Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2018	Feb. 22, 2019
Document And Entity Information [Abstract]
Entity Registrant Name	TENABLE HOLDINGS, INC.
Entity Central Index Key	0001660280
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding (in shares)		94,955,182
Entity Emerging Growth Company	true
Entity Small Business	false
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float	$ 687.5

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 165,116	$ 27,210
Short-term investments	118,119	0
Accounts receivable (net of allowance for doubtful accounts of $188 and $160 at December 31, 2018 and 2017, respectively)	68,261	50,881
Deferred commissions	23,272	17,170
Prepaid expenses and other current assets	22,020	15,994
Total current assets	396,788	111,255
Property and equipment, net	11,348	10,754
Construction in progress	0	2,252
Deferred commissions (net of current portion)	36,162	33,006
Operating lease right-of-use assets	8,504	0
Other assets	7,810	7,070
Total assets	460,612	164,337
Current liabilities:
Accounts payable	171	338
Accrued expenses	5,554	4,878
Accrued compensation	29,594	18,482
Deferred revenue	213,644	154,898
Operating lease liabilities	4,262	0
Other current liabilities	1,079	1,750
Total current liabilities	254,304	180,346
Deferred revenue (net of current portion)	76,259	70,920
Operating lease liabilities (net of current portion)	6,055	0
Financing obligation	0	1,802
Other liabilities	2,231	5,199
Total liabilities	338,849	258,267
Stockholders’ equity (deficit):
Common stock (par value: $0.01; 500,000 and 93,855 shares authorized, 93,126 and 24,472 shares issued and outstanding at December 31, 2018 and 2017, respectively)	931	246
Additional paid-in capital	586,940	20,676
Accumulated deficit	(466,108)	(392,587)
Total stockholders’ equity (deficit)	121,763	(371,665)
Total liabilities, redeemable convertible preferred stock and stockholders’ equity (deficit)	460,612	164,337
Series A Redeemable Convertible Preferred Stock
Current liabilities:
Redeemable convertible preferred stock	0	49,935
Series B Redeemable Convertible Preferred Stock
Current liabilities:
Redeemable convertible preferred stock	$ 0	$ 227,800

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accounts receivable, allowance for doubtful accounts	$ 188	$ 160
Common stock, par value (in usd per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	500,000,000	93,855,000
Common stock, shares issued (in shares)	93,126,000	24,472,000
Common stock, shares outstanding (in shares)	93,126,000	24,472,000
Series A Redeemable Convertible Preferred Stock
Redeemable convertible preferred stock, par value (in usd per share)		$ 0.01
Redeemable convertible preferred stock, shares authorized (in shares)		15,848,000
Redeemable convertible preferred stock, shares issued (in shares)		15,848,000
Redeemable convertible preferred stock, shares outstanding (in shares)	0	15,848,000
Redeemable convertible preferred stock, liquidation value		$ 50,000
Series B Redeemable Convertible Preferred Stock
Redeemable convertible preferred stock, par value (in usd per share)		$ 0.01
Redeemable convertible preferred stock, shares authorized (in shares)		42,000,000
Redeemable convertible preferred stock, shares issued (in shares)		39,538,000
Redeemable convertible preferred stock, shares outstanding (in shares)	0	39,538,000
Redeemable convertible preferred stock, liquidation value		$ 230,008

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Revenue	$ 267,360	$ 187,727	$ 124,371
Cost of revenue	43,167	25,588	14,219
Gross profit	224,193	162,139	110,152
Operating expenses:
Sales and marketing	173,344	116,299	85,736
Research and development	76,698	57,673	40,085
General and administrative	46,732	28,927	20,164
Total operating expenses	296,774	202,899	145,985
Loss from operations	(72,581)	(40,760)	(35,833)
Other income (expense), net	1,424	(91)	(532)
Total loss before income taxes	(71,157)	(40,851)	(36,365)
Provision for income taxes	2,364	171	843
Net loss	(73,521)	(41,022)	(37,208)
Comprehensive Loss	(73,521)	(41,022)	(37,208)
Accretion of Series A and B redeemable convertible preferred stock	(434)	(763)	(763)
Net loss attributable to common stockholders	$ (73,955)	$ (41,785)	$ (37,971)
Net loss per share attributable to common stockholders, basic and diluted (in usd per share)	$ (1.38)	$ (1.88)	$ (1.81)
Weighted-average shares used to compute net loss per share attributable to common stockholders, basic and diluted (in shares)	53,669	22,211	20,974

CONSOLIDATED STATEMENTS OF REDEEMABLE CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Series A Redeemable Convertible Preferred Stock	Series B Redeemable Convertible Preferred Stock
Balance (in shares) at Dec. 31, 2015					15,848	39,538
Balance at Dec. 31, 2015					$ 49,891	$ 226,318
Redeemable Convertible Preferred Stock [Roll Forward]
Accretion of Series A and B redeemable convertible preferred stock					$ 22	$ 741
Balance (in shares) at Dec. 31, 2016					15,848	39,538
Balance at Dec. 31, 2016					$ 49,913	$ 227,059
Balance (in shares) at Dec. 31, 2015		20,670
Balance at Dec. 31, 2015	$ (266,862)	$ 207	$ 8,870	$ (275,939)
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Accretion of Series A and B redeemable convertible preferred stock	$ (763)		(763)
Exercise of stock options (in shares)	495	495
Exercise of stock options	$ 495	$ 5	490
Stock-based compensation	2,447		2,447
Income tax benefit from stock options	(27)		(27)
Net loss	(37,208)			(37,208)
Balance (in shares) at Dec. 31, 2016		21,165
Balance at Dec. 31, 2016	(301,918)	$ 212	11,017	(313,147)
Redeemable Convertible Preferred Stock [Roll Forward]
Accretion of Series A and B redeemable convertible preferred stock					$ 22	$ 741
Balance (in shares) at Dec. 31, 2017					15,848	39,538
Balance at Dec. 31, 2017					$ 49,935	$ 227,800
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Accretion of Series A and B redeemable convertible preferred stock	(763)		(763)
Issuance of restricted stock award (in shares)		1,583
Issuance of restricted stock award	$ 0	$ 16	(16)
Exercise of stock options (in shares)	1,870	1,870
Exercise of stock options	$ 3,020	$ 19	3,001
Repurchase of common stock (in shares)		(146)
Repurchase of common stock	(385)	$ (1)	(384)
Stock-based compensation	7,760		7,760
Net loss	$ (41,022)			(41,022)
Balance (in shares) at Dec. 31, 2017	24,472	24,472
Balance at Dec. 31, 2017	$ (371,665)	$ 246	20,676	(392,587)
Redeemable Convertible Preferred Stock [Roll Forward]
Accretion of Series A and B redeemable convertible preferred stock					$ 13	$ 421
Conversion of redeemable convertible preferred stock to common stock upon initial public offering (in shares)					(15,848)	(39,538)
Conversion of redeemable convertible preferred stock to common stock upon initial public offering					$ (49,948)	$ (228,221)
Balance (in shares) at Dec. 31, 2018					0	0
Balance at Dec. 31, 2018					$ 0	$ 0
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Accretion of Series A and B redeemable convertible preferred stock	$ (434)		(434)
Exercise of stock options (in shares)	740	740
Exercise of stock options	$ 1,668	$ 7	1,661
Repurchase of common stock (in shares)		(7)
Repurchase of common stock	(75)	$ (1)	(74)
Stock-based compensation	23,022		23,022
Issuance of common stock in connection with initial public offering, net of underwriting discounts and commissions and other offering expenses (in shares)		12,535
Issuance of common stock in connection with initial public offering, net of underwriting discounts and commissions and other offering expenses	264,599	$ 125	264,474
Conversion of redeemable convertible preferred stock to common stock upon initial public offering (in shares)		55,386
Conversion of redeemable convertible preferred stock to common stock upon initial public offering	278,169	$ 554	277,615
Net loss	$ (73,521)			(73,521)
Balance (in shares) at Dec. 31, 2018	93,126	93,126
Balance at Dec. 31, 2018	$ 121,763	$ 931	$ 586,940	$ (466,108)

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net loss	$ (73,521)	$ (41,022)	$ (37,208)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	6,192	4,692	3,060
Stock-based compensation	22,875	7,760	2,532
Other	533	(748)	953
Changes in operating assets and liabilities:
Accounts receivable	(17,408)	(14,769)	(13,560)
Prepaid expenses and other current assets	(6,105)	(8,345)	(605)
Deferred commissions	(9,258)	(20,058)	(9,777)
Other assets	(1,876)	(3,267)	(1,856)
Accounts payable and accrued expenses	294	1,922	825
Accrued compensation	11,112	4,298	10,957
Deferred revenue	64,085	63,404	44,228
Other current liabilities	408	421	(1,749)
Other liabilities	110	(554)	(585)
Net cash used in operating activities	(2,559)	(6,266)	(2,785)
Cash flows from investing activities:
Purchases of property and equipment	(5,733)	(2,755)	(5,776)
Purchases of short-term investments	(117,488)	0	0
Business combination	0	0	(2,075)
Net cash used in investing activities	(123,221)	(2,755)	(7,851)
Cash flows from financing activities:
Proceeds from initial public offering, net of underwriting discounts and commissions	268,531	0	0
Payments of costs related to initial public offering	(3,932)	0	0
Principal payments under finance lease obligations	(1,443)	(306)	(47)
Proceeds from grant agreement	0	0	1,000
Credit facility issuance costs	0	(238)	0
Proceeds from the exercise of stock options	1,668	3,020	495
Repurchases of common stock	(75)	(385)	(85)
Net cash provided by financing activities	264,749	2,091	1,363
Effect of exchange rate changes on cash and cash equivalents and restricted cash	(1,063)	(68)	0
Net increase (decrease) in cash and cash equivalents and restricted cash	137,906	(6,998)	(9,273)
Cash and cash equivalents and restricted cash at beginning of year	27,472	34,470	43,743
Cash and cash equivalents and restricted cash at end of year	165,378	27,472	34,470
Supplemental disclosure of cash flow information:
Cash paid for interest	111	79	6
Cash paid for income taxes	1,207	642	307
Supplemental disclosure of non-cash investing and financing activities:
Assets acquired under finance leases	15	1,311	527
Asset retirement obligations	$ 58	$ 764	$ 0

Business and Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2018

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Business and Summary of Significant Accounting Policies

Business Description

Tenable Holdings, Inc. (the “Company,” “we,” "us," or “our”) is a provider of Cyber Exposure solutions, which is a discipline for managing and measuring cybersecurity risk in the digital era. Our enterprise software platform enables broad visibility into an organization’s cyber exposure across the modern attack surface and deep insights that help organizations translate technical data into business insights to understand and reduce their cybersecurity risk.

Basis of Presentation

The accompanying consolidated financial statements include the accounts of Tenable Holdings, Inc. and our wholly owned subsidiaries and have been prepared in conformity with United States generally accepted accounting principles (“GAAP”). All intercompany accounts and transactions have been eliminated in consolidation.

Initial Public Offering

On July 30, 2018, we completed our initial public offering ("IPO"), in which we issued and sold 12,535,000 shares of common stock at a price to the public of $23.00 per share, including 1,635,000 shares of common stock purchased by our underwriters from the full exercise of their over-allotment option. All of the shares sold in the IPO were sold by the Company. We received net proceeds of $264.6 million after deducting underwriting discounts and commissions and other offering expenses.

Upon the completion of our IPO, all 15,847,500 shares of our Series A Redeemable Convertible Preferred Stock ("Series A") and 39,538,354 shares of our Series B Redeemable Convertible Preferred Stock ("Series B") automatically converted into an aggregate of 55,385,854 shares of our common stock. Our newly adopted Amended and Restated Certificate of Incorporation authorizes a total of 500,000,000 shares of common stock and 10,000,000 shares of preferred stock.

Use of Estimates

The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. These estimates include, but are not limited to, the determination of the estimated economic life of perpetual licenses for revenue recognition, the estimated period of benefit for deferred commissions, useful lives of long-lived assets, the valuation of stock-based compensation, including the estimated underlying fair value of our common stock prior to our IPO, the incremental borrowing rate for operating leases, and the valuation of deferred tax assets. We base these estimates on historical experience and on various other assumptions that we believe to be reasonable. Actual results could differ significantly from these estimates.

Foreign Currency

The functional currency for all of our foreign subsidiaries is the U.S. dollar. Assets and liabilities denominated in other currencies are remeasured into U.S. dollars at current exchange rates for monetary assets and liabilities and at historical exchange rates for non-monetary assets and liabilities. We bill our customers in U.S. dollars. Expenses incurred in non U.S. dollar currencies are remeasured into U.S. dollars when incurred. Remeasurement losses in currencies other than the functional currency were $1.0 million, $0.1 million and $0.5 million in 2018, 2017 and 2016, respectively, and are included as a component of other income (expense), net in the consolidated statements of operations and comprehensive loss.

Revenue Recognition

We early adopted Accounting Standards Codification (“ASC”) Topic 606, Revenue From Contracts With Customers (“ASC 606”), on January 1, 2017 using the modified retrospective method and applying the guidance to all contracts as of January 1, 2017. The most significant impact of adopting ASC 606 was the deferral of perpetual license revenue over an estimated economic life, including estimated maintenance renewal periods, whereas under the previous guidance we recognized perpetual license revenue upon delivery of the perpetual license. Additionally, the incremental costs of obtaining a contract with a customer are deferred, and will be amortized over a longer estimated period of benefit, whereas under previous guidance we amortized such costs over the contract term.

The adoption of ASC 606 resulted in a cumulative adjustment to increase our accumulated deficit by $38.4 million at January 1, 2017, which included a $55.0 million increase to deferred revenue, primarily related to the deferral of perpetual license revenue, offset by a $16.6 million increase to deferred commissions related to the longer estimated period of benefit compared to our historical practice. Of the $55.0 million increase to deferred revenue at January 1, 2017, $19.0 million was recognized as revenue in 2017, and $16.7 million was recognized as revenue in 2018, and $11.8 million, $5.6 million and $1.9 million will be recognized as revenue in 2019, 2020 and 2021, respectively. The impact to revenue in 2017 was a net increase of $3.5 million after giving effect to the recognition of perpetual license revenue from prior year sales and the deferral of perpetual license revenue from 2017 sales.

The core principle of ASC 606 is that revenue should be recognized to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. To achieve the core principle of ASC 606, we apply the following steps:


•	Identify the contract with a customer


•	Identify the performance obligations in the contract


•	Determine the transaction price


•	Allocate the transaction price to the performance obligations in the contract


•	Recognize revenue when or as performance obligations are satisfied

We generate revenue from subscription arrangements for software and cloud-based solutions, perpetual licenses, maintenance associated with perpetual licenses, and professional services and other revenue. We begin to recognize revenue when control of our software or services is transferred to the customer, which for sales made through distributors is concurrent with the transfer to the end user.

The following table presents a summary of revenue:



	Year Ended December 31,
(in thousands)	2018		2017		2016
Subscription revenue	$	205,827	$	132,873	$	80,399
Perpetual license and maintenance revenue	54,622		50,337		40,328
Professional services and other revenue	6,911		4,517		3,644
Revenue	$	267,360	$	187,727	$	124,371

Subscription Revenue

Subscription arrangements generally have annual or multi-year contractual terms and allow customers to use our software or cloud solutions, including ongoing software updates and the ability to identify the latest cybersecurity vulnerabilities. Revenue is recognized ratably over the subscription term given the critical utility provided by the ongoing updates that are released throughout the contract period.

Perpetual License and Maintenance Revenue

Our perpetual licenses are generally sold with one or more years of maintenance, which include ongoing software updates and the ongoing ability to identify the latest cybersecurity vulnerabilities. Given the critical utility provided by the

ongoing software updates and updated ability to identify network vulnerabilities included in maintenance, we combine the perpetual license and the maintenance into a single performance obligation. Perpetual license arrangements generally contain a material right related to the customer’s ability to renew maintenance at a price that is less than the initial license fee. We apply a practical alternative to allocating a portion of the transaction price to the material right performance obligation and estimate a hypothetical transaction price which includes fees for expected maintenance renewals based on the estimated economic life of the perpetual license contracts. We allocate the transaction price between the cybersecurity subscription provided in the initial contract and the material right related to expected contract renewals based on the hypothetical transaction price. We recognize the amount allocated to the combined license and maintenance performance obligation over the initial contractual period, which is generally one year. We recognize the amount allocated to the material right over the expected maintenance renewal period, which begins at the end of the initial contractual term and is generally four years. We have estimated the five-year economic life of perpetual license contracts based on historical contract attrition, expected renewal periods, the lifecycle of the our technology and other factors. While we believe that the estimates we have made are reasonable and appropriate, different assumptions and estimates could materially impact our reported financial results.

Professional Services and Other Revenue

Professional services and other revenue is primarily comprised of advisory services and training related to the deployment and optimization of our products. These services do not result in significant customization of our products. Professional services and other revenue is recognized as the services are performed.

Contracts with Multiple Performance Obligations

In cases where our contracts with customers contain multiple performance obligations, the contract transaction price is allocated on a relative standalone selling price basis. We typically determine standalone selling price based on observable selling prices of our products and services.

Variable Consideration

We record revenue from sales at the net sales price, which is the transaction price, including estimates of variable consideration when applicable. Certain of our customers may be entitled to receive credits and in certain circumstances, refunds, if service level commitments are not met. We have not historically experienced significant incidents affecting the ability to meet these service level commitments and any estimated refunds related to these agreements have not been material.

Sales through our channel network of distributors and resellers are generally discounted as compared to the price that we would sell to an end user. Revenue for sales through our channel network is recorded net of any distributor or reseller margin.

Concentrations

We sell our products and services through a channel network of distributors and resellers, along with our own sales teams. We derived 88%, 83% and 80% of revenue through our channel network in 2018, 2017 and 2016, respectively. One of our distributors accounted for 46%, 45% and 42% of revenue in 2018, 2017 and 2016, respectively. That same distributor accounted for 46% and 51% of accounts receivable at December 31, 2018 and 2017, respectively.

Contract Balances

We generally bill our customers in advance and accounts receivable are recorded when we have the right to invoice the customer. Contract liabilities consist of deferred revenue and include customer billings and payments received in advance of performance under the contract. In 2018 and 2017, we recognized revenue of $154.9 million and $106.8 million, respectively, that was included in the deferred revenue balance at the beginning of each of the respective periods.

Remaining Performance Obligations

At December 31, 2018, the future estimated revenue related to unsatisfied performance obligations was $293.2 million, with 73% expected to be recognized as revenue over the succeeding twelve months, and the remainder expected to be recognized over the four years thereafter.

Legacy Revenue Accounting Policies

For periods prior to January 1, 2017, we recognized revenue when all the following criteria were met: (1) persuasive evidence of an arrangement exists, (2) delivery has occurred, (3) the fee is fixed or determinable and (4) collectability is reasonably assured.

We recognized subscription revenue ratably over the term of the subscription period in accordance with ASC 605, Revenue Recognition. When subscription arrangements involved multiple elements that qualified as separate units of accounting, we allocated arrangement consideration at the inception of the arrangement to all deliverables based on the relative selling price method in accordance with the selling price hierarchy, which included (i) vendor-specific objective evidence (VSOE) if available, (ii) third-party evidence (TPE) if VSOE was not available, and (iii) best estimate of selling price (BESP) if neither VSOE nor TPE were available. When VSOE could not be established for deliverables within subscription arrangements, we utilized BESP in our allocation of arrangement consideration, as we generally could not establish TPE. BESP was determined by considering multiple factors including, but not limited to, prices charged for similar offerings, market conditions, competitive landscape, and pricing practices.

We recognized perpetual license revenue upon delivery of the license in accordance with ASC 985-605, Software—Revenue Recognition. We established VSOE of fair value for substantially all products and services with the exception of new subscription agreements and perpetual licenses. VSOE was established for maintenance and support based upon actual renewals and historical pricing when sold separately. Revenue from maintenance agreements was deferred and recognized ratably over the term of the maintenance period. The VSOE of fair value for professional services was based on the price for these same services when they were sold separately.

Other services revenue was recognized as the services were performed.

Cash and Cash Equivalents

We consider all highly liquid financial instruments with an original maturity of three months or less when purchased to be cash equivalents.

As of December 31, 2018 and 2017, cash and cash equivalents excluded $0.3 million of restricted cash, which is related to an account established as collateral for a lease arrangement and was included in other assets on the consolidated balance sheets.

Fair Value of Financial Instruments

Fair value is defined as 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. We apply fair value accounting for all financial assets and liabilities that are recognized or disclosed at fair value in the financial statements on a recurring basis. We measure cash and cash equivalents and short-term investments at fair value using a fair value hierarchy of inputs. We approximate fair value by using the carrying amounts for accounts receivable, accounts payable and accrued expenses due to their short-term nature.

Investments

We currently invest in commercial paper, corporate bonds, and U.S. treasury and agency obligations. Our investments are classified as available-for-sale and recorded at fair value, with unrealized gains and losses reported in accumulated other comprehensive loss within stockholders’ equity (deficit). We review our investment portfolio to determine whether investments have indicators of possible impairment.

Accounts Receivable

Accounts receivable are recorded at the invoiced amount, less an allowance for doubtful accounts, and do not bear interest. We maintain an allowance for doubtful accounts at an amount estimated to be sufficient to cover the risk of collecting less than full payment of the receivables. At each balance sheet date, we evaluate our receivables and assess the allowance for doubtful accounts based on specific customer collection issues and historical write-off trends.

Deferred Commissions

Sales commissions, including related incremental fringe benefit costs, are considered to be incremental costs of obtaining a contract. Sales commissions on initial sales are not commensurate with sales commissions on contract renewals and therefore are recognized over an estimated period of benefit, which ranges between three and four years for subscription arrangements and five years for perpetual license arrangements. We estimated the period of benefit based on the expected contract term including renewal periods, the lifecycle of our technology, and other factors. Sales commissions on contract renewals are capitalized and amortized ratably over the contract term, with the exception of contracts with renewal periods that are one year or less, in which case the incremental costs are expensed as incurred.

The following summarizes the activity of deferred incremental costs of obtaining a contract:



	Year Ended December 31,
(in thousands)	2018			2017
Beginning balance	$	50,176		$	30,118
Capitalization of contract acquisition costs	29,075			34,632
Amortization of deferred contract acquisition costs	(19,817		)	(14,574		)
Ending balance	$	59,434		$	50,176

Amortization of deferred contract acquisition costs is included in sales and marketing expense in the consolidated statements of operations and comprehensive loss.

Prior to January 1, 2017, we capitalized sales commissions and recognized the expense over the corresponding period in which the related revenue was recognized. Commissions on perpetual license sales were recognized upon the delivery of the license.

Property and Equipment, net

Property and equipment, net is stated at historical cost less accumulated depreciation. Depreciation is computed using the straight-line method over the estimated useful lives of the assets: three years for computer software and equipment and five years for furniture and fixtures. Leasehold improvements are amortized using the straight-line method over the shorter of the estimated useful lives of the assets or the terms of the respective leases. Property and equipment, net includes right-of-use assets acquired under finance leases. Amortization of assets acquired under finance leases is included in depreciation expense. Repairs and maintenance costs are expensed as incurred.

Leases

In October 2017, we entered into a lease of approximately six of the twelve floors of a building currently being constructed by the landlord in Columbia Maryland for our new corporate headquarters. Under accounting guidance in effect in 2017 for build-to-suit lease arrangements, we concluded that we were the deemed owner of the building during the construction period. Accordingly, we recorded a construction-in-progress asset of $2.3 million for which there was a corresponding construction financing obligation of $1.8 million, net of a $0.5 million deposit, recorded in the consolidated balance sheet at December 31, 2017.

In December 2018 we early adopted ASC Topic 842, Leases ("ASC 842"), as of January 1, 2018 using the modified retrospective method applying the transition provisions at the beginning of the period of adoption, rather than at the beginning of the earliest comparative period presented in these financial statements. We elected the package of practical

expedients as permitted under the transition guidance, which allowed us to not reassess whether arrangements contain leases, not reassess lease classification, and not reassess initial direct costs.

The most significant impact of adopting ASC 842 was the recognition of right-of-use ("ROU") assets and lease liabilities for operating leases of $10.1 million and $12.3 million, respectively on January 1, 2018, which included reclassifying prepaid rent and deferred rent as a component of the ROU asset. Additionally, we concluded that we do not control the building under construction for our new corporate headquarters, and upon adoption, derecognized $2.3 million of construction-in-progress and a $1.8 million construction financing obligation on January 1, 2018 and recognized a $0.5 million deposit. Our accounting for finance leases (formerly referred to as capital leases prior to the adoption of ASC 842) remained substantially unchanged.

The impact of the adoption of ASC 842 on previously reported interim financial statements included the recognition of ROU assets and lease liabilities, as well as the derecognition of the construction-in-progress and construction financing obligation and the recognition of the deposit referred to above. There was no material impact to previously reported results of operations for any interim period.

We determine if an arrangement contains a lease and the classification of that lease, if applicable, at inception. We have elected to not recognize a lease liability or ROU asset for short-term leases (leases with a term of twelve months or less). For contracts with lease and non-lease components, we have elected to not allocate the contract consideration, and account for the lease and non-lease components as a single lease component. Additionally, we enter into arrangements to use shared office spaces and other facilities, and have determined that these arrangements do not contain leases as we do not have the right to use an identified asset. Operating leases are included in operating lease ROU assets, operating lease liabilities and operating lease liabilities (net of current portion) in our consolidated balance sheets. Finance leases are included in property and equipment, other current liabilities and other liabilities in our consolidated balance sheets.

ROU assets represent our right to use an underlying asset for the lease term and lease liabilities represent our obligation to make lease payments under the lease. Operating lease ROU assets and liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term. The implicit rate within our operating leases are generally not determinable and we use our incremental borrowing rate at the lease commencement date to determine the present value of lease payments. The determination of our incremental borrowing rate requires judgment. We determine our incremental borrowing rate for each lease using our current borrowing rate, adjusted for various factors including level of collateralization, term and currency to align with the terms of the lease. The operating lease ROU asset also includes any lease prepayments, offset by lease incentives. Certain of our leases include options to extend or terminate the lease. An option to extend the lease is considered in connection with determining the ROU asset and lease liability when it is reasonably certain we will exercise that option. An option to terminate is considered unless it is reasonably certain we will not exercise the option.

Lease expense for lease payments is recognized on a straight-line basis over the term of the lease.

Impairment of Long-Lived Assets

We evaluate our long-lived assets for impairment whenever events or changes in circumstance indicate that the carrying amount may not be fully recoverable. Recoverability of the long-lived assets is measured by a comparison of the carrying amount of the assets to future undiscounted net cash flows expected to be generated by the assets. If such assets are considered to be impaired, the impairment to be recognized is measured as the excess of the carrying amount over the fair value. There was no impairment of long-lived assets in 2018, 2017 and 2016.

Business Combinations

We account for business combinations by recognizing the fair value of acquired assets and liabilities. The excess purchase consideration over the fair value of acquired assets and liabilities is recorded as goodwill. Acquisition-related transaction costs are expensed as incurred.

When determining the fair value of assets acquired and liabilities assumed, we make estimates and assumptions, especially with respect to intangible assets. Estimates in valuing certain identifiable assets include, but are not limited to,

expected long-term market growth, future expected operating expenses, costs of capital, and appropriate discount rates. Our estimate of fair value is based upon assumptions we believe to be reasonable, but which are inherently uncertain and, as a result, actual results may differ from estimates.

In September 2016, we purchased the technology and related assets of a company whose software performs vulnerability and malware detection, along with continuous monitoring, for containers. The purchase consideration was $2.1 million in cash, which included $1.8 million of purchased technology and $0.3 million of goodwill, and is included in other assets on the consolidated balance sheets. No tangible assets were acquired. Acquisition-related costs were not material.

Intangible Assets, Net

Intangible assets consisted of $1.8 million of purchased technology, which is amortized over a three-year period. Accumulated amortization was $1.4 million and $0.8 million at December 31, 2018 and 2017, respectively.

Amortization of intangible assets was $0.6 million, $0.6 million and $0.2 million in 2018, 2017 and 2016, respectively. At December 31, 2018, estimated future amortization of intangible assets was $0.4 million in 2019.

Advertising

Advertising costs are expensed as they are incurred. We incurred advertising costs of $3.3 million, $3.2 million and $1.1 million in 2018, 2017 and 2016, respectively, which was included in sales and marketing expense in the consolidated statements of operations and comprehensive loss.

Software Development Costs

Research and development costs to develop software to be sold, leased or marketed are expensed as incurred up to the point of technological feasibility for the related software product. We have not capitalized development costs for software to be sold, leased or marketed to date, as the software development process is essentially completed concurrent with the establishment of technological feasibility. As such, these costs are expensed as incurred and recognized in research and development costs in the consolidated statements of operations and comprehensive loss.

Software developed for internal use, with no substantive plans to market such software at the time of development, are capitalized and included in property and equipment, net in the consolidated balance sheets. Costs incurred during the preliminary planning and evaluation and post implementation stages of the project are expensed as incurred. Costs incurred during the application development stage of the project are capitalized. In 2018, we capitalized $2.4 million of development costs related to internal use software. In 2017 and 2016, capitalized costs related to software developed for internal use were immaterial.

Stock-Based Compensation

Stock-based compensation expense related to our stock options, restricted stock, restricted stock units ("RSUs") and purchase rights issued under our 2018 Employee Stock Purchase Plan ("2018 ESPP") is calculated based on the fair value of the awards granted and is recognized on a straight-line basis over the requisite service period, which is generally two to four years, with the exception of RSUs that include performance-based vesting conditions and are expensed using the accelerated attribution method. The fair value of stock options and 2018 ESPP purchase rights is estimated on the grant date using the Black-Scholes option pricing model, which requires us to make assumptions and judgments, including the expected term, expected volatility, and risk-free interest rates.

Prior to our IPO, we estimated the fair value of our common stock at the date of grant. Following our IPO, we use the market price of our common stock at the date of grant.

We adopted Accounting Standards Update (“ASU”) No. 2016-09 - Compensation-Stock Compensation (Topic 718) (“ASU 2016-09”) on January 1, 2017 and made an accounting policy election to account for forfeitures as they occur. This election was applied on a modified retrospective basis. ASU 2016-09 also requires excess tax benefits and tax

deficiencies to be recorded in the income statement as opposed to additional paid-in capital when the awards vest or are settled, and we applied this on a prospective basis beginning on January 1, 2017. In addition, ASU 2016-09 eliminated the requirement that excess tax benefits be realized before they can be recorded.

Net Loss per Share

We calculate basic and diluted net loss per share attributable to common stockholders in conformity with the two-class method required for participating securities. Under the two-class method, the net loss attributable to common stockholders is not allocated to the redeemable convertible preferred stock as the holders of our redeemable convertible preferred stock do not have a contractual obligation to share in losses.

Under the two-class method, basic net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding during the period. Net loss attributable to common stockholders is calculated by adjusting net loss by the current period accretion of redeemable convertible preferred stock.

Upon the completion of our IPO, all of our Series A and Series B redeemable convertible preferred stock automatically converted into shares of our common stock.

Diluted earnings per share attributable to common stockholders is computed by giving effect to all potentially dilutive common stock equivalents in the period, including stock options, unvested restricted shares, redeemable convertible preferred stock and shares to be issued under our 2018 ESPP. As we have reported losses for all periods presented, all potentially dilutive securities have been excluded from the calculation of diluted net loss per share attributable to common stockholders as their effect would be antidilutive.

Segment Information

We operate as one operating segment as our chief executive officer, who is our chief operating decision maker, reviews financial information on a consolidated basis for purposes of making operating decisions, allocating resources, and evaluating financial performance.

Income Taxes

Income taxes are accounted for under the asset and liability method. This method requires recognition of deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the financial statement carrying amounts and the tax basis of existing assets and liabilities, net operating loss carryforwards, and tax credit carryforwards. A valuation allowance is provided if it is more likely than not that some or all of the deferred tax assets will not be realized.

We recognize tax benefits from an uncertain tax position if it is more likely than not to be sustained upon audit by the relevant taxing authority. Interest and penalties associated with such uncertain tax positions are classified as a component of income tax expense.

Recently Issued Accounting Pronouncements Not Yet Adopted

In June 2016, the Financial Accounting Standards Board ("FASB") issued ASU No. 2016-13 - Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. This ASU amends guidance on reporting credit losses for assets held at amortized cost basis and available-for-sale debt securities to require that credit losses on available-for-sale debt securities be presented as an allowance rather than as a write-down. The measurement of credit losses for newly recognized financial assets and subsequent changes in the allowance for credit losses are recorded in the statements of operations. This guidance will be effective for us beginning January 1, 2020, with early adoption permitted. We are currently evaluating the potential impact of this standard on our consolidated financial statements.

Fair Value Measurements

12 Months Ended

Dec. 31, 2018

Fair Value Disclosures [Abstract]

Fair Value Measurements

We measure certain financial instruments at fair value using a fair value hierarchy. In the hierarchy, assets are classified based on the lowest level inputs used in valuation into the following categories:


•	Level 1 — Quoted prices in active markets for identical assets and liabilities;


•	Level 2 — Observable inputs including quoted market prices for similar assets and liabilities in active markets, quoted prices for identical assets and liabilities in inactive markets, or inputs that are corroborated by observable market data; and


•	Level 3 — Unobservable inputs.

The following table summarizes assets that are measured at fair value on a recurring basis at December 31, 2018:



(in thousands)	Level 1		Level 2		Level 3		Total
Cash and cash equivalents
Money market funds	$	38,022	$	—	$	—	$	38,022

Short-term investments
Commercial paper	$	—	$	79,634	$	—	$	79,634
Corporate bonds	$	—	$	16,119	$	—	$	16,119
U.S. Treasury and agency obligations	$	—	$	22,366	$	—	$	22,366

We did not have any liabilities measured and recorded at fair value at December 31, 2018, and we did not have any assets or liabilities measured at fair value at December 31, 2017.

- Definition

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

+ References + Details

Debt	12 Months Ended
Debt	Dec. 31, 2018
Debt Disclosure [Abstract]
Debt	Debt On May 4, 2017, we entered into a $25.0 million revolving credit facility (“Credit Facility”) with Silicon Valley Bank, which is available for use until May 4, 2020. The Credit Facility is intended to be used to fund working capital and to provide increased liquidity and financial flexibility and bears interest at either LIBOR plus 2%, or the lender's prime rate plus 1%. In addition, we pay quarterly in arrears 0.25% of the average unused portion. The Credit Facility is secured by a first priority security interest in all of our assets, with a negative pledge on our Intellectual Property, as defined in the credit agreement. The Credit Facility contains certain restrictive covenants customary for facilities of this type including restrictions on indebtedness, liens, acquisitions and investments, restricted payments and dispositions. If, as of the last day of any quarter, the outstanding balance of the Credit Facility exceeds $5.0 million, there are financial covenants that require us to maintain a minimum level of earnings before income taxes, interest, depreciation and amortization (“EBITDA”) adjusted to add changes in deferred revenue in the period, and a minimum current ratio level. There were no borrowings or letters of credit issued under the Credit Facility in 2018 or 2017.

Leases

12 Months Ended

Dec. 31, 2018

Leases [Abstract]

Leases

We have operating leases for office facilities and finance leases for computer and office equipment. Our leases have remaining terms of less than one year to 8.5 years, some of which include one or more options to renew, with renewal terms up to five years and some of which include options to terminate the leases within the next three years. The ROU assets and liabilities as of December 31, 2018 assume the option to early terminate one of our leases in 2021.

The components of lease expense were as follows:



(in thousands)	Year Ended December 31, 2018
Operating lease cost	$	3,694

Finance lease cost:
Amortization of ROU assets	$	614
Interest on lease liabilities	35
Total finance lease cost	$	649

Rent expense for short-term leases in 2018 was not material.

Supplemental balance sheet information related to lease liabilities was as follows:



(in thousands, except lease term and discount rate)	December 31, 2018
Operating leases
Operating ROU assets	$	8,504

Operating lease liabilities (current)	$	4,262
Operating lease liabilities (net of current portion)	6,055
Total operating lease liabilities	$	10,317

Weighted average remaining lease term	3.1 years
Weighted average discount rate	7.1%

Finance leases
Property and equipment	$	1,854
Accumulated depreciation	(1,004		)
Property and equipment, net	$	850

Other current liabilities	$	14
Other liabilities	39
Total finance lease liabilities	$	53

Supplemental cash flow information related to leases was as follows:



(in thousands)	Year Ended December 31, 2018
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$	4,313
Operating cash flows from finance leases	35
Financing cash flows from finance leases	1,443

ROU assets obtained in exchange for lease obligations:
Operating leases	1,525
Finance leases	15

Maturities of operating lease liabilities at December 31, 2018 were as follows:



(in thousands)
Year ending December 31,
2019	$	4,429
2020	3,736
2021	1,747
2022	465
2023	301
Thereafter	1,052
Total lease payments	11,730
Less imputed interest	(1,413		)
Total	$	10,317

As of December 31, 2018, the operating lease for our future headquarters had not commenced and we did not have control of the space to be leased. We plan to take possession of the leased office space in mid-2019, at which time we will record a right-of-use asset and corresponding lease liability, and begin to record rent expense. Future lease payments related to this lease are $68.2 million and the lease payments are expected to commence in the first quarter of 2021.

Rent expense related to operating leases for office facilities was $3.6 million and $2.5 million in 2017 and 2016, respectively.

Total obligations for finance leases, formerly referred to as capital leases prior to the adoption of ASC 842 on January 1, 2018, were $1.5 million at December 31, 2017.

Redeemable Convertible Preferred Stock and Common Stock	12 Months Ended
Redeemable Convertible Preferred Stock and Common Stock	Dec. 31, 2018
Stockholders' Equity Note [Abstract]
Redeemable Convertible Preferred Stock and Common Stock	Redeemable Convertible Preferred Stock and Common Stock Redeemable Convertible Preferred Stock In October 2012, Tenable, Inc. (now a wholly owned subsidiary of Tenable Holdings, Inc.) issued 15,847,500 shares of Series A redeemable convertible preferred stock. In December 2015, we issued 15,847,500 shares, par value of $0.01, of Series A redeemable convertible preferred stock ("Series A") in exchange for Series A redeemable convertible preferred stock of Tenable, Inc. in connection with a recapitalization. This exchange was made on a one for one basis. In addition, we authorized 42,000,000 shares and issued 39,538,354 shares, par value of $0.01, of Series B redeemable convertible preferred stock ("Series B"). Upon completion of our IPO, Series A and Series B (together, the “Redeemable Convertible Preferred Stock”) automatically converted into an aggregate of 55,385,854 shares of our common stock. We accreted the Redeemable Convertible Preferred Stock to the redemption price at the redemption date using the effective interest method. Upon completion of our IPO, the accretion rights of the Redeemable Convertible Preferred Stock were terminated. Upon the completion of our IPO, we filed an Amended and Restated Certificate of Incorporation, authorizing a total of 500,000,000 shares of common stock and 10,000,000 shares of preferred stock. At December 31, 2018, no shares of preferred stock were issued or outstanding. Common Stock The voting, dividend, and liquidation rights of common stockholders are subject to, and qualified by, the rights of preferred stockholders. The common stockholders are entitled to receive dividends when, as and if, declared by the Board of Directors, subject to preferential dividend rights of preferred stockholders. Upon dissolution or liquidation, our common stockholders will be entitled to receive all assets available for distribution to stockholders, subject to any preferential rights of preferred stockholders.

Stock-Based Compensation

12 Months Ended

Dec. 31, 2018

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

Stock-Based Compensation

We have various stock incentive plans under which we have issued stock-based awards. Stock options granted under our stock incentive plans have a maximum term of ten years, generally vest over a period of three to four years, and the exercise price cannot be less than the fair market value on the date of grant. RSUs granted under our stock incentive plans generally vest over a period of two to four years.

In 2018, our board of directors adopted, and our stockholders approved, our 2018 Equity Incentive Plan ("2018 Plan"), which reserved 9.9 million shares of our common stock that may be issued as stock-based awards. The 2018 Plan became effective upon the execution of the underwriting agreement related to our IPO, at which point no further grants were made under our 2016 Stock Incentive Plan ("2016 Plan"). Any shares subject to stock options or other stock awards granted under our 2016 Plan, 2012 Stock Incentive Plan or 2002 Stock Incentive Plan that would have otherwise returned to such plan (such as upon the expiration or termination of a stock award prior to vesting) were added to, and are available for issuance under, our 2018 Plan. In addition, the number of shares of our common stock reserved for issuance under our 2018 Plan will automatically increase on January 1 of each year, beginning on January 1, 2019 and continuing through and including January 1, 2028, by 5% of the total number of shares of our capital stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares determined by our board of directors. There were 10,908,158 shares available for grant under the 2018 Plan at December 31, 2018.

Stock-based compensation expense included in the consolidated statements of operations and comprehensive loss was as follows:



	Year Ended December 31,
(in thousands)	2018		2017		2016
Cost of revenue	$	1,707	$	281	$	223
Sales and marketing	6,911		1,579		969
Research and development	5,804		1,782		602
General and administrative	8,453		4,118		738
Total stock-based compensation expense	$	22,875	$	7,760	$	2,532

At December 31, 2018, the total unrecognized stock-based compensation expense related to outstanding stock options was $47.9 million, which is expected to be recognized over an estimated remaining weighted average period of 3.0 years.

At December 31, 2018, the unrecognized stock-based compensation expense related to unvested awards of restricted stock was $3.4 million, which is expected to be recognized over an estimated remaining period of 2.0 years.

At December 31, 2018, the unrecognized stock-based compensation expense related to unvested RSUs was $15.7 million, which is expected to be recognized over an estimated remaining period of 2.3 years.

Stock Options

A summary of our stock option activity for the periods presented is below:



(in thousands, except for per share data and years)	Number of Shares	Weighted Average Exercise Price		Weighted-Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value
Outstanding at December 31, 2015	7,616	$	2.15	7.4	$	17,237
Granted	2,800	4.15
Exercised	(495)	1.00			1,567
Forfeited/canceled	(585)	2.84
Outstanding at December 31, 2016	9,336	2.77		7.2	15,374
Granted	9,022	5.22
Exercised	(1,870)	1.62			7,667
Forfeited/canceled	(1,915)	3.21
Outstanding at December 31, 2017	14,573	4.38		8.2	77,020
Granted	6,108	15.17
Exercised	(740)	2.26			9,902
Forfeited/canceled	(722)	7.23
Outstanding at December 31, 2018	19,219	7.78		8.0	277,114
Exercisable at December 31, 2018	6,758	3.75		6.6	124,629

At December 31, 2018, there were 19.2 million stock options outstanding that were vested and expected to vest.

In 2018, 2017 and 2016, we granted stock options to employees that vest over three to four years and had a per share weighted average grant date fair value of $6.84, $2.48 and $2.03, respectively. Estimating the fair value of stock options using the Black-Scholes option-pricing model requires assumptions as to the estimated term of the option, the risk-free interest rate, the expected volatility of the price of our common stock, the expected dividend yield, and the fair value of our underlying common stock prior to our IPO.

Fair Value of Common Stock. Following our IPO, we use the market price of our common stock at the date of grant. Prior to our IPO, the lack of an active public market for our common stock requires an estimate of the fair value of the common stock for granting stock options and restricted shares, and for determining stock-based compensation expense. Contemporaneous third-party valuations were obtained to assist in determining the fair value of our common stock. The contemporaneous valuations were performed in accordance with applicable methodologies, approaches and assumptions of the technical practice-aid issued by the American Institute of Certified Public Accountants Practice Aid entitled Valuation of Privately-Held Company Equity Securities Issued as Compensation.

Expected Term. This is the period of time that the options granted are expected to remain unexercised. We employ the simplified method to calculate the average expected term.

Expected Volatility. Volatility is a measure of the amount by which a financial variable, such as a share price, has fluctuated (historical volatility) or is expected to fluctuate (expected volatility) during a period. As we do not yet have sufficient history of our own volatility, we have identified several public entities of similar size, complexity, and stage of development and estimate volatility based on the volatility of these companies.

Risk-Free Interest Rate. This is the U.S. Treasury rate, having a term that most closely resembles the expected life of the stock option.

Expected Dividend Yield. We have never declared or paid dividends and have no plans to do so in the foreseeable future.

The fair value of each stock option was estimated on the grant date based on the following assumptions:



	Year Ended December 31,
	2018	2017	2016
Expected term (in years)	6.3	6.3	6.3
Expected volatility	41.3% — 43.3%	45.2% — 47.0%	50.0% — 50.1%
Risk-free interest rate	2.7% — 2.9%	1.9% — 2.4%	1.1% — 1.5%
Expected dividend yield	—	—	—
Expected forfeiture rate	—	—	1.4% — 5.8%

Restricted Stock and Restricted Stock Units

A summary of our restricted stock and RSU activity is presented below:



	Restricted Stock			Restricted Stock Units
(in thousands, except for per share data and years)	Number of Shares	Weighted Average Grant Date Fair Value		Number of Shares	Weighted Average Grant Date Fair Value
Unvested balance at December 31, 2016	—	$	—	—	$	—
Granted	1,583	4.25		—	—
Vested	—	—		—	—
Forfeited	—	—		—	—
Unvested balance at December 31, 2017	1,583	4.25		—	—
Granted	—	—		1,200	18.75
Vested	(693)	4.25		—	—
Forfeited	—	—		(71)	16.27
Unvested balance at December 31, 2018	890	4.25		1,129	18.90

The grant date fair value was based on the estimated fair value of our common stock on the date of grant. RSUs granted before July 30, 2018 vest upon the satisfaction of both service-based and performance-based vesting conditions. The performance-based condition was satisfied upon the completion of our IPO. RSUs granted after July 30, 2018 vest upon the satisfaction of a service-based vesting condition.

Compensation expense for restricted stock and RSUs is recognized on a straight-line basis over the requisite service period, with the exception of RSUs that include performance-based vesting conditions, which are expensed using the accelerated attribution method. The performance-based condition for RSUs granted before July 30, 2018 was satisfied upon the completion of our IPO.

2018 Employee Stock Purchase Plan

In 2018, our board of directors adopted, and our stockholders approved, our 2018 ESPP, which became effective upon the execution of the underwriting agreement related our IPO. Our 2018 ESPP initially reserved 4,000,000 shares of our common stock to be issued and the number of shares of our common stock reserved for issuance under our 2018 ESPP will automatically increase on January 1 of each year, beginning on January 1, 2019 and continuing through and including January 1, 2028, by the lesser of (1) 1.5% of the total number of shares of our common stock outstanding on December 31 of the preceding calendar year, (2) 8,000,000 shares of our common stock or (3) such lesser number of shares of common stock as determined by our board of directors.

Under our 2018 ESPP, employees may set aside up to 15% of their gross earnings, on an after-tax basis, to purchase our common stock at a discounted price, which is calculated at 85% of the lower of the fair market value of our common stock on the first day of an offering or on the date of purchase. The 2018 ESPP permits offerings up to 27 months in

duration, with one or more purchase periods in each offering. The initial offering period began on July 25, 2018 and is scheduled to end on September 1, 2020, with purchase periods ending on March 1, 2019, September 1, 2019, March 1, 2020 and September 1, 2020.

At December 31, 2018, there was $6.3 million of employee contributions to the 2018 ESPP included in accrued compensation, and no shares of our common stock have been purchased. The unrecognized stock-based compensation expense related to our 2018 ESPP was $8.2 million, which is expected to be recognized over the remaining offering period of 1.7 years.

The fair value of the 2018 ESPP purchase rights was estimated on the grant date using a Black-Scholes option-pricing model and the following assumptions:



	Year Ended December 31, 2018
Expected term (in years)	0.6 — 2.1
Expected volatility	31.9% — 33.5%
Risk-free interest rate	2.3% — 2.7%
Expected dividend yield	—

Income Taxes

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Income Taxes

U.S. and international components of loss before income taxes were as follows:



	Year Ended December 31,
(in thousands)	2018			2017			2016
U.S. income (loss)	$	1,429		$	(29,357	)	$	(40,330	)
Foreign (loss) income	(72,586		)	(11,494		)	3,965
Total loss before income taxes	$	(71,157	)	$	(40,851	)	$	(36,365	)

The components of the provision for income taxes were as follows:



	Year Ended December 31,
(in thousands)	2018		2017			2016
Current
Federal	$	—	$	140		$	(71	)
State	58		6			(80		)
Foreign	2,306		898			359
Total current tax expense	2,364		1,044			208
Deferred
Foreign	—		(873		)	635
Total deferred tax expense (benefit)	—		(873		)	635
Total provision for income taxes	$	2,364	$	171		$	843

The items accounting for the difference between income taxes computed at the federal statutory rate and our effective tax rate were as follows:



	Year Ended December 31,
	2018		2017		2016
U.S. federal statutory tax rate	21.0	%	34.0	%	34.0	%
State and local taxes	(1.5	)	2.4		4.9
Research and development tax credit	1.9		3.0		2.2
Uncertain tax positions	(1.0	)	(0.2	)	0.5
Foreign tax rate differential	(9.4	)	(4.0	)	1.4
Transition tax	—		(2.7	)	—
Revaluation of U.S. deferred income taxes	—		(34.5	)	—
Change in valuation allowance	(12.6	)	2.7		(43.3	)
Other	(1.7	)	(1.1	)	(2.0	)
Effective tax rate	(3.3	)%	(0.4	)%	(2.3	)%

We maintain a valuation allowance on U.S. federal, state and foreign net deferred tax assets as the realization of our deferred tax assets is dependent upon future earnings, if any, the timing and amount of which are uncertain.

The components of the deferred tax assets and liabilities were as follows:



	December 31,
(in thousands)	2018			2017
Deferred tax assets:
Net operating losses	$	32,745		$	29,227
Deferred revenue	16,488			14,327
Stock-based compensation	5,581			663
Tax credits	5,320			4,112
Leases	2,436			567
Accrued compensation	697			415
Other	68			37
Total deferred tax assets	63,335			49,348
Valuation allowance	(47,266		)	(36,403		)
Net deferred tax assets	16,069			12,945
Deferred tax liabilities:
Deferred commissions	(13,273		)	(12,306		)
Property and equipment	(2,166		)	(367		)
Intangible assets	(353		)	—
Other	(277		)	(272		)
Total deferred tax liabilities	(16,069		)	(12,945		)
Net deferred tax liabilities	$	—		$	—

At December 31, 2018, we had net operating loss (“NOL”) carryforwards for federal, state and foreign tax purposes of $85.9 million, $24.1 million, and $102.3 million, respectively, which will begin to expire in 2030, as well as $6.8 million of federal, state and foreign research and development tax credits, foreign tax credits, minimum tax credits and certain states’ job creation tax credits. The federal research and development and foreign tax credits will begin to expire in 2032 and the state job creation tax credits will begin to expire in 2019.

In 2018, we recorded a deferred tax asset of $1.7 million related to our operating lease liability and recorded a deferred tax liability of $1.7 million related to our operating lease right-of-use asset due to the adoption of ASU 842. In connection with our IPO, we recorded a $1.9 million increase in our valuation allowance related to certain transaction costs.

In 2017, we recorded deferred tax assets of $21.0 million related to deferred revenue previously recognized for tax purposes, deferred tax liabilities of $6.3 million related to capitalizing commission and fringe benefit costs previously expensed for tax purposes, and a corresponding valuation allowance of $14.7 million from adopting ASC 606.

We are currently subject to the annual limitation under Sections 382 and 383 of the Internal Revenue Code. We will not be precluded from realizing the NOL carryforward and tax credits but may be limited in the amount we could utilize in any given tax year in the event that the federal and state taxable income will exceed the limitation imposed by Section 382. The amount of the annual limitation is determined based on our value immediately prior to the ownership change. Subsequent ownership changes may further affect the limitation in future years.

At December 31, 2018 and 2017, the total amount of gross unrecognized tax benefits was $4.8 million and $1.2 million, respectively, which, if recognized, would impact our effective tax rate by less than $0.1 million in each year. Interest and penalties associated with uncertain tax positions recognized as a component of income tax expense were immaterial in 2018, 2017 and 2016.

The change in gross unrecognized tax benefits, excluding accrued interest, were as follows:



	Year Ended December 31,
(in thousands)	2018			2017			2016
Unrecognized tax benefits at the beginning of the period	$	1,199		$	736		$	663
Additions for tax positions in the current year	3,571			446			233
Increase in prior year positions	102			30			—
Decrease in prior year positions	(58		)	(13		)	(160		)
Unrecognized tax benefits at the end of the period	$	4,814		$	1,199		$	736

We file income tax returns in the United States, including various state jurisdictions. Our subsidiaries file income tax returns in various foreign jurisdictions. The tax years 2014 to 2018 remain open to examination by the major taxing jurisdictions in which we are subject to tax. At December 31, 2018, we were not under examination by the Internal Revenue Service or any state or foreign tax jurisdiction.

U.S. 2017 Tax Cuts and Jobs Act

On December 22, 2017, the Tax Cuts and Jobs Act (the “2017 Tax Act”) was enacted into law, and contains several significant changes, including the reduction of the corporate income tax rate from 35% to 21% effective January 1, 2018. As a result, we re-measured our U.S. federal and state deferred tax assets and liabilities to reflect the reduction to the federal tax rate. The re-measurement resulted in a reduction of $14.1 million to the U.S. federal and state deferred tax assets and a corresponding change in our valuation allowance.

The new legislation also includes a variety of other changes, such as a one-time repatriation tax on accumulated foreign earnings (“transition tax”), acceleration of business asset expensing and reduction in the amount of executive pay that could qualify as a tax deduction.

The 2017 Tax Act also included international tax provisions that will affect us, including the favorable tax regime for taxing foreign derived intangible income. Additional international provisions include the global intangible low taxed income (“GILTI”) regime and the base erosion anti-abuse tax (“BEAT”). As of December 31, 2018, we are not subject to US tax on Global Intangible Low-taxed Income (“GILTI”) and have concluded it will not have a material impact on our financial statements. Under US GAAP, we can make an accounting policy election to either treat taxes due on the GILTI inclusion as a current period expense or factor such amounts into our measurement of deferred taxes. We will make our accounting policy election in the period we become subject to GILTI, or in which a GILTI deferred item would need to be recorded, if earlier.

The 2017 Tax Act includes a mandatory one-time tax on accumulated earnings of foreign subsidiaries, and as a result, all previously unremitted earnings are no longer subject to U.S. tax after 2017. We did not incur any cash taxes related to the one-time transition tax on the mandatory deemed repatriation of foreign earnings due to current period tax loss that the U.S. group generated. In determining the U.S. group taxable loss, we included the one-time deemed repatriation income of $1.8 million. At December 31, 2018, we have completed the accounting for the tax effects of the enactment of the 2017 Tax Act and no changes were made to the provisional amounts that were recorded in 2017.

Depending on the jurisdiction, distributions of earnings could be subject to withholding taxes at rates applicable to the distributing jurisdiction. As we intend to continue to reinvest the earnings of foreign subsidiaries indefinitely, we did not provide for a U.S. income tax liability and foreign withholding taxes on undistributed foreign earnings of foreign subsidiaries. Our share of undistributed earnings of foreign subsidiaries that could be subject to foreign withholding taxes was immaterial at December 31, 2018 and 2017. As a result of the 2017 Tax Act, companies are no longer required to pay U.S. tax on dividends from foreign subsidiaries. While federal income tax expense has been recognized as a result of the 2017 Tax Act, we have not provided any additional deferred taxes with respect to items such as foreign withholding taxes, state income taxes, or foreign exchange gain or loss. It is not practicable for us to determine the amount of unrecognized tax expense on these reinvested international earnings.

Geographic Information

12 Months Ended

Dec. 31, 2018

Segment Reporting [Abstract]

Geographic Information

We operate as one operating segment. Our chief executive officer, who is our chief operating decision maker, reviews financial information on a consolidated basis for purposes of making operating decisions, allocating resources, and evaluating financial performance.

Revenue by region, based on the address of the end user as specified in our subscription, license or service agreements, was as follows:



	Year Ended December 31,
(in thousands)	2018		2017		2016
Americas	$	191,204	$	138,876	$	92,377
Europe, Middle East and Africa	53,839		34,121		22,211
Asia Pacific	22,317		14,730		9,783
Revenue	$	267,360	$	187,727	$	124,371

Customers located in the United States accounted for 67%, 69% and 69% of revenue in 2018, 2017 and 2016, respectively. No other country accounted for 10% or more of revenue in the periods presented.

Our property and equipment, net by geographic area is summarized as follows:



	December 31,
(in thousands)	2018		2017
United States	$	6,487	$	6,581
International	4,861		4,173
Property and equipment, net	$	11,348	$	10,754

Quarterly Results (unaudited)

12 Months Ended

Dec. 31, 2018

Quarterly Financial Information Disclosure [Abstract]

Quarterly Results (unaudited)

The following tables summarize our unaudited quarterly consolidated statements of operations data for each of the eight quarters through the period ended December 31, 2018. The information for each of these quarters has been prepared on the same basis as our audited annual consolidated financial statements and reflect, in the opinion of management, all adjustments of a normal, recurring nature that are necessary for the fair presentation of the results of operations for these periods. This data should be read in conjunction with our consolidated financial statements included elsewhere in this Annual Report on Form 10-K. Historical results are not necessarily indicative of the results that may be expected in the future, and the quarterly results are not necessarily indicative of the results that may be expected for the full year or any other period.



	Three Months Ended
(in thousands, except per share amounts)	March 31, 2018			June 30, 2018			September 30, 2018			December 31, 2018
Revenue	$	59,107		$	63,592		$	69,440		$	75,221
Cost of revenue	8,728			9,879			12,161			12,399
Gross profit	50,379			53,713			57,279			62,822
Operating expenses:
Sales and marketing	39,588			41,826			44,550			47,380
Research and development	17,185			17,791			20,553			21,169
General and administrative	9,055			10,541			13,272			13,864
Total operating expenses	65,828			70,158			78,375			82,413
Loss from operations	(15,449		)	(16,445		)	(21,096		)	(19,591		)
Other (expense) income, net	(8		)	(461		)	709			1,184
Loss before income taxes	(15,457		)	(16,906		)	(20,387		)	(18,407		)
Provision for income taxes	431			244			482			1,207
Net loss and comprehensive loss	(15,888		)	(17,150		)	(20,869		)	(19,614		)
Accretion of Series A and B redeemable convertible preferred stock	(188		)	(191		)	(55		)	—
Net loss attributable to common stockholders	$	(16,076	)	$	(17,341	)	$	(20,924	)	$	(19,614	)
Net loss per share attributable to common stockholders, basic and diluted	$	(0.68	)	$	(0.73	)	$	(0.28	)	$	(0.21	)



	Three Months Ended
(in thousands, except per share amounts)	March 31, 2017			June 30, 2017			September 30, 2017			December 31, 2017
Revenue	$	40,481		$	44,149		$	48,980		$	54,117
Cost of revenue	4,438			5,348			7,424			8,378
Gross profit	36,043			38,801			41,556			45,739
Operating expenses:
Sales and marketing	26,168			27,773			29,574			32,784
Research and development	12,458			13,713			15,869			15,633
General and administrative	6,163			6,544			7,275			8,945
Total operating expenses	44,789			48,030			52,718			57,362
Loss from operations	(8,746		)	(9,229		)	(11,162		)	(11,623		)
Other (expense) income, net	(29		)	56			(92		)	(26		)
Loss before income taxes	(8,775		)	(9,173		)	(11,254		)	(11,649		)
Provision for income taxes	51			41			59			20
Net loss and comprehensive loss	(8,826		)	(9,214		)	(11,313		)	(11,669		)
Accretion of Series A and B redeemable convertible preferred stock	(187		)	(191		)	(192		)	(193		)
Net loss attributable to common stockholders	$	(9,013	)	$	(9,405	)	$	(11,505	)	$	(11,862	)
Net loss per share attributable to common stockholders, basic and diluted	$	(0.42	)	$	(0.43	)	$	(0.51	)	$	(0.52	)

Business and Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2018

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Basis of Presentation

Basis of PresentationThe accompanying consolidated financial statements include the accounts of Tenable Holdings, Inc. and our wholly owned subsidiaries and have been prepared in conformity with United States generally accepted accounting principles (“GAAP”). All intercompany accounts and transactions have been eliminated in consolidation.

Use of Estimates

Use of EstimatesThe preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. These estimates include, but are not limited to, the determination of the estimated economic life of perpetual licenses for revenue recognition, the estimated period of benefit for deferred commissions, useful lives of long-lived assets, the valuation of stock-based compensation, including the estimated underlying fair value of our common stock prior to our IPO, the incremental borrowing rate for operating leases, and the valuation of deferred tax assets. We base these estimates on historical experience and on various other assumptions that we believe to be reasonable. Actual results could differ significantly from these estimates.

Foreign Currency

Foreign CurrencyThe functional currency for all of our foreign subsidiaries is the U.S. dollar. Assets and liabilities denominated in other currencies are remeasured into U.S. dollars at current exchange rates for monetary assets and liabilities and at historical exchange rates for non-monetary assets and liabilities. We bill our customers in U.S. dollars. Expenses incurred in non U.S. dollar currencies are remeasured into U.S. dollars when incurred.

Revenue Recognition

Subscription Revenue

Perpetual License and Maintenance Revenue

Professional Services and Other Revenue

Contracts with Multiple Performance Obligations

Variable Consideration

Concentrations

Contract Balances

Remaining Performance Obligations

Legacy Revenue Accounting Policies

Other services revenue was recognized as the services were performed.Amortization of deferred contract acquisition costs is included in sales and marketing expense in the consolidated statements of operations and comprehensive loss.Prior to January 1, 2017, we capitalized sales commissions and recognized the expense over the corresponding period in which the related revenue was recognized. Commissions on perpetual license sales were recognized upon the delivery of the license.Deferred CommissionsSales commissions, including related incremental fringe benefit costs, are considered to be incremental costs of obtaining a contract. Sales commissions on initial sales are not commensurate with sales commissions on contract renewals and therefore are recognized over an estimated period of benefit, which ranges between three and four years for subscription arrangements and five years for perpetual license arrangements. We estimated the period of benefit based on the expected contract term including renewal periods, the lifecycle of our technology, and other factors. Sales commissions on contract renewals are capitalized and amortized ratably over the contract term, with the exception of contracts with renewal periods that are one year or less, in which case the incremental costs are expensed as incurred.Revenue Recognition


•	Identify the contract with a customer


•	Identify the performance obligations in the contract


•	Determine the transaction price


•	Allocate the transaction price to the performance obligations in the contract


•	Recognize revenue when or as performance obligations are satisfied

Cash and Cash Equivalents

Cash and Cash EquivalentsWe consider all highly liquid financial instruments with an original maturity of three months or less when purchased to be cash equivalents.

Fair Value of Financial Instruments

Fair Value of Financial InstrumentsFair value is defined as 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. We apply fair value accounting for all financial assets and liabilities that are recognized or disclosed at fair value in the financial statements on a recurring basis. We measure cash and cash equivalents and short-term investments at fair value using a fair value hierarchy of inputs. We approximate fair value by using the carrying amounts for accounts receivable, accounts payable and accrued expenses due to their short-term nature.

Investments

InvestmentsWe currently invest in commercial paper, corporate bonds, and U.S. treasury and agency obligations. Our investments are classified as available-for-sale and recorded at fair value, with unrealized gains and losses reported in accumulated other comprehensive loss within stockholders’ equity (deficit). We review our investment portfolio to determine whether investments have indicators of possible impairment.

Accounts Receivable

Accounts ReceivableAccounts receivable are recorded at the invoiced amount, less an allowance for doubtful accounts, and do not bear interest. We maintain an allowance for doubtful accounts at an amount estimated to be sufficient to cover the risk of collecting less than full payment of the receivables. At each balance sheet date, we evaluate our receivables and assess the allowance for doubtful accounts based on specific customer collection issues and historical write-off trends.

Property and Equipment, net

Property and Equipment, netProperty and equipment, net is stated at historical cost less accumulated depreciation. Depreciation is computed using the straight-line method over the estimated useful lives of the assets: three years for computer software and equipment and five years for furniture and fixtures. Leasehold improvements are amortized using the straight-line method over the shorter of the estimated useful lives of the assets or the terms of the respective leases. Property and equipment, net includes right-of-use assets acquired under finance leases. Amortization of assets acquired under finance leases is included in depreciation expense. Repairs and maintenance costs are expensed as incurred.

Leases

expedients as permitted under the transition guidance, which allowed us to not reassess whether arrangements contain leases, not reassess lease classification, and not reassess initial direct costs.

Lease expense for lease payments is recognized on a straight-line basis over the term of the lease.

Impairment of Long-Lived Assets

Impairment of Long-Lived AssetsWe evaluate our long-lived assets for impairment whenever events or changes in circumstance indicate that the carrying amount may not be fully recoverable. Recoverability of the long-lived assets is measured by a comparison of the carrying amount of the assets to future undiscounted net cash flows expected to be generated by the assets. If such assets are considered to be impaired, the impairment to be recognized is measured as the excess of the carrying amount over the fair value.

Business Combinations

Advertising

AdvertisingAdvertising costs are expensed as they are incurred.

Software Development Costs

Stock-Based Compensation

Prior to our IPO, we estimated the fair value of our common stock at the date of grant. Following our IPO, we use the market price of our common stock at the date of grant.

Net Loss per Share

Upon the completion of our IPO, all of our Series A and Series B redeemable convertible preferred stock automatically converted into shares of our common stock.

Segment Information

Segment InformationWe operate as one operating segment as our chief executive officer, who is our chief operating decision maker, reviews financial information on a consolidated basis for purposes of making operating decisions, allocating resources, and evaluating financial performance.

Income Taxes

Recently Issued Accounting Pronouncements Not Yet Adopted

Recently Issued Accounting Pronouncements Not Yet AdoptedIn June 2016, the Financial Accounting Standards Board ("FASB") issued ASU No. 2016-13 - Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. This ASU amends guidance on reporting credit losses for assets held at amortized cost basis and available-for-sale debt securities to require that credit losses on available-for-sale debt securities be presented as an allowance rather than as a write-down. The measurement of credit losses for newly recognized financial assets and subsequent changes in the allowance for credit losses are recorded in the statements of operations. This guidance will be effective for us beginning January 1, 2020, with early adoption permitted. We are currently evaluating the potential impact of this standard on our consolidated financial statements.

Business and Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2018

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Summary of revenue

The following table presents a summary of revenue:



	Year Ended December 31,
(in thousands)	2018		2017		2016
Subscription revenue	$	205,827	$	132,873	$	80,399
Perpetual license and maintenance revenue	54,622		50,337		40,328
Professional services and other revenue	6,911		4,517		3,644
Revenue	$	267,360	$	187,727	$	124,371

Activity of deferred contract costs

The following summarizes the activity of deferred incremental costs of obtaining a contract:



	Year Ended December 31,
(in thousands)	2018			2017
Beginning balance	$	50,176		$	30,118
Capitalization of contract acquisition costs	29,075			34,632
Amortization of deferred contract acquisition costs	(19,817		)	(14,574		)
Ending balance	$	59,434		$	50,176

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2018

Fair Value Disclosures [Abstract]

Schedule of assets measured at fair value on recurring basis

The following table summarizes assets that are measured at fair value on a recurring basis at December 31, 2018:



(in thousands)	Level 1		Level 2		Level 3		Total
Cash and cash equivalents
Money market funds	$	38,022	$	—	$	—	$	38,022

Short-term investments
Commercial paper	$	—	$	79,634	$	—	$	79,634
Corporate bonds	$	—	$	16,119	$	—	$	16,119
U.S. Treasury and agency obligations	$	—	$	22,366	$	—	$	22,366

Leases (Tables)

12 Months Ended

Dec. 31, 2018

Leases [Abstract]

Components of leases

The components of lease expense were as follows:



(in thousands)	Year Ended December 31, 2018
Operating lease cost	$	3,694

Finance lease cost:
Amortization of ROU assets	$	614
Interest on lease liabilities	35
Total finance lease cost	$	649

Rent expense for short-term leases in 2018 was not material.

Supplemental balance sheet information related to lease liabilities was as follows:



(in thousands, except lease term and discount rate)	December 31, 2018
Operating leases
Operating ROU assets	$	8,504

Operating lease liabilities (current)	$	4,262
Operating lease liabilities (net of current portion)	6,055
Total operating lease liabilities	$	10,317

Weighted average remaining lease term	3.1 years
Weighted average discount rate	7.1%

Finance leases
Property and equipment	$	1,854
Accumulated depreciation	(1,004		)
Property and equipment, net	$	850

Other current liabilities	$	14
Other liabilities	39
Total finance lease liabilities	$	53

Supplemental cash flow information related to leases

Supplemental cash flow information related to leases was as follows:



(in thousands)	Year Ended December 31, 2018
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$	4,313
Operating cash flows from finance leases	35
Financing cash flows from finance leases	1,443

ROU assets obtained in exchange for lease obligations:
Operating leases	1,525
Finance leases	15

Schedule of maturities of operating lease liabilities

Maturities of operating lease liabilities at December 31, 2018 were as follows:



(in thousands)
Year ending December 31,
2019	$	4,429
2020	3,736
2021	1,747
2022	465
2023	301
Thereafter	1,052
Total lease payments	11,730
Less imputed interest	(1,413		)
Total	$	10,317

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

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

Stock-based compensation expense

Stock-based compensation expense included in the consolidated statements of operations and comprehensive loss was as follows:



	Year Ended December 31,
(in thousands)	2018		2017		2016
Cost of revenue	$	1,707	$	281	$	223
Sales and marketing	6,911		1,579		969
Research and development	5,804		1,782		602
General and administrative	8,453		4,118		738
Total stock-based compensation expense	$	22,875	$	7,760	$	2,532

Stock option activity

A summary of our stock option activity for the periods presented is below:



(in thousands, except for per share data and years)	Number of Shares	Weighted Average Exercise Price		Weighted-Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value
Outstanding at December 31, 2015	7,616	$	2.15	7.4	$	17,237
Granted	2,800	4.15
Exercised	(495)	1.00			1,567
Forfeited/canceled	(585)	2.84
Outstanding at December 31, 2016	9,336	2.77		7.2	15,374
Granted	9,022	5.22
Exercised	(1,870)	1.62			7,667
Forfeited/canceled	(1,915)	3.21
Outstanding at December 31, 2017	14,573	4.38		8.2	77,020
Granted	6,108	15.17
Exercised	(740)	2.26			9,902
Forfeited/canceled	(722)	7.23
Outstanding at December 31, 2018	19,219	7.78		8.0	277,114
Exercisable at December 31, 2018	6,758	3.75		6.6	124,629

Valuation assumptions

The fair value of the 2018 ESPP purchase rights was estimated on the grant date using a Black-Scholes option-pricing model and the following assumptions:



	Year Ended December 31, 2018
Expected term (in years)	0.6 — 2.1
Expected volatility	31.9% — 33.5%
Risk-free interest rate	2.3% — 2.7%
Expected dividend yield	—

The fair value of each stock option was estimated on the grant date based on the following assumptions:



	Year Ended December 31,
	2018	2017	2016
Expected term (in years)	6.3	6.3	6.3
Expected volatility	41.3% — 43.3%	45.2% — 47.0%	50.0% — 50.1%
Risk-free interest rate	2.7% — 2.9%	1.9% — 2.4%	1.1% — 1.5%
Expected dividend yield	—	—	—
Expected forfeiture rate	—	—	1.4% — 5.8%

Summary of restricted stock and restricted stock units

A summary of our restricted stock and RSU activity is presented below:



	Restricted Stock			Restricted Stock Units
(in thousands, except for per share data and years)	Number of Shares	Weighted Average Grant Date Fair Value		Number of Shares	Weighted Average Grant Date Fair Value
Unvested balance at December 31, 2016	—	$	—	—	$	—
Granted	1,583	4.25		—	—
Vested	—	—		—	—
Forfeited	—	—		—	—
Unvested balance at December 31, 2017	1,583	4.25		—	—
Granted	—	—		1,200	18.75
Vested	(693)	4.25		—	—
Forfeited	—	—		(71)	16.27
Unvested balance at December 31, 2018	890	4.25		1,129	18.90

Net Loss Per Share Attributable to Common Stockholders (Tables)

12 Months Ended

Dec. 31, 2018

Earnings Per Share [Abstract]

Computation of basic and diluted net loss per share

The following table sets forth the computation of basic and diluted net loss per share attributable to common stockholders:



	Year Ended December 31,
(in thousands, except per share data)	2018			2017			2016
Net loss attributable to common stockholders	$	(73,955	)	$	(41,785	)	$	(37,971	)

Weighted-average shares used to compute net loss per share attributable to common stockholders, basic and diluted	53,669			22,211			20,974

Net loss per share attributable to common stockholders, basic and diluted	$	(1.38	)	$	(1.88	)	$	(1.81	)

Potentially dilutive securities

The following potentially dilutive securities have been excluded from the diluted per share calculations because they would have been antidilutive:



	Year Ended December 31,
(in thousands)	2018	2017	2016
Stock options	19,219	14,573	9,336
Restricted stock units	1,129	—	—
Restricted shares	890	1,583	—
Shares to be issued under ESPP	320	—	—
Redeemable convertible preferred stock	—	55,386	55,386
Total	21,558	71,542	64,722

Income Taxes Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Schedule of Components of Loss Before Income Taxes

U.S. and international components of loss before income taxes were as follows:



	Year Ended December 31,
(in thousands)	2018			2017			2016
U.S. income (loss)	$	1,429		$	(29,357	)	$	(40,330	)
Foreign (loss) income	(72,586		)	(11,494		)	3,965
Total loss before income taxes	$	(71,157	)	$	(40,851	)	$	(36,365	)

Schedule of Components of the Provision for Income Taxes

The components of the provision for income taxes were as follows:



	Year Ended December 31,
(in thousands)	2018		2017			2016
Current
Federal	$	—	$	140		$	(71	)
State	58		6			(80		)
Foreign	2,306		898			359
Total current tax expense	2,364		1,044			208
Deferred
Foreign	—		(873		)	635
Total deferred tax expense (benefit)	—		(873		)	635
Total provision for income taxes	$	2,364	$	171		$	843

Schedule of Effective Income Tax Rate Reconciliation

The items accounting for the difference between income taxes computed at the federal statutory rate and our effective tax rate were as follows:



	Year Ended December 31,
	2018		2017		2016
U.S. federal statutory tax rate	21.0	%	34.0	%	34.0	%
State and local taxes	(1.5	)	2.4		4.9
Research and development tax credit	1.9		3.0		2.2
Uncertain tax positions	(1.0	)	(0.2	)	0.5
Foreign tax rate differential	(9.4	)	(4.0	)	1.4
Transition tax	—		(2.7	)	—
Revaluation of U.S. deferred income taxes	—		(34.5	)	—
Change in valuation allowance	(12.6	)	2.7		(43.3	)
Other	(1.7	)	(1.1	)	(2.0	)
Effective tax rate	(3.3	)%	(0.4	)%	(2.3	)%

Components of Deferred Tax Assets and Liabilities

The components of the deferred tax assets and liabilities were as follows:



	December 31,
(in thousands)	2018			2017
Deferred tax assets:
Net operating losses	$	32,745		$	29,227
Deferred revenue	16,488			14,327
Stock-based compensation	5,581			663
Tax credits	5,320			4,112
Leases	2,436			567
Accrued compensation	697			415
Other	68			37
Total deferred tax assets	63,335			49,348
Valuation allowance	(47,266		)	(36,403		)
Net deferred tax assets	16,069			12,945
Deferred tax liabilities:
Deferred commissions	(13,273		)	(12,306		)
Property and equipment	(2,166		)	(367		)
Intangible assets	(353		)	—
Other	(277		)	(272		)
Total deferred tax liabilities	(16,069		)	(12,945		)
Net deferred tax liabilities	$	—		$	—

Schedule Change of Gross Unrealized Tax Benefits

The change in gross unrecognized tax benefits, excluding accrued interest, were as follows:



	Year Ended December 31,
(in thousands)	2018			2017			2016
Unrecognized tax benefits at the beginning of the period	$	1,199		$	736		$	663
Additions for tax positions in the current year	3,571			446			233
Increase in prior year positions	102			30			—
Decrease in prior year positions	(58		)	(13		)	(160		)
Unrecognized tax benefits at the end of the period	$	4,814		$	1,199		$	736

Geographic Information (Tables)

12 Months Ended

Dec. 31, 2018

Segment Reporting [Abstract]

Revenue by region

Revenue by region, based on the address of the end user as specified in our subscription, license or service agreements, was as follows:



	Year Ended December 31,
(in thousands)	2018		2017		2016
Americas	$	191,204	$	138,876	$	92,377
Europe, Middle East and Africa	53,839		34,121		22,211
Asia Pacific	22,317		14,730		9,783
Revenue	$	267,360	$	187,727	$	124,371

Property and equipment, net by geographic area

Our property and equipment, net by geographic area is summarized as follows:



	December 31,
(in thousands)	2018		2017
United States	$	6,487	$	6,581
International	4,861		4,173
Property and equipment, net	$	11,348	$	10,754

Quarterly Results (unaudited) (Tables)

12 Months Ended

Dec. 31, 2018

Quarterly Financial Information Disclosure [Abstract]

Quarterly Results (unaudited)



	Three Months Ended
(in thousands, except per share amounts)	March 31, 2018			June 30, 2018			September 30, 2018			December 31, 2018
Revenue	$	59,107		$	63,592		$	69,440		$	75,221
Cost of revenue	8,728			9,879			12,161			12,399
Gross profit	50,379			53,713			57,279			62,822
Operating expenses:
Sales and marketing	39,588			41,826			44,550			47,380
Research and development	17,185			17,791			20,553			21,169
General and administrative	9,055			10,541			13,272			13,864
Total operating expenses	65,828			70,158			78,375			82,413
Loss from operations	(15,449		)	(16,445		)	(21,096		)	(19,591		)
Other (expense) income, net	(8		)	(461		)	709			1,184
Loss before income taxes	(15,457		)	(16,906		)	(20,387		)	(18,407		)
Provision for income taxes	431			244			482			1,207
Net loss and comprehensive loss	(15,888		)	(17,150		)	(20,869		)	(19,614		)
Accretion of Series A and B redeemable convertible preferred stock	(188		)	(191		)	(55		)	—
Net loss attributable to common stockholders	$	(16,076	)	$	(17,341	)	$	(20,924	)	$	(19,614	)
Net loss per share attributable to common stockholders, basic and diluted	$	(0.68	)	$	(0.73	)	$	(0.28	)	$	(0.21	)



	Three Months Ended
(in thousands, except per share amounts)	March 31, 2017			June 30, 2017			September 30, 2017			December 31, 2017
Revenue	$	40,481		$	44,149		$	48,980		$	54,117
Cost of revenue	4,438			5,348			7,424			8,378
Gross profit	36,043			38,801			41,556			45,739
Operating expenses:
Sales and marketing	26,168			27,773			29,574			32,784
Research and development	12,458			13,713			15,869			15,633
General and administrative	6,163			6,544			7,275			8,945
Total operating expenses	44,789			48,030			52,718			57,362
Loss from operations	(8,746		)	(9,229		)	(11,162		)	(11,623		)
Other (expense) income, net	(29		)	56			(92		)	(26		)
Loss before income taxes	(8,775		)	(9,173		)	(11,254		)	(11,649		)
Provision for income taxes	51			41			59			20
Net loss and comprehensive loss	(8,826		)	(9,214		)	(11,313		)	(11,669		)
Accretion of Series A and B redeemable convertible preferred stock	(187		)	(191		)	(192		)	(193		)
Net loss attributable to common stockholders	$	(9,013	)	$	(9,405	)	$	(11,505	)	$	(11,862	)
Net loss per share attributable to common stockholders, basic and diluted	$	(0.42	)	$	(0.43	)	$	(0.51	)	$	(0.52	)

Business and Summary of Significant Accounting Policies - Initial Public Offering (Details) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
	Jul. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Subsidiary, Sale of Stock [Line Items]
Common stock, authorized (in shares)	500,000,000	500,000,000	93,855,000
Preferred stock, authorized (in shares)	10,000,000
IPO
Subsidiary, Sale of Stock [Line Items]
Stock sold, price per share (in usd per share)	$ 23.00
Net proceeds from sale of stock	$ 264.6
Common Stock
Subsidiary, Sale of Stock [Line Items]
Issuance of common stock upon conversion of redeemable convertible preferred stock (in shares)		55,386,000
Common Stock \| IPO
Subsidiary, Sale of Stock [Line Items]
Stock sold (in shares)	12,535,000
Issuance of common stock upon conversion of redeemable convertible preferred stock (in shares)	55,385,854
Common Stock \| Over-allotment option
Subsidiary, Sale of Stock [Line Items]
Stock sold (in shares)	1,635,000
Redeemable convertible Series A preferred stock \| IPO
Subsidiary, Sale of Stock [Line Items]
Issuance of common stock upon conversion of redeemable convertible preferred stock (in shares)	15,847,500
Redeemable convertible Series B preferred stock \| IPO
Subsidiary, Sale of Stock [Line Items]
Issuance of common stock upon conversion of redeemable convertible preferred stock (in shares)	39,538,354

Business and Summary of Significant Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Thousands		12 Months Ended
	Jan. 01, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative effect of adoptions of new accounting standards	$ (38,357)
Increase to deferred revenue		$ 64,085	$ 63,404	$ 44,228
Revenue recognized that was included in deferred revenue		154,900	106,800
Accumulated Deficit
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative effect of adoptions of new accounting standards	(38,418)
Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Increase to deferred revenue	55,000
Increase to capitalized contract costs	16,600
Net increase to revenue			3,500
Revenue recognized that was included in deferred revenue		$ 16,700	$ 19,000
Accounting Standards Update 2014-09 \| Accumulated Deficit
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative effect of adoptions of new accounting standards	$ (38,400)

Business and Summary of Significant Accounting Policies - Remaining Performance Obligations (Details) $ in Millions	Dec. 31, 2018 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Future estimated revenue	$ 293.2
Expected recognized percentage over succeeding 12 months	73.00%
Expected timing of satisfaction	12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected timing of satisfaction	4 years
Perpetual license and maintenance revenue \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected timing of satisfaction	1 year
Perpetual license and maintenance revenue \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected timing of satisfaction	1 year
Perpetual license and maintenance revenue \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected timing of satisfaction	1 year
Accounting Standards Update 2014-09 \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Future estimated revenue	$ 11.8
Accounting Standards Update 2014-09 \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Future estimated revenue	5.6
Accounting Standards Update 2014-09 \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Future estimated revenue	$ 1.9

Business and Summary of Significant Accounting Policies - Summary of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Revenue	$ 75,221	$ 69,440	$ 63,592	$ 59,107	$ 54,117	$ 48,980	$ 44,149	$ 40,481	$ 267,360	$ 187,727	$ 124,371
Subscription revenue
Disaggregation of Revenue [Line Items]
Revenue									205,827	132,873	80,399
Perpetual license and maintenance revenue
Disaggregation of Revenue [Line Items]
Revenue									54,622	50,337	40,328
Professional services and other revenue
Disaggregation of Revenue [Line Items]
Revenue									$ 6,911	$ 4,517	$ 3,644

Business and Summary of Significant Accounting Policies - Concentrations (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue \| Sales method risk
Concentration Risk [Line Items]
Concentration risk, percentage	88.00%	83.00%	80.00%
One distributor \| Revenue \| Customer concentration risk
Concentration Risk [Line Items]
Concentration risk, percentage	46.00%	45.00%	42.00%
One distributor \| Accounts receivable \| Customer concentration risk
Concentration Risk [Line Items]
Concentration risk, percentage	46.00%	51.00%

Business and Summary of Significant Accounting Policies - Cash and Cash Equivalents (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Restricted Cash	$ 0.3	$ 0.3

Business and Summary of Significant Accounting Policies - Deferred Commissions (Details)	Dec. 31, 2018
Perpetual license and maintenance revenue
Capitalized Contract Cost [Line Items]
Estimated period of benefit	5 years
Minimum \| Subscription revenue
Capitalized Contract Cost [Line Items]
Estimated period of benefit	3 years
Maximum \| Subscription revenue
Capitalized Contract Cost [Line Items]
Estimated period of benefit	4 years

Business and Summary of Significant Accounting Policies - Activity of Deferred Contract Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Capitalized Contract Cost [Roll Forward]
Beginning balance	$ 50,176	$ 30,118
Capitalization of contract acquisition costs	29,075	34,632
Amortization of deferred contract acquisition costs	(19,817)	(14,574)
Ending balance	$ 59,434	$ 50,176

Business and Summary of Significant Accounting Policies - Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Construction in progress	$ 0		$ 2,252
Financing obligation	0		1,802
Operating lease right-of-use assets	8,504	$ 10,100	$ 0
Operating lease liabilities	$ 10,317	12,300
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Construction in progress		2,300
Financing obligation		1,800
Deposit		$ 500

Business and Summary of Significant Accounting Policies - Business Combinations (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Combination, Separately Recognized Transactions [Line Items]
Purchase consideration	$ 2,100	$ 0	$ 0	$ 2,075
Goodwill	300
Purchased technology
Business Combination, Separately Recognized Transactions [Line Items]
Purchase consideration including technology	$ 1,800

Business and Summary of Significant Accounting Policies - Intangible Assets, Net (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 0.6	$ 0.6	$ 0.2
Estimated future amortization of intangible assets	0.4
Purchased technology
Finite-Lived Intangible Assets [Line Items]
Intangible assets	$ 1.8
Amortization period	3 years
Accumulated amortization	$ 1.4	$ 0.8

Fair Value Measurements (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	$ 79,634
Commercial paper \| Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0
Commercial paper \| Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	79,634
Commercial paper \| Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	16,119
Corporate bonds \| Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0
Corporate bonds \| Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	16,119
Corporate bonds \| Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0
U.S. Treasury and agency obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	22,366
U.S. Treasury and agency obligations \| Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0
U.S. Treasury and agency obligations \| Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	22,366
U.S. Treasury and agency obligations \| Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	38,022
Money market funds \| Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	38,022
Money market funds \| Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0
Money market funds \| Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 0

Property and Equipment, Net - Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Total	$ 24,534	$ 19,482
Less: accumulated depreciation and amortization	(13,186)	(8,728)
Property and equipment, net	11,348	10,754
Computer software and equipment
Property, Plant and Equipment [Line Items]
Total	13,038	9,089
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total	2,376	2,102
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total	7,266	6,452
Right-of-use assets under finance leases
Property, Plant and Equipment [Line Items]
Total	1,854	$ 1,839
Less: accumulated depreciation and amortization	(1,004)
Property and equipment, net	$ 850

Debt (Details) - USD ($)	12 Months Ended
Debt (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	May 04, 2017
Line of Credit Facility [Line Items]
Revolving credit facility, maximum borrowing capacity			$ 25,000,000.0
Arrears paid on average unused portion	0.25%
Outstanding balance of credit facility, amount requiring covenant compliance	$ 5,000,000.0
Borrowings against debt instrument	$ 0	$ 0
Line of Credit \| LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.00%
Line of Credit \| Prime Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.00%

Leases - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
Leases - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2021
Operating Leased Assets [Line Items]
Lease renewal terms	5 years
Option to terminate lease	3 years
Operating lease, rent expense		$ 3.6	$ 2.5
Obligations for capital lease		$ 1.5
Maximum
Operating Leased Assets [Line Items]
Remaining terms of leases	8 years 6 months
Minimum
Operating Leased Assets [Line Items]
Remaining terms of leases	1 year
Scenario, Forecast
Operating Leased Assets [Line Items]
Obligations for operating lease				$ 68.2

Leases - Components of Lease Expense (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)
Leases [Abstract]
Operating lease cost	$ 3,694
Finance lease cost:
Amortization of ROU assets	614
Interest on lease liabilities	35
Total finance lease cost	$ 649

Leases - Supplemental Balance Sheet Information (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Operating leases
Operating lease right-of-use assets	$ 8,504	$ 10,100	$ 0
Operating lease liabilities (current)	4,262		0
Operating lease liabilities (net of current portion)	6,055		0
Total operating lease liabilities	$ 10,317	$ 12,300
Weighted average remaining lease term	3 years 1 month 6 days
Weighted average discount rate	7.10%
Finance leases
Property and equipment	$ 24,534		19,482
Accumulated depreciation	(13,186)		(8,728)
Property and equipment, net	11,348		10,754
Other current liabilities	14
Other liabilities	39
Total finance lease liabilities	53
Right-of-use assets under finance leases
Finance leases
Property and equipment	1,854		$ 1,839
Accumulated depreciation	(1,004)
Property and equipment, net	$ 850

Leases - Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 4,313
Operating cash flows from finance leases	35
Financing cash flows from finance leases	1,443	$ 306	$ 47
ROU assets obtained in exchange for lease obligations:
Operating leases	1,525
Finance leases	$ 15

Leases - Operating Lease Liability Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018
Leases [Abstract]
2019	$ 4,429
2020	3,736
2021	1,747
2022	465
2023	301
Thereafter	1,052
Total lease payments	11,730
Less imputed interest	(1,413)
Total operating lease liabilities	$ 10,317	$ 12,300

Redeemable Convertible Preferred Stock and Common Stock (Details)		1 Months Ended		12 Months Ended
	Jul. 30, 2018 shares	Dec. 31, 2015 $ / shares shares	Oct. 31, 2012 shares	Dec. 31, 2018 shares	Dec. 31, 2017 $ / shares shares
Class of Stock [Line Items]
Redeemable convertible preferred stock, conversion ratio		1
Common stock, authorized (in shares)	500,000,000			500,000,000	93,855,000
Preferred stock, authorized (in shares)	10,000,000
Preferred stock, issued (in shares)				0
Preferred stock, outstanding (in shares)				0
Series A Redeemable Convertible Preferred Stock
Class of Stock [Line Items]
Stock sold (in shares)		15,847,500	15,847,500
Redeemable convertible preferred stock, par value (in usd per share) \| $ / shares		$ 0.01			$ 0.01
Redeemable convertible preferred stock, shares authorized (in shares)					15,848,000
Series B Redeemable Convertible Preferred Stock
Class of Stock [Line Items]
Stock sold (in shares)		39,538,354
Redeemable convertible preferred stock, par value (in usd per share) \| $ / shares		$ 0.01			$ 0.01
Redeemable convertible preferred stock, shares authorized (in shares)		42,000,000			42,000,000
Common Stock
Class of Stock [Line Items]
Issuance of common stock upon conversion of redeemable convertible preferred stock (in shares)				55,386,000
Common Stock \| IPO
Class of Stock [Line Items]
Stock sold (in shares)	12,535,000
Issuance of common stock upon conversion of redeemable convertible preferred stock (in shares)	55,385,854

Stock-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock-based compensation expense, outstanding stock options	$ 47.9
Stock options vested and expected to vest (in shares)	19,200,000
2018 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares outstanding	5.00%
Shares available for grant (in shares)	10,908,158
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options, stock incentive plans, maximum term	10 years
Estimated remaining weighted average period	3 years
Weighted average grant date fair value (in USD per share)	$ 6.84	$ 2.48	$ 2.03
Stock options \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options, stock incentive plan, vesting period	3 years
Stock options \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options, stock incentive plan, vesting period	4 years
Stock-based awards \| 2018 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (in shares)	9,900,000
Restricted shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Estimated remaining weighted average period	2 years
Unrecognized stock-based compensation expense, unvested restricted stock or RSUs	$ 3.4
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Estimated remaining weighted average period	2 years 3 months 18 days
Unrecognized stock-based compensation expense, unvested restricted stock or RSUs	$ 15.7
Restricted stock units \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options, stock incentive plan, vesting period	2 years
Restricted stock units \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options, stock incentive plan, vesting period	4 years
Employee stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (in shares)	4,000,000
Percentage of shares outstanding	1.50%
Shares of common stock outstanding (in shares)	8,000,000
Estimated remaining weighted average period	1 year 8 months 12 days

Stock-Based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 22,875	$ 7,760	$ 2,532
Cost of revenue
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	1,707	281	223
Sales and marketing
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	6,911	1,579	969
Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	5,804	1,782	602
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 8,453	$ 4,118	$ 738

Stock-Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Number of Shares
Number of shares outstanding, beginning of period (in shares)	14,573	9,336	7,616
Number of shares, granted (in shares)	6,108	9,022	2,800
Number of shares, exercised (in shares)	(740)	(1,870)	(495)
Number of shares, forfeited/canceled (in shares)	(722)	(1,915)	(585)
Number of shares outstanding, end of period (in shares)	19,219	14,573	9,336	7,616
Number of shares exercisable (in shares)	6,758
Weighted Average Exercise Price
Weighted average exercise price, outstanding, beginning of period (in USD per share)	$ 4.38	$ 2.77	$ 2.15
Weighted average exercise price, granted (in USD per share)	15.17	5.22	4.15
Weighted average exercise price, exercised (in USD per share)	2.26	1.62	1.00
Weighted average exercise price, forfeited/canceled (in USD per share)	7.23	3.21	2.84
Weighted average exercise price, outstanding, end of period (in USD per share)	7.78	$ 4.38	$ 2.77	$ 2.15
Weighted average exercise price, exercisable (in USD per share)	$ 3.75
Weighted average remaining contractual term (in years), outstanding	8 years	8 years 2 months 12 days	7 years 2 months 12 days	7 years 4 months 24 days
Weighted average remaining contractual term (in years), exercisable	6 years 7 months 6 days
Aggregate intrinsic value, outstanding, beginning of period	$ 77,020	$ 15,374	$ 17,237
Aggregate intrinsic value, exercised	9,902	7,667	1,567
Aggregate intrinsic value, outstanding, end of period	277,114	$ 77,020	$ 15,374	$ 17,237
Aggregate intrinsic value, exercisable	$ 124,629

Stock-Based Compensation - Fair Value of Stock Options Assumptions (Details) - Stock options	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 years 3 months 18 days	6 years 3 months 18 days	6 years 3 months 18 days
Expected volatility, minimum	41.30%	45.20%	50.00%
Expected volatility, maximum	43.30%	47.00%	50.10%
Risk - free interest rate, minimum	2.70%	1.90%	1.10%
Risk - free interest rate, maximum	2.90%	2.40%	1.50%
Expected dividend yield	0.00%	0.00%	0.00%
Expected forfeiture rate	0.00%	0.00%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected forfeiture rate			1.40%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected forfeiture rate			5.80%

Stock-Based Compensation - Restricted Stock and Restricted Stock Units (Details) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Restricted shares
Number of Shares
Number of shares unvested, beginning of period (in shares)	1,583	0
Number of shares, granted (in shares)	0	1,583
Number of shares, vested (in shares)	(693)	0
Number of shares, forfeited (in shares)	0	0
Number of shares unvested, end of period (in shares)	890	1,583
Weighted Average Grant Date Fair Value
Weighted average grant date fair value, beginning of period (in USD per share)	$ 4.25	$ 0
Weighted average grant date fair value, granted (in USD per share)	0	4.25
Weighted average grant date fair value, vested (in USD per share)	4.25	0
Weighted average grant date fair value, forfeited (in USD per share)	0	0
Weighted average grant date fair value, end of period (in USD per share)	$ 4.25	$ 4.25
Restricted stock units
Number of Shares
Number of shares unvested, beginning of period (in shares)	0	0
Number of shares, granted (in shares)	1,200	0
Number of shares, vested (in shares)	0	0
Number of shares, forfeited (in shares)	(71)	0
Number of shares unvested, end of period (in shares)	1,129	0
Weighted Average Grant Date Fair Value
Weighted average grant date fair value, beginning of period (in USD per share)	$ 0	$ 0
Weighted average grant date fair value, granted (in USD per share)	18.75	0
Weighted average grant date fair value, vested (in USD per share)	0	0
Weighted average grant date fair value, forfeited (in USD per share)	16.27	0
Weighted average grant date fair value, end of period (in USD per share)	$ 18.90	$ 0

Stock-Based Compensation - 2018 Employee Stock Purchase Plan (Details) - Employee stock purchase plan $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of employee earnings allowed	15.00%
Discount price percentage	85.00%
Offering period (up to)	27 months
Employee contributions	$ 6.3
Common stock purchased (in shares) \| shares	0
Unrecognized stock-based compensation expense	$ 8.2
Remaining offering period	1 year 8 months 12 days

Stock-Based Compensation - Fair Value of ESPP Purchase Rights (Details) - Employee stock purchase plan	12 Months Ended
	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility, minimum	31.90%
Expected volatility, maximum	33.50%
Risk - free interest rate, minimum	2.30%
Risk - free interest rate, maximum	2.70%
Expected dividend yield	0.00%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	7 months 6 days
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	2 years 1 month 6 days

Net Loss Per Share Attributable to Common Stockholders - Computation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Net loss attributable to common stockholders	$ (19,614)	$ (20,924)	$ (17,341)	$ (16,076)	$ (11,862)	$ (11,505)	$ (9,405)	$ (9,013)	$ (73,955)	$ (41,785)	$ (37,971)
Weighted-average shares used to compute net loss per share attributable to common stockholders, basic and diluted (in shares)									53,669	22,211	20,974
Net loss per share attributable to common stockholders, basic and diluted (in usd per share)	$ (0.21)	$ (0.28)	$ (0.73)	$ (0.68)	$ (0.52)	$ (0.51)	$ (0.43)	$ (0.42)	$ (1.38)	$ (1.88)	$ (1.81)

Net Loss Per Share Attributable to Common Stockholders - Schedule of Potentially Dilutive Securities (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	21,558	71,542	64,722
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	19,219	14,573	9,336
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	1,129	0	0
Restricted shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	890	1,583	0
ESPP
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	320	0	0
Redeemable convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	0	55,386	55,386

Income Taxes - Components of Loss Before Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
U.S. income (loss)									$ 1,429	$ (29,357)	$ (40,330)
Foreign (loss) income									(72,586)	(11,494)	3,965
Total loss before income taxes	$ (18,407)	$ (20,387)	$ (16,906)	$ (15,457)	$ (11,649)	$ (11,254)	$ (9,173)	$ (8,775)	$ (71,157)	$ (40,851)	$ (36,365)

Income Taxes - Components of the Provision for Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current
Federal									$ 0	$ 140	$ (71)
State									58	6	(80)
Foreign									2,306	898	359
Total current tax expense									2,364	1,044	208
Deferred
Foreign									0	(873)	635
Total deferred tax expense (benefit)									0	(873)	635
Total provision for income taxes	$ 1,207	$ 482	$ 244	$ 431	$ 20	$ 59	$ 41	$ 51	$ 2,364	$ 171	$ 843

Income Taxes - Differences Between Federal and Effective Tax Rate (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
U.S. federal statutory tax rate	21.00%	34.00%	34.00%
State and local taxes	(1.50%)	2.40%	4.90%
Research and development tax credit	1.90%	3.00%	2.20%
Uncertain tax positions	(1.00%)	(0.20%)	0.50%
Foreign tax rate differential	(9.40%)	(4.00%)	1.40%
Transition tax	0.00%	(2.70%)	0.00%
Revaluation of U.S. deferred income taxes	0.00%	(34.50%)	0.00%
Change in valuation allowance	(12.60%)	2.70%	(43.30%)
Other	(1.70%)	(1.10%)	(2.00%)
Effective tax rate	(3.30%)	(0.40%)	(2.30%)

Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Net operating loss	$ 32,745	$ 29,227
Deferred revenue	16,488	14,327
Stock-based compensation	5,581	663
Tax credits	5,320	4,112
Leases	2,436	567
Accrued compensation	697	415
Other	68	37
Total deferred tax assets	63,335	49,348
Valuation allowance	(47,266)	(36,403)
Net deferred tax assets	16,069	12,945
Deferred tax liabilities:
Deferred commissions	(13,273)	(12,306)
Property and equipment	(2,166)	(367)
Intangible assets	(353)	0
Other	(277)	(272)
Total deferred tax liabilities	(16,069)	(12,945)
Net deferred tax liabilities	$ 0	$ 0

Income Taxes - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Income Taxes - Narrative (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Loss Carryforwards [Line Items]
Tax credits carryforwards		$ 6,800
Deferred tax assets, deferred revenue		16,488	$ 14,327
Deferred tax liabilities, capitalizing commission and fringe benefits		13,273	12,306
Unrecognized tax benefits		4,814	1,199	$ 736	$ 663
Effective tax rate impact		100	100
Reduction to deferred tax assets			14,100
One-time deemed repatriation income			$ 1,800
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards		85,900
State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards		24,100
Foreign
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards		102,300
Accounting Standards Update 2016-02
Operating Loss Carryforwards [Line Items]
Deferred tax asset, operating lease liability		1,700
Deferred tax liability, operating lease right-of-use asset		1,700
Accounting Standards Update 2014-09
Operating Loss Carryforwards [Line Items]
Valuation allowance	$ 14,700
Deferred tax assets, deferred revenue	21,000
Deferred tax liabilities, capitalizing commission and fringe benefits	$ 6,300
IPO
Operating Loss Carryforwards [Line Items]
Valuation allowance		$ 1,900

Income Taxes - Changes in Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits at the beginning of the period	$ 1,199	$ 736	$ 663
Additions for tax positions in the current year	3,571	446	233
Increase in prior year positions	102	30	0
Decrease in prior year positions	(58)	(13)	(160)
Unrecognized tax benefits at the end of the period	$ 4,814	$ 1,199	$ 736

Geographic Information - Narrative (Details) - segment	12 Months Ended
Geographic Information - Narrative (Details) - segment	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting [Abstract]
Number of operating segments	1
United States \| Revenue \| Geographic concentration risk
Concentration Risk [Line Items]
Concentration risk, percentage	67.00%	69.00%	69.00%

Geographic Information - Revenue by Geographic Region (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 75,221	$ 69,440	$ 63,592	$ 59,107	$ 54,117	$ 48,980	$ 44,149	$ 40,481	$ 267,360	$ 187,727	$ 124,371
Americas
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									191,204	138,876	92,377
Europe, Middle East and Africa
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									53,839	34,121	22,211
Asia Pacific
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									$ 22,317	$ 14,730	$ 9,783

Geographic Information - Property And Equipment, Net By Geographic Area (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Property and equipment, net	$ 11,348	$ 10,754
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Property and equipment, net	6,487	6,581
International
Revenues from External Customers and Long-Lived Assets [Line Items]
Property and equipment, net	$ 4,861	$ 4,173

Quarterly Results (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 75,221	$ 69,440	$ 63,592	$ 59,107	$ 54,117	$ 48,980	$ 44,149	$ 40,481	$ 267,360	$ 187,727	$ 124,371
Cost of revenue	12,399	12,161	9,879	8,728	8,378	7,424	5,348	4,438	43,167	25,588	14,219
Gross profit	62,822	57,279	53,713	50,379	45,739	41,556	38,801	36,043	224,193	162,139	110,152
Operating expenses:
Sales and marketing	47,380	44,550	41,826	39,588	32,784	29,574	27,773	26,168	173,344	116,299	85,736
Research and development	21,169	20,553	17,791	17,185	15,633	15,869	13,713	12,458	76,698	57,673	40,085
General and administrative	13,864	13,272	10,541	9,055	8,945	7,275	6,544	6,163	46,732	28,927	20,164
Total operating expenses	82,413	78,375	70,158	65,828	57,362	52,718	48,030	44,789	296,774	202,899	145,985
Loss from operations	(19,591)	(21,096)	(16,445)	(15,449)	(11,623)	(11,162)	(9,229)	(8,746)	(72,581)	(40,760)	(35,833)
Other income (expense), net	1,184	709	(461)	(8)	(26)	(92)	56	(29)	1,424	(91)	(532)
Total loss before income taxes	(18,407)	(20,387)	(16,906)	(15,457)	(11,649)	(11,254)	(9,173)	(8,775)	(71,157)	(40,851)	(36,365)
Provision for income taxes	1,207	482	244	431	20	59	41	51	2,364	171	843
Net loss	(19,614)	(20,869)	(17,150)	(15,888)	(11,669)	(11,313)	(9,214)	(8,826)	(73,521)	(41,022)	(37,208)
Accretion of Series A and B redeemable convertible preferred stock	0	(55)	(191)	(188)	(193)	(192)	(191)	(187)	(434)	(763)	(763)
Net loss attributable to common stockholders	$ (19,614)	$ (20,924)	$ (17,341)	$ (16,076)	$ (11,862)	$ (11,505)	$ (9,405)	$ (9,013)	$ (73,955)	$ (41,785)	$ (37,971)
Net loss per share attributable to common stockholders, basic and diluted (in usd per share)	$ (0.21)	$ (0.28)	$ (0.73)	$ (0.68)	$ (0.52)	$ (0.51)	$ (0.43)	$ (0.42)	$ (1.38)	$ (1.88)	$ (1.81)

Benefit Plans	12 Months Ended
Benefit Plans	Dec. 31, 2018
Retirement Benefits [Abstract]
Benefit Plans	Benefit PlansWe maintain a contributory defined contribution 401(k) plan for our U.S. employees. We adopted a Safe Harbor Plan effective January 1, 2016, and as a result, company-matched contributions are fully vested. Additional contributory plans are in effect internationally. Our contribution expense for such plans was $4.8 million, $3.3 million and $2.7 million in 2018, 2017 and 2016, respectively.

Business and Summary of Significant Accounting Policies - Perpetual License and Maintenance Revenue (Details) - Perpetual license and maintenance revenue	12 Months Ended
	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
License and maintenance period	1 year
Estimated maintenance renewal period	4 years
Economic life of perpetual license contracts	5 years

Business and Summary of Significant Accounting Policies - Software Development Costs (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Capitalized development costs of internal use software	$ 2.4

Business and Summary of Significant Accounting Policies - Segment Information (Details)	12 Months Ended
	Dec. 31, 2018 segment
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of operating segments	1

Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
Benefit Plans (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Contribution expense	$ 4.8	$ 3.3	$ 2.7

Label	Element	Value
Additional Paid-in Capital [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ 61,000