Rocket Fuel 10-K 14 Mar 16 2015 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2015	Feb. 29, 2016	Jun. 30, 2015
Document and Entity Information
Entity Registrant Name	Rocket Fuel Inc.
Entity Central Index Key	1,477,200
Document Type	10-K
Document Period End Date	Dec. 31, 2015
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Public Float			$ 190,023,061
Entity Common Stock, Shares Outstanding		43,627,818
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	FY

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Current Assets:
Cash and cash equivalents	$ 78,560	$ 107,056
Accounts receivable, net	124,998	135,400
Prepaid expenses	3,803	3,698
Other current assets	2,081	12,531
Total current assets	209,442	258,685
Property, equipment and software, net	82,781	89,441
Restricted cash	2,141	2,915
Intangible assets	50,919	69,299
Goodwill	0	115,412
Deferred tax assets, net	718	2,367
Other assets	1,053	1,146
Total assets	347,054	539,265
Current Liabilities:
Accounts payable	71,292	76,085
Accrued and other current liabilities	40,734	33,258
Deferred revenue	2,116	593
Current portion of capital leases	8,602	5,482
Current portion of debt	45,720	45,705
Total current liabilities	168,464	161,123
Debt - Less current portion	17,617	23,335
Capital leases—Less current portion	11,855	12,341
Deferred rent—Less current portion	14,042	26,818
Deferred tax liabilities	40	2,068
Other liabilities	1,136	814
Total liabilities	$ 213,154	$ 226,499
Commitments and contingencies (Note 12)
Stockholders’ Equity
Common stock, $0.001 par value— 1,000,000,000 authorized as of December 31, 2015 and 2014, respectively; 43,567,016 and 42,002,533 issued and outstanding as of December 31, 2015 and 2014, respectively	$ 44	$ 42
Additional paid-in capital	453,338	421,630
Accumulated other comprehensive loss	(151)	(120)
Accumulated deficit	(319,331)	(108,786)
Total stockholders’ equity	133,900	312,766
Total liabilities and stockholders’ equity	$ 347,054	$ 539,265

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2015	Dec. 31, 2013
Statement of Financial Position [Abstract]
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized	1,000,000,000	1,000,000,000
Common stock, shares issued	43,567,016	42,002,533
Common stock, shares outstanding	43,567,016	42,002,533
Preferred Stock, Shares Authorized	100,000,000	100,000,000
Preferred Stock, Shares Issued	0	0
Preferred Stock, Shares Outstanding	0	0

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statement [Abstract]
Revenue	$ 461,637	$ 408,641	$ 240,605
Costs and expenses:
Media costs	189,089	173,477	103,637
Other cost of revenue	79,867	48,586	21,883
Research and development	44,922	39,794	17,714
Sales and marketing	166,140	146,430	83,345
General and administrative	58,354	60,545	28,708
Goodwill, Impairment Loss	117,521	0	0
Restructuring Charges	7,393	0	0
Total costs and expenses	663,286	468,832	255,287
Operating loss	(201,649)	(60,191)	(14,682)
Other expense, net:
Interest expense	(4,563)	(3,092)	(917)
Other (income) expense, net	3,112	5,267	308
Change in fair value of convertible preferred stock warrant liability	0	0	(4,740)
Total other expense, net	7,675	8,359	5,965
Loss before income taxes	(209,324)	(68,550)	(20,647)
Income tax provision (benefit)	(1,221)	4,239	(285)
Net loss	$ (210,545)	$ (64,311)	$ (20,932)
Basic and diluted net loss per share attributable to common stockholders	$ (4.95)	$ (1.74)	$ (1.38)
Basic and diluted weighted-average shares used to compute net loss per share attributable to common stockholders	42,551	37,001	15,177

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Net loss	$ (210,545)	$ (64,311)	$ (20,932)
Other comprehensive loss:
Foreign currency translation adjustments	(31)	(105)	69
Comprehensive loss	$ (210,576)	$ (64,416)	$ (20,863)

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Series C1 Preferred Stock [Member]	Convertible Preferred Stock [Member]	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Balance at Dec. 31, 2012	$ 40,863		$ 60,617	$ 8	$ 3,865	$ (84)	$ (23,543)
Balance (in shares) at Dec. 31, 2012			19,478,932	8,680,041
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercises of employee stock options, net of repurchases	$ 0			$ 19	60,598
Stock Issued During Period, Shares, Restricted Stock Award, Gross	266,530
Stock Issued During Period, Value, Restricted Stock Award, Gross	$ 7,580				7,579
Issuance of common stock upon exercises of employee stock options, net of repurchases (in shares)				19,478,932
Issuance of stock, net of issuance costs	637	$ 0
Issuance of stock, net of issuance costs (in shares)		0
Stock-based compensation	103,307				103,303
Foreign currency translation adjustment	11,643					0
Net loss	(20,932)						(20,932)
Balance at Dec. 31, 2013	143,167		$ 0	$ 33	187,624	(15)	(44,475)
Balance (in shares) at Dec. 31, 2013			0	32,825,992
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercises of employee stock options, net of repurchases	4,545			$ 2	4,543
Stock Issued During Period, Shares, Conversion of Convertible Securities			0	(38,242)
Stock Issued During Period, Value, Conversion of Convertible Securities	$ (567)		$ 0	$ 0	(567)
Common Stock Issued During Period Shares Conversion of Warrants	5,253,084
Common Stock Issued During Period Value Conversion of Warrants	$ 82,421			$ 5	82,416
Issuance of common stock upon exercises of employee stock options, net of repurchases (in shares)				1,473,565
Issuance of stock, net of issuance costs	$ 115,403			$ 2	115,401
Issuance of stock, net of issuance costs (in shares)	2,000,000
Stock-based compensation	$ 25,481				25,481
Foreign currency translation adjustment	(105)					(105)
Net loss	(64,311)						(64,311)
Balance at Dec. 31, 2014	312,766			$ 42	421,630	(120)	(108,786)
Balance (in shares) at Dec. 31, 2014				42,002,533
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercises of employee stock options, net of repurchases	$ 1,145			$ 0	1,145
Issuance of common stock upon exercises of employee stock options, net of repurchases (in shares)	446,495			420,163
Issuance of common stock upon vesting of restricted stock units	$ 1			$ 1
Issuance of common stock upon exercise vesting of restricted stock units (in shares)				646,395
Shares withheld related to net share settlement of restricted stock units	(1,432)				(1,432)
Shares withheld related to net share settlement of restricted stock units (in shares)				(230,666)
Issuance of common stock in connection with employee stock purchase plan	3,580			$ 1	3,579
Issuance of common stock in connection with employee stock purchase plan (in shares)				728,591
Stock-based compensation	28,589				28,589
Foreign currency translation adjustment	(31)					(31)
Tax shortfalls, net of benefits, from stock-based award activity	(173)				(173)
Net loss	(210,545)						(210,545)
Balance at Dec. 31, 2015	$ 133,900			$ 44	$ 453,338	$ (151)	$ (319,331)
Balance (in shares) at Dec. 31, 2015				43,567,016

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
OPERATING ACTIVITIES:
Net loss	$ (210,545)	$ (64,311)	$ (20,932)
Goodwill, Impairment Loss	117,521	0	0
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	50,762	23,670	7,855
Impairment of Leasehold	6,633	0	0
Stock-based compensation	25,974	23,838	10,921
Deferred taxes	(379)	(5,418)	0
Excess tax benefit from stock-based activity	0	(278)	0
Other non-cash adjustments, net	1,499	871	1,016
Change in fair value of preferred stock warrant liability	0	0	4,740
Changes in operating assets and liabilities, net of effects of acquisition:
Accounts receivable	9,275	(25,134)	(43,803)
Prepaid expenses and other assets	9,128	(9,153)	(5,182)
Accounts payable	(4,015)	26,952	21,009
Accrued and other liabilities	269	(1,085)	14,317
Deferred rent	(3,184)	24,068	3,189
Deferred revenue	1,523	(334)	732
Net cash provided by (used in) operating activities	4,461	(6,314)	(6,138)
INVESTING ACTIVITIES:
Purchases of property, equipment and software	(11,512)	(47,865)	(14,294)
Business acquisition, net	(367)	(97,444)	0
Capitalized internal-use software development costs	(12,402)	(7,600)	(5,592)
Changes in restricted cash	689	(2,203)	0
Net cash used in investing activities	(23,592)	(155,112)	(19,886)
FINANCING ACTIVITIES:
Proceeds from the issuance of common stock in initial and follow-on public offering, net of underwriting discounts, commission and issuance costs	0	115,403	103,612
Proceeds from exercise of common stock options and common stock warrants	940	3,725	1,400
Excess tax benefit from stock-based activity	0	278	0
Proceeds from issuance of common stock from employee stock purchase plan	3,579	6,454	0
Tax withholdings related to net share settlements of restricted stock units	(1,432)	(567)	0
Repayment of capital lease obligations	(6,239)	(1,335)	0
Proceeds from debt facilities, net of debt issuance costs	(242)	44,479	46,804
Repayment of debt facilities	(6,000)	(13,578)	(26,967)
Net cash (used in) provided by financing activities	(9,394)	154,859	124,849
EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS	29	(250)	152
CHANGE IN CASH AND CASH EQUIVALENTS	(28,496)	(6,817)	98,977
CASH AND CASH EQUIVALENTS—Beginning of period	107,056	113,873	14,896
CASH AND CASH EQUIVALENTS—End of period	78,560	107,056	113,873
SUPPLEMENTAL DISCLOSURES OF OTHER CASH FLOW INFORMATION:
Cash paid for income taxes, net of refunds	1,251	1,035	492
Cash paid for interest	3,936	2,840	835
SUPPLEMENTAL DISCLOSURES OF NONCASH INVESTING AND FINANCING ACTIVITIES:
Purchases of property and equipment recorded in accounts payable and accruals	1,048	2,077	2,349
Offering costs recorded in accrued liabilities	0	0	413
Property, plant and equipment acquired under capital lease obligations	8,797	18,619	615
Vesting of early exercised options	167	742	416
Stock-based compensation capitalized in internal-use software costs	2,616	1,643	722
Issuance of common stock in connection with acquisition	0	82,421	0
Conversion of convertible preferred stock to common stock	0	0	60,617
Conversion of preferred stock warrants to common stock	$ 0	$ 0	$ 7,481

NATURE OF BUSINESS AND SUMMARY

NATURE OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
NATURE OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	NOTE 1. NATURE OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Rocket Fuel Inc. (the “Company”) is a technology company that brings the power of machine learning to the world of digital marketing, offering a Programmatic Marketing Platform designed to help marketers and their agencies connect with consumers through digital media at moments when that connection is most likely to be influential and most likely to achieve the advertiser’s objectives. The Company's technology autonomously purchases ad spots, or impressions, one at a time, on real-time advertising exchanges to create portfolios of impressions designed to optimize the goals of our advertisers, such as increased sales, heightened brand awareness and decreased cost per customer acquisition. The Company was incorporated as a Delaware corporation on March 25, 2008 and is headquartered in Redwood City, California, with offices in various cities across the United States, Europe and Australia. In September 2013, the Company completed the initial public offering of its common stock (the “IPO”) whereby 4,000,000 shares of common stock were sold by the Company and 600,000 shares of common stock were sold by selling stockholders. The public offering price of the shares sold in the offering was $29.00 per share. The Company did not receive any proceeds from the sale of shares by the selling stockholders. The total gross proceeds from the offering to the Company were $116.0 million . After deducting underwriters’ discounts and commissions and offering expenses, the aggregate net proceeds received by the Company totaled approximately $103.3 million . In February 2014, the Company completed an underwritten follow-on public offering (the “Follow-on Offering”) of its common stock in which 2,000,000 shares of common stock were sold by the Company and 3,000,000 shares of common stock were sold by selling stockholders. The public offering price of the shares sold in the offering was $61.00 per share. The Company did not receive any proceeds from the sale of shares by the selling stockholders. The total gross proceeds from the offering to the Company were $122.0 million . After deducting underwriters’ discounts and commissions and offering expenses, the aggregate net proceeds received by the Company totaled approximately $115.4 million . In September 2014, the Company acquired X Plus Two Solutions, Inc., the parent company of [x+1], a privately held programmatic marketing technology company for 5.3 million shares of common stock and $98.0 million in cash. The acquisition of [x+1] added important assets to the Company's technology solutions, principally the Data Management Platform, or DMP. Principles of Consolidation —The consolidated financial statements include the Company and its wholly-owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation. Use of Estimates —The preparation of consolidated financial statements in accordance with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities and disclosures of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reporting period. Such estimates include, but are not limited to, provisions for doubtful accounts, the amount of software development costs which should be capitalized, future taxable income, future cash flows to be derived from the Company, the useful lives of long-lived and intangible assets, and the assumptions used for purposes of determining stock-based compensation. Actual results could differ from those estimates. Foreign Currency Translation —The Company’s foreign subsidiaries record their assets, liabilities and results of operations in their local currencies, which are their functional currencies. The Company translates its subsidiaries' consolidated financial statements into U.S. dollars each reporting period for purposes of consolidation. Assets and liabilities of the Company’s foreign subsidiaries are translated at the period-end currency exchange rates, certain equity accounts are translated at historical exchange rates and revenue, expenses, gains and losses are translated at the average currency exchange rates in effect for the period. The net effect of these translation adjustments are reported in a separate component of stockholders’ equity titled accumulated other comprehensive loss. Fair Value of Financial Instruments —The Company’s financial instruments consist principally of cash equivalents, accounts receivable, accounts payable, term debt and revolving credit facilities. The fair value of the Company’s cash equivalents is determined based on quoted prices in active markets for identical assets for its money market funds. The recorded values of the Company’s accounts receivable, accounts payable and accrued and other current liabilities approximate their current fair values due to the relatively short-term nature of these accounts. The Company believes that the fair value of the capital leases, term debt and revolving credit facilities approximate their respective recorded amounts as of December 31, 2015 as the interest rates on the term debt and revolving credit facilities are variable and the rates for each are based on market interest rates after consideration of default and credit risk (using level 2 inputs). Cash and Cash Equivalents —Cash consists of cash maintained in checking and savings accounts. All highly liquid investments purchased with an original maturity date of 90 days or less at the date of purchase are considered to be cash equivalents. Cash equivalents consist of money market funds. Restricted Cash —Restricted cash as of December 31, 2015 consists of cash required to be deposited with financial institutions for security deposits for some of the Company's office lease agreements. Concentration of Credit Risk —Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash and accounts receivable. A significant portion of the Company’s cash is held at four major financial institutions that the Company's management has assessed to be of high credit quality. The Company has not experienced any losses in such accounts. The Company mitigates its credit risk with respect to accounts receivable by performing credit evaluations and monitoring agencies' and advertisers' accounts receivable balances. As of December 31, 2015 , two agency holding companies and no single advertiser accounted for 10% of more of accounts receivable. As of December 31, 2014 , two agency holding companies and no single advertiser accounted for 10% or more of accounts receivable. With respect to revenue concentration, the Company defines a customer as an advertiser that is a distinct source of revenue and is legally bound to pay for the advertising services that the Company delivers on the advertiser’s behalf. The Company counts all advertisers within a single corporate structure as one customer even in cases where multiple brands, branches or divisions of an organization enter into separate contracts with the Company. During the years ended December 31, 2015, 2014 and 2013 , no single customer represented 10% or more of revenue. The Company also monitors the percentage of revenue from advertising agencies, even though advertising agencies that act on behalf of the Company’s advertisers are not considered customers based on the definition above. If all branches and divisions within each global advertising agency were considered to be a single agency for this purpose, two agency holding companies would have been associated with 10% or more of revenue during the years ended December 31, 2015, 2014 and 2013 . Provision for Doubtful Accounts and Sales Reserves —The Company records a provision for doubtful accounts based on historical experience and a detailed assessment of the collectability of its accounts receivable. In estimating the allowance for doubtful accounts, management considers, among other factors, the aging of the accounts receivable, historical write-offs and the credit-worthiness of each customer. The Company also estimates sales returns and allowances in the same period the related revenue is recorded. These estimates are based on an analysis of credits issued for billing corrections. If circumstances change, such as higher-than-expected defaults or an unexpected material adverse change in a major customer’s ability to meet its financial obligations, the Company’s estimate of these provisions could change by a material amount. The following is a summary of activities in allowance for doubtful accounts and sales reserves for the fiscal years indicated (in thousands): Years ended December 31, Allowances Beginning Balance Charged Against Revenue Charged to Expense Write-offs, Adjustments, Net of Recovery Allowances Ending Balance 2015 $ 2,211 $ 1,252 $ 390 $ (515 ) $ 3,338 2014 1,752 796 523 (860 ) $ 2,211 2013 1,003 160 569 20 $ 1,752 Property and Equipment —Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation and amortization is computed using the straight-line method over the estimated useful lives of the related assets, or if the estimate of the useful live subsequently changes, the depreciation is accelerated. Maintenance and repairs are charged to expense as incurred, and improvements and betterments are capitalized. When assets are retired or otherwise disposed of, the cost and accumulated depreciation or amortization, as applicable, are removed from the balance sheet and any resulting gain or loss is reflected in operations in the period realized. Construction in progress primarily includes costs related to the leasehold improvements. Leasehold improvements are amortized on a straight-line basis over the term of the lease, or the useful life of the assets, whichever is shorter. Depreciation and amortization periods for the Company’s property and equipment are as follows: Asset Classification Estimated Useful Life Capitalized internal-use software costs 2–3 years Computer hardware and software 2–3 years Furniture and fixtures 5 years Internal-Use Software Development Costs —The Company incurs costs to develop software for internal use. The Company expenses all costs that relate to the planning and post implementation phases of development as research and development expense. The Company capitalizes costs when preliminary efforts are successfully completed, management has authorized and committed project funding, and it is probable that the project will be completed and will be used as intended. Costs incurred for enhancements that are expected to result in additional material functionality are capitalized. The Company capitalized $15.5 million , $9.4 million and $6.3 million for the years ended December 31, 2015, 2014 and 2013 , respectively. These capitalized amounts are included in property, equipment and software—net on the consolidated balance sheets. Amortization commences when the website or software for internal use is ready for its intended use. The amortization period utilized for capitalized software is the estimated useful life of the related asset. Impairment of Long-lived Assets —The Company periodically reviews long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset is impaired or the estimated useful life is no longer appropriate. If indicators of impairment exist and the undiscounted projected cash flows associated with an asset are less than the carrying amount of the asset, an impairment loss is recorded to write the asset down to its estimated fair value. Fair value is estimated based on discounted future cash flows. The Company incurred $6.6 million in impairment charges for leasehold improvements and certain other assets during the twelve months ended December 31, 2015 . Refer to Note 7 for details of the impairment charges for some of the Company's leasehold improvement assets. No impairment charges were recorded during the years ended December 31, 2014 and 2013. Business Combinations —The Company accounts for business combinations using the acquisition accounting method as required under the provisions of FASB ASC 805, Business Combinations, or ASC 805. The total purchase price is allocated to the assets acquired and liabilities assumed based on fair values at the date of acquisition. Goodwill as of the acquisition date is measured as the excess of consideration transferred over the net of the acquisition date fair values of the identifiable assets acquired and the liabilities assumed. Best estimates and assumptions are used in the purchase price allocation process to accurately value assets acquired and liabilities assumed at the business combination date. These estimates and assumptions are inherently uncertain and subject to refinement. As a result, during the preliminary purchase price allocation period, which may be up to one year from the business combination date, the Company may record adjustments to the assets acquired and liabilities assumed, with the corresponding adjustment to goodwill. After the preliminary purchase price allocation period, adjustments are recorded in the operating results in the period in which the adjustments were determined. The fair value assigned to identifiable intangible assets acquired is determined using the income approach which discounts expected future cash flows to present value using estimations and assumptions determined by management. The identifiable intangible assets are subject to amortization on a straight-line basis as this best approximates the benefit period related to these assets. The excess of the purchase price over the identified tangible and intangible assets, less liabilities assumed, is recorded as goodwill and primarily reflects the value of the synergies expected to be generated from combining the Company's and the acquired entity’s technology and operations. Generally, the goodwill is not deductible for income tax purposes. Goodwill —The Company performs an annual impairment test near the end of its fiscal year on December 1 and whenever events or changes in circumstances indicate that the carrying value of goodwill may not be recoverable. Since the Company operates its business in one reporting unit, the goodwill is tested for impairment at the enterprise level. Due to a stock price decline during the third quarter of 2015, the Company’s market capitalization declined to a value below the net book value of the Company’s equity, triggering the Company to conduct a goodwill impairment test. The outcome of the goodwill impairment test resulted in a non-cash impairment of goodwill of $117.5 million , which was recorded in the Consolidated Statements of Operations for the period ended September 30, 2015. Refer to Note 14 for details of the Company's goodwill impairment test. Revenue Recognition —The Company recognizes revenue when persuasive evidence of an arrangement exists, delivery has occurred or a service has been provided, customer fees are fixed or determinable, and collection is reasonably assured. Demand Side Platform—To date, the Company has generated most of its revenue by delivering digital advertisements to Internet users through various channels, including display, mobile, social and video. This aspect of its business is referred to as a demand side platform, or “DSP.” These arrangements are typically with advertising agencies on behalf of their advertiser clients and are generally evidenced by a fully-executed insertion order (“IO”) that are generally cancellable by the customer as to any unfulfilled portion without penalty. Generally, IOs describe the campaign objectives, state the number and type of advertising impressions to be delivered, the agreed upon rate for each delivered impression, and a fixed period of time for delivery. Customers are typically billed on a monthly basis for each campaign for impressions delivered during the prior month. The Company determines collectability by performing ongoing credit evaluations and monitoring its customers’ accounts receivable balances. For new customers and their agents, which may be advertising agencies or other third parties, the Company performs a credit check with an independent credit agency and may check credit references to determine creditworthiness. The Company only recognizes revenue when collection is reasonably assured. The determination of whether revenue from DSP arrangements should be reported on a gross or net basis is based on an assessment of whether the Company is acting as the principal or an agent in the transaction. In determining whether the Company acts as the principal or an agent, the Company follows the accounting guidance for principal-agent considerations. While none of the factors identified in this guidance is individually considered presumptive or determinative, the Company has concluded that it acts as a principal with respect to these arrangements because (a) the Company is the primary obligor and is responsible for (i) fulfilling the advertisement delivery, (ii) establishing the selling prices for delivery of the advertisements, (iii) selecting the media to fulfill the insertion order, and (iv) performing all billing and collection activities including retaining credit risk, and (b) the Company has the risk of fluctuating costs from its media vendors relative to fixed pricing negotiated with its customers and has discretion in selecting media vendors when fulfilling a customer’s campaign. Based on this conclusion, the Company reports revenue earned and costs incurred with respect to its full-service DSP on a gross basis. In addition to delivering internet advertising through its full-service DSP, the Company licenses a self-service version of its DSP. Based on the accounting guidance for principal-agent considerations, the Company has concluded that it acts as an agent with respect to a minority of these arrangements in cases where (i) the Company is not the primary obligor, (ii) the Company does not have inventory risk as the customer chooses the inventory to purchase on a real-time basis, (iii) the media spend of the campaign is determined by the customer through the real-time bidding process, and (iv) the amount earned by the Company is based on a percentage of the media spend of the customer’s campaign. Based on this conclusion, the Company reports revenue earned and costs incurred with respect to this type of self-service DSP arrangements on a net basis. For the majority of self-serve DSP arrangements where these principal-agent criteria are more akin to full-service DSP arrangements, revenue and costs are reported on a gross basis. On occasion, the Company has offered customer incentive programs that provide rebates after achieving a specified level of advertising spending. The Company records reductions to revenue for estimated commitments related to these customer incentive programs. For transactions involving incentives, the Company recognizes revenue net of the estimated amount to be paid by rebate, provided that the rebate amount can be reasonably and reliably estimated and the other conditions for revenue recognition have been met. The Company’s policy requires that, if rebates cannot be reliably estimated, revenue is not recognized until reliable estimates can be made or the rebate program lapses. Data Management Platform—The Company licenses the right to access its data management platform ("DMP") to agencies and advertisers for their own use. These arrangements typically run over a period of one year or more and do not provide the customer with the right or ability to take possession of the platform. Revenue from license agreements is recognized ratably over the license term and was not material in the twelve months ended December 31, 2015 . The Company also provides professional services such as implementation, training or support for its platform. Revenue is deferred until the implementation services are completed or recognized ratably over the term of the support agreement. Multiple-Element Arrangements—The Company enters into arrangements to sell advertising that includes different media placements or ad services that are delivered at the same time during the campaign period, or within close proximity of one another. The Company allocates arrangement consideration in multiple-deliverable revenue arrangements at the inception of an arrangement to all deliverables, based on the relative selling price method in accordance with the selling price hierarchy, which includes: (1) vendor-specific objective evidence (“VSOE”), if available; (2) third-party evidence (“TPE”), if VSOE is not available; and (3) best estimate of selling price (“BESP”), if neither VSOE nor TPE is available. To date, the Company has not been able to establish VSOE or selling price based on TPE for any of its advertising offerings. When it is unable to establish selling price using VSOE or TPE, the Company uses BESP in its allocation of arrangement consideration. The objective of BESP is to determine the price at which the Company would transact a sale if the service were sold on a stand-alone basis. BESP is generally used to allocate the selling price to deliverables in the Company’s multiple element arrangements. The Company determines BESP for deliverables by considering multiple factors, including, but not limited to, prices it charges for similar offerings, market conditions, competitive landscape and pricing practices. In particular, the Company reviews multiple data points to determine BESP, including price lists used by the Company’s sales team in pricing negotiations, historical average and median pricing achieved in prior contractual customer arrangements and input from the Company’s sales operation department regarding what it believes the deliverables could be sold for on a stand-alone basis. BESP is determined at an advertising unit level that is consistent with the Company’s underlying market strategy and stratified based on specific consideration of channel, geography, industry and size, as deemed necessary. The Company regularly reviews BESP. With some customers, the Company enters into arrangements for both DMP and DSP services at the same time, or within close proximity of one another. In such circumstances, each element is accounted for as a separate unit of accounting because the following criteria are met: the delivered services have value to the customer on a standalone basis as the services are sold separately; the arrangement does not provide the right to return any of the delivered services; and performance of the undelivered services is considered probable and is substantially controlled by the Company. The Company recognizes the relative fair value of advertising services as they are delivered, assuming all other revenue recognition criteria are met. The Company limits the amount of revenue reported in multiple-element arrangements to amounts that are fixed or determinable and that are not contingent on future performance or future deliverables. Deferred revenue is comprised of contractual billings in excess of recognized revenue and payments received in advance of revenue recognition. Media costs —Media costs consists primarily of cost for advertising impressions purchased from real-time advertising exchanges and other third parties. Other cost of revenue —Other cost of revenue consists primarily of third-party inventory validation and data vendor costs, data center hosting costs, depreciation and amortization expense, amortization of internal-use software development costs, personnel costs and allocated costs of the Company’s operations group, which sets up, initiates and monitors the Company’s advertising campaigns. Allocated costs include charges for facilities, office expenses, and other miscellaneous expenses. Research and Development —Research and development expenses include costs associated with the maintenance and ongoing development of the Company’s technology, including compensation and employee benefits and allocated costs associated with the Company’s engineering and research and development departments, as well as costs for contracted services and supplies. The Company reviews costs incurred in the application development stage and assesses such costs for potential capitalization. Sales and Marketing —Sales and marketing expenses consist primarily of compensation (including commissions) and employee benefits of sales and marketing personnel and related support teams, allocated costs, amortization of acquired intangible assets, certain advertising costs, travel, trade shows and marketing materials. The Company incurred advertising costs of $7.8 million , $6.0 million and $3.6 million for the years ended December 31, 2015, 2014 and 2013 , respectively. General and Administrative —General and administrative expenses include facilities costs, executive and administrative compensation and employee benefits, depreciation, professional services fees, insurance costs, bad debt and other allocated costs, such as facility-related expenses, supplies and other fixed costs. Stock-based Compensation —The Company measures compensation expense for all stock-based payment awards, including stock options granted to employees, based on the estimated fair value of the awards on the date of the grant. The fair value of each stock option granted is estimated using the Black-Scholes option pricing model. Stock-based compensation is recognized on a straight-line basis over the requisite vesting period, net of estimated forfeitures. The forfeiture rate is based on an analysis of the Company’s actual historical forfeitures. Preferred Stock Warrant Liability —Free standing warrants related to shares that are redeemable or contingently redeemable were classified as a liability on the Company’s consolidated balance sheet. The fully-vested convertible preferred stock warrants were subject to re-measurement at each balance sheet date, and any change in fair value is recognized as a component of other expense, net. As completion of the Company’s initial public offering constituted a liquidation event, the convertible preferred stock warrants were converted into common stock or warrants to purchase common stock, and the liability was reclassified to additional paid-in capital in the third quarter of 2013. Income Taxes —The Company accounts for income taxes using an asset and liability approach. Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Operating loss and tax credit carry-forwards are measured by applying currently enacted tax laws. Valuation allowances are provided when necessary to reduce net deferred tax assets to an amount that is more likely than not to be realized. The Company recognizes the tax effects of an uncertain tax position only if it is more likely than not to be sustained based solely on its technical merits as of the reporting date, and then, only in an amount more likely than not to be sustained upon review by the tax authorities. The Company considers many factors when evaluating and estimating its tax positions and tax benefits, which may require periodic adjustments and which may not accurately anticipate actual outcomes. Recently Issued and Adopted Accounting Pronouncements —Under the Jumpstart Our Business Startups Act (the "JOBS Act"), the Company qualifies as an “emerging growth company” and 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, and, therefore, will be subject to the same new or revised accounting standards as other public companies that are not “emerging growth companies.” In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Codification (“ASC”) 842 (“ASC 842”), “Leases” which replaces the existing guidance in ASC 840, Leases. The amendment is effective for the Company for fiscal years, and interim periods within those years, beginning after December 15, 2018. ASC 842 requires a dual approach for lessee accounting under which a lessee would account for leases as finance leases or operating leases. Both finance leases and operating leases will result in the lessee recognizing a right-of-use ("ROU") asset and a corresponding lease liability. For finance leases the lessee would recognize interest expense and amortization of the ROU asset and for operating leases the lessee would recognize a straight-line total lease expense. The Company is evaluating the impact of the adoption on the consolidated financial statements. In November 2015, the FASB issued Accounting Standards Update (“ASU”) No. 2015-17, Balance Sheet Classification of Deferred Taxes (“ASU 2015-17”), which simplifies the presentation of deferred income taxes by eliminating the need for entities to separate deferred income tax liabilities and assets into current and noncurrent amounts in a classified statement of financial position. This amendment is effective for the Company in the fiscal year beginning October 1, 2017. We early adopted this guidance for the current fiscal year ended December 31, 2015 retrospectively. Adoption of this guidance resulted in a reclassification of the net current deferred tax asset to net non-current deferred tax asset in the consolidated balance sheet as of December 31, 2015 for all periods presented. In September 2015, the FASB issued accounting guidance which simplifies measurement period adjustments in a business combination under ASU 2015-16. The guidance is effective for fiscal years beginning after December 15, 2015, including interim periods within those fiscal years and early adoption is permitted. The Company early adopted the guidance for the fiscal year ended December 31, 2015 . In April 2015, the FASB issued accounting guidance which clarifies the circumstances under which a cloud computing customer would account for the arrangement as a license of internal-use software under ASC 350-40. The guidance is effective for annual periods and interim periods therein beginning after December 15, 2015. The Company utilizes cloud based applications in its administration and sales functions, and is evaluating the impact from the adoption of this guidance on its consolidated financial statements. In April 2015, the FASB issued accounting guidance which requires that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability under ASU 2015-03. The guidance is effective for fiscal years beginning after December 15, 2015, including interim periods within those fiscal years and early adoption is permitted. The Company early adopted the guidance for the fiscal year ended December 31, 2015 . In August 2014, the FASB provided accounting guidance about management’s responsibility to evaluate whether there is substantial doubt about an entity’s ability to continue as a going concern and to provide related footnote disclosures under ASU 2014-15. The amendments are effective for the annual period ending after December 15, 2016, and for annual periods and interim periods thereafter. Early adoption is permitted. The Company is currently evaluating the impact of this ASU and expects no material modifications to its financial statements. In May 2014, the FASB issued accounting guidance which requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers under ASU 2014-09. The ASU will replace most existing revenue recognition guidance in U.S. GAAP when it becomes effective. In July 2015, the FASB decided to delay the effective date of ASU 2014-09 by one year allowing early adoption as of the original effective date January 1, 2017. The deferral results in the new revenue standard being effective January 1, 2018. The Company is currently evaluating the impact of this ASU on its consolidated financial position, results of operations and cash flows.

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	12 Months Ended
	Dec. 31, 2015
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	NOTE 2. FAIR VALUE MEASUREMENTS Fair value is defined as the price that would be received on the sale of an asset or paid to transfer a liability (exit price) in an orderly transaction between market participants at the measurement date. The FASB has established a fair value hierarchy that distinguishes between (1) market participant assumptions developed based on market data obtained from independent sources (observable inputs) and (2) an entity’s own assumptions about market participant assumptions developed based on the best information available in the circumstances (unobservable inputs). The fair value hierarchy consists of three broad levels, which gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1) and the lowest priority to unobservable inputs (Level 3). The three levels of the fair value hierarchy under the guidance for fair value measurement are described below: Level 1 Inputs are unadjusted quoted prices in active markets for identical assets or liabilities. Pricing inputs are based upon quoted prices in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date. For securities, the valuations are based on quoted prices of the security that are readily and regularly available in an active market, and accordingly, a significant degree of judgment is not required. As of December 31, 2015 and 2014, the Company used Level 1 assumptions for its money market funds. Level 2 Pricing inputs are based upon quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, and model-based valuation techniques for which all significant assumptions are observable in the market or can be corroborated by observable market data for substantially the full term of the assets or liabilities. As of December 31, 2015 and 2014, the Company did not have any Level 2 financial assets or liabilities. Level 3 Pricing inputs are generally unobservable for the assets or liabilities and include situations where there is little, if any, market activity for the investment. The inputs into the determination of fair value require management’s judgment or estimation of assumptions that market participants would use in pricing the assets or liabilities. The fair values are therefore determined using model-based techniques that include option pricing models, discounted cash flow models, and similar techniques. As of December 31, 2015 and 2014, the Company did not have any Level 3 financial assets or liabilities. The following tables set forth the Company’s financial instruments that were measured at fair value on a recurring basis as of December 31, 2015 and 2014 , by level within the fair value hierarchy (in thousands): December 31, 2015 Fair Value Level 1 Level 2 Level 3 Money market funds (included in cash and cash equivalents) $ 22,906 $ 22,906 $ — $ — December 31, 2014 Fair Value Level 1 Level 2 Level 3 Money market funds (included in cash and cash equivalents) $ 22,904 $ 22,904 $ — $ —

PROPERTY, EQUIPMENT AND SOFTWAR

PROPERTY, EQUIPMENT AND SOFTWARE, NET	12 Months Ended
	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
PROPERTY, EQUIPMENT AND SOFTWARE, NET	NOTE 3. PROPERTY, EQUIPMENT AND SOFTWARE, NET Property, equipment and software, net as of December 31, 2015 and 2014 , consisted of the following (in thousands): December 31, 2015 2014 Capitalized internal-use software costs $ 38,879 $ 23,385 Computer hardware and software 57,827 46,299 Furniture and fixtures 13,619 11,674 Leasehold improvements 39,956 36,811 Total 150,281 118,169 Accumulated depreciation and amortization (67,500 ) (28,728 ) Total property, equipment and software, net $ 82,781 $ 89,441 Total depreciation and amortization expense related to property, equipment and software, exclusive of the amortization of capitalized internal-use software costs, was $24.8 million , $13.1 million and $4.5 million for the years ended December 31, 2015, 2014 and 2013 , respectively. Amortization expense of the capitalized internal-use software costs was $7.6 million , $5.2 million and $3.4 million for the years ended December 31, 2015, 2014 and 2013 , respectively. The Company recorded an impairment charge of $6.6 million during the year ended December 31, 2015 for certain of its leasehold improvements in connection with its restructuring activities. Refer to Note 7 for details of the Company's restructuring plan. Refer to Note 6 for details of the Company's capital leases utilized to acquire property and equipment as of December 31, 2015 and 2014 .

BUSINESS COMBINATIONS BUSINESS

BUSINESS COMBINATIONS BUSINESS COMBINATIONS	12 Months Ended
	Dec. 31, 2015
Business Combinations [Abstract]
BUSINESS COMBINATION	NOTE 4. BUSINESS COMBINATIONS On September 5, 2014, the Company acquired X Plus Two Solutions, Inc., a Delaware corporation (“X Plus Two”), which wholly owns X Plus One Solutions, Inc, known in the industry as [x+1] ("[x+1]"). The acquisition of [x+1] expands the market opportunity and accelerated the Company’s entry into the digital marketing enterprise software-as-a-service ("SaaS") market. At closing, all outstanding shares of [x+1]'s capital stock and stock options were canceled in exchange for an aggregate of $98.0 million in cash and 5.3 million shares of the Company’s common stock. The total purchase consideration was as follows (in thousands): Purchase consideration: Cash $ 98,045 Fair value of shares of common stock transferred 82,421 Total purchase price $ 180,466 The acquisition of [x+1] was accounted for in accordance with the acquisition method of accounting for business combinations with the Company as the accounting acquirer. The Company expensed the acquisition-related transaction costs in the amount of $ 4.9 million in general and administrative expenses. The total purchase price as shown in the table above was allocated to the tangible and identifiable intangible assets acquired and liabilities assumed based on their estimated fair values as of September 5, 2014, as set forth below. The Company finalized its estimates of fair value for certain of the acquired current assets and liabilities resulting in an adjustment to goodwill of $2.1 million which was recorded during the three months ended September 30, 2015. The total purchase price was allocated as follows (in thousands): Current assets $ 29,853 Non-current assets 3,999 Current liabilities (29,354 ) Non-current liabilities (16,253 ) Net acquired tangible assets (11,755 ) Identifiable intangible assets 74,700 Goodwill 117,521 Total purchase price $ 180,466 The goodwill is primarily attributable to synergies expected to be generated from combining the Company's and [x+1]’s technology and operations. None of the goodwill recorded as part of the acquisition will be deductible for U.S. federal income tax purposes. The changes in the carrying amount of goodwill for the year ended December 31, 2015 are as follows (in thousands): Goodwill Balance as of December 31, 2013 $ — Goodwill acquired 114,871 Goodwill adjustments (1) 541 Balance as of December 31, 2014 $ 115,412 Goodwill adjustment recorded during the three months ended September 30, 2015 (1) 2,109 Goodwill impairment recorded during the three months ended September 30, 2015 (117,521 ) Balance as of September 30, 2015 and December 30, 2015 $ — (1) Pursuant to business combinations accounting guidance, goodwill adjustments, for the effect of changes to net assets acquired during the measurement period, may be recorded up to one year from the date of an acquisition. Goodwill adjustments were not significant to our previously reported operating results or financial position. The estimated useful life and carrying values of the identifiable intangible assets were as follows (in thousands): As of December 31, 2015 As of December 31, 2014 Estimated Useful Life (in years) Gross Accumulated Amortization Net Gross Accumulated Amortization Net Developed technology 3-4 $ 42,100 $ (15,295 ) $ 26,805 $ 42,100 $ (3,703 ) $ 38,397 Customer relationships 7-8 27,700 (4,573 ) 23,127 27,700 (1,107 ) 26,593 Trademarks 5 2,000 (2,000 ) — 2,000 (128 ) 1,872 Non-compete agreements 2 2,900 (1,913 ) 987 2,900 (463 ) 2,437 Total $ 74,700 (23,781 ) 50,919 $ 74,700 (5,401 ) 69,299 Amortization expense of intangible assets for the year ended December 31, 2015 was $18.4 million . The expected annual amortization expense of intangible assets as of December 31, 2015 is presented below (in thousands): Year ending December 31, Amortization 2016 $ 16,045 2017 13,695 2018 8,451 2019 3,466 2020 3,466 Thereafter 5,796 Total $ 50,919 The results of operations of [x+1] have been included in the Company's consolidated statements of operations from the acquisition date. The following unaudited pro forma combined financial information reflects the Company's results of operations for the periods indicated and assumes that the business had been acquired at the beginning of fiscal year 2014. Acquisition costs are excluded from the year ended December 31, 2014 and included in the year ended December 31, 2013. The pro forma results also include amortization associated with the acquired intangible assets and the associated tax impact on these unaudited pro forma adjustments. The tax benefit of $4.2 million that resulted from the acquisition is recorded in the year ended December 31, 2013. The pro forma results are presented for informational purposes only and are not necessarily indicative of results that would have occurred had the acquisition taken place at the beginning of the earliest period presented, or of future results (in thousands): Year ended December 31, 2014 2013 Pro forma revenue $ 468,881 $ 310,469 Pro forma revenue less media costs $ 259,029 $ 165,959 Pro forma net loss $ (78,312 ) $ (50,666 )

ACCRUED AND OTHER CURRENT LIABI

ACCRUED AND OTHER CURRENT LIABILITIES	12 Months Ended
	Dec. 31, 2015
Payables and Accruals [Abstract]
ACCRUED AND OTHER CURRENT LIABILITIES	NOTE 5. ACCRUED AND OTHER CURRENT LIABILITIES Accrued and other current liabilities as of December 31, 2015 and 2014 consisted of the following (in thousands): December 31, 2015 2014 Payroll and benefit related expenses $ 15,255 $ 16,379 Deferred rent 10,708 1,172 Other accrued expenses 14,771 15,707 Total accrued and other current liabilities $ 40,734 $ 33,258

CAPITAL LEASES

CAPITAL LEASES	12 Months Ended
	Dec. 31, 2015
Leases [Abstract]
CAPITAL LEASES	NOTE 6. CAPITAL LEASES Property, equipment and software - net at December 31, 2015 and 2014 included $27.6 million and $19.2 million , respectively, acquired under capital lease agreements, of which the majority consists of computer hardware. The remaining future minimum lease payments under these non-cancelable capital leases as of December 31, 2015 were as follows (in thousands): Year ending December 31, Future Payments 2016 $ 9,560 2017 7,817 2018 4,322 2019 370 Thereafter — Total minimum lease payments $ 22,069 Less: amount representing interest and taxes (1,612 ) Less: current portion of minimum lease payments (8,602 ) Capital lease obligations, net of current portion $ 11,855

RESTRUCTURING COSTS Restructuri

RESTRUCTURING COSTS Restructuring and Related Activities Disclosure (Notes)	12 Months Ended
	Dec. 31, 2015
Restructuring and Related Activities [Abstract]
Restructuring and Related Activities Disclosure [Text Block]	NOTE 7. RESTRUCTURING COSTS In April 2015, the Company announced a restructuring plan intended to improve its operational efficiency, which included a reduction of its workforce, and sublease or termination of certain excess leased office space, among other cost reduction measures. As of December 31, 2015 , the Company had incurred approximately $3.4 million in employee severance costs and $0.9 million in real estate broker costs associated with subleasing or termination of the excess office space in Los Angeles, San Francisco and New York. The Company also incurred $6.6 million in non-cash impairment charges for leasehold improvements and certain other assets, and released $3.5 million of deferred rent liabilities related to terminated office leases. During the twelve months ended December 31, 2015 , the Company incurred a total of $7.4 million under the restructuring plan.

DEBT

DEBT	12 Months Ended
	Dec. 31, 2015
Debt Disclosure [Abstract]
DEBT	NOTE 8. DEBT On December 31, 2014, the Company entered into a Second Amended and Restated Revolving Credit and Term Loan Agreement with certain lenders, the ("2014 Loan Facility"), which was last amended on March 10, 2016. The 2014 Loan Facility amended and restated the Company's then-existing Amended and Restated Revolving Credit and Term Loan Agreement, dated as of December 20, 2013. Through March 10, 2016, the 2014 Loan Facility provided for an $80.0 million revolving credit facility which matures on December 31, 2017, with a $12.0 million letter of credit subfacility and a $2.5 million swingline subfacility, and a $30.0 million secured term loan that matures on December 31, 2019. Revolving loans may be advanced under the revolving credit facility in amounts up to the lesser of (i) 85% of eligible accounts receivable and (ii) $80.0 million . If at any time the aggregate amounts outstanding exceed the allowable maximum advance, then the Company must make a repayment in an amount sufficient to eliminate the excess. If the aggregated cash balances on deposit with the lenders and certain other domestic financial institutions fall below $40.0 million , the lenders have the right to use future cash collections from accounts receivable directly to reduce the outstanding balance of the revolving credit facility. The Company is also obligated to prepay the term loan with proceeds from the occurrence of certain events. The Company may repay revolving loans and term loans under the 2014 Loan Facility in whole or in part at any time without premium or penalty, subject to certain conditions. As of December 31, 2015 , $24.0 million in term loans, $40.0 million under the revolving credit facility and letters of credit in the amount of $6.0 million were outstanding. On March 10, 2016, the Company amended the 2014 Loan Facility and terminated the term loan. On March 11, 2016, the then-remaining balance of the term loan was repaid and refinanced by an additional draw down on the revolving credit facility. In the amendment the minimum bank-defined EBITDA covenant and the liquidity ratio covenant were changed. The Company paid customary closing fees in connection with establishing and amending this facility, and pays customary commitment fees and letter of credit fees. Revolving loans bear interest, at the Company's option, at (i) a base rate determined pursuant to the terms of the 2014 Loan Facility, plus a spread of 1.625% to 2.125% , or (ii) a LIBOR rate determined pursuant to the terms of the Loan Facility, plus a spread of 2.625% to 3.125% . Term loans bear interest, at the Company's option, at (i) a base rate determined pursuant to the terms of the Loan Facility, plus a spread of 2.50% to 3.00% , or (ii) a LIBOR rate determined pursuant to the terms of the Loan Facility, plus a spread of 3.50% to 4.00% . In each case, the spread is based on the cash reflected on the Company’s balance sheet for the preceding fiscal quarter, plus an amount equal to the average unused portion of the revolving credit commitments during such fiscal quarter. The base rate is determined as the highest of (i) the prime rate announced by Comerica Bank, (ii) the federal funds rate plus a margin equal to 1.00% and (iii) the daily adjusted LIBOR rate plus a margin equal to 1.00% . Under certain circumstances, a default interest rate of 2.00% above the applicable interest rate will apply on all obligations during the existence of an event of default under the 2014 Loan Facility. The Company is required to maintain a minimum of $30.0 million of cash on deposit with the lenders and comply with certain financial covenants under the 2014 Loan Facility, including the following: Bank-defined EBITDA. The Company is required to maintain specified bank-defined EBITDA, which is defined for this purpose, with respect to any trailing twelve month period, as an amount equal to the sum of (i) consolidated net income (loss) in accordance with GAAP, after eliminating all extraordinary nonrecurring items of income, plus (ii) depreciation and amortization; income tax expense; total interest expense; non-cash expenses or losses; stock-based compensation expense; costs and expenses from permitted acquisitions up to certain limits; costs and expenses in connection with the 2014 Loan Facility up to certain limits; certain legal fees up to certain limits incurred through December 2015; integration costs related to the [x+1] acquisition up to certain limits incurred through December 31, 2014 and any other expenses agreed with Comerica and the lenders; less (iii) all extraordinary and non-recurring revenues and gains (including income tax benefits). Liquidity ratio. Under the Loan Facility, the ratio of (i) the sum of all cash on deposit with Comerica and certain other domestic financial institutions and the aggregate amount of all eligible accounts receivable to (ii) all indebtedness owing to the lenders under the 2014 Loan Facility must be at least 1.10 to 1.00 . In March 2016, the liquidity ratio was changed to (i) the sum of all cash and accounts receivable to (ii) the sum of all accounts payable and all indebtedness owing to the lenders under the 2014 Loan Facility. The revised ratio must be at least 1.00 to 1.00 . The terms of the 2014 Loan Facility also require the Company to comply with certain other financial and non-financial covenants. As of December 31, 2015 , the Company was in compliance with all covenants. Future principal payments of term loan as of December 31, 2015 were as follows (in thousands): Year ending December 31, Future Payments 2016 $ 6,000 2017 6,000 2018 6,000 2019 6,000 2020 — Total 24,000 Less: current portion of term loan (6,000 ) Term loan, net of current portion $ 18,000 In March 2016, the Company repaid the entire balance then outstanding under the term loan. As of December 31, 2015 , the $40.0 million balance outstanding under the revolving credit facility had a maturity date of December 31, 2017, and because the Company has the option to draw upon the facility or repay borrowed funds at any time, the balance is shown as a current liability in the accompanying consolidated balance sheets. The debt on the consolidated balance sheet are shown net of $0.7 million and $1.0 million in debt issuance costs as of December 31, 2015 and 2014, respectively. Debt of $11.1 million that was assumed with the acquisition of [x+1] and was paid in full immediately following the closing of the merger in September 2014.

STOCKHOLDERS' EQUITY

STOCKHOLDERS' EQUITY	12 Months Ended
	Dec. 31, 2015
Stockholders' Equity Note [Abstract]
STOCKHOLDERS' EQUITY	NOTE 9. STOCKHOLDERS’ EQUITY In February 2014, the Company completed an underwritten follow-on public offering of its common stock in which 2,000,000 shares of common stock were sold by the Company and 3,000,000 shares of common stock were sold by selling stockholders. The public offering price of the shares sold in the offering was $61.00 per share. The Company did not receive any proceeds from the sale of shares by the selling stockholders. The total gross proceeds from the offering to the Company were $122.0 million . After deducting underwriters’ discounts and commissions and offering expenses, the aggregate net proceeds received by the Company totaled $115.4 million . On September 5, 2014, the Company acquired X Plus Two, which wholly owns [x+1], for 5.3 million shares of the Company’s common stock and $98.0 million in cash. In addition to 1,000,000,000 shares of common stock 100,000,000 shares of undesignated preferred stock were authorized as of December 31, 2015 and 2014 of which no shares were issued or outstanding. Reserved Shares of Common Stock —The Company’s shares of capital stock reserved for issuance under the Company's equity incentive plans as of December 31, 2015 were as follows: December 31, 2015 Options outstanding 5,386,521 Restricted stock awards and units outstanding 3,604,070 Available for future stock option and restricted stock unit grants 4,751,976 Available for future employee stock purchase plan purchases 1,397,991 Total shares reserved 15,140,558 2008 Equity Incentive Plan —The 2008 Equity Incentive Plan (the “2008 Plan”) provides for the grant of incentive stock options and nonqualified stock options. The compensation committee of the Company's board of directors has the authority to approve the employees and non-employees to whom options are granted and determine the terms of each option, including (i) the number of shares of common stock subject to the option; (ii) when the option becomes exercisable; (iii) the option exercise price, which, in the case of incentive stock options, must be at least 100% of the fair market value of the common stock as of the date of grant; and (iv) the duration of the option (which, in the case of incentive stock options, may not exceed 10 years ). Options granted under the 2008 Plan generally vest over four years and expire no later than 10 years from the date of grant. The Company has terminated the 2008 Plan for future use, and no further equity awards are to be granted under the 2008 Plan. All outstanding awards under the 2008 Plan will continue to be governed by their existing terms. Under the terms of the 2008 Plan, certain employees received the right to early exercise unvested options. Upon termination of service, an employee’s unvested shares may be repurchased by the Company at the original purchase price. As of December 31, 2015 and 2014 , 13,134 and 98,787 unvested shares, respectively, were subject to repurchase. During the years ended December 31, 2015 and 2014 , the Company repurchased 18,850 and 25,625 shares of unvested stock, respectively. 2013 Equity Incentive Plan —Since its initial public offering in September 2013, the Company has made equity grants pursuant to its 2013 Equity Incentive Plan (the “2013 Plan”). The 2013 Plan permits the grant of incentive stock options to the Company’s employees and any parent and subsidiary corporations’ employees, and the grant of non-statutory stock options, restricted stock, restricted stock units, stock appreciation rights, performance units and performance shares to the Company’s employees, directors and consultants and the Company’s subsidiary corporations’ employees and consultants. A total of 5,000,000 shares of common stock were reserved for issuance upon initial adoption of the 2013 Plan. In addition, the shares to be reserved for issuance under the 2013 Plan also include shares subject to stock options or similar awards granted under the 2008 Plan that expire or terminate without having been exercised in full and shares issued pursuant to awards granted under the 2008 Plan that are forfeited to or repurchased by the Company, provided that the maximum number of shares that may be added to the 2013 Plan pursuant to this provision is 7,900,000 shares. The number of shares available for issuance under the 2013 Plan also includes an annual increase on the first day of each fiscal year equal to the least of (i) 4,000,000 shares; (ii) 5% of the outstanding shares of common stock as of the last day of the immediately preceding fiscal year; or (iii) such other amount as the Company’s board of directors may determine. Effective January 1, 2015 and 2016, 2,100,126 and 2,178,350 shares, respectively, were added to the shares reserved for issuance under the 2013 Plan according to the terms described above. The compensation committee of the board of directors has the authority to approve the employees and other service providers to whom equity awards are granted and to determine the terms of each award, subject to the terms of the 2013 Plan. The compensation committee may determine the number of shares subject to an award, except that awards to non-employee members of the board of directors are determined under the Company's Outside Director Compensation Policy. Options and stock appreciation rights granted under the 2013 Plan must have a per share exercise price equal to at least 100% of the fair market value of a shares of the Company's common stock as of the date of grant and may not expire later than 10 years from the date of grant. The following tables summarize option award activity: Number of Weighted- Weighted- Aggregate Balance at December 31, 2014 6,290,519 $ 11.18 7.8 $ 46,926 Options granted (weighted average fair value of $3.87 per share) 722,567 7.17 Options exercised (446,495) 2.21 Options forfeited (1,180,070) 17.47 Balance at December 31, 2015 5,386,521 $ 10.00 5.3 $ 1,976 Options vested and expected to vest—December 31, 2015 5,198,429 $ 9.93 5.2 $ 1,975 Options vested and exercisable—December 31, 2015 4,080,741 $ 9.18 4.3 $ 1,967 Aggregate intrinsic value represents the difference between the Company’s fair value of its common stock and the exercise price of outstanding in-the-money options. The total intrinsic value of options exercised was approximately $2.7 million , $38.1 million and $11.9 million for the years ended December 31, 2015, 2014 and 2013 , respectively. As of December 31, 2015 , unamortized stock-based compensation expense related to unvested common stock options was $8.2 million . The weighted-average period over which such stock-based compensation expense will be recognized is approximately 2.2 years. Restricted Stock Units ("RSUs") and Restricted Stock Awards ("RSAs") —A summary of RSU and RSA activity for the year ended December 31, 2015 is as follows: Number of Shares Weighted Average Grant Date Fair Value Unvested at December 31, 2014 2,515,311 $ 23.20 Granted 3,078,179 7.56 Vested and issued (646,395 ) 23.96 Canceled (1,335,237 ) 17.33 Unvested at December 31, 2015 3,611,858 $ 11.90 The total intrinsic value of RSUs and RSAs vested and issued during the year ended December 31, 2015 was approximately $3.9 million . At December 31, 2015 , unrecognized compensation expense related to the RSUs and RSAs was $29.9 million . The unrecognized compensation expense will be amortized on a straight-line basis for each individual grant through 2019. The total fair value of RSUs and RSAs vested and issued during the year ended December 31, 2015 was $3.9 million . 2016 Inducement Equity Incentive Plan —Effective March 4, 2016, the Company's board of directors adopted the 2016 Inducement Equity Incentive Plan (the “2016 Plan”) pursuant to Nasdaq Listing Rule 5635(c)(4) (the "Listing Rule"). The Listing Rule permits a company to adopt a plan without stockholder approval if each grant is made to a new employee of the company, or an employee returning to the company after a bona fide period of non-employment, and in each case was offered the grant as a material inducement for the employee to join the company. The 2016 Plan permits the grant of non-statutory stock options, restricted stock, restricted stock units, stock appreciation rights, performance units and performance shares to eligible participants. A total of 2,200,000 shares of common stock were reserved for issuance upon initial adoption of the 2016 Plan. The 2016 Plan has a term of one year from its effective date. The compensation committee of the board of directors has the authority to approve the employees to whom equity awards are granted and to determine the terms of each award, subject to the terms of the 2016 Plan. The compensation committee may determine the number of shares subject to an award. Options and stock appreciation rights granted under the 2016 Plan must have a per share exercise price equal to at least 100% of the fair market value of a shares of the Company's common stock as of the date of grant and may not expire later than 10 years from the date of grant. To date, no awards have been granted under the 2016 Plan. Employee Stock Purchase Plan —In August 2013, the Company’s board of directors adopted and the stockholders approved the Company’s 2013 Employee Stock Purchase Plan (the “ESPP”), which became effective upon adoption by the Company’s board of directors. 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. Under the ESPP as originally adopted, the offering periods generally start on the first trading day on or after June 1 and December 1 of each year and end on the first trading day on or before November 30 and May 31 approximately six months later. The administrator may, in its discretion, modify the terms of future offering periods. At the end of each offering period, employees are able to purchase shares at 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. As of December 31, 2015 , total compensation costs related to outstanding rights to purchase shares of common stock under the ESPP offering period ending on the first trading day on or before May 31, 2015, were approximately $0.7 million , which will be recognized over the offering period. Effective January 15, 2016, the compensation committee of the Company's board of directors adopted an amendment and restatement of the ESPP that will apply to offering periods beginning on and after June 1, 2016. Pursuant to the amendment, future offering periods will start on the first trading day on or after June 1 and December 1 of each year and terminate on the first trading day or before the May 31 and November 30 that occurs approximately 24 months later. Each twenty-four month offering period will generally have four purchase periods of approximately six months in length, with the first purchase period of an offering period commencing on the date the offering period commences. At the end of each purchase period, employees are able to purchase shares, subject to any plan limitations, at 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 purchase period. Offering periods may overlap. However, if the fair market value of the Company's stock has declined between the first date of an offering period and the end of a purchase period, the offering period will terminate on the purchase date that is at the end of that purchase period immediately after the purchase and participants in that offering period will automatically be re-enrolled in the immediately following offering period. Employee Stock-based Compensation —The fair value of options on the date of grant is estimated based on the Black-Scholes option-pricing model using the single-option award approach with the weighted-average assumptions set forth below. Expected term represents the period that the Company’s stock-based awards are expected to be outstanding and is determined based on the simplified method. Due to the lack of historical exercise activity for the Company, the simplified method calculates the expected term as the mid-point between the vesting date and the contractual expiration date of the award. Volatility is estimated using comparable public company volatility for similar option terms until a sufficient amount of historical information regarding the volatility of the Company's share price becomes available. The risk-free interest rate is determined using a U.S. Treasury rate for the period that coincides with the expected term. As the Company has never paid cash dividends, and at present, has no intention to pay cash dividends in the future, expected dividends are zero . Expected forfeitures are based on the Company’s historical experience. The fair value of restricted stock unit awards is the grant date closing price of the Company's common stock. The Company uses the straight-line method for expense recognition over the vesting period of the award or option. The assumptions used to value options granted to employees were as follows: Years ended December 31, 2015 2014 2013 Expected term (years) 6.3 5.5–6.3 5.3–6.6 Volatility 50.7%–58.0% 55.6%–59.5% 53.8%–64.9% Risk-free interest rate 1.44%–1.89% 1.84%–1.97% 1.04%–1.88% Dividend yield — — — The assumptions used to calculate our stock-based compensation for each stock purchase right granted under the ESPP were as follows: Years ended December 31, 2015 2014 2013 Expected term (years) 0.5 0.5–0.7 0.7 Volatility 65.0%–73.3% 66.2%–77.4% 66.2% Risk-free interest rate 0.07%–0.42% 0.06%–0.08% 0.07% Dividend yield — — — Equity compensation allocation The following table summarizes the allocation of stock-based compensation in the accompanying consolidated statements of operations (in thousands): Years ended December 31, 2015 2014 2013 Other cost of revenue $ 1,975 $ 1,758 $ 471 Research and development 7,706 5,039 2,308 Sales and marketing 9,894 10,372 4,482 General and administrative 6,399 6,361 3,581 Total $ 25,974 $ 23,530 $ 10,842

NET INCOME (LOSS) PER SHARE

NET INCOME (LOSS) PER SHARE	12 Months Ended
	Dec. 31, 2015
Earnings Per Share [Abstract]
NET INCOME (LOSS) PER SHARE	NOTE 10. NET LOSS PER SHARE The Company calculates its basic and diluted net loss per share attributable to common stockholders in conformity with the two-class method required for companies with participating securities. Under the two-class method, in periods when the Company has net income, net income attributable to common stockholders is determined by allocating undistributed earnings, calculated as net income less current period convertible preferred stock non-cumulative dividends, between common stock and convertible preferred stock. In computing diluted net income attributable to common stockholders, undistributed earnings are re-allocated to reflect the potential impact of dilutive securities. The Company’s basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding for the period. The diluted net loss per share attributable to common stockholders is computed by giving effect to all potential dilutive common stock equivalents outstanding for the period. For purposes of this calculation, convertible preferred stock, options to purchase common stock and preferred stock warrants are considered common stock equivalents but have been excluded from the calculation of diluted net loss per share attributable to common stockholders as their effect is antidilutive. Basic loss per share is calculated by dividing net loss by the weighted-average number of shares of common stock outstanding during the period, less shares subject to repurchase, and excludes any dilutive effects of employee stock-based awards and warrants. Because the Company had net losses for the years ended December 31, 2015, 2014 and 2013 , all potential shares of common stock were determined to be anti-dilutive. The following table sets forth the computation of net loss per share of common stock (in thousands, except per share amounts): Years ended December 31, 2015 2014 2013 Net loss $ (210,545 ) $ (64,311 ) $ (20,932 ) Weighted-average shares used to compute basic and diluted net loss per share 42,551 37,001 15,177 Basic and diluted net loss per share $ (4.95 ) $ (1.74 ) $ (1.38 ) The following securities were excluded from the calculation of diluted net loss per share attributable to common stockholders because their effect would have been anti-dilutive for the periods presented (in thousands): Years ended December 31, 2015 2014 2013 Employee stock options 3,616 6,291 7,409 Shares subject to repurchase 13 99 316 Restricted stock units (RSUs) and restricted stock awards (RSAs) 5,387 2,508 383 Employee stock purchase plan 157 58 58 9,173 8,956 8,166

INCOME TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2015
Income Tax Disclosure [Abstract]
INCOME TAXES	NOTE 11. INCOME TAXES The Company recorded an income tax provision of $1.2 million , an income tax benefit of $4.2 million , and an income tax provision of $0.3 million for the years ended December 31, 2015, 2014 and 2013 , respectively. The tax provision for the year ended December 31, 2015 is mainly due to foreign and state income tax expense. The tax benefit for the year ended December 31, 2014 is primarily due to a partial release of valuation allowance against the Company’s deferred tax assets as a result of net deferred tax liabilities generated from intangibles acquired from the [x+1] acquisition. The tax expense for the year ended December 31, 2013 is primarily due to foreign and state income tax expense. The following table presents domestic and foreign components of loss before income taxes for the periods presented (in thousands): Years ended December 31, 2015 2014 2013 Domestic $ (211,160 ) $ (70,438 ) $ (21,568 ) Foreign 1,836 1,888 921 Total loss before income taxes $ (209,324 ) $ (68,550 ) $ (20,647 ) The components of the income tax provision (benefit) for income taxes were as follows (in thousands): Years ended December 31, 2015 2014 2013 Current: Federal $ — $ — $ — State 9 9 (4 ) Foreign 1,778 1,159 289 Deferred: Federal 14 (4,042 ) — State (327 ) (713 ) — Foreign (253 ) (652 ) — Total provision (benefit) for income taxes $ 1,221 $ (4,239 ) $ 285 The following table presents a reconciliation of the statutory federal rate to the Company’s effective tax rate for the periods presented: Years ended December 31, 2015 2014 2013 Tax benefit at federal statutory rate 34.00 % 34.00 % 34.00 % State income taxes, net of federal effect 0.29 6.17 0.01 Foreign rate differential (0.38 ) 0.20 0.12 Goodwill Impairment (19.09 ) — — Change in valuation allowance (15.04 ) (31.94 ) (28.42 ) Meals and entertainment (0.41 ) (1.44 ) (2.07 ) Warrant liability — — (7.81 ) Research credits 0.60 2.86 2.79 Transaction costs — (2.24 ) — Other (0.55 ) (1.41 ) — Total provision (0.58 )% 6.20 % (1.38 )% Deferred income taxes reflect the net tax effects of temporary differences between the carrying amount of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. The following table presents the significant components of the Company’s deferred tax assets and liabilities for the periods presented (in thousands): December 31, 2015 2014 Deferred tax assets: Tax credit carry-forwards $ 10,183 $ 6,877 Net operating loss carry-forwards 62,269 45,281 Charitable contributions 411 323 Accrued liabilities and allowances 8,134 7,168 Stock Compensation 11,331 11,003 92,328 70,652 Deferred tax liability: Depreciation and amortization (23,732 ) (32,194 ) (23,732 ) (32,194 ) Net deferred tax assets before valuation allowance $ 68,596 $ 38,458 Valuation allowance (67,918 ) (38,159 ) Net deferred tax assets (liabilities) $ 678 $ 299 A valuation allowance is provided for net deferred tax assets where the recoverability of the assets is uncertain. The determination to provide a valuation allowance is dependent upon the assessment of whether it is more likely than not that sufficient future taxable income will be generated to utilize the deferred tax assets. Based on the weight of the available evidence, which includes the Company’s historical operating losses, lack of taxable income and the accumulated deficit, the Company provided a full valuation allowance against the U.S federal and state deferred tax assets resulting from the tax loss and credits carried forward. The valuation allowance increased by $29.8 million and $22.4 million during the years ended December 31, 2015 and 2014 , respectively. The change in valuation allowance is mainly attributable to the increase in deferred tax assets due to the current year taxable loss, deductible temporary differences and research credits. As of December 31, 2015 , the Company had $0.7 million of net deferred tax assets primarily related to deductible foreign stock compensation which it expects to realize in future foreign tax filings. The Company does not provide for federal income taxes on the undistributed earnings of its foreign subsidiaries as such earnings are determined to be reinvested indefinitely. Upon distribution of those earnings in the form of dividends or otherwise, the Company may be subject to U.S. federal and state income taxes, the determination of which is not practical as it is dependent on the amount of U.S. tax losses or other tax attributes available at the time of repatriation. As of December 31, 2015 , undistributed earnings of the Company's foreign subsidiaries amounted to $3.2 million . As of December 31, 2015 , the Company had net operating loss carry-forwards of approximately $219.5 million for federal income taxes, which expire beginning in 2020 and $76.9 million operating loss carry-forwards for state income taxes which expire beginning in 2020. Internal Revenue Code Section 382 limits the use of net operating loss and tax credit carryforwards in certain situations where changes occur in the stock ownership of a company. If the Company experiences a change of ownership, then utilization of the net operating loss and tax credit carry-forwards may be restricted. The federal and state net operating loss carryforwards include excess tax benefits from stock option exercises of $46.6 million and $5.2 million , respectively. An increase to additional paid-in capital for the excess tax benefits would not be recognized until that deduction reduces income tax payable. On December 18, 2015 the “Protecting Americans from Tax Hikes Act of 2015” was signed into law making the U.S. R&D credit permanent. Consequently, the Company recorded deferred tax assets on federal research and development credit of $2.3 million generated in 2015, which was fully offset by valuation allowance. As of December 31, 2015 , the Company had federal and California state research and development tax credits of $10.0 million and $4.7 million , respectively. If not utilized, the federal carry forwards will begin to expire in various amounts beginning in 2019. The state tax credit can be carried forward indefinitely. ASC 740-10 requires that the tax effects of a position be recognized only if it is "more likely than not" to be sustained based solely on its technical merits as of the reporting date. The Company considers many factors when evaluating and estimating its tax positions and tax benefits, which may require periodic adjustments and which may not accurately anticipate actual outcomes. The table below provides a reconciliation of the beginning and ending amount of unrecognized tax benefits (excluding interest and penalties), related to uncertain tax positions, for the years ended December 31, 2015, 2014 and 2013 (in thousands): Years ended December 31, 2015 2014 2013 Unrecognized benefit—beginning of period $ 3,464 $ 669 $ 272 Gross increases—prior year tax positions — 46 126 Gross increases—current year tax positions 1,096 2,749 271 Unrecognized benefit—end of period $ 4,560 $ 3,464 $ 669 The unrecognized tax benefits of $4.6 million as of December 31, 2015 would have no impact on the Company’s effective tax rate if recognized because the Company has fully reserved such tax benefits due to the Company’s current assessment with regard to its ability to utilize any such future tax benefits. At December 31, 2015 , the Company had no cumulative interest and penalties related to the uncertain tax positions. The Company is currently unaware of any uncertain tax positions that could result in significant additional payments, accruals, or other material deviation in this estimate over the next twelve months. The Company files income tax returns in the United States, various individual states, and certain foreign jurisdictions. As a result of net operating loss carryforwards, all of our tax years are open to federal and state examination in the United States. Tax years from 2011 are open to examination in various foreign countries.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	12 Months Ended
	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	NOTE 12. COMMITMENTS AND CONTINGENCIES Operating Leases —The Company has operating lease agreements for office space for administration, research and development and sales and marketing activities in the United States as of December 31, 2015 that expire at various dates through 2024. The Company recognizes rent expense on a straight-line basis over the lease term and records the difference between cash rent payments and the recognition of rent expense as a deferred rent liability. Rent expense was $15.6 million , $14.7 million and $4.3 million for the years ended December 31, 2015, 2014 and 2013 , respectively. Approximate remaining future minimum cash lease payments under these non-cancelable operating leases as of December 31, 2015 were as follows (in thousands): Year ending December 31, Future Payments 2016 $ 17,553 2017 14,067 2018 12,890 2019 14,241 2020 5,015 Thereafter 8,763 $ 72,529 Please refer to Note 6 for details of the Company's capital lease commitments as of December 31, 2015 . Letters of Credit Bank Guarantees and Restricted Cash —As of December 31, 2015 and 2014 , the Company had irrevocable letters of credit outstanding, with all financial institutions, in the amount of $6.3 million and $6.8 million , respectively, for facilities leases. The letters of credit have various expiration dates, with the latest being November 2022. As of December 31, 2015 , the Company had $2.1 million in cash reserved to support bank guarantees for certain office lease agreements. These amounts are classified as restricted cash on the Company's consolidated balance sheets. Indemnification Agreements —In the ordinary course of business, the Company enters into agreements providing for indemnification 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, 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 demands have been made upon the Company to provide indemnification under such agreements, and thus there are no claims that the Company is aware of that could have a material effect on the Company’s consolidated balance sheets, consolidated statements of operations, consolidated statements of comprehensive loss, or consolidated statements of cash flows. Legal Proceedings —The Company is involved from time to time in claims, proceedings, and litigation, including the following: On September 3, 2014 and September 10, 2014, respectively, two purported class actions were filed in the Northern District of California against the Company and certain of its officers and directors at the time. The actions are Shah v. Rocket Fuel Inc., et al. , Case No. 4:14-cv-03998, and Mehrotra v. Rocket Fuel Inc., et al. , Case No. 4:14-cv-04114. The underwriters in the initial public offering on September 19, 2013 (the “IPO”) and the secondary offering on February 5, 2013 (the “Secondary Offering”) were also named as defendants. These actions were consolidated and a consolidated complaint, In re Rocket Fuel Securities Litigation , was filed on February 27, 2015. The consolidated complaint alleges that the defendants made false and misleading statements about the ability of the Company's technology to detect and eliminate fraudulent web traffic, and about Rocket Fuel’s future prospects. The consolidated complaint also alleges that the Company’s registration statements and prospectuses for the IPO and the Secondary Offering contained false and misleading statements on these topics. The consolidated complaint purports to assert claims for violations of Sections 10(b) and 20(a) of the Securities Exchange Act of 1934, as amended, and SEC Rule 10b-5 (the “Exchange Act” claims), and for violations of Sections 11 and 15 of the Securities Act of 1933, as amended (the “Securities Act” claims), on behalf of those who purchased the Company’s common stock between September 20, 2013 and August 5, 2014, inclusive, as well as those who purchased stock in the IPO, and a claim for violation of Section 12(a)(2) of the Securities Act in connection with the Secondary Offering. The consolidated complaint seeks monetary damages in an unspecified amount. All defendants moved to dismiss the consolidated complaint and on December 23, 2015, the court granted in part and denied in part the defendants’ motions to dismiss. The court dismissed the Securities Act claims and all but one of the statements on which the Exchange Act claims were based. The court also dismissed all claims against the outside directors and the underwriters of the Company’s public offerings. On March 23, 2015, a purported shareholder derivative complaint for breach of fiduciary duty, waste of corporate assets, and unjust enrichment was filed in San Mateo, California Superior Court against certain of the then-current and former officers and the Company’s board of directors at that time. The action is Davydov v. George H. John , et.al, Case No. CIV 53304. This state court action has been stayed pending the resolution of the Victor Veloso v. George H. John et al. action described below. On October 6, 2015, a purported verified shareholder derivative complaint was filed in the Northern District of California. The action is Victor Veloso v. George H. John et al. , Case No. 4:15-cv-04625-PJH. Beginning in January 2016, three substantially similar related cases, Gervat v. Wootton et al. , 4:16-cv-00332-PJH, Pack v. John et al. , 4:16-cv-00608-EDL, and McCawley v. Wootton et al ., Case No. 4:16-cv-00812, also were filed in the Northern District of California on January 21, 2016, February 4, 2016 and February 18, 2016, respectively. The complaints in these related actions are based on substantially the same facts as the In re Rocket Fuel Securities Litigation, and name as defendants the Company’s board of directors at the time of filing and certain then-current and former executives. The Veloso action has been related to the In re Rocket Fuel Securities Litigation and motions to relate the other actions are pending. A motion to consolidate the four actions into the earlier-filed Veloso action will be heard by the court in March 2016. The motion is unopposed and therefore the Company expects the cases to be consolidated. On January 27, 2016, a purported shareholder derivative complaint was filed in the Delaware Court of Chancery. The action was Gee v. Wootton et al. , Case No. 11940-VCL. The plaintiff voluntarily dismissed this action on February 9, 2016. The Company intends to vigorously defend itself against these actions. The outcomes of the legal proceedings are inherently unpredictable, subject to significant uncertainties, and could be material to the Company's operating results and cash flows for a particular period. Legal fees are expensed in the period in which they are incurred.

SEGMENTS

SEGMENTS	12 Months Ended
	Dec. 31, 2015
Segment Reporting [Abstract]
SEGMENTS	NOTE 13. SEGMENTS The Company considers operating segments to be components of the Company's business for which separate financial information is available that is evaluated regularly by the Company’s chief operating decision maker in deciding how to allocate resources and in assessing performance. The chief operating decision maker for the Company is the Chief Executive Officer. The Chief Executive Officer reviews financial information presented on a consolidated basis for purposes of allocating resources and evaluating financial performance. The Company has one business activity, and there are no segment managers who are held accountable for operations, operating results or plans for levels or components below the consolidated unit level. Accordingly, the Company has determined that it has a single operating and reportable segment. The following table summarizes total revenue generated through sales personnel located in the respective locations (in thousands): Years ended December 31, 2015 2014 2013 North America $ 385,449 $ 349,289 $ 213,601 All Other Countries 76,188 59,352 27,004 Total revenue $ 461,637 $ 408,641 $ 240,605 The following table summarizes total long-lived assets in the respective locations (in thousands): December 31, 2015 2014 North America $ 77,038 $ 85,355 All Other Countries 5,743 4,086 Total long-lived assets $ 82,781 $ 89,441 With respect to revenue concentration, the Company defines a customer as an advertiser that is a distinct source of revenue and is legally bound to pay for the advertising services that the Company delivers on the advertiser’s behalf. The Company counts all advertisers within a single corporate structure as one customer even in cases where multiple brands, branches or divisions of an organization enter into separate contracts with the Company. During the years ended December 31, 2015, 2014 and 2013 , no single customer represented 10% or more of revenue. The Company also monitors the percentage of revenue from advertising agencies, even though advertising agencies that act on behalf of the Company’s advertisers are not considered customers based on the definition above. If all branches and divisions within each global advertising agency were considered to be a single agency for this purpose, two agency holding companies would have been associated with 10% or more of revenue during the years ended December 31, 2015, 2014 and 2013 .

RELATED PARTY TRANSACTIONS (Not

RELATED PARTY TRANSACTIONS (Notes)	12 Months Ended
	Dec. 31, 2015
Related Party Transactions [Abstract]
Related Party Transactions Disclosure [Text Block]	NOTE 15. RELATED PARTY TRANSACTIONS John J. Lewis, Global President of Nielsen Holding Plc ("Nielsen"), joined the Board of Directors of Rocket Fuel Inc. after the end of fiscal year 2015 on January 19, 2016. Mr. Lewis was also appointed to the Audit Committee of the Board. Nielsen is one of the Company's data vendors. Total expense recognized for services delivered by Nielsen and its affiliates in fiscal year 2015 was $5.4 million . Total accounts payable as of December 31, 2015 were $1.2 million .

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	12 Months Ended
	Dec. 31, 2015
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	NOTE 16. SUBSEQUENT EVENTS On March 10, 2016, the Company entered into an amendment to its 2014 Loan Facility that changed the minimum bank-defined EBITDA (see Note 8 for definition) covenant and the liquidity ratio covenant. The Company also terminated the term loan. On March 11, 2016, the then remaining balance of the term loan was repaid and refinanced by an additional draw down on the revolving credit facility. See Note 8 for details about the 2014 Loan Facility and the recent amendment. Effective March 4, 2016, the Company's board of directors adopted the 2016 Inducement Equity Incentive Plan (the "2016 Plan") pursuant to Nasdaq Listing Rule 5635(c)(4), which permits a company to adopt a plan without stockholder approval if each grant is made to a new employee of the company or an employee returning after a bona fide period of non-employment, in each case if the grant was offered as a material inducement for the employee to join the company. See Note 9 for more details about the 2016 Plan. The compensation committee of the Company's board of directors adopted an amendment and restatement to the 2013 Employee Stock Purchase Plan ("ESPP") that will apply to offering periods beginning on June 1, 2016 and after. Pursuant to the amendment, future offering periods will start on the first trading day on or after June 1 and December 1 of each year and terminate on or before the May 31 and November 30 that occurs approximately 24 months later, rather than approximately six months later. See Note 9 for more details about this amendment to the ESPP.

NATURE OF BUSINESS AND SUMMAR23

NATURE OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Principles of Consolidation	Principles of Consolidation —The consolidated financial statements include the Company and its wholly-owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation.
Use of Estimates	Use of Estimates —The preparation of consolidated financial statements in accordance with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities and disclosures of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reporting period. Such estimates include, but are not limited to, provisions for doubtful accounts, the amount of software development costs which should be capitalized, future taxable income, future cash flows to be derived from the Company, the useful lives of long-lived and intangible assets, and the assumptions used for purposes of determining stock-based compensation. Actual results could differ from those estimates.
Foreign Currency Translation	Foreign Currency Translation —The Company’s foreign subsidiaries record their assets, liabilities and results of operations in their local currencies, which are their functional currencies. The Company translates its subsidiaries' consolidated financial statements into U.S. dollars each reporting period for purposes of consolidation. Assets and liabilities of the Company’s foreign subsidiaries are translated at the period-end currency exchange rates, certain equity accounts are translated at historical exchange rates and revenue, expenses, gains and losses are translated at the average currency exchange rates in effect for the period. The net effect of these translation adjustments are reported in a separate component of stockholders’ equity titled accumulated other comprehensive loss.
Fair Value of Financial Instruments	Fair Value of Financial Instruments —The Company’s financial instruments consist principally of cash equivalents, accounts receivable, accounts payable, term debt and revolving credit facilities. The fair value of the Company’s cash equivalents is determined based on quoted prices in active markets for identical assets for its money market funds. The recorded values of the Company’s accounts receivable, accounts payable and accrued and other current liabilities approximate their current fair values due to the relatively short-term nature of these accounts. The Company believes that the fair value of the capital leases, term debt and revolving credit facilities approximate their respective recorded amounts as of December 31, 2015 as the interest rates on the term debt and revolving credit facilities are variable and the rates for each are based on market interest rates after consideration of default and credit risk (using level 2 inputs).
Cash and Cash Equivalents & Restricted Cash	Cash and Cash Equivalents —Cash consists of cash maintained in checking and savings accounts. All highly liquid investments purchased with an original maturity date of 90 days or less at the date of purchase are considered to be cash equivalents. Cash equivalents consist of money market funds. Restricted Cash —Restricted cash as of December 31, 2015 consists of cash required to be deposited with financial institutions for security deposits for some of the Company's office lease agreements.
Concentration of Credit Risk	Concentration of Credit Risk —Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash and accounts receivable. A significant portion of the Company’s cash is held at four major financial institutions that the Company's management has assessed to be of high credit quality. The Company has not experienced any losses in such accounts. The Company mitigates its credit risk with respect to accounts receivable by performing credit evaluations and monitoring agencies' and advertisers' accounts receivable balances. As of December 31, 2015 , two agency holding companies and no single advertiser accounted for 10% of more of accounts receivable. As of December 31, 2014 , two agency holding companies and no single advertiser accounted for 10% or more of accounts receivable. With respect to revenue concentration, the Company defines a customer as an advertiser that is a distinct source of revenue and is legally bound to pay for the advertising services that the Company delivers on the advertiser’s behalf. The Company counts all advertisers within a single corporate structure as one customer even in cases where multiple brands, branches or divisions of an organization enter into separate contracts with the Company. During the years ended December 31, 2015, 2014 and 2013 , no single customer represented 10% or more of revenue. The Company also monitors the percentage of revenue from advertising agencies, even though advertising agencies that act on behalf of the Company’s advertisers are not considered customers based on the definition above. If all branches and divisions within each global advertising agency were considered to be a single agency for this purpose, two agency holding companies would have been associated with 10% or more of revenue during the years ended December 31, 2015, 2014 and 2013 .
Provision for Doubtful Accounts	Provision for Doubtful Accounts and Sales Reserves —The Company records a provision for doubtful accounts based on historical experience and a detailed assessment of the collectability of its accounts receivable. In estimating the allowance for doubtful accounts, management considers, among other factors, the aging of the accounts receivable, historical write-offs and the credit-worthiness of each customer. The Company also estimates sales returns and allowances in the same period the related revenue is recorded. These estimates are based on an analysis of credits issued for billing corrections. If circumstances change, such as higher-than-expected defaults or an unexpected material adverse change in a major customer’s ability to meet its financial obligations, the Company’s estimate of these provisions could change by a material amount.
Property and Equipment	Property and Equipment —Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation and amortization is computed using the straight-line method over the estimated useful lives of the related assets, or if the estimate of the useful live subsequently changes, the depreciation is accelerated. Maintenance and repairs are charged to expense as incurred, and improvements and betterments are capitalized. When assets are retired or otherwise disposed of, the cost and accumulated depreciation or amortization, as applicable, are removed from the balance sheet and any resulting gain or loss is reflected in operations in the period realized. Construction in progress primarily includes costs related to the leasehold improvements. Leasehold improvements are amortized on a straight-line basis over the term of the lease, or the useful life of the assets, whichever is shorter. Depreciation and amortization periods for the Company’s property and equipment are as follows: Asset Classification Estimated Useful Life Capitalized internal-use software costs 2–3 years Computer hardware and software 2–3 years Furniture and fixtures 5 years
Internal Use Software Development Costs	Internal-Use Software Development Costs —The Company incurs costs to develop software for internal use. The Company expenses all costs that relate to the planning and post implementation phases of development as research and development expense. The Company capitalizes costs when preliminary efforts are successfully completed, management has authorized and committed project funding, and it is probable that the project will be completed and will be used as intended. Costs incurred for enhancements that are expected to result in additional material functionality are capitalized. The Company capitalized $15.5 million , $9.4 million and $6.3 million for the years ended December 31, 2015, 2014 and 2013 , respectively. These capitalized amounts are included in property, equipment and software—net on the consolidated balance sheets. Amortization commences when the website or software for internal use is ready for its intended use. The amortization period utilized for capitalized software is the estimated useful life of the related asset.
Impairment of Long-lived Asset	Impairment of Long-lived Assets —The Company periodically reviews long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset is impaired or the estimated useful life is no longer appropriate. If indicators of impairment exist and the undiscounted projected cash flows associated with an asset are less than the carrying amount of the asset, an impairment loss is recorded to write the asset down to its estimated fair value. Fair value is estimated based on discounted future cash flows. The Company incurred $6.6 million in impairment charges for leasehold improvements and certain other assets during the twelve months ended December 31, 2015 . Refer to Note 7 for details of the impairment charges for some of the Company's leasehold improvement assets. No impairment charges were recorded during the years ended December 31, 2014 and 2013.
Business Combinations	Business Combinations —The Company accounts for business combinations using the acquisition accounting method as required under the provisions of FASB ASC 805, Business Combinations, or ASC 805. The total purchase price is allocated to the assets acquired and liabilities assumed based on fair values at the date of acquisition. Goodwill as of the acquisition date is measured as the excess of consideration transferred over the net of the acquisition date fair values of the identifiable assets acquired and the liabilities assumed. Best estimates and assumptions are used in the purchase price allocation process to accurately value assets acquired and liabilities assumed at the business combination date. These estimates and assumptions are inherently uncertain and subject to refinement. As a result, during the preliminary purchase price allocation period, which may be up to one year from the business combination date, the Company may record adjustments to the assets acquired and liabilities assumed, with the corresponding adjustment to goodwill. After the preliminary purchase price allocation period, adjustments are recorded in the operating results in the period in which the adjustments were determined. The fair value assigned to identifiable intangible assets acquired is determined using the income approach which discounts expected future cash flows to present value using estimations and assumptions determined by management. The identifiable intangible assets are subject to amortization on a straight-line basis as this best approximates the benefit period related to these assets. The excess of the purchase price over the identified tangible and intangible assets, less liabilities assumed, is recorded as goodwill and primarily reflects the value of the synergies expected to be generated from combining the Company's and the acquired entity’s technology and operations. Generally, the goodwill is not deductible for income tax purposes.
Goodwill	Goodwill —The Company performs an annual impairment test near the end of its fiscal year on December 1 and whenever events or changes in circumstances indicate that the carrying value of goodwill may not be recoverable. Since the Company operates its business in one reporting unit, the goodwill is tested for impairment at the enterprise level. Due to a stock price decline during the third quarter of 2015, the Company’s market capitalization declined to a value below the net book value of the Company’s equity, triggering the Company to conduct a goodwill impairment test. The outcome of the goodwill impairment test resulted in a non-cash impairment of goodwill of $117.5 million , which was recorded in the Consolidated Statements of Operations for the period ended September 30, 2015. Refer to Note 14 for details of the Company's goodwill impairment test.
Revenue Recognition	Revenue Recognition —The Company recognizes revenue when persuasive evidence of an arrangement exists, delivery has occurred or a service has been provided, customer fees are fixed or determinable, and collection is reasonably assured. Demand Side Platform—To date, the Company has generated most of its revenue by delivering digital advertisements to Internet users through various channels, including display, mobile, social and video. This aspect of its business is referred to as a demand side platform, or “DSP.” These arrangements are typically with advertising agencies on behalf of their advertiser clients and are generally evidenced by a fully-executed insertion order (“IO”) that are generally cancellable by the customer as to any unfulfilled portion without penalty. Generally, IOs describe the campaign objectives, state the number and type of advertising impressions to be delivered, the agreed upon rate for each delivered impression, and a fixed period of time for delivery. Customers are typically billed on a monthly basis for each campaign for impressions delivered during the prior month. The Company determines collectability by performing ongoing credit evaluations and monitoring its customers’ accounts receivable balances. For new customers and their agents, which may be advertising agencies or other third parties, the Company performs a credit check with an independent credit agency and may check credit references to determine creditworthiness. The Company only recognizes revenue when collection is reasonably assured. The determination of whether revenue from DSP arrangements should be reported on a gross or net basis is based on an assessment of whether the Company is acting as the principal or an agent in the transaction. In determining whether the Company acts as the principal or an agent, the Company follows the accounting guidance for principal-agent considerations. While none of the factors identified in this guidance is individually considered presumptive or determinative, the Company has concluded that it acts as a principal with respect to these arrangements because (a) the Company is the primary obligor and is responsible for (i) fulfilling the advertisement delivery, (ii) establishing the selling prices for delivery of the advertisements, (iii) selecting the media to fulfill the insertion order, and (iv) performing all billing and collection activities including retaining credit risk, and (b) the Company has the risk of fluctuating costs from its media vendors relative to fixed pricing negotiated with its customers and has discretion in selecting media vendors when fulfilling a customer’s campaign. Based on this conclusion, the Company reports revenue earned and costs incurred with respect to its full-service DSP on a gross basis. In addition to delivering internet advertising through its full-service DSP, the Company licenses a self-service version of its DSP. Based on the accounting guidance for principal-agent considerations, the Company has concluded that it acts as an agent with respect to a minority of these arrangements in cases where (i) the Company is not the primary obligor, (ii) the Company does not have inventory risk as the customer chooses the inventory to purchase on a real-time basis, (iii) the media spend of the campaign is determined by the customer through the real-time bidding process, and (iv) the amount earned by the Company is based on a percentage of the media spend of the customer’s campaign. Based on this conclusion, the Company reports revenue earned and costs incurred with respect to this type of self-service DSP arrangements on a net basis. For the majority of self-serve DSP arrangements where these principal-agent criteria are more akin to full-service DSP arrangements, revenue and costs are reported on a gross basis. On occasion, the Company has offered customer incentive programs that provide rebates after achieving a specified level of advertising spending. The Company records reductions to revenue for estimated commitments related to these customer incentive programs. For transactions involving incentives, the Company recognizes revenue net of the estimated amount to be paid by rebate, provided that the rebate amount can be reasonably and reliably estimated and the other conditions for revenue recognition have been met. The Company’s policy requires that, if rebates cannot be reliably estimated, revenue is not recognized until reliable estimates can be made or the rebate program lapses. Data Management Platform—The Company licenses the right to access its data management platform ("DMP") to agencies and advertisers for their own use. These arrangements typically run over a period of one year or more and do not provide the customer with the right or ability to take possession of the platform. Revenue from license agreements is recognized ratably over the license term and was not material in the twelve months ended December 31, 2015 . The Company also provides professional services such as implementation, training or support for its platform. Revenue is deferred until the implementation services are completed or recognized ratably over the term of the support agreement. Multiple-Element Arrangements—The Company enters into arrangements to sell advertising that includes different media placements or ad services that are delivered at the same time during the campaign period, or within close proximity of one another. The Company allocates arrangement consideration in multiple-deliverable revenue arrangements at the inception of an arrangement to all deliverables, based on the relative selling price method in accordance with the selling price hierarchy, which includes: (1) vendor-specific objective evidence (“VSOE”), if available; (2) third-party evidence (“TPE”), if VSOE is not available; and (3) best estimate of selling price (“BESP”), if neither VSOE nor TPE is available. To date, the Company has not been able to establish VSOE or selling price based on TPE for any of its advertising offerings. When it is unable to establish selling price using VSOE or TPE, the Company uses BESP in its allocation of arrangement consideration. The objective of BESP is to determine the price at which the Company would transact a sale if the service were sold on a stand-alone basis. BESP is generally used to allocate the selling price to deliverables in the Company’s multiple element arrangements. The Company determines BESP for deliverables by considering multiple factors, including, but not limited to, prices it charges for similar offerings, market conditions, competitive landscape and pricing practices. In particular, the Company reviews multiple data points to determine BESP, including price lists used by the Company’s sales team in pricing negotiations, historical average and median pricing achieved in prior contractual customer arrangements and input from the Company’s sales operation department regarding what it believes the deliverables could be sold for on a stand-alone basis. BESP is determined at an advertising unit level that is consistent with the Company’s underlying market strategy and stratified based on specific consideration of channel, geography, industry and size, as deemed necessary. The Company regularly reviews BESP. With some customers, the Company enters into arrangements for both DMP and DSP services at the same time, or within close proximity of one another. In such circumstances, each element is accounted for as a separate unit of accounting because the following criteria are met: the delivered services have value to the customer on a standalone basis as the services are sold separately; the arrangement does not provide the right to return any of the delivered services; and performance of the undelivered services is considered probable and is substantially controlled by the Company. The Company recognizes the relative fair value of advertising services as they are delivered, assuming all other revenue recognition criteria are met. The Company limits the amount of revenue reported in multiple-element arrangements to amounts that are fixed or determinable and that are not contingent on future performance or future deliverables. Deferred revenue is comprised of contractual billings in excess of recognized revenue and payments received in advance of revenue recognition.
Multiple-Element Arrangements	Multiple-Element Arrangements—The Company enters into arrangements to sell advertising that includes different media placements or ad services that are delivered at the same time during the campaign period, or within close proximity of one another. The Company allocates arrangement consideration in multiple-deliverable revenue arrangements at the inception of an arrangement to all deliverables, based on the relative selling price method in accordance with the selling price hierarchy, which includes: (1) vendor-specific objective evidence (“VSOE”), if available; (2) third-party evidence (“TPE”), if VSOE is not available; and (3) best estimate of selling price (“BESP”), if neither VSOE nor TPE is available. To date, the Company has not been able to establish VSOE or selling price based on TPE for any of its advertising offerings. When it is unable to establish selling price using VSOE or TPE, the Company uses BESP in its allocation of arrangement consideration. The objective of BESP is to determine the price at which the Company would transact a sale if the service were sold on a stand-alone basis. BESP is generally used to allocate the selling price to deliverables in the Company’s multiple element arrangements. The Company determines BESP for deliverables by considering multiple factors, including, but not limited to, prices it charges for similar offerings, market conditions, competitive landscape and pricing practices. In particular, the Company reviews multiple data points to determine BESP, including price lists used by the Company’s sales team in pricing negotiations, historical average and median pricing achieved in prior contractual customer arrangements and input from the Company’s sales operation department regarding what it believes the deliverables could be sold for on a stand-alone basis. BESP is determined at an advertising unit level that is consistent with the Company’s underlying market strategy and stratified based on specific consideration of channel, geography, industry and size, as deemed necessary. The Company regularly reviews BESP. With some customers, the Company enters into arrangements for both DMP and DSP services at the same time, or within close proximity of one another. In such circumstances, each element is accounted for as a separate unit of accounting because the following criteria are met: the delivered services have value to the customer on a standalone basis as the services are sold separately; the arrangement does not provide the right to return any of the delivered services; and performance of the undelivered services is considered probable and is substantially controlled by the Company. The Company recognizes the relative fair value of advertising services as they are delivered, assuming all other revenue recognition criteria are met. The Company limits the amount of revenue reported in multiple-element arrangements to amounts that are fixed or determinable and that are not contingent on future performance or future deliverables.
Cost of Revenue	costs —Media costs consists primarily of cost for advertising impressions purchased from real-time advertising exchanges and other third parties.
Research and Development	Research and Development —Research and development expenses include costs associated with the maintenance and ongoing development of the Company’s technology, including compensation and employee benefits and allocated costs associated with the Company’s engineering and research and development departments, as well as costs for contracted services and supplies. The Company reviews costs incurred in the application development stage and assesses such costs for potential capitalization.
Sales and Marketing	Sales and Marketing —Sales and marketing expenses consist primarily of compensation (including commissions) and employee benefits of sales and marketing personnel and related support teams, allocated costs, amortization of acquired intangible assets, certain advertising costs, travel, trade shows and marketing materials. The Company incurred advertising costs of $7.8 million , $6.0 million and $3.6 million for the years ended December 31, 2015, 2014 and 2013 , respectively.
General and Administrative	General and Administrative —General and administrative expenses include facilities costs, executive and administrative compensation and employee benefits, depreciation, professional services fees, insurance costs, bad debt and other allocated costs, such as facility-related expenses, supplies and other fixed costs.
Stock-Based Compensation	Stock-based Compensation —The Company measures compensation expense for all stock-based payment awards, including stock options granted to employees, based on the estimated fair value of the awards on the date of the grant. The fair value of each stock option granted is estimated using the Black-Scholes option pricing model. Stock-based compensation is recognized on a straight-line basis over the requisite vesting period, net of estimated forfeitures. The forfeiture rate is based on an analysis of the Company’s actual historical forfeitures.
Preferred Stock Warrant Liability	Preferred Stock Warrant Liability —Free standing warrants related to shares that are redeemable or contingently redeemable were classified as a liability on the Company’s consolidated balance sheet. The fully-vested convertible preferred stock warrants were subject to re-measurement at each balance sheet date, and any change in fair value is recognized as a component of other expense, net. As completion of the Company’s initial public offering constituted a liquidation event, the convertible preferred stock warrants were converted into common stock or warrants to purchase common stock, and the liability was reclassified to additional paid-in capital in the third quarter of 2013.
Income Taxes	Income Taxes —The Company accounts for income taxes using an asset and liability approach. Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Operating loss and tax credit carry-forwards are measured by applying currently enacted tax laws. Valuation allowances are provided when necessary to reduce net deferred tax assets to an amount that is more likely than not to be realized. The Company recognizes the tax effects of an uncertain tax position only if it is more likely than not to be sustained based solely on its technical merits as of the reporting date, and then, only in an amount more likely than not to be sustained upon review by the tax authorities. The Company considers many factors when evaluating and estimating its tax positions and tax benefits, which may require periodic adjustments and which may not accurately anticipate actual outcomes.
Recently Issued and Adopted Accounting Pronouncements	Recently Issued and Adopted Accounting Pronouncements —Under the Jumpstart Our Business Startups Act (the "JOBS Act"), the Company qualifies as an “emerging growth company” and 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, and, therefore, will be subject to the same new or revised accounting standards as other public companies that are not “emerging growth companies.” In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Codification (“ASC”) 842 (“ASC 842”), “Leases” which replaces the existing guidance in ASC 840, Leases. The amendment is effective for the Company for fiscal years, and interim periods within those years, beginning after December 15, 2018. ASC 842 requires a dual approach for lessee accounting under which a lessee would account for leases as finance leases or operating leases. Both finance leases and operating leases will result in the lessee recognizing a right-of-use ("ROU") asset and a corresponding lease liability. For finance leases the lessee would recognize interest expense and amortization of the ROU asset and for operating leases the lessee would recognize a straight-line total lease expense. The Company is evaluating the impact of the adoption on the consolidated financial statements. In November 2015, the FASB issued Accounting Standards Update (“ASU”) No. 2015-17, Balance Sheet Classification of Deferred Taxes (“ASU 2015-17”), which simplifies the presentation of deferred income taxes by eliminating the need for entities to separate deferred income tax liabilities and assets into current and noncurrent amounts in a classified statement of financial position. This amendment is effective for the Company in the fiscal year beginning October 1, 2017. We early adopted this guidance for the current fiscal year ended December 31, 2015 retrospectively. Adoption of this guidance resulted in a reclassification of the net current deferred tax asset to net non-current deferred tax asset in the consolidated balance sheet as of December 31, 2015 for all periods presented. In September 2015, the FASB issued accounting guidance which simplifies measurement period adjustments in a business combination under ASU 2015-16. The guidance is effective for fiscal years beginning after December 15, 2015, including interim periods within those fiscal years and early adoption is permitted. The Company early adopted the guidance for the fiscal year ended December 31, 2015 . In April 2015, the FASB issued accounting guidance which clarifies the circumstances under which a cloud computing customer would account for the arrangement as a license of internal-use software under ASC 350-40. The guidance is effective for annual periods and interim periods therein beginning after December 15, 2015. The Company utilizes cloud based applications in its administration and sales functions, and is evaluating the impact from the adoption of this guidance on its consolidated financial statements. In April 2015, the FASB issued accounting guidance which requires that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability under ASU 2015-03. The guidance is effective for fiscal years beginning after December 15, 2015, including interim periods within those fiscal years and early adoption is permitted. The Company early adopted the guidance for the fiscal year ended December 31, 2015 . In August 2014, the FASB provided accounting guidance about management’s responsibility to evaluate whether there is substantial doubt about an entity’s ability to continue as a going concern and to provide related footnote disclosures under ASU 2014-15. The amendments are effective for the annual period ending after December 15, 2016, and for annual periods and interim periods thereafter. Early adoption is permitted. The Company is currently evaluating the impact of this ASU and expects no material modifications to its financial statements. In May 2014, the FASB issued accounting guidance which requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers under ASU 2014-09. The ASU will replace most existing revenue recognition guidance in U.S. GAAP when it becomes effective. In July 2015, the FASB decided to delay the effective date of ASU 2014-09 by one year allowing early adoption as of the original effective date January 1, 2017. The deferral results in the new revenue standard being effective January 1, 2018. The Company is currently evaluating the impact of this ASU on its consolidated financial position, results of operations and cash flows.

NATURE OF BUSINESS AND SUMMAR24

NATURE OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	12 Months Ended
	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of changes in the allowance for doubtful accounts	The following is a summary of activities in allowance for doubtful accounts and sales reserves for the fiscal years indicated (in thousands): Years ended December 31, Allowances Beginning Balance Charged Against Revenue Charged to Expense Write-offs, Adjustments, Net of Recovery Allowances Ending Balance 2015 $ 2,211 $ 1,252 $ 390 $ (515 ) $ 3,338 2014 1,752 796 523 (860 ) $ 2,211 2013 1,003 160 569 20 $ 1,752
Schedule of depreciation and amortization periods for the Company's property and equipment	Depreciation and amortization periods for the Company’s property and equipment are as follows: Asset Classification Estimated Useful Life Capitalized internal-use software costs 2–3 years Computer hardware and software 2–3 years Furniture and fixtures 5 years

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	12 Months Ended
	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Schedule of Company's fair value hierarchy for its financial assets and financial liabilities that are carried at fair value	The following tables set forth the Company’s financial instruments that were measured at fair value on a recurring basis as of December 31, 2015 and 2014 , by level within the fair value hierarchy (in thousands): December 31, 2015 Fair Value Level 1 Level 2 Level 3 Money market funds (included in cash and cash equivalents) $ 22,906 $ 22,906 $ — $ — December 31, 2014 Fair Value Level 1 Level 2 Level 3 Money market funds (included in cash and cash equivalents) $ 22,904 $ 22,904 $ — $ —

PROPERTY, EQUIPMENT AND SOFTW26

PROPERTY, EQUIPMENT AND SOFTWARE, NET (Tables)	12 Months Ended
	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Schedule of property, equipment and software	Property, equipment and software, net as of December 31, 2015 and 2014 , consisted of the following (in thousands): December 31, 2015 2014 Capitalized internal-use software costs $ 38,879 $ 23,385 Computer hardware and software 57,827 46,299 Furniture and fixtures 13,619 11,674 Leasehold improvements 39,956 36,811 Total 150,281 118,169 Accumulated depreciation and amortization (67,500 ) (28,728 ) Total property, equipment and software, net $ 82,781 $ 89,441

BUSINESS COMBINATIONS BUSINES27

BUSINESS COMBINATIONS BUSINESS COMBINATIONS (Tables)	12 Months Ended
	Dec. 31, 2015
Business Combinations [Abstract]
Schedule of Consideration For Business Acquisitions	The total purchase consideration was as follows (in thousands): Purchase consideration: Cash $ 98,045 Fair value of shares of common stock transferred 82,421 Total purchase price $ 180,466
Schedule of Purchase Price Allocation	The changes in the carrying amount of goodwill for the year ended December 31, 2015 are as follows (in thousands): Goodwill Balance as of December 31, 2013 $ — Goodwill acquired 114,871 Goodwill adjustments (1) 541 Balance as of December 31, 2014 $ 115,412 Goodwill adjustment recorded during the three months ended September 30, 2015 (1) 2,109 Goodwill impairment recorded during the three months ended September 30, 2015 (117,521 ) Balance as of September 30, 2015 and December 30, 2015 $ — The total purchase price was allocated as follows (in thousands): Current assets $ 29,853 Non-current assets 3,999 Current liabilities (29,354 ) Non-current liabilities (16,253 ) Net acquired tangible assets (11,755 ) Identifiable intangible assets 74,700 Goodwill 117,521 Total purchase price $ 180,466
Schedule of Finite-Lived Intangible Assets	The estimated useful life and carrying values of the identifiable intangible assets were as follows (in thousands): As of December 31, 2015 As of December 31, 2014 Estimated Useful Life (in years) Gross Accumulated Amortization Net Gross Accumulated Amortization Net Developed technology 3-4 $ 42,100 $ (15,295 ) $ 26,805 $ 42,100 $ (3,703 ) $ 38,397 Customer relationships 7-8 27,700 (4,573 ) 23,127 27,700 (1,107 ) 26,593 Trademarks 5 2,000 (2,000 ) — 2,000 (128 ) 1,872 Non-compete agreements 2 2,900 (1,913 ) 987 2,900 (463 ) 2,437 Total $ 74,700 (23,781 ) 50,919 $ 74,700 (5,401 ) 69,299
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense	The expected annual amortization expense of intangible assets as of December 31, 2015 is presented below (in thousands): Year ending December 31, Amortization 2016 $ 16,045 2017 13,695 2018 8,451 2019 3,466 2020 3,466 Thereafter 5,796 Total $ 50,919
Pro Forma Information	The pro forma results are presented for informational purposes only and are not necessarily indicative of results that would have occurred had the acquisition taken place at the beginning of the earliest period presented, or of future results (in thousands): Year ended December 31, 2014 2013 Pro forma revenue $ 468,881 $ 310,469 Pro forma revenue less media costs $ 259,029 $ 165,959 Pro forma net loss $ (78,312 ) $ (50,666 )

ACCRUED AND OTHER CURRENT LIA28

ACCRUED AND OTHER CURRENT LIABILITIES (Tables)	12 Months Ended
	Dec. 31, 2015
Payables and Accruals [Abstract]
Schedule of accrued and other current liabilities	Accrued and other current liabilities as of December 31, 2015 and 2014 consisted of the following (in thousands): December 31, 2015 2014 Payroll and benefit related expenses $ 15,255 $ 16,379 Deferred rent 10,708 1,172 Other accrued expenses 14,771 15,707 Total accrued and other current liabilities $ 40,734 $ 33,258

CAPITAL LEASES (Tables)

CAPITAL LEASES (Tables)	12 Months Ended
	Dec. 31, 2015
Leases [Abstract]
Schedule of approximate remaining future minimum lease payments under non-cancelable capital leases	The remaining future minimum lease payments under these non-cancelable capital leases as of December 31, 2015 were as follows (in thousands): Year ending December 31, Future Payments 2016 $ 9,560 2017 7,817 2018 4,322 2019 370 Thereafter — Total minimum lease payments $ 22,069 Less: amount representing interest and taxes (1,612 ) Less: current portion of minimum lease payments (8,602 ) Capital lease obligations, net of current portion $ 11,855

DEBT (Tables)

DEBT (Tables)	12 Months Ended
	Dec. 31, 2015
Debt Disclosure [Abstract]
Schedule of future principal payments of long-term debt	Future principal payments of term loan as of December 31, 2015 were as follows (in thousands): Year ending December 31, Future Payments 2016 $ 6,000 2017 6,000 2018 6,000 2019 6,000 2020 — Total 24,000 Less: current portion of term loan (6,000 ) Term loan, net of current portion $ 18,000

STOCKHOLDERS' EQUITY (Tables)

STOCKHOLDERS' EQUITY (Tables)	12 Months Ended
	Dec. 31, 2015
Stockholders' Equity Note [Abstract]
Schedule of shares of common stock reserved for issuance	The Company’s shares of capital stock reserved for issuance under the Company's equity incentive plans as of December 31, 2015 were as follows: December 31, 2015 Options outstanding 5,386,521 Restricted stock awards and units outstanding 3,604,070 Available for future stock option and restricted stock unit grants 4,751,976 Available for future employee stock purchase plan purchases 1,397,991 Total shares reserved 15,140,558
Summary of option award activity	The following tables summarize option award activity: Number of Weighted- Weighted- Aggregate Balance at December 31, 2014 6,290,519 $ 11.18 7.8 $ 46,926 Options granted (weighted average fair value of $3.87 per share) 722,567 7.17 Options exercised (446,495) 2.21 Options forfeited (1,180,070) 17.47 Balance at December 31, 2015 5,386,521 $ 10.00 5.3 $ 1,976 Options vested and expected to vest—December 31, 2015 5,198,429 $ 9.93 5.2 $ 1,975 Options vested and exercisable—December 31, 2015 4,080,741 $ 9.18 4.3 $ 1,967
Schedule of assumptions used to value stock-based awards granted to employees	The assumptions used to value options granted to employees were as follows: Years ended December 31, 2015 2014 2013 Expected term (years) 6.3 5.5–6.3 5.3–6.6 Volatility 50.7%–58.0% 55.6%–59.5% 53.8%–64.9% Risk-free interest rate 1.44%–1.89% 1.84%–1.97% 1.04%–1.88% Dividend yield — — —
Summary of RSU activity	Restricted Stock Units ("RSUs") and Restricted Stock Awards ("RSAs") —A summary of RSU and RSA activity for the year ended December 31, 2015 is as follows: Number of Shares Weighted Average Grant Date Fair Value Unvested at December 31, 2014 2,515,311 $ 23.20 Granted 3,078,179 7.56 Vested and issued (646,395 ) 23.96 Canceled (1,335,237 ) 17.33 Unvested at December 31, 2015 3,611,858 $ 11.90
Schedule of assumptions used to calculate stock-based compensation for each stock purchase right granted under the ESPP	The assumptions used to calculate our stock-based compensation for each stock purchase right granted under the ESPP were as follows: Years ended December 31, 2015 2014 2013 Expected term (years) 0.5 0.5–0.7 0.7 Volatility 65.0%–73.3% 66.2%–77.4% 66.2% Risk-free interest rate 0.07%–0.42% 0.06%–0.08% 0.07% Dividend yield — — — The assumptions used to calculate our stock-based compensation for each stock purchase right granted under the ESPP were as follows: Years ended December 31, 2015 2014 2013 Expected term (years) 0.5 0.5–0.7 0.7 Volatility 65.0%–73.3% 66.2%–77.4% 66.2% Risk-free interest rate 0.07%–0.42% 0.06%–0.08% 0.07% Dividend yield — — — Equity compensation allocation The following table summarizes the allocation of stock-based compensation in the accompanying consolidated statements of operations (in thousands): Years ended December 31, 2015 2014 2013 Other cost of revenue $ 1,975 $ 1,758 $ 471 Research and development 7,706 5,039 2,308 Sales and marketing 9,894 10,372 4,482 General and administrative 6,399 6,361 3,581 Total $ 25,974 $ 23,530 $ 10,842

NET INCOME (LOSS) PER SHARE (Ta

NET INCOME (LOSS) PER SHARE (Tables)	12 Months Ended
	Dec. 31, 2015
Earnings Per Share [Abstract]
Schedule of computation of net loss per common share	The following table sets forth the computation of net loss per share of common stock (in thousands, except per share amounts): Years ended December 31, 2015 2014 2013 Net loss $ (210,545 ) $ (64,311 ) $ (20,932 ) Weighted-average shares used to compute basic and diluted net loss per share 42,551 37,001 15,177 Basic and diluted net loss per share $ (4.95 ) $ (1.74 ) $ (1.38 )
Schedule of anti-dilutive securities that were excluded from the calculation of diluted net loss per share attributable to common stockholders	The following securities were excluded from the calculation of diluted net loss per share attributable to common stockholders because their effect would have been anti-dilutive for the periods presented (in thousands): Years ended December 31, 2015 2014 2013 Employee stock options 3,616 6,291 7,409 Shares subject to repurchase 13 99 316 Restricted stock units (RSUs) and restricted stock awards (RSAs) 5,387 2,508 383 Employee stock purchase plan 157 58 58 9,173 8,956 8,166

INCOME TAXES INCOME TAXES (Tabl

INCOME TAXES INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Summary of Income Tax Contingencies [Table Text Block]	The table below provides a reconciliation of the beginning and ending amount of unrecognized tax benefits (excluding interest and penalties), related to uncertain tax positions, for the years ended December 31, 2015, 2014 and 2013 (in thousands): Years ended December 31, 2015 2014 2013 Unrecognized benefit—beginning of period $ 3,464 $ 669 $ 272 Gross increases—prior year tax positions — 46 126 Gross increases—current year tax positions 1,096 2,749 271 Unrecognized benefit—end of period $ 4,560 $ 3,464 $ 669
Schedule of Income before Income Tax, Domestic and Foreign [Table Text Block]	he following table presents domestic and foreign components of loss before income taxes for the periods presented (in thousands): Years ended December 31, 2015 2014 2013 Domestic $ (211,160 ) $ (70,438 ) $ (21,568 ) Foreign 1,836 1,888 921 Total loss before income taxes $ (209,324 ) $ (68,550 ) $ (20,647 )
Schedule of Components of Income Tax Expense (Benefit)	The components of the income tax provision (benefit) for income taxes were as follows (in thousands): Years ended December 31, 2015 2014 2013 Current: Federal $ — $ — $ — State 9 9 (4 ) Foreign 1,778 1,159 289 Deferred: Federal 14 (4,042 ) — State (327 ) (713 ) — Foreign (253 ) (652 ) — Total provision (benefit) for income taxes $ 1,221 $ (4,239 ) $ 285
Schedule of Deferred Tax Assets and Liabilities [Table Text Block]	December 31, 2015 2014 Deferred tax assets: Tax credit carry-forwards $ 10,183 $ 6,877 Net operating loss carry-forwards 62,269 45,281 Charitable contributions 411 323 Accrued liabilities and allowances 8,134 7,168 Stock Compensation 11,331 11,003 92,328 70,652 Deferred tax liability: Depreciation and amortization (23,732 ) (32,194 ) (23,732 ) (32,194 ) Net deferred tax assets before valuation allowance $ 68,596 $ 38,458 Valuation allowance (67,918 ) (38,159 ) Net deferred tax assets (liabilities) $ 678 $ 299

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Tables)	12 Months Ended
	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Schedule of future minimum lease payments under non-cancelable operating leases	Approximate remaining future minimum cash lease payments under these non-cancelable operating leases as of December 31, 2015 were as follows (in thousands): Year ending December 31, Future Payments 2016 $ 17,553 2017 14,067 2018 12,890 2019 14,241 2020 5,015 Thereafter 8,763 $ 72,529

SEGMENTS (Tables)

SEGMENTS (Tables)	12 Months Ended
	Dec. 31, 2015
Segment Reporting [Abstract]
Schedule of total revenue generated through sales personnel located in the respective locations	The following table summarizes total revenue generated through sales personnel located in the respective locations (in thousands): Years ended December 31, 2015 2014 2013 North America $ 385,449 $ 349,289 $ 213,601 All Other Countries 76,188 59,352 27,004 Total revenue $ 461,637 $ 408,641 $ 240,605
Schedule of total long-lived assets in the respective locations	The following table summarizes total long-lived assets in the respective locations (in thousands): December 31, 2015 2014 North America $ 77,038 $ 85,355 All Other Countries 5,743 4,086 Total long-lived assets $ 82,781 $ 89,441

NATURE OF BUSINESS AND SUMMAR36

NATURE OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		9 Months Ended	12 Months Ended
	Feb. 28, 2014	Sep. 30, 2013	Sep. 30, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Feb. 18, 2014
Initial public offering
Number of shares of common stock sold by the entity	2,000,000				2,000,000
Number of shares of common stock sold by selling stockholders	3,000,000
Issuance Price Per Share (in dollars per share)							$ 61
Total gross proceeds from the offering	$ 122,000
Aggregate net proceeds received from offering	$ 115,400			$ 0	$ 115,403	$ 103,612
Stock Issued During Period, Shares, Acquisitions			5,253,084
Payments to Acquire Businesses, Gross			$ 98,000
Initial Public Offering
Initial public offering
Sale of Stock, Number of Shares Issued in Transaction		4,000,000
Number of shares of common stock sold by selling stockholders		600,000
Issuance Price Per Share (in dollars per share)		$ 29
Total gross proceeds from the offering		$ 116,000
Aggregate net proceeds received from offering		$ 103,300

NATURE OF BUSINESS AND SUMMAR37

NATURE OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 2)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2015advertiser	Dec. 31, 2015agency	Dec. 31, 2014advertiser	Dec. 31, 2014USD ($)	Dec. 31, 2014agency	Dec. 31, 2013advertiser	Dec. 31, 2013USD ($)	Dec. 31, 2013agency
Concentration of credit risk
Impairment of long-lived assets					$ 0			$ 0
Cash | Credit concentration
Concentration of credit risk
Number of financial institutions where a significant portion of cash is held	4
Accounts receivable | Customer concentration
Concentration of credit risk
Number of customers		0	2	0		0
Revenue | Customer concentration
Concentration of credit risk
Number of customers		0	2	0		2	0		3

NATURE OF BUSINESS AND SUMMAR38

NATURE OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 3) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Internal Use Software Development Costs
Internal-use software costs capitalized	$ 15,500,000	$ 9,400,000	$ 6,300,000
Amortization expense	7,600,000	5,200,000	3,400,000
Impairment of Long-lived Assets
Impairment of long-lived assets		0	0
Sales and Marketing
Advertising costs	$ 7,800,000	$ 6,000,000	$ 3,600,000
Computer hardware and purchased software | Minimum
Property and equipment
Estimated useful life	2 years
Computer hardware and purchased software | Maximum
Property and equipment
Estimated useful life	3 years
Capitalized internal-use software costs | Minimum
Property and equipment
Estimated useful life	2 years
Capitalized internal-use software costs | Maximum
Property and equipment
Estimated useful life	3 years
Office equipment, furniture and fixtures
Property and equipment
Estimated useful life	5 years
Restructuring Plan [Member]
Impairment of Long-lived Assets
Impairment of long-lived assets	$ 6,600,000

NATURE OF BUSINESS AND SUMMAR39

NATURE OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Allowance for Doubtful Accounts Rollforward) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Allowance for Doubtful Accounts Receivable, Beginning Balance	$ 2,211	$ 1,752	$ 1,003
Charged Against Revenue	1,252	796	160
Charged to Expense	390	523	569
Write-offs, Adjustments, Net of Recovery	515	860	(20)
Allowance for Doubtful Accounts Receivable, Ending Balance	$ 3,338	$ 2,211	$ 1,752

FAIR VALUE MEASUREMENTS (Detail

FAIR VALUE MEASUREMENTS (Details) - Recurring - Money market funds (included in cash and cash equivalents) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets	$ 22,906	$ 22,904
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets	22,906	22,904
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets	0	0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets	$ 0	$ 0

PROPERTY, EQUIPMENT AND SOFTW41

PROPERTY, EQUIPMENT AND SOFTWARE, NET (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property, equipment and software
Total	$ 150,281	$ 118,169
Accumulated depreciation and amortization	(67,500)	(28,728)
Total property, equipment and software, net	82,781	89,441
Depreciation and amortization expense, excluding amortization of internal use software costs	24,800	13,100	$ 4,500
Amortization expense	7,600	5,200	3,400
Capital leases	27,600	19,200
Impairment of Leasehold	6,633	0	$ 0
Capitalized internal-use software costs
Property, equipment and software
Total	38,879	23,385
Computer hardware and software
Property, equipment and software
Total	57,827	46,299
Furniture and fixtures
Property, equipment and software
Total	13,619	11,674
Leasehold improvements
Property, equipment and software
Total	$ 39,956	$ 36,811

BUSINESS COMBINATIONS - Narrati

BUSINESS COMBINATIONS - Narrative (Details) - USD ($) $ in Thousands	Sep. 05, 2014	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Business Acquisition [Line Items]
Cash payment		$ 98,000
Shares issued		5,253,084
Goodwill				$ 0	$ 115,412
Tax benefit				1,221	$ (4,239)	$ 285
x Plus 1
Business Acquisition [Line Items]
Cash payment	$ 98,045
Shares issued	5,253,084
Fair value of shares of common stock transferred	$ 82,421
Total preliminary purchase price	180,466
Goodwill	117,521
Amortization of intangible assets				$ 18,400
Tax benefit			$ (4,100)
x Plus 1 | General and administrative
Business Acquisition [Line Items]
Acquisition costs	$ 4,900

BUSINESS COMBINATIONS - Schedul

BUSINESS COMBINATIONS - Schedule of Purchase Price Allocation (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Sep. 05, 2014
Business Acquisition [Line Items]
Goodwill	$ 0	$ 115,412
x Plus 1
Business Acquisition [Line Items]
Current assets			$ 29,853
Non-current assets			3,999
Current liabilities			(29,354)
Non-current liabilities			(16,253)
Net acquired tangible assets			(11,755)
Identifiable intangible assets			74,700
Goodwill			117,521
Total purchase price			$ 180,466

BUSINESS COMBINATIONS - Intangi

BUSINESS COMBINATIONS - Intangible Assets Acquired (Details) - x Plus 1 - USD ($) $ in Thousands	Sep. 05, 2014	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Amortization of Intangible Assets		$ 18,400
Preliminary Fair Value	$ 74,700	74,700
Accumulated Amortization		(23,781)	$ (5,401)
Net Book Value		50,919
Developed technology
Business Acquisition [Line Items]
Preliminary Fair Value	42,100	42,100
Accumulated Amortization		15,295	(3,703)
Net Book Value		26,805
Customer relationships
Business Acquisition [Line Items]
Preliminary Fair Value	$ 27,700	27,700
Accumulated Amortization		4,573	(1,107)
Net Book Value		23,127
Trademarks
Business Acquisition [Line Items]
Estimated Useful Life (in years)	5 years
Preliminary Fair Value	$ 2,000	2,000
Accumulated Amortization		2,000	(128)
Net Book Value		0
Non-compete agreements
Business Acquisition [Line Items]
Estimated Useful Life (in years)	2 years
Preliminary Fair Value	$ 2,900	2,900
Accumulated Amortization		1,913	$ (463)
Net Book Value		$ 987
Minimum | Developed technology
Business Acquisition [Line Items]
Estimated Useful Life (in years)	3 years
Minimum | Customer relationships
Business Acquisition [Line Items]
Estimated Useful Life (in years)	7 years
Maximum | Developed technology
Business Acquisition [Line Items]
Estimated Useful Life (in years)	4 years
Maximum | Customer relationships
Business Acquisition [Line Items]
Estimated Useful Life (in years)	8 years

BUSINESS COMBINATIONS - Sched45

BUSINESS COMBINATIONS - Schedule of Amortization Expense (Details) $ in Thousands	Dec. 31, 2015USD ($)
Business Combinations [Abstract]
2,016	$ 16,045
2,015	13,695
2,016	8,451
2,017	3,466
2,018	3,466
Thereafter	5,796
Total	$ 50,919

BUSINESS COMBINATIONS - Pro For

BUSINESS COMBINATIONS - Pro Forma (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Business Acquisition [Line Items]
Income Tax Expense (Benefit)		$ 1,221	$ (4,239)	$ 285
Business Combination, Pro Forma Revenue Less Media Costs			259,029	165,959
x Plus 1
Business Acquisition [Line Items]
Income Tax Expense (Benefit)	$ (4,100)
Pro forma revenue			468,881	310,469
Pro forma net loss			$ (78,312)	$ (50,666)

ACCRUED AND OTHER CURRENT LIA47

ACCRUED AND OTHER CURRENT LIABILITIES (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Payables and Accruals [Abstract]
Payroll and benefit related expenses	$ 15,255	$ 16,379
Accrued Rent, Current	10,708	1,172
Other accrued expenses	14,771	15,707
Total accrued and other current liabilities	$ 40,734	$ 33,258

CAPITAL LEASES (Details)

CAPITAL LEASES (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Leases [Abstract]
Property and equipment acquired under capital lease agreements	$ 27,600	$ 19,200
Approximate remaining future minimum lease payments under non-cancelable capital leases
2,016	9,560
2,015	7,817
2,016	4,322
2,017	370
Thereafter	0
Total minimum lease payments	22,069
Less: amount representing interest and taxes	(1,612)
Less: current portion of minimum lease payments	(8,602)	(5,482)
Capital lease obligations, net of current portion	$ 11,855	$ 12,341

RESTRUCTURING COSTS Restructu49

RESTRUCTURING COSTS Restructuring Costs (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Restructuring Cost and Reserve [Line Items]
Impairment of long-lived assets		$ 0	$ 0
Restructuring charges	$ 7,393,000	$ 0	$ 0
Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Severance costs	3,400,000
Real estate broker costs	900,000
Impairment of long-lived assets	6,600,000
Release of deferred rent liability	$ 3,500,000

DEBT (Details)

DEBT (Details)	12 Months Ended
	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Sep. 30, 2014
Debt
Amount outstanding	$ 40,000,000
Applicable margin over variable rate basis (as a percent)	2.00%
Liquidity ratio			1.10
Future principal payments of long-term debt
2,016	$ 6,000,000
2,017	6,000,000
2,018	6,000,000
2,019	0
Total	24,000,000
Term loan, net of current portion	17,617,000	$ 23,335,000
Unamortized discounts	700,000
Repayments of assumed debt	11,100,000
2,016	$ 6,000,000
Federal funds rate
Debt
Applicable margin over variable rate basis (as a percent)	1.00%
Daily adjusting LIBOR rate
Debt
Applicable margin over variable rate basis (as a percent)	1.00%
Revolving line of credit, as amended in June 2013
Debt
Maximum amount available for borrowing	$ 80,000,000
Amount outstanding	$ 40,000,000
Maximum amount available for borrowing expressed as a percentage of certain eligible accounts	85.00%
Revolving line of credit | Base rate
Debt
Applicable margin over variable rate basis (as a percent)	2.125%
Revolving line of credit | Minimum | Base rate
Debt
Applicable margin over variable rate basis (as a percent)	1.625%
Revolving line of credit | Minimum | LIBOR
Debt
Applicable margin over variable rate basis (as a percent)	2.625%
Revolving line of credit | Maximum | LIBOR
Debt
Applicable margin over variable rate basis (as a percent)	3.125%
Letter of credit subfacility
Debt
Maximum amount available for borrowing	$ 12,000,000
Debt Instrument, Aggregate Minimum Cash on Deposit	40,000,000
Amount outstanding	6,000,000
Debt Instrument, Required Cash on Deposit	30,000,000
Swing line subfacility
Debt
Maximum amount available for borrowing	2,500,000
Term loans
Future principal payments of long-term debt
Less: current portion of term loan	(6,000,000)
Term loan, net of current portion	$ 18,000,000
Term loans | Minimum | Base rate
Debt
Applicable margin over variable rate basis (as a percent)	2.50%
Term loans | Minimum | LIBOR
Debt
Applicable margin over variable rate basis (as a percent)	3.50%
Term loans | Maximum | Base rate
Debt
Applicable margin over variable rate basis (as a percent)	3.00%
Term loans | Maximum | LIBOR
Debt
Applicable margin over variable rate basis (as a percent)	4.00%
Revolving line of credit amended in March 2012
Debt
Maximum amount available for borrowing	$ 30,000,000
Amount outstanding	$ 24,000,000

STOCKHOLDERS' EQUITY (Details)

STOCKHOLDERS' EQUITY (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	2 Months Ended	9 Months Ended	12 Months Ended
	Feb. 28, 2014	Mar. 01, 2016	Sep. 30, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Feb. 18, 2014
STOCKHOLDERS' EQUITY (DEFICIT)
Total intrinsic value of options exercised				$ 2,700	$ 38,100	$ 11,900
Number of shares of common stock sold by the entity	2,000,000				2,000,000
Number of shares of common stock sold by selling stockholders	3,000,000
Issuance Price Per Share (in dollars per share)							$ 61
Total gross proceeds from the offering	$ 122,000
Aggregate net proceeds received from offering	$ 115,400			$ 0	$ 115,403	$ 103,612
Shares of capital stock reserved for issuance
Total shares reserved				15,140,558
Stock Issued During Period, Shares, Acquisitions			5,253,084
Payments to Acquire Businesses, Gross			$ 98,000
2013 Equity Incentive Plan
STOCKHOLDERS' EQUITY (DEFICIT)
Additional shares authorized				2,100,126
Employee stock purchase plan
Shares of capital stock reserved for issuance
Total shares reserved				1,397,991
Options
Shares of capital stock reserved for issuance
Total shares reserved				5,386,521
Unamortized stock-based compensation expense related to unvested common stock options				$ 8,200
Restricted stock units (RSUs) and restricted stock awards (RSAs)
Shares of capital stock reserved for issuance
Total shares reserved				3,604,070
Stock option and restricted stock unit grants
Shares of capital stock reserved for issuance
Total shares reserved				4,751,976
Subsequent Event [Member] | 2013 Equity Incentive Plan
STOCKHOLDERS' EQUITY (DEFICIT)
Additional shares authorized		2,178,350

STOCKHOLDERS' EQUITY (Details 2

STOCKHOLDERS' EQUITY (Details 2) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Number of Shares Outstanding
Balance at the beginning of the period (in shares)	6,290,519
Options granted (weighted average fair value of $3.87 per share)	722,567
Options exercised (in shares)	(446,495)
Options forfeited (in shares)	(1,180,070)
Balance at the end of the period (in shares)	5,386,521	6,290,519
Options vested and expected to vest (in shares)	5,198,429
Options vested and exercisable (in shares)	4,080,741
Weighted average fair value (in dollars per share)	$ 3.87
Weighted-Average Exercise Price
Balance at the beginning of the period (in dollars per share)	11.18
Options granted (weighted average fair value of $3.87 per share)	7.17
Options exercised (in dollars per share)	2.21
Options forfeited (in dollars per share)	17.47
Balance at the end of the period (in dollars per share)	10	$ 11.18
Options vested and expected to vest (in dollars per share)	9.93
Options vested and exercisable (in dollars per share)	$ 9.18
Weighted-Average Remaining Contractual Life
Balance	5 years 3 months 22 days	7 years 10 months 2 days
Options vested and expected to vest	5 years 2 months 1 day
Options vested and exercisable	4 years 3 months 26 days
Aggregate Intrinsic Value
Balance	$ 1,976	$ 46,926
Options vested and expected to vest	1,975
Options vested and exercisable	1,967
Total intrinsic value of options exercised	$ 2,700	$ 38,100	$ 11,900
2008 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise price as a percentage of the fair market value of the common stock	100.00%
Expiration period	10 years
Vesting period	4 years
Number of shares of unvested stock repurchased	18,850	25,625
2013 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise price as a percentage of the fair market value of the common stock	100.00%
Expiration period	10 years
Common stock reserved for issuance	5,000,000
Number of shares added to current plan for award granted but not exercised in full, pursuant to the terminated equity incentive plan	7,900,000
Annual increase in number of shares available for issuance on first day of each fiscal year following latest fiscal year	4,000,000
Annual increase in number of shares available for issuance on first day of each fiscal year following latest fiscal year as a percentage of outstanding common stock, as on last day of the immediately preceding fiscal year	5.00%
Additional shares authorized	2,100,126
Options | 2008 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of unvested shares	13,134	98,787

STOCKHOLDERS' EQUITY (Details 3

STOCKHOLDERS' EQUITY (Details 3) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Summary of options outstanding and vested
Expected dividends		$ 0
Assumptions used to value stock-based awards granted to employees
Volatility, lower end (as a percent)		50.70%	55.60%	53.80%
Volatility, higher end (as a percent)		58.00%	59.50%	64.90%
Risk-free interest rate, lower end (as a percent)		1.44%	1.84%	1.04%
Risk-free interest rate, higher end (as a percent)		1.89%	1.97%	1.88%
Minimum
Assumptions used to value stock-based awards granted to employees
Expected term		6 years 3 months 18 days	5 years 5 months 18 days	5 years 3 months 18 days
Maximum
Assumptions used to value stock-based awards granted to employees
Expected term		6 years 3 months 18 days	6 years 7 months 6 days	6 years 7 months 18 days
Employee stock purchase plan
Assumptions used to value stock-based awards granted to employees
Expected term			6 months 12 days
Volatility (as a percent)			66.20%
Risk-free interest rate (as a percent)			0.06%
Dividend yield (as a percent)	0.00%
Employee stock purchase plan | Minimum
Assumptions used to value stock-based awards granted to employees
Expected term		6 months
Volatility (as a percent)		65.00%
Risk-free interest rate (as a percent)		7.00%
Employee stock purchase plan | Maximum
Assumptions used to value stock-based awards granted to employees
Expected term		6 months	8 months 12 days
Volatility (as a percent)		73.30%	77.40%
Risk-free interest rate (as a percent)		42.00%	0.08%

STOCKHOLDERS' EQUITY (Details 4

STOCKHOLDERS' EQUITY (Details 4) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Allocation of stock-based compensation and restricted stock for employees and non-employees
Total		$ 25,974	$ 23,530	$ 10,842
Options
Allocation of stock-based compensation and restricted stock for employees and non-employees
Unamortized stock-based compensation expense related to unvested common stock options		8,200
Weighted-average period over which stock-based compensation expense will be recognized	2 years 2 months
Cost of revenue
Allocation of stock-based compensation and restricted stock for employees and non-employees
Total		1,975	1,758	471
Research and development
Allocation of stock-based compensation and restricted stock for employees and non-employees
Total		7,706	5,039	2,308
Sales and marketing
Allocation of stock-based compensation and restricted stock for employees and non-employees
Total		9,894	10,372	4,482
General and administrative
Allocation of stock-based compensation and restricted stock for employees and non-employees
Total		$ 6,399	$ 6,361	$ 3,581

STOCKHOLDERS' EQUITY (Details 5

STOCKHOLDERS' EQUITY (Details 5) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted		722,567
Stock-based compensation expense		$ 25,974	$ 23,530	$ 10,842
Options outstanding (in shares)		5,386,521	6,290,519
2008 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Purchase price expressed as a percentage of fair market value of common stock on the first or the last trading day of the offering period		100.00%
2013 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Purchase price expressed as a percentage of fair market value of common stock on the first or the last trading day of the offering period		100.00%
Employee stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of deduction from eligible compensation authorized by employee to purchase common stock at discount		15.00%
Purchase price expressed as a percentage of fair market value of common stock on the first or the last trading day of the offering period		85.00%
Total compensation costs related to rights to purchase common shares but not yet vested which will be recognized over the offering period		$ 700
Assumptions used to calculate stock-based compensation for each stock purchase right granted under the Employee Stock Purchase Plan (ESPP)
Expected term			6 months 12 days
Volatility (as a percent)			66.20%
Risk-free interest rate (as a percent)			0.06%
Dividend yield (as a percent)	0.00%
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of awards issued (in shares)		3,078,179
Granted		$ 7.56
Number of awards released (in shares)		646,395
Number of awards cancelled (in shares)		1,335,237
Unrecognized compensation expense		$ 29,900

STOCKHOLDERS' EQUITY (Details 6

STOCKHOLDERS' EQUITY (Details 6) - Restricted stock units (RSUs) and restricted stock awards (RSAs) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value | $	$ 3.9
Number of Shares
Unvested, beginning balance | shares	2,515,311
Granted | shares	3,078,179
Vested and issued | shares	(646,395)
Canceled | shares	(1,335,237)
Unvested, ending balance | shares	3,611,858
Weighted Average Grant Date Fair Value
Unvested, beginning balance | $ / shares	$ 23.20
Granted | $ / shares	7.56
Vested and issued | $ / shares	23.96
Canceled | $ / shares	17.33
Unvested, ending balance | $ / shares	$ 11.90

NET INCOME (LOSS) PER SHARE (De

NET INCOME (LOSS) PER SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Computation of net loss per common share
Net loss	$ (210,545)	$ (64,311)	$ (20,932)
Weighted-average shares used to compute basic and diluted net loss per share	42,551	37,001	15,177
Basic and diluted net loss per share (in dollars per share)	$ (4.95)	$ (1.74)	$ (1.38)
Anti-dilutive securities that were excluded from the calculation of diluted net loss per share attributable to common stockholders
Anti-dilutive securities that were excluded from the calculation of diluted net loss per share attributable to common stockholders (in shares)	9,173	8,956	8,166
Employee stock options
Anti-dilutive securities that were excluded from the calculation of diluted net loss per share attributable to common stockholders
Anti-dilutive securities that were excluded from the calculation of diluted net loss per share attributable to common stockholders (in shares)	3,616	6,291	7,409
Shares subject to repurchase
Anti-dilutive securities that were excluded from the calculation of diluted net loss per share attributable to common stockholders
Anti-dilutive securities that were excluded from the calculation of diluted net loss per share attributable to common stockholders (in shares)	13	99	316
Restricted stock units (RSUs) and restricted stock awards (RSAs)
Anti-dilutive securities that were excluded from the calculation of diluted net loss per share attributable to common stockholders
Anti-dilutive securities that were excluded from the calculation of diluted net loss per share attributable to common stockholders (in shares)	5,387	2,508	383
Employee stock purchase plan
Anti-dilutive securities that were excluded from the calculation of diluted net loss per share attributable to common stockholders
Anti-dilutive securities that were excluded from the calculation of diluted net loss per share attributable to common stockholders (in shares)	157	58	58

INCOME TAXES (Details)

INCOME TAXES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Examination [Line Items]
Unrecognized Tax Benefits	$ 4,560	$ 3,464	$ 669	$ 272
Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions	0	46	126
Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions	1,096	2,749	271
Domestic	$ (211,160)	$ (70,438)	$ (21,568)
Tax benefit at federal statutory rate	34.00%	34.00%	34.00%
Tax credit carry-forwards	$ 10,183	$ 6,877
Deferred Tax Assets, Gross	92,328	70,652
Valuation allowance	(67,918)	(38,159)
Depreciation and amortization	(23,732)	(32,194)
Gross deferred tax liability	23,732	32,194
Deferred Tax Assets (Liabilities) Before Valuation Allowance, Net	68,596	38,458
Deferred Tax Assets, Net of Valuation Allowance	678	299
Valuation Allowance, Deferred Tax Asset, Change in Amount	29,800	22,400
Income tax (benefit) provision	1,221	(4,239)	$ 285
Foreign	(253)	(652)	0
State	(327)	(713)	0
Federal	14	(4,042)	0
Foreign	1,778	1,159	289
State	9	9	(4)
Federal	0	0	$ 0
Operating Loss Carryforwards	62,269	45,281
Charitable contributions	411	323
Accrued liabilities and allowances	8,134	7,168
Stock Compensation	11,331	$ 11,003
Undistributed Earnings of Foreign Subsidiaries	$ 3,200
State income taxes, net of federal effect	0.29%	6.17%	0.01%
Foreign rate differential	(0.38%)	0.20%	0.12%
Goodwill Impairment	(19.09%)	0.00%	0.00%
Change in valuation allowance	(15.04%)	(31.94%)	(28.42%)
Meals and entertainment	(0.41%)	(1.44%)	(2.07%)
Warrant liability	0.00%	0.00%	(7.81%)
Research credits	0.60%	2.86%	2.79%
Effective Income Tax Rate Reconciliation, Transaction Costs	0.00%	(2.24%)	0.00%
Other	(0.55%)	(1.41%)	0.00%
Total provision	(0.58%)	6.20%	(1.38%)
International	$ 1,836	$ 1,888	$ 921
Total	(209,324)	$ (68,550)	$ (20,647)
Deferred tax liabilities related to acquisition	2,300
Federal
Income Tax Examination [Line Items]
Operating Loss Carryforwards	219,500
Deferred Tax Assets, Tax Credit Carryforwards, Research	10,000
Excess Deduction Not to be Recognized Until Stock Option Exercise Deduction Reduces Taxes Payable	46,600
State
Income Tax Examination [Line Items]
Operating Loss Carryforwards	76,900
Deferred Tax Assets, Tax Credit Carryforwards, Research	4,700
Excess Deduction Not to be Recognized Until Stock Option Exercise Deduction Reduces Taxes Payable	$ 5,200

COMMITMENTS AND CONTINGENCIES59

COMMITMENTS AND CONTINGENCIES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Leases
Rent expense	$ 15,600	$ 14,700	$ 4,300
Future minimum lease payments under non-cancelable operating leases
2014 (remaining 9 months)	17,553
2,015	14,067
2,016	12,890
2,017	14,241
2,018	5,015
Thereafter	8,763
Total future payments	72,529
Letters of Credit and Bank Guarantees
Irrevocable letters of credit outstanding	6,300	6,800
Bank guarantees for security deposits	$ 2,141	$ 2,915

SEGMENTS (Details)

SEGMENTS (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015USD ($)advertiser	Dec. 31, 2015USD ($)	Dec. 31, 2015USD ($)agency	Dec. 31, 2015USD ($)segment	Dec. 31, 2015USD ($)manager	Dec. 31, 2015USD ($)business_activity	Dec. 31, 2014USD ($)advertiser	Dec. 31, 2014USD ($)	Dec. 31, 2014USD ($)agency	Dec. 31, 2013advertiser	Dec. 31, 2013USD ($)	Dec. 31, 2013agency
Segment Reporting [Abstract]
Number of business activities | business_activity						1
Number of segment managers held accountable for operations, operating results or plans for levels or components below the consolidated unit level | manager					0
Number of reportable segments | segment				1
Number of operating segments | segment				1
Segments
Total revenue		$ 461,637						$ 408,641			$ 240,605
Total long-lived assets	$ 82,781	82,781	$ 82,781	$ 82,781	$ 82,781	$ 82,781	$ 89,441	89,441	$ 89,441
Revenue | Customer concentration
Segments
Number of customers	0		2				0		2	0		3
Accounts receivable | Customer concentration
Segments
Number of customers	0		2				0		0
North America
Segments
Total revenue		385,449						349,289			213,601
Total long-lived assets	$ 77,038	77,038	$ 77,038	77,038	77,038	77,038	$ 85,355	85,355	$ 85,355
All Other Countries
Segments
Total revenue		76,188						59,352			$ 27,004
Total long-lived assets	$ 5,743	$ 5,743	$ 5,743	$ 5,743	$ 5,743	$ 5,743	$ 4,086	$ 4,086	$ 4,086

GOODWILL (Details)

GOODWILL (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Goodwill [Line Items]
Goodwill, Impairment Loss	$ 117,521	$ 0	$ 0

RELATED PARTY TRANSACTIONS (Det

RELATED PARTY TRANSACTIONS (Details) - Affiliated Entity [Member] - Nielsen Data Services [Member] $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)
Related Party Transaction [Line Items]
Related party expenses recognized	$ 5.4
Related party accounts payable	$ 1.2

SUBSEQUENT EVENTS SUBSEQUENT EV

SUBSEQUENT EVENTS SUBSEQUENT EVENTS (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)
Letter of credit subfacility
Subsequent Event [Line Items]
Debt Instrument, Aggregate Minimum Cash on Deposit	$ 40