve and additional information becomes available, these estimates may materially change in future periods.
Marketable Securities	Marketable Securities —The Company considers highly liquid treasury notes, U.S. agency securities, corporate debt securities, money market funds and other funds with maturities of more than three months to be marketable securities. Securities with less than one year to maturity are included in short-term marketable securities, and all other securities are classified as long-term marketable securities. The Company has a policy that generally requires its securities to be investment grade (i.e. rated ‘A+’ or higher by bond rating firms) with the objective of minimizing the potential risk of principal loss. The Company determines the classification of its marketable securities based on its investment strategy. Marketable securities are classified as held-to-maturity when the Company has the positive intent and ability to hold the securities to maturity, and it has an established history of holding investments to maturity. Held-to-maturity securities are stated at amortized cost and are periodically assessed for impairment. Amortized costs of debt securities are adjusted for amortization of premiums and accretion of discounts to maturity, and these adjustments are included in interest income. Marketable securities are classified as available-for-sale when the Company has established a practice of selling investments prior to maturity, or if the Company does not have the intent to hold securities to maturity to allow flexibility in response to liquidity needs. In the event that the Company classifies its investments as available-for-sale, it will only return to classifying investments as held-to-maturity once it has reestablished a practice and intent of holding investments to maturity. Available-for-sale securities are stated at fair value as of each balance sheet date and are periodically assessed for impairment. For the Company's available-for-sale securities, an investment is impaired if the fair value of the investment is less than its amortized cost basis. In assessing whether a credit loss exists, the Company compares the present value of cash flows expected to be collected from the security with the amortized cost basis of the security. If the present value of expected cash flows is less than the amortized cost basis of the security, an allowance for credit loss is recorded as a component of other income (expense), net. Any remaining unrealized losses are recorded to other comprehensive income (loss). The Company determines any realized gains or losses on the sale of marketable securities on a specific identification method and records such gains and losses as a component of other income (expense), net. Amortization of premiums and accretion of discounts are included in interest income. If the Company has the intent to sell an available-for-sale security in an unrealized loss position or it is more likely than not that it will be required to sell the security prior to recovery of its amortized cost basis, any previously recorded allowance is reversed and the entire difference between the amortized cost basis of the security and its fair value is recognized in the condensed consolidated statements of operations.
Allowance for Doubtful Accounts	Allowance for Doubtful Accounts—The Company maintains an allowance for doubtful accounts receivable. The allowance reflects the Company's best estimate of probable losses associated with 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 based on the credit risk of those accounts, known delinquent accounts, as well as current conditions and reasonable and supportable economic forecasts. 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.
Goodwill	Goodwill —Goodwill represents the excess of the purchase price in a business combination over the fair value of net tangible and intangible assets acquired. The carrying amount of goodwill is reviewed at least annually, or more frequently if events or changes in circumstances indicate that the carrying value of goodwill may not be recoverable. The Company has the option to first assess qualitative factors to determine whether it is more likely than not that the fair value of a reporting unit is less than its carrying amount. If the Company determines that it is more likely than not that its fair value is less than the carrying amount, or opts not to perform a qualitative assessment, then the Company will compare the 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 carrying value of goodwill will be written down to fair value. No impairment charges associated with goodwill have been recorded by the Company to date.
Stock-Based Compensation	Stock-Based Compensation —The Company accounts for stock-based employee compensation plans under the fair value recognition and measurement provisions, which require all stock-based payments to employees, including grants of stock options, restricted stock awards, restricted stock units ("RSUs"), performance-based restricted stock units ("PRSUs") and issuances under its 2012 Employee Stock Purchase Plan, as amended ("ESPP"), to be measured based on the grant-date fair value of the awards. The Company accounts for forfeitures as they occur. The fair value of options granted to employees is estimated on the grant date using the Black-Scholes-Merton option valuation model. This valuation model for stock-based compensation expense requires the Company to make assumptions and judgments about the variables used in the calculation, including the expected term (weighted-average period of time that the options granted are expected to be outstanding), the expected volatility in the fair market value of the Company’s common stock, a risk-free interest rate and expected dividends. No compensation cost is recorded for options that do not vest. The Company uses the simplified calculation of expected life as the contractual term for options of 10 years is longer than the Company has been publicly traded. Expected volatility is based on an average of the historical volatilities of the common stock of several entities with characteristics similar to those of the Company. The risk-free rate is based on the U.S. Treasury yield curve in effect at the time of grant for periods corresponding with the expected life of the option. The Company uses the straight-line method for expense attribution. The fair value of RSUs is measured using the closing price of the Company's common stock on the New York Stock Exchange on the grant date. The Company uses the straight-line method for expense attribution. No compensation cost is recorded for RSUs that do not vest. In May 2020, the Company changed its method of settling the employee tax liabilities associated with the vesting of RSUs from withholding a portion of the vested shares and covering such taxes with cash from its balance sheet ("Net Share Withholding"), to selling a portion of the vested shares to cover taxes ("Sell-to-Cover"). The Company has two types of PRSUs outstanding — awards for which the vesting is subject to both a time-based vesting schedule and either (a) a market condition or (b) the achievement of performance goals. For the awards subject to a market condition, the Company uses a Monte Carlo model to determine the fair value of the PRSUs. The Company uses the accelerated method for expense attribution. Compensation costs are recorded if the service condition is met regardless of whether the market performance condition is satisfied. No compensation cost is recorded if the service condition is not met. For the awards subject to performance goals, compensation costs are recorded when the Company concludes that it is probable that the performance conditions will be achieved. The Company performs an analysis in each reporting period to determine the probability that the performance goals will be met, and recognizes a cumulative catch-up adjustment to compensation cost for changes in its probability assessment in subsequent reporting periods, if required, until the performance period has expired. The fair value of the PRSUs is measured using the closing price of the Company's common stock on the New York Stock Exchange on the grant date. The Company uses the accelerated method for expense attribution. No compensation cost is recorded if the service condition is not met.
Recently Adopted Accounting Pronouncements and Recent Accounting Pronouncements Not Yet Effective	Recently Adopted Accounting Pronouncements In June 2016, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update No. 2016-13, "Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments" ("ASU 2016-13"). ASU 2016-13 requires certain types of financial instruments, including trade receivables and held-to-maturity investments measured at amortized cost, to be presented as the net amount expected to be collected based on historical events, current conditions and forecast information. The Company adopted and began applying ASU 2016-13 on January 1, 2020 by recording a cumulative-effect adjustment to retained earnings. This adjustment recorded an allowance related to expected credit losses on the Company's held-to-maturity debt securities, which was subsequently reversed upon its change in investment strategy in March 2020. This allowance took into consideration the composition and credit quality of the financial instruments, their respective historical credit loss activity, and reasonable and supportable economic forecasts and conditions at the time of adoption. The adoption did not have a material impact on the Company's consolidated financial statements. In January 2017, the FASB issued Accounting Standards Update No. 2017-04, "Intangibles—Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment" ("ASU 2017-04"). ASU 2017-04 simplified the subsequent measurement of goodwill by eliminating Step 2 from the goodwill impairment test. Under the new standard, entities perform goodwill impairment tests by comparing the 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 Company adopted ASU 2017-04 on January 1, 2020 and the adoption did not have a material impact on its consolidated financial statements. In August 2018, the FASB issued Accounting Standards Update No. 2018-13, "Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement" ("ASU 2018-13"), which amended Accounting Standards Codification 820, "Fair Value Measurement." ASU 2018-13 modified the disclosure requirements for fair value measurements by removing, modifying and adding certain disclosures. The Company adopted ASU 2018-13 on January 1, 2020 and the adoption did not have a material impact on its consolidated financial statements. In August 2018, the 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"). ASU 2018-15 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 which to recognize as assets. 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. The Company adopted ASU 2018-15 prospectively and began applying it on January 1, 2020. The adoption did not have a material impact on the Company's financial statements. Recent Accounting Pronouncements Not Yet Effective In December 2019, the FASB issued Accounting Standards Update No. 2019-12, Income Taxes (Topic 740): "Simplifying the Accounting for Income Taxes" ("ASU 2019-12"), which simplifies the accounting for income taxes by removing certain exceptions to the general principles for recording income taxes, while also simplifying certain recognition and allocation approaches to accounting for income taxes. ASU 2019-12 will be effective for the first interim period within annual periods beginning after December 15, 2020 on a prospective basis, and early adoption is permitted. The Company is currently evaluating the impact of ASU 2019-12 on its consolidated financial statements and related disclosures.

CASH, CASH EQUIVALENTS AND RE_2

CASH, CASH EQUIVALENTS AND RESTRICTED CASH (Tables)	9 Months Ended
	Sep. 30, 2020
Cash and Cash Equivalents [Abstract]
Schedule of Cash and Cash Equivalents	Cash, cash equivalents and restricted cash as of September 30, 2020 and December 31, 2019 consisted of the following (in thousands): September 30, December 31, Cash $ 80,698 $ 43,581 Cash equivalents 510,091 126,700 Total cash and cash equivalents $ 590,789 $ 170,281 Restricted cash 826 22,037 Total cash, cash equivalents and restricted cash $ 591,615 $ 192,318
Restrictions on Cash and Cash Equivalents	Cash, cash equivalents and restricted cash as of September 30, 2020 and December 31, 2019 consisted of the following (in thousands): September 30, December 31, Cash $ 80,698 $ 43,581 Cash equivalents 510,091 126,700 Total cash and cash equivalents $ 590,789 $ 170,281 Restricted cash 826 22,037 Total cash, cash equivalents and restricted cash $ 591,615 $ 192,318

FAIR VALUE OF FINANCIAL INSTR_2

FAIR VALUE OF FINANCIAL INSTRUMENTS (Tables)	9 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Schedule of Financial Instruments Measured at Fair Value	The following table represents the fair value of the Company’s financial instruments, including those measured at fair value on a recurring basis, as of September 30, 2020 and December 31, 2019 as well as those held-to-maturity as of December 31, 2019 (in thousands): September 30, 2020 December 31, 2019 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 510,091 $ — $ — $ 510,091 $ 126,700 $ — $ — $ 126,700 Marketable securities: Commercial paper — — — — — 130,472 — 130,472 Corporate bonds — — — — — 85,611 — 85,611 Agency bonds — — — — — 79,750 — 79,750 Total cash equivalents and marketable securities $ 510,091 $ — $ — $ 510,091 $ 126,700 $ 295,833 $ — $ 422,533

MARKETABLE SECURITIES (Tables)

MARKETABLE SECURITIES (Tables)	9 Months Ended
	Sep. 30, 2020
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 marketable securities classified as held-to-maturity as of December 31, 2019 were as follows (in thousands): December 31, 2019 Amortized Gross Gross Fair Short-term marketable securities: Commercial paper $ 130,464 $ 17 $ (9) $ 130,472 Corporate bonds 85,396 225 (10) 85,611 Agency bonds 26,140 90 — 26,230 Total short-term marketable securities 242,000 332 (19) 242,313 Long-term marketable securities: Agency bonds 53,499 21 — 53,520 Total long-term marketable securities 53,499 21 — 53,520 Total marketable securities $ 295,499 $ 353 $ (19) $ 295,833
Schedule of Securities in an Unrealized Loss Position	The following table presents gross unrealized losses and fair values for those securities that were in an unrealized loss position as of December 31, 2019, aggregated by investment category and the length of time that the individual securities had been in a continuous loss position (in thousands): December 31, 2019 Less Than 12 Months 12 Months or Greater Total Fair Unrealized Loss Fair Unrealized Loss Fair Unrealized Loss Commercial paper $ 63,639 $ (9) $ — $ — $ 63,639 $ (9) Corporate bonds 20,979 (10) — — 20,979 (10) Total $ 84,618 $ (19) $ — $ — $ 84,618 $ (19)

PREPAID EXPENSES AND OTHER CU_2

PREPAID EXPENSES AND OTHER CURRENT ASSETS (Tables)	9 Months Ended
	Sep. 30, 2020
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets as of September 30, 2020 and December 31, 2019 consisted of the following (in thousands): September 30, 2020 December 31, 2019 Prepaid expenses $ 9,612 $ 10,188 Other current assets 8,978 4,008 Total prepaid expenses and other current assets $ 18,590 $ 14,196

PROPERTY, EQUIPMENT, AND SOFTWA

PROPERTY, EQUIPMENT, AND SOFTWARE, NET (Tables)	9 Months Ended
	Sep. 30, 2020
Property, Plant and Equipment [Abstract]
Schedule of Property, Equipment and Software, Net	Property, equipment and software, net as of September 30, 2020 and December 31, 2019 consisted of the following (in thousands): September 30, December 31, Capitalized website and internal-use software development costs $ 164,488 $ 140,886 Leasehold improvements 88,436 86,089 Computer equipment 46,049 43,626 Furniture and fixtures 18,271 18,403 Telecommunication 4,956 5,154 Software 1,687 1,687 Total 323,887 295,845 Less accumulated depreciation (218,399) (184,896) Property, equipment and software, net $ 105,488 $ 110,949

GOODWILL AND INTANGIBLE ASSETS

GOODWILL AND INTANGIBLE ASSETS (Tables)	9 Months Ended
	Sep. 30, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	The changes in carrying amount of goodwill during the nine months ended September 30, 2020 were as follows (in thousands): Balance as of December 31, 2019 $ 104,589 Effect of currency translation 2,183 Balance as of September 30, 2020 $ 106,772
Schedule of Intangible Assets	Intangible assets at September 30, 2020 and December 31, 2019 consisted of the following (dollars in thousands): September 30, 2020 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Weighted Average Remaining Life Business relationships $ 9,918 $ (3,571) $ 6,347 8.0 years Developed technology 7,709 (5,934) 1,775 1.5 years Licensing agreements 6,129 (54) 6,075 9.4 years Content 3,938 (3,938) — 0.0 years Domains and data licenses 2,869 (2,826) 43 2.0 years Trademarks 877 (877) — 0.0 years User relationships 146 (146) — 0.0 years Total $ 31,586 $ (17,346) $ 14,240 December 31, 2019 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Weighted Average Remaining Life Business relationships $ 9,918 $ (2,841) $ 7,077 8.6 years Developed technology 7,832 (4,959) 2,873 2.2 years Content 3,814 (3,814) — 0.0 years Domain and data licenses 2,869 (2,748) 121 1.7 years Trademarks 877 (872) 5 0.2 years User relationships 146 (140) 6 0.2 years Total $ 25,456 $ (15,374) $ 10,082
Schedule of Future Amortization Expense	As of September 30, 2020, the estimated future amortization of purchased intangible assets for (i) the remaining three months of 2020, (ii) each of the succeeding five years, and (iii) thereafter was as follows (in thousands): Year Ending December 31, Amount 2020 (from October 1, 2020) $ 719 2021 2,848 2022 1,676 2023 1,359 2024 1,353 2025 1,353 Thereafter 4,932 Total amortization $ 14,240

LEASES (Tables)

LEASES (Tables)	9 Months Ended
	Sep. 30, 2020
Leases [Abstract]
Lease Cost and Supplemental Cash Flow Information	The components of lease cost, net for the three and nine months ended September 30, 2020 and 2019 were as follows (in thousands): Three Months Ended Nine Months Ended 2020 2019 2020 2019 Operating lease cost $ 13,714 $ 13,544 $ 41,512 $ 40,878 Short-term lease cost (12 months or less) 369 291 1,070 938 Sublease income (1,954) (1,475) (5,868) (2,764) Total lease cost, net $ 12,129 $ 12,360 $ 36,714 $ 39,052 Supplemental cash flow information related to leases for the nine months ended September 30, 2020 and 2019 was as follows (in thousands): September 30, 2020 September 30, 2019 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ 44,181 $ 42,323
Lessee, Operating Lease, Liability, Maturity	As of September 30, 2020, maturities of lease liabilities for (i) the remaining three months of 2020, (ii) each of the succeeding five years, and (iii) thereafter were as follows (in thousands): Year Ending December 31, Operating 2020 (from October 1, 2020) $ 14,858 2021 52,067 2022 46,400 2023 43,495 2024 41,263 2025 22,316 Thereafter 24,009 Total minimum lease payments 244,408 Less imputed interest (34,715) Present value of lease liabilities $ 209,693
Assets And Liabilities, Lessee Information	As of September 30, 2020 and December 31, 2019, the weighted-average remaining lease terms and weighted-average discount rates were as follows: September 30, 2020 December 31, Weighted-average remaining lease term (years) — operating leases 5.2 5.5 Weighted-average discount rate — operating leases 6.0 % 6.1 %

OTHER NON-CURRENT ASSETS (Table

OTHER NON-CURRENT ASSETS (Tables)	9 Months Ended
	Sep. 30, 2020
Other Assets, Noncurrent Disclosure [Abstract]
Schedule of Other Non-Current Assets	Other non-current assets as of September 30, 2020 and December 31, 2019 consisted of the following (in thousands): September 30, December 31, Deferred tax assets $ 26,590 $ 20,054 Deferred contract costs 11,250 15,138 Other non-current assets 2,989 3,177 Total other non-current assets $ 40,829 $ 38,369
Capitalized Contract Cost	Deferred contract costs as of September 30, 2020 and December 31, 2019, and changes in deferred contract costs during the nine months ended September 30, 2020, were as follows (in thousands): Nine Months Ended Balance, beginning of period $ 15,138 Add: costs deferred on new contracts 8,960 Less: amortization recorded in sales and marketing expenses (12,848) Balance, end of period $ 11,250

CONTRACT BALANCES (Tables)

CONTRACT BALANCES (Tables)	9 Months Ended
	Sep. 30, 2020
Revenue from Contract with Customer [Abstract]
Schedule of Allowance for Doubtful Accounts Receivable	The allowance for doubtful accounts as of September 30, 2020 and 2019 and changes in the allowance for doubtful accounts during the nine months ended September 30, 2020 and 2019 were as follows (in thousands): Nine Months Ended 2020 2019 Balance, beginning of period $ 7,686 $ 8,685 Add: provision for doubtful accounts 26,802 15,259 Less: write-offs, net of recoveries (23,172) (16,165) Balance, end of period $ 11,316 $ 7,779
Contract with Customer, Liability	Changes in deferred revenue during the nine months ended September 30, 2020 were as follows (in thousands): Nine Months Ended Balance, beginning of period $ 4,315 Less: recognition of deferred revenue from beginning balance (3,713) Add: net increase in current period contract liabilities 4,129 Balance, end of period $ 4,731

ACCRUED LIABILITIES AND ACCRU_2

ACCRUED LIABILITIES AND ACCRUED LIABILITIES (Tables)	9 Months Ended
	Sep. 30, 2020
Payables and Accruals [Abstract]
Schedule of Accrued Liabilities	Accounts payable and accrued liabilities as of September 30, 2020 and December 31, 2019 consisted of the following (in thousands): September 30, December 31, Accounts payable $ 10,614 $ 6,002 Employee related liabilities 60,986 41,488 Accrued sales and marketing expenses 3,601 2,982 Taxes payable 4,988 3,695 Accrued cost of revenue 5,640 7,208 Other accrued liabilities 17,549 10,958 Total accounts payable and accrued liabilities $ 103,378 $ 72,333

STOCKHOLDERS' EQUITY (Tables)

STOCKHOLDERS' EQUITY (Tables)	9 Months Ended
	Sep. 30, 2020
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, 2020 December 31, 2019 Shares Authorized Shares Issued Shares Authorized Shares Issued Stockholders’ equity: Common stock, $0.000001 par value 200,000,000 73,976,487 200,000,000 71,185,468 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, 2020 is as follows: Number of Shares Weighted-Average Exercise Price Weighted-Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2019 6,210,385 $ 25.10 4.3 $ 75,805 Granted 146,500 31.42 Exercised (285,388) 12.64 Canceled (182,616) 47.34 Outstanding at September 30, 2020 5,888,881 $ 25.17 3.9 $ 21,260 Options vested and exercisable at September 30, 2020 5,199,107 $ 23.63 3.4 $ 21,260
Schedule of RSU Activity	A summary of RSU and PRSU activity for the nine months ended September 30, 2020 is as follows: Number of Shares Weighted-Average Grant Date Fair Value Nonvested at December 31, 2019 7,625,584 $ 36.51 Granted 3,424,706 32.69 Vested (1) (2,411,208) 36.80 Canceled (1,391,090) 36.56 Nonvested at September 30, 2020 7,247,992 $ 34.60 (1) Includes 339,274 shares that vested but were not issued due to net share settlement for payment of employee taxes.
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, 2020 2019 2020 2019 Cost of revenue $ 849 $ 1,054 $ 2,835 $ 3,415 Sales and marketing 7,196 7,683 22,194 23,143 Product development 15,551 15,250 50,133 46,572 General and administrative 6,659 5,249 17,428 17,876 Total stock-based compensation recorded to income (loss) before income taxes 30,255 29,236 92,590 91,006 Provision for (benefit from) income taxes 378 (7,661) (23,831) (23,766) Total stock-based compensation recorded to net (loss) income $ 30,633 $ 21,575 $ 68,759 $ 67,240

OTHER INCOME, NET (Tables)

OTHER INCOME, NET (Tables)	9 Months Ended
	Sep. 30, 2020
Other Income and Expenses [Abstract]
Schedule of Other Income, Net	Other income, net for the three and nine months ended September 30, 2020 and 2019 consisted of the following (in thousands): Three Months Ended Nine Months Ended 2020 2019 2020 2019 Interest income, net $ 7 $ 2,830 $ 2,304 $ 10,946 Transaction gain (loss) on foreign exchange 28 (20) (32) 93 Other non-operating income, net 364 253 1,005 606 Other income, net $ 399 $ 3,063 $ 3,277 $ 11,645

NET (LOSS) INCOME PER SHARE (Ta

NET (LOSS) INCOME PER SHARE (Tables)	9 Months Ended
	Sep. 30, 2020
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 (loss) income per share for the periods presented (in thousands, except per share data): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Basic net (loss) income per share: Net (loss) income $ (1,020) $ 10,061 $ (40,513) $ 23,729 Shares used in computation: Weighted-average common shares outstanding 73,514 70,773 72,495 75,975 Basic net (loss) income per share attributable to common stockholders $ (0.01) $ 0.14 $ (0.56) $ 0.31 Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Diluted net (loss) income per share: Net (loss) income $ (1,020) $ 10,061 $ (40,513) $ 23,729 Shares used in computation: Weighted-average common shares outstanding 73,514 70,773 72,495 75,975 Stock options — 2,345 — 2,429 Restricted stock units — 478 — 870 Employee stock purchase program — 116 — 41 Number of shares used in diluted calculation 73,514 73,712 72,495 79,315 Diluted net (loss) income per share attributable to common stockholders $ (0.01) $ 0.14 $ (0.56) $ 0.30
Schedule of Anti-dilutive Securities	The following stock-based instruments were excluded from the calculation of diluted net (loss) 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, 2020 2019 2020 2019 Stock options 5,889 2,718 5,889 2,629 Restricted stock units 7,248 2,718 7,248 2,530 ESPP 228 — 228 —

INFORMATION ABOUT REVENUE AND_2

INFORMATION ABOUT REVENUE AND GEOGRAPHIC AREAS (Tables)	9 Months Ended
	Sep. 30, 2020
Segment Reporting [Abstract]
Schedule of Revenue by Product Line	The following table presents the Company’s net revenue by major product line for the periods presented (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Net revenue by product: Advertising $ 211,167 $ 253,098 $ 613,493 $ 717,973 Transactions 4,412 3,074 11,019 9,528 Other services 5,228 6,302 15,226 17,870 Total net revenue $ 220,807 $ 262,474 $ 639,738 $ 745,371
Schedule of Net Revenue by Geographic Region	The following table presents the Company’s net revenue by major geographic region for the periods presented (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 United States $ 218,563 $ 258,820 $ 632,360 $ 735,169 All other countries 2,244 3,654 7,378 10,202 Total net revenue $ 220,807 $ 262,474 $ 639,738 $ 745,371
Schedule of Long-Lived Assets by Geographic Location	The following table presents the Company’s long-lived assets by major geographic region for the periods presented (in thousands): September 30, December 31, United States $ 101,335 $ 109,849 All other countries 4,153 1,100 Total long-lived assets $ 105,488 $ 110,949

CASH, CASH EQUIVALENTS AND RE_3

CASH, CASH EQUIVALENTS AND RESTRICTED CASH (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Cash and Cash Equivalents [Abstract]
Cash	$ 80,698	$ 43,581
Cash equivalents	510,091	126,700
Total cash and cash equivalents	590,789	170,281
Restricted cash	826	22,037
Total cash, cash equivalents and restricted cash	$ 591,615	$ 192,318	$ 145,529	$ 354,835

CASH, CASH EQUIVALENTS AND RE_4

CASH, CASH EQUIVALENTS AND RESTRICTED CASH - Narrative (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Sep. 30, 2020	May 31, 2020	Dec. 31, 2019
Cash and Cash Equivalents [Abstract]
Proceeds from sale of debt securities, available-for-sale	$ 253,400
Marketable securities proceeds reinvested	$ 73,000
Restricted cash		$ 826		$ 22,037
Letters of credit outstanding			$ 21,500

FAIR VALUE OF FINANCIAL INSTR_3

FAIR VALUE OF FINANCIAL INSTRUMENTS (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities		$ 295,833
Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	$ 510,091	422,533
Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	510,091	126,700
Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	0	295,833
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	0	130,472
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	0	130,472
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	0	85,611
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	0	85,611
Recurring | Corporate 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	0	79,750
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	0	79,750
Recurring | Agency bonds | 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	510,091	126,700
Recurring | Money market funds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents	510,091	126,700
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

MARKETABLE SECURITIES - Narrati

MARKETABLE SECURITIES - Narrative (Details) $ in Millions	6 Months Ended
	Jun. 30, 2020USD ($)
Statement of Financial Position [Abstract]
Debt securities, available-for-sale, amortized cost	$ 300.2
Proceeds from sale of debt securities, available-for-sale	253.4
Proceeds from maturities reinvested	$ 73

MARKETABLE SECURITIES (Schedule

MARKETABLE SECURITIES (Schedule of the Fair Value to Amortized Cost Basis of Securities Held-to-Maturity) (Details) $ in Thousands	Dec. 31, 2019USD ($)
Cash equivalents and Short-term marketable securities:
Amortized Cost	$ 242,000
Gross Unrealized Gains	332
Gross Unrealized Losses	(19)
Fair Value	242,313
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost	53,499
Gross Unrealized Gains	21
Gross Unrealized Losses	0
Fair Value	53,520
Amortized Cost	295,499
Gross Unrealized Gains	353
Gross Unrealized Losses	(19)
Fair Value	295,833
Commercial paper
Cash equivalents and Short-term marketable securities:
Amortized Cost	130,464
Gross Unrealized Gains	17
Gross Unrealized Losses	(9)
Fair Value	130,472
Corporate bonds
Cash equivalents and Short-term marketable securities:
Amortized Cost	85,396
Gross Unrealized Gains	225
Gross Unrealized Losses	(10)
Fair Value	85,611
Agency bonds
Cash equivalents and Short-term marketable securities:
Amortized Cost	26,140
Gross Unrealized Gains	90
Gross Unrealized Losses	0
Fair Value	$ 26,230

MARKETABLE SECURITIES (Schedu_2

MARKETABLE SECURITIES (Schedule of Securities in an Unrealized Loss Position) (Details) $ in Thousands	Dec. 31, 2019USD ($)
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Fair Value [Abstract]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	$ 84,618
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	0
Debt Securities, Held-to-maturity, Unrealized Loss Position, Fair Value, Total	84,618
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss [Abstract]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(19)
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	(19)
Commercial paper
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Fair Value [Abstract]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	63,639
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	0
Debt Securities, Held-to-maturity, Unrealized Loss Position, Fair Value, Total	63,639
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss [Abstract]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(9)
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	(9)
Corporate bonds
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Fair Value [Abstract]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	20,979
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	0
Debt Securities, Held-to-maturity, Unrealized Loss Position, Fair Value, Total	20,979
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss [Abstract]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(10)
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	$ (10)

PREPAID EXPENSES AND OTHER CU_3

PREPAID EXPENSES AND OTHER CURRENT ASSETS (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid expenses	$ 9,612	$ 10,188
Other current assets	8,978	4,008
Total prepaid expenses and other current assets	$ 18,590	$ 14,196

PREPAID EXPENSES AND OTHER CU_4

PREPAID EXPENSES AND OTHER CURRENT ASSETS - Narrative (Details) $ in Millions	Sep. 30, 2020USD ($)
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Other current asset, resulting from legislation	$ 4.7

PROPERTY, EQUIPMENT AND SOFTW_2

PROPERTY, EQUIPMENT AND SOFTWARE, NET (Schedule of Property, Equipment and Software) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	$ 323,887	$ 295,845
Less accumulated depreciation	(218,399)	(184,896)
Property, equipment and software, net	105,488	110,949
Capitalized website and internal-use software development costs
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	164,488	140,886
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	88,436	86,089
Computer equipment
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	46,049	43,626
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	18,271	18,403
Telecommunication
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	4,956	5,154
Software
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	$ 1,687	$ 1,687

PROPERTY, EQUIPMENT, AND SOFT_2

PROPERTY, EQUIPMENT, AND SOFTWARE, NET (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 11.9	$ 11.6	$ 35.6	$ 33.9

GOODWILL AND INTANGIBLE ASSET_2

GOODWILL AND INTANGIBLE ASSETS (Schedule of Goodwill) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2020USD ($)
Goodwill [Roll Forward]
Beginning balance	$ 104,589
Effect of currency translation	2,183
Ending balance	$ 106,772

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, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 31,586	$ 25,456
Accumulated Amortization	(17,346)	(15,374)
Total amortization	14,240	10,082
Business relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	9,918	9,918
Accumulated Amortization	(3,571)	(2,841)
Total amortization	$ 6,347	$ 7,077
Weighted Average Remaining Life	8 years	8 years 7 months 6 days
Developed technology
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 7,709	$ 7,832
Accumulated Amortization	(5,934)	(4,959)
Total amortization	$ 1,775	$ 2,873
Weighted Average Remaining Life	1 year 6 months	2 years 2 months 12 days
Licensing agreements
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 6,129
Accumulated Amortization	(54)
Total amortization	$ 6,075
Weighted Average Remaining Life	9 years 4 months 24 days
Content
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 3,938	$ 3,814
Accumulated Amortization	(3,938)	(3,814)
Total amortization	$ 0	$ 0
Weighted Average Remaining Life	0 years	0 years
Domains and data licenses
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 2,869	$ 2,869
Accumulated Amortization	(2,826)	(2,748)
Total amortization	$ 43	$ 121
Weighted Average Remaining Life	2 years	1 year 8 months 12 days
Trademarks
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 877	$ 877
Accumulated Amortization	(877)	(872)
Total amortization	$ 0	$ 5
Weighted Average Remaining Life	0 years	2 months 12 days
User relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 146	$ 146
Accumulated Amortization	(146)	(140)
Total amortization	$ 0	$ 6
Weighted Average Remaining Life	0 years	2 months 12 days

GOODWILL AND INTANGIBLE ASSET_4

GOODWILL AND INTANGIBLE ASSETS (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 600,000	$ 800,000	$ 1,800,000	$ 2,600,000
Goodwill and intangible asset impairment	0
Licensing agreements
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	$ 6,100,000
Useful life	9 years 6 months

GOODWILL AND INTANGIBLE ASSET_5

GOODWILL AND INTANGIBLE ASSETS (Schedule of Future Amortization Expense) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Year Ending December 31,
2020 (from October 1, 2020)	$ 719
2021	2,848
2022	1,676
2023	1,359
2024	1,353
2025	1,353
Thereafter	4,932
Total amortization	$ 14,240	$ 10,082

LEASES (Lease Cost) (Details)

LEASES (Lease Cost) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Leases [Abstract]
Operating lease cost	$ 13,714	$ 13,544	$ 41,512	$ 40,878
Short-term lease cost (12 months or less)	369	291	1,070	938
Sublease income	(1,954)	(1,475)	(5,868)	(2,764)
Total lease cost, net	$ 12,129	$ 12,360	$ 36,714	$ 39,052

LEASES (Supplemental Cash Flow

LEASES (Supplemental Cash Flow Information) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 44,181	$ 42,323

LEASES (Operating Lease Maturit

LEASES (Operating Lease Maturities) (Details) $ in Thousands	Sep. 30, 2020USD ($)
Leases [Abstract]
2020 (from October 1, 2020)	$ 14,858
2021	52,067
2022	46,400
2023	43,495
2024	41,263
2025	22,316
Thereafter	24,009
Total minimum lease payments	244,408
Less imputed interest	(34,715)
Present value of lease liabilities	$ 209,693

LEASES (Additional Information)

LEASES (Additional Information) (Details)	Sep. 30, 2020	Dec. 31, 2019
Leases [Abstract]
Weighted-average remaining lease term (years) — operating leases	5 years 2 months 12 days	5 years 6 months
Weighted-average discount rate — operating leases	6.00%	6.10%

LEASES (Narrative) (Details)

LEASES (Narrative) (Details) $ in Millions	Oct. 31, 2020USD ($)
Subsequent Event
Lessee, Lease, Description [Line Items]
Lease not yet commenced	$ 9

OTHER NON-CURRENT ASSETS (Detai

OTHER NON-CURRENT ASSETS (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Other Assets, Noncurrent Disclosure [Abstract]
Deferred tax assets	$ 26,590	$ 20,054
Deferred contract costs	11,250	15,138
Other non-current assets	2,989	3,177
Total other non-current assets	$ 40,829	$ 38,369

OTHER NON-CURRENT ASSETS (Chang

OTHER NON-CURRENT ASSETS (Changes in Deferred Contract Costs) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2020USD ($)
Changes In Capitalized Contract Costs [Roll Forward]
Balance, beginning of period	$ 15,138
Add: costs deferred on new contracts	8,960
Less: amortization recorded in sales and marketing expenses	(12,848)
Balance, end of period	$ 11,250

OTHER NON-CURRENT ASSETS (Narra

OTHER NON-CURRENT ASSETS (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2020	Sep. 30, 2020
Other Assets, Noncurrent Disclosure [Abstract]
Deferred contract cost term	26 months	32 months		32 months
Amortization of deferred sales commissions			$ 3.4

CONTRACT BALANCES (Schedule of

CONTRACT BALANCES (Schedule of Changes in Allowance for Doubtful Accounts) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	$ 7,686	$ 8,685
Add: provision for doubtful accounts	26,802	15,259
Less: write-offs, net of recoveries	(23,172)	(16,165)
Balance, end of period	$ 11,316	$ 7,779

CONTRACT BALANCES (Narrative) (

CONTRACT BALANCES (Narrative) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Deferred revenue	$ 4,731	$ 4,315

CONTRACT BALANCES (Changes in D

CONTRACT BALANCES (Changes in Deferred Revenue) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2020USD ($)
Change in Contract with Customer, Liability [Roll Forward]
Balance, beginning of period	$ 4,315
Less: recognition of deferred revenue from beginning balance	(3,713)
Add: net increase in current period contract liabilities	4,129
Balance, end of period	$ 4,731

ACCRUED LIABILITIES AND ACCRU_3

ACCRUED LIABILITIES AND ACCRUED LIABILITIES (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Accounts payable	$ 10,614	$ 6,002
Employee related liabilities	60,986	41,488
Accrued sales and marketing expenses	3,601	2,982
Taxes payable	4,988	3,695
Accrued cost of revenue	5,640	7,208
Other accrued liabilities	17,549	10,958
Total accounts payable and accrued liabilities	$ 103,378	$ 72,333

ACCRUED LIABILITIES AND ACCRU_4

ACCRUED LIABILITIES AND ACCRUED LIABILITIES - Narrative (Details) $ in Millions	9 Months Ended
	Sep. 30, 2020USD ($)
Payables and Accruals [Abstract]
Increase in employee related activities	$ 19.5
Deferred income tax liabilities, employer taxes	10.6
Increase in accrued vacation costs	$ 6

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Details) - USD ($)	1 Months Ended
	May 31, 2020	Sep. 30, 2020
Line of Credit Facility [Line Items]
Letters of credit outstanding	$ 21,500,000
Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility term	3 years
Line of credit facility, maximum borrowing capacity	$ 75,000,000
Commitment fee percentage	0.25%
Debt issuance costs		$ 400,000
Remaining borrowing capacity		53,500,000
Long-term line of credit		$ 0
Revolving Credit Facility | London Interbank Offered Rate (LIBOR)
Line of Credit Facility [Line Items]
Basis spread	1.25%
Revolving Credit Facility | Base Rate
Line of Credit Facility [Line Items]
Basis spread	0.25%
Letter of Credit
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 25,000,000
Unused capacity, commitment fee percentage	0.70%
Credit Agreement Sublimit
Line of Credit Facility [Line Items]
Letters of credit outstanding	$ 21,500,000

STOCKHOLDERS' EQUITY (Schedule

STOCKHOLDERS' EQUITY (Schedule of Stock by Class) (Details) - $ / shares	Sep. 30, 2020	Dec. 31, 2019
Stockholders’ equity:
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	73,976,487	71,185,468
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

STOCKHOLDERS' EQUITY (Narrative

STOCKHOLDERS' EQUITY (Narrative) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2020USD ($)$ / sharesshares	Sep. 30, 2019USD ($)shares	Sep. 30, 2020USD ($)scheduleplan$ / sharesshares	Sep. 30, 2019USD ($)$ / sharesshares	Jan. 31, 2020USD ($)	Feb. 11, 2019USD ($)	Nov. 27, 2018USD ($)	Jul. 31, 2017USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Treasury stock (in shares) | shares		0		0
Number of equity incentive plans | plan			3
Granted (in shares) | shares			146,500
Fair value as of vest date of RSUs			$ 64,100,000	$ 84,900,000
Stock-based compensation	$ 30,255,000	$ 29,236,000	92,590,000	91,006,000
Capitalized stock-based compensation expense	$ 2,600,000	2,600,000	$ 7,100,000	7,600,000
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Target vesting range	0.00%		0.00%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Target vesting range	200.00%		200.00%
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of vesting schedules | schedule			3
Exercisable period			10 years
Intrinsic value of options exercised	$ 700,000	$ 3,400,000	$ 5,100,000	$ 6,200,000
Weighted average grant date fair value (in USD per share) | $ / shares	$ 7.61		$ 9.69	$ 17.64
Granted (in shares) | shares		0
Unrecognized compensation costs	$ 10,600,000		$ 10,600,000
Unrecognized compensation costs, period for recognition			2 years 1 month 6 days
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 | 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	$ 229,300,000		$ 229,300,000
Unrecognized compensation costs, period for recognition			2 years 6 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%
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			4 years
Performance goal stock price at which Performance Restricted Stock Unit awards would vest (usd per share) | $ / shares	$ 45.3125		$ 45.3125
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value (in USD per share) | $ / shares			$ 18.48	$ 26.12
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	433,697	288,529
Stock-based compensation	$ 600,000	$ 700,000	$ 1,900,000	$ 2,000,000
July 2017 Share Repurchase Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock repurchase program, authorized amount	950,000,000		950,000,000		$ 250,000,000	$ 250,000,000	$ 250,000,000	$ 200,000,000
Remaining authorized repurchase amount	$ 269,000,000		$ 269,000,000
Stock repurchased (in shares) | shares			0
Stock repurchased and retired (in shares) | shares				13,994,909
Repurchased and retired amount				$ 475,000,000

STOCKHOLDERS' EQUITY (Schedul_2

STOCKHOLDERS' EQUITY (Schedule of Stock Option Activity) (Details) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020USD ($)$ / sharesshares	Dec. 31, 2019USD ($)$ / sharesshares
Number of Shares
Outstanding, beginning balance (in shares) | shares	6,210,385
Granted (in shares) | shares	146,500
Exercised (in shares) | shares	(285,388)
Canceled (in shares) | shares	(182,616)
Outstanding, ending balance (in shares) | shares	5,888,881	6,210,385
Options vested and exercisable (in shares) | shares	5,199,107
Weighted-Average Exercise Price
Outstanding, beginning balance (in USD per share) | $ / shares	$ 25.10
Granted (in USD per share) | $ / shares	31.42
Exercised (in USD per share) | $ / shares	12.64
Canceled (in USD per share) | $ / shares	47.34
Outstanding, ending balance (in USD per share) | $ / shares	25.17	$ 25.10
Options vested and exercisable (in USD per share) | $ / shares	$ 23.63
Weighted- Average Remaining Contractual Term
Outstanding, Weighted-Average Remaining Contractual Term (in years)	3 years 10 months 24 days	4 years 3 months 18 days
Options vested and exercisable, Weighted-Average Remaining Contractual Term (in years)	3 years 4 months 24 days
Aggregate Intrinsic Value
Outstanding, Aggregate Intrinsic Value | $	$ 21,260	$ 75,805
Options vested and exercisable, Aggregate Intrinsic Value | $	$ 21,260

STOCKHOLDERS' EQUITY (Schedul_3

STOCKHOLDERS' EQUITY (Schedule of Restricted Stock Units Activity) (Details) - Restricted Stock Units	9 Months Ended
	Sep. 30, 2020$ / sharesshares
Number of Shares
Unvested, beginning balance (in shares)	7,625,584
Granted (in shares)	3,424,706
Vested (in shares)	(2,411,208)
Canceled (in shares)	(1,391,090)
Unvested, ending balance (in shares)	7,247,992
Weighted-Average Grant Date Fair Value
Unvested, beginning balance (in USD per share) | $ / shares	$ 36.51
Granted (in USD per share) | $ / shares	32.69
Released (in USD per share) | $ / shares	36.80
Canceled (in USD per share) | $ / shares	36.56
Unvested, ending balance (in USD per share) | $ / shares	$ 34.60
Shares withheld for taxes (in shares)	339,274

STOCKHOLDERS' EQUITY (Schedul_4

STOCKHOLDERS' EQUITY (Schedule of Stock-Based Compensation Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation recorded to income (loss) before income taxes	$ 30,255	$ 29,236	$ 92,590	$ 91,006
Provision for (benefit from) income taxes	378	(7,661)	(23,831)	(23,766)
Total stock-based compensation recorded to net (loss) income	30,633	21,575	68,759	67,240
Cost of revenue
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation recorded to income (loss) before income taxes	849	1,054	2,835	3,415
Sales and marketing
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation recorded to income (loss) before income taxes	7,196	7,683	22,194	23,143
Product development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation recorded to income (loss) before income taxes	15,551	15,250	50,133	46,572
General and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation recorded to income (loss) before income taxes	$ 6,659	$ 5,249	$ 17,428	$ 17,876

OTHER INCOME, NET (Details)

OTHER INCOME, NET (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Other Income and Expenses [Abstract]
Interest income, net	$ 7	$ 2,830	$ 2,304	$ 10,946
Transaction gain (loss) on foreign exchange	28	(20)	(32)	93
Other non-operating income, net	364	253	1,005	606
Other income, net	$ 399	$ 3,063	$ 3,277	$ 11,645

INCOME TAXES - Narrative (Detai

INCOME TAXES - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Income tax provision (benefit)	$ (10,744)	$ (2,552)	$ 9,484	$ (5,781)
Income tax provision due to U.S. federal and state income taxes and foreign income taxes			17,100	5,500
Net discrete tax benefit			7,600	$ 300
Unrecognized tax benefits	46,800		46,800
Unrecognized tax benefits that would not impact the effective tax rate	20,000		20,000
Earnings of foreign subsidiaries to be reinvested indefinitely	$ 5,700		$ 5,700

NET (LOSS) INCOME PER SHARE (Sc

NET (LOSS) 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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share Reconciliation [Line Items]
Net (loss) income	$ (1,020)	$ 10,061	$ (40,513)	$ 23,729
Basic net (loss) income per share:
Weighted-average common shares outstanding (in shares)	73,514	70,773	72,495	75,975
Basic net income per share attributable to common stockholders (in USD per share)	$ (0.01)	$ 0.14	$ (0.56)	$ 0.31
Diluted net (loss) income per share:
Weighted-average common shares outstanding (in shares)	73,514	70,773	72,495	75,975
Number of shares used in diluted calculation (in shares)	73,514	73,712	72,495	79,315
Diluted net income per share attributable to common stockholders (in USD per share)	$ (0.01)	$ 0.14	$ (0.56)	$ 0.30
Stock options
Diluted net (loss) income per share:
Incremental common shares (in shares)	0	2,345	0	2,429
Restricted stock units
Diluted net (loss) income per share:
Incremental common shares (in shares)	0	478	0	870
Employee stock purchase program
Diluted net (loss) income per share:
Incremental common shares (in shares)	0	116	0	41

NET (LOSS) INCOME PER SHARE (_2

NET (LOSS) INCOME PER SHARE (Schedule of Anti-Dilutive Employee Stock Awards) (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive awards (in shares)	5,889	2,718	5,889	2,629
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive awards (in shares)	7,248	2,718	7,248	2,530
ESPP
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive awards (in shares)	228	0	228	0

INFORMATION ABOUT REVENUE AND_3

INFORMATION ABOUT REVENUE AND GEOGRAPHIC AREAS (Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue	$ 220,807	$ 262,474	$ 639,738	$ 745,371
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue	218,563	258,820	632,360	735,169
All other countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue	2,244	3,654	7,378	10,202
Advertising
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue	211,167	253,098	613,493	717,973
Transactions
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue	4,412	3,074	11,019	9,528
Other services
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue	$ 5,228	$ 6,302	$ 15,226	$ 17,870

INFORMATION ABOUT REVENUE AND_4

INFORMATION ABOUT REVENUE AND GEOGRAPHIC AREAS - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020
Income Statement [Abstract]
Customer incentives	$ 2.9	$ 20.8
Free advertising for customers		$ 14.5

INFORMATION ABOUT REVENUE AND_5

INFORMATION ABOUT REVENUE AND GEOGRAPHIC AREAS (Long-Lived Assets) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 105,488	$ 110,949
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	101,335	109,849
All other countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 4,153	$ 1,100

RESTRUCTURING (Details)

RESTRUCTURING (Details) $ in Millions	Jul. 13, 2020employee	Apr. 09, 2020employee	Sep. 30, 2020USD ($)	Sep. 30, 2020USD ($)
Restructuring and Related Activities [Abstract]
Number of positions eliminated	60	1,000
Number of positions furloughed		1,100
Restructuring incurred cost | $			$ 0.5	$ 3.8