Five9 (FIVN) 10-K 25 Feb 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Feb. 15, 2019	Jun. 30, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	Five9, Inc.
Trading Symbol	FIVN
Entity Central Index Key	1,288,847
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Shell Company	false
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding		59,253,048
Entity Public Float			$ 1,526.5

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 81,912	$ 68,947
Marketable investments	209,907	0
Accounts receivable, net	24,797	19,048
Prepaid expenses and other current assets	8,014	4,840
Deferred contract acquisition costs	9,372	0
Total current assets	334,002	92,835
Property and equipment, net	25,885	19,888
Intangible assets, net	631	1,073
Goodwill	11,798	11,798
Other assets	836	2,602
Deferred contract acquisition costs — less current portion	21,514	0
Total assets	394,666	128,196
Current liabilities:
Accounts payable	7,010	4,292
Accrued and other current liabilities	13,771	11,787
Accrued federal fees	1,434	1,151
Sales tax liability	1,741	1,326
Notes payable	0	336
Capital leases	6,647	6,651
Deferred revenue	17,391	13,975
Total current liabilities	47,994	39,518
Convertible senior notes	196,763	0
Revolving line of credit	0	32,594
Sales tax liability — less current portion	841	1,044
Capital leases — less current portion	4,509	7,161
Other long-term liabilities	1,811	1,041
Total liabilities	251,918	81,358
Commitments and contingencies (Note 10)
Stockholders’ equity:
Preferred stock, $0.001 par value; 5,000 shares authorized, no shares issued and outstanding as of December 31, 2018 and 2017	0	0
Common stock, $0.001 par value; 450,000 shares authorized, 59,210 shares and 56,632 shares issued and outstanding as of December 31, 2018 and 2017, respectively	59	57
Additional paid-in capital	294,279	222,202
Accumulated other comprehensive loss	(93)	0
Accumulated deficit	(151,497)	(175,421)
Total stockholders’ equity	142,748	46,838
Total liabilities and stockholders’ equity	$ 394,666	$ 128,196

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Preferred stock, par value (in USD per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in USD per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	450,000,000	450,000,000
Common stock, shares issued (in shares)	59,210,496	56,631,647
Common stock, shares outstanding (in shares)	59,210,496	56,631,647

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Revenue	$ 257,664	$ 200,225	$ 162,090
Cost of revenue	104,034	83,104	66,934
Gross profit	153,630	117,121	95,156
Operating expenses:
Research and development	34,172	27,120	23,878
Sales and marketing	72,001	66,570	52,748
General and administrative	40,448	29,151	25,072
Total operating expenses	146,621	122,841	101,698
Income (loss) from operations	7,009	(5,720)	(6,542)
Other income (expense), net:
Extinguishment of debt	0	0	(1,026)
Interest expense	(10,245)	(3,471)	(4,226)
Interest income and other	3,315	490	(12)
Total other income (expense), net	(6,930)	(2,981)	(5,264)
Income (loss) before income taxes	79	(8,701)	(11,806)
Provision for income taxes	300	268	54
Net loss	$ (221)	$ (8,969)	$ (11,860)
Net loss per share:
Basic and diluted (in USD per share)	$ 0	$ (0.16)	$ (0.23)
Shares used in computing net loss per share:
Basic and diluted (in shares)	58,076	54,946	52,342
Comprehensive Loss:
Net loss	$ (221)	$ (8,969)	$ (11,860)
Other comprehensive loss	(93)	0	0
Comprehensive loss	$ (314)	$ (8,969)	$ (11,860)

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands		Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning balance (in share) at Dec. 31, 2015			51,165
Beginning balance at Dec. 31, 2015		$ 26,280	$ 51	$ 180,649		$ (154,420)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options and warrants (in share)			982
Issuance of common stock upon exercise of stock options and warrants		4,286	$ 1	4,285
Issuance of common stock upon vesting of restricted stock units (in shares)			896
Issuance of common stock upon vesting of restricted stock units		0	$ 1	(1)
Issuance of common stock under ESPP (in shares)			320
Issuance of common stock under ESPP		1,979		1,979
Stock-based compensation		9,643		9,643
Other comprehensive loss		0
Net loss		(11,860)				(11,860)
Ending balance at Dec. 31, 2016		30,328	$ 53	196,555		(166,280)
Ending balance (in shares) at Dec. 31, 2016			53,363
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options and warrants (in share)			2,033
Issuance of common stock upon exercise of stock options and warrants		6,035	$ 2	6,033
Issuance of common stock upon vesting of restricted stock units (in shares)			971
Issuance of common stock upon vesting of restricted stock units		0	$ 1	(1)
Issuance of common stock under ESPP (in shares)			265
Issuance of common stock under ESPP		4,101	$ 1	4,100
Stock-based compensation		15,343		15,343
Other	[1]	0		172		(172)
Other comprehensive loss		0
Net loss		(8,969)				(8,969)
Ending balance at Dec. 31, 2017		46,838	$ 57	222,202	$ 0	(175,421)
Ending balance (in shares) at Dec. 31, 2017			56,632
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity component of issuance of convertible senior notes		30,346		30,346
Issuance of common stock upon exercise of stock options and warrants (in share)			1,285
Issuance of common stock upon exercise of stock options and warrants		7,779	$ 1	7,778
Issuance of common stock upon vesting of restricted stock units (in shares)			1,047
Issuance of common stock upon vesting of restricted stock units		0	$ 1	(1)
Issuance of common stock under ESPP (in shares)			246
Issuance of common stock under ESPP		5,730	$ 0	5,730
Stock-based compensation		28,484		28,484
Shares held for tax withholdings		(260)		(260)
Other comprehensive loss		(93)			(93)
Net loss		(221)				(221)
Ending balance at Dec. 31, 2018		$ 142,748	$ 59	$ 294,279	$ (93)	$ (151,497)
Ending balance (in shares) at Dec. 31, 2018			59,210
[1]	Effective January 2017, the Company adopted Accounting Standards Update (“ASU”) 2016-09 - Improvements to Employee Share-Based Payment Accounting. Accordingly, the Company accounted for forfeitures as they occurred rather than by estimating expected forfeitures. This amount represents the net effect of this change. See Note 1 for more information.

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net loss	$ (221)	$ (8,969)	$ (11,860)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization	10,274	8,314	8,390
Amortization of premium on marketable investments	(670)	0	0
Provision for doubtful accounts	90	95	75
Stock-based compensation	28,484	15,343	9,643
Loss on extinguishment of debt	0	0	1,026
Reversal of interest and penalties on accrued federal fees	0	(2,133)	0
Gain on sale of convertible note held for investment	(312)	0	0
Reversal of accrued federal fees	0	0	(3,114)
Non-cash adjustment on investment	(40)	(366)	0
Accretion of interest	44	21	20
Others	27	(48)	(10)
Changes in operating assets and liabilities:
Accounts receivable	(5,829)	(5,163)	(3,389)
Prepaid expenses and other current assets	(2,806)	(1,912)	(859)
Deferred contract acquisition costs	(7,748)	0	0
Other assets	193	(33)	203
Accounts payable	2,418	813	811
Accrued and other current liabilities	1,865	1,061	2,262
Accrued federal fees and sales tax liability	495	90	(182)
Deferred revenue	3,956	3,882	3,680
Other liabilities	392	31	(99)
Net cash provided by operating activities	38,622	11,106	6,838
Cash flows from investing activities:
Purchases of marketable investments	(220,704)	0	0
Proceeds from Sale and Maturity of Debt Securities, Available-for-sale	11,293	0	0
Purchases of property and equipment	(9,261)	(2,650)	(1,131)
Purchases of convertible notes held for investment	0	0	(1,206)
Proceeds from sale of convertible note held for investment	1,923	0	0
Increase in restricted cash	0	0	(60)
Net cash (used in) investing activities	(216,749)	(2,650)	(2,397)
Cash flows from financing activities:
Proceeds from issuance of convertible senior notes, net of issuance costs paid $8,039	250,711	0	0
Payments for capped call transactions	(31,412)	0	0
Proceeds from exercise of common stock options	7,779	6,035	4,286
Proceeds from sale of common stock under ESPP	5,730	4,101	1,979
Payments of employee taxes related to vested common stock	(260)	0	0
Proceeds from revolving line of credit	0	0	32,594
Repayments on revolving line of credit	(32,594)	0	(12,500)
Repayments of notes payable	(318)	(699)	(24,351)
Payments of capital leases	(8,544)	(7,068)	(6,237)
Payment of prepayment penalty and related fees	0	0	(368)
Payments for debt issuance costs	0	0	(206)
Net cash provided by (used in) financing activities	191,092	2,369	(4,803)
Net increase (decrease) in cash and cash equivalents	12,965	10,825	(362)
Cash and cash equivalents:
Beginning of year	68,947	58,122	58,484
End of year	81,912	68,947	58,122
Supplemental disclosures of cash flow data:
Cash paid for interest	2,288	3,311	4,234
Cash paid for income taxes	159	121	115
Non-cash investing and financing activities:
Equipment obtained under capital lease	5,142	10,261	8,202
Equipment purchased and unpaid at period-end	1,583	145	163
Capitalization of leasehold improvement through non-cash lease incentive	0	142	0
Line of Credit
Adjustments to reconcile net loss to net cash provided by operating activities:
Amortization of debt discount and issuance costs	129	80	241
Convertible debt
Adjustments to reconcile net loss to net cash provided by operating activities:
Amortization of debt discount and issuance costs	7,881	$ 0	$ 0
Cash flows from financing activities:
Payments for debt issuance costs	$ (8,039)

Description of Business and Sum

Description of Business and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Description of Business and Summary of Significant Accounting Policies	Description of Business and Summary of Significant Accounting Policies Five9, Inc. and its wholly-owned subsidiaries (the “Company”) is a provider of cloud software for contact centers. The Company was incorporated in Delaware in 2001 and is headquartered in San Ramon, California. The Company has offices in Europe and Asia, which primarily provide research, development, sales, marketing, and client support services. Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (“SEC”) regarding annual financial reporting. All intercompany transactions and balances have been eliminated in consolidation. Certain prior period amounts included in the consolidated financial statements have been reclassified to conform to the current period presentation. 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 and liabilities and disclosure 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. The significant estimates made by management affect revenue and related reserves. Management periodically evaluates such estimates and they are adjusted prospectively based upon such periodic evaluation. Actual results could differ from those estimates. Foreign Currency The functional currency of the Company’s foreign subsidiaries is the U.S. dollar. For these subsidiaries, the monetary assets and liabilities are re-measured into U.S. dollars at the current exchange rate as of the balance sheet date, and all non-monetary assets and liabilities are re-measured into U.S. dollars at historical exchange rates. Revenues are primarily denominated in U.S dollars. Expenses are converted using average rates in effect on a monthly basis. Exchange gains and losses resulting from foreign currency transactions were not significant in any period and are reported in “Other income (expense), net” in the consolidated statements of operations and comprehensive loss. Cash and Cash Equivalents The Company’s cash and cash equivalents consist of highly liquid investments with maturities of three months or less at the time of purchase. The Company’s cash equivalents consist of investments in money market funds, U.S. treasury securities, U.S. agency securities and commercial paper. Marketable Investments The Company’s marketable investments consist of U.S agency securities and government sponsored securities, U.S. treasury securities, certificates of deposit, municipal bonds, corporate bonds and commercial paper. The Company determines the appropriate classification of its investments in marketable investments at the time of purchase and re-evaluates such designation at each balance sheet date. The Company’s marketable investments have been classified and accounted for as available-for-sale. Marketable investments are carried at fair value. Concentration Risks Financial instruments, which potentially subject the Company to significant concentrations of credit risk, consist primarily of cash and cash equivalents, marketable investments and accounts receivable. A significant portion of the Company’s cash and cash equivalents is held at three large reputable financial institutions. Total cash and cash equivalents in excess of insured limits were $81.0 million and $68.3 million as of December 31, 2018 and 2017 , respectively. The Company has not experienced any losses in such accounts. As of December 31, 2018 and 2017 , no single client represented more than 10% of accounts receivable . For the years ended December 31, 2018 , 2017 and 2016 , no single client represented more than 10% of revenue . Allowance for Doubtful Accounts 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 creditworthiness of each client. If circumstances change, such as higher-than-expected defaults or an unexpected material adverse change in a major client’s ability to meet its financial obligations, the Company’s estimate of the recoverability of the amounts due could be reduced by a material amount. The following table presents the changes in the allowance for doubtful accounts (in thousands): Year Ended December 31, 2018 2017 2016 Balance, beginning of period $ 33 $ 12 $ 15 Add: bad debt expense 90 95 75 Less: write-offs, net of recoveries (111 ) (74 ) (78 ) Balance, end of period $ 12 $ 33 $ 12 Property and Equipment, Net Property and equipment is stated at cost less accumulated depreciation and amortization, and is depreciated using the straight-line method over the estimated useful lives of the assets as follows: Asset Category Estimated Useful Lives Computer and network equipment 3 to 5 years Computer software 3 years Development costs 1 to 5 years Furniture and fixtures 7 years Leasehold improvements Shorter of useful life or lease term 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 and amortization are removed from the consolidated balance sheet and any resulting gain or loss is reflected in the consolidated statements of operations and comprehensive loss in the period realized. The Company evaluates the recoverability of property and equipment for possible impairment whenever events or circumstances indicate that the carrying amount of such assets or asset groups may not be recoverable. Recoverability of these assets is measured by a comparison of the carrying amounts to the future undiscounted cash flows the assets or asset groups are expected to generate. If such evaluation indicates that the carrying amount of the assets or asset groups is not recoverable, the carrying amount of such assets or asset groups is reduced to fair value. No impairment losses have been recognized in any of the periods presented. Goodwill and Intangible Assets The Company records goodwill when the consideration paid in a business combination exceeds the fair value of the net tangible assets and the identified intangible assets acquired. Goodwill is not amortized, but instead is required to be tested for impairment annually and whenever events or changes in circumstances indicate that the carrying value of goodwill may exceed its fair value. The Company performs testing for impairment of goodwill in its fourth quarter, or as events occur or circumstances change that would more likely than not reduce the fair value of the Company’s single reporting unit below its carrying amount. A qualitative assessment is first made to determine whether it is necessary to perform the two-step quantitative goodwill impairment test. This initial qualitative assessment includes, among other things, consideration of: (i) market capitalization of the Company, (ii) past, current and projected future earnings and equity; (iii) recent trends and market conditions; and (iv) valuation metrics involving similar companies that are publicly-traded and acquisitions of similar companies, if available. If this initial qualitative assessment indicates that it is more likely than not that impairment exists, a second analysis will be performed, involving a comparison between the estimated fair values of the Company’s reporting unit with its respective carrying amount including goodwill. If the carrying value exceeds estimated fair value, there is an indication of potential impairment, and a third analysis is performed to measure the amount of impairment. The third analysis involves calculating an implied fair value of goodwill by measuring the excess of the estimated fair value of the reporting unit over the aggregate estimated fair values of the individual assets less liabilities. If the carrying value of goodwill exceeds the implied fair value of goodwill, an impairment charge is recorded for the excess. Intangible assets, consisting of acquired developed technology, domain names and customer relationships, are carried at cost less accumulated amortization. All intangible assets have been determined to have definite lives and are amortized on a straight-line basis over their estimated remaining economic lives, ranging from five to seven years. Amortization expense related to developed technology is included in cost of revenue. Amortization expense related to customer relationships is included in sales and marketing expense. Amortization expense related to domain names is included in general and administrative expense. Intangible assets are reviewed for impairment whenever events or changes in circumstances indicate an asset’s carrying value may not be recoverable. Revenue Recognition Revenue is recognized when control of the promised services are transferred to customers in an amount that reflects the consideration that the Company expects to receive in exchange for those services. The Company generates all of its revenue from contracts with customers. In contracts with multiple performance obligations, it identifies each performance obligation and evaluates whether the performance obligations are distinct within the context of the contract at contract inception. Performance obligations that are not distinct at contract inception are combined. The Company allocates the transaction price to each distinct performance obligation proportionately based on the estimated standalone selling price for each performance obligation. The Company then looks to how services are transferred to the customer in order to determine the timing of revenue recognition. Most services provided under the Company’s agreements result in the transfer of control over time. The Company’s revenue consists of subscription services and related usage as well as professional services. The Company charges clients subscription fees, usually billed on a monthly basis, for access to the Company’s VCC solution. The subscription fees are primarily based on the number of agent seats, as well as the specific VCC functionalities and applications deployed by the client. Agent seats are defined as the maximum number of named agents allowed to concurrently access the VCC cloud platform. Clients typically have more named agents than agent seats. Multiple named agents may use an agent seat, though not simultaneously. Substantially all of the Company’s clients purchase both subscriptions and related telephony usage. A small percentage of the Company’s clients subscribe to its platform but purchase telephony usage directly from a wholesale telecommunications service provider. The Company does not sell telephony usage on a stand-alone basis to any client. The related usage fees are based on the volume of minutes used for inbound and outbound client interactions. The Company also offers bundled plans, generally for smaller deployments, whereby the client is charged a single monthly fixed fee per agent seat that includes both subscription and unlimited usage in the contiguous 48 states and, in some cases, Canada. Professional services revenue is derived primarily from VCC implementations, including application configuration, system integration, optimization, education and training services. Clients are not permitted to take possession of the Company’s software. The Company offers monthly, annual and multiple-year contracts to its clients, generally with 30 days’ notice required for changes in the number of agent seats and sometimes with a minimum number of agent seats required. Larger clients typically choose annual contracts, which generally include an implementation and ramp period of several months. Fixed subscription fees (including bundled plans) are generally billed monthly in advance, while related usage fees are billed in arrears. Support activities include technical assistance for the Company’s solution and upgrades and enhancements to the VCC cloud platform on a when-and-if-available basis, which are not billed separately. The Company generally requires advance deposits from its clients based on estimated usage when such usage is not billed as part of a bundled plan. Any unused portion of the deposit is refundable to the client upon termination of the arrangement, provided all amounts due have been paid. All fees, except usage deposits, are non-refundable. Professional services are primarily billed on a fixed-fee basis and are performed by the Company directly or, alternatively, clients may also choose to perform these services themselves or engage their own third-party service providers. Revenue for professional services is recognized over time, as services are performed. The estimation of variable consideration for each performance obligation requires the Company to make subjective judgments resulting in estimated variable consideration that is included in the transaction fee. This is done to the extent that it is probable, in the Company’s judgment, that a significant reversal in the amount of cumulative revenue recognized under the contract will not occur. The Company estimates the variable consideration in order to allocate the overall transaction fee on a relative stand-alone selling price basis to its multiple performance obligations. This requires the estimate of unit quantities, especially during the initial ramp period of the contract, during which the Company bills under an ‘actual usage’ model for subscription-related services. The Company recognizes revenue on fixed fee professional services performance obligations based on the proportion of labor hours expended compared to the total hours expected to complete the related performance obligation. The determination of the total labor hours expected to complete the performance obligations involves judgment, which influences the initial stand-alone selling price estimate as well as the timing of professional services revenue recognition, although this is typically resolved in a short time frame. When a contract with a customer is signed, the Company assesses whether collection of the fees under the arrangement is probable. The Company assesses collection based on a number of factors, including past transaction history and the creditworthiness of the client. The Company maintains a revenue reserve for potential credits to be issued in accordance with service level agreements or for other revenue adjustments. Deferred Revenue Deferred revenue consists of billings or payments received from clients for subscription service, usage and professional services in advance of revenue recognition and is recognized in accordance with the Company’s revenue recognition policy discussed above. The Company generally invoices its clients monthly in advance for subscription services. Accordingly, the deferred revenue balance does not represent the total contract value of sales arrangements. Cost of Revenue Cost of revenue consists primarily of personnel costs, including stock-based compensation, fees that the Company pays to telecommunications providers for usage, Universal Service Fund and related funds, or USF, contributions and other regulatory costs, depreciation and related expenses of the servers and equipment, costs to build out and maintain co-location data centers, and allocated office and facility costs and amortization of acquired technology. Personnel costs include those associated with support of the Company’s solution, clients and data center operations, as well as with providing professional services. Data center costs include costs to build out and setup, as well as co-location fees for the right to place the Company’s servers in data centers owned by third parties. Research and Development Research and development expenses consist primarily of salary and related expenses, including stock-based compensation, for personnel related to the development of improvements and expanded features for our services, as well as quality assurance, testing, product management and allocated overhead. Research and development costs are expensed as incurred except for internal use software development costs that qualify for capitalization. The Company reviews development costs incurred for internal-use software in the application development stage and assesses costs for capitalization. Advertising Costs The Company primarily advertises its services through the web and in conjunction with partners. Advertising costs are expensed as incurred and were $12.2 million , $11.4 million and $10.7 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. Commissions Commissions consist of variable compensation earned by sales personnel and referral fees the Company pays to third parties. Under Accounting Standard Codification 605 - Revenue Recognition (“ASC 605”), all sales commissions associated with the acquisition or renewal of a client contract were recognized as sales and marketing expense as incurred. On January 1, 2018, the Company adopted Accounting Standard Codification 606 - Revenue from Contracts with Customers (“ASC 606”). In connection with the adoption of ASC 606, the Company also adopted ASC 340-40, Other Assets and Deferred Costs - Contracts with Customers (“ASC 340-40”), which requires the deferral of incremental costs of obtaining a contract with a customer. Collectively, the Company refers to ASC 606 and ASC 340-40 as the “new standard.” Under the new standard, the Company defers all incremental commission costs to obtain the contract, and amortizes these costs over a period of benefit determined to be five years. See Note 2 for more information. Commission expense was $10.3 million , $14.0 million and $10.2 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. The Company’s sales commission expense under ASC 606 decreased by approximately $7.7 million in 2018 as compared to 2017. Stock-Based Compensation All stock-based compensation granted to employees and non-employee directors is measured as the grant date fair value of the award. The Company estimates the fair value of stock options and purchase rights under the Company’s Equity Incentive Plans and the 2014 Employee Stock Purchase Plan, or ESPP, respectively, using the Black-Scholes option-pricing model. The fair value of restricted stock awards is equal to the fair value of the Company’s common stock on the date of grant. Compensation expense is recognized net of forfeitures using the straight-line method over the service period, which is generally the vesting period. Income Taxes The Company accounts for income taxes using the asset and liability method. Deferred tax assets and liabilities are recognized for the estimated future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax basis. Deferred tax assets and liabilities are measured using enacted tax rates in effect for the year in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in operations in the period that includes the enactment date. The Company records a valuation allowance to reduce its deferred tax assets to the amount of future tax benefit that is more likely than not to be realized. As of December 31, 2018 and 2017 , the Company recorded a full valuation allowance against the net deferred tax assets because of its history of operating losses in the United States. The Company classifies interest and penalties on unrecognized tax benefits as income tax expense. Comprehensive loss Comprehensive loss consists of net loss, unrealized gains or losses on available-for-sale marketable investments and the effects of foreign currency translation adjustments. The Company presents comprehensive loss as part of the consolidated statements of operations. The changes in the accumulated balances of the components of other comprehensive loss were not material for the periods presented. Net Income (Loss) Per Share Basic net income (loss) per share is calculated by dividing net income (loss) by the weighted average number of shares of common stock outstanding during the period, and excludes any dilutive effects of employee stock-based awards and warrants. Diluted net income (loss) per share is computed giving effect to all potentially dilutive common shares, including common stock issuable upon exercise of stock options and warrants, vesting of restricted stock units and purchases under the ESPP. In periods of net loss, all potentially issuable shares of common stock are excluded from the diluted net loss per share computation because they are anti-dilutive. Therefore, basic and diluted net loss per share are the same for all years presented in the Company’s consolidated statements of operations and comprehensive loss. Indemnification Certain of the Company’s agreements with clients include provisions for indemnification against liabilities if the Company’s solution infringes a third-party’s intellectual property rights. To date, the Company has not incurred any material costs as a result of such indemnification provisions and the Company has not accrued any liabilities related to such obligations in the consolidated financial statements as of December 31, 2018 and 2017 . Segment Information The Company has determined that its Chief Executive Officer is its chief operating decision maker. The Company’s Chief Executive Officer reviews financial information presented on a consolidated basis for purposes of assessing performance and making decisions on how to allocate resources. Accordingly, the Company has determined that it operates in a single reportable segment. Recently Adopted Accounting Pronouncements In March 2016, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standard Update (“ASU”) No. 2016-09, Compensation-Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting . This ASU simplifies several aspects of the accounting for share-based payment transactions, including the accounting for income taxes, forfeitures, and statutory tax withholding requirements, as well as classification in the statement of cash flows. The guidance was effective for the Company beginning in the first quarter of 2017. Accordingly, commencing in January 2017, the Company accounted for forfeitures as they occurred, rather than by estimating expected forfeitures. The net effect of this change was recognized as a $0.2 million reduction to accumulated deficit in the consolidated financial statements. Upon adoption of the new standard, all excess tax benefits and tax deficiencies (including tax benefits of dividends on share-based payment awards) are recognized as income tax expense or benefit in the income statement. The tax effects of exercised or vested awards are treated as discrete items in the reporting period in which they occur. The Company also recognizes excess tax benefits regardless of whether the benefit reduces taxes payable in the current period. The Company applied the modified retrospective adoption approach beginning January 1, 2017 and prior periods have not been adjusted. As a result, the Company established a net operating loss deferred tax asset of $5.3 million to account for prior period excess tax benefits through retained earnings, however an offsetting valuation allowance of $5.3 million was also established through retained earnings because it is not more likely than not that the deferred tax asset will be realized due to historical and expected future losses, such that there is no impact on the Company’s consolidated financial statements. In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers: Topic 606, amending revenue recognition guidance and requiring more detailed disclosures to enable users of financial statements to understand the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. ASU 2014-09 also includes Subtopic 340-40, Other Assets and Deferred Costs - Contracts with Customers , which requires the deferral of incremental costs of obtaining a contract with a customer. The Company adopted ASU 2014-09 and its related amendments (collectively “ASC 606”) effective on January 1, 2018 using the modified retrospective method. See Note 2 for disclosure on the impact of adopting this standard. Recent Accounting Pronouncements Not Yet Effective In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments , which requires measurement and recognition of expected credit losses for certain types of financial assets held. ASU 2016-13 is effective for the Company in its first quarter of 2020, and earlier adoption is permitted beginning in the first quarter of 2019. The Company is currently evaluating the impact of ASU 2016-13 on its consolidated financial statements. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) and issued subsequent amendments to the initial guidance in 2017 and 2018 within ASU 2017-13, ASU 2018-01, ASU 2018-10, ASU 2018-11 and ASU 2018-20 (collectively, “Topic 842”). Under the new guidance, a lessee will be required to recognize assets and liabilities for both finance, or capital, and operating leases with lease terms of more than 12 months. The ASU also will require disclosures to help investors and other financial statement users better understand the amount, timing, and uncertainty of cash flows arising from leases. Lessor accounting will remain largely unchanged from current GAAP. In transition, lessees and lessors are required to recognize and measure leases at the beginning of the earliest period presented using a modified retrospective approach that includes a number of optional practical expedients that entities may elect to apply. The Company will adopt Topic 842 using the modified retrospective method on January 1, 2019. The Company will elect the available practical expedients that it will apply and implement internal controls to enable the preparation of financial information upon adoption. The most significant impact will be the recognition of right-of use (ROU) assets and lease liabilities for operating leases, while the Company’s accounting for capital leases remained substantially unchanged. Adoption of Topic 842 will result in the recognition of ROU assets of $7.0 million to $10.0 million , and offsetting lease liabilities for operating leases of $7.0 million to $10.0 million , as of January 1, 2019. In August 2018, the FASB issued ASU 2018-15, Intangibles—Goodwill and Other—Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract (“ASU 2018-15”), which clarifies the accounting for implementation costs in cloud computing arrangements. ASU 2018-15 is effective for the Company in the first quarter of fiscal 2020. Early adoption is permitted. The Company is currently evaluating the impact this guidance will have on its consolidated financial statements. There are several other new accounting pronouncements issued by the FASB, which the Company will adopt. However, the Company does not believe any of those accounting pronouncements will have a material impact on its consolidated financial position, operating results or statements of cash flows.

ASC 606 Adoption Impact and Rev

ASC 606 Adoption Impact and Revenue from Contracts with Customers	12 Months Ended
	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
ASC 606 Adoption Impact and Revenue from Contracts with Customers	ASC 606 Adoption Impact and Revenue from Contracts with Customers ASC 606 Adoption Impact On January 1, 2018, the Company adopted ASC 606 using the modified retrospective method, applying to all contracts. The Company recognized the cumulative effect of applying the new revenue standard as an adjustment to the opening balance of accumulated deficit at the beginning of 2018. The comparative information has not been restated and continues to be reported under the accounting standards in effect for the period presented, or ASC 605. Adoption of the new standard resulted in changes to the Company’s accounting policies for revenue recognition, commissions and deferred commissions as discussed below. The Company recorded a net reduction to opening accumulated deficit of $24.1 million as of January 1, 2018 due to the cumulative impact of adopting the new standard. The primary impact of adopting the new standard related to the deferral of $23.1 million in incremental commission costs of obtaining subscription contracts. Under ASC 605, the Company expensed all commission costs as incurred. Under the new standard, the Company defers all incremental commission costs to obtain the contract, and amortizes these costs over a period of benefit determined to be five years . The remaining $1.0 million impact of adopting the new standard related to revenue being recognized earlier than it would have been under ASC 605. Practical Expedients and Exemptions The Company applies a practical expedient that permits the Company to apply ASC 340-40 to a single portfolio of contracts, as they are similar in their characteristics, and the financial statement effects of applying ASC 340-40 to that portfolio would not differ materially from applying it to the individual contracts within that portfolio. Additionally, the Company has elected the optional exemption which allows for the exclusion of the amounts for remaining performance obligations that are part of contracts with an original expected duration of one year or less. Impact on Consolidated Financial Statements Select consolidated balance sheet line items, which reflect the adoption impact of the new standard, were as follows: December 31, 2018 (in thousands) As Reported Balances without adoption of ASC 606 Effect of Change Assets: Accounts receivable, net $ 24,797 $ 24,694 $ 103 Prepaid expenses and other current assets 8,014 8,228 (214 ) Deferred contract acquisition costs 30,886 — 30,886 Liabilities: Deferred revenue - current 17,391 19,116 (1,725 ) Shareholders’ Equity: Accumulated deficit (151,497 ) (183,997 ) 32,500 Select consolidated statement of operations line items, which reflect the adoption of the new standard, were as follows: Year ended December 31, 2018 (in thousands, except per share amounts) As Reported Balances without adoption of ASC 606 Effect of Change Revenue $ 257,664 $ 256,548 $ 1,116 Cost of revenue 104,034 103,525 509 Gross profit 153,630 153,023 607 Sales and marketing 72,001 79,749 (7,748 ) Income from operations 7,009 (1,346 ) 8,355 Net loss (221 ) (8,576 ) 8,355 Basic and diluted net loss per share $ — $ (0.15 ) $ 0.15 Select consolidated cash flow line items, which reflect the adoption of the new standard, were as follows: Year ended December 31, 2018 (in thousands) As Reported Balances without adoption of ASC 606 Effect of Change Accounts receivable $ (5,829 ) $ (5,726 ) $ (103 ) Prepaid expenses and other current assets (2,806 ) (3,020 ) 214 Deferred contract acquisition costs (7,748 ) — (7,748 ) Deferred revenue 3,956 5,681 (1,725 ) Net cash provided by operating activities 38,622 38,622 — Contract Balances The following table provides information about accounts receivable, net, deferred contract acquisition costs, contract assets and contract liabilities from contracts with customers (in thousands): December 31, 2018 January 1, 2018 Accounts receivable, net $ 24,797 $ 19,151 Deferred contract acquisition costs: Current $ 9,372 $ 7,059 Non-current 21,514 16,079 Total deferred contract acquisition costs $ 30,886 $ 23,138 Contract assets and contract liabilities: Contract assets (included in prepaid expenses and other current assets) $ 330 $ 736 Contract liabilities (deferred revenue) 17,391 13,568 Net contract assets (liabilities) $ (17,061 ) $ (12,832 ) The Company receives payments from customers based upon billing cycles. Invoice payment terms are usually 30 days or less. Accounts receivable are recorded when the right to consideration becomes unconditional. The Company’s deferred contract acquisition costs are recorded when incurred and are amortized over a customer benefit period of five years . The Company’s contract assets consist of unbilled amounts typically resulting from professional services revenue recognition when it exceeds the total amounts billed to the customer. The Company’s contract liabilities consist of advance payments and billings in excess of revenue recognized. In the year ended December 31, 2018 , the Company recognized revenue of $10.2 million related to its contract liabilities at January 1, 2018 . Deferred Contract Acquisition Costs In connection with the adoption of ASC 340-40, the Company capitalizes certain contract acquisition costs consisting primarily of commissions paid when contracts are signed and related incremental fringe benefits. As of January 1, 2018, the date of ASC 340-40 adoption, the Company had $23.1 million capitalized in deferred contract acquisition costs related to contracts where the benefit period had not yet expired. In the year ended December 31, 2018 , amortization from amounts capitalized was $8.4 million and amounts expensed as incurred was $1.9 million . As of December 31, 2018 , the Company had no impairment loss in relation to costs capitalized. Remaining Performance Obligations As of December 31, 2018 , the aggregate amount of the total transaction price allocated in contracts with original duration of greater than one year to the remaining performance obligations was $96.8 million . The Company expects to recognize revenue on approximately three-fourths of the remaining performance obligation over the next 24 months, with the balance recognized thereafter. The Company has elected the optional exemption, which allows for the exclusion of the amounts for remaining performance obligations that are part of contracts with an original expected duration of one year or less. Such remaining performance obligations represent unsatisfied or partially unsatisfied performance obligations pursuant to ASC 606.

Investments and Fair Value Meas

Investments and Fair Value Measurements	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Investments and fair value measurements	Investments and Fair Value Measurements Marketable Investments The Company’s marketable investments have been classified and accounted for as available-for-sale. The Company’s marketable investments as of December 31, 2018 were as follows (in thousands): December 31, 2018 Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Certificates of deposit $ 4,259 $ — $ — $ 4,259 U.S. treasury 637 — — 637 U.S. agency securities and government sponsored securities 154,314 1 (111 ) 154,204 Commercial paper 3,475 — — 3,475 Municipal bonds 6,090 — (4 ) 6,086 Corporate bonds 41,307 — (61 ) 41,246 Total $ 210,082 $ 1 $ (176 ) $ 209,907 The following table presents the gross unrealized losses and the fair value for those marketable investments that were in an unrealized loss position for less than 12 months as of December 31, 2018 (in thousands): December 31, 2018 Gross Unrealized Losses Fair Value U.S. treasury $ — $ 637 U.S. agency securities and government sponsored securities (111 ) 153,212 Municipal bonds (4 ) 6,086 Corporate bonds (61 ) 41,246 Total $ (176 ) $ 201,181 The contractual maturities of the Company’s marketable investments as of December 31, 2018 were less than one year. Fair Value Measurements The Company carries cash equivalents and marketable investments at fair value. Fair value is based on the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Fair value is estimated by applying the following hierarchy, which prioritizes the inputs used to measure fair value into three levels and bases the categorization within the hierarchy upon the lowest level of input that is available and significant to the fair value measurement: Level 1 — Observable inputs, which include unadjusted quoted prices in active markets for identical assets or liabilities. Level 2 — Observable inputs other than Level 1 inputs, such as quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 — Unobservable inputs that are supported by little or no market activity and that are based on management’s assumptions, including fair value measurements determined by using pricing models, discounted cash flow methodologies or similar techniques. The Company determined the fair value of its Level 1 financial instruments, which are traded in active markets, using quoted market prices for identical instruments. Marketable investments classified within Level 2 of the fair value hierarchy are valued based on other observable inputs, including broker or dealer quotations or alternative pricing sources. When quoted prices in active markets for identical assets or liabilities are not available, the Company relies on non-binding quotes from its investment managers, which are based on proprietary valuation models of independent pricing services. These models generally use inputs such as observable market data, quoted market prices for similar instruments, historical pricing trends of a security as relative to its peers. To validate the fair value determination provided by its investment managers, the Company reviews the pricing movement in the context of overall market trends and trading information from its investment managers. The Company performs routine procedures such as comparing prices obtained from independent source to ensure that appropriate fair values are recorded. The following table sets forth the Company’s assets measured at fair value by level within the fair value hierarchy (in thousands): December 31, 2018 Level 1 Level 2 Level 3 Total Assets Cash equivalents Money market funds $ 10,833 $ — $ — $ 10,833 U.S. Treasury 638 — — 638 U.S. agency securities — 50 — 50 Commercial paper — 498 — 498 Total cash equivalents $ 11,471 $ 548 $ — $ 12,019 Marketable investments Certificates of deposit $ — $ 4,259 $ — $ 4,259 U.S. Treasury 637 — — 637 U.S. agency securities and government sponsored securities — 154,204 — 154,204 Commercial paper — 3,475 — 3,475 Municipal bonds — 6,086 — 6,086 Corporate bonds — 41,246 — 41,246 Total marketable investments $ 637 $ 209,270 $ — $ 209,907 December 31, 2017 Level 1 Level 2 Level 3 Total Assets Cash equivalents: Money market funds $ 20,092 $ — $ — $ 20,092 Other Assets Embedded conversion option held for investment $ — $ — $ 984 $ 984 In February 2018, the Company exercised its embedded option held for investment, related to the Company’s investment in a privately-held company, or the Investee company, to convert its convertible note into common shares of the Investee company prior to the Investee company’s acquisition. In March 2018, the Company received proceeds of $1.9 million from the conversion and sale of the convertible note of the Investee company with a carrying value of $1.6 million . Proceeds from the sale of the investment totaled $2.1 million . The Company expects to receive the remainder of the proceeds in the first half of 2019. As of December 31, 2018 , the estimated fair value of the Company’s outstanding 0.125% convertible senior notes due 2023 was $316.1 million . The fair value was determined based on the quoted price of the convertible senior notes in an inactive market on the last trading day of the reporting period and has been classified as Level 2 in the fair value hierarchy. See Note 6 for further information on the Company’s 0.125% convertible senior notes due 2023. There were no assets or liabilities measured at fair value on a non-recurring basis as of December 31, 2018 . The Company’s other financial instruments’ fair value, including accounts receivable, accounts payable and other current liabilities, approximate its carrying value due to the relatively short maturity of those instruments. The carrying amounts of the Company’s capital leases approximate their fair value, which is the present value of expected future cash payments based on assumptions about current interest rates and the creditworthiness of the Company.

Financial Statement Components

Financial Statement Components	12 Months Ended
	Dec. 31, 2018
Financial Statement Components [Abstract]
Financial Statement Components	Financial Statement Components Cash and cash equivalents consisted of the following (in thousands): December 31, 2018 2017 Cash and cash equivalents: Cash $ 69,893 $ 48,855 Money market funds 10,833 20,092 U.S. Treasury 638 — U.S. agency securities 50 — Commercial paper 498 — Total cash and cash equivalents $ 81,912 $ 68,947 Accounts receivable, net consisted of the following (in thousands): December 31, 2018 2017 Trade accounts receivable $ 23,068 $ 17,481 Unbilled trade accounts receivable, net of advance client deposits 1,741 1,600 Allowance for doubtful accounts (12 ) (33 ) Accounts receivable, net $ 24,797 $ 19,048 Prepaid expenses and other current assets consisted of the following (in thousands): December 31, 2018 2017 Prepaid expenses $ 5,005 $ 2,437 Other current assets 2,679 2,403 Contract assets 330 — Prepaid expenses and other current assets $ 8,014 $ 4,840 Property and equipment, net consisted of the following (in thousands): December 31, 2018 2017 Computer and network equipment $ 54,452 $ 47,195 Computer software 10,064 6,974 Internal-use software development costs 500 500 Furniture and fixtures 1,491 1,282 Leasehold improvements 855 801 Property and equipment 67,362 56,752 Accumulated depreciation and amortization (41,477 ) (36,864 ) Property and equipment, net $ 25,885 $ 19,888 In accordance with the Company’s property and equipment policy, the Company reviews the estimated useful lives of its fixed assets on an ongoing basis. The Company’s review of its existing estimates indicated that the actual lives of certain data center assets were longer than the previously estimated useful lives used for depreciation purposes in the Company’s financial statements. As a result, effective July 1, 2017, the Company changed the estimated useful lives of certain data center assets to better reflect the estimated periods during which these assets will remain in service. The estimated useful lives of these assets, which the Company previously depreciated for three years, was increased to a range of three to five years. For the year ended December 31, 2017 , this change in accounting estimate decreased depreciation expense by $1.6 million and decreased both basic and diluted net loss per share by $0.03 . Depreciation and amortization expense associated with property and equipment was $9.8 million , $7.8 million , and $7.9 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. Property and equipment capitalized under capital lease obligations consists primarily of computer and network equipment and was as follows (in thousands): December 31, 2018 2017 Gross $ 47,383 $ 46,624 Less: accumulated depreciation and amortization (33,547 ) (30,438 ) Total $ 13,836 $ 16,186 Accrued and other current liabilities consisted of the following (in thousands): December 31, 2018 2017 Accrued expenses $ 3,494 $ 3,130 Accrued compensation and benefits 10,277 8,657 Accrued and other current liabilities $ 13,771 $ 11,787

Goodwill and Intangible Assets

Goodwill and Intangible Assets	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	Goodwill and Intangible Assets Goodwill Goodwill was recorded as a result of the Company’s acquisition in October 2013 of Face It, Corp., which the Company also refers to as SoCoCare. During the fourth quarter of 2018 , the Company completed its annual goodwill impairment test. Based on its assessment of the qualitative factors, the Company’s management concluded that the fair value of the Company’s goodwill was more likely than not greater than its carrying amount as of December 31, 2018 . As such, it was not necessary to perform the two-step quantitative goodwill impairment test. Subsequent to the 2018 annual impairment test, the Company believes there have been no significant events or circumstances negatively affecting the valuation of goodwill. As of December 31, 2018 and 2017 , there was no impairment to the carrying value of the Company’s goodwill. Intangible Assets Intangible assets were acquired in connection with the Company’s acquisition of SoCoCare in October 2013 . The components of intangible assets were as follows (in thousands): December 31, 2018 December 31, 2017 Gross Carrying Amount Accumulated Net Gross Accumulated Net Developed technology $ 2,460 $ (1,829 ) $ 631 $ 2,460 $ (1,478 ) $ 982 Customer relationships 520 (520 ) — 520 (437 ) 83 Domain names 50 (50 ) — 50 (42 ) 8 Total $ 3,030 $ (2,399 ) $ 631 $ 3,030 $ (1,957 ) $ 1,073 Amortization expense related to intangible assets was $0.4 million , $0.5 million and $0.5 million for the years ended December 31, 2018 , 2017 and 2016 . As of December 31, 2018 , the expected future amortization expense for intangible assets was as follows (in thousands): Period Expected Future 2019 $ 351 2020 280 Total $ 631 Intangible assets are reviewed for impairment whenever events or changes in circumstances indicate an asset’s carrying value may not be recoverable. The Company concluded that there was no impairment to the carrying value of its intangible assets as of December 31, 2018 and 2017 .

Debt

Debt	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Debt	Debt 0.125% Convertible Senior Notes and Capped Call In May 2018, the Company issued $258.8 million aggregate principal amount of 0.125% convertible senior notes (“Notes”) due May 1, 2023 in a private offering. The Notes are the Company’s senior unsecured obligations and bear interest at a fixed rate of 0.125% per annum, payable semiannually in arrears on May 1 and November 1 of each year, beginning on November 1, 2018 . The total net proceeds from the offering, after deducting initial purchase discounts and estimated debt issuance costs, were approximately $250.7 million . Each $1,000 principal amount of the Notes is initially convertible into 24.4978 shares of the Company’s common stock (the “Conversion Option”), which is equivalent to an initial conversion price of approximately $40.82 per share of common stock, subject to adjustment upon the occurrence of specified events. The Notes are convertible, in multiples of $1,000 principal amount, at the option of the holders at any time prior to the close of business on the business day immediately preceding November 1, 2022 , only under the following circumstances: (1) during any calendar quarter commencing after the calendar quarter ended on September 30, 2018 (and only during such calendar quarter), if the last reported sale price of the Company’s common stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price on each applicable trading day; (2) during the five business day period after any five consecutive trading day period (the “Measurement Period”) in which the trading price (as defined in the indenture governing the Notes) per $1,000 principal amount of Notes for each trading day of the Measurement Period was less than 98% of the product of the last reported sale price of the Company’s common stock and the conversion rate in effect on each such trading day; (3) if the Company calls any or all of the Notes for redemption, at any time prior to the close of business on the second scheduled trading day immediately preceding the redemption date; or (4) upon the occurrence of specified corporate events. On or after November 1, 2022 until the close of business on the second scheduled trading day immediately preceding the maturity date, holders may convert all or any portion of their Notes, in multiples of $1,000 principal amount, at the option of the holder regardless of the foregoing circumstances. Upon conversion, the Company will pay or deliver, as the case may be, cash, shares of the Company’s common stock or a combination of cash and shares of the Company’s common stock, at the Company’s election. If the Company undergoes a fundamental change (as defined in the indenture governing the Notes), subject to certain conditions, holders may require the Company to repurchase for cash all or any portion of their Notes, in principal amounts of $1,000 or a multiple thereof, at a fundamental change repurchase price equal to 100% of the principal amount of the Notes to be repurchased, plus accrued and unpaid interest, if any, to, but excluding, the fundamental change repurchase date. In addition, following certain corporate events that occur prior to the maturity date or if the Company issues a notice of redemption, it will, under certain circumstances, increase the conversion rate for holders who elect to convert their Notes in connection with such corporate event or during the relevant redemption period. During the year ended December 31, 2018 , the conditions allowing holders of the Notes to convert were not met. The Notes were therefore not convertible during the year ended December 31, 2018 and were classified as long-term debt. The Company may not redeem the Notes prior to May 5, 2021. The Company may redeem for cash all or any portion of the Notes, at its option, on or after May 5, 2021 if the last reported sale price of its common stock has been at least 130% of the conversion price then in effect for at least 20 trading days (whether or not consecutive) during any 30 consecutive trading day period (including the last trading day of such period) ending not more than two trading days immediately preceding the date on which the Company provides notice of redemption at a redemption price equal to 100% of the principal amount of the Notes to be redeemed, plus accrued and unpaid interest, if any, to, but excluding, the redemption date. No sinking fund is provided for the Notes. The Notes are the Company’s senior unsecured obligations and will rank senior in right of payment to any of the Company’s indebtedness that is expressly subordinated in right of payment to the Notes; equal in right of payment to any of the Company’s unsecured indebtedness that is not so subordinated; effectively junior in right of payment to any of the Company’s secured indebtedness to the extent of the value of the assets securing such indebtedness; and structurally junior to all indebtedness and other liabilities (including trade payables) of the Company’s subsidiaries. In accounting for the transaction, the Notes were separated into liability and equity components. The carrying amount of the liability component was calculated by measuring the fair value of a similar debt instrument that does not have an associated conversion feature. The carrying amount of the equity component representing the conversion option was $63.8 million and was determined by deducting the fair value of the liability component from the par value of the Notes. The equity component was recorded in additional paid-in-capital and is not remeasured as long as it continues to meet the conditions for equity classification. The excess of the principal amount of the liability component over its carrying amount (the “Debt Discount”) is being amortized to interest expense over the contractual term of the Notes at an effective interest rate of 6.39% . In accounting for the debt issuance cost of $8.1 million related to the Notes, the Company allocated the total amount incurred to the liability and equity components of the Notes based on their relative values. Issuance costs attributable to the liability component were $6.1 million and are being amortized to interest expense using the effective interest method over the contractual term of the Notes. Issuance costs attributable to the equity component were netted with the equity component in additional paid-in-capital. The net carrying amount of the liability component of the Notes was as follows (in thousands): December 31, 2018 Principal $ 258,750 Unamortized debt discount (56,564 ) Unamortized issuance costs (5,423 ) Net carrying amount $ 196,763 The net carrying amount of the equity component of the Notes was as follows (in thousands): December 31, 2018 Debt discount for conversion option $ 63,756 Issuance costs (1,998 ) Net carrying amount $ 61,758 Interest expense related to the Notes was as follows (in thousands): Year Ended December 31, 2018 Contractual interest expense $ 209 Amortization of debt discount 7,192 Amortization of issuance costs 689 Total interest expense $ 8,090 In connection with the pricing of the Notes, the Company entered into privately negotiated capped call transactions (the “Capped Call Transactions”) with certain financial institutions. The Capped Call Transactions are expected generally to reduce the potential dilution to the Company’s common stock upon any conversion of the Notes and/or offset any cash payments the Company is required to make in excess of the principal amount of converted Notes, as the case may be, with such reduction and/or offset subject to a cap based on the cap price. The initial cap price of the Capped Call Transactions is $62.80 per share, and is subject to certain adjustments under the terms of the Capped Call Transactions. The Capped Call Transactions cover, subject to anti-dilution adjustments, approximately 6.3 million shares of the Company’s common stock. For accounting purposes, the Capped Call Transactions are separate transactions, and not part of the terms of the Notes. As these transactions meet certain accounting criteria, the Capped Call Transactions are recorded in stockholders’ equity and are not accounted for as derivatives. The cost of $31.4 million incurred in connection with the Capped Call Transactions was recorded as a reduction to additional paid-in capital. The net impact to the Company’s stockholders’ equity, included in additional paid-in capital, relating to the issuance of the Notes was as follows (in thousands): December 31, 2018 Conversion option $ 63,756 Payments for capped call transactions (31,412 ) Issuance costs (1,998 ) Total $ 30,346 2016 Loan and Security Agreement In August 2016, the Company entered into a loan and security agreement, or the 2016 Loan and Security Agreement, with the lenders party thereto and City National Bank, as agent for such lenders. The 2016 Loan and Security Agreement provided for a revolving line of credit, of up to $50.0 million and was scheduled to mature on August 1, 2019. The revolving line of credit bore a variable interest rate equal to the prime rate plus 0.50% , subject to a 0.25% increase if the Company’s adjusted EBITDA was negative at the end of any fiscal quarter. The Company was also required to pay a commitment fee equal to 0.25% of the unused portion of the revolving line of credit as well as an anniversary fee of $31,250 on each of August 1, 2017 and 2018. The obligations of the Company under the 2016 Loan and Security Agreement were guaranteed by its subsidiary, Five9 Acquisition LLC, and were secured by a first priority lien on substantially all of the assets of the Company and Five9 Acquisition LLC. In May 2018, the Company paid off the then outstanding principal balance of the revolving line of credit and, in July 2018, the Company terminated the 2016 Loan and Security Agreement. The proceeds from the 2016 Loan and Security Agreement were used to extinguish indebtedness under all prior loan and security agreements and for working capital and other general corporate purposes. The Company recorded a $1.0 million loss on extinguishment of prior debts in the third quarter of 2016. The loss was comprised of $0.4 million in prepayment penalties, a $0.4 million write-off of unamortized debt discounts, and a $0.2 million write-off of unamortized debt issuance costs. FCC Civil Penalty In June 2015, the Company entered into a consent decree with the FCC Enforcement Bureau (See Note 10 for more information), in which the Company agreed to pay a civil penalty of $2.0 million to the U.S. Treasury in twelve equal quarterly installments starting in July 2015 without interest. As a result, the Company discounted the $2.0 million liability, which was accrued in the third quarter of 2014 for the then tentative civil penalty, to its then present value of $1.7 million at an annual interest rate of 12.75% to reflect the imputed interest and reclassified this discounted liability from ‘Accrued federal fees’ to ‘Notes payable.’ The $0.3 million discount was recorded as a reduction to general and administrative expense in the three months ended June 30, 2015 and was recognized as interest expense over the payment term of the civil penalty. As of December 31, 2018 , the Company did not have any outstanding obligations under the civil penalty. As of December 31, 2017 , the outstanding civil penalty payable was $0.3 million , of which the net carrying value was $0.3 million , and was included as ‘Notes payable’ in the accompanying consolidated balance sheets. The Company’s outstanding debt as of the dates set forth below is summarized as follows (in thousands): December 31, 2018 2017 Note payable - FCC civil penalty, gross $ — $ 333 Less: discount — (7 ) Note payable, net carrying value — 326 Convertible senior notes 196,763 — Revolving line of credit — 32,594 Interest accretion under 2016 line of credit — $ 10 Total debt, net carrying value $ 196,763 $ 32,930 Less: current portion of debt * $ — $ 336 Total debt, less current portion ** $ 196,763 $ 32,594 * Included in ‘Notes payable’ in the consolidated balance sheet as of December 31, 2017. ** Included in ‘Convertible senior notes’ and ‘Revolving line of credit’ as of December 31, 2018 and 2017, respectively, in the consolidated balance sheets. Maturity of the Company’s outstanding debt as of December 31, 2018 was as follows (in thousands): Period Amount to Mature 2023 $ 258,750 Total $ 258,750

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Stockholders' Equity	Stockholders’ Equity Capital Structure Common Stock The Company is authorized to issue 450,000,000 shares of common stock with a par value of $0.001 per share. As of December 31, 2018 and 2017 , the Company had 59,210,496 and 56,631,647 shares of common stock issued and outstanding, respectively. Holders of the Company’s common stock are entitled to dividends, if and when declared by the board of directors. In the event of liquidation, dissolution or winding up, subject to the rights of the holders of any then outstanding shares of preferred stock, holders of common stock will be entitled to receive the assets and funds of the Company that are legally available for distribution. Preferred Stock The Company is authorized to designate and issue up to 5,000,000 shares of preferred stock with a par value of $0.001 per share in one or more series without stockholder approval and to fix the rights, preferences, privileges and restrictions thereof. As of December 31, 2018 and 2017 , there were no shares of preferred stock issued and outstanding. Warrants As of December 31, 2017 , the Company had outstanding warrants to purchase 13,013 shares of common stock with a weighted average exercise price of $5.76 per share. The warrants were exercised in the third quarter of 2018 . As of December 31, 2018 , the Company had no warrants outstanding. Common Stock Reserved for Future Issuance Shares of common stock reserved for future issuance related to outstanding equity awards and employee equity incentive plans as of December 31, 2018 , were as follows (in thousands): Common Stock Reserved Stock options outstanding 3,122 Restricted stock units outstanding 2,325 Shares available for future grant under 2014 Plan 8,443 Shares available for future issuance under ESPP 1,691 Total shares of common stock reserved 15,581 Equity Incentive Plans Prior to the Company’s initial public offering, or IPO, in April 2014, the Company granted stock options under its Amended and Restated 2004 Equity Incentive Plan, as amended, or the 2004 Plan. Under the terms of the 2004 Plan, the Company had the ability to grant incentive and nonstatutory stock options. Incentive stock options could only be granted to Company employees. Nonstatutory stock options could be granted to Company employees, directors and consultants. Such options are exercisable at prices, as determined by the board of directors, generally equal to the fair value of the Company’s common stock at the date of grant. Options granted to employees generally vest over a four -year period, with an initial vesting period of 12 months for 25% of the shares, and the remaining 75% of the shares vesting monthly on a ratable basis over the remaining 36 months . Options generally expire 10 years after the grant date and are generally exercisable upon vesting. Vested options generally expire 90 days after termination of the optionee’s employment or relationship as a consultant or director, unless otherwise extended by the terms of the stock option agreement. In March 2014, the Company’s board of directors and stockholders approved the 2014 Equity Incentive Plan, or 2014 Plan, and 5,300,000 shares of common stock were authorized for issuance under the 2014 Plan. In addition, on the first day of each year beginning in 2015 and ending in 2024, the 2014 Plan provides for an annual automatic increase to the shares reserved for issuance in an amount equal to 5% of the total number of shares outstanding on December 31st of the preceding calendar year or a lesser number as determined by the Company’s board of directors. Pursuant to the automatic annual increase, 2,960,524 additional shares were reserved under the 2014 Plan on January 1, 2019. No further grants were made under the 2004 Plan once the 2014 Plan became effective on April 3, 2014. Upon the effectiveness of the 2014 Plan, all shares reserved for future issuance under the 2004 Plan became available for issuance under the 2014 Plan. Additionally, any forfeited or expired shares that would have otherwise returned to the 2004 Plan instead return to the 2014 Plan. The 2014 Plan allows the Company to grant stock options, restricted stock units, or RSUs, restricted stock awards, performance stock awards, stock appreciation rights, performance cash awards, and other stock awards. To date, the Company has granted stock options and RSUs under the 2014 Plan. Stock options granted under the 2014 Plan are in general at a price equal to the fair market value of the common stock on the date of grant and vest over four years. The Company’s stock options expire 10 years from the date of grant. Each RSU granted under the 2014 Plan represents a right to receive one share of the Company’s common stock when the RSU vests. RSUs generally vest over one to four years. Stock Options A summary of the Company’s stock option activity during the year ended December 31, 2018 is as follows (in thousands, except years and per share data): Number of Shares Weighted Weighted Average Remaining Contractual Life (Years) Aggregate (1) Outstanding as of December 31, 2017 4,047 $ 8.00 Options granted 477 35.00 Options exercised (1,274 ) 6.11 Options forfeited or expired (128 ) 17.69 Outstanding as of December 31, 2018 3,122 $ 12.52 6.2 97,423 Vested and expected to vest as of December 31, 2018 3,122 12.52 6.2 97,423 Exercisable as of December 31, 2018 2,234 7.86 5.2 80,112 (1) The aggregate intrinsic value amounts are computed based on the difference between the exercise price of the stock options and the fair market value of the Company’s common stock of $43.72 per share as of December 31, 2018 for all in-the-money stock options outstanding. Following is additional information pertaining to the Company’s stock option activity (in thousands, except per share data): Year Ended December 31, 2018 2017 2016 Weighted average grant date fair value per share of options granted $ 16.33 $ 8.81 $ 4.50 Intrinsic value of options exercised (1) 34,785 33,820 5,865 Total fair value of options vested during the period 4,744 7,296 3,813 Cash received from options exercised 7,779 6,047 4,286 (1) Intrinsic value of options exercised is the difference between the fair market value of the Company’s common stock at the time of exercise and the exercise price paid. Restricted Stock Units A summary of RSU activity during the year ended December 31, 2018 is as follows (in thousands, except years and per share data): Number of Shares Weighted Average Grant Date Fair Value Per Share Outstanding as of December 31, 2017 2,033 $ 12.81 RSUs granted 1,586 32.30 RSUs vested and released (1,053 ) 13.16 RSUs forfeited (241 ) 18.47 Outstanding as of December 31, 2018 2,325 $ 25.36 Following is additional information pertaining to the Company’s RSU activity (in thousands, except per share data): Year Ended December 31, 2018 2017 2016 Weighted average grant date fair value per share of RSUs granted $ 32.30 $ 18.29 $ 9.71 Total fair value of RSUs vested during the period 41,245 21,161 10,706 Employee Stock Purchase Plan In March 2014, the Company’s board of directors and stockholders adopted the 2014 Employee Stock Purchase Plan, or ESPP, and the shares authorized for issuance thereunder. The ESPP became effective on April 3, 2014. The ESPP permits eligible employees to purchase shares of the Company’s common stock through payroll deductions with up to 15% of their pre-tax earnings subject to certain Internal Revenue Code limitations. The purchase price of the shares is 85% of the lower of the fair market value of the Company’s common stock on the first day of a six month offering period, except for the initial offering period, or the relevant purchase date. In addition, no participant may purchase more than 1,500 shares of common stock in each purchase period. The number of shares of common stock originally reserved for issuance under the ESPP was 880,000 shares, which increases automatically each year, beginning on January 1, 2015 and continuing through January 1, 2024, by the lesser of (i) 1% of the total number of shares of our common stock outstanding on December 31 of the preceding calendar year; (ii) 1,000,000 shares of common stock (subject to adjustment to reflect any split or combination of our common stock); or (iii) such lesser number as determined by the Company’s board of directors. Pursuant to the automatic annual increase, 592,104 additional shares were reserved under the ESPP on January 1, 2019. During 2018 , 246,079 shares were purchased by employees under the ESPP at a weighted average price of $23.29 per share. Stock-Based Compensation Stock-based compensation expenses for the years ended December 31, 2018 , 2017 and 2016 were as follows (in thousands): Year Ended December 31, 2018 2017 2016 Cost of revenue $ 3,333 $ 2,202 $ 1,375 Research and development (1) 5,303 3,042 2,059 Sales and marketing 6,307 4,364 2,363 General and administrative (2) 13,541 5,735 3,846 Total stock-based compensation $ 28,484 $ 15,343 $ 9,643 (1) Includes an incremental stock-based compensation cost due to modification of certain stock-based awards of a former executive of the Company in the third quarter of 2018. (2) Effective December 2017, the Company’s former Chief Executive Officer and President resigned from his position and became the Executive Chairman of the Board. Due to this substantive change in status, certain of his stock option and RSU awards were modified which resulted in incremental stock based compensation expense of approximately $ 1.0 million in the fourth quarter of 2017. As of December 31, 2018 , unrecognized stock-based compensation expense by award type and their expected weighted-average recognition periods are summarized in the following table (in thousands, except years). Stock Option RSU ESPP Unrecognized stock-based compensation expense $ 11,369 $ 53,668 $ 1,048 Weighted-average amortization period 2.9 years 2.8 years 0.4 years The Company recognizes stock-based compensation expense that is calculated based upon awards that have vested, reduced for actual forfeitures. All stock-based compensation for equity awards granted to employees and non-employee directors is measured based on the grant date fair value of the award. The Company values RSUs at the closing market price of its common stock on the date of grant. The Company estimates the fair value of each stock option and purchase right under the ESPP granted to employees on the date of grant using the Black-Scholes option-pricing model and using the assumptions disclosed in the table below. Expected volatility is based upon the historical volatility of a peer group of publicly traded companies. The expected term of options granted is estimated using the simplified method by taking the average of the vesting term and the contractual term of the option. The expected volatility assumption for purchase rights under the ESPP is based on the historical volatility of the Company’s common stock. The risk-free rate for the expected term of the awards is based on U.S. Treasury zero-coupon issues at the time of grant. The Company has not paid, and does not anticipate paying, cash dividends on its shares of common stock. Accordingly, the expected dividend yield is zero. The weighted average assumptions used to value stock options and purchase rights under the ESPP granted during the years ended December 31, 2018 , 2017 and 2016 were as follows: Stock Options Year Ended December 31, 2018 2017 2016 Expected term (years) 6.0 5.9 5.7 Volatility 45% 49% 46% Risk-free interest rate 2.8% 2.1% 1.4% Dividend yield — — — ESPP Granted In November 2018 May 2018 November 2017 May 2017 November 2016 May 2016 Expected term (years) 0.5 0.5 0.5 0.5 0.5 0.5 Volatility 37% 36% 36% 43% 42% 58% Risk-free interest rate 2.1% 1.4% 1.4% 1.0% 0.6% 0.4% Dividend yield — — — — — —

Net Loss Per Share

Net Loss Per Share	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Net Loss Per Share	Net Loss Per Share Basic net loss per share is calculated by dividing net loss by the weighted average number of shares of common stock outstanding during the period, and excludes any dilutive effects of employee stock-based awards and warrants. Diluted net income per share is computed giving effect to all potentially dilutive shares of common stock, including common stock issuable upon exercise of stock options and warrants and vesting of restricted stock. As the Company had net losses for the years ended December 31, 2018 , 2017 and 2016 , all potentially issuable shares of common stock were determined to be anti-dilutive. The following table presents the calculation of basic and diluted net loss per share (in thousands, except per share data). Year Ended December 31, 2018 2017 2016 Net loss $ (221 ) $ (8,969 ) $ (11,860 ) Weighted-average shares used in computing basic and diluted net loss per share 58,076 54,946 52,342 Basic and diluted net loss per share $ — $ (0.16 ) $ (0.23 ) The following securities were excluded from the calculation of diluted net loss per share because their effect would have been anti-dilutive (in thousands). December 31, 2018 2017 2016 Stock options 3,122 4,047 5,556 Restricted stock units 2,325 2,033 2,019 Common stock warrants — 13 132 Total 5,447 6,093 7,707 The Company expects to settle the principal amount of its Notes outstanding as of December 31, 2018 in cash, and therefore, uses the treasury stock method for calculating any potential dilutive effect of the conversion spread. The conversion spread will have a dilutive impact when the average market price of the Company’s common stock for a given period exceeds the initial conversion price of $40.82 per share for the Notes. The potential shares of common stock from Notes were excluded from the calculation of diluted net loss per share because their effect would have been anti-dilutive.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The following table presents components of loss before income taxes for the periods presented (in thousands): Year Ended December 31, 2018 2017 2016 United States $ (638 ) $ (9,434 ) $ (12,222 ) International 717 733 416 Income (loss) before income taxes $ 79 $ (8,701 ) $ (11,806 ) Provision for income taxes for the periods presented consisted of (in thousands): Year Ended December 31, 2018 2017 2016 Current: U.S. federal $ — $ — $ — U.S. state 28 42 16 Foreign 272 226 38 Total provision for income taxes $ 300 $ 268 $ 54 Income tax expense differed from the amount computed by applying the U.S. federal statutory income tax rate of 21% to pre-tax income (loss) for the periods presented as a result of the following (in thousands): Year Ended December 31, 2018 2017 2016 U.S. federal tax at statutory rate $ 17 $ (2,958 ) $ (4,014 ) U.S. state income taxes 2,539 (708 ) 490 Non-deductible expense (benefit) 14,485 (5,673 ) 931 Research and development credit (339 ) (402 ) (262 ) Stock-based compensation (11,360 ) (14,622 ) 983 Impact of 2017 Tax Act — 25,952 — Other 106 2 (104 ) Change in valuation allowance (5,148 ) (1,323 ) 2,030 Total provision for income taxes $ 300 $ 268 $ 54 The tax effects of temporary differences that give rise to significant portions of the Company’s deferred tax assets and liabilities as of December 31, 2018 and 2017 related to the following (in thousands): December 31, 2018 2017 Deferred tax assets: Net operating loss and credit carryforwards $ 54,966 $ 47,991 Accrued liabilities 4,271 3,183 Allowance for doubtful accounts 400 416 Deferred revenue 832 140 Accrued compensation 1,081 900 Intangibles 4 7 Gross deferred tax assets 61,554 52,637 Valuation allowance (47,127 ) (52,275 ) Net deferred tax assets 14,427 362 Deferred tax liabilities: Property and equipment (370 ) (98 ) Amortized intangibles (155 ) (264 ) Convertible senior notes (13,902 ) — Gross deferred tax liabilities (14,427 ) (362 ) Net deferred taxes $ — $ — The Company has not provided for U.S. income taxes on undistributed earnings of its foreign subsidiaries because it intends to permanently re-invest those earnings outside the United States. The undistributed earnings of the Company’s foreign subsidiaries were immaterial as of December 31, 2018 and 2017 , and was $1.2 million as of December 31, 2016 . A valuation allowance is provided for 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, for the year ended December 31, 2018 , the Company has provided a valuation allowance against its U.S. net deferred tax assets. The net change in the valuation allowance for the years ended December 31, 2018 and 2017 was an increase of $5.1 million and a decrease of $1.3 million , respectively. As of December 31, 2018 , the Company had net operating loss carryforwards for federal and state income tax purposes of $216.8 million and $120.0 million , respectively, available to reduce future income subject to income taxes. If not utilized, the federal and state net operating loss carryforwards will begin to expire in 2024 and 2028 , respectively. As of December 31, 2018 , the Company also had research credit carryforwards for federal and California state tax purposes of $3.2 million and $2.8 million , available to reduce future income subject to income taxes. The federal research credit carryforwards will begin to expire in 2022 and the California state research credits can be carried forward indefinitely . The Internal Revenue Code (“IRC”) of 1986, as amended, imposes restrictions on the utilization of net operating losses in the event of an “ownership change” of a corporation. Accordingly, a company’s ability to use net operating losses may be limited as prescribed under the IRC Section 382. Events that may cause limitations in the amount of the net operating losses that the Company may use in any one year include, but are not limited to, a cumulative ownership change of more than 50% over a three -year period. Utilization of federal and state net operating losses may be subject to substantial annual limitation due to the ownership change limitations provided by the IRC Section 382 and similar state provisions. In the event the Company has changes in ownership, net operating losses and research and development credit carryforwards, which are fully reserved by the deferred tax asset valuation allowance, could be limited and may expire unutilized. Unrecognized Tax Benefits The table below shows the changes in the gross amount of unrecognized tax benefits for the periods presented (in thousands): Year Ended December 31, 2018 2017 2016 Unrecognized benefit — beginning of period $ 3,115 $ 2,805 $ 2,485 Gross increases — current year tax positions 7,608 310 324 Gross decreases — prior year tax positions — — (4 ) Unrecognized benefit — end of period $ 10,723 $ 3,115 $ 2,805 As of December 31, 2018 and 2017 , an immaterial amount of the total unrecognized tax benefits, if recognized, would have an impact on the Company’s effective tax rate. The Company recognizes interest and penalties related to uncertain tax positions as income tax expense. The Company does not anticipate its total unrecognized tax benefits as of December 31, 2018 will significantly change due to settlement of examination or the expiration of statute of limitations during the next 12 months. 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 12 months. The Company is subject to taxation in the United States, various states and several foreign jurisdictions. Due to the Company’s net carryover of unused operating losses, all years from 2001 forward remain subject to future examination by the U.S. federal and state tax authorities. The Company’s foreign tax returns are open to audit under the statutes of limitations of the respective foreign countries in which the subsidiaries are located. The Company considers all undistributed earnings of its foreign subsidiaries indefinitely reinvested. Tax Reform In December 2017 , new legislation (the “2017 Tax Act”) was enacted that significantly revised the Internal Revenue Code of 1986, as amended. The 2017 Tax Act, among other things, contains significant changes to corporate taxation, including reduction of the corporate tax rate from a top marginal rate of 35% to a flat rate of 21% , limitation of the tax deduction for interest expense to 30% of adjusted earnings, limitation of the deduction for newly generated net operating losses to 80% of current year taxable income and elimination of net operating loss carrybacks, one time taxation of offshore earnings at reduced rates regardless of whether they are repatriated (the “Transition Tax”), future taxation of certain classes of offshore earnings regardless of whether they are repatriated, immediate deductions for certain new investments instead of deductions for depreciation expense over time, and modifying or repealing many business deductions and credits beginning in 2018. In December 2017, the SEC issued Staff Accounting Bulletin No. 118 which provided a measurement period of up to one year from the enactment of the 2017 Tax Act for companies to complete the accounting for the 2017 Tax Act and its related impacts. Upon completion of the accounting related to the income tax effect of the 2017 Tax Act, there were no material adjustments made to the previous estimates.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Commitments As of December 31, 2018, $258.8 million of the Notes were outstanding. The Notes are due May 1, 2023. See Note 6 for more information. Leases The Company has operating lease agreements for offices, research and development, and sales and marketing facilities that expire at various dates through 2021 . The Company recognizes rent expense on a straight-line basis over the lease term and records the difference between cash rent payments and the recognized rent expense as a deferred rent liability. Rent expense was $2.8 million , $2.6 million and $2.1 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. The Company enters into capital leases to finance data center and other computer and networking equipment. As of December 31, 2018 , approximate remaining future minimum lease payments under non-cancelable leases were as follows (in thousands): Year Ending December 31, Capital Leases Operating Leases 2019 $ 7,220 $ 3,041 2020 4,284 2,634 2021 704 653 2022 — — Total future minimum lease payment $ 12,208 $ 6,328 Less — amount representing interest (1,052 ) Present value of total capital lease obligation $ 11,156 Capital lease obligation — current portion 6,647 Capital lease obligation — net of current portion 4,509 Hosting, Telecommunication Usage and Maintenance Services The Company has agreements with third parties to provide co-location hosting and telecommunication usage services. The agreements require payments per month for a fixed period of time in exchange for certain guarantees of network and telecommunication availability. The Company is also committed to make future payments under maintenance service contracts for certain data center equipment. As of December 31, 2018 , future minimum payments under these arrangements were as follows (in thousands): Year Ending December 31, Hosting Services Telecommunication Usage Services Equipment Maintenance Services 2019 $ 1,942 $ 3,138 $ 345 2020 1,209 1,781 243 2021 500 875 76 2022 700 294 — Total future minimum payment $ 4,351 $ 6,088 $ 664 Universal Services Fund Liability The Company’s business is regulated by the FCC and the Company is required to make contributions to the USF. The Company is registered with the Universal Service Administrative Company, or USAC, which is charged by the FCC with administering the USF. The Company has been remitting the required contributions to USAC since its registration with the USAC in April 2013. However, the Company was also required to pay assessments for periods prior to its registration with the USAC. In this connection, the Company had recorded a disputed liability of $3.9 million related to its obligations for contributions for the period from 2008 to 2012. In January 2017, the FCC’s Wireline Competition Bureau ruled in the Company’s favor with respect to most of the disputed amount. In September 2017, USAC issued a credit to the Company reflecting the FCC’s ruling for the $3.1 million of the $3.9 million in disputed liability. In addition, USAC dropped its claim for interest and penalties related to the disputed liability of $3.1 million . The remaining $0.8 million in dispute involves USAC’s assessment of liability for the period of 2003 through 2007, which was prior to the five year window during which the Company was required to maintain financial records for USF contribution purposes. The Company filed a Request for Review (a form of appeal) of this disputed amount with the FCC’s Wireline Competition Bureau in 2013, which remains pending. If the Request for Review is not resolved in the Company’s favor, it is possible that the Company will be required to pay the assessments relating to 2003 through 2017. As of December 31, 2018 , the Company had accrued $0.9 million in respect of the remaining disputed assessments, including interest and penalties, for the period of 2003 through 2007. State and Local Taxes and Surcharges In April 2012, the Company commenced collecting and remitting sales taxes on sales of subscription services in all the U.S. states in which it determined it was obligated to do so. During the first quarter of 2015, the Company conducted an updated sales tax review of the taxability of sales of its subscription services. As a result, the Company determined that it may be obligated to collect and remit sales taxes on such sales in four additional states. Based on its best estimate of the probable sales tax liability in those four states relating to its sales of subscription services during the period 2011 through 2014, during the three months ended March 31, 2015, the Company recorded a general and administrative expense of $0.6 million to accrue for such taxes. During 2013, the Company analyzed its activities and determined it may be obligated to collect and remit various state and local taxes and surcharges on its usage-based fees. The Company had not remitted state and local taxes on usage-based fees in any of the periods prior to 2014 and therefore accrued a sales tax liability for this contingency. In January 2014, the Company commenced paying such taxes and surcharges to certain state authorities. In June 2014, the Company commenced collecting state and local taxes or surcharges on usage-based fees from its clients on a current basis and remitting such taxes to the applicable U.S. state taxing authorities. During 2016, the Company analyzed its activities and determined that it may be obligated to collect and remit sales, excise and utility user taxes on certain charges related to toll free service in certain U.S. states and municipalities. The Company had neither collected nor remitted state or local taxes on such charges prior to December 2016. In the third quarter of 2016, the Company recorded an accrual for potential tax exposure related to toll free call charges for all periods open under the applicable statutes of limitations for assessment. During 2018, the Company analyzed its activities and determined that it may be obligated to collect and remit sales tax on separately-stated service-based charges related to its subscription services. The Company had neither collected nor remitted sales tax on such charges prior to September 2018. In the third quarter of 2018, the Company began collecting applicable taxes on such charges. During 2018 , 2017 and 2016 , the Company remitted $0.1 million , zero and $0.3 million , respectively, for contingent sales taxes on both usage-based fees and sales of subscription services. For the years ended December 31, 2018 , 2017 and 2016 , the Company recognized a gain of $0.3 million , a gain of $0.6 million , and a gain of $0.4 million , respectively, as an adjustment to general and administrative expense related to its estimated sales tax liability on both usage-based fees and sales of subscription services in the U.S. and Canada, which was not being collected from its clients. As of December 31, 2018 and 2017 , the Company had total accrued liabilities of $1.1 million and $1.5 million , respectively, for such contingent sales taxes and surcharges that were not being collected from its clients but may be imposed by various taxing authorities, of which $0.1 million and $0.4 million , respectively, were included in current “Sales tax liability” on the consolidated balance sheets, and the remaining were included in non-current “Sales tax liability” on the consolidated balance sheets. The Company’s estimate of the probable loss incurred under this contingency is based on its analysis of the source location of its usage-based fees and the regulations and rules in each tax jurisdiction. Legal Matters The Company is involved in various legal and regulatory matters arising in the normal course of business. In management’s opinion, resolution of these matters is not expected to have a material impact on the Company’s consolidated results of operations, cash flows, or its financial position. However, due to the uncertain nature of legal matters, an unfavorable resolution of a matter could materially affect the Company’s future consolidated results of operations, cash flows or financial position in a particular period. The Company expenses legal fees as incurred. The Company is currently involved in the following lawsuits as a defendant. Melcher Litigation On September 28, 2016, a complaint was filed in the United States District Court for the Southern District of California against Five9, Inc., or Five9, as the successor in interest to Face It, Corp., or Face It, and Lance Fried, a former Five9 employee who was the former Chief Executive Officer of Face It. The action, captioned Melcher, et al. v. Five9, Inc., et al., No. 16-cv-02440, or the Melcher Litigation, was filed as a direct action by Carl Melcher, or Melcher, a purported former stockholder of Face It, and his related investment entity Melcher Family Limited Partnership, or MFLP. In the complaint, the plaintiffs alleged that Face It repurchased the plaintiffs’ stock in September 2013 before Five9 acquired Face It, and that in connection with the repurchase, Fried made material misstatements or omissions to Melcher by failing to disclose that Face It allegedly was in concurrent discussions about a potential sale of its company to Five9. The complaint alleged violations of Sections 10(b) and 20(a) of the Securities Exchange Act of 1934 and Rule 10b-5 promulgated thereunder, as well as various claims under state law and common law. The complaint sought to set aside Face It’s September 2013 stock repurchase from the plaintiffs, as well as an unspecified amount of damages and an award of attorney’s fees and costs, in addition to other relief. On November 8, 2016, the court entered an order staying the lawsuit and ordered the parties to proceed to arbitration of the dispute before the American Arbitration Association, or AAA. On November 16, 2016, Melcher and MFLP submitted a Demand for Arbitration to AAA against Five9, asserting claims identical to those alleged in the lawsuit. On March 31, 2017, Five9 reached a settlement with the plaintiffs that fully resolved the plaintiffs’ claims against Five9 and provided for mutual releases between the plaintiffs and Five9 in exchange for a one-time payment by Five9 to the plaintiffs of $1.7 million . As a result of the settlement, the AAA arbitration was concluded, and on July 10, 2017 the plaintiffs filed an amended complaint in the Melcher Litigation solely against Fried, removing Five9 as a defendant. For a discussion of the indemnification claims arising out of this matter, see “—Indemnification Agreements.” Indemnification Agreements In the ordinary course of business, the Company enters into agreements of varying scope and terms pursuant to which it agrees to indemnify clients, 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 its directors, officers and certain employees that will require it, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors, officers or employees. Other than as described below, there are no claims that it is aware of that could have a material effect on the consolidated balance sheet, consolidated statement of operations and comprehensive loss, or consolidated statements of cash flows. On October 27, 2016, the Company received notice from Lance Fried, a former officer and director of Face It, Corp. of his claim for indemnification by the Company (as successor in interest to Face It), and for advancement of all legal fees and expenses he incurs in connection with the defense of the lawsuit captioned Melcher, et al. v. Five9, Inc., et al., No. 16-cv-02440, in the U.S. District Court for the Southern District of California. In the lawsuit, plaintiff Carl Melcher, a purported former stockholder of Face It, and his related investment entity, Melcher Family Limited Partnership, allege that Face It repurchased the plaintiffs’ stock in September 2013 before the Company acquired Face It, and that in connection with the repurchase, Fried made material misstatements or omissions to Melcher by failing to disclose that Face It allegedly was in concurrent discussions about a potential sale of its company to the Company. The lawsuit alleges violations of Sections 10(b) and 20(a) of the Securities Exchange Act of 1934 and Rule 10b-5 promulgated thereunder, as well as various claims under state law and common law. On January 9, 2018, Mr. Fried initiated an arbitration against the Company in which he alleged that the Company breached advancement obligations to him. On June 11, 2018, the arbitrator ordered the Company to advance the fees Mr. Fried incurs (and has already incurred) in connection with the defense of the Melcher litigation. To date, the Company has advanced approximately $0.5 million in fees and expenses, included in general and administrative expenses, on behalf of Mr. Fried. Regardless of the arbitrator’s order, Mr. Fried is required to reimburse the Company for any amounts advanced to him if it is ultimately determined that Mr. Fried is not entitled to indemnification in connection with the Melcher litigation. In addition, the Company believes that it has indemnification rights against the former stockholders of Face It (including Mr. Fried) for all losses that are incurred by the Company in connection with the Melcher litigation, including without limitation, amounts incurred to indemnify or advance the legal fees and expenses of Mr. Fried pursuant to his indemnification claim against the Company. The Company has asserted claims in arbitration against both Mr. Fried and the representative of the former Face It stockholders to recoup these losses. These claims are stayed pending the resolution of the Melcher litigation.

Geographical Information

Geographical Information	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Geographical Information	Geographical Information The following table is a summary of revenues by geographic region based on client billing address and has been estimated based on the amounts billed to clients during the periods (in thousands). Year Ended December 31, 2018 2017 2016 United States $ 239,378 $ 188,303 $ 151,484 International 18,286 11,922 10,606 Total revenue $ 257,664 $ 200,225 $ 162,090 The following table summarizes total property and equipment, net in the respective locations (in thousands). December 31, 2018 2017 2016 United States $ 23,931 $ 17,949 $ 13,025 International 1,954 1,939 1,663 Property and equipment, net $ 25,885 $ 19,888 $ 14,688

Retirement Plans

Retirement Plans	12 Months Ended
	Dec. 31, 2018
Retirement Benefits [Abstract]
Retirement Plans	Retirement Plans The Company has a 401(k) plan to provide tax deferred salary deductions for all eligible employees. Participants may make voluntary contributions to the 401(k) plan, limited by certain Internal Revenue Service restrictions. The Company is responsible for the administrative costs of the 401(k) plan. The Company does not match employee contributions. The Company complies with the requirement of maintaining a retirement plan for employees in the Philippines. This plan is a non-contributory and defined benefit type that provides retirement to employees equal to approximately one month salary for every year of credited service for employees who attain the normal retirement of age of 60 with at least five years of service. The benefits are paid in a lump sum amount upon retirement from the Company. Total defined benefit liability was $0.7 million and $0.5 million as of December 31, 2018 and 2017 , respectively. Total retirement expense for this plan was $0.1 million , $0.3 million , and $0.1 million for the years ended December 31, 2018 , 2017 , and 2016 , respectively.

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data (Unaudited)	Selected Quarterly Financial Data (Unaudited) Selected quarterly financial information for 2018 and 2017 is as follows: Quarter Ended Dec. 31, 2018 Sept. 30, 2018 Jun. 30, 2018 Mar. 31, 2018 Dec. 31, 2017 Sept. 30, 2017 Jun. 30, 2017 Mar. 31, 2017 (unaudited, in thousands, except per share data) Revenue $ 72,335 $ 65,304 $ 61,120 $ 58,905 $ 55,403 $ 50,081 $ 47,727 $ 47,014 Cost of revenue (1)(2) 28,339 26,179 24,814 24,702 22,363 20,497 20,273 19,971 Gross profit 43,996 39,125 36,306 34,203 33,040 29,584 27,454 27,043 Operating expenses: Research and development (1)(2) 8,451 9,582 8,367 7,772 6,748 6,689 6,836 6,847 Sales and marketing (1)(2) 18,793 17,818 17,912 17,478 17,358 16,502 16,932 15,778 General and administrative (1)(2) 10,766 10,746 9,833 9,103 8,767 4,679 6,845 8,860 Total operating expenses 38,010 38,146 36,112 34,353 32,873 27,870 30,613 31,485 Income (loss) from operations 5,986 979 194 (150 ) 167 1,714 (3,159 ) (4,442 ) Other income (expense), net: Extinguishment of debt — — — — — — — — Interest expense (3,462 ) (3,595 ) (2,378 ) (810 ) (836 ) (865 ) (888 ) (882 ) Interest income and other 1,359 1,352 206 398 164 118 90 118 Total other income (expense), net (2,103 ) (2,243 ) (2,172 ) (412 ) (672 ) (747 ) (798 ) (764 ) Income (loss) before income taxes 3,883 (1,264 ) (1,978 ) (562 ) (505 ) 967 (3,957 ) (5,206 ) Provision for income taxes 150 41 64 45 126 43 50 49 Net income (loss) $ 3,733 $ (1,305 ) $ (2,042 ) $ (607 ) $ (631 ) $ 924 $ (4,007 ) $ (5,255 ) Net income (loss) per share: Basic $ 0.06 $ (0.02 ) $ (0.04 ) $ (0.01 ) $ (0.01 ) $ 0.02 $ (0.07 ) $ (0.10 ) Diluted $ 0.06 $ (0.02 ) $ (0.04 ) $ (0.01 ) $ (0.01 ) $ 0.02 $ (0.07 ) $ (0.10 ) Shares used in computing net loss per share: Basic 58,926 58,454 57,903 56,399 56,034 55,310 54,723 53,688 Diluted 62,071 58,454 57,903 56,399 56,034 59,441 54,723 53,688 (1) Included stock-based compensation as follows: Quarter Ended Dec. 31, 2018 Sept. 30, 2018 Jun. 30, 2018 Mar. 31, 2018 Dec. 31, 2017 Sept. 30, 2017 Jun. 30, 2017 Mar. 31, 2017 (unaudited, in thousands) Cost of revenue $ 942 $ 860 $ 853 $ 678 $ 594 $ 599 $ 575 $ 434 Research and development 1,010 2,352 1,064 877 807 797 801 637 Sales and marketing 1,747 1,613 1,585 1,362 1,128 1,084 1,224 928 General and administrative 3,794 4,044 3,295 2,408 2,111 1,240 1,254 1,130 Total stock-based compensation $ 7,493 $ 8,869 $ 6,797 $ 5,325 $ 4,640 $ 3,720 $ 3,854 $ 3,129 (2) Included depreciation and amortization expenses as follows: Quarter Ended Dec. 31, 2018 Sept. 30, 2018 Jun. 30, 2018 Mar. 31, 2018 Dec. 31, 2017 Sept. 30, 2017 Jun. 30, 2017 Mar. 31, 2017 (unaudited, in thousands) Cost of revenue $ 2,129 $ 2,021 $ 1,864 $ 1,794 $ 1,611 $ 1,397 $ 1,716 $ 1,576 Research and development 331 278 233 194 170 182 237 206 Sales and marketing 6 30 30 29 30 30 30 30 General and administrative 372 338 322 303 257 272 287 283 Total depreciation and amortization $ 2,838 $ 2,667 $ 2,449 $ 2,320 $ 2,068 $ 1,881 $ 2,270 $ 2,095

Description of Business and S_2

Description of Business and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (“SEC”) regarding annual financial reporting. All intercompany transactions and balances have been eliminated in consolidation. Certain prior period amounts included in the consolidated financial statements have been reclassified to conform to the current period presentation.
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 and liabilities and disclosure 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. The significant estimates made by management affect revenue and related reserves. Management periodically evaluates such estimates and they are adjusted prospectively based upon such periodic evaluation. Actual results could differ from those estimates.
Foreign Currency	Foreign Currency The functional currency of the Company’s foreign subsidiaries is the U.S. dollar. For these subsidiaries, the monetary assets and liabilities are re-measured into U.S. dollars at the current exchange rate as of the balance sheet date, and all non-monetary assets and liabilities are re-measured into U.S. dollars at historical exchange rates. Revenues are primarily denominated in U.S dollars. Expenses are converted using average rates in effect on a monthly basis. Exchange gains and losses resulting from foreign currency transactions were not significant in any period and are reported in “Other income (expense), net” in the consolidated statements of operations and comprehensive loss.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company’s cash and cash equivalents consist of highly liquid investments with maturities of three months or less at the time of purchase. The Company’s cash equivalents consist of investments in money market funds, U.S. treasury securities, U.S. agency securities and commercial paper.
Marketable Investments	Marketable Investments The Company’s marketable investments consist of U.S agency securities and government sponsored securities, U.S. treasury securities, certificates of deposit, municipal bonds, corporate bonds and commercial paper. The Company determines the appropriate classification of its investments in marketable investments at the time of purchase and re-evaluates such designation at each balance sheet date. The Company’s marketable investments have been classified and accounted for as available-for-sale. Marketable investments are carried at fair value.
Concentration Risks	Concentration Risks Financial instruments, which potentially subject the Company to significant concentrations of credit risk, consist primarily of cash and cash equivalents, marketable investments and accounts receivable. A significant portion of the Company’s cash and cash equivalents is held at three large reputable financial institutions.
Allowance for Doubtful Accounts	Allowance for Doubtful Accounts 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 creditworthiness of each client. If circumstances change, such as higher-than-expected defaults or an unexpected material adverse change in a major client’s ability to meet its financial obligations, the Company’s estimate of the recoverability of the amounts due could be reduced by a material amount.
Property and Equipment, Net	Property and Equipment, Net Property and equipment is stated at cost less accumulated depreciation and amortization, and is depreciated using the straight-line method over the estimated useful lives of the assets as follows: Asset Category Estimated Useful Lives Computer and network equipment 3 to 5 years Computer software 3 years Development costs 1 to 5 years Furniture and fixtures 7 years Leasehold improvements Shorter of useful life or lease term 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 and amortization are removed from the consolidated balance sheet and any resulting gain or loss is reflected in the consolidated statements of operations and comprehensive loss in the period realized. The Company evaluates the recoverability of property and equipment for possible impairment whenever events or circumstances indicate that the carrying amount of such assets or asset groups may not be recoverable. Recoverability of these assets is measured by a comparison of the carrying amounts to the future undiscounted cash flows the assets or asset groups are expected to generate. If such evaluation indicates that the carrying amount of the assets or asset groups is not recoverable, the carrying amount of such assets or asset groups is reduced to fair value. No impairment losses have been recognized in any of the periods presented.
Goodwill and Intangible Assets	Goodwill and Intangible Assets The Company records goodwill when the consideration paid in a business combination exceeds the fair value of the net tangible assets and the identified intangible assets acquired. Goodwill is not amortized, but instead is required to be tested for impairment annually and whenever events or changes in circumstances indicate that the carrying value of goodwill may exceed its fair value. The Company performs testing for impairment of goodwill in its fourth quarter, or as events occur or circumstances change that would more likely than not reduce the fair value of the Company’s single reporting unit below its carrying amount. A qualitative assessment is first made to determine whether it is necessary to perform the two-step quantitative goodwill impairment test. This initial qualitative assessment includes, among other things, consideration of: (i) market capitalization of the Company, (ii) past, current and projected future earnings and equity; (iii) recent trends and market conditions; and (iv) valuation metrics involving similar companies that are publicly-traded and acquisitions of similar companies, if available. If this initial qualitative assessment indicates that it is more likely than not that impairment exists, a second analysis will be performed, involving a comparison between the estimated fair values of the Company’s reporting unit with its respective carrying amount including goodwill. If the carrying value exceeds estimated fair value, there is an indication of potential impairment, and a third analysis is performed to measure the amount of impairment. The third analysis involves calculating an implied fair value of goodwill by measuring the excess of the estimated fair value of the reporting unit over the aggregate estimated fair values of the individual assets less liabilities. If the carrying value of goodwill exceeds the implied fair value of goodwill, an impairment charge is recorded for the excess. Intangible assets, consisting of acquired developed technology, domain names and customer relationships, are carried at cost less accumulated amortization. All intangible assets have been determined to have definite lives and are amortized on a straight-line basis over their estimated remaining economic lives, ranging from five to seven years. Amortization expense related to developed technology is included in cost of revenue. Amortization expense related to customer relationships is included in sales and marketing expense. Amortization expense related to domain names is included in general and administrative expense. Intangible assets are reviewed for impairment whenever events or changes in circumstances indicate an asset’s carrying value may not be recoverable.
Revenue Recognition	Revenue Recognition Revenue is recognized when control of the promised services are transferred to customers in an amount that reflects the consideration that the Company expects to receive in exchange for those services. The Company generates all of its revenue from contracts with customers. In contracts with multiple performance obligations, it identifies each performance obligation and evaluates whether the performance obligations are distinct within the context of the contract at contract inception. Performance obligations that are not distinct at contract inception are combined. The Company allocates the transaction price to each distinct performance obligation proportionately based on the estimated standalone selling price for each performance obligation. The Company then looks to how services are transferred to the customer in order to determine the timing of revenue recognition. Most services provided under the Company’s agreements result in the transfer of control over time. The Company’s revenue consists of subscription services and related usage as well as professional services. The Company charges clients subscription fees, usually billed on a monthly basis, for access to the Company’s VCC solution. The subscription fees are primarily based on the number of agent seats, as well as the specific VCC functionalities and applications deployed by the client. Agent seats are defined as the maximum number of named agents allowed to concurrently access the VCC cloud platform. Clients typically have more named agents than agent seats. Multiple named agents may use an agent seat, though not simultaneously. Substantially all of the Company’s clients purchase both subscriptions and related telephony usage. A small percentage of the Company’s clients subscribe to its platform but purchase telephony usage directly from a wholesale telecommunications service provider. The Company does not sell telephony usage on a stand-alone basis to any client. The related usage fees are based on the volume of minutes used for inbound and outbound client interactions. The Company also offers bundled plans, generally for smaller deployments, whereby the client is charged a single monthly fixed fee per agent seat that includes both subscription and unlimited usage in the contiguous 48 states and, in some cases, Canada. Professional services revenue is derived primarily from VCC implementations, including application configuration, system integration, optimization, education and training services. Clients are not permitted to take possession of the Company’s software. The Company offers monthly, annual and multiple-year contracts to its clients, generally with 30 days’ notice required for changes in the number of agent seats and sometimes with a minimum number of agent seats required. Larger clients typically choose annual contracts, which generally include an implementation and ramp period of several months. Fixed subscription fees (including bundled plans) are generally billed monthly in advance, while related usage fees are billed in arrears. Support activities include technical assistance for the Company’s solution and upgrades and enhancements to the VCC cloud platform on a when-and-if-available basis, which are not billed separately. The Company generally requires advance deposits from its clients based on estimated usage when such usage is not billed as part of a bundled plan. Any unused portion of the deposit is refundable to the client upon termination of the arrangement, provided all amounts due have been paid. All fees, except usage deposits, are non-refundable. Professional services are primarily billed on a fixed-fee basis and are performed by the Company directly or, alternatively, clients may also choose to perform these services themselves or engage their own third-party service providers. Revenue for professional services is recognized over time, as services are performed. The estimation of variable consideration for each performance obligation requires the Company to make subjective judgments resulting in estimated variable consideration that is included in the transaction fee. This is done to the extent that it is probable, in the Company’s judgment, that a significant reversal in the amount of cumulative revenue recognized under the contract will not occur. The Company estimates the variable consideration in order to allocate the overall transaction fee on a relative stand-alone selling price basis to its multiple performance obligations. This requires the estimate of unit quantities, especially during the initial ramp period of the contract, during which the Company bills under an ‘actual usage’ model for subscription-related services. The Company recognizes revenue on fixed fee professional services performance obligations based on the proportion of labor hours expended compared to the total hours expected to complete the related performance obligation. The determination of the total labor hours expected to complete the performance obligations involves judgment, which influences the initial stand-alone selling price estimate as well as the timing of professional services revenue recognition, although this is typically resolved in a short time frame. When a contract with a customer is signed, the Company assesses whether collection of the fees under the arrangement is probable. The Company assesses collection based on a number of factors, including past transaction history and the creditworthiness of the client. The Company maintains a revenue reserve for potential credits to be issued in accordance with service level agreements or for other revenue adjustments. Deferred Revenue Deferred revenue consists of billings or payments received from clients for subscription service, usage and professional services in advance of revenue recognition and is recognized in accordance with the Company’s revenue recognition policy discussed above. The Company generally invoices its clients monthly in advance for subscription services. Accordingly, the deferred revenue balance does not represent the total contract value of sales arrangements. Cost of Revenue Cost of revenue consists primarily of personnel costs, including stock-based compensation, fees that the Company pays to telecommunications providers for usage, Universal Service Fund and related funds, or USF, contributions and other regulatory costs, depreciation and related expenses of the servers and equipment, costs to build out and maintain co-location data centers, and allocated office and facility costs and amortization of acquired technology. Personnel costs include those associated with support of the Company’s solution, clients and data center operations, as well as with providing professional services. Data center costs include costs to build out and setup, as well as co-location fees for the right to place the Company’s servers in data centers owned by third parties.
Research and Development	Research and Development Research and development expenses consist primarily of salary and related expenses, including stock-based compensation, for personnel related to the development of improvements and expanded features for our services, as well as quality assurance, testing, product management and allocated overhead. Research and development costs are expensed as incurred except for internal use software development costs that qualify for capitalization. The Company reviews development costs incurred for internal-use software in the application development stage and assesses costs for capitalization.
Advertising Costs	Advertising Costs The Company primarily advertises its services through the web and in conjunction with partners. Advertising costs are expensed as incurred
Commissions	Commissions Commissions consist of variable compensation earned by sales personnel and referral fees the Company pays to third parties. Under Accounting Standard Codification 605 - Revenue Recognition (“ASC 605”), all sales commissions associated with the acquisition or renewal of a client contract were recognized as sales and marketing expense as incurred.
Stock-Based Compensation	Stock-Based Compensation All stock-based compensation granted to employees and non-employee directors is measured as the grant date fair value of the award. The Company estimates the fair value of stock options and purchase rights under the Company’s Equity Incentive Plans and the 2014 Employee Stock Purchase Plan, or ESPP, respectively, using the Black-Scholes option-pricing model. The fair value of restricted stock awards is equal to the fair value of the Company’s common stock on the date of grant. Compensation expense is recognized net of forfeitures using the straight-line method over the service period, which is generally the vesting period.
Income Taxes	Income Taxes The Company accounts for income taxes using the asset and liability method. Deferred tax assets and liabilities are recognized for the estimated future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax basis. Deferred tax assets and liabilities are measured using enacted tax rates in effect for the year in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in operations in the period that includes the enactment date. The Company records a valuation allowance to reduce its deferred tax assets to the amount of future tax benefit that is more likely than not to be realized. As of December 31, 2018 and 2017 , the Company recorded a full valuation allowance against the net deferred tax assets because of its history of operating losses in the United States. The Company classifies interest and penalties on unrecognized tax benefits as income tax expense.
Comprehensive Loss	Comprehensive loss Comprehensive loss consists of net loss, unrealized gains or losses on available-for-sale marketable investments and the effects of foreign currency translation adjustments. The Company presents comprehensive loss as part of the consolidated statements of operations. The changes in the accumulated balances of the components of other comprehensive loss were not material for the periods presented.
Net Income (Loss) Per Share	Net Income (Loss) Per Share Basic net income (loss) per share is calculated by dividing net income (loss) by the weighted average number of shares of common stock outstanding during the period, and excludes any dilutive effects of employee stock-based awards and warrants. Diluted net income (loss) per share is computed giving effect to all potentially dilutive common shares, including common stock issuable upon exercise of stock options and warrants, vesting of restricted stock units and purchases under the ESPP. In periods of net loss, all potentially issuable shares of common stock are excluded from the diluted net loss per share computation because they are anti-dilutive. Therefore, basic and diluted net loss per share are the same for all years presented in the Company’s consolidated statements of operations and comprehensive loss.
Indemnification	Indemnification Certain of the Company’s agreements with clients include provisions for indemnification against liabilities if the Company’s solution infringes a third-party’s intellectual property rights.
Segment Information	Segment Information The Company has determined that its Chief Executive Officer is its chief operating decision maker. The Company’s Chief Executive Officer reviews financial information presented on a consolidated basis for purposes of assessing performance and making decisions on how to allocate resources. Accordingly, the Company has determined that it operates in a single reportable segment.
Recent Accounting Pronouncements	Recently Adopted Accounting Pronouncements In March 2016, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standard Update (“ASU”) No. 2016-09, Compensation-Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting . This ASU simplifies several aspects of the accounting for share-based payment transactions, including the accounting for income taxes, forfeitures, and statutory tax withholding requirements, as well as classification in the statement of cash flows. The guidance was effective for the Company beginning in the first quarter of 2017. Accordingly, commencing in January 2017, the Company accounted for forfeitures as they occurred, rather than by estimating expected forfeitures. The net effect of this change was recognized as a $0.2 million reduction to accumulated deficit in the consolidated financial statements. Upon adoption of the new standard, all excess tax benefits and tax deficiencies (including tax benefits of dividends on share-based payment awards) are recognized as income tax expense or benefit in the income statement. The tax effects of exercised or vested awards are treated as discrete items in the reporting period in which they occur. The Company also recognizes excess tax benefits regardless of whether the benefit reduces taxes payable in the current period. The Company applied the modified retrospective adoption approach beginning January 1, 2017 and prior periods have not been adjusted. As a result, the Company established a net operating loss deferred tax asset of $5.3 million to account for prior period excess tax benefits through retained earnings, however an offsetting valuation allowance of $5.3 million was also established through retained earnings because it is not more likely than not that the deferred tax asset will be realized due to historical and expected future losses, such that there is no impact on the Company’s consolidated financial statements. In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers: Topic 606, amending revenue recognition guidance and requiring more detailed disclosures to enable users of financial statements to understand the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. ASU 2014-09 also includes Subtopic 340-40, Other Assets and Deferred Costs - Contracts with Customers , which requires the deferral of incremental costs of obtaining a contract with a customer. The Company adopted ASU 2014-09 and its related amendments (collectively “ASC 606”) effective on January 1, 2018 using the modified retrospective method. See Note 2 for disclosure on the impact of adopting this standard. Recent Accounting Pronouncements Not Yet Effective In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments , which requires measurement and recognition of expected credit losses for certain types of financial assets held. ASU 2016-13 is effective for the Company in its first quarter of 2020, and earlier adoption is permitted beginning in the first quarter of 2019. The Company is currently evaluating the impact of ASU 2016-13 on its consolidated financial statements. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) and issued subsequent amendments to the initial guidance in 2017 and 2018 within ASU 2017-13, ASU 2018-01, ASU 2018-10, ASU 2018-11 and ASU 2018-20 (collectively, “Topic 842”). Under the new guidance, a lessee will be required to recognize assets and liabilities for both finance, or capital, and operating leases with lease terms of more than 12 months. The ASU also will require disclosures to help investors and other financial statement users better understand the amount, timing, and uncertainty of cash flows arising from leases. Lessor accounting will remain largely unchanged from current GAAP. In transition, lessees and lessors are required to recognize and measure leases at the beginning of the earliest period presented using a modified retrospective approach that includes a number of optional practical expedients that entities may elect to apply. The Company will adopt Topic 842 using the modified retrospective method on January 1, 2019. The Company will elect the available practical expedients that it will apply and implement internal controls to enable the preparation of financial information upon adoption. The most significant impact will be the recognition of right-of use (ROU) assets and lease liabilities for operating leases, while the Company’s accounting for capital leases remained substantially unchanged. Adoption of Topic 842 will result in the recognition of ROU assets of $7.0 million to $10.0 million , and offsetting lease liabilities for operating leases of $7.0 million to $10.0 million , as of January 1, 2019. In August 2018, the FASB issued ASU 2018-15, Intangibles—Goodwill and Other—Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract (“ASU 2018-15”), which clarifies the accounting for implementation costs in cloud computing arrangements. ASU 2018-15 is effective for the Company in the first quarter of fiscal 2020. Early adoption is permitted. The Company is currently evaluating the impact this guidance will have on its consolidated financial statements. There are several other new accounting pronouncements issued by the FASB, which the Company will adopt. However, the Company does not believe any of those accounting pronouncements will have a material impact on its consolidated financial position, operating results or statements of cash flows.

Description of Business and S_3

Description of Business and Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Schedule of allowance for doubtful accounts	The following table presents the changes in the allowance for doubtful accounts (in thousands): Year Ended December 31, 2018 2017 2016 Balance, beginning of period $ 33 $ 12 $ 15 Add: bad debt expense 90 95 75 Less: write-offs, net of recoveries (111 ) (74 ) (78 ) Balance, end of period $ 12 $ 33 $ 12
Schedule of property and equipment	Property and equipment is stated at cost less accumulated depreciation and amortization, and is depreciated using the straight-line method over the estimated useful lives of the assets as follows: Asset Category Estimated Useful Lives Computer and network equipment 3 to 5 years Computer software 3 years Development costs 1 to 5 years Furniture and fixtures 7 years Leasehold improvements Shorter of useful life or lease term Property and equipment, net consisted of the following (in thousands): December 31, 2018 2017 Computer and network equipment $ 54,452 $ 47,195 Computer software 10,064 6,974 Internal-use software development costs 500 500 Furniture and fixtures 1,491 1,282 Leasehold improvements 855 801 Property and equipment 67,362 56,752 Accumulated depreciation and amortization (41,477 ) (36,864 ) Property and equipment, net $ 25,885 $ 19,888

ASC 606 Adoption Impact and R_2

ASC 606 Adoption Impact and Revenue from Contracts with Customers (Tables)	12 Months Ended
	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Schedule of impacts from new accounting pronouncements	Select consolidated balance sheet line items, which reflect the adoption impact of the new standard, were as follows: December 31, 2018 (in thousands) As Reported Balances without adoption of ASC 606 Effect of Change Assets: Accounts receivable, net $ 24,797 $ 24,694 $ 103 Prepaid expenses and other current assets 8,014 8,228 (214 ) Deferred contract acquisition costs 30,886 — 30,886 Liabilities: Deferred revenue - current 17,391 19,116 (1,725 ) Shareholders’ Equity: Accumulated deficit (151,497 ) (183,997 ) 32,500 Select consolidated statement of operations line items, which reflect the adoption of the new standard, were as follows: Year ended December 31, 2018 (in thousands, except per share amounts) As Reported Balances without adoption of ASC 606 Effect of Change Revenue $ 257,664 $ 256,548 $ 1,116 Cost of revenue 104,034 103,525 509 Gross profit 153,630 153,023 607 Sales and marketing 72,001 79,749 (7,748 ) Income from operations 7,009 (1,346 ) 8,355 Net loss (221 ) (8,576 ) 8,355 Basic and diluted net loss per share $ — $ (0.15 ) $ 0.15 Select consolidated cash flow line items, which reflect the adoption of the new standard, were as follows: Year ended December 31, 2018 (in thousands) As Reported Balances without adoption of ASC 606 Effect of Change Accounts receivable $ (5,829 ) $ (5,726 ) $ (103 ) Prepaid expenses and other current assets (2,806 ) (3,020 ) 214 Deferred contract acquisition costs (7,748 ) — (7,748 ) Deferred revenue 3,956 5,681 (1,725 ) Net cash provided by operating activities 38,622 38,622 —
Contract with customer, asset and liability	The following table provides information about accounts receivable, net, deferred contract acquisition costs, contract assets and contract liabilities from contracts with customers (in thousands): December 31, 2018 January 1, 2018 Accounts receivable, net $ 24,797 $ 19,151 Deferred contract acquisition costs: Current $ 9,372 $ 7,059 Non-current 21,514 16,079 Total deferred contract acquisition costs $ 30,886 $ 23,138 Contract assets and contract liabilities: Contract assets (included in prepaid expenses and other current assets) $ 330 $ 736 Contract liabilities (deferred revenue) 17,391 13,568 Net contract assets (liabilities) $ (17,061 ) $ (12,832 )

Investments and Fair Value Me_2

Investments and Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Schedule of marketable investments	The Company’s marketable investments have been classified and accounted for as available-for-sale. The Company’s marketable investments as of December 31, 2018 were as follows (in thousands): December 31, 2018 Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Certificates of deposit $ 4,259 $ — $ — $ 4,259 U.S. treasury 637 — — 637 U.S. agency securities and government sponsored securities 154,314 1 (111 ) 154,204 Commercial paper 3,475 — — 3,475 Municipal bonds 6,090 — (4 ) 6,086 Corporate bonds 41,307 — (61 ) 41,246 Total $ 210,082 $ 1 $ (176 ) $ 209,907
Schedule of gross unrealized losses and fair value of marketable investments	The following table presents the gross unrealized losses and the fair value for those marketable investments that were in an unrealized loss position for less than 12 months as of December 31, 2018 (in thousands): December 31, 2018 Gross Unrealized Losses Fair Value U.S. treasury $ — $ 637 U.S. agency securities and government sponsored securities (111 ) 153,212 Municipal bonds (4 ) 6,086 Corporate bonds (61 ) 41,246 Total $ (176 ) $ 201,181
Schedule of assets carried at fair value	The following table sets forth the Company’s assets measured at fair value by level within the fair value hierarchy (in thousands): December 31, 2018 Level 1 Level 2 Level 3 Total Assets Cash equivalents Money market funds $ 10,833 $ — $ — $ 10,833 U.S. Treasury 638 — — 638 U.S. agency securities — 50 — 50 Commercial paper — 498 — 498 Total cash equivalents $ 11,471 $ 548 $ — $ 12,019 Marketable investments Certificates of deposit $ — $ 4,259 $ — $ 4,259 U.S. Treasury 637 — — 637 U.S. agency securities and government sponsored securities — 154,204 — 154,204 Commercial paper — 3,475 — 3,475 Municipal bonds — 6,086 — 6,086 Corporate bonds — 41,246 — 41,246 Total marketable investments $ 637 $ 209,270 $ — $ 209,907 December 31, 2017 Level 1 Level 2 Level 3 Total Assets Cash equivalents: Money market funds $ 20,092 $ — $ — $ 20,092 Other Assets Embedded conversion option held for investment $ — $ — $ 984 $ 984

Financial Statement Components

Financial Statement Components (Tables)	12 Months Ended
	Dec. 31, 2018
Financial Statement Components [Abstract]
Schedule of cash and cash equivalents	Cash and cash equivalents consisted of the following (in thousands): December 31, 2018 2017 Cash and cash equivalents: Cash $ 69,893 $ 48,855 Money market funds 10,833 20,092 U.S. Treasury 638 — U.S. agency securities 50 — Commercial paper 498 — Total cash and cash equivalents $ 81,912 $ 68,947
Schedule of accounts receivable	Accounts receivable, net consisted of the following (in thousands): December 31, 2018 2017 Trade accounts receivable $ 23,068 $ 17,481 Unbilled trade accounts receivable, net of advance client deposits 1,741 1,600 Allowance for doubtful accounts (12 ) (33 ) Accounts receivable, net $ 24,797 $ 19,048
Schedule of prepaid expenses and other current assets	Prepaid expenses and other current assets consisted of the following (in thousands): December 31, 2018 2017 Prepaid expenses $ 5,005 $ 2,437 Other current assets 2,679 2,403 Contract assets 330 — Prepaid expenses and other current assets $ 8,014 $ 4,840
Schedule of useful lives of property and equipment	Property and equipment is stated at cost less accumulated depreciation and amortization, and is depreciated using the straight-line method over the estimated useful lives of the assets as follows: Asset Category Estimated Useful Lives Computer and network equipment 3 to 5 years Computer software 3 years Development costs 1 to 5 years Furniture and fixtures 7 years Leasehold improvements Shorter of useful life or lease term Property and equipment, net consisted of the following (in thousands): December 31, 2018 2017 Computer and network equipment $ 54,452 $ 47,195 Computer software 10,064 6,974 Internal-use software development costs 500 500 Furniture and fixtures 1,491 1,282 Leasehold improvements 855 801 Property and equipment 67,362 56,752 Accumulated depreciation and amortization (41,477 ) (36,864 ) Property and equipment, net $ 25,885 $ 19,888
Schedule of capital lease obligations	Property and equipment capitalized under capital lease obligations consists primarily of computer and network equipment and was as follows (in thousands): December 31, 2018 2017 Gross $ 47,383 $ 46,624 Less: accumulated depreciation and amortization (33,547 ) (30,438 ) Total $ 13,836 $ 16,186
Schedule of accrued and other current liabilities	Accrued and other current liabilities consisted of the following (in thousands): December 31, 2018 2017 Accrued expenses $ 3,494 $ 3,130 Accrued compensation and benefits 10,277 8,657 Accrued and other current liabilities $ 13,771 $ 11,787

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of intangible assets	The components of intangible assets were as follows (in thousands): December 31, 2018 December 31, 2017 Gross Carrying Amount Accumulated Net Gross Accumulated Net Developed technology $ 2,460 $ (1,829 ) $ 631 $ 2,460 $ (1,478 ) $ 982 Customer relationships 520 (520 ) — 520 (437 ) 83 Domain names 50 (50 ) — 50 (42 ) 8 Total $ 3,030 $ (2,399 ) $ 631 $ 3,030 $ (1,957 ) $ 1,073
Schedule of expected future amortization expense of intangible assets	As of December 31, 2018 , the expected future amortization expense for intangible assets was as follows (in thousands): Period Expected Future 2019 $ 351 2020 280 Total $ 631

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Schedule of net carrying amount of the liability component of the notes	The net carrying amount of the liability component of the Notes was as follows (in thousands): December 31, 2018 Principal $ 258,750 Unamortized debt discount (56,564 ) Unamortized issuance costs (5,423 ) Net carrying amount $ 196,763 The net carrying amount of the equity component of the Notes was as follows (in thousands): December 31, 2018 Debt discount for conversion option $ 63,756 Issuance costs (1,998 ) Net carrying amount $ 61,758
Schedule of interest expense related to notes	Interest expense related to the Notes was as follows (in thousands): Year Ended December 31, 2018 Contractual interest expense $ 209 Amortization of debt discount 7,192 Amortization of issuance costs 689 Total interest expense $ 8,090
Schedule of outstanding debt	The Company’s outstanding debt as of the dates set forth below is summarized as follows (in thousands): December 31, 2018 2017 Note payable - FCC civil penalty, gross $ — $ 333 Less: discount — (7 ) Note payable, net carrying value — 326 Convertible senior notes 196,763 — Revolving line of credit — 32,594 Interest accretion under 2016 line of credit — $ 10 Total debt, net carrying value $ 196,763 $ 32,930 Less: current portion of debt * $ — $ 336 Total debt, less current portion ** $ 196,763 $ 32,594 * Included in ‘Notes payable’ in the consolidated balance sheet as of December 31, 2017. ** Included in ‘Convertible senior notes’ and ‘Revolving line of credit’ as of December 31, 2018 and 2017, respectively, in the consolidated balance sheets.
Schedule of maturities of debt	Maturity of the Company’s outstanding debt as of December 31, 2018 was as follows (in thousands): Period Amount to Mature 2023 $ 258,750 Total $ 258,750

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Schedule of common stock reserved for future issuance	Shares of common stock reserved for future issuance related to outstanding equity awards and employee equity incentive plans as of December 31, 2018 , were as follows (in thousands): Common Stock Reserved Stock options outstanding 3,122 Restricted stock units outstanding 2,325 Shares available for future grant under 2014 Plan 8,443 Shares available for future issuance under ESPP 1,691 Total shares of common stock reserved 15,581
Schedule of stock option activities	A summary of the Company’s stock option activity during the year ended December 31, 2018 is as follows (in thousands, except years and per share data): Number of Shares Weighted Weighted Average Remaining Contractual Life (Years) Aggregate (1) Outstanding as of December 31, 2017 4,047 $ 8.00 Options granted 477 35.00 Options exercised (1,274 ) 6.11 Options forfeited or expired (128 ) 17.69 Outstanding as of December 31, 2018 3,122 $ 12.52 6.2 97,423 Vested and expected to vest as of December 31, 2018 3,122 12.52 6.2 97,423 Exercisable as of December 31, 2018 2,234 7.86 5.2 80,112 (1) The aggregate intrinsic value amounts are computed based on the difference between the exercise price of the stock options and the fair market value of the Company’s common stock of $43.72 per share as of December 31, 2018 for all in-the-money stock options outstanding. Following is additional information pertaining to the Company’s stock option activity (in thousands, except per share data): Year Ended December 31, 2018 2017 2016 Weighted average grant date fair value per share of options granted $ 16.33 $ 8.81 $ 4.50 Intrinsic value of options exercised (1) 34,785 33,820 5,865 Total fair value of options vested during the period 4,744 7,296 3,813 Cash received from options exercised 7,779 6,047 4,286 (1) Intrinsic value of options exercised is the difference between the fair market value of the Company’s common stock at the time of exercise and the exercise price paid.
Schedule of RSU activities	A summary of RSU activity during the year ended December 31, 2018 is as follows (in thousands, except years and per share data): Number of Shares Weighted Average Grant Date Fair Value Per Share Outstanding as of December 31, 2017 2,033 $ 12.81 RSUs granted 1,586 32.30 RSUs vested and released (1,053 ) 13.16 RSUs forfeited (241 ) 18.47 Outstanding as of December 31, 2018 2,325 $ 25.36 Following is additional information pertaining to the Company’s RSU activity (in thousands, except per share data): Year Ended December 31, 2018 2017 2016 Weighted average grant date fair value per share of RSUs granted $ 32.30 $ 18.29 $ 9.71 Total fair value of RSUs vested during the period 41,245 21,161 10,706
Schedule of stock-based compensation expense	Stock-based compensation expenses for the years ended December 31, 2018 , 2017 and 2016 were as follows (in thousands): Year Ended December 31, 2018 2017 2016 Cost of revenue $ 3,333 $ 2,202 $ 1,375 Research and development (1) 5,303 3,042 2,059 Sales and marketing 6,307 4,364 2,363 General and administrative (2) 13,541 5,735 3,846 Total stock-based compensation $ 28,484 $ 15,343 $ 9,643 (1) Includes an incremental stock-based compensation cost due to modification of certain stock-based awards of a former executive of the Company in the third quarter of 2018. (2) Effective December 2017, the Company’s former Chief Executive Officer and President resigned from his position and became the Executive Chairman of the Board. Due to this substantive change in status, certain of his stock option and RSU awards were modified which resulted in incremental stock based compensation expense of approximately $ 1.0 million in the fourth quarter of 2017.
Schedule of unrecognized compensation expense	As of December 31, 2018 , unrecognized stock-based compensation expense by award type and their expected weighted-average recognition periods are summarized in the following table (in thousands, except years). Stock Option RSU ESPP Unrecognized stock-based compensation expense $ 11,369 $ 53,668 $ 1,048 Weighted-average amortization period 2.9 years 2.8 years 0.4 years
Schedule of valuation assumptions, stock option	The weighted average assumptions used to value stock options and purchase rights under the ESPP granted during the years ended December 31, 2018 , 2017 and 2016 were as follows: Stock Options Year Ended December 31, 2018 2017 2016 Expected term (years) 6.0 5.9 5.7 Volatility 45% 49% 46% Risk-free interest rate 2.8% 2.1% 1.4% Dividend yield — — —
Schedule of valuation assumptions for stock option purchase plan	ESPP Granted In November 2018 May 2018 November 2017 May 2017 November 2016 May 2016 Expected term (years) 0.5 0.5 0.5 0.5 0.5 0.5 Volatility 37% 36% 36% 43% 42% 58% Risk-free interest rate 2.1% 1.4% 1.4% 1.0% 0.6% 0.4% Dividend yield — — — — — —

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Schedule of basic and diluted net loss per share	The following table presents the calculation of basic and diluted net loss per share (in thousands, except per share data). Year Ended December 31, 2018 2017 2016 Net loss $ (221 ) $ (8,969 ) $ (11,860 ) Weighted-average shares used in computing basic and diluted net loss per share 58,076 54,946 52,342 Basic and diluted net loss per share $ — $ (0.16 ) $ (0.23 )
Schedule of securities excluded from calculation of diluted net loss per share	The following securities were excluded from the calculation of diluted net loss per share because their effect would have been anti-dilutive (in thousands). December 31, 2018 2017 2016 Stock options 3,122 4,047 5,556 Restricted stock units 2,325 2,033 2,019 Common stock warrants — 13 132 Total 5,447 6,093 7,707

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Schedule of components of loss before income taxes	The following table presents components of loss before income taxes for the periods presented (in thousands): Year Ended December 31, 2018 2017 2016 United States $ (638 ) $ (9,434 ) $ (12,222 ) International 717 733 416 Income (loss) before income taxes $ 79 $ (8,701 ) $ (11,806 )
Schedule of components of provision for income taxes	Provision for income taxes for the periods presented consisted of (in thousands): Year Ended December 31, 2018 2017 2016 Current: U.S. federal $ — $ — $ — U.S. state 28 42 16 Foreign 272 226 38 Total provision for income taxes $ 300 $ 268 $ 54
Schedule of effective income tax reconciliation	Income tax expense differed from the amount computed by applying the U.S. federal statutory income tax rate of 21% to pre-tax income (loss) for the periods presented as a result of the following (in thousands): Year Ended December 31, 2018 2017 2016 U.S. federal tax at statutory rate $ 17 $ (2,958 ) $ (4,014 ) U.S. state income taxes 2,539 (708 ) 490 Non-deductible expense (benefit) 14,485 (5,673 ) 931 Research and development credit (339 ) (402 ) (262 ) Stock-based compensation (11,360 ) (14,622 ) 983 Impact of 2017 Tax Act — 25,952 — Other 106 2 (104 ) Change in valuation allowance (5,148 ) (1,323 ) 2,030 Total provision for income taxes $ 300 $ 268 $ 54
Schedule of deferred tax assets and liabilities	The tax effects of temporary differences that give rise to significant portions of the Company’s deferred tax assets and liabilities as of December 31, 2018 and 2017 related to the following (in thousands): December 31, 2018 2017 Deferred tax assets: Net operating loss and credit carryforwards $ 54,966 $ 47,991 Accrued liabilities 4,271 3,183 Allowance for doubtful accounts 400 416 Deferred revenue 832 140 Accrued compensation 1,081 900 Intangibles 4 7 Gross deferred tax assets 61,554 52,637 Valuation allowance (47,127 ) (52,275 ) Net deferred tax assets 14,427 362 Deferred tax liabilities: Property and equipment (370 ) (98 ) Amortized intangibles (155 ) (264 ) Convertible senior notes (13,902 ) — Gross deferred tax liabilities (14,427 ) (362 ) Net deferred taxes $ — $ —
Schedule of unrecognized tax benefits rollforward	The table below shows the changes in the gross amount of unrecognized tax benefits for the periods presented (in thousands): Year Ended December 31, 2018 2017 2016 Unrecognized benefit — beginning of period $ 3,115 $ 2,805 $ 2,485 Gross increases — current year tax positions 7,608 310 324 Gross decreases — prior year tax positions — — (4 ) Unrecognized benefit — end of period $ 10,723 $ 3,115 $ 2,805

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Schedule of future minimum lease payments	As of December 31, 2018 , approximate remaining future minimum lease payments under non-cancelable leases were as follows (in thousands): Year Ending December 31, Capital Leases Operating Leases 2019 $ 7,220 $ 3,041 2020 4,284 2,634 2021 704 653 2022 — — Total future minimum lease payment $ 12,208 $ 6,328 Less — amount representing interest (1,052 ) Present value of total capital lease obligation $ 11,156 Capital lease obligation — current portion 6,647 Capital lease obligation — net of current portion 4,509
Schedule of future minimum lease payments for hosting, telecommunication usage, and maintenance services	As of December 31, 2018 , future minimum payments under these arrangements were as follows (in thousands): Year Ending December 31, Hosting Services Telecommunication Usage Services Equipment Maintenance Services 2019 $ 1,942 $ 3,138 $ 345 2020 1,209 1,781 243 2021 500 875 76 2022 700 294 — Total future minimum payment $ 4,351 $ 6,088 $ 664

Geographical Information (Table

Geographical Information (Tables)	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Schedule of revenues and property and equipment by geographic region	The following table is a summary of revenues by geographic region based on client billing address and has been estimated based on the amounts billed to clients during the periods (in thousands). Year Ended December 31, 2018 2017 2016 United States $ 239,378 $ 188,303 $ 151,484 International 18,286 11,922 10,606 Total revenue $ 257,664 $ 200,225 $ 162,090 The following table summarizes total property and equipment, net in the respective locations (in thousands). December 31, 2018 2017 2016 United States $ 23,931 $ 17,949 $ 13,025 International 1,954 1,939 1,663 Property and equipment, net $ 25,885 $ 19,888 $ 14,688

Selected Quarterly Financial _2

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	Selected quarterly financial information for 2018 and 2017 is as follows: Quarter Ended Dec. 31, 2018 Sept. 30, 2018 Jun. 30, 2018 Mar. 31, 2018 Dec. 31, 2017 Sept. 30, 2017 Jun. 30, 2017 Mar. 31, 2017 (unaudited, in thousands, except per share data) Revenue $ 72,335 $ 65,304 $ 61,120 $ 58,905 $ 55,403 $ 50,081 $ 47,727 $ 47,014 Cost of revenue (1)(2) 28,339 26,179 24,814 24,702 22,363 20,497 20,273 19,971 Gross profit 43,996 39,125 36,306 34,203 33,040 29,584 27,454 27,043 Operating expenses: Research and development (1)(2) 8,451 9,582 8,367 7,772 6,748 6,689 6,836 6,847 Sales and marketing (1)(2) 18,793 17,818 17,912 17,478 17,358 16,502 16,932 15,778 General and administrative (1)(2) 10,766 10,746 9,833 9,103 8,767 4,679 6,845 8,860 Total operating expenses 38,010 38,146 36,112 34,353 32,873 27,870 30,613 31,485 Income (loss) from operations 5,986 979 194 (150 ) 167 1,714 (3,159 ) (4,442 ) Other income (expense), net: Extinguishment of debt — — — — — — — — Interest expense (3,462 ) (3,595 ) (2,378 ) (810 ) (836 ) (865 ) (888 ) (882 ) Interest income and other 1,359 1,352 206 398 164 118 90 118 Total other income (expense), net (2,103 ) (2,243 ) (2,172 ) (412 ) (672 ) (747 ) (798 ) (764 ) Income (loss) before income taxes 3,883 (1,264 ) (1,978 ) (562 ) (505 ) 967 (3,957 ) (5,206 ) Provision for income taxes 150 41 64 45 126 43 50 49 Net income (loss) $ 3,733 $ (1,305 ) $ (2,042 ) $ (607 ) $ (631 ) $ 924 $ (4,007 ) $ (5,255 ) Net income (loss) per share: Basic $ 0.06 $ (0.02 ) $ (0.04 ) $ (0.01 ) $ (0.01 ) $ 0.02 $ (0.07 ) $ (0.10 ) Diluted $ 0.06 $ (0.02 ) $ (0.04 ) $ (0.01 ) $ (0.01 ) $ 0.02 $ (0.07 ) $ (0.10 ) Shares used in computing net loss per share: Basic 58,926 58,454 57,903 56,399 56,034 55,310 54,723 53,688 Diluted 62,071 58,454 57,903 56,399 56,034 59,441 54,723 53,688 (1) Included stock-based compensation as follows: Quarter Ended Dec. 31, 2018 Sept. 30, 2018 Jun. 30, 2018 Mar. 31, 2018 Dec. 31, 2017 Sept. 30, 2017 Jun. 30, 2017 Mar. 31, 2017 (unaudited, in thousands) Cost of revenue $ 942 $ 860 $ 853 $ 678 $ 594 $ 599 $ 575 $ 434 Research and development 1,010 2,352 1,064 877 807 797 801 637 Sales and marketing 1,747 1,613 1,585 1,362 1,128 1,084 1,224 928 General and administrative 3,794 4,044 3,295 2,408 2,111 1,240 1,254 1,130 Total stock-based compensation $ 7,493 $ 8,869 $ 6,797 $ 5,325 $ 4,640 $ 3,720 $ 3,854 $ 3,129 (2) Included depreciation and amortization expenses as follows: Quarter Ended Dec. 31, 2018 Sept. 30, 2018 Jun. 30, 2018 Mar. 31, 2018 Dec. 31, 2017 Sept. 30, 2017 Jun. 30, 2017 Mar. 31, 2017 (unaudited, in thousands) Cost of revenue $ 2,129 $ 2,021 $ 1,864 $ 1,794 $ 1,611 $ 1,397 $ 1,716 $ 1,576 Research and development 331 278 233 194 170 182 237 206 Sales and marketing 6 30 30 29 30 30 30 30 General and administrative 372 338 322 303 257 272 287 283 Total depreciation and amortization $ 2,838 $ 2,667 $ 2,449 $ 2,320 $ 2,068 $ 1,881 $ 2,270 $ 2,095

Description of Business and S_4

Description of Business and Summary of Significant Accounting Policies - Concentration Risks (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Cash, uninsured amount	$ 81	$ 68.3

Description of Business and S_5

Description of Business and Summary of Significant Accounting Policies - Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance, beginning of period	$ 33	$ 12	$ 15
Add: bad debt expense	90	95	75
Less: write-offs, net of recoveries	(111)	(74)	(78)
Balance, end of period	$ 12	$ 33	$ 12

Description of Business and S_6

Description of Business and Summary of Significant Accounting Policies - Property and Equipment, Net (Details)	12 Months Ended
	Dec. 31, 2018
Computer and network equipment | Minimum
Property, Plant and Equipment [Line Items]
Useful life, in years	3 years
Computer and network equipment | Maximum
Property, Plant and Equipment [Line Items]
Useful life, in years	5 years
Computer software
Property, Plant and Equipment [Line Items]
Useful life, in years	3 years
Development costs | Minimum
Property, Plant and Equipment [Line Items]
Useful life, in years	1 year
Development costs | Maximum
Property, Plant and Equipment [Line Items]
Useful life, in years	5 years
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Useful life, in years	7 years

Description of Business and S_7

Description of Business and Summary of Significant Accounting Policies - Goodwill and Intangible Assets (Details)	12 Months Ended
	Dec. 31, 2018
Minimum
Finite-Lived Intangible Assets [Line Items]
Finite-live intangible asset, useful life	5 years
Maximum
Finite-Lived Intangible Assets [Line Items]
Finite-live intangible asset, useful life	7 years

Description of Business and S_8

Description of Business and Summary of Significant Accounting Policies - Advertising Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Advertising expense	$ 12.2	$ 11.4	$ 10.7

Description of Business and S_9

Description of Business and Summary of Significant Accounting Policies - Commissions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Commissions [Line Items]
Commission expense	$ 10.3	$ 14	$ 10.2
Effect of Change Higher (Lower) | ASU 2014-09
Commissions [Line Items]
Commission expense	$ (7.7)

Description of Business and _10

Description of Business and Summary of Significant Accounting Policies - Recently Adopted Accounting Pronouncements (Details) - USD ($) $ in Thousands	Jan. 01, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred tax asset		$ 61,554	$ 52,637
Deferred tax asset, valuation allowance		$ 47,127	$ 52,275
ASU 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred tax asset				$ 5,300
Deferred tax asset, valuation allowance				5,300
Minimum | Forecast | ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right of use asset	$ 7,000
Operating lease liability	7,000
Maximum | Forecast | ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right of use asset	10,000
Operating lease liability	$ 10,000
Accumulated Deficit | ASU 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Effect on financial statements				$ 200

ASC 606 Adoption Impact and R_3

ASC 606 Adoption Impact and Revenue from Contracts with Customers - Narrative (Details) - USD ($)	Jan. 01, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract revenue recognized		$ 10,200,000
Commission expense increase (decrease)		$ 10,300,000	$ 14,000,000	$ 10,200,000
Remaining performance obligation					$ 96,800,000
Retained earnings | ASU 340-40
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Effect on retained earnings	$ 23,100,000
Retained earnings | ASU 2014-09, timing of revenue recognition
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Effect on retained earnings	$ 1,000,000
Contract acquisition costs
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Amortization period of capitalized contract cost		5 years
Amortization of capitalized contract cost		$ 8,400,000
Commission expense increase (decrease)		1,900,000
Impairment loss		$ 0

ASC 606 Adoption Impact and R_4

ASC 606 Adoption Impact and Revenue from Contracts with Customers - Balance Sheet Impact (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	$ 24,797	$ 19,151	$ 19,048
Prepaid expenses and other current assets	8,014		4,840
Deferred contract acquisition costs	30,886	23,138
Deferred revenue	17,391	$ 13,568	13,975
Accumulated deficit	(151,497)		$ (175,421)
Balances without adoption of ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	24,694
Prepaid expenses and other current assets	8,228
Deferred contract acquisition costs	0
Deferred revenue	19,116
Accumulated deficit	(183,997)
Effect of Change Higher (Lower) | ASU 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	103
Prepaid expenses and other current assets	(214)
Deferred contract acquisition costs	30,886
Deferred revenue	(1,725)
Accumulated deficit	$ 32,500

ASC 606 Adoption Impact and R_5

ASC 606 Adoption Impact and Revenue from Contracts with Customers - Income Statement Impact (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	$ 72,335	$ 65,304	$ 61,120	$ 58,905	$ 55,403	$ 50,081	$ 47,727	$ 47,014	$ 257,664	$ 200,225	$ 162,090
Cost of revenue	28,339	26,179	24,814	24,702	22,363	20,497	20,273	19,971	104,034	83,104	66,934
Gross profit	43,996	39,125	36,306	34,203	33,040	29,584	27,454	27,043	153,630	117,121	95,156
Sales and marketing	18,793	17,818	17,912	17,478	17,358	16,502	16,932	15,778	72,001	66,570	52,748
Income from operations	5,986	979	194	(150)	167	1,714	(3,159)	(4,442)	7,009	(5,720)	(6,542)
Net loss	$ 3,733	$ (1,305)	$ (2,042)	$ (607)	$ (631)	$ 924	$ (4,007)	$ (5,255)	$ (221)	$ (8,969)	$ (11,860)
Basic and diluted (in USD per share)									$ 0	$ (0.16)	$ (0.23)
Balances without adoption of ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue									$ 256,548
Cost of revenue									103,525
Gross profit									153,023
Sales and marketing									79,749
Income from operations									(1,346)
Net loss									$ (8,576)
Basic and diluted (in USD per share)									$ (0.15)
Effect of Change Higher (Lower) | ASU 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue									$ 1,116
Cost of revenue									509
Gross profit									607
Sales and marketing									(7,748)
Income from operations									8,355
Net loss									$ 8,355
Basic and diluted (in USD per share)									$ 0.15

ASC 606 Adoption Impact and R_6

ASC 606 Adoption Impact and Revenue from Contracts with Customers - Cash Flow Impact (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable	$ (5,829)	$ (5,163)	$ (3,389)
Prepaid expenses and other current assets	(2,806)	(1,912)	(859)
Deferred contract acquisition costs	(7,748)	0	0
Deferred revenue	3,956	3,882	3,680
Net cash provided by operating activities	38,622	$ 11,106	$ 6,838
Balances without adoption of ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable	(5,726)
Prepaid expenses and other current assets	(3,020)
Deferred contract acquisition costs	0
Deferred revenue	5,681
Net cash provided by operating activities	38,622
Effect of Change Higher (Lower) | ASU 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable	(103)
Prepaid expenses and other current assets	214
Deferred contract acquisition costs	(7,748)
Deferred revenue	(1,725)
Net cash provided by operating activities	$ 0

ASC 606 Adoption Impact and R_7

ASC 606 Adoption Impact and Revenue from Contracts with Customers - Contract Balances (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue from Contract with Customer [Abstract]
Accounts receivable, net	$ 24,797	$ 19,151	$ 19,048
Deferred contract acquisition costs, current	9,372	7,059	0
Deferred contract acquisition costs, non-current	21,514	16,079	0
Total deferred contract acquisition costs	30,886	23,138
Contract assets (included in prepaid expenses and other current assets)	330	736	0
Contract liabilities (deferred revenue)	17,391	13,568	$ 13,975
Net contract assets (liabilities)	$ (17,061)	$ (12,832)

Investments and Fair Value Me_3

Investments and Fair Value Measurements - Schedule of Marketable Investments (Details) $ in Thousands	Dec. 31, 2018USD ($)
Debt Securities, Available-for-sale [Line Items]
Cost	$ 210,082
Gross Unrealized Gains	1
Gross Unrealized Losses	(176)
Fair Value	209,907
Certificates of deposit
Debt Securities, Available-for-sale [Line Items]
Cost	4,259
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	4,259
U.S. treasury
Debt Securities, Available-for-sale [Line Items]
Cost	637
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	637
U.S. agency securities and government sponsored securities
Debt Securities, Available-for-sale [Line Items]
Cost	154,314
Gross Unrealized Gains	1
Gross Unrealized Losses	(111)
Fair Value	154,204
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Cost	3,475
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	3,475
Municipal bonds
Debt Securities, Available-for-sale [Line Items]
Cost	6,090
Gross Unrealized Gains	0
Gross Unrealized Losses	(4)
Fair Value	6,086
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Cost	41,307
Gross Unrealized Gains	0
Gross Unrealized Losses	(61)
Fair Value	$ 41,246

Investments and Fair Value Me_4

Investments and Fair Value Measurements - Schedule of Continuous Unrealized Loss Position (Details) $ in Thousands	Dec. 31, 2018USD ($)
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, gross unrealized losses	$ (176)
Less than 12 months, fair value	201,181
U.S. treasury
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, gross unrealized losses	0
Less than 12 months, fair value	637
U.S. agency securities and government sponsored securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, gross unrealized losses	(111)
Less than 12 months, fair value	153,212
Municipal bonds
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, gross unrealized losses	(4)
Less than 12 months, fair value	6,086
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, gross unrealized losses	(61)
Less than 12 months, fair value	$ 41,246

Investments and Fair Value Me_5

Investments and Fair Value Measurements - Schedule of Assets Carried at Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Assets
Cash equivalents	$ 12,019
Marketable investments	209,907
Level 1
Assets
Cash equivalents	11,471
Marketable investments	637
Level 2
Assets
Cash equivalents	548
Marketable investments	209,270
Level 3
Assets
Cash equivalents	0
Marketable investments	0
Money market funds
Assets
Cash equivalents	10,833	$ 20,092
Marketable investments	6,086
Money market funds | Level 1
Assets
Cash equivalents	10,833	20,092
Marketable investments	0
Money market funds | Level 2
Assets
Cash equivalents	0	0
Marketable investments	6,086
Money market funds | Level 3
Assets
Cash equivalents	0	0
Marketable investments	0
Certificates of deposit
Assets
Marketable investments	4,259
Certificates of deposit | Level 1
Assets
Marketable investments	0
Certificates of deposit | Level 2
Assets
Marketable investments	4,259
Certificates of deposit | Level 3
Assets
Marketable investments	0
U.S. treasury
Assets
Cash equivalents	638
Marketable investments	637
U.S. treasury | Level 1
Assets
Cash equivalents	638
Marketable investments	637
U.S. treasury | Level 2
Assets
Cash equivalents	0
Marketable investments	0
U.S. treasury | Level 3
Assets
Cash equivalents	0
Marketable investments	0
U.S. agency securities and government sponsored securities
Assets
Cash equivalents	50
Marketable investments	154,204
U.S. agency securities and government sponsored securities | Level 1
Assets
Cash equivalents	0
Marketable investments	0
U.S. agency securities and government sponsored securities | Level 2
Assets
Cash equivalents	50
Marketable investments	154,204
U.S. agency securities and government sponsored securities | Level 3
Assets
Cash equivalents	0
Marketable investments	0
Commercial paper
Assets
Cash equivalents	498
Marketable investments	3,475
Commercial paper | Level 1
Assets
Cash equivalents	0
Marketable investments	0
Commercial paper | Level 2
Assets
Cash equivalents	498
Marketable investments	3,475
Commercial paper | Level 3
Assets
Cash equivalents	0
Marketable investments	0
Corporate bonds
Assets
Marketable investments	41,246
Corporate bonds | Level 1
Assets
Marketable investments	0
Corporate bonds | Level 2
Assets
Marketable investments	41,246
Corporate bonds | Level 3
Assets
Marketable investments	$ 0
Embedded conversion option held for investment
Assets
Other assets		984
Embedded conversion option held for investment | Level 1
Assets
Other assets		0
Embedded conversion option held for investment | Level 2
Assets
Other assets		0
Embedded conversion option held for investment | Level 3
Assets
Other assets		$ 984

Investments and Fair Value Me_6

Investments and Fair Value Measurements - Narrative (Details) - USD ($)	1 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	May 31, 2018
Debt Instrument [Line Items]
Proceeds from sale of convertible note held for investment	$ 1,900,000	$ 1,923,000	$ 0	$ 0
Carrying value of convertible notes sold	1,600,000
Total proceeds from sale of convertible notes receivable	$ 2,100,000
Nonrecurring
Debt Instrument [Line Items]
Assets measured at fair value on nonrecurring basis					$ 0
Convertible Senior Notes | Convertible debt
Debt Instrument [Line Items]
Stated interest rate on debt						0.125%
Convertible Senior Notes | Level 2 | Convertible debt
Debt Instrument [Line Items]
Fair value of long-term debt		$ 316,100,000

Financial Statement Component_2

Financial Statement Components - Schedule of Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash and Cash Equivalents
Cash and cash equivalents	$ 81,912	$ 68,947	$ 58,122	$ 58,484
Cash
Cash and Cash Equivalents
Cash and cash equivalents	69,893	48,855
Money market funds
Cash and Cash Equivalents
Cash and cash equivalents	10,833	20,092
U.S. Treasury
Cash and Cash Equivalents
Cash and cash equivalents	638	0
U.S. agency securities
Cash and Cash Equivalents
Cash and cash equivalents	50	0
Commercial paper
Cash and Cash Equivalents
Cash and cash equivalents	$ 498	$ 0

Financial Statement Component_3

Financial Statement Components - Schedule of Accounts Receivable (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounts Receivable
Allowance for doubtful accounts	$ (12)		$ (33)	$ (12)	$ (15)
Accounts receivable, net	24,797	$ 19,151	19,048
Trade accounts receivable
Accounts Receivable
Trade accounts receivable	23,068		17,481
Unbilled trade accounts receivable, net of advance client deposits
Accounts Receivable
Trade accounts receivable	$ 1,741		$ 1,600

Financial Statement Component_4

Financial Statement Components - Schedule of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Financial Statement Components [Abstract]
Prepaid expenses	$ 5,005		$ 2,437
Other current assets	2,679		2,403
Contract assets (included in prepaid expenses and other current assets)	330	$ 736	0
Prepaid expenses and other current assets	$ 8,014		$ 4,840

Financial Statement Component_5

Financial Statement Components - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment	$ 67,362	$ 56,752
Accumulated depreciation and amortization	(41,477)	(36,864)
Property and equipment, net	25,885	19,888	$ 14,688
Computer and network equipment
Property, Plant and Equipment [Line Items]
Property and equipment	54,452	47,195
Computer software
Property, Plant and Equipment [Line Items]
Property and equipment	10,064	6,974
Internal-use software development costs
Property, Plant and Equipment [Line Items]
Property and equipment	500	500
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment	1,491	1,282
Leasehold Improvements
Property, Plant and Equipment [Line Items]
Property and equipment	$ 855	$ 801

Financial Statement Component_6

Financial Statement Components - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	Jul. 01, 2017	Jun. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Depreciation and amortization of property and equipment			$ 9.8	$ 7.8	$ 7.9
Basic and diluted (in USD per share)			$ 0	$ (0.16)	$ (0.23)
Previously reported
Property, Plant and Equipment [Line Items]
Useful life, in years		3 years
Service life | Adjustment
Property, Plant and Equipment [Line Items]
Depreciation and amortization of property and equipment				$ (1.6)
Basic and diluted (in USD per share)				$ 0.03
Minimum | Service life
Property, Plant and Equipment [Line Items]
Useful life, in years	3 years
Maximum | Service life
Property, Plant and Equipment [Line Items]
Useful life, in years	5 years

Financial Statement Component_7

Financial Statement Components - Schedule of Capital Leased Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financial Statement Components [Abstract]
Gross	$ 47,383	$ 46,624
Less: accumulated depreciation and amortization	(33,547)	(30,438)
Total	$ 13,836	$ 16,186

Financial Statement Component_8

Financial Statement Components - Schedule of Accrued and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financial Statement Components [Abstract]
Accrued expenses	$ 3,494	$ 3,130
Accrued compensation and benefits	10,277	8,657
Accrued and other current liabilities	$ 13,771	$ 11,787

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill impairment, accumulated	$ 0	$ 0
Amortization of intangible assets	400,000	500,000	$ 500,000
Impairment of intangible assets	$ 0	$ 0

Goodwill and Intangible Asset_3

Goodwill and Intangible Assets - Schedule of Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Acquired Finite-Lived Intangible Assets
Gross Carrying Amount	$ 3,030	$ 3,030
Accumulated Amortization	(2,399)	(1,957)
Total Net Carrying Amount	631	1,073
Developed technology
Acquired Finite-Lived Intangible Assets
Gross Carrying Amount	2,460	2,460
Accumulated Amortization	(1,829)	(1,478)
Total Net Carrying Amount	631	982
Customer relationships
Acquired Finite-Lived Intangible Assets
Gross Carrying Amount	520	520
Accumulated Amortization	(520)	(437)
Total Net Carrying Amount	0	83
Domain names
Acquired Finite-Lived Intangible Assets
Gross Carrying Amount	50	50
Accumulated Amortization	(50)	(42)
Total Net Carrying Amount	$ 0	$ 8

Goodwill and Intangible Asset_4

Goodwill and Intangible Assets - Schedule of Expected Future Amortization Expense of Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
2,019	$ 351
2,020	280
Total Net Carrying Amount	$ 631	$ 1,073

Debt - Convertible Senior Notes

Debt - Convertible Senior Notes and Capped Call (Details) $ / shares in Units, shares in Millions	1 Months Ended	12 Months Ended
	May 31, 2018USD ($)day$ / shares	Dec. 31, 2018USD ($)shares	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Debt Instrument [Line Items]
Payment on debt issuance cost		$ 0	$ 0	$ 206,000
Convertible debt
Debt Instrument [Line Items]
Payment on debt issuance cost		$ 8,039,000
Convertible debt | Convertible Senior Notes
Debt Instrument [Line Items]
Stated interest rate on debt	0.125%
Proceeds from issuance of debt	$ 250,700,000
Conversion ratio on convertible debt		24.4978
Conversion price on convertible debt (in USD per share) | $ / shares	$ 40.82
Sinking fund payment	$ 0
Conversion option		$ 63,756,000
Effective interest rate on debt	6.39%
Payment on debt issuance cost	$ 8,100,000
Debt issuance costs	$ 6,100,000	$ 5,423,000
Cap price of the Capped Call Transactions (in dollars per share) | $ / shares	$ 62.80
Number of shares covered in the Capped Call Transactions (in shares) | shares		6.3
Cost of Capped Call Transactions recorded in additional paid in capital		$ 31,412,000
Convertible debt | Convertible Senior Notes | Fundamental change event
Debt Instrument [Line Items]
Debt redemption price as percentage of principal amount	100.00%
Convertible debt | Convertible Senior Notes | On or after May 5, 2021
Debt Instrument [Line Items]
Number of trading days | day	20
Number of consecutive trading days | day	30
Threshold percentage of stock price trigger	130.00%
Debt redemption price as percentage of principal amount	100.00%
Private placement | Convertible debt | Convertible Senior Notes
Debt Instrument [Line Items]
Aggregate principal amount of debt	$ 258,800,000
Convertible, term one | Convertible debt | Convertible Senior Notes
Debt Instrument [Line Items]
Number of trading days | day	20
Number of consecutive trading days | day	30
Threshold percentage of stock price trigger	130.00%
Convertible, term two | Convertible debt | Convertible Senior Notes
Debt Instrument [Line Items]
Number of trading days | day	5
Number of consecutive trading days | day	5
Threshold percentage of stock price trigger	98.00%

Debt - Schedule of Net Carrying

Debt - Schedule of Net Carrying Amount of the Liability Component of the Notes (Details) - USD ($) $ in Thousands	Dec. 31, 2018	May 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Principal	$ 258,750
Total debt, net carrying value	196,763		$ 32,930
Convertible debt
Debt Instrument [Line Items]
Principal	196,763		$ 0
Convertible debt | Convertible Senior Notes
Debt Instrument [Line Items]
Principal	258,750
Debt Instrument, Unamortized Discount	(56,564)
Unamortized issuance costs	(5,423)	$ (6,100)
Total debt, net carrying value	$ 196,763

Debt - Schedule of Net Carryi_2

Debt - Schedule of Net Carrying Amount of Equity Component of the Notes (Details) - Convertible debt - Convertible Senior Notes $ in Thousands	Dec. 31, 2018USD ($)
Debt Instrument [Line Items]
Conversion option	$ 63,756
Issuance costs	(1,998)
Net carrying amount	$ 61,758

Debt - Schedule of Interest Exp

Debt - Schedule of Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Interest Expense	$ 3,462	$ 3,595	$ 2,378	$ 810	$ 836	$ 865	$ 888	$ 882	$ 10,245	$ 3,471	$ 4,226
Convertible Senior Notes | Convertible debt
Debt Instrument [Line Items]
Contractual interest expense									209
Amortization of debt discount									7,192
Amortization of issuance costs									689
Interest Expense									$ 8,090

Debt - Schedule of Equity Compo

Debt - Schedule of Equity Component of Debt (Details) - Convertible debt - Convertible Senior Notes $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)
Debt Instrument [Line Items]
Conversion option	$ 63,756
Payments for capped call transactions	(31,412)
Issuance costs	(1,998)
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt	$ 30,346

Debt - 2016 Loan and Security A

Debt - 2016 Loan and Security Agreement (Details) - USD ($)	Aug. 01, 2016	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Line of Credit Facility [Line Items]
Loss on extinguishment of debt		$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 1,026,000
Prepayment penalties on extinguishment of debt										$ 0	$ 0	$ 368,000
Loan and Security Agreements 2014 and 2013
Line of Credit Facility [Line Items]
Loss on extinguishment of debt							1,000,000
Prepayment penalties on extinguishment of debt							400,000
Write-off of unamortized debt discounts							400,000
Write-off of unamortized debt issuance costs							$ 200,000
Line of Credit | Loan and Security Agreement 2016 | Revolving Credit Facility
Line of Credit Facility [Line Items]
Credit facility, maximum borrowing capacity	$ 50,000,000
Unused line of credit capacity fee	0.25%
First and second anniversary fee for line of credit	$ 31,250
Prime Rate | Line of Credit | Loan and Security Agreement 2016 | Revolving Credit Facility
Line of Credit Facility [Line Items]
Debt instrument, basis spread	0.50%
Percentage increase in interest rate if adjusted EBITDA is negative at the end of the quarter	0.25%

Debt - FCC Civil Penalty (Detai

Debt - FCC Civil Penalty (Details) $ in Thousands	1 Months Ended
	Jun. 30, 2015USD ($)payment	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2014USD ($)
Debt Instrument [Line Items]
Principal		$ 258,750
Total debt, net carrying value		196,763	$ 32,930
FCC Civil Penalty
Debt Instrument [Line Items]
Accrued civil penalty liability				$ 2,000
Notes Payable
Debt Instrument [Line Items]
Principal		0	333
Discount on debt		0	7
Total debt, net carrying value		$ 0	$ 326
Notes Payable | FCC Civil Penalty
Debt Instrument [Line Items]
Principal	$ 2,000
Debt instrument, number of quarterly payments (in payments) | payment	12
Debt instrument, stated interest rate	12.75%
Discount on debt	$ 300
Total debt, net carrying value	$ 1,700

Debt - Schedule of Outstanding

Debt - Schedule of Outstanding Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Principal	$ 258,750
Total debt, net carrying value	196,763	$ 32,930
Less: current portion of debt	0	336
Total debt, less current portion	196,763	32,594
Notes Payable
Debt Instrument [Line Items]
Principal	0	333
Less: discount	0	(7)
Total debt, net carrying value	0	326
Convertible debt
Debt Instrument [Line Items]
Principal	196,763	0
Line of Credit
Debt Instrument [Line Items]
Principal	0	32,594
Interest accretion under 2016 line of credit	$ 0	$ 10

Debt - Schedule of Maturities o

Debt - Schedule of Maturities of Debt (Details) $ in Thousands	Dec. 31, 2018USD ($)
Debt Disclosure [Abstract]
2,023	$ 258,750
Total	$ 258,750

Stockholders' Equity - Capital

Stockholders' Equity - Capital Structure (Details) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Common stock, shares authorized (in shares)	450,000,000	450,000,000
Common stock, shares outstanding (in shares)	59,210,496	56,631,647
Common stock, par value (in USD per share)	$ 0.001	$ 0.001
Common stock, shares issued (in shares)	59,210,496	56,631,647
Preferred stock, shares outstanding (in shares)	0	0
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, par value (in USD per share)	$ 0.001	$ 0.001
Preferred stock, shares issued (in shares)	0	0

Stockholders' Equity - Warrants

Stockholders' Equity - Warrants (Details) - Common Stock - $ / shares	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Class of Warrant or Right [Line Items]
Warrants outstanding (in shares)	0		13,013
Outstanding warrants weighted average exercise price (in USD per share)		$ 5.76

Stockholders' Equity - Common S

Stockholders' Equity - Common Stock Reserved for Future Issuance (Details) shares in Thousands	Dec. 31, 2018shares
Class of Stock [Line Items]
Shares of common stock reserved for future issuance (in shares)	15,581
Shares available for future grant under 2014 Plan
Class of Stock [Line Items]
Shares of common stock reserved for future issuance (in shares)	8,443
Stock options outstanding
Class of Stock [Line Items]
Shares of common stock reserved for future issuance (in shares)	3,122
Restricted stock units outstanding
Class of Stock [Line Items]
Shares of common stock reserved for future issuance (in shares)	2,325
Shares available for future issuance under ESPP
Class of Stock [Line Items]
Shares of common stock reserved for future issuance (in shares)	1,691

Stockholders' Equity - Equity I

Stockholders' Equity - Equity Incentive Plans (Details) - shares	12 Months Ended
	Dec. 31, 2018	Jan. 01, 2019	Mar. 31, 2014
2004 Equity Incentive Plan | Stock options outstanding
Share-based Compensation Arrangement by Share-based Payment Award
Award vesting period	4 years
Award expiration period	10 years
Expiration period, after termination of employment or relationship of consultant or director	90 days
2004 Equity Incentive Plan | Stock options outstanding | Tranche One
Share-based Compensation Arrangement by Share-based Payment Award
Award vesting period	12 months
Award vesting, percentage of award	25.00%
2004 Equity Incentive Plan | Stock options outstanding | Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award
Award vesting period	36 months
Award vesting, percentage of award	75.00%
2014 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award
Number of shares authorized for issuance (in shares)			5,300,000
Automatic annual increase in common stock reserved for issuance, percentage	5.00%
2014 Equity Incentive Plan | Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award
Shares of common stock reserved for future issuance (in shares)		2,960,524
2014 Equity Incentive Plan | Stock options outstanding
Share-based Compensation Arrangement by Share-based Payment Award
Award expiration period	10 years
2014 Equity Incentive Plan | Restricted stock units outstanding | Minimum
Share-based Compensation Arrangement by Share-based Payment Award
Award vesting period	1 year
2014 Equity Incentive Plan | Restricted stock units outstanding | Maximum
Share-based Compensation Arrangement by Share-based Payment Award
Award vesting period	4 years

Stockholders' Equity - Stock Op

Stockholders' Equity - Stock Option Activities (Details) - Stock options outstanding - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Number of Shares
Outstanding, beginning balance (in shares)	4,047
Options granted (in shares)	477
Options exercised (in shares)	(1,274)
Options forfeited or expired (in shares)	(128)
Outstanding, ending balance (in shares)	3,122	4,047
Weighted Average Exercise Price
Outstanding, beginning balance, weighted-average exercise price (in USD per share)	$ 8
Options granted, weighted-average exercise price (in USD per share)	35
Options exercised, weighted-average exercise price (in USD per share)	6.11
Options forfeited or expired, weighted-average exercise price (in USD per share)	17.69
Outstanding, ending balance, weighted-average exercise price (in USD per share)	$ 12.52	$ 8
Weighted average remaining contractual life	6 years 2 months 12 days
Outstanding, Aggregate intrinsic value	$ 97,423
Vested and expected to vest as of December 31, 2018
Vested and expected to vest (in shares)	3,122
Outstanding, weighted-average exercise price (in USD per share)	$ 12.52
Outstanding, weighted average remaining contractual life	6 years 2 months 12 days
Vested and expected to vest, aggregate intrinsic value	$ 97,423
Additional information pertaining to stock options
Exercisable (in shares)	2,234
Exercisable, weighted-average exercise price (in USD per share)	$ 7.86
Exercisable, weighted average remaining contractual life	5 years 2 months 12 days
Exercisable, aggregate intrinsic value	$ 80,112
Fair market value of common stock (in usd per share)	$ 43.72
Weighted average grant date fair value per share of options granted (in USD per share)	$ 16.33	$ 8.81	$ 4.50
Intrinsic value of options exercised	$ 34,785	$ 33,820	$ 5,865
Total fair value of options vested during the period	4,744	7,296	3,813
Cash received from options exercised	$ 7,779	$ 6,047	$ 4,286

Stockholders' Equity - RSU Acti

Stockholders' Equity - RSU Activities (Details) - Restricted stock units outstanding - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Number of Shares
Outstanding, beginning balance (in shares)	2,033
RSUs granted (in shares)	1,586
RSUs vested and released (in shares)	(1,053)
RSUs forfeited (in shares)	(241)
Outstanding, ending balance (in shares)	2,325	2,033
Weighted Average Grant Date Fair Value Per Share
Outstanding, beginning balance, weighted-average grant date fair value per share (in USD per share)	$ 12.81
Weighted average grant date fair value per share of RSUs granted (in USD per share)	32.30	$ 18.29	$ 9.71
RSUs vested and released, weighted-average grant date fair value per share (in USD per share)	13.16
RSUs forfeited, weighted-average grant date fair value per share (in USD per share)	18.47
Outstanding, ending balance, weighted-average grant date fair value per share (in USD per share)	25.36	12.81
Weighted average grant date fair value per share of RSUs granted (in USD per share)	$ 32.30	$ 18.29	$ 9.71
Total fair value of RSUs vested during the period	$ 41,245	$ 21,161	$ 10,706

Stockholders' Equity - ESPP (De

Stockholders' Equity - ESPP (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Jan. 01, 2019	Apr. 03, 2014
Share-based Compensation Arrangement by Share-based Payment Award
Shares of common stock reserved for future issuance (in shares)	15,581,000
ESPP
Share-based Compensation Arrangement by Share-based Payment Award
Maximum employee subscription rate, percentage of pre-tax earnings	15.00%
Purchase price of shares, percentage of the fair market value of the Company's common stock	85.00%
Maximum number of shares per employee per purchase period (in shares)	1,500
Shares of common stock reserved for future issuance (in shares)			880,000
Automatic annual increase in common stock reserved for issuance, percentage	1.00%
Maximum annual increase of shares reserved (in shares)	1,000,000
Issuance of common stock under ESPP (in shares)	246,079
Weighted-average price per share (in USD per share)	$ 23.29
ESPP | Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award
Shares of common stock reserved for future issuance (in shares)		592,104

Stockholders' Equity - Stock-Ba

Stockholders' Equity - Stock-Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock-based Compensation Expense
Stock-based compensation expense		$ 28,484	$ 15,343	$ 9,643
Stock options outstanding
Stock-based Compensation Expense
Unrecognized stock-based compensation expense	$ 11,369	$ 11,369
Weighted-average amortization period		2 years 10 months 24 days
Restricted stock units outstanding
Stock-based Compensation Expense
Unrecognized stock-based compensation expense	53,668	$ 53,668
Weighted-average amortization period		2 years 9 months 18 days
ESPP
Stock-based Compensation Expense
Unrecognized stock-based compensation expense	1,048	$ 1,048
Weighted-average amortization period		4 months 24 days
Cost of revenue
Stock-based Compensation Expense
Stock-based compensation expense		$ 3,333	2,202	1,375
Research and development
Stock-based Compensation Expense
Stock-based compensation expense		5,303	3,042	2,059
Sales and marketing
Stock-based Compensation Expense
Stock-based compensation expense		6,307	4,364	2,363
General and administrative
Stock-based Compensation Expense
Stock-based compensation expense		$ 13,541	$ 5,735	$ 3,846
Board of Directors Executive Chairman | General and administrative
Stock-based Compensation Expense
Stock-based compensation expense	$ 1,000

Stockholders' Equity - Option a

Stockholders' Equity - Option and ESPP Valuation Assumptions (Details)	1 Months Ended						12 Months Ended
	Nov. 30, 2018	May 31, 2018	Nov. 30, 2017	May 31, 2017	Nov. 30, 2016	May 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock options outstanding
Class of Stock [Line Items]
Expected term (years)							6 years	5 years 10 months 24 days	5 years 8 months 12 days
Volatility							45.00%	49.00%	46.00%
Risk-free interest rate							2.80%	2.10%	1.40%
Dividend yield							0.00%	0.00%	0.00%
ESPP
Class of Stock [Line Items]
Expected term (years)	6 months	6 months	6 months	6 months	6 months	6 months
Volatility	37.00%	36.00%	36.00%	43.00%	42.00%	58.00%
Risk-free interest rate	2.10%	1.40%	1.40%	1.00%	0.60%	0.40%
Dividend yield	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%

Net Loss Per Share - Basic and

Net Loss Per Share - Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Net loss	$ 3,733	$ (1,305)	$ (2,042)	$ (607)	$ (631)	$ 924	$ (4,007)	$ (5,255)	$ (221)	$ (8,969)	$ (11,860)
Weighted-average shares used in computing basic and diluted net loss per share (in shares)									58,076	54,946	52,342
Basic and diluted (in USD per share)									$ 0	$ (0.16)	$ (0.23)

Net Loss Per Share - Antidiluti

Net Loss Per Share - Antidilutive Securities Excluded from Computation of Diluted Net Loss Per Share (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)	5,447	6,093	7,707
Stock options outstanding
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)	3,122	4,047	5,556
Restricted stock units outstanding
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)	2,325	2,033	2,019
Common stock warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)	0	13	132

Net Loss Per Share - Narrative

Net Loss Per Share - Narrative (Details)	May 31, 2018$ / shares
Convertible Senior Notes | Convertible debt
Debt Instrument [Line Items]
Conversion price on convertible debt (in USD per share)	$ 40.82

Income Taxes - Schedule of Comp

Income Taxes - Schedule of Components of Loss before Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
United States	$ (638)	$ (9,434)	$ (12,222)
International	717	733	416
Income (loss) before income taxes	$ 79	$ (8,701)	$ (11,806)

Income Taxes - Schedule of Co_2

Income Taxes - Schedule of Components of Provision for Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
U.S. federal									$ 0	$ 0	$ 0
U.S. state									28	42	16
Foreign									272	226	38
Total provision for income taxes	$ 150	$ 41	$ 64	$ 45	$ 126	$ 43	$ 50	$ 49	$ 300	$ 268	$ 54

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
U.S. federal income tax rate (percent)	21.00%
Undistributed earnings of foreign subsidiaries			$ 1.2
Limitation on use of net operating loss, cumulative ownership change, more than	50.00%
Limitation on use of net operating loss, cumulative ownership change, period of change	3 years
Federal
Operating Loss Carryforwards [Line Items]
Increase (decrease) in valuation allowance for deferred tax assets	$ 5.1	$ (1.3)
Net operating loss carryforwards	216.8
Federal | Research and Development Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Research and development credit carryforwards	3.2
State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	120
State | Research and Development Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Research and development credit carryforwards	$ 2.8

Income Taxes - Schedule of Effe

Income Taxes - Schedule of Effective Income Tax Amount Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
U.S. federal tax at statutory rate									$ 17	$ (2,958)	$ (4,014)
U.S. state income taxes									2,539	(708)	490
Non-deductible expense (benefit)									14,485	(5,673)	931
Research and development credit									(339)	(402)	(262)
Stock-based compensation									(11,360)	(14,622)	983
Impact of 2017 Tax Act									0	25,952	0
Other									106	2	(104)
Change in valuation allowance									(5,148)	(1,323)	2,030
Total provision for income taxes	$ 150	$ 41	$ 64	$ 45	$ 126	$ 43	$ 50	$ 49	$ 300	$ 268	$ 54

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Net operating loss and credit carryforwards	$ 54,966	$ 47,991
Accrued liabilities	4,271	3,183
Allowance for doubtful accounts	400	416
Deferred revenue	832	140
Accrued compensation	1,081	900
Intangibles	4	7
Gross deferred tax assets	61,554	52,637
Valuation allowance	(47,127)	(52,275)
Net deferred tax assets	14,427	362
Deferred tax liabilities:
Property and equipment	(370)	(98)
Amortized intangibles	(155)	(264)
Convertible senior notes	(13,902)	0
Gross deferred tax liabilities	(14,427)	(362)
Net deferred taxes	$ 0	$ 0

Income Taxes - Schedule of Unre

Income Taxes - Schedule of Unrecognized Tax Benefits Rollforward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits
Unrecognized benefit — beginning of period	$ 3,115	$ 2,805	$ 2,485
Gross increases — current year tax positions	7,608	310	324
Gross decreases — prior year tax positions	0	0	(4)
Unrecognized benefit — end of period	$ 10,723	$ 3,115	$ 2,805

Commitments and Contingencies -

Commitments and Contingencies - Commitments and Leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Promissory note payable	$ 258,750
Rent expense	2,800	$ 2,600	$ 2,100
Capital Leases
2,019	7,220
2,020	4,284
2,021	704
2,022	0
Total future minimum lease payment	12,208
Less — amount representing interest	(1,052)
Present value of total capital lease obligation	11,156
Capital lease obligation — current portion	6,647	6,651
Capital lease obligation — net of current portion	4,509	$ 7,161
Operating Leases
2,019	3,041
2,020	2,634
2,021	653
2,022	0
Total future minimum lease payment	$ 6,328

Commitments and Contingencies_2

Commitments and Contingencies - Hosting, Telecommunications Usage and Maintenance Services (Details) $ in Thousands	Dec. 31, 2018USD ($)
Hosting Services
Unrecorded Unconditional Purchase Obligation [Line Items]
2,019	$ 1,942
2,020	1,209
2,021	500
2,022	700
Total future minimum payment	4,351
Telecommunication Usage Services
Unrecorded Unconditional Purchase Obligation [Line Items]
2,019	3,138
2,020	1,781
2,021	875
2,022	294
Total future minimum payment	6,088
Equipment Maintenance Services
Unrecorded Unconditional Purchase Obligation [Line Items]
2,019	345
2,020	243
2,021	76
2,022	0
Total future minimum payment	$ 664

Commitments and Contingencies_3

Commitments and Contingencies - Universal Services Fund Liability (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2017
Loss Contingencies [Line Items]
Accrued federal fees	$ 1,434	$ 1,151
Disputed portion | Year 2003 through 2012 | USF Obligations
Loss Contingencies [Line Items]
Accrued federal fees			$ 3,900
USF credits			3,100
Disputed liability related to reversal of interest and penalties			3,100
Disputed portion | Year 2003 To Year 2007 | USF Obligations
Loss Contingencies [Line Items]
Accrued federal fees	$ 900		$ 800

Commitments and Contingencies_4

Commitments and Contingencies - State and Local Taxes and Surcharges (Details)	3 Months Ended									12 Months Ended
	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Mar. 31, 2015USD ($)state	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Loss Contingencies [Line Items]
General and administrative expense	$ 10,766,000	$ 10,746,000	$ 9,833,000	$ 9,103,000	$ 8,767,000	$ 4,679,000	$ 6,845,000	$ 8,860,000		$ 40,448,000	$ 29,151,000	$ 25,072,000
Sales tax liability - current	1,741,000				1,326,000					1,741,000	1,326,000
Contingent sales tax liabilities
Loss Contingencies [Line Items]
Number of states with sales tax liability (in states) | state									4
General and administrative expense									$ 600,000
Payments on usage-based fees										100,000	0	300,000
Sales tax liability gain										300,000	600,000	$ 400,000
Sales tax liability	1,100,000				1,500,000					1,100,000	1,500,000
Sales tax liability - current	$ 100,000				$ 400,000					$ 100,000	$ 400,000

Commitments and Contingencies_5

Commitments and Contingencies - Legal Matters (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2018
Settled Litigation | Melcher Litigation
Loss Contingencies [Line Items]
Litigation settlement amount awarded to other party	$ 1.7
Indemnification Agreement
Loss Contingencies [Line Items]
Legal fees		$ 0.5

Geographical Information - Sche

Geographical Information - Schedule of Revenue and Property and Equipment by Geographic Region (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues from External Customers and Long-Lived Assets
Revenue	$ 72,335	$ 65,304	$ 61,120	$ 58,905	$ 55,403	$ 50,081	$ 47,727	$ 47,014	$ 257,664	$ 200,225	$ 162,090
Property and equipment, net	25,885				19,888				25,885	19,888	14,688
United States
Revenues from External Customers and Long-Lived Assets
Revenue									239,378	188,303	151,484
Property and equipment, net	23,931				17,949				23,931	17,949	13,025
International
Revenues from External Customers and Long-Lived Assets
Revenue									18,286	11,922	10,606
Property and equipment, net	$ 1,954				$ 1,939				$ 1,954	$ 1,939	$ 1,663

Retirement Plans (Details)

Retirement Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Defined benefit liability	$ 0.7	$ 0.5
Retirement expense	$ 0.1	$ 0.3	$ 0.1

Selected Quarterly Financial _3

Selected Quarterly Financial Data (Unaudited) - Schedule of Quarterly Financial Information (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 72,335	$ 65,304	$ 61,120	$ 58,905	$ 55,403	$ 50,081	$ 47,727	$ 47,014	$ 257,664	$ 200,225	$ 162,090
Cost of revenue	28,339	26,179	24,814	24,702	22,363	20,497	20,273	19,971	104,034	83,104	66,934
Gross profit	43,996	39,125	36,306	34,203	33,040	29,584	27,454	27,043	153,630	117,121	95,156
Operating expenses:
Research and development	8,451	9,582	8,367	7,772	6,748	6,689	6,836	6,847	34,172	27,120	23,878
Sales and marketing	18,793	17,818	17,912	17,478	17,358	16,502	16,932	15,778	72,001	66,570	52,748
General and administrative	10,766	10,746	9,833	9,103	8,767	4,679	6,845	8,860	40,448	29,151	25,072
Total operating expenses	38,010	38,146	36,112	34,353	32,873	27,870	30,613	31,485	146,621	122,841	101,698
Income (loss) from operations	5,986	979	194	(150)	167	1,714	(3,159)	(4,442)	7,009	(5,720)	(6,542)
Other income (expense), net:
Extinguishment of debt	0	0	0	0	0	0	0	0	0	0	(1,026)
Interest expense	(3,462)	(3,595)	(2,378)	(810)	(836)	(865)	(888)	(882)	(10,245)	(3,471)	(4,226)
Interest income and other	1,359	1,352	206	398	164	118	90	118	3,315	490	(12)
Total other income (expense), net	(2,103)	(2,243)	(2,172)	(412)	(672)	(747)	(798)	(764)	(6,930)	(2,981)	(5,264)
Income (loss) before income taxes	3,883	(1,264)	(1,978)	(562)	(505)	967	(3,957)	(5,206)	79	(8,701)	(11,806)
Provision for income taxes	150	41	64	45	126	43	50	49	300	268	54
Net loss	$ 3,733	$ (1,305)	$ (2,042)	$ (607)	$ (631)	$ 924	$ (4,007)	$ (5,255)	$ (221)	$ (8,969)	$ (11,860)
Net income (loss) per share:
Net income (loss) per share, basic (in USD per share)	$ 0.06	$ (0.02)	$ (0.04)	$ (0.01)	$ (0.01)	$ 0.02	$ (0.07)	$ (0.10)
Net income (loss) per share, diluted (in USD per share)	$ 0.06	$ (0.02)	$ (0.04)	$ (0.01)	$ (0.01)	$ 0.02	$ (0.07)	$ (0.10)
Shares used in computing net loss per share:
Basic (in shares)	58,926	58,454	57,903	56,399	56,034	55,310	54,723	53,688
Diluted (in shares)	62,071	58,454	57,903	56,399	56,034	59,441	54,723	53,688

Selected Quarterly Financial _4

Selected Quarterly Financial Data (Unaudited) - Allocation of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Total stock-based compensation	$ 7,493	$ 8,869	$ 6,797	$ 5,325	$ 4,640	$ 3,720	$ 3,854	$ 3,129	$ 28,484	$ 15,343	$ 9,643
Cost of revenue
Total stock-based compensation	942	860	853	678	594	599	575	434
Research and development
Total stock-based compensation	1,010	2,352	1,064	877	807	797	801	637
Sales and marketing
Total stock-based compensation	1,747	1,613	1,585	1,362	1,128	1,084	1,224	928
General and administrative
Total stock-based compensation	$ 3,794	$ 4,044	$ 3,295	$ 2,408	$ 2,111	$ 1,240	$ 1,254	$ 1,130

Selected Quarterly Financial _5

Selected Quarterly Financial Data (Unaudited) - Allocation of Depreciation and Amortization Expense (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Total depreciation and amortization	$ 2,838	$ 2,667	$ 2,449	$ 2,320	$ 2,068	$ 1,881	$ 2,270	$ 2,095	$ 10,274	$ 8,314	$ 8,390
Cost of revenue
Total depreciation and amortization	2,129	2,021	1,864	1,794	1,611	1,397	1,716	1,576
Research and development
Total depreciation and amortization	331	278	233	194	170	182	237	206
Sales and marketing
Total depreciation and amortization	6	30	30	29	30	30	30	30
General and administrative
Total depreciation and amortization	$ 372	$ 338	$ 322	$ 303	$ 257	$ 272	$ 287	$ 283

Uncategorized Items - fivn-2018

Label	Element	Value	[1]
Accounting Standards Update 2014-09 [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ 24,145,000
Accounting Standards Update 2014-09 [Member] | Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ 24,145,000
[1]	Effective January 2018, the Company adopted ASU 2014-09 - Revenue from Contracts with Customers: Topic 606. Accordingly, the Company recorded a net reduction to opening accumulated deficit of $24.1 million as of January 1, 2018 due to the cumulative impact of adopting the new standard. See Note 2 for more information.