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Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2018	Jul. 26, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	RUBICON PROJECT, INC.
Entity Central Index Key	0001595974
Document Type	10-Q
Document Period End Date	Jun. 30, 2018
Amendment Flag	false
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q2
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		50,750,139

Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 72,247	$ 76,642
Marketable securities	32,072	52,504
Accounts receivable, net	153,163	165,890
Prepaid expenses and other current assets	9,041	9,620
TOTAL CURRENT ASSETS	266,523	304,656
Property and equipment, net	36,571	47,393
Internal use software development costs, net	14,340	12,734
Other assets, non-current	1,197	5,493
Intangible assets, net	11,767	13,359
TOTAL ASSETS	330,398	383,635
Current liabilities:
Accounts payable and accrued expenses	198,504	214,103
Other current liabilities	2,899	3,141
TOTAL CURRENT LIABILITIES	201,403	217,244
Other liabilities, non-current	1,331	1,780
TOTAL LIABILITIES	202,734	219,024
Commitments and contingencies (Note 10)
STOCKHOLDERS' EQUITY
Preferred stock, $0.00001 par value, 10,000 shares authorized at June 30, 2018 and December 31, 2017; 0 shares issued and outstanding at June 30, 2018 and December 31, 2017	0	0
Common stock, $0.00001 par value; 500,000 shares authorized at June 30, 2018 and December 31, 2017; 50,750 and 50,239 shares issued and outstanding at June 30, 2018 and December 31, 2017, respectively	1	0
Additional paid-in capital	427,324	418,354
Accumulated other comprehensive loss	(77)	41
Accumulated deficit	(299,584)	(253,784)
TOTAL STOCKHOLDERS' EQUITY	127,664	164,611
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ 330,398	$ 383,635

Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, par or stated value per share (usd per share)	$ 0.00001	$ 0.00001
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par or stated value per share	$ 0.00001	$ 0.00001
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares, issued	50,750,000	50,239,000
Common stock, shares, outstanding	50,750,000	50,239,000

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
Revenue	$ 28,648	$ 42,922	$ 53,524	$ 88,937
Expenses:
Cost of revenue	15,044	13,698	29,827	28,386
Sales and marketing	11,135	12,529	23,392	27,157
Technology and development	9,245	12,044	19,739	24,797
General and administrative	11,441	14,355	23,985	29,435
Restructuring and other exit costs	974	1,621	3,440	5,959
Total expenses	47,839	54,247	100,383	115,734
Loss from operations	(19,191)	(11,325)	(46,859)	(26,797)
Other (income) expense:
Interest income, net	(274)	(228)	(545)	(395)
Other income	(210)	(167)	(420)	(379)
Foreign exchange (gain) loss, net	(797)	479	(243)	851
Total other (income) expense, net	(1,281)	84	(1,208)	77
Loss before income taxes	(17,910)	(11,409)	(45,651)	(26,874)
Provision for income taxes	74	146	149	521
Net loss	$ (17,984)	$ (11,555)	$ (45,800)	$ (27,395)
Net loss per share:
Basic and Diluted (usd per share)	$ (0.36)	$ (0.24)	$ (0.92)	$ (0.56)
Weighted average shares used to compute net loss per share:
Basic and Diluted (in shares)	50,071	48,783	49,883	48,559

Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net loss	$ (17,984)	$ (11,555)	$ (45,800)	$ (27,395)
Other comprehensive income (loss):
Unrealized gain on investments	16	4	6	0
Foreign currency translation adjustments	(338)	173	(124)	270
Other comprehensive income (loss)	(322)	177	(118)	270
Comprehensive loss	$ (18,306)	$ (11,378)	$ (45,918)	$ (27,125)

Consolidated Statements of Stockholders' Equity (Deficit) - 6 months ended Jun. 30, 2018 - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning Balance (in shares) at Dec. 31, 2017	50,239,000	50,239,000
Beginning Balance at Dec. 31, 2017	$ 164,611	$ 0	$ 418,354	$ 41	$ (253,784)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options (in shares)		49,000
Exercise of common stock options	45		45
Restricted stock awards, net (in shares)		(156,000)
Restricted stock awards, net	0	$ 0
Issuance of common stock related to employee stock purchase plan (in shares)		89,000
Issuance of common stock related to employee stock purchase plan	143		143
Issuance of common stock related to RSU vesting (in shares)		830,000
Issuance of common stock related to RSU vesting	1	$ 1
Shares withheld related to net share settlement (in shares)		(301,000)
Shares withheld related to net share settlement	(658)		(658)
Stock-based compensation	9,440		9,440
Other comprehensive loss	(118)			(118)
Net loss	$ (45,800)				(45,800)
Ending Balance (in shares) at Jun. 30, 2018	50,750,000	50,750,000
Ending Balance at Jun. 30, 2018	$ 127,664	$ 1	$ 427,324	$ (77)	$ (299,584)

Consolidated Statement of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
OPERATING ACTIVITIES:
Net loss	$ (45,800)	$ (27,395)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	17,588	18,976
Stock-based compensation	9,156	11,542
Loss on disposal of property and equipment	120	271
Provision for doubtful accounts	215	566
Accretion of available for sale securities	(318)	(76)
Unrealized foreign currency gains, net	(766)	1,130
Deferred income taxes	0	274
Changes in operating assets and liabilities, net of effect of business acquisitions:
Accounts receivable	12,342	52,917
Prepaid expenses and other assets	2,351	(393)
Accounts payable and accrued expenses	(15,287)	(44,561)
Other liabilities	(691)	(446)
Net cash provided by (used in) operating activities	(21,090)	12,805
INVESTING ACTIVITIES:
Purchases of property and equipment	(1,216)	(4,839)
Capitalized internal use software development costs	(4,817)	(4,327)
Investments in available-for-sale securities	(23,991)	(31,789)
Maturities of available-for-sale securities	41,150	45,050
Sales of available-for-sale securities	6,086	0
Net cash provided by investing activities	17,212	4,095
FINANCING ACTIVITIES:
Proceeds from exercise of stock options	45	384
Proceeds from issuance of common stock under employee stock purchase plan	143	444
Taxes paid related to net share settlement	(658)	(2,048)
Net cash used in financing activities	(470)	(1,220)
EFFECT OF EXCHANGE RATE CHANGES ON CASH, CASH EQUIVALENTS AND RESTRICTED CASH	(47)	140
CHANGE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	(4,395)	15,820
CASH, CASH EQUIVALENTS AND RESTRICTED CASH — Beginning of period	76,642	149,498
CASH, CASH EQUIVALENTS AND RESTRICTED CASH — End of period	72,247	165,318
SUPPLEMENTAL DISCLOSURES OF OTHER CASH FLOW INFORMATION:
Capitalized assets financed by accounts payable and accrued expenses	712	3,944
Capitalized stock-based compensation	$ 284	$ 251

Organization and Summary of Significant Accounting Policies

6 Months Ended

Jun. 30, 2018

Accounting Policies [Abstract]

Organization and Summary of Significant Accounting Policies

Company Overview

The Rubicon Project, Inc., or Rubicon Project (the "Company"), was formed on April 20, 2007 in Delaware and began operations in April 2007. The Company is headquartered in Los Angeles, California.

The Company is a global advertising exchange that helps websites and applications thrive by giving them tools and expertise to sell ads easily and safely. In addition, the world’s leading agencies and brands rely on the Company's technology to execute tens of billions of advertising transactions each month. The Company provides a technology solution to automate the purchase and sale of digital advertising inventory for buyers and sellers. The Company's platform features applications and services for digital advertising sellers, including websites, mobile applications and other digital media properties, and their representatives, to sell their digital advertising inventory; applications and services for buyers, including advertisers, agencies, agency trading desks, demand side platforms, or DSPs, to buy digital advertising inventory; and a marketplace over which such transactions are executed. Together, these features power and enhance a comprehensive, transparent, independent advertising marketplace that brings buyers and sellers together and facilitates intelligent decision making and automated transaction execution for the digital advertising inventory managed on the Company's platform. The Company's clients include many of the world's leading publishers of websites and mobile applications and buyers of digital advertising inventory.

Advertising inventory takes different forms, referred to as advertising units, is purchased and sold through different transactional methodologies, and allows advertising content to be presented to consumers through different channels. The Company's solution enables buyers and sellers to purchase and sell:


•	a comprehensive range of advertising units, including display, audio and video;


•	that are transacted through real-time bidding ("RTB"), which includes (i) direct sale of premium inventory, which the Company refers to as private marketplace ("PMP"), and (ii) open auction bidding, which the Company refers to as open marketplace ("OMP"); and


•	that are displayed across digital channels, including mobile web, mobile application, and desktop, as well as across various out-of-home channels, such as digital billboards.

Risks and Uncertainties

The Company has been negatively impacted by rapid changes in the ad tech industry including demand by ad tech buyers

for more efficiency and lower costs, changes in bidding technologies, and increased competition. In response to these challenges,

the Company made significant reductions in fees charged to buyers during 2017 and in November 2017 eliminated its buyer fees

altogether. The competitive pressures and reduced take rate resulted in lower revenue and cash flows in the first half of 2018 compared to the prior year. In an effort to bring its costs into better alignment with reduced take rates, the Company has undertaken restructuring activities to reduce headcount and related operating costs, and has also reduced its capital expenditures, which may make execution against its strategic business plans more difficult. Unless and until the Company is able to compensate for the fee reductions and reduced gross margins by continuing to increase advertising spending on its platform, or sufficiently reducing costs, it may not be able to grow its business and may continue to operate at a loss, depleting its cash resources and liquidity. If the Company continues to experience significant operating losses in the future, the Company may require additional liquidity to fund its operations. The Company’s current credit facility expires in September 2018. There can be no guarantee that additional financing will be available on commercially reasonable terms, if at all.

Basis of Presentation and Summary of Significant Accounting Policies

The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with United States Generally Accepted Accounting Principles, or GAAP, for interim financial information and the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In the opinion of management, all adjustments (consisting of normal recurring adjustments) considered necessary for a fair statement of the results for the interim period presented have been included. Operating results for the six months ended June 30, 2018 are not necessarily indicative of the results that may be expected for any future interim period, the year ending December 31, 2018, or for any future year.

The condensed consolidated balance sheet at December 31, 2017 has been derived from the audited financial statements at that date, but does not include all of the disclosures required by GAAP. The accompanying condensed consolidated financial statements should be read in conjunction with the Company's audited consolidated financial statements and notes thereto for the year ended December 31, 2017 included in its 2017 Annual Report on Form 10-K.

There have been no significant changes in the Company's accounting policies from those disclosed in its audited consolidated financial statements and notes thereto for the year ended December 31, 2017 included in its Annual Report on Form 10-K.

Reclassifications

Certain prior period amounts have been reclassified to conform to the current period presentation. Specifically, this includes amounts reclassified to conform to the current year presentation in the condensed consolidated statements of cash flows.

Use of Estimates

The preparation of condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported and disclosed financial statements and accompanying footnotes. Actual results could differ materially from these estimates.

Recently Adopted Accounting Pronouncements

On January 1, 2018, the Company adopted the following accounting pronouncements, using a prospective adoption method, which did not have an impact on the Company's condensed consolidated financial statements and did not result in any significant policy changes:


•	Accounting Standards Update ("ASU") 2017-01—Business Combinations (Topic 805): Clarifying the Definition of a Business; and


•	ASU 2017-09—Compensation—Stock Compensation (Topic 718): Scope of Modification Accounting.

The Company has also adopted ASU 2016-15—Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments, although the retrospective adoption method did not have an impact on periods presented. The Company will apply this guidance to applicable future transactions.

Recent Accounting Pronouncements

Under the Jumpstart Our Business Startups Act, or the JOBS Act, the Company meets the definition of an emerging growth company. The Company has irrevocably elected to opt out of the extended transition period for complying with new or revised accounting standards pursuant to Section 107(b) of the JOBS Act.

In February 2016, the Financial Accounting Standards Board ("FASB") issued ASU 2016-02—Leases (Topic 842) ("ASU-2016-02"), which requires an entity to recognize right-of-use assets and lease liabilities on its balance sheet and disclose key information about leasing arrangements. ASU 2016-02 offers specific accounting guidance for a lessee, a lessor, and sale and leaseback transactions. Lessees and lessors are required to disclose qualitative and quantitative information about leasing arrangements to enable a user of the financial statements to assess the amount, timing and uncertainty of cash flows arising from leases. Leases will be classified as either finance or operating, with classification affecting the pattern of expense recognition in the income statement. ASU 2016-02 is effective for annual reporting periods beginning after December 15, 2018, including interim periods within that reporting period, and requires a modified retrospective adoption, with early adoption permitted. The Company is currently evaluating the effect this guidance will have on its condensed consolidated financial statements and related disclosures, and anticipates the guidance to result in increases in its assets and liabilities as most of its operating lease commitments will be subject to the new standard and recognized as right-of-use assets and lease liabilities.

In June 2018, the FASB issued ASU 2018-07—Stock Compensation (Topic 718) ("ASU 2018-07"), which expands the scope of Accounting Standards Codification Topic 718, Compensation—Stock Compensation to include share-based payments granted to non-employees in exchange for goods or services. Upon adoption, the fair value of awards granted to non-employees will be determined as of the grant date, which will be recognized over the service period. Previous guidance required the awards to be remeasured at fair value periodically when determining the related expense. ASU 2018-07 is effective for annual reporting periods beginning after December 15, 2018, including interim periods within that reporting period, and requires a modified retrospective adoption, with early adoption permitted. Upon adoption, the entity is required to measure the non-employee awards at fair value as of the adoption date. The Company is currently evaluating the effect this guidance will have on its condensed consolidated financial statements and related disclosures.

Net Income (Loss) Per Share

6 Months Ended

Jun. 30, 2018

Earnings Per Share [Abstract]

Net Income (Loss) Per Share

The following table presents the basic and diluted net loss per share:



	Three Months Ended						Six Months Ended
	June 30, 2018			June 30, 2017			June 30, 2018			June 30, 2017
	(in thousands, except per share data)
Basic and Diluted EPS:
Net loss	$	(17,984	)	$	(11,555	)	$	(45,800	)	$	(27,395	)
Weighted-average common shares outstanding	50,443			49,666			50,346			49,557
Weighted-average unvested restricted shares	(372		)	(883		)	(463		)	(998		)
Weighted-average common shares outstanding used to compute net loss per share	50,071			48,783			49,883			48,559
Basic and diluted net loss per share	$	(0.36	)	$	(0.24	)	$	(0.92	)	$	(0.56	)

The following weighted-average shares have been excluded from the calculation of diluted net loss per share attributable to common stockholders for each period presented because they are anti-dilutive:



	Three Months Ended		Six Months Ended
	June 30, 2018	June 30, 2017	June 30, 2018	June 30, 2017
	(in thousands)		(in thousands)
Options to purchase common stock	18	88	27	137
Unvested restricted stock awards	301	367	244	295
Unvested restricted stock units	1,434	585	1,401	623
ESPP	36	44	49	52
Total shares excluded from net loss per share	1,789	1,084	1,721	1,107

Revenues

6 Months Ended

Jun. 30, 2018

Revenue from Contract with Customer [Abstract]

Revenues

On January 1, 2018, the Company adopted Accounting Standards Update 2014-09—Revenue from Contracts with Customers (Topic 606) ("ASU 2014-09") using a modified retrospective approach applied to all contracts that generated revenue in the preceding year. The adoption of this guidance did not have an impact on the amount or timing of revenue recognized by the Company.

The Company generates revenue from transactions where it provides a platform for the purchase and sale of digital advertising inventory. The Company’s advertising automation solution is a marketplace for sellers of digital advertising inventory (providers of websites, mobile applications and other digital media properties, and their representatives) and buyers of digital advertising inventory (including advertisers, agencies, agency trading desks, and demand-side platforms). This solution incorporates proprietary machine-learning algorithms, sophisticated data processing, high-volume storage, detailed analytics capabilities, and a distributed infrastructure. Together, these features form the basis for the Company’s automated advertising solution that brings buyers and sellers together and facilitates intelligent decision-making and automated transaction execution for the digital advertising inventory managed on the Company's platform. Digital advertising inventory is created when consumers access sellers’ content. Sellers provide digital advertising inventory to the Company’s platform in the form of advertising requests, or ad requests. When the Company receives ad requests from sellers, it sends bid requests to buyers, which enable buyers to bid on sellers’ digital advertising inventory. Winning bids can create advertising, or paid impressions, for the seller to present to the consumer.

The total volume of spending between buyers and sellers on the Company’s platform is referred to as advertising spend. The Company keeps a percentage of that advertising spend as a fee, and remits the remainder to the seller. The fee or “take rate” that the Company retains from the gross advertising spend on its platform is recognized as revenue. The fee earned on each transaction is based on the pre-existing agreement between the Company and the seller and the clearing price of the winning bid. The Company recognizes revenue upon fulfillment of its performance obligation to a customer, which occurs at the point in time an ad renders and is counted as a paid impression, subject to an underlying agreement existing with the customer and a fixed or determinable transaction price. Performance obligations for all transactions are satisfied, and the corresponding revenue is recognized, at a distinct point in time when an ad renders. The Company does not have arrangements with multiple performance obligations. The Company considers the following when determining if a contract exists under which the performance obligations have been satisfied: (i) contract approval by all parties, (ii) identification of each party’s rights regarding the goods or services to be transferred, (iii) specified payment terms, (iv) commercial substance of the contract, and (v) collectability of substantially all of the consideration is probable.

The Company has determined that it does not act as the principal in the purchase and sale of digital advertising inventory because it does not have control of the digital advertising inventory and does not set prices agreed upon within the auction marketplace, and therefore reports revenue on a net basis. In periods prior to the second quarter of 2017, the Company reported revenue on a gross basis for revenue associated with its intent marketing solution, as the Company determined that it acted as the principal in the purchase and sale of digital advertising inventory. The Company ceased offering its intent marketing solution after the first quarter of 2017, after which time, all of the Company’s revenues have been recorded on a net basis. Revenue generated by the Company’s intent marketing solution in 2017 prior to its cessation was $1.3 million, which is included in total revenue for the six months ended June 30, 2017.

Payment terms are specified in agreements between the Company and the buyers and sellers on its exchange platform. The Company generally bills buyers at the end of each month for the full purchase price of impressions filled in that month. The Company recognizes volume discounts as a reduction of revenue as they are incurred. Specific payment terms may vary by agreement, but are generally seventy-five days or less. The Company's accounts receivable are recorded at the amount of gross billings to buyers, net of allowances for the amounts the company is responsible to collect. The Company's accounts payable related to amounts due to sellers are recorded at the net amount payable to sellers (see Note 5). Accordingly, both accounts receivable and accounts payable appear large in relation to revenue reported on a net basis.

The following table presents our revenue by channel for the three and six months ended June 30, 2018 and 2017:



	Three Months Ended								Six Months Ended
	June 30, 2018				June 30, 2017				June 30, 2018				June 30, 2017
	(in thousands, except percentages)
Channel:
Desktop	$	13,663	48	%	$	23,746	55	%	$	27,972	52	%	$	52,075	59	%
Mobile	14,985		52		19,176		45		25,552		48		36,862		41
Total	$	28,648	100	%	$	42,922	100	%	$	53,524	100	%	$	88,937	100	%

The following table presents our revenue disaggregated by geographic location, based on the location of the Company's sellers:



	Three Months Ended				Six Months Ended
	June 30, 2018		June 30, 2017		June 30, 2018		June 30, 2017
	(in thousands)				(in thousands)
United States	$	18,966	$	28,000	$	34,470	$	55,661
International	9,682		14,922		19,054		33,276
Total	$	28,648	$	42,922	$	53,524	$	88,937

Fair Value Measurements

6 Months Ended

Jun. 30, 2018

Fair Value Disclosures [Abstract]

Fair Value Measurements

Fair value represents the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Observable inputs are based on market data obtained from independent sources. The fair value hierarchy is based on the following three levels of inputs, of which the first two are considered observable and the last one is considered unobservable:


•	Level 1 – Quoted prices (unadjusted) in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date.


•	Level 2 – Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly.


•	Level 3 – Unobservable inputs.

The table below sets forth a summary of financial instruments that are measured at fair value on a recurring basis at June 30, 2018:



	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	(in thousands)
Cash equivalents	$	14,334	$	14,334	$	—	$	—
Corporate debt securities	$	12,112	$	—	$	12,112	$	—
U.S. Treasury, government and agency debt securities	$	19,960	$	19,960	$	—	$	—

The table below sets forth a summary of financial instruments that are measured at fair value on a recurring basis at December 31, 2017:



	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	(in thousands)
Cash equivalents	$	1,807	$	210	$	1,597	$	—
Corporate debt securities	$	25,098	$	—	$	25,098	$	—
U.S. Treasury, government and agency debt securities	$	29,901	$	29,901	$	—	$	—

At June 30, 2018 and December 31, 2017, cash equivalents of $14.3 million and $1.8 million, respectively, consisted of money market funds and commercial paper, with original maturities of three months or less. The carrying amounts of cash equivalents are classified as Level 1 or Level 2 depending on whether or not their fair values are based on quoted market prices for identical securities that are traded in an active market. The commercial paper included in cash equivalents at December 31, 2017 is classified as Level 2 since its fair value is not based on quoted market prices for identical securities that are traded in an active market, but rather is derived from similar securities. Corporate debt securities (which are included in marketable securities on the balance sheet) with fair values derived from similar securities rather than based on quoted market prices for identical securities, are classified as Level 2 as well. The fair values of the Company's U.S. treasury, government and agency debt securities are based on quoted market prices and classified as Level 1, and are included within marketable securities.

There were no transfers between Level 1 and Level 2 fair value measurements during the three months ended June 30, 2018 and 2017.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Other Balance Sheet Amounts

6 Months Ended

Jun. 30, 2018

Balance Sheet Related Disclosures [Abstract]

Other Balance Sheet Amounts

Investments in marketable securities as of June 30, 2018 consisted of the following:



	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	(in thousands)
Available-for-sale—short-term:
U.S. Treasury, government and agency debt securities	$	19,983	$	—	$	(23	)	$	19,960
Corporate debt securities	12,112		—		—			12,112
Total	$	32,095	$	—	$	(23	)	$	32,072

Investments in marketable securities as of December 31, 2017 consisted of the following:



	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	(in thousands)
Available-for-sale—short-term:
U.S. Treasury, government and agency debt securities	$	27,426	$	—	$	(20	)	$	27,406
Corporate debt securities	25,098		—		—			25,098
Total	$	52,524	$	—	$	(20	)	$	52,504
Available-for-sale—long-term:
U.S. Treasury, government and agency debt securities	$	2,504	$	—	$	(9	)	$	2,495

The Company's available-for-sale securities had a weighted remaining contractual maturity of 0.3 years as of June 30, 2018. For the three and six months ended June 30, 2018, the Company sold $6.1 million of available-for-sale investments, on which the realized gains were de minimis and there were no unrealized holding gains (losses) reclassified out of accumulated other comprehensive loss into the condensed consolidated statements of operations.

Accounts payable and accrued expenses included the following:



	June 30, 2018		December 31, 2017
	(in thousands)
Accounts payable—seller	$	187,332	$	203,694
Accounts payable—trade	4,663		3,764
Accrued employee-related payables	6,509		6,645
Total	$	198,504	$	214,103

As of December 31, 2016, the Company had $0.1 million of restricted cash, which is included in the beginning balance of cash, cash equivalents and restricted cash in the condensed consolidated statement of cash flows for the six months ended June 30, 2017. There was no restricted cash as of June 30, 2018 and December 31, 2017.

Intangible Assets

6 Months Ended

Jun. 30, 2018

Goodwill and Intangible Assets Disclosure [Abstract]

Intangible Assets

The Company’s intangible assets as of June 30, 2018 and December 31, 2017 included the following:



	June 30, 2018			December 31, 2017
	(in thousands)
Amortizable intangible assets:
Developed technology	$	16,878		$	16,878
Non-compete agreements	690			690
Trademarks	20			20
Total identifiable intangible assets, gross	17,588			17,588
Accumulated amortization—intangible assets:
Developed technology	(5,475		)	(4,062		)
Non-compete agreements	(333		)	(161		)
Trademarks	(13		)	(6		)
Total accumulated amortization—intangible assets	(5,821		)	(4,229		)
Total identifiable intangible assets, net	$	11,767		$	13,359

Amortization of intangible assets for the three months ended June 30, 2018 and 2017 were $0.8 million and $0.8 million, respectively, and $1.6 million and $2.4 million for the six months ended June 30, 2018 and 2017, respectively. The estimated remaining amortization expense associated with the Company's intangible assets was as follows as of June 30, 2018:



Fiscal Year	Amount
	(in thousands)
Remaining 2018	$	1,593
2019	3,010
2020	2,826
2021	2,826
2022	1,512
Thereafter	—
Total	$	11,767

Stock-Based Compensation

6 Months Ended

Jun. 30, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stock-Based Compensation

The Company’s equity incentive plans provide for the grant of equity awards, including non-statutory or incentive stock options, restricted stock, and restricted stock units, to the Company's employees, officers, directors, and consultants. The Company's board of directors administers the plans. Outstanding options vest based upon continued service at varying rates, but generally over four years from issuance with 25% vesting after one year of service and the remainder vesting monthly thereafter. Restricted stock and restricted stock units vest at varying rates, typically approximately 25% vesting after approximately one year of service and the remainder vesting semi-annually thereafter. The restricted stock units granted in the first half of 2018 included 2,725,000 restricted stock units that vest 50% on each of the first and second anniversaries of the grant date. Options, restricted stock, and restricted stock units granted under the plans accelerate under certain circumstances for certain participants upon a change in control, as defined in the governing plan. An aggregate of 6,094,345 shares remained available for future grants at June 30, 2018 under the plans.

Stock Options

A summary of stock option activity for the six months ended June 30, 2018 is as follows:



	Shares Under Option		Weighted- Average Exercise Price		Weighted- Average Contractual Life	Aggregate Intrinsic Value
	(in thousands)					(in thousands)
Outstanding at December 31, 2017	4,363		$	8.75
Granted	658		$	1.97
Exercised	(49	)	$	0.91
Expired	(1,101	)	$	10.24
Forfeited	(49	)	$	4.54
Outstanding at June 30, 2018	3,822		$	7.30	7.14 years	$	1,470
Exercisable at June 30, 2018	2,188		$	9.80	5.81 years	$	309

The total intrinsic values of options exercised during the six months ended June 30, 2018 was $0.1 million. At June 30, 2018, the Company had unrecognized employee stock-based compensation expense relating to nonvested stock options of approximately $4.2 million, which is expected to be recognized over a weighted-average period of 2.8 years. The weighted-average grant date fair value per share of stock options granted during the six months ended June 30, 2018 was $1.03. Total fair value of options vested during the six months ended June 30, 2018 was $2.1 million.

The Company estimates the fair value of stock options that contain service and/or performance conditions using the Black-Scholes option pricing model. The weighted-average input assumptions used by the Company were as follows:



	Three Months Ended			Six Months Ended
	June 30, 2018	June 30, 2017		June 30, 2018		June 30, 2017
Expected term (in years)	N/A	5.7		6.1		6.0
Risk-free interest rate	N/A	1.87	%	2.66	%	2.10	%
Expected volatility	N/A	55	%	57	%	55	%
Dividend yield	N/A	—	%	—	%	—	%

There were no stock options granted during the three months ended June 30, 2018.

Restricted Stock

A summary of restricted stock activity for the six months ended June 30, 2018 is as follows:



	Number of Shares		Weighted-Average Grant Date Fair Value
	(in thousands)
Nonvested shares of restricted stock outstanding at December 31, 2017	558		$	12.60
Granted	—		$	—
Canceled	(156	)	$	13.82
Vested	(132	)	$	14.08
Nonvested shares of restricted stock outstanding at June 30, 2018	270		$	11.18

The aggregate fair value of restricted stock with service conditions that vested during the six months ended June 30, 2018 was $0.3 million. At June 30, 2018, the Company had unrecognized stock-based compensation expense for restricted stock with service conditions of $0.9 million, which is expected to be recognized over a weighted-average period of 1.4 years.

Restricted Stock Units

A summary of restricted stock unit activity for the six months ended June 30, 2018 is as follows:



	Number of Shares		Weighted-Average Grant Date Fair Value
	(in thousands)
Nonvested restricted stock units outstanding at December 31, 2017	3,609		$	7.55
Granted	4,707		$	2.20
Canceled	(788	)	$	5.60
Vested	(830	)	$	8.02
Nonvested restricted stock units outstanding at June 30, 2018	6,698		$	3.96

The weighted-average grant date fair value per share of restricted stock units granted during the six months ended June 30, 2018 was $2.20. The aggregate fair value of restricted stock units that vested during six months ended June 30, 2018 was $1.8 million. At June 30, 2018, the intrinsic value of nonvested restricted stock units was $19.1 million. At June 30, 2018, the Company had unrecognized stock-based compensation expense relating to nonvested restricted stock units of approximately $22.8 million, which is expected to be recognized over a weighted-average period of 2.60 years.

Employee Stock Purchase Plan

In November 2013, the Company adopted the Company's 2014 Employee Stock Purchase Plan ("ESPP"). The ESPP is designed to enable eligible employees to periodically purchase shares of the Company's common stock at a discount through payroll deductions of up to 10% of their eligible compensation, subject to any plan limitations. At the end of each six-month offering period, employees are able to purchase shares at a price per share equal to 85% of the lower of the fair market value of the Company's common stock on the first trading day of the offering period or on the last trading day of the offering period. Offering periods generally commence and end in May and November of each year.

As of June 30, 2018, the Company has reserved 1,692,373 shares of its common stock for issuance under the ESPP.

Stock-Based Compensation Expense

Total stock-based compensation expense recorded in the condensed consolidated statements of operations was as follows:



	Three Months Ended				Six Months Ended
	June 30, 2018		June 30, 2017		June 30, 2018		June 30, 2017
	(in thousands)				(in thousands)
Cost of revenue	$	77	$	96	$	184	$	180
Sales and marketing	1,158		974		2,343		2,409
Technology and development	623		981		1,472		2,056
General and administrative	2,402		2,628		4,759		5,337
Restructuring and other exit costs	352		624		398		1,560
Total stock-based compensation expense	$	4,612	$	5,303	$	9,156	$	11,542

Restructuring and Other Exit Costs

6 Months Ended

Jun. 30, 2018

Restructuring and Related Activities [Abstract]

Restructuring and Other Exit Costs

As part of its on-going efforts to control costs and create efficiencies, the Company underwent restructuring events throughout 2017 and in the first quarter of 2018. The objective of these restructuring activities was to streamline operations, prioritize resources for growth initiatives and increase profitability.

In January 2017, the Company announced that it would cease providing intent marketing services and would close its Toronto, Canada office as a result. For the three and six months ended June 30, 2017, the Company recognized expenses of $1.6 million and $6.0 million, respectively, as restructuring and other exit costs related to the cessation of our intent marketing solution, including the closure of the Toronto office, as well as the realignment of the management team to a more cost efficient structure (collectively, the "2017 Restructuring Events"). A majority of the costs incurred in the three and six months ended June 30, 2017 were severance and one-time termination benefit costs, of which $0.7 million and $1.6 million, respectively, related to non-cash stock-based compensation, the remainder of which related to facility closure costs.

In the first quarter of 2018, the Company announced its restructuring plan to reduce headcount to bring the Company's general and administrative operations into better alignment with the current size of the business and de-layer certain functions, and to reduce its investment in unprofitable projects (the "2018 Restructuring Events"). During the three and six months ended June 30, 2018, the Company incurred restructuring and other exit costs of $1.0 million and $3.4 million, respectively, for severance and one-time termination benefits.

The following table summarizes restructuring and other exit cost activity for the 2018 Restructuring Events (in thousands):



Accrued restructuring and other exit costs at December 31, 2017	$	—
Restructuring and other exit costs	3,440
Cash paid for restructuring and other exit costs	(2,561		)
Non-cash stock-based compensation for restructuring and other exit costs	(398		)
Accrued restructuring and other exit costs at June 30, 2018	$	481

Accrued restructuring costs related to the 2017 Restructuring Events were $0.1 million at December 31, 2017 and were paid in the first half of 2018. Accrued restructuring costs are included within other liabilities on the Company's condensed consolidated balance sheets.

Income Taxes	6 Months Ended
Income Taxes	Jun. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes In determining quarterly provisions for income taxes, the Company uses the annual estimated effective tax rate applied to the actual year-to-date income. The Company's annual estimated effective tax rate differs from the statutory rate primarily as a result of state taxes, foreign taxes, nondeductible stock option expenses, and changes in the Company's valuation allowance. The Company recorded income tax expenses of $0.1 million and $0.1 million for the three months ended June 30, 2018 and 2017, respectively and $0.1 million and $0.5 million for the six months ended June 30, 2018 and 2017, respectively. The tax provision for the three and six months ended June 30, 2018 is primarily the result of the domestic valuation allowance and the tax liability associated with the foreign subsidiaries. On December 22, 2017, the U.S. government enacted the Tax Cuts and Jobs Act (the “Tax Act”). The Tax Act includes significant changes to the U.S. corporate income tax system including the following: a federal corporate rate reduction from 34% to 21%; limitations on the deductibility of executive compensation and research and development (“R&D”) expenditures; immediate expensing of qualified property; the creation of new minimum taxes such as the base erosion anti-abuse tax (“BEAT”) and Global Intangible Low Taxed Income (“GILTI”) tax; and the transition of U.S. international taxation from a worldwide tax system to a modified territorial tax system, which will result in a one time U.S. tax liability on those earning which have not previously been repatriated to the U.S. (the “Transition Tax”). The Tax Act imposes a Transition Tax on previously untaxed accumulated and current earnings and profits (“E&P”) of certain of our foreign subsidiaries. To determine the amount of the Transition Tax, the Company determined, among other things, the amount of post-1986 E&P of the relevant subsidiaries. The Company recorded a provisional Transition Tax of $0.6 million, which reduced its U.S. net deferred tax assets for the year ended December 31, 2017. For the six months ended June 30, 2018, there was no change to the provisional Transaction Tax recorded in the prior period. The SEC staff issued Staff Accounting Bulletin No. 118 (“SAB 118”) to address the application of U.S. GAAP in situations when a registrant does not have the necessary information available, prepared or analyzed in reasonable detail to complete the accounting for certain income tax effects of the Tax Act and allows the registrant to record provisional amounts during a measurement period not to extend beyond one year of the enactment date. The Company has recognized the actual impact of the revaluation of deferred tax balances and the provisional impact related to the one-time Transition Tax. The Company included these amounts in its consolidated financial statements for the year ended December 31, 2017. The ultimate impact may materially differ from these provisional amounts, due to, among other things, additional analysis, changes in interpretations and assumptions that have been made, additional regulatory guidance that may be issued, and actions that may be taken as a result of the Tax Act. The Company expects to complete its analysis within the measurement period in accordance with SAB 118. In addition, it is unclear how many U.S. states will incorporate the federal law changes, or portions thereof, into their tax codes and foreign governments may enact tax laws in response to the Tax Act that could result in further changes to global taxation and materially affect the Company's financial position and results of operations. Finally, the Tax Act imposes a new BEAT, essentially a 10% minimum tax (5% for tax years beginning after December 31, 2017, increasing to 10% for years beginning after December 31, 2018) calculated on a base equal to taxpayer’s income determined without tax benefits arising from base erosion payments. BEAT does not apply to corporations whose annual gross receipts for the three-taxable-year period ending with the preceding taxable year are less than $500 million. BEAT does not apply to the Company for the year ending December 31, 2018. Also, the Tax Act requires certain GILTI income earned by controlled foreign corporations (“CFCs”) to be included in the gross income of the CFCs’ U.S. shareholder (for tax years beginning after December 31, 2017). For the six months ended June 30, 2018, the Company has included a provisional GILTI inclusion of $1.2 million for purposes of Accounting Standards Codification Topic 740. GAAP allows the Company to either (i) treat taxes due on future U.S. inclusions in taxable income related to BEAT and GILTI as current-period expense when incurred (the “period cost method”); or (ii) factor such amounts into the measurement of deferred taxes (the “deferred method”). The Company elected the period cost method. Due to uncertainty as to the realization of benefits from the Company's domestic and certain international deferred tax assets, including net operating loss carryforwards and research and development tax credits, the Company has a full valuation allowance reserved against such assets. The Company intends to continue to maintain a full valuation allowance on the deferred tax assets until there is sufficient evidence to support the reversal of all or some portion of these allowances. There were no material changes to the Company's unrecognized tax benefits in the six months ended June 30, 2018, and the Company does not expect to have any significant changes to unrecognized tax benefits through the end of the fiscal year. Because of the Company's history of tax losses, all years remain open to tax audit. During the first quarter of 2017, the Internal Revenue Service commenced an examination of the 2015 tax year. During the second quarter of 2018, the Company received a Letter 590 from the IRS indicating that they had completed the examination and found no income tax related adjustments.

Commitments and Contingencies	6 Months Ended
Commitments and Contingencies	Jun. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Operating Leases The Company has commitments under non-cancelable operating leases for facilities, certain equipment, and its managed data center facilities. Total rental expenses were $3.3 million and $3.0 million for the three months ended June 30, 2018 and 2017, respectively, and $6.5 million and $6.3 million for the six months ended June 30, 2018 and 2017, respectively. Additionally, expenses for cloud-based services related to data centers were $1.5 million and $1.1 million for the three months ended June 30, 2018 and 2017, respectively, and $3.4 million and $2.8 million for the six months ended June 30, 2018 and 2017, respectively. As of June 30, 2018 and December 31, 2017, the Company had $2.9 million of letters of credit associated with office leases available for borrowing, on which there were no outstanding borrowings as of either date. Guarantees and Indemnification The Company’s agreements with sellers, buyers, and other third parties typically obligate it to provide indemnity and defense for losses resulting from claims of intellectual property infringement, damages to property or persons, business losses, or other liabilities. Generally, these indemnity and defense obligations relate to the Company’s own business operations, obligations, and acts or omissions. However, under some circumstances, the Company agrees to indemnify and defend contract counterparties against losses resulting from their own business operations, obligations, and acts or omissions, or the business operations, obligations, and acts or omissions of third parties. For example, because the Company’s business interposes the Company between buyers and sellers in various ways, buyers often require the Company to indemnify them against acts and omissions of sellers, and sellers often require the Company to indemnify them against acts and omissions of buyers. In addition, the Company’s agreements with sellers, buyers, and other third parties typically include provisions limiting the Company’s liability to the counterparty, and the counterparty’s liability to the Company. These limits sometimes do not apply to certain liabilities, including indemnity obligations. These indemnity and limitation of liability provisions generally survive termination or expiration of the agreements in which they appear. The Company has also entered into indemnification agreements with its directors, executive officers and certain other officers that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors, officers or employees. No material demands have been made upon the Company to provide indemnification under such agreements and there are no claims that the Company is aware of that could have a material effect on the Company’s condensed consolidated financial statements. Litigation The Company and its subsidiaries may from time to time be parties to legal or regulatory proceedings, lawsuits and other claims incident to their business activities and to the Company’s status as a public company. Such matters may include, among other things, assertions of contract breach or intellectual property infringement, claims for indemnity arising in the course of the Company’s business, regulatory investigations or enforcement proceedings, and claims by persons whose employment has been terminated. Such matters are subject to many uncertainties, and outcomes are not predictable with assurance. Consequently, management is unable to ascertain the ultimate aggregate amount of monetary liability, amounts which may be covered by insurance or recoverable from third parties, or the financial impact with respect to such matters as of June 30, 2018. However, based on management’s knowledge as of June 30, 2018, management believes that the final resolution of these matters known at such date, individually and in the aggregate, will not have a material adverse effect upon the Company’s condensed consolidated financial position, results of operations or cash flows. On March 31, 2017, Guardian News & Media Limited ("Guardian") issued proceedings (the "Complaint") against the Company in the Chancery Division of the High Court of Justice in England & Wales. The Complaint alleges that the Company underpaid Guardian for digital advertising inventory sold by Guardian through the Company's platform as a result of the fact that the Company charged fees to buyers of that inventory. Guardian claims the Company was precluded from charging buyer fees as a result of the contractual arrangements with Guardian and English agency law principles, as well as representations it allegedly made to Guardian. The Complaint claims damages including loss of revenue, interest, and costs. The Company disputes Guardian’s claims and is defending them vigorously, but the Complaint involves disputed facts and complex legal questions, and its outcome is therefore uncertain. Even if Guardian were to prevail in this action, the Company does not believe an unfavorable outcome would have a material adverse effect upon its condensed consolidated financial position, results of operations, or cash flows. Employment Contracts The Company has entered into severance agreements with certain employees and officers. The Company may be required to pay severance and accelerate the vesting of certain equity awards in the event of involuntary terminations.

Organization and Summary of Significant Accounting Policies (Policies)

6 Months Ended

Jun. 30, 2018

Accounting Policies [Abstract]

Basis of Presentation and Summary of Significant Accounting Policies

Reclassifications

Use of Estimates

Recent Accounting Pronouncements

Recently Adopted Accounting Pronouncements


•	Accounting Standards Update ("ASU") 2017-01—Business Combinations (Topic 805): Clarifying the Definition of a Business; and


•	ASU 2017-09—Compensation—Stock Compensation (Topic 718): Scope of Modification Accounting.

Recent Accounting Pronouncements

Net Income (Loss) Per Share (Tables)

6 Months Ended

Jun. 30, 2018

Earnings Per Share [Abstract]

Schedule of Earnings Per Share, Basic and Diluted

The following table presents the basic and diluted net loss per share:



	Three Months Ended						Six Months Ended
	June 30, 2018			June 30, 2017			June 30, 2018			June 30, 2017
	(in thousands, except per share data)
Basic and Diluted EPS:
Net loss	$	(17,984	)	$	(11,555	)	$	(45,800	)	$	(27,395	)
Weighted-average common shares outstanding	50,443			49,666			50,346			49,557
Weighted-average unvested restricted shares	(372		)	(883		)	(463		)	(998		)
Weighted-average common shares outstanding used to compute net loss per share	50,071			48,783			49,883			48,559
Basic and diluted net loss per share	$	(0.36	)	$	(0.24	)	$	(0.92	)	$	(0.56	)

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share



	Three Months Ended		Six Months Ended
	June 30, 2018	June 30, 2017	June 30, 2018	June 30, 2017
	(in thousands)		(in thousands)
Options to purchase common stock	18	88	27	137
Unvested restricted stock awards	301	367	244	295
Unvested restricted stock units	1,434	585	1,401	623
ESPP	36	44	49	52
Total shares excluded from net loss per share	1,789	1,084	1,721	1,107

Revenues (Tables)

6 Months Ended

Jun. 30, 2018

Revenue from Contract with Customer [Abstract]

Disaggregation of Revenue

The following table presents our revenue by channel for the three and six months ended June 30, 2018 and 2017:



	Three Months Ended								Six Months Ended
	June 30, 2018				June 30, 2017				June 30, 2018				June 30, 2017
	(in thousands, except percentages)
Channel:
Desktop	$	13,663	48	%	$	23,746	55	%	$	27,972	52	%	$	52,075	59	%
Mobile	14,985		52		19,176		45		25,552		48		36,862		41
Total	$	28,648	100	%	$	42,922	100	%	$	53,524	100	%	$	88,937	100	%

The following table presents our revenue disaggregated by geographic location, based on the location of the Company's sellers:



	Three Months Ended				Six Months Ended
	June 30, 2018		June 30, 2017		June 30, 2018		June 30, 2017
	(in thousands)				(in thousands)
United States	$	18,966	$	28,000	$	34,470	$	55,661
International	9,682		14,922		19,054		33,276
Total	$	28,648	$	42,922	$	53,524	$	88,937

Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2018

Fair Value Disclosures [Abstract]

Fair Value, Assets Measured on Recurring Basis

The table below sets forth a summary of financial instruments that are measured at fair value on a recurring basis at June 30, 2018:



	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	(in thousands)
Cash equivalents	$	14,334	$	14,334	$	—	$	—
Corporate debt securities	$	12,112	$	—	$	12,112	$	—
U.S. Treasury, government and agency debt securities	$	19,960	$	19,960	$	—	$	—

The table below sets forth a summary of financial instruments that are measured at fair value on a recurring basis at December 31, 2017:



	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	(in thousands)
Cash equivalents	$	1,807	$	210	$	1,597	$	—
Corporate debt securities	$	25,098	$	—	$	25,098	$	—
U.S. Treasury, government and agency debt securities	$	29,901	$	29,901	$	—	$	—

Other Balance Sheet Amounts (Tables)

6 Months Ended

Jun. 30, 2018

Balance Sheet Related Disclosures [Abstract]

Investments in Marketable Securities

Investments in marketable securities as of June 30, 2018 consisted of the following:



	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	(in thousands)
Available-for-sale—short-term:
U.S. Treasury, government and agency debt securities	$	19,983	$	—	$	(23	)	$	19,960
Corporate debt securities	12,112		—		—			12,112
Total	$	32,095	$	—	$	(23	)	$	32,072

Investments in marketable securities as of December 31, 2017 consisted of the following:



	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	(in thousands)
Available-for-sale—short-term:
U.S. Treasury, government and agency debt securities	$	27,426	$	—	$	(20	)	$	27,406
Corporate debt securities	25,098		—		—			25,098
Total	$	52,524	$	—	$	(20	)	$	52,504
Available-for-sale—long-term:
U.S. Treasury, government and agency debt securities	$	2,504	$	—	$	(9	)	$	2,495

Schedule of Accounts Payable and Accrued Liabilities

Accounts payable and accrued expenses included the following:



	June 30, 2018		December 31, 2017
	(in thousands)
Accounts payable—seller	$	187,332	$	203,694
Accounts payable—trade	4,663		3,764
Accrued employee-related payables	6,509		6,645
Total	$	198,504	$	214,103

Intangible Assets (Tables)

6 Months Ended

Jun. 30, 2018

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of Finite-Lived Intangible Assets

The Company’s intangible assets as of June 30, 2018 and December 31, 2017 included the following:



	June 30, 2018			December 31, 2017
	(in thousands)
Amortizable intangible assets:
Developed technology	$	16,878		$	16,878
Non-compete agreements	690			690
Trademarks	20			20
Total identifiable intangible assets, gross	17,588			17,588
Accumulated amortization—intangible assets:
Developed technology	(5,475		)	(4,062		)
Non-compete agreements	(333		)	(161		)
Trademarks	(13		)	(6		)
Total accumulated amortization—intangible assets	(5,821		)	(4,229		)
Total identifiable intangible assets, net	$	11,767		$	13,359

Schedule of Finite-Lived Intangible Assets, Future Amortization Expense

The estimated remaining amortization expense associated with the Company's intangible assets was as follows as of June 30, 2018:



Fiscal Year	Amount
	(in thousands)
Remaining 2018	$	1,593
2019	3,010
2020	2,826
2021	2,826
2022	1,512
Thereafter	—
Total	$	11,767

Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of Share-based Compensation, Stock Options, Activity

A summary of stock option activity for the six months ended June 30, 2018 is as follows:



	Shares Under Option		Weighted- Average Exercise Price		Weighted- Average Contractual Life	Aggregate Intrinsic Value
	(in thousands)					(in thousands)
Outstanding at December 31, 2017	4,363		$	8.75
Granted	658		$	1.97
Exercised	(49	)	$	0.91
Expired	(1,101	)	$	10.24
Forfeited	(49	)	$	4.54
Outstanding at June 30, 2018	3,822		$	7.30	7.14 years	$	1,470
Exercisable at June 30, 2018	2,188		$	9.80	5.81 years	$	309

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions



	Three Months Ended			Six Months Ended
	June 30, 2018	June 30, 2017		June 30, 2018		June 30, 2017
Expected term (in years)	N/A	5.7		6.1		6.0
Risk-free interest rate	N/A	1.87	%	2.66	%	2.10	%
Expected volatility	N/A	55	%	57	%	55	%
Dividend yield	N/A	—	%	—	%	—	%

Nonvested Restricted Stock Shares Activity

A summary of restricted stock activity for the six months ended June 30, 2018 is as follows:



	Number of Shares		Weighted-Average Grant Date Fair Value
	(in thousands)
Nonvested shares of restricted stock outstanding at December 31, 2017	558		$	12.60
Granted	—		$	—
Canceled	(156	)	$	13.82
Vested	(132	)	$	14.08
Nonvested shares of restricted stock outstanding at June 30, 2018	270		$	11.18

Schedule of Nonvested Restricted Stock Units Activity

A summary of restricted stock unit activity for the six months ended June 30, 2018 is as follows:



	Number of Shares		Weighted-Average Grant Date Fair Value
	(in thousands)
Nonvested restricted stock units outstanding at December 31, 2017	3,609		$	7.55
Granted	4,707		$	2.20
Canceled	(788	)	$	5.60
Vested	(830	)	$	8.02
Nonvested restricted stock units outstanding at June 30, 2018	6,698		$	3.96

Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs for all Plans

Total stock-based compensation expense recorded in the condensed consolidated statements of operations was as follows:



	Three Months Ended				Six Months Ended
	June 30, 2018		June 30, 2017		June 30, 2018		June 30, 2017
	(in thousands)				(in thousands)
Cost of revenue	$	77	$	96	$	184	$	180
Sales and marketing	1,158		974		2,343		2,409
Technology and development	623		981		1,472		2,056
General and administrative	2,402		2,628		4,759		5,337
Restructuring and other exit costs	352		624		398		1,560
Total stock-based compensation expense	$	4,612	$	5,303	$	9,156	$	11,542

Restructuring and Other Exit Costs (Tables)

6 Months Ended

Jun. 30, 2018

Restructuring and Related Activities [Abstract]

Schedule of Restructuring and Other Exit Costs

The following table summarizes restructuring and other exit cost activity for the 2018 Restructuring Events (in thousands):



Accrued restructuring and other exit costs at December 31, 2017	$	—
Restructuring and other exit costs	3,440
Cash paid for restructuring and other exit costs	(2,561		)
Non-cash stock-based compensation for restructuring and other exit costs	(398		)
Accrued restructuring and other exit costs at June 30, 2018	$	481

Net Income (Loss) Per Share (Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Basic and Diluted EPS:
Net loss	$ (17,984)	$ (11,555)	$ (45,800)	$ (27,395)
Weighted-average common shares outstanding	50,443	49,666	50,346	49,557
Weighted-average unvested restricted shares	(372)	(883)	(463)	(998)
Weighted-average common shares outstanding used to compute net loss per share	50,071	48,783	49,883	48,559
Basic and diluted net loss per share	$ (0.36)	$ (0.24)	$ (0.92)	$ (0.56)

Net Income (Loss) Per Share (Shares Excluded and Included in Calculation of Diluted Earnings Per Share) (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares excluded from net income (loss) per share (in shares)	1,789	1,084	1,721	1,107
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares excluded from net income (loss) per share (in shares)	18	88	27	137
Unvested restricted stock awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares excluded from net income (loss) per share (in shares)	301	367	244	295
Unvested restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares excluded from net income (loss) per share (in shares)	1,434	585	1,401	623
ESPP
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares excluded from net income (loss) per share (in shares)	36	44	49	52

Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
Revenues (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Revenue	$ 28,648	$ 42,922	$ 53,524	$ 88,937
Payment terms			75 days
Intent Marketing Solution
Disaggregation of Revenue [Line Items]
Revenue				$ 1,300

Revenues (Revenue Disaggregated by Geographic Location) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Revenue	$ 28,648	$ 42,922	$ 53,524	$ 88,937
United States
Disaggregation of Revenue [Line Items]
Revenue	18,966	28,000	34,470	55,661
International
Disaggregation of Revenue [Line Items]
Revenue	$ 9,682	$ 14,922	$ 19,054	$ 33,276

Revenues (Revenue Disaggregated by Sales Distribution Channel) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 28,648	$ 42,922	$ 53,524	$ 88,937
Concentration risk, percentage	100.00%	100.00%	100.00%	100.00%
Desktop
Disaggregation of Revenue [Line Items]
Revenues	$ 13,663	$ 23,746	$ 27,972	$ 52,075
Concentration risk, percentage	48.00%	55.00%	52.00%	59.00%
Mobile
Disaggregation of Revenue [Line Items]
Revenues	$ 14,985	$ 19,176	$ 25,552	$ 36,862
Concentration risk, percentage	52.00%	45.00%	48.00%	41.00%

Fair Value Measurements (Financial Instruments) (Details) - Recurring - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Cash equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 14,334	$ 1,807
Cash equivalents \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	14,334	210
Cash equivalents \| Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	1,597
Cash equivalents \| Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	12,112	25,098
Corporate debt securities \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	0	0
Corporate debt securities \| Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	12,112	25,098
Corporate debt securities \| Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	0	0
U.S. Treasury, government and agency debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	19,960	29,901
U.S. Treasury, government and agency debt securities \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	19,960	29,901
U.S. Treasury, government and agency debt securities \| Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	0	0
U.S. Treasury, government and agency debt securities \| Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	$ 0	$ 0

Fair Value Measurements (Narrative) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Cash equivalents \| Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 14,334	$ 1,807

Other Balance Sheet Amounts (Investments in Marketable Securities) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Available-for-sale—short-term
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 32,095	$ 52,524
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(23)	(20)
Fair Value	32,072	52,504
Available-for-sale—short-term \| U.S. Treasury, government and agency debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	19,983	27,426
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(23)	(20)
Fair Value	19,960	27,406
Available-for-sale—short-term \| Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	12,112	25,098
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	$ 12,112	25,098
Available-for-sale — long-term \| U.S. Treasury, government and agency debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		2,504
Gross Unrealized Gains		0
Gross Unrealized Losses		(9)
Fair Value		$ 2,495

Other Balance Sheet Amounts (Narrative) (Details) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Balance Sheet Related Disclosures [Abstract]
Weighted remaining contractual maturity		3 months 7 days
Sales of available-for-sale securities	$ 6,100,000	$ 6,086,000	$ 0
Unrealized gain (loss)	0	0
Realized gain (loss)	0	0
Restricted cash	$ 0	$ 0		$ 0	$ 100,000

Other Balance Sheet Amounts (Accounts Payable and Accrued Expenses) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Balance Sheet Related Disclosures [Abstract]
Accounts payable—seller	$ 187,332	$ 203,694
Accounts payable—trade	4,663	3,764
Accrued employee-related payables	6,509	6,645
Accounts payable and accrued expenses	$ 198,504	$ 214,103

Intangible Assets (Finite-Lived Intangible Assets) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, gross	$ 17,588	$ 17,588
Total accumulated amortization—intangible assets	(5,821)	(4,229)
Total	11,767	13,359
Developed technology
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, gross	16,878	16,878
Total accumulated amortization—intangible assets	(5,475)	(4,062)
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, gross	690	690
Total accumulated amortization—intangible assets	(333)	(161)
Trademarks
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, gross	20	20
Total accumulated amortization—intangible assets	$ (13)	$ (6)

Intangible Assets (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense of intangible assets	$ 0.8	$ 0.8	$ 1.6	$ 2.4

Intangible Assets (Finite-Lived Intangible Assets, Future Amortization Expense) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Remaining 2018	$ 1,593
2019	3,010
2020	2,826
2021	2,826
2022	1,512
Thereafter	0
Total	$ 11,767	$ 13,359

Stock-Based Compensation (Details)	3 Months Ended	6 Months Ended
Stock-Based Compensation (Details)	Jun. 30, 2018 shares	Jun. 30, 2018 shares
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Number of shares available for grant	6,094,345	6,094,345
Restricted awards
Number of Shares
Award vesting rights, percentage		25.00%
Stock Option
Number of Shares
Vesting period		4 years
Award vesting rights, percentage		25.00%
Restricted Stock Units (RSUs) \| Two Year RSUs
Number of Shares
Award vesting rights, percentage		50.00%
Number of awards granted	2,725,000

Stock-Based Compensation (Stock Options Outstanding) (Details) $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning balance (in shares) \| shares	4,363
Granted (in shares) \| shares	658
Exercised (in shares) \| shares	(49)
Expired (in shares) \| shares	(1,101)
Forfeited (in shares) \| shares	(49)
Ending balance (in shares) \| shares	3,822
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Beginning balance (usd per share) \| $ / shares	$ 8.75
Granted (usd per share) \| $ / shares	1.97
Exercised (usd per share) \| $ / shares	0.91
Expired (usd per share) \| $ / shares	10.24
Forfeited (usd per share) \| $ / shares	4.54
Ending balance (usd per share) \| $ / shares	$ 7.30
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Outstanding	7 years 1 month 21 days
Outstanding, aggregate intrinsic value \| $	$ 1,470
Exercisable (in shares) \| shares	2,188
Exercisable (usd per share) \| $ / shares	$ 9.80
Exercisable	5 years 9 months 22 days
Exercisable, aggregate intrinsic value \| $	$ 309

Stock-Based Compensation (Stock Options Narrative) (Details) - USD ($) $ / shares in Units, shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Number of Shares
Intrinsic values of options exercised			$ 70,500
Unrecognized employee stock-based compensation	$ 4,200,000		$ 4,200,000
Weighted average grant date fair value			$ 1.03
Options outstanding (in shares)	3,822		3,822		4,363
Beginning balance (usd per share)			$ 8.75
Stock-based compensation expense	$ 4,612,000	$ 5,303,000	$ 9,156,000	$ 11,542,000
Fair value of options vested in period			$ 2,100,000
Stock Option
Number of Shares
Unrecognized employee stock-based compensation, period for recognition			2 years 9 months 26 days

Stock-Based Compensation (Valuation Assumptions) (Details) - Stock Option	3 Months Ended	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Number of Shares
Expected term (in years)	5 years 8 months 12 days	6 years 28 days	6 years
Risk-free interest rate	1.87%	2.66%	2.10%
Expected volatility	55.00%	57.00%	55.00%
Dividend yield	0.00%	0.00%	0.00%

Stock-Based Compensation (Restricted Stock Activity) (Details) - Restricted Stock Awards shares in Thousands	6 Months Ended
	Jun. 30, 2018 $ / shares shares
Number of Shares
Beginning balance \| shares	558
Granted \| shares	0
Canceled \| shares	(156)
Vested \| shares	(132)
Ending balance \| shares	270
Weighted-Average Grant Date Fair Value
Beginning balance (in dollars per share) \| $ / shares	$ 12.60
Granted (in dollars per share) \| $ / shares	0.00
Canceled (in dollars per share) \| $ / shares	13.82
Vested (in dollars per share) \| $ / shares	14.08
Ending balance (in dollars per share) \| $ / shares	$ 11.18

Stock-Based Compensation (Restricted Stock Narrative) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Number of Shares
Stock-based compensation expense	$ 4,612	$ 5,303	$ 9,156	$ 11,542
Unvested restricted stock awards
Number of Shares
Granted			0
Unrecognized employee stock-based compensation	$ 900		$ 900
Unrecognized employee stock-based compensation, period for recognition			1 year 4 months 17 days
Granted (in dollars per share)			$ 0.00
Fair value of restricted stock			$ 309

Stock-Based Compensation (Restricted Stock Units Activity) (Details) - Restricted Stock Units (RSUs) shares in Thousands	6 Months Ended
	Jun. 30, 2018 $ / shares shares
Number of Shares
Beginning balance \| shares	3,609
Granted \| shares	4,707
Canceled \| shares	(788)
Vested \| shares	(830)
Ending balance \| shares	6,698
Weighted-Average Grant Date Fair Value
Beginning balance (in dollars per share) \| $ / shares	$ 7.55
Granted (in dollars per share) \| $ / shares	2.20
Canceled (in dollars per share) \| $ / shares	5.60
Vested (in dollars per share) \| $ / shares	8.02
Ending balance (in dollars per share) \| $ / shares	$ 3.96

Stock-Based Compensation (Restricted Stock Units Narrative) (Details) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($) $ / shares
Unvested restricted stock awards
Number of Shares
Unrecognized employee stock-based compensation	$ 900
Unrecognized employee stock-based compensation, period for recognition	1 year 4 months 17 days
Grant date fair value \| $ / shares	$ 0.00
Fair value of restricted stock vested	$ 309
Restricted Stock Units (RSUs)
Number of Shares
Unrecognized employee stock-based compensation	$ 22,800
Grant date fair value \| $ / shares	$ 2.20
Fair value of restricted stock vested	$ 1,800
Intrinsic value of nonvested unit	$ 19,100
Employee Service Share-Based Compensation, Non-Vested Restricted Stock Units, Compensation Cost Not Yet Recognized, Period for Recognition	2 years 7 months 6 days

Stock-Based Compensation (Employee Stock Purchase Plan Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Number of Shares
Stock-based compensation expense	$ 4,612	$ 5,303	$ 9,156	$ 11,542
2014 Employee Stock Purchase Plan \| Employee Stock
Number of Shares
Maximum employee subscription rate	10.00%		10.00%
Purchase price of common stock, percent			85.00%
Number of shares reserved	1,692,373		1,692,373

(Fair Value of Stock Options Using the Black Scholes Option Pricing Model) (Details) - Stock Option	3 Months Ended	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Number of Shares
Expected term (in years)	5 years 8 months 12 days	6 years 28 days	6 years
Risk-free interest rate (in percentage)	1.87%	2.66%	2.10%
Expected volatility (in percentage)	55.00%	57.00%	55.00%
Dividend yield (in percentage)	0.00%	0.00%	0.00%

Stock-Based Compensation (Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 4,612	$ 5,303	$ 9,156	$ 11,542
Cost of revenue
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	77	96	184	180
Sales and marketing
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	1,158	974	2,343	2,409
Technology and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	623	981	1,472	2,056
General and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	2,402	2,628	4,759	5,337
Restructuring and other exit costs
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 352	$ 624	$ 398	$ 1,560

Restructuring and Other Exit Costs - Schedule of Restructuring and Other Exit Costs (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Restructuring Reserve [Roll Forward]
Restructuring and other exit costs	$ 974	$ 1,621	$ 3,440	$ 5,959
The 2018 Restructuring Events
Restructuring Reserve [Roll Forward]
Accrued restructuring and other exit costs at December 31, 2017			0
Restructuring and other exit costs	1,000		3,440
Cash paid for restructuring and other exit costs			(2,561)
Non-cash stock-based compensation for restructuring and other exit costs			(398)
Accrued restructuring and other exit costs at June 30, 2018	$ 481		$ 481

Restructuring and Other Exit Costs - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Restructuring Cost and Reserve [Line Items]
Restructuring and other exit costs	$ 974	$ 1,621	$ 3,440	$ 5,959
The 2017 Restructuring Events
Restructuring Cost and Reserve [Line Items]
Restructuring and other exit costs		1,600		6,000
Accrued restructuring costs					$ 100
The 2018 Restructuring Events
Restructuring Cost and Reserve [Line Items]
Restructuring and other exit costs	1,000		3,440
Accrued restructuring costs	$ 481		$ 481		$ 0
Non-cash stock-based compensation \| The 2017 Restructuring Events
Restructuring Cost and Reserve [Line Items]
Restructuring and other exit costs		$ 700		$ 1,600

Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 74	$ 146	$ 149	$ 521
Provisional Transition Tax recorded due to Tax Act					$ 600
Provisional GILTI inclusion for ASC Topic 740			$ 1,200

Commitments and Contingencies (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Other Commitments [Line Items]
Rental expense	$ 3.3	$ 3.0	$ 6.5	$ 6.3
Data Centers For Cloud-Based Services
Other Commitments [Line Items]
Rental expense	1.5	$ 1.1	3.4	$ 2.8
Office Lease \| Financial Standby Letter of Credit
Other Commitments [Line Items]
Letters of credit outstanding, amount	$ 2.9		$ 2.9		$ 2.9