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Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2019	Apr. 26, 2019
Document and Entity Information [Abstract]
Entity Registrant Name	Five9, Inc.
Trading Symbol	FIVN
Entity Central Index Key	0001288847
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding		59,676,850

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 93,492	$ 81,912
Marketable investments	205,450	209,907
Accounts receivable, net	25,840	24,797
Prepaid expenses and other current assets	9,719	8,014
Deferred contract acquisition costs	10,095	9,372
Total current assets	344,596	334,002
Property and equipment, net	27,496	25,885
Operating lease right-of-use assets	6,735
Intangible assets, net	543	631
Goodwill	11,798	11,798
Other assets	936	836
Deferred contract acquisition costs — less current portion	23,262	21,514
Total assets	415,366	394,666
Current liabilities:
Accounts payable	7,233	7,010
Accrued and other current liabilities	17,965	13,771
Operating lease liabilities	4,322
Accrued federal fees	1,348	1,434
Sales tax liabilities	1,404	1,741
Finance lease liabilities	6,208
Finance lease liabilities		6,647
Deferred revenue	17,853	17,391
Total current liabilities	56,333	47,994
Convertible senior notes	199,842	196,763
Sales tax liabilities — less current portion	839	841
Operating lease liabilities — less current portion	3,012
Finance lease liabilities — less current portion	3,316
Finance lease liabilities — less current portion		4,509
Other long-term liabilities	1,358	1,811
Total liabilities	264,700	251,918
Commitments and contingencies (Note 10)
Stockholders’ equity:
Common stock	60	59
Additional paid-in capital	303,946	294,279
Accumulated other comprehensive income (loss)	81	(93)
Accumulated deficit	(153,421)	(151,497)
Total stockholders’ equity	150,666	142,748
Total liabilities and stockholders’ equity	$ 415,366	$ 394,666

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Revenue	$ 74,538	$ 58,905
Cost of revenue	30,851	24,702
Gross profit	43,687	34,203
Operating expenses:
Research and development	10,546	7,772
Sales and marketing	21,701	17,478
General and administrative	11,762	9,103
Total operating expenses	44,009	34,353
Loss from operations	(322)	(150)
Other income (expense), net:
Interest expense	(3,396)	(810)
Interest income and other	1,745	398
Total other income (expense), net	(1,651)	(412)
Loss before income taxes	(1,973)	(562)
Provision for (benefit from) income taxes	(49)	45
Net loss	$ (1,924)	$ (607)
Net loss per share:
Basic and diluted (in usd per share)	$ (0.03)	$ (0.01)
Shares used in computing net loss per share:
Basic and diluted (in shares)	59,367	56,399
Comprehensive Loss:
Net loss	$ (1,924)	$ (607)
Other comprehensive income	174	5
Comprehensive loss	$ (1,750)	$ (602)

Consolidated Statement of Stockholders' Equity Statement - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Balance (in shares) at Dec. 31, 2017		56,632
Balance at Dec. 31, 2017	$ 46,838	$ 57	$ 222,202	$ 0	$ (175,421)
Issuance of common stock upon exercise of stock options (in shares)		786
Issuance of common stock upon exercise of stock options	4,746	$ 1	4,745
Issuance of common stock upon vesting of restricted stock units (in shares)		236
Issuance of common stock upon vesting of restricted stock units	0	$ 0
Stock-based compensation	5,325		5,325
Other comprehensive income	5			5
Net loss	(607)				(607)
Balance (in shares) at Mar. 31, 2018		57,654
Balance at Mar. 31, 2018	80,452	$ 58	232,272	5	(151,883)
Balance (in shares) at Dec. 31, 2018		59,210
Balance at Dec. 31, 2018	142,748	$ 59	294,279	(93)	(151,497)
Issuance of common stock upon exercise of stock options (in shares)		216
Issuance of common stock upon exercise of stock options	982	$ 1	981
Issuance of common stock upon vesting of restricted stock units (in shares)		211
Issuance of common stock upon vesting of restricted stock units	0	$ 0
Stock-based compensation	8,686		8,686
Other comprehensive income	174			174
Net loss	(1,924)				(1,924)
Balance (in shares) at Mar. 31, 2019		59,637
Balance at Mar. 31, 2019	$ 150,666	$ 60	$ 303,946	$ 81	$ (153,421)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net loss	$ (1,924)	$ (607)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization	3,192	2,320
Amortization of operating lease right-of-use asset	1,010	0
Amortization of premium on marketable investments	(421)	0
Provision for doubtful accounts	14	48
Stock-based compensation	8,686	5,325
Gain on sale of convertible note held for investment	(217)	(312)
Amortization of debt discount and issuance costs	3,079	0
Others	(17)	(14)
Changes in operating assets and liabilities:
Accounts receivable	(1,046)	519
Prepaid expenses and other current assets	(1,721)	(1,833)
Deferred contract acquisition costs	(2,471)	(1,662)
Other assets	(7,845)	(90)
Accounts payable	552	1,181
Accrued and other current liabilities	7,724	2,791
Accrued federal fees and sales tax liability	(425)	(115)
Deferred revenue	416	121
Other liabilities	2,604	325
Net cash provided by operating activities	11,190	7,997
Cash flows from investing activities:
Purchases of marketable investments	(34,427)	0
Proceeds from maturities of marketable investments	39,497	0
Purchases of property and equipment	(3,985)	(433)
Proceeds from sale of convertible note held for investment	217	1,923
Net cash provided by investing activities	1,302	1,490
Cash flows from financing activities:
Proceeds from exercise of common stock options	982	4,751
Payments of notes payable	0	(157)
Payments of finance leases	(1,894)	(2,352)
Net cash (used in) provided by financing activities	(912)	2,242
Net increase in cash and cash equivalents	11,580	11,729
Cash and cash equivalents:
Beginning of period	81,912	68,947
End of period	93,492	80,676
Supplemental disclosures of cash flow data:
Cash paid for interest	235	765
Cash paid for income taxes	42	33
Non-cash investing and financing activities:
Equipment obtained under capital lease	0	2,635
Equipment purchased and unpaid at period-end	$ 1,875	$ 281

Description of Business and Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2019
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 condensed 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 interim financial reporting. Certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. Therefore, these condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018. In the opinion of management, the condensed consolidated financial statements reflect all adjustments, which are normal and recurring in nature, necessary for fair financial statement presentation. All intercompany transactions and balances have been eliminated in consolidation. Certain prior period amounts included in the condensed consolidated financial statements have been reclassified to conform to the current period presentation. Use of Estimates The preparation of condensed 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 condensed 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. Significant Accounting Policies The Company’s significant accounting policies are disclosed in its Annual Report on Form 10-K for the year ended December 31, 2018. Other than the accounting policies discussed in Note 12 related to the adoption of Accounting Standards Codification (“ASC”) 842, Leases, there has been no material change to the Company’s significant accounting policies during the three months ended March 31, 2019. See Note 12 for the updated accounting policies. Recently Adopted Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standard Update (“ASU”) No. 2016-02, Leases (Topic 842) and issued subsequent amendments to the initial guidance in 2017, 2018 and 2019 (collectively “ASC 842”). Under the new guidance, a lessee is required to recognize assets and liabilities for both finance, previously known as capital, and operating leases with lease terms of more than 12 months. The ASU also requires disclosures to help investors and other financial statement users better understand the amount, timing, and uncertainty of cash flows arising from leases. Lessor accounting remained largely unchanged from current GAAP. In transition, the Company was required to recognize and measure leases at the beginning of the earliest period presented using a modified retrospective approach that included a number of optional practical expedients that the Company elected to apply. The Company adopted ASC 842 using the modified retrospective method on January 1, 2019. See Note 12 for disclosure on the impact of adopting this standard. 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. The Company early adopted ASU 2018-15 prospectively effective January 1, 2019, to align the requirements for capitalizing implementation costs in a hosting arrangement that is a service contract with the requirements for capitalization costs incurred to develop or obtain internal-use software and hosting arrangements that include an internal-use software license. The adoption of ASU 2018-15 did not have a material impact on the Company’s consolidated financial position, operating results or cash flows. Recent Accounting Pronouncements Not Yet Effective The Company has reviewed or is in the process of evaluating all other issued, but not yet effective, accounting pronouncements and does not believe the future adoption of any such accounting pronouncements will cause a material impact on its consolidated financial position, operating results or cash flows.

Revenue

3 Months Ended

Mar. 31, 2019

Revenue from Contract with Customer [Abstract]

Revenue

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):



	March 31, 2019			December 31, 2018
Accounts receivable, net	$	25,840		$	24,797

Deferred contract acquisition costs:
Current	$	10,095		$	9,372
Non-current	23,262			21,514
Total deferred contract acquisition costs	$	33,357		$	30,886

Contract assets and contract liabilities:
Contract assets (included in prepaid expenses and other current assets)	$	427		$	330
Contract liabilities (deferred revenue)	17,853			17,391
Net contract assets (liabilities)	$	(17,426	)	$	(17,061	)

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.

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 three months ended March 31, 2019, the Company recognized revenue of $11.3 million related to its contract liabilities at January 1, 2019.

Remaining Performance Obligations

As of March 31, 2019, 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 $105.6 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 Measurements

3 Months Ended

Mar. 31, 2019

Fair Value Disclosures [Abstract]

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 March 31, 2019 and December 31, 2018 were as follows (in thousands):



	March 31, 2019
	Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Certificates of deposit	$	3,083	$	—	$	—		$	3,083
U.S. treasury	7,290		3		—			7,293
U.S. agency securities and government sponsored securities	129,630		12		(7		)	129,635
Commercial paper	11,296		—		—			11,296
Municipal bonds	5,989		—		—			5,989
Corporate bonds	48,144		11		(1		)	48,154
Total	$	205,432	$	26	$	(8	)	$	205,450



	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 March 31, 2019 and December 31, 2018 (in thousands):



	March 31, 2019					December 31, 2018
	Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value
U.S. treasury	$	—		$	140	$	—		$	637
U.S. agency securities and government sponsored securities	(7		)	83,007		(111		)	153,212
Municipal bonds	—			5,989		(4		)	6,086
Corporate bonds	(1		)	12,307		(61		)	41,246
Total	$	(8	)	$	101,443	$	(176	)	$	201,181

The contractual maturities of the Company’s marketable investments as of March 31, 2019 and 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):



	March 31, 2019
	Level 1		Level 2		Level 3		Total
Assets
Cash equivalents
Money market funds	$	26,140	$	—	$	—	$	26,140
U.S. treasury	8,979		—		—		8,979
Commercial paper	—		2,793		—		2,793
Total cash equivalents	$	35,119	$	2,793	$	—	$	37,912
Marketable investments
Certificates of deposit	$	—	$	3,083	$	—	$	3,083
U.S. treasury	7,293		—		—		7,293
U.S. agency securities and government sponsored securities	—		129,635		—		129,635
Commercial paper	—		11,296		—		11,296
Municipal bonds	—		5,989		—		5,989
Corporate bonds	—		48,154		—		48,154
Total marketable investments	$	7,293	$	198,157	$	—	$	205,450

	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

As of March 31, 2019 and December 31, 2018, the estimated fair value of the Company’s outstanding 0.125% convertible senior notes due 2023 was $363.7 million and $316.1 million, respectively. 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 March 31, 2019 and December 31, 2018.

Financial Statement Components

3 Months Ended

Mar. 31, 2019

Financial Statement Components [Abstract]

Financial Statement Components

Cash and cash equivalents consisted of the following (in thousands):



	March 31, 2019		December 31, 2018
Cash	$	55,580	$	69,893
Money market funds	26,140		10,833
U.S. treasury	8,979		638
U.S. agency securities	—		50
Commercial paper	2,793		498
Total cash and cash equivalents	$	93,492	$	81,912

Accounts receivable, net consisted of the following (in thousands):



	March 31, 2019			December 31, 2018
Trade accounts receivable	$	23,729		$	23,068
Unbilled trade accounts receivable, net of advance client deposits	2,122			1,741
Allowance for doubtful accounts	(11		)	(12		)
Accounts receivable, net	$	25,840		$	24,797

Prepaid expenses and other current assets consisted of the following (in thousands):



	March 31, 2019		December 31, 2018
Prepaid expenses	$	5,741	$	5,005
Other current assets	3,551		2,679
Contract assets	427		330
Prepaid expenses and other current assets	$	9,719	$	8,014

Property and equipment, net consisted of the following (in thousands):



	March 31, 2019			December 31, 2018
Computer and network equipment	$	57,302		$	54,452
Computer software	11,241			10,064
Internal-use software development costs	500			500
Furniture and fixtures	1,889			1,491
Leasehold improvements	894			855
Property and equipment	71,826			67,362
Accumulated depreciation and amortization	(44,330		)	(41,477		)
Property and equipment, net	$	27,496		$	25,885

Depreciation and amortization expense associated with property and equipment was $3.1 million and $2.2 million for the three months ended March 31, 2019 and 2018, respectively.

Property and equipment capitalized under finance lease obligations consists primarily of computer and network equipment and was as follows (in thousands):



	March 31, 2019			December 31, 2018
Gross	$	47,114		$	47,383
Less: accumulated depreciation and amortization	(35,002		)	(33,547		)
Total	$	12,112		$	13,836

Accrued and other current liabilities consisted of the following (in thousands):



	March 31, 2019		December 31, 2018
Accrued compensation and benefits	$	13,901	$	10,277
Accrued expenses	4,064		3,494
Accrued and other current liabilities	$	17,965	$	13,771

Intangible Assets

3 Months Ended

Mar. 31, 2019

Goodwill and Intangible Assets Disclosure [Abstract]

Intangible Assets

The component of intangible assets was as follows (in thousands):



	March 31, 2019							December 31, 2018
	Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount		Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount
Developed technology	$	2,460	$	(1,917	)	$	543	$	2,460	$	(1,829	)	$	631

Amortization expense for intangible assets was $88 thousand and $116 thousand for the three months ended March 31, 2019 and 2018, respectively.

As of March 31, 2019, the expected future amortization expense for intangible assets was as follows (in thousands):



Period	Expected Future Amortization Expense
2019	263
2020	280
Total	$	543

Debt

3 Months Ended

Mar. 31, 2019

Debt Disclosure [Abstract]

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 initially 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 initial 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.

The closing market price of the Company’s common stock of $52.83 per share as of March 29, 2019, the last trading day, during the three months ended March 31, 2019, was below $53.07 per share, which represents 130% of the initial conversion price of $40.82 per share. Additionally, 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, March 29, 2019, was not greater than or equal to 130% of the initial conversion price on each applicable trading day. As such, during the three months ended March 31, 2019, the conditions allowing holders of the Notes to convert were not met. The Notes were therefore not convertible during the three months ended March 31, 2019 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):



	March 31, 2019			December 31, 2018
Principal	$	258,750		$	258,750
Unamortized debt discount	(53,755		)	(56,564		)
Unamortized issuance costs	(5,153		)	(5,423		)
Net carrying amount	$	199,842		$	196,763

There was no change to net carrying amount of the equity component of the Notes since it continued to meet the conditions for equity classification as presented below (in thousands):



	March 31, 2019			December 31, 2018
Debt discount for conversion option	$	63,756		$	63,756
Issuance costs	(1,998		)	(1,998		)
Net carrying amount	$	61,758		$	61,758

Interest expense related to the Notes was as follows (in thousands):



	Three Months Ended
	March 31, 2019		March 31, 2018
Contractual interest expense	$	81	$	—
Amortization of debt discount	2,810		—
Amortization of issuance costs	269		—
Total interest expense	$	3,160	$	—

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 in May 2018 was as follows (in thousands):



	March 31, 2019		December 31, 2018
Conversion option	$	—	$	63,756
Payments for capped call transactions	—		(31,412		)
Issuance costs	—		(1,998		)
Total	$	—	$	30,346

Maturity of the Company’s outstanding debt as of March 31, 2019 was as follows (in thousands):



Period	Amount to Mature
2023	$	258,750
Total	$	258,750

Stockholders' Equity

3 Months Ended

Mar. 31, 2019

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 March 31, 2019 and December 31, 2018, the Company had 59,636,995 and 59,210,496 shares of common stock issued and outstanding, respectively.

Preferred Stock

The Company is also 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 March 31, 2019 and December 31, 2018, the Company had no shares of preferred stock issued and 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 were as follows (in thousands):



		March 31, 2019
Stock options outstanding		3,123
Restricted stock units outstanding		2,969
Shares available for future grant under 2014 Plan		10,332
Shares available for future issuance under ESPP		2,283
Total shares of common stock reserved		18,707

Stock Options

A summary of the Company’s stock option activity during the three months ended March 31, 2019 is as follows (in thousands, except years and per share data):



	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Life (Years)	Aggregate Intrinsic Value
Outstanding as of December 31, 2018	3,122		$	12.52
Options granted (weighted average grant date fair value of $23.91 per share)	223		50.38
Options exercised	(216	)	4.55
Options forfeited or expired	(6	)	33.77
Outstanding as of March 31, 2019	3,123		$	15.73	6.3	$	115,907

The aggregate intrinsic value disclosed in the above table is 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 $52.83 per share as of March 31, 2019 for all in-the-money stock options outstanding.

Restricted Stock Units

A summary of the Company’s restricted stock unit or RSU activity during the three months ended March 31, 2019 is as follows (in thousands, except per share data):



	Number of Shares		Weighted Average Grant Date Fair Value Per Share
Outstanding as of December 31, 2018	2,325		$	25.36
RSUs granted	904		52.19
RSUs vested and released	(211	)	16.93
RSUs forfeited	(49	)	31.28
Outstanding as of March 31, 2019	2,969		$	34.03

Stock-Based Compensation

Stock-based compensation expenses were as follows (in thousands):



	Three Months Ended
	March 31, 2019		March 31, 2018
Cost of revenue	$	1,229	$	678
Research and development	1,470		877
Sales and marketing	2,249		1,362
General and administrative	3,738		2,408
Total stock-based compensation	$	8,686	$	5,325

As of March 31, 2019, 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	$	15,240	$	90,804	$	339
Weighted-average amortization period	3.1 years		3.3 years		0.1 years

The weighted-average assumptions used to value stock options granted during the periods presented were as follows:



Stock Options	Three Months Ended
	March 31, 2019		March 31, 2018
Expected term (years)	6.0		6.0
Volatility	46	%	45	%
Risk-free interest rate	2.5	%	2.7	%
Dividend yield ⁽¹⁾	—		—


(1)	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.

Net Loss Per Share

3 Months Ended

Mar. 31, 2019

Earnings Per Share [Abstract]

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 loss 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, vesting of restricted stock units and shares of common stock issuable upon conversion of convertible senior notes.

The following table presents the calculation of basic and diluted net loss per share (in thousands, except per share data):



	Three Months Ended
	March 31, 2019			March 31, 2018
Net loss	$	(1,924	)	$	(607	)
Weighted-average shares of common stock outstanding	59,367			56,399
Basic and diluted net loss per share	$	(0.03	)	$	(0.01	)

The following securities were excluded from the calculation of diluted net loss per share because their effect would have been anti-dilutive (in thousands):



	Three Months Ended
	March 31, 2019	March 31, 2018
Stock options	3,123	3,491
Restricted stock units	2,969	2,427
Convertible senior notes	1,249	—
Common stock warrants	—	13
Total	7,341	5,931

The Company expects to settle the principal amount of its Notes outstanding at March 31, 2019 in cash, and therefore, uses the treasury stock method for calculating any potential dilutive effect of the conversion spread. The conversion spread had a dilutive impact during the three months ended March 31, 2019, since the average market price of the Company’s common stock during the period exceeded the initial conversion price of $40.82 per share for the Notes. However, 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	3 Months Ended
Income Taxes	Mar. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The provision for (benefit from) income taxes for the three months ended March 31, 2019 and 2018 was approximately $(49) thousand and $45 thousand, respectively. The provision for income taxes consisted primarily of foreign income taxes, as well as a benefit for a true-up to foreign income taxes. For the three months ended March 31, 2019 and 2018, the provision for income taxes differed from the statutory amount primarily due to the Company realizing no benefit for current year losses due to maintaining a full valuation allowance against its domestic net deferred tax assets. The realization of tax benefits of deferred tax assets is dependent upon future levels of taxable income, of an appropriate character, in the periods the items are expected to be deductible or taxable. Based on the available objective evidence, the Company does not believe it is more likely than not that the net deferred tax assets will be realizable. Accordingly, the Company has provided a full valuation allowance against the domestic net deferred tax assets as of March 31, 2019 and December 31, 2018. The Company intends to maintain the remaining valuation allowance until sufficient positive evidence exists to support a reversal of, or decrease in, the valuation allowance. During the three months ended March 31, 2019, there were no material changes to the total amount of unrecognized tax benefits.

Commitments and Contingencies	3 Months Ended
Commitments and Contingencies	Mar. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Commitments The Company’s principal commitments consist of future payment obligations under finance leases to finance data centers and other computer and networking equipment purchases, debt (see Note 6), operating leases agreements for office space, and agreements with third parties to provide co-location hosting, telecommunication usage and equipment maintenance services. These commitments as of December 31, 2018 are disclosed in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018, and did not change materially during the three months ended March 31, 2019, except for certain hosting and telecommunications agreements. As of March 31, 2019, $258.8 million of the Notes were outstanding. The Notes are due May 1, 2023. For more information concerning the Notes, see Note 6. As of March 31, 2019, the Company’s commitment under various hosting and telecommunications agreements totaled $7.9 million for terms of 12 to 36 months. These agreements require the Company to make monthly payments over the service term in exchange for certain network services. 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. 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. The Company has incurred approximately $1.0 million in fees and expenses, which are included in general and administrative expenses, on behalf of Mr. Fried through March 31, 2019. 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

3 Months Ended

Mar. 31, 2019

Segment Reporting [Abstract]

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):



	Three Months Ended
	March 31, 2019		March 31, 2018
United States	$	68,883	$	55,171
International	5,655		3,734
Total revenue	$	74,538	$	58,905

The following table summarizes total property and equipment, net in the respective locations (in thousands):



	March 31, 2019		December 31, 2018
United States	$	25,663	$	23,931
International	1,833		1,954
Property and equipment, net	$	27,496	$	25,885

ASC 842 Adoption Impact

3 Months Ended

Mar. 31, 2019

Leases [Abstract]

ASC 842 Adoption Impact

The Company has leases for offices, data centers and other computer and networking equipment that expire at various dates through 2021. The Company’s leases have remaining terms of one to three years, some of the leases include a Company option to extend the leases for up to three to five years, and some of the leases include the option to terminate the leases upon 30-days notice.

The Company adopted ASC 842 using the modified retrospective method on January 1, 2019. The Company elected the available practical expedients, implemented internal controls, and a lease accounting system to enable the preparation of financial information upon adoption. The most significant impact of the adoption of ASC 842 was the recognition of right-of-use, or ROU, assets and lease liabilities for operating leases of $8.4 million and $8.4 million, respectively, and a reversal of deferred rent of $0.6 million on January 1, 2019. The Company’s accounting for finance leases remained substantially unchanged. The adoption of ASC 842 did not have any impact on the Company’s operating results or cash flows.

The components of lease expenses were as follows (in thousands):



	Three Months Ended
	March 31, 2019		March 31, 2018
Operating lease cost	$	1,103	$	—
Finance lease cost:
Amortization of right-of-use assets	$	1,455	$	1,822
Interest on lease liabilities	236		354
Total finance lease cost	$	1,691	$	2,176

Supplemental cash flow information related to leases was as follows (in thousands):



	Three Months Ended
	March 31, 2019			March 31, 2018
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash used in operating leases	$	(1,144	)	$	—
Financing cash used in finance leases	(1,894		)	(2,352		)
Right of use assets obtained in exchange for lease obligations:
Finance leases	—			3,151

Supplemental balance sheet information related to leases was as follows (in thousands):



	March 31, 2019			December 31, 2018
Operating leases
Operating lease right-of-use assets	$	6,735		$	—

Operating lease liabilities	$	4,322		$	—
Operating lease liabilities — less current portion	3,012			—
Total operating lease liabilities	$	7,334		$	—
Finance leases
Property and equipment, gross	$	47,114		$	47,383
Less: accumulated depreciation and amortization	(35,002		)	(33,547		)
Property and equipment, net	$	12,112		$	13,836

Finance leases	$	6,208		$	6,647
Finance lease liabilities — less current portion	3,316			4,509
Total finance lease liabilities	$	9,524		$	11,156

Weighted average remaining terms were as follows (in years):



	March 31, 2019	December 31, 2018
Weighted average remaining lease term
Operating leases	1.7	2.0
Finance leases	2.3	2.6

Weighted average discount rates were as follows:



	March 31, 2019		December 31, 2018
Weighted average discount rate
Operating leases	4.8	%	—	%
Finance leases	9.0	%	9.0	%

Maturities of lease liabilities were as follows:



Year Ending December 31,	Operating Leases			Finance Leases
2019	$	4,570		$	5,335
2020	3,075			4,284
2021	—			704
Total lease payments	7,645			10,323
Less: imputed interest	(311		)	(799		)
Total	$	7,334		$	9,524

As of March 31, 2019, the Company had additional operating leases for office space, that have not yet commenced of $4.1 million. These operating leases are expected to commence during 2019 with lease terms of two to six years.

Impact on Condensed Consolidated Balance Sheet

The impact of the adoption of ASC 842 on select condensed consolidated balance sheet line items, was as follows:



	March 31, 2019
(in thousands)	As Reported		Balances without adoption of ASC 842		Effect of Change Higher (Lower)
Assets:
Operating lease right-of-use-assets	$	6,735	$	—	$	6,735
Liabilities:
Operating lease liabilities	4,322		—		4,322
Operating lease liabilities — less current portion	3,012		—		3,012

Change in Accounting Policy

Leases

The Company determines if an arrangement is or contains a lease at inception. Operating leases are included in operating lease ROU assets and operating lease liabilities in the Company’s condensed consolidated balance sheets. Finance leases are included in property and equipment, and finance lease liabilities in the Company’s condensed consolidated balance sheets.

ROU assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease ROU assets and liabilities are recognized at the commencement date based on an amount equal to the present value of lease payments over the lease term. As most of the Company’s leases do not provide an implicit rate, the Company uses an incremental borrowing rate based on the information available at the commencement date in determining the present value of lease payments. The Company uses the implicit rate when it is readily determinable. The operating lease ROU asset also includes any lease payments made and excludes lease incentives. The Company’s lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Operating lease expense for lease payments is recognized on a straight-line basis over the lease term. The Company has lease agreements with lease and non-lease components, which are generally accounted for separately.

Description of Business and Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed 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 interim financial reporting. Certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. Therefore, these condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018. In the opinion of management, the condensed consolidated financial statements reflect all adjustments, which are normal and recurring in nature, necessary for fair financial statement presentation. All intercompany transactions and balances have been eliminated in consolidation. Certain prior period amounts included in the condensed consolidated financial statements have been reclassified to conform to the current period presentation.
Use of Estimates	Use of Estimates The preparation of condensed 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 condensed 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.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standard Update (“ASU”) No. 2016-02, Leases (Topic 842) and issued subsequent amendments to the initial guidance in 2017, 2018 and 2019 (collectively “ASC 842”). Under the new guidance, a lessee is required to recognize assets and liabilities for both finance, previously known as capital, and operating leases with lease terms of more than 12 months. The ASU also requires disclosures to help investors and other financial statement users better understand the amount, timing, and uncertainty of cash flows arising from leases. Lessor accounting remained largely unchanged from current GAAP. In transition, the Company was required to recognize and measure leases at the beginning of the earliest period presented using a modified retrospective approach that included a number of optional practical expedients that the Company elected to apply. The Company adopted ASC 842 using the modified retrospective method on January 1, 2019. See Note 12 for disclosure on the impact of adopting this standard. 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. The Company early adopted ASU 2018-15 prospectively effective January 1, 2019, to align the requirements for capitalizing implementation costs in a hosting arrangement that is a service contract with the requirements for capitalization costs incurred to develop or obtain internal-use software and hosting arrangements that include an internal-use software license. The adoption of ASU 2018-15 did not have a material impact on the Company’s consolidated financial position, operating results or cash flows. Recent Accounting Pronouncements Not Yet Effective The Company has reviewed or is in the process of evaluating all other issued, but not yet effective, accounting pronouncements and does not believe the future adoption of any such accounting pronouncements will cause a material impact on its consolidated financial position, operating results or cash flows.
Receivables	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.
Deferred Contract Acquisition	Deferred contract acquisition costs are recorded when incurred and are amortized over a customer benefit period of five years.
Revenue	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.

- Definition

Disclosure of accounting policy for trade and other accounts receivable, and finance, loan and lease receivables, including those classified as held for investment and held for sale. This disclosure may include (1) the basis at which such receivables are carried in the entity's statements of financial position (2) how the level of the valuation allowance for receivables is determined (3) when impairments, charge-offs or recoveries are recognized for such receivables (4) the treatment of origination fees and costs, including the amortization method for net deferred fees or costs (5) the treatment of any premiums or discounts or unearned income (6) the entity's income recognition policies for such receivables, including those that are impaired, past due or placed on nonaccrual status and (7) the treatment of foreclosures or repossessions (8) the nature and amount of any guarantees to repurchase receivables.

+ References + Details

Revenue (Tables)

3 Months Ended

Mar. 31, 2019

Revenue from Contract with Customer [Abstract]

Schedule of impacts from new accounting pronouncements

The impact of the adoption of ASC 842 on select condensed consolidated balance sheet line items, was as follows:



	March 31, 2019
(in thousands)	As Reported		Balances without adoption of ASC 842		Effect of Change Higher (Lower)
Assets:
Operating lease right-of-use-assets	$	6,735	$	—	$	6,735
Liabilities:
Operating lease liabilities	4,322		—		4,322
Operating lease liabilities — less current portion	3,012		—		3,012

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):



	March 31, 2019			December 31, 2018
Accounts receivable, net	$	25,840		$	24,797

Deferred contract acquisition costs:
Current	$	10,095		$	9,372
Non-current	23,262			21,514
Total deferred contract acquisition costs	$	33,357		$	30,886

Contract assets and contract liabilities:
Contract assets (included in prepaid expenses and other current assets)	$	427		$	330
Contract liabilities (deferred revenue)	17,853			17,391
Net contract assets (liabilities)	$	(17,426	)	$	(17,061	)

Investments and Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2019

Fair Value Disclosures [Abstract]

Schedule of Marketable Investments



	March 31, 2019
	Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Certificates of deposit	$	3,083	$	—	$	—		$	3,083
U.S. treasury	7,290		3		—			7,293
U.S. agency securities and government sponsored securities	129,630		12		(7		)	129,635
Commercial paper	11,296		—		—			11,296
Municipal bonds	5,989		—		—			5,989
Corporate bonds	48,144		11		(1		)	48,154
Total	$	205,432	$	26	$	(8	)	$	205,450



	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



	March 31, 2019					December 31, 2018
	Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value
U.S. treasury	$	—		$	140	$	—		$	637
U.S. agency securities and government sponsored securities	(7		)	83,007		(111		)	153,212
Municipal bonds	—			5,989		(4		)	6,086
Corporate bonds	(1		)	12,307		(61		)	41,246
Total	$	(8	)	$	101,443	$	(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):



	March 31, 2019
	Level 1		Level 2		Level 3		Total
Assets
Cash equivalents
Money market funds	$	26,140	$	—	$	—	$	26,140
U.S. treasury	8,979		—		—		8,979
Commercial paper	—		2,793		—		2,793
Total cash equivalents	$	35,119	$	2,793	$	—	$	37,912
Marketable investments
Certificates of deposit	$	—	$	3,083	$	—	$	3,083
U.S. treasury	7,293		—		—		7,293
U.S. agency securities and government sponsored securities	—		129,635		—		129,635
Commercial paper	—		11,296		—		11,296
Municipal bonds	—		5,989		—		5,989
Corporate bonds	—		48,154		—		48,154
Total marketable investments	$	7,293	$	198,157	$	—	$	205,450

	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

Financial Statement Components (Tables)

3 Months Ended

Mar. 31, 2019

Financial Statement Components [Abstract]

Schedule of Cash and Cash Equivalents

Cash and cash equivalents consisted of the following (in thousands):



	March 31, 2019		December 31, 2018
Cash	$	55,580	$	69,893
Money market funds	26,140		10,833
U.S. treasury	8,979		638
U.S. agency securities	—		50
Commercial paper	2,793		498
Total cash and cash equivalents	$	93,492	$	81,912

Schedule of Accounts Receivable

Accounts receivable, net consisted of the following (in thousands):



	March 31, 2019			December 31, 2018
Trade accounts receivable	$	23,729		$	23,068
Unbilled trade accounts receivable, net of advance client deposits	2,122			1,741
Allowance for doubtful accounts	(11		)	(12		)
Accounts receivable, net	$	25,840		$	24,797

Schedule of Prepaid Expenses and Other Current Assets

Prepaid expenses and other current assets consisted of the following (in thousands):



	March 31, 2019		December 31, 2018
Prepaid expenses	$	5,741	$	5,005
Other current assets	3,551		2,679
Contract assets	427		330
Prepaid expenses and other current assets	$	9,719	$	8,014

Schedule of Property and Equipment

Property and equipment, net consisted of the following (in thousands):



	March 31, 2019			December 31, 2018
Computer and network equipment	$	57,302		$	54,452
Computer software	11,241			10,064
Internal-use software development costs	500			500
Furniture and fixtures	1,889			1,491
Leasehold improvements	894			855
Property and equipment	71,826			67,362
Accumulated depreciation and amortization	(44,330		)	(41,477		)
Property and equipment, net	$	27,496		$	25,885

Schedule of Capital Leased Property and Equipment

Property and equipment capitalized under finance lease obligations consists primarily of computer and network equipment and was as follows (in thousands):



	March 31, 2019			December 31, 2018
Gross	$	47,114		$	47,383
Less: accumulated depreciation and amortization	(35,002		)	(33,547		)
Total	$	12,112		$	13,836

Schedule of Accrued and Other Current Liabilities

Accrued and other current liabilities consisted of the following (in thousands):



	March 31, 2019		December 31, 2018
Accrued compensation and benefits	$	13,901	$	10,277
Accrued expenses	4,064		3,494
Accrued and other current liabilities	$	17,965	$	13,771

Intangible Assets (Tables)

3 Months Ended

Mar. 31, 2019

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of Intangible Assets

The component of intangible assets was as follows (in thousands):



	March 31, 2019							December 31, 2018
	Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount		Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount
Developed technology	$	2,460	$	(1,917	)	$	543	$	2,460	$	(1,829	)	$	631

Schedule of Expected Future Amortization Expense of Intangible Assets

As of March 31, 2019, the expected future amortization expense for intangible assets was as follows (in thousands):



Period	Expected Future Amortization Expense
2019	263
2020	280
Total	$	543

Debt (Tables)

3 Months Ended

Mar. 31, 2019

Debt Disclosure [Abstract]

Schedule of Net Carrying Amount of Notes and Impact 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 in May 2018 was as follows (in thousands):



	March 31, 2019		December 31, 2018
Conversion option	$	—	$	63,756
Payments for capped call transactions	—		(31,412		)
Issuance costs	—		(1,998		)
Total	$	—	$	30,346

The net carrying amount of the liability component of the Notes was as follows (in thousands):



	March 31, 2019			December 31, 2018
Principal	$	258,750		$	258,750
Unamortized debt discount	(53,755		)	(56,564		)
Unamortized issuance costs	(5,153		)	(5,423		)
Net carrying amount	$	199,842		$	196,763

There was no change to net carrying amount of the equity component of the Notes since it continued to meet the conditions for equity classification as presented below (in thousands):



	March 31, 2019			December 31, 2018
Debt discount for conversion option	$	63,756		$	63,756
Issuance costs	(1,998		)	(1,998		)
Net carrying amount	$	61,758		$	61,758

Schedule of Interest Expense Related to the Notes

Interest expense related to the Notes was as follows (in thousands):



	Three Months Ended
	March 31, 2019		March 31, 2018
Contractual interest expense	$	81	$	—
Amortization of debt discount	2,810		—
Amortization of issuance costs	269		—
Total interest expense	$	3,160	$	—

Schedule of Maturities of Debt

Maturity of the Company’s outstanding debt as of March 31, 2019 was as follows (in thousands):



Period	Amount to Mature
2023	$	258,750
Total	$	258,750

Stockholders' Equity (Tables)

3 Months Ended

Mar. 31, 2019

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 were as follows (in thousands):



		March 31, 2019
Stock options outstanding		3,123
Restricted stock units outstanding		2,969
Shares available for future grant under 2014 Plan		10,332
Shares available for future issuance under ESPP		2,283
Total shares of common stock reserved		18,707

Schedule of Stock Option Activity

A summary of the Company’s stock option activity during the three months ended March 31, 2019 is as follows (in thousands, except years and per share data):



	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Life (Years)	Aggregate Intrinsic Value
Outstanding as of December 31, 2018	3,122		$	12.52
Options granted (weighted average grant date fair value of $23.91 per share)	223		50.38
Options exercised	(216	)	4.55
Options forfeited or expired	(6	)	33.77
Outstanding as of March 31, 2019	3,123		$	15.73	6.3	$	115,907

Schedule of RSU Activity

A summary of the Company’s restricted stock unit or RSU activity during the three months ended March 31, 2019 is as follows (in thousands, except per share data):



	Number of Shares		Weighted Average Grant Date Fair Value Per Share
Outstanding as of December 31, 2018	2,325		$	25.36
RSUs granted	904		52.19
RSUs vested and released	(211	)	16.93
RSUs forfeited	(49	)	31.28
Outstanding as of March 31, 2019	2,969		$	34.03

Schedule of Stock-based Compensation Expense

Stock-based compensation expenses were as follows (in thousands):



	Three Months Ended
	March 31, 2019		March 31, 2018
Cost of revenue	$	1,229	$	678
Research and development	1,470		877
Sales and marketing	2,249		1,362
General and administrative	3,738		2,408
Total stock-based compensation	$	8,686	$	5,325

Schedule of Unrecognized Compensation Expense



	Stock Option		RSU		ESPP
Unrecognized stock-based compensation expense	$	15,240	$	90,804	$	339
Weighted-average amortization period	3.1 years		3.3 years		0.1 years

Schedule of Valuation Assumptions, Stock Option

The weighted-average assumptions used to value stock options granted during the periods presented were as follows:



Stock Options	Three Months Ended
	March 31, 2019		March 31, 2018
Expected term (years)	6.0		6.0
Volatility	46	%	45	%
Risk-free interest rate	2.5	%	2.7	%
Dividend yield ⁽¹⁾	—		—


(1)	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.

Net Loss Per Share (Tables)

3 Months Ended

Mar. 31, 2019

Earnings Per Share [Abstract]

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):



	Three Months Ended
	March 31, 2019			March 31, 2018
Net loss	$	(1,924	)	$	(607	)
Weighted-average shares of common stock outstanding	59,367			56,399
Basic and diluted net loss per share	$	(0.03	)	$	(0.01	)

Schedule of Antidilutive Securities Excluded from Computation of 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):



	Three Months Ended
	March 31, 2019	March 31, 2018
Stock options	3,123	3,491
Restricted stock units	2,969	2,427
Convertible senior notes	1,249	—
Common stock warrants	—	13
Total	7,341	5,931

Geographical Information (Tables)

3 Months Ended

Mar. 31, 2019

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):



	Three Months Ended
	March 31, 2019		March 31, 2018
United States	$	68,883	$	55,171
International	5,655		3,734
Total revenue	$	74,538	$	58,905

The following table summarizes total property and equipment, net in the respective locations (in thousands):



	March 31, 2019		December 31, 2018
United States	$	25,663	$	23,931
International	1,833		1,954
Property and equipment, net	$	27,496	$	25,885

ASC 842 Adoption Impact (Tables)

3 Months Ended

Mar. 31, 2019

Leases [Abstract]

Schedule of lease expenses

The components of lease expenses were as follows (in thousands):



	Three Months Ended
	March 31, 2019		March 31, 2018
Operating lease cost	$	1,103	$	—
Finance lease cost:
Amortization of right-of-use assets	$	1,455	$	1,822
Interest on lease liabilities	236		354
Total finance lease cost	$	1,691	$	2,176

Supplemental cash flow information related to leases was as follows (in thousands):



	Three Months Ended
	March 31, 2019			March 31, 2018
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash used in operating leases	$	(1,144	)	$	—
Financing cash used in finance leases	(1,894		)	(2,352		)
Right of use assets obtained in exchange for lease obligations:
Finance leases	—			3,151

Weighted average remaining terms were as follows (in years):



	March 31, 2019	December 31, 2018
Weighted average remaining lease term
Operating leases	1.7	2.0
Finance leases	2.3	2.6

Weighted average discount rates were as follows:



	March 31, 2019		December 31, 2018
Weighted average discount rate
Operating leases	4.8	%	—	%
Finance leases	9.0	%	9.0	%

Schedule of operating lease maturities

Maturities of lease liabilities were as follows:



Year Ending December 31,	Operating Leases			Finance Leases
2019	$	4,570		$	5,335
2020	3,075			4,284
2021	—			704
Total lease payments	7,645			10,323
Less: imputed interest	(311		)	(799		)
Total	$	7,334		$	9,524

Schedule of balance sheet information related to leases

Supplemental balance sheet information related to leases was as follows (in thousands):



	March 31, 2019			December 31, 2018
Operating leases
Operating lease right-of-use assets	$	6,735		$	—

Operating lease liabilities	$	4,322		$	—
Operating lease liabilities — less current portion	3,012			—
Total operating lease liabilities	$	7,334		$	—
Finance leases
Property and equipment, gross	$	47,114		$	47,383
Less: accumulated depreciation and amortization	(35,002		)	(33,547		)
Property and equipment, net	$	12,112		$	13,836

Finance leases	$	6,208		$	6,647
Finance lease liabilities — less current portion	3,316			4,509
Total finance lease liabilities	$	9,524		$	11,156

Schedule of finance lease maturities

Maturities of lease liabilities were as follows:



Year Ending December 31,	Operating Leases			Finance Leases
2019	$	4,570		$	5,335
2020	3,075			4,284
2021	—			704
Total lease payments	7,645			10,323
Less: imputed interest	(311		)	(799		)
Total	$	7,334		$	9,524

Schedule of impacts from new accounting pronouncements

The impact of the adoption of ASC 842 on select condensed consolidated balance sheet line items, was as follows:



	March 31, 2019
(in thousands)	As Reported		Balances without adoption of ASC 842		Effect of Change Higher (Lower)
Assets:
Operating lease right-of-use-assets	$	6,735	$	—	$	6,735
Liabilities:
Operating lease liabilities	4,322		—		4,322
Operating lease liabilities — less current portion	3,012		—		3,012

Revenue - Narrative (Details) $ in Millions	3 Months Ended
Revenue - Narrative (Details) $ in Millions	Mar. 31, 2019 USD ($)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract revenue recognized	$ 11.3
Contract acquisition costs
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Amortization period of capitalized contract cost	5 years

Revenue - Contract Balances (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Accounts receivable, net	$ 25,840	$ 24,797
Deferred contract acquisition costs, current	10,095	9,372
Deferred contract acquisition costs, non-current	23,262	21,514
Total deferred contract acquisition costs	33,357	30,886
Contract assets	427	330
Contract liabilities (deferred revenue)	17,853	17,391
Net contract assets (liabilities)	$ (17,426)	$ (17,061)

Revenue - Remaining Performance Obligations (Details) - Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-04-01 $ in Millions	Mar. 31, 2019 USD ($)
Revenue from Contract with Customer [Abstract]
Remaining performance obligation	$ 105.6
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, expected period of recognition	24 months

Investments and Fair Value Measurements - Schedule of Marketable Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Cost	$ 205,432	$ 210,082
Gross Unrealized Gains	26	1
Gross Unrealized Losses	(8)	(176)
Fair Value	205,450	209,907
Certificates of deposit
Debt Securities, Available-for-sale [Line Items]
Cost	3,083	4,259
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	3,083	4,259
U.S. treasury
Debt Securities, Available-for-sale [Line Items]
Cost	7,290	637
Gross Unrealized Gains	3	0
Gross Unrealized Losses	0	0
Fair Value	7,293	637
U.S. agency securities and government sponsored securities
Debt Securities, Available-for-sale [Line Items]
Cost	129,630	154,314
Gross Unrealized Gains	12	1
Gross Unrealized Losses	(7)	(111)
Fair Value	129,635	154,204
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Cost	11,296	3,475
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	11,296	3,475
Municipal bonds
Debt Securities, Available-for-sale [Line Items]
Cost	5,989	6,090
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	(4)
Fair Value	5,989	6,086
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Cost	48,144	41,307
Gross Unrealized Gains	11	0
Gross Unrealized Losses	(1)	(61)
Fair Value	$ 48,154	$ 41,246

Investments and Fair Value Measurements - Schedule of Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, gross unrealized losses	$ (8)	$ (176)
Less than 12 months, fair value	101,443	201,181
U.S. treasury
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, gross unrealized losses	0	0
Less than 12 months, fair value	140	637
U.S. agency securities and government sponsored securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, gross unrealized losses	(7)	(111)
Less than 12 months, fair value	83,007	153,212
Municipal bonds
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, gross unrealized losses	0	(4)
Less than 12 months, fair value	5,989	6,086
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, gross unrealized losses	(1)	(61)
Less than 12 months, fair value	$ 12,307	$ 41,246

Investments and Fair Value Measurements - Schedule of Assets Carried at Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Assets
Cash equivalents	$ 37,912	$ 12,019
Marketable investments	205,450	209,907
Level 1
Assets
Cash equivalents	35,119	11,471
Marketable investments	7,293	637
Level 2
Assets
Cash equivalents	2,793	548
Marketable investments	198,157	209,270
Level 3
Assets
Cash equivalents	0	0
Marketable investments	0	0
Certificates of deposit
Assets
Marketable investments	3,083	4,259
Certificates of deposit \| Level 1
Assets
Marketable investments	0	0
Certificates of deposit \| Level 2
Assets
Marketable investments		4,259
Certificates of deposit \| Level 3
Assets
Marketable investments	0	0
U.S. treasury
Assets
Marketable investments	7,293	637
U.S. treasury \| Level 1
Assets
Marketable investments		637
U.S. treasury \| Level 2
Assets
Marketable investments	0	0
U.S. treasury \| Level 3
Assets
Marketable investments	0	0
U.S. agency securities and government sponsored securities
Assets
Marketable investments	129,635	154,204
U.S. agency securities and government sponsored securities \| Level 1
Assets
Marketable investments	0	0
U.S. agency securities and government sponsored securities \| Level 2
Assets
Marketable investments		154,204
U.S. agency securities and government sponsored securities \| Level 3
Assets
Marketable investments	0	0
Commercial paper
Assets
Marketable investments	11,296	3,475
Commercial paper \| Level 1
Assets
Marketable investments	0	0
Commercial paper \| Level 2
Assets
Marketable investments		3,475
Commercial paper \| Level 3
Assets
Marketable investments	0	0
Municipal bonds
Assets
Marketable investments	5,989	6,086
Municipal bonds \| Level 1
Assets
Marketable investments	0	0
Municipal bonds \| Level 2
Assets
Marketable investments		6,086
Municipal bonds \| Level 3
Assets
Marketable investments	0	0
Corporate bonds
Assets
Marketable investments	48,154	41,246
Corporate bonds \| Level 1
Assets
Marketable investments	0	0
Corporate bonds \| Level 2
Assets
Marketable investments		41,246
Corporate bonds \| Level 3
Assets
Marketable investments	0	0
Money market funds
Assets
Cash equivalents	26,140	10,833
Money market funds \| Level 1
Assets
Cash equivalents	26,140	10,833
Money market funds \| Level 2
Assets
Cash equivalents	0	0
Money market funds \| Level 3
Assets
Cash equivalents	0	0
U.S. treasury
Assets
Cash equivalents	8,979	638
U.S. treasury \| Level 1
Assets
Cash equivalents	8,979	638
U.S. treasury \| Level 2
Assets
Cash equivalents	0	0
U.S. treasury \| Level 3
Assets
Cash equivalents	0	0
Commercial paper
Assets
Cash equivalents	2,793	498
Commercial paper \| Level 1
Assets
Cash equivalents	0	0
Commercial paper \| Level 2
Assets
Cash equivalents	2,793	498
Commercial paper \| Level 3
Assets
Cash equivalents	$ 0	0
U.S. agency securities and government sponsored securities
Assets
Cash equivalents		50
U.S. agency securities and government sponsored securities \| Level 1
Assets
Cash equivalents		0
U.S. agency securities and government sponsored securities \| Level 2
Assets
Cash equivalents		50
U.S. agency securities and government sponsored securities \| Level 3
Assets
Cash equivalents		$ 0

Investments and Fair Value Measurements - Narrative (Details) - USD ($)	Mar. 31, 2019	Dec. 31, 2018	May 31, 2018
Level 2 \| Convertible debt
Debt Instrument [Line Items]
Fair value of long-term debt	$ 363,700,000	$ 316,100,000
Nonrecurring
Debt Instrument [Line Items]
Assets measured at fair value on nonrecurring basis	$ 0
Liabilities measured at fair value on nonrecurring basis		$ 0
Convertible Senior Notes \| Convertible debt
Debt Instrument [Line Items]
Stated interest rate on debt	0.125%		0.125%

Financial Statement Components - Schedule of Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 93,492	$ 81,912
Cash
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	55,580	69,893
Money market funds
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	26,140	10,833
U.S. treasury
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	8,979	638
U.S. agency securities
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	0	50
Commercial paper
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 2,793	$ 498

Financial Statement Components - Schedule of Accounts Receivable (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accounts Receivable [Line Items]
Allowance for doubtful accounts	$ (11)	$ (12)
Accounts receivable, net	25,840	24,797
Trade accounts receivable
Accounts Receivable [Line Items]
Trade accounts receivable	23,729	23,068
Unbilled trade accounts receivable, net of advance client deposits
Accounts Receivable [Line Items]
Trade accounts receivable	$ 2,122	$ 1,741

Financial Statement Components - Schedule of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financial Statement Components [Abstract]
Prepaid expenses	$ 5,741	$ 5,005
Other current assets	3,551	2,679
Contract assets	427	330
Prepaid expenses and other current assets	$ 9,719	$ 8,014

Financial Statement Components - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property and equipment	$ 71,826		$ 67,362
Accumulated depreciation and amortization	(44,330)		(41,477)
Property and equipment, net	27,496		25,885
Depreciation expense	3,100	$ 2,200
Computer and network equipment
Property, Plant and Equipment [Line Items]
Property and equipment	57,302		54,452
Computer software
Property, Plant and Equipment [Line Items]
Property and equipment	11,241		10,064
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	1,889		1,491
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment	$ 894		$ 855

Financial Statement Components - Schedule of Capital Leased Property and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financial Statement Components [Abstract]
Gross	$ 47,114
Less: accumulated depreciation and amortization	(35,002)
Total	$ 12,112
Gross		$ 47,383
Less: accumulated depreciation and amortization		(33,547)
Total		$ 13,836

Financial Statement Components - Schedule of Accrued and Other Current Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financial Statement Components [Abstract]
Accrued compensation and benefits	$ 13,901	$ 10,277
Accrued expenses	4,064	3,494
Accrued and other current liabilities	$ 17,965	$ 13,771

Intangible Assets - Schedule of Intangible Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Acquired Finite-Lived Intangible Assets
Total	$ 543
Developed technology
Acquired Finite-Lived Intangible Assets
Gross Carrying Amount	2,460	$ 2,460
Accumulated Amortization	(1,917)	(1,829)
Total	$ 543	$ 631

Intangible Assets - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Intangible Assets, Net (Excluding Goodwill) [Abstract]
Amortization expense related to intangible assets	$ 88	$ 116

Intangible Assets - Future Amortization Expense (Details) $ in Thousands	Mar. 31, 2019 USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2019	$ 263
2020	280
Total	$ 543

Debt - Convertible Senior Notes and Capped Call (Details) $ / shares in Units, shares in Millions	1 Months Ended
	May 31, 2018 USD ($) day $ / shares	Mar. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($)
Debt Instrument [Line Items]
Conversion price on convertible debt (in USD per share) \| $ / shares		$ 40.82
Closing market price of common stock (in USD per share) \| $ / shares		$ 52.83
Convertible debt \| Convertible Senior Notes
Debt Instrument [Line Items]
Stated interest rate on debt	0.125%	0.125%
Proceeds from issuance of debt	$ 250,700,000
Conversion ratio on convertible debt	0.0244978
Conversion price on convertible debt (in USD per share) \| $ / shares	$ 40.82
Conversion price per share, requiring conversion of instrument (in USD per share) \| $ / shares		$ 53.07
Sinking fund payment	$ 0
Debt discount for conversion option		$ 63,756,000	$ 63,756,000
Effective interest rate on debt	6.39%
Payment on debt issuance cost	$ 8,100,000
Debt issuance costs	$ 6,100,000	$ 5,153,000	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 \| shares		6.3
Cost of Capped Call Transactions recorded in additional paid in capital		$ 31,400,000	$ 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	$ 258,800,000.0
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 Amount of the Liability Component of the Notes (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	May 31, 2018
Debt Instrument [Line Items]
Principal	$ 258,750
Convertible debt \| Convertible Senior Notes
Debt Instrument [Line Items]
Principal	258,750	$ 258,750
Unamortized debt discount	(53,755)	(56,564)
Unamortized issuance costs	(5,153)	(5,423)	$ (6,100)
Total debt, net carrying value	$ 199,842	$ 196,763

Debt - Schedule of Equity Component of Debt (Details) - Convertible debt - Convertible Senior Notes - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Mar. 31, 2019
Debt Instrument [Line Items]
Debt discount for conversion option	$ 63,756	$ 63,756
Payments for capped call transactions	(31,412)	(31,400)
Issuance costs	(1,998)	(1,998)
Net carrying amount	61,758	$ 61,758
Total	$ 30,346

Debt - Schedule of Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Debt Instrument [Line Items]
Interest Expense	$ 3,396	$ 810
Convertible Senior Notes \| Convertible debt
Debt Instrument [Line Items]
Contractual interest expense	81	0
Amortization of debt discount	2,810	0
Amortization of issuance costs	269	0
Interest Expense	$ 3,160	$ 0

Debt - Schedule of Maturities of Debt (Details) $ in Thousands	Mar. 31, 2019 USD ($)
Debt Disclosure [Abstract]
2023	$ 258,750
Total	$ 258,750

Stockholders' Equity - Capital Structure (Details) - $ / shares	Mar. 31, 2019	Dec. 31, 2018
Equity [Abstract]
Common Stock, shares authorized (in shares)	450,000,000
Common Stock, par value (in USD per share)	$ 0.001
Common Stock, shares issued (in shares)	59,636,995	59,210,496
Common Stock, shares outstanding (in shares)	59,636,995	59,210,496
Preferred Stock, shares authorized (in shares)	5,000,000
Preferred Stock, par value (in USD per share)	$ 0.001
Preferred Stock, shares issued (in shares)	0	0
Preferred Stock, shares outstanding (in shares)	0	0

Stockholders' Equity - Common Stock Reserved for Future Issuance (Details) shares in Thousands	Mar. 31, 2019 shares
Class of Stock
Common stock reserved for future issuance (in shares)	18,707
Stock options
Class of Stock
Common stock reserved for future issuance (in shares)	3,123
Restricted stock units
Class of Stock
Common stock reserved for future issuance (in shares)	2,969
ESPP
Class of Stock
Common stock reserved for future issuance (in shares)	2,283
2014 Plan
Class of Stock
Common stock reserved for future issuance (in shares)	10,332

Stockholders' Equity - Stock Option Activity (Details) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) $ / shares shares
Options Outstanding, Weighted Average Exercise Price [Roll Forward]
Closing market price of common stock (in USD per share)	$ 52.83
Stock options
Options Outstanding [Roll Forward]
Outstanding, beginning balance (in shares) \| shares	3,122
Options granted (weighted average grant date fair value of $14.14 per share) (in shares) \| shares	223
Options exercised (in shares) \| shares	(216)
Options forfeited or expired (in shares) \| shares	(6)
Outstanding, ending balance (in shares) \| shares	3,123
Options Outstanding, Weighted Average Exercise Price [Roll Forward]
Outstanding, beginning balance, weighted average exercise price (in USD per share)	$ 12.52
Options granted, weighted average exercise price (in USD per share)	50.38
Options exercised, weighted average exercise price (in USD per share)	4.55
Options forfeited or expired, weighted average exercise price (in USD per share)	33.77
Outstanding, ending balance, weighted average exercise price (in USD per share)	$ 15.73
Outstanding, ending balance, weighted average remaining contractual life	6 years 3 months 18 days
Outstanding, ending balance, aggregate intrinsic value \| $	$ 115,907
Weighted average grant date fair value, options granted (in USD per share)	$ 23.91

Stockholders' Equity - RSU Activity (Details) - Restricted stock units shares in Thousands	3 Months Ended
	Mar. 31, 2019 $ / shares shares
Number of Shares
Outstanding, beginning balance (in shares) \| shares	2,325
RSUs granted (in shares) \| shares	904
RSUs vested and released (in shares) \| shares	(211)
RSUs forfeited (in shares) \| shares	(49)
Outstanding, ending balance (in shares) \| shares	2,969
Weighted Average Grant Date Fair Value Per Share
Outstanding, beginning balance, weighted-average grant date fair value per share (in USD per share) \| $ / shares	$ 25.36
RSUs granted, weighted average grant date fair value (in USD per share) \| $ / shares	52.19
RSUs vested and released, weighted average grant date fair value (in USD per share) \| $ / shares	16.93
RSUs forfeited, weighted average grant date fair value (in USD per share) \| $ / shares	31.28
Outstanding, ending balance, weighted-average grant date fair value per share (in USD per share) \| $ / shares	$ 34.03

Stockholders' Equity - Stock-based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Stock-based Compensation Expense
Stock-based compensation expense	$ 8,686	$ 5,325
Cost of revenue
Stock-based Compensation Expense
Stock-based compensation expense	1,229	678
Research and development
Stock-based Compensation Expense
Stock-based compensation expense	1,470	877
Sales and marketing
Stock-based Compensation Expense
Stock-based compensation expense	2,249	1,362
General and administrative
Stock-based Compensation Expense
Stock-based compensation expense	3,738	$ 2,408
Stock options
Stock-based Compensation Expense
Unrecognized stock-based compensation expense	$ 15,240
Weighted-average amortization period	3 years 1 month 6 days
Restricted stock units
Stock-based Compensation Expense
Unrecognized stock-based compensation expense	$ 90,804
Weighted-average amortization period	3 years 3 months 22 days
ESPP
Stock-based Compensation Expense
Unrecognized stock-based compensation expense	$ 339
Weighted-average amortization period	1 month 16 days

Stockholders' Equity - Valuation Assumptions (Details) - Stock options	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Class of Stock
Expected term (years)	6 years	6 years
Volatility	46.00%	45.00%
Risk-free interest rate	2.50%	2.70%
Dividend yield	0.00%	0.00%

Net Loss Per Share - Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Net loss	$ (1,924)	$ (607)
Weighted-average shares of common stock outstanding (in shares)	59,367	56,399
Basic net income (loss) per share (in USD per share)	$ (0.03)	$ (0.01)

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(19))
-URI http://asc.fasb.org/extlink&oid=114873790&loc=SL114874131-224263

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=109260490&loc=d3e1337-109256

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 55
-Paragraph 52
-URI http://asc.fasb.org/extlink&oid=109256448&loc=d3e4984-109258

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(21))
-URI http://asc.fasb.org/extlink&oid=115205541&loc=SL114868664-224227

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22694-107794

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109260490&loc=d3e1252-109256

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(23))
-URI http://asc.fasb.org/extlink&oid=114873765&loc=SL114874048-224260

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 60B
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=109260490&loc=SL5780133-109256

+ Details

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Net Loss Per Share - Antidilutive Securities Excluded from Computation of Diluted Net Loss Per Share (Details) - $ / shares shares in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive securities excluded from calculation of diluted net loss per share	7,341	5,931
Conversion price on convertible debt (in USD per share)	$ 40.82
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive securities excluded from calculation of diluted net loss per share	3,123	3,491
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive securities excluded from calculation of diluted net loss per share	2,969	2,427
Convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive securities excluded from calculation of diluted net loss per share	1,249	0
Common stock warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive securities excluded from calculation of diluted net loss per share	0	13

Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended
Income Taxes (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Provision for income taxes	$ (49)	$ 45

Commitments and Contingencies (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Other Commitments [Line Items]
Debt balance	$ 258,750
Indemnification Agreement
Other Commitments [Line Items]
Advancement of legal fees	1,000
Hosting and telecommunications agreement
Other Commitments [Line Items]
Total commitments under agreements	$ 7,900
Minimum \| Hosting and telecommunications agreement
Other Commitments [Line Items]
Period for various agreements	12 months
Maximum \| Hosting and telecommunications agreement
Other Commitments [Line Items]
Period for various agreements	36 months
Convertible Senior Notes \| Convertible debt
Other Commitments [Line Items]
Debt balance	$ 258,750	$ 258,750

Geographical Information - Schedule of Revenue and Property and Equipment by Geographic Region (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Revenues from External Customers and Long-Lived Assets
Revenue	$ 74,538	$ 58,905
Property and equipment, net	27,496		$ 25,885
United States
Revenues from External Customers and Long-Lived Assets
Revenue	68,883	55,171
Property and equipment, net	25,663		23,931
International
Revenues from External Customers and Long-Lived Assets
Revenue	5,655	$ 3,734
Property and equipment, net	$ 1,833		$ 1,954

ASC 842 Adoption Impact - Narrative (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets	$ 6,735
Operating lease liability	7,334
Amount of lease obligation, not yet commenced	$ 4,100
Minimum
Lessee, Lease, Description [Line Items]
Operating lease, term of contract	1 year
Operating lease, extension term	3 years
Operating lease not yet commenced, term of lease	2 years
Maximum
Lessee, Lease, Description [Line Items]
Operating lease, term of contract	3 years
Operating lease, extension term	5 years
Operating lease not yet commenced, term of lease	6 years
ASC 842
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets	$ 6,735	$ 8,400
Operating lease liability		8,400
Reversal of deferred rent		$ 600

ASC 842 Adoption Impact - Lease Cost and Supplemental Cash Flow (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Leases [Abstract]
Operating lease cost	$ 1,103	$ 0
Finance lease cost:
Amortization of right-of-use assets	1,455	1,822
Interest on lease liabilities	236	354
Total finance lease cost	1,691	2,176
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash used in operating leases	(1,144)	0
Financing cash used in finance leases	(1,894)	(2,352)
Right of use assets obtain in exchange for finance leases	$ 0	$ 3,151

ASC 842 Adoption Impact - Balance Sheet Disclosures (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Operating lease right-of-use assets	$ 6,735
Operating lease liabilities	4,322
Operating lease liabilities — less current portion	3,012
Total operating lease liabilities	7,334
Property and equipment, gross	47,114
Less: accumulated depreciation and amortization	(35,002)
Property and equipment, net	12,112
Property and equipment, gross		$ 47,383
Less: accumulated depreciation and amortization		(33,547)
Property and equipment, net		13,836
Finance lease liabilities	6,208
Finance lease liabilities		6,647
Finance lease liabilities — less current portion	3,316
Finance lease liabilities — less current portion		4,509
Total finance lease liabilities	$ 9,524
Total finance lease liabilities		$ 11,156

ASC 842 Adoption Impact - Weighted Average Remaining Terms and Discount Rates (Details)	Mar. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Weighted average remaining lease term, Operating leases	1 year 8 months 12 days	2 years
Weighted average remaining lease term, Finance leases	2 years 3 months 18 days	2 years 7 months 6 days
Weighted average discount rate, Operating leases	4.80%	0.00%
Weighted average discount rate, Finance leases	9.00%	9.00%

ASC 842 Adoption Impact - Lease Maturities (Details) $ in Thousands	Mar. 31, 2019 USD ($)
Operating Leases
2019	$ 4,570
2020	3,075
2021	0
Total lease payments	7,645
Less: imputed interest	(311)
Total	7,334
Finance Leases
2019	5,335
2020	4,284
2023	704
Total lease payments	10,323
Less: imputed interest	(799)
Total	$ 9,524

ASC 842 Adoption Impact - Balance Sheet Impacts (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets	$ 6,735
Operating lease liabilities	4,322
Operating lease liabilities — less current portion	3,012
ASC 842
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets	6,735	$ 8,400
Operating lease liabilities	4,322
Operating lease liabilities — less current portion	$ 3,012

Label	Element	Value
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ 24,145,000
Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ 24,145,000