HubSpot (HUBS) 10-K 13 Feb 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Feb. 07, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Trading Symbol	HUBS
Entity Registrant Name	HUBSPOT INC
Entity Central Index Key	1,404,655
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		37,858,197
Entity Public Float			$ 3,304,897,251

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 87,680	$ 59,702
Short-term investments	416,663	54,648
Accounts receivable—net of allowance for doubtful accounts of $638 and $617 at December 31, 2017 and 2016, respectively	60,676	38,984
Deferred commission expense	13,343	9,025
Restricted cash	4,757	162
Prepaid hosting costs	4,964	5,299
Prepaid expenses and other current assets	14,418	8,433
Total current assets	602,501	176,253
Long-term investments	31,394	35,718
Property and equipment, net	43,294	30,201
Capitalized software development costs, net	8,760	6,523
Restricted cash	347	321
Other assets	4,617	950
Intangible assets, net	6,312	16
Goodwill	14,950	9,773
Total assets	712,175	259,755
Current liabilities:
Accounts payable	4,657	4,350
Accrued compensation costs	16,329	11,415
Other accrued expenses	20,430	16,192
Deferred revenue	136,880	95,426
Total current liabilities	178,296	127,383
Deferred rent, net of current portion	18,868	10,079
Deferred revenue, net of current portion	2,277	1,171
Other long-term liabilities	3,927	2,422
Convertible senior notes	298,447
Total liabilities	501,815	141,055
Commitments and contingencies (Note 9)
Stockholders’ equity:
Common stock, $0.001 par value—authorized, 500,000 shares; issued and outstanding, 37,503 and 35,784 at December 31, 2017 and 2016, respectively	38	36
Additional paid-in capital	496,461	365,444
Accumulated other comprehensive loss	(57)	(864)
Accumulated deficit	(286,082)	(245,916)
Total stockholders’ equity	210,360	118,700
Total liabilities and stockholders’ equity	$ 712,175	$ 259,755

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Accounts receivable, net of allowance for doubtful accounts	$ 638	$ 617
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	37,503,000	35,784,000
Common stock, shares outstanding	37,503,000	35,784,000

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue:
Subscription	$ 356,727	$ 254,775	$ 167,920
Professional services and other	18,885	16,192	14,023
Total revenue	375,612	270,967	181,943
Cost of Revenue:
Subscription	51,563	41,182	32,271
Professional services and other	24,166	20,683	15,652
Total cost of revenue	75,729	61,865	47,923
Gross profit	299,883	209,102	134,020
Operating expenses:
Research and development	70,373	45,997	32,457
Sales and marketing	212,859	162,647	112,629
General and administrative	56,787	45,120	35,408
Total operating expenses	340,019	253,764	180,494
Loss from operations	(40,136)	(44,662)	(46,474)
Other (expense) income:
Interest income	3,837	854	390
Interest expense	(13,181)	(265)	(185)
Other (expense) income	(559)	(956)	628
Total other (expense) income	(9,903)	(367)	833
Loss before income tax benefit (expense)	(50,039)	(45,029)	(45,641)
Income tax benefit (expense)	10,325	(533)	(412)
Net loss	$ (39,714)	$ (45,562)	$ (46,053)
Net loss per common share, basic and diluted	$ (1.08)	$ (1.29)	$ (1.39)
Weighted average common shares used in computing basic and diluted net loss per common share:	36,827	35,197	33,222

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (39,714)	$ (45,562)	$ (46,053)
Other comprehensive loss:
Foreign currency translation adjustments	968	(172)	(272)
Changes in unrealized (loss) gain on investments, net of income taxes of $0 in 2017, $71 in 2016, and $0 in 2015.	(161)	113	(388)
Comprehensive loss	$ (38,907)	$ (45,621)	$ (46,713)

Consolidated Statements of Com6

Consolidated Statements of Comprehensive Loss (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Changes in unrealized (loss) gain on investments, income taxes	$ 0	$ 71	$ 0

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Secondary Public Offering [Member]	Common Stock [Member]	Common Stock [Member]Secondary Public Offering [Member]	Additional Paid-In Capital [Member]	Additional Paid-In Capital [Member]Secondary Public Offering [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]
Beginning Balance, Amount at Dec. 31, 2014	$ 110,699		$ 32		$ 265,113		$ (145)	$ (154,301)
Beginning Balance, Shares at Dec. 31, 2014			31,431
Issuance of common stock under stock plans, net of shares withheld for employee taxes	2,253		$ 1		2,252
Issuance of common stock under stock plans, net of shares withheld for employee taxes, Shares			1,910
Stock-based compensation	21,800				21,800
Proceeds from secondary public offering, net of deferred offering costs		$ 33,669		$ 1		$ 33,668
Proceeds from secondary public offering, net of deferred offering costs, Shares				972
Unrealized gain (loss) on investments, net of income taxes	(388)						(388)
Cumulative translation adjustment	(272)						(272)
Net loss	(46,053)							(46,053)
Ending Balance, Amount at Dec. 31, 2015	121,708		$ 34		322,833		(805)	(200,354)
Ending Balance, Shares at Dec. 31, 2015			34,313
Issuance of common stock under stock plans, net of shares withheld for employee taxes	8,747		$ 2		8,745
Issuance of common stock under stock plans, net of shares withheld for employee taxes, Shares			1,471
Stock-based compensation	33,866				33,866
Unrealized gain (loss) on investments, net of income taxes	113						113
Cumulative translation adjustment	(172)						(172)
Net loss	(45,562)							(45,562)
Ending Balance, Amount at Dec. 31, 2016	118,700		$ 36		365,444		(864)	(245,916)
Ending Balance, Shares at Dec. 31, 2016			35,784
Issuance of common stock under stock plans, net of shares withheld for employee taxes	7,921		$ 2		7,919
Issuance of common stock under stock plans, net of shares withheld for employee taxes, Shares			1,719
Stock-based compensation	48,933				48,933
Unrealized gain (loss) on investments, net of income taxes	(161)						(161)
Cumulative adjustment from adoption of stock compensation standard					452			(452)
Cumulative translation adjustment	968						968
Equity component of 2022 Notes (Note 7)	73,713				73,713
Net loss	(39,714)							(39,714)
Ending Balance, Amount at Dec. 31, 2017	$ 210,360		$ 38		$ 496,461		$ (57)	$ (286,082)
Ending Balance, Shares at Dec. 31, 2017			37,503

Consolidated Statements of Sto8

Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Stockholders Equity [Abstract]
Unrealized gain (loss) on investments, tax	$ 0	$ 71	$ 0

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Activities:
Net loss	$ (39,714)	$ (45,562)	$ (46,053)
Adjustments to reconcile net loss to net cash and cash equivalents provided by (used in) operating activities:
Depreciation and amortization	15,786	11,177	7,343
Stock-based compensation	47,317	32,675	21,308
Deferred income tax benefit	(11,546)	(133)	(50)
Amortization of debt discount and issuance costs	12,366
(Accretion) amortization of bond discount premium	(1,576)	647	671
Non-cash rent expense	5,039	3,968	1,793
Unrealized currency translation	(139)	81	(329)
Changes in assets and liabilities
Accounts receivable	(20,180)	(14,099)	(11,249)
Prepaid expenses and other assets	(5,588)	(6,126)	(3,373)
Deferred commission expense	(4,004)	(453)	(2,119)
Accounts payable	1,100	983	(508)
Accrued expenses	8,195	4,004	7,085
Deferred rent	3,559	(107)	392
Deferred revenue	38,999	32,311	24,666
Net cash and cash equivalents provided by (used in) operating activities	49,614	19,366	(423)
Investing Activities:
Purchases of investments	(890,009)	(52,131)	(113,615)
Maturities and sales of investments	533,660	50,840	23,018
Purchases of property and equipment	(20,276)	(15,789)	(8,427)
Capitalization of software development costs	(7,071)	(5,749)	(4,314)
Acquisition of a business and purchase of technology	(9,415)		(600)
Purchase of strategic investments	(3,500)
Restricted cash	(4,586)	(128)	(166)
Net cash and cash equivalents used in investing activities	(401,197)	(22,957)	(104,104)
Financing Activities:
Proceeds from common stock offerings, net of offering costs paid of $583			33,669
Employee taxes paid related to the net share settlement of stock-based awards	(4,419)	(2,368)	(8,607)
Proceeds related to the issuance of common stock under stock plans	13,086	11,584	12,083
Proceeds from issuance of convertible notes, net of issuance costs paid of $10,767	389,233
Purchase of note hedge related to convertible notes	(78,920)
Proceeds from the issuance of warrants related to convertible notes, net of issuance costs paid of $200	58,880
Repayment of capital lease obligations	(1,054)	(743)	(206)
Net cash and cash equivalents provided by financing activities	376,806	8,473	36,939
Effect on exchange rate changes on cash and cash equivalents	2,755	(760)	(553)
Net increase (decrease) in cash and cash equivalents	27,978	4,122	(68,141)
Cash and cash equivalents, beginning of year	59,702	55,580	123,721
Cash and cash equivalents, end of year	87,680	59,702	55,580
Supplemental cash flow disclosure:
Cash paid for interest	762	174	185
Cash paid for income taxes	855	954	215
Non-cash investing and financing activities:
Property and equipment acquired under capital lease	1,039	995	847
Capital expenditures incurred but not yet paid	680	1,383	$ 435
Asset retirement obligations	$ 575	$ 561

Consolidated Statements of Ca10

Consolidated Statements of Cash Flows (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Convertible notes, issuance costs	$ 10,767
Common Stock [Member]
Offering and issuance costs paid	583
Warrant [Member]
Offering and issuance costs paid	$ 200

Organization and Operations

Organization and Operations	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Organization and Operations	1. Organization and Operations HubSpot, Inc. (the “Company”), was formed as a limited liability company in Delaware on April 4, 2005. The Company converted to a Delaware corporation on June 7, 2007. The Company provides a cloud-based inbound marketing and sales platform which features integrated applications to help businesses attract visitors to their websites, convert visitors into leads, close leads into customers and delight customers so they become promoters of those businesses. These integrated applications include social media, search engine optimization, blogging, website content management, marketing automation, email, sales productivity, CRM, analytics, and reporting.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation —The consolidated financial statements have been prepared in U.S. dollars, in accordance with accounting principles generally accepted in the United States of America (“GAAP”). The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany transactions have been eliminated in consolidation. Use of Estimates —The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expenses during the reporting period. Actual results could differ from those estimates. Operating Segments —The Company operates as one operating segment. Operating segments are defined as components of an enterprise for which separate financial information is regularly evaluated by the chief operating decision makers (“CODMs”), which are the Company’s chief executive officer and chief operating officer, in deciding how to allocate resources and assess performance. The Company’s CODMs evaluate the Company’s financial information and resources and assess the performance of these resources on a consolidated basis. Since the Company operates in one operating segment, all required financial segment information can be found in the consolidated financial statements. Loss Per Share — Basic net loss per share is computed by dividing net loss by the weighted average number of common shares outstanding for the period. Diluted net loss per share is computed by giving effect to all potential dilutive common stock equivalents outstanding for the period. For purposes of this calculation, options to purchase common stock, restricted stock units (“RSUs”), Employee Stock Purchase Plan (“ESPP”), and the Conversion Option of the 2022 Notes (Note 7) are considered to be potential common stock equivalents. A reconciliation of the denominator used in the calculation of basic and diluted loss per share is as follows: Year Ended December 31, 2017 2016 2015 (in thousands, except per share amounts) Net loss $ (39,714 ) $ (45,562 ) $ (46,053 ) Weighted-average common shares outstanding—basic 36,827 35,197 33,222 Dilutive effect of share equivalents resulting from stock options, RSUs, ESPP and the Conversion Option of the 2022 Notes — — — Weighted-average common shares outstanding-diluted 36,827 35,197 33,222 Net loss per common share, basic and diluted $ (1.08 ) $ (1.29 ) $ (1.39 ) Additionally, since the Company incurred net losses for each of the periods presented, diluted net loss per share is the same as basic net loss per share. The Company’s outstanding stock options, RSUs, ESPP, and Conversion Option of the 2022 Notes were not included in the calculation of diluted net loss per share as the effect would be anti-dilutive. The following table contains all potentially dilutive common stock equivalents. Year Ended December 31, 2017 2016 2015 (in thousands) Options to purchase common shares 2,085 2,709 3,331 RSUs 2,315 2,264 1,703 ESPP 10 11 — The Company expects to settle the principal amount of the 2022 Notes in cash, and therefore, the Company uses the treasury stock method for calculating any potential dilutive effect of the Conversion Option on diluted net income per share, if applicable. The Conversion Option will have a dilutive impact on net income per share of common stock when the average market price of the Company’s common stock for a given period exceeds the conversion price of the 2022 Notes of $94.77 per share. During the year ended December 31, 2017, the Company's weighted average common stock price was below the conversion price of the 2022 Notes. Cash and Cash Equivalents —The Company considers all highly liquid investments purchased with original maturity of three months or less to be cash equivalents. Cash and cash equivalents consist of cash held in bank deposit accounts and short-term, highly-liquid investments with remaining maturities of three months or less at the date of purchase, consisting of money-market funds. Investments — Investments consist of corporate debt securities, U.S. government agency obligations, and U.S. Treasury securities. Securities having remaining maturities of more than three months at the date of purchase and less than one year from the date of the balance sheets are classified as short-term, and those with maturities of more than one year from the date of the balance sheet are classified as long-term in the consolidated balance sheets. The Company classifies its debt investments with readily determinable market values as available-for-sale. These investments are classified as investments on the consolidated balance sheets and are carried at fair market value, with unrealized gains and losses considered to be temporary in nature reported as accumulated other comprehensive loss, a separate component of stockholders’ equity. The Company reviews all investments for reductions in fair value that are other-than-temporary. When such reductions occur, the cost of the investment is adjusted to fair value through recording a loss on investments in the consolidated statements of operations. Gains and losses on investments are calculated on the basis of specific identification. Investments are considered to be impaired when a decline in fair value below cost basis is determined to be other-than-temporary. The Company periodically evaluates whether a decline in fair value below cost basis is other-than-temporary by considering available evidence regarding these investments including, among other factors: the duration of the period that, and extent to which, the fair value is less than cost basis; the financial health of, and business outlook for the issuer, including industry and sector performance and operational and financing cash flow factors; overall market conditions and trends and the Company’s intent and ability to retain its investment in the security for a period of time sufficient to allow for an anticipated recovery in market value. Once a decline in fair value is determined to be other-than-temporary, a write-down is recorded and a new cost basis in the security is established. Strategic investments — Strategic investments consist of non-controlling equity investments in privately held companies. These investments without readily determinable fair values for which the Company does not have the ability to exercise significant influence are accounted for using the cost method of accounting. Under the cost method of accounting, the non-marketable securities are carried at cost and are adjusted only for other-than-temporary impairments, certain distributions and additional investments. Accounts Receivable and Allowance for Doubtful Accounts —Accounts receivable are carried at the original invoiced amount less an allowance for doubtful accounts based on the probability of future collection. When management becomes aware of circumstances that may decrease the likelihood of collection to a point where a receivable is no longer probable of being collected, it records an allowance against amounts due, which reduces the receivable to the amount that management reasonably believes will be collected. For all other customers, management determines the adequacy of the allowance based on historical loss patterns, the number of days that billings are past due and an evaluation of the potential risk of loss associated with specific accounts. To date, losses resulting from uncollected receivables have not exceeded management’s expectations. The following is a roll forward of the Company’s allowance for doubtful accounts (in thousands): Balance Beginning of Period Charged to Statement of Operations Deductions (1) Balance at End of Period Allowance for doubtful accounts Year ended December 31, 2017 $ 617 $ 3,353 $ (3,332 ) $ 638 Year ended December 31, 2016 $ 371 $ 2,517 $ (2,271 ) $ 617 Year ended December 31, 2015 $ 218 $ 1,367 $ (1,214 ) $ 371 (1) Deductions include actual accounts written-off, net of recoveries. Restricted Cash —The Company had restricted cash of $5.1 million at December 31, 2017 and $483 thousand at December 31, 2016 related to leased facilities. Property and Equipment —Property and equipment are stated at cost and depreciated using the straight-line method over the estimated useful lives of the related assets. Expenditures for maintenance and repairs are charged to expense as incurred, whereas major betterments are capitalized as additions to leasehold improvements. Depreciation is recorded over the following estimated useful lives: Estimated Useful Life Employee related computer equipment 2 – 3 years Computer equipment and purchased software 3 years Office equipment 5 years Furniture and fixtures 5 years Internal use software 5 years Leasehold improvements Lesser of lease Internal use software The Company capitalizes certain payroll and stock compensation costs incurred to develop functionality for certain of the Company’s internally built software platforms. The costs incurred during the preliminary stages of development are expensed as incurred. Once a piece of incremental functionality has reached the development stage certain internal costs are capitalized until the functionality is ready for its intended use. Internal use software is included within property and equipment on the balance sheet. The costs are generally amortized on a straight-line basis over an estimated useful life of approximately five years. Asset Retirement Obligations — The Company recognizes Assets Retirement Obligations (“AROs”) for any significant lease restoration obligation, if required by a lease agreement. The fair values of these AROs are recorded on a discounted basis, at the time the obligation is incurred, and accreted over time for the change in present value. Additionally, the Company capitalizes asset retirement costs by increasing the carrying amount of the related long-lived assets and depreciating these assets over their remaining useful life. The changes in these obligations during the year ending December 31, 2017 and December 31, 2016 are as follows: Year Ended December 31, 2017 2016 (in thousands) Beginning balance $ 591 $ — Additions 580 561 Accretion 46 30 Settlements (26 ) — Ending balance $ 1,191 $ 591 Impairment of Long-Lived Assets —Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable or that the useful lives of those assets are no longer appropriate. Management considers the following potential indicators of impairment of its long-lived assets (asset group): a substantial decrease in the Company’s stock price, a significant adverse change in the extent or manner in which a long-lived asset (asset group) is being used, a significant adverse change in legal factors or in the business climate that could affect the value of the long-lived asset (asset group), an accumulation of costs significantly in excess of the amount originally expected for the acquisition or construction of a long-lived asset (asset group), and a current expectation that, more likely than not, a long lived asset (asset group) will be sold or otherwise disposed of significantly before the end of its previously estimated useful life. When such events occur, the Company compares the carrying amounts of the assets to their undiscounted expected future cash flows. If this comparison indicates that there may be an impairment, the amount of the impairment is calculated as the difference between the carrying value and fair value. For the years presented, the Company did not recognize an impairment charge. Intangible Assets — Intangible assets consist acquired technology and intellectual property. We record acquired intangible assets at fair value on the date of acquisition. and amortize such assets using the straight-line method over the expected useful life of the asset. The estimated useful life of acquired technology and intellectual property is two to three years. The Company evaluates the useful lives of these assets on an annual basis and tests for impairment whenever events or changes in circumstances occur that could impact the recoverability of these assets. If the estimate of an intangible asset’s remaining useful life is changed, we amortize the remaining carrying value of the intangible asset prospectively over the revised remaining useful life. Goodwill —Goodwill represents the excess of cost over the fair value of the net tangible and identifiable intangible assets acquired in a business combination. The Company has no other intangible assets with indefinite useful lives. Goodwill is not subject to amortization, but is monitored annually for impairment or more frequently if there are indicators of impairment. Management considers the following potential indicators of impairment: significant underperformance relative to historical or projected future operating results, significant changes in the Company’s use of acquired assets or the strategy of the Company’s overall business, significant negative industry or economic trends and a significant decline in the Company’s stock price for a sustained period. The Company performs its annual impairment test on November 30. Currently, the Company’s goodwill is evaluated at the entity level as it is determined there is only one reporting unit. The Company performs a two-step impairment test. In the first step, the fair value of each reporting unit is compared to its carrying amount. If the fair value exceeds the carrying value of the net assets assigned, goodwill is not considered impaired and the second step is not required. If the carrying value exceeds the fair value, then the second step of the impairment test is performed in order to determine the implied fair value of the reporting unit’s goodwill. If the carrying value of the goodwill exceeds the fair value, then an impairment charge is recorded. On November 30, 2017, the fair value of the Company’s single reporting unit exceeded its carrying amount. Because the fair value of the Company’s single reporting unit was in excess of its carrying value and there were no indicators that the Company’s goodwill had become impaired since that date, there was no impairment as of November 30, 2017 or December 31, 2017. For the years ended December 31, 2017, 2016 and 2015, the Company did not recognize an impairment charge. Advertising Expense —The Company expenses advertising as incurred, which is included in sales and marketing expense in the accompanying consolidated statements of operations. The Company incurred $5.5 million of advertising expense in 2017, $4.2 million in 2016, and $4.9 million in 2015. Revenue Recognition —The Company primarily generates revenue from multiple-element arrangements, which typically include subscriptions to its online software solution and professional services which includes on-boarding and training services. The Company’s customers do not have the right to take possession of the online software solution. The Company recognizes revenue when all of the following have occurred: • persuasive evidence of an arrangement with the customer exists; • service has been or is being provided; • the fees are fixed or determinable; and • collectability of the fees is reasonably assured. The Company’s arrangements do not contain general rights of return. In order to treat elements in a multiple-element arrangement as separate units of accounting, the delivered elements must have standalone value and delivery of the undelivered element is probable and within control of the Company. The Company has determined that subscriptions for its online software solution have standalone value because, once a customer launches its initial site, the online software solution is fully functional and does not require any additional development, modification, or customization. Professional services consists primarily of on-boarding and web-based and in-person training, are not required to use the online software solution, and are determined to have stand-alone value from the related subscription services because they are sold separately by the Company and third parties. When multiple-element arrangements are separated into different units of accounting, the arrangement consideration is allocated to the identified separate units based on a relative selling price hierarchy. The estimated fair value of each element is determined based upon the following hierarchy: (1) vendor specific objective evidence (“VSOE”) of fair value, (2) third party evidence of selling price (“TPE”), or (3) the Company’s best estimate of selling price (“BESP”). There is not an available measure of TPE of selling price and, as such, arrangement consideration is allocated amongst multiple deliverable arrangements using VSOE, if VSOE can be established, and BESP if VSOE cannot be established. The Company establishes VSOE and BESP for each deliverable primarily considering the median or average of actual sales prices (stand-alone sales prices for VSOE) of each type of subscription and other professional services sold. The Company considers each type of subscription and service as well as pricing and geographic information when establishing VSOE and BESP. Arrangement consideration is allocated such that the revenue recognized does not exceed the fee subject to refund. Revenue from subscriptions is recognized ratably over the subscription period beginning on the date the Company’s subscription is made available to customers. Substantially all subscription contracts are one year or less. The Company recognizes revenue from on-boarding and training services as the services are provided. The Company pays its marketing and sales agency partners (“Partners”) a commission of the subscription sales price for sales to customers. The classification of the commission paid on the Company’s consolidated statements of operations depends on who is purchasing its subscription. In instances where the customer is purchasing the subscription, the Company is the primary obligor and records the commission paid to the Partners as sales and marketing expense. When the Partner purchases the subscription directly from the Company, the Company nets the consideration paid to the Partner against the associated revenue it recognizes, as in these instances the Company’s customer is the Partner and the Company’s remaining obligations are to the Partner. The Company does not believe that it receives a tangible benefit from the payment back to the Partner. Sales taxes collected from customers and remitted to government authorities are excluded from revenue. Amounts that have been invoiced are recorded in accounts receivable and deferred revenue or revenue, depending on whether the revenue recognition criteria have been met. Deferred revenue represents amounts billed for which revenue has not yet been recognized. Deferred revenue that will be recognized during the succeeding 12-month period is recorded as current deferred revenue and the remaining portion is recorded as long-term deferred revenue. Concentrations of Credit Risk and Significant Customers —Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, investments and accounts receivable. A significant portion of the Company’s cash and cash equivalents is held at four financial institutions that management believes to be of high credit quality. Although the Company deposits it cash and cash equivalents with multiple financial institutions, its deposits exceed federally insured limits. The Company’s investments consist of highly rated corporate debt securities and U.S. government agency obligations, and U.S. Treasury securities . The Company limits the amount of investments in any single issuer. The Company believes that, as of December 31, 2017, its concentration of credit risk related to investments was not significant. The Company has no significant off-balance sheet risk such as foreign exchange contracts, option contracts, or other hedging arrangements. The Company generally does not require collateral from its customers and generally requires payment 30 days from the invoice date. The Company maintains an allowance for doubtful accounts based on its assessment of the collectability of accounts receivable. Credit risk arising from accounts receivable is mitigated as a result of transacting with a large number of geographically dispersed customers spread across various industries. At December 31, 2017 and 2016 there were no customers that represented more than 10% of the net accounts receivable balance. There were no customers that individually exceeded 10% of the Company’s revenue in any of the periods presented. Foreign Currency —The functional currency of the Company’s foreign subsidiaries is the local currency. Assets and liabilities denominated in a foreign currency are translated into U.S. dollars at the exchange rates in effect at the balance sheet dates; with the resulting translation adjustments directly recorded to a separate component of accumulated other comprehensive loss. Income and expense accounts are translated at the weighted-average exchange rates during the period. Foreign currency transaction gains and losses are recorded in other income (expense). Research and Development —Research and development expenses include payroll, employee benefits and other expenses associated with product development. Capitalized Software Development Costs —Certain payroll and stock compensation costs incurred to develop functionality for the Company’s software and internally built software platforms, as well as certain upgrades and enhancements that are expected to result in increased functionality are capitalized. The costs incurred in the preliminary stages of development are expensed as incurred. Once an application has reached the development stage, certain internal costs are capitalized until the software is substantially complete and ready for its intended use. Capitalized software development costs are amortized on a straight-line basis over their estimated useful life of two to five years. Management evaluates the useful lives of these assets on a quarterly basis and tests for impairment whenever events or changes in circumstances occur that could impact the recoverability of these assets. Capitalized software development costs, exclusive of those costs recorded within property and equipment, consisted of the following: December 31, 2017 December 31, (in thousands) Gross capitalized software development costs $ 33,360 $ 25,152 Accumulated amortization (24,600 ) (18,629 ) Capitalized software development costs, net $ 8,760 $ 6,523 The Company capitalized software development costs, exclusive of costs recorded within property and equipment, of $8.2 million in 2017, $6.4 million in 2016, and $4.5 million in 2015. Stock-based compensation costs included in capitalized software were $1.6 million in 2017, $1.2 million in 2016, and $492 thousand in 2015. Amortization of capitalized software development costs, exclusive of costs recorded within property and equipment, was $6.3 million in 2017, $5.1 million in 2016, and $4.6 million in 2015. Amortization expense is included in cost of revenue in the consolidated statements of operations. Income Taxes —Deferred tax assets and liabilities are recognized for the differences between the financial statement carrying amounts and the tax bases of existing assets and liabilities using tax rates expected to be in effect in the years in which the differences are expected to reverse. Deferred tax assets are reduced by a valuation allowance if it is more likely than not that some portion or all of the deferred tax assets will not be realized. Accounting for uncertainty in income taxes recognized in the financial statements is in accordance with accounting authoritative guidance, which prescribes a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination. If the tax position is deemed “more-likely-than-not” to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50 percent likelihood of being realized upon ultimate settlement. Undistributed foreign earnings of approximately $6.9 million have been taxed in 2017 due to a one-time transition tax on previously undistributed foreign earnings. For any future foreign earnings, the Company will generally be free of additional U.S. federal tax consequences due to a dividends received deduction implemented as part of the move to a territorial tax system for foreign subsidiary earnings. Stock-Based Compensation —The Company accounts for all stock options and awards granted to employees and nonemployees using a fair value method. Stock-based compensation is recognized as an expense and is measured at the fair value of the award. The measurement date for employee awards is generally the date of the grant. The measurement date for nonemployee awards is generally the date the awards vest. Stock-based compensation costs are recognized as expense over the requisite service period, which is generally the vesting period for awards, on a straight-line basis for awards with only a service condition, and using the graded-method for awards with both a performance and service that were granted prior to our IPO, and on a straight-line basis for the awards that were granted following our IPO, which only have service conditions. Recent Accounting Pronouncements — Recent accounting standards not included below are not expected to have a material impact on our consolidated financial position and results of operations. The Company adopted updated guidance related to certain aspects of share-based payments to employees. The guidance requires the recognition of the income tax effects of awards in the income statement when the awards vest or are settled, thus eliminating additional paid-in capital pools. As a result of the adoption, we recorded an increase to deferred tax assets with a corresponding increase to the valuation allowance of $30.4 million to recognize net operating loss carryforwards attributable to excess tax benefits on stock compensation that had not been previously recognized as additional paid-in capital. In addition, the Company changed its policy election to account for forfeitures as they occur rather than on an estimated basis. The change in the policy election related to forfeitures resulted in the Company reclassifying $452 thousand from additional paid-in capital to accumulative deficit for the net cumulative-effect adjustment in stock compensation expense related to prior periods. In January 2017, the Financial Accounting Standards Board (“FASB”) In January 2017, the FASB issued guidance simplifying the accounting for goodwill impairment by removing Step 2 of the goodwill impairment test. Under current guidance, Step 2 of the goodwill impairment test requires entities to calculate the implied fair value of goodwill in the same manner as the amount of goodwill recognized in a business combination by assigning the fair value of a reporting unit to all of the assets and liabilities of the reporting unit. The carrying value in excess of the implied fair value is recognized as goodwill impairment. Under the new standard, goodwill impairment is recognized based on Step 1 of the current guidance, which calculates the carrying value in excess of the reporting unit’s fair value. The new standard is effective beginning in January 2020, with early adoption permitted. We do not believe the adoption of this guidance will have a material impact on our consolidated financial statements. In November 2016, the FASB issued guidance related to the presentation of restricted cash within the statement of cash flows. The guidance requires entities to show the changes in cash, cash equivalents, and restricted cash in the statement of cash flows. Entities will no longer present transfers between cash and cash equivalents and restricted cash in the statement of cash flows. As of December 31, 2017, we had $5.1 million in restricted cash. The new standard is effective beginning in the first quarter of 2018, with early adoption permitted. The impact of including restricted cash with cash and cash equivalents when reconciling the beginning-of-year and end-of-year total amounts presented on the consolidated statement of cash flows would increase net cash flows for the year ended December 31, 2017 by approximately $4.6 million. In February 2016, the FASB issued guidance that requires lessees to recognize most leases on their balance sheets but record expenses on their income statements in a manner similar to current accounting. For lessors, the guidance modifies the classification criteria and the accounting for sales-type and direct financing leases. The guidance is effective in 2019 with early adoption permitted. The Company is currently evaluating the impact of this guidance on the consolidated financial statements. In June 2016, the FASB issued guidance that introduces a new methodology for accounting for credit losses on financial instruments, including available-for-sale debt securities. The guidance establishes a new "expected loss model" that requires entities to estimate current expected credit losses on financial instruments by using all practical and relevant information. Any expected credit losses are to be reflected as allowances rather than reductions in the amortized cost of available-for-sale debt securities. This guidance will be effective for the Company on January 1, 2020. The Company is currently evaluating the impact of this guidance on the consolidated financial statements. In May 2014, the FASB issued updated guidance and disclosure requirements for recognizing revenue. The new revenue recognition standard provides a five-step analysis of transactions to determine when and how revenue is recognized. The core principle is that a company should recognize revenue 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. The standard also provides guidance on the recognition of costs related to obtaining customer contracts. The new standard is effective for the Company for its annual reporting periods beginning January 1, 2018. The Company will adopt the standard on January 1, 2018, using the modified retrospective method, which will result in a cumulative effect adjustment as of the date of adoption. The Company established a team that has assessed the impact of the standard including the timing of revenue recognition and the accounting for deferred commission costs and related balances. The Company has determined that there will be a change to the period over which sales commissions will be amortized to incorporate an estimated customer life and the amortization period over which internally developed new features and increased functionality for our software platform is recorded, in addition to the initial contract period. This will result in a longer amortization period for deferred sales commissions, which will reduce the expense in any one period compared to today. There will also be a change to the scope of capitalized sales commissions based on the definition of incremental costs of obtaining a contract. This will result in a higher capitalized commissions balance upon adoption. In addition, there will be a change in relation to the timing of revenue recognition for certain sales contracts, where free or discounted services are bundled with our subscription offering due primarily to the removal of the current limitation on contingent revenue. This will accelerate revenue recognition on these contracts when these services are provided up front as compared to today. The change in the period over which sales commissions will be amortized will have a material impact to the consolidated financial statements and disclosures. The change in the timing of revenue recognition for certain sales contracts, where free or discounted services are bundled with our subscription offering, will not have a material impact to the con

Fair Value of Financial Instrum

Fair Value of Financial Instruments	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	3. Fair Value of Financial Instruments The Company measures certain financial assets at fair value. Fair value is determined based upon the exit price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants, as determined by either the principal market or the most advantageous market. Inputs used in the valuation techniques to derive fair values are classified based on a three-level hierarchy, as follows: Level 1 — Quoted prices in active markets for identical assets or liabilities. Level 2 — Observable inputs other than Level 1 prices such as quoted prices for similar assets or liabilities; quoted prices in markets with insufficient volume or infrequent transactions (less active markets); or model-derived valuations in which all significant inputs are observable or can be derived principally from or corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 — Unobservable inputs to the valuation methodology that are significant to the measurement of fair value of assets or liabilities. The following table details the fair value measurements within the fair value hierarchy of the Company’s financial assets and liabilities at December 31, 2017 and December 31, 2016: December 31, 2017 Level 1 Level 2 Level 3 Total (in thousands) Cash equivalents and investments: Money market funds $ 12,845 $ — $ — $ 12,845 Commercial paper — 5,867 — 5,867 Corporate bonds — 81,668 — 81,668 U.S. government agency obligations — 3,987 — 3,987 U.S. Treasury securities — 356,535 — 356,535 Restricted cash: Certificates of deposit — 5,105 — 5,105 Total $ 12,845 $ 453,162 $ — $ 466,007 December 31, 2016 Level 1 Level 2 Level 3 Total (in thousands) Cash equivalents and investments: Money market funds $ 32,260 $ — $ — $ 32,260 Commercial paper — 12,439 — 12,439 Corporate bonds — 66,947 — 66,947 U.S. government agency obligations — 10,980 — 10,980 Total $ 32,260 $ 90,366 $ — $ 122,626 The Company considers all highly liquid investments purchased with a remaining maturity of three months or less to be cash equivalents. The fair value of the Company’s investments in certain money market funds is their face value and such instruments are classified as Level 1 and are included in cash and cash equivalents on the consolidated balance sheets. At December 31, 2017 and December 31, 2016, our Level 2 securities were priced by pricing vendors. These pricing vendors utilize the most recent observable market information in pricing these securities or, if specific prices are not available for these securities, use other observable inputs like market transactions involving identical or comparable securities. As of December 31, 2017, the fair value of the 2022 Notes (Note 7) was $460.0 million. The fair value was determined based on the quoted price of the 2022 Notes in an inactive market on the last trading day of the reporting period and has been classified as Level 2 within the fair value hierarchy. For certain other financial instruments, including accounts receivable, accounts payable, capital leases and other current liabilities, the carrying amounts approximate their fair value due to the relatively short maturity of these balances. Restricted cash is comprised of certificates of deposit related to landlord guarantees for our leased facilities. These restricted cash balances have been excluded from our cash and cash equivalents balance on our consolidated balance sheets. Strategic investments consist of non-controlling equity investments in privately held companies. These investments without readily determinable fair values for which the Company does not have the ability to exercise significant influence are accounted for using the cost method of accounting. Under the cost method of accounting, the non-marketable securities are carried at cost and are adjusted only for other-than-temporary impairments, certain distributions and additional investments. These investments are valued using significant unobservable inputs or data in an inactive market and the valuation requires the Company's judgment due to the absence of market prices and inherent lack of liquidity. The estimated fair value is based on quantitative and qualitative factors including, but not limited to, subsequent financing activities by the investee and projected discounted cash flows. Fair value is not estimated for non-marketable equity securities if there are no identified events or changes in circumstances that may have an effect on the fair value of the investment. The carrying value of the strategic investments was $3.5 million at December 31, 2017 and $0 at December 31, 2016. Strategic investments are included with other assets on the consolidated balance sheets. The following tables summarize the composition of our short- and long-term investments at December 31, 2017 and 2016: December 31, 2017 Amortized Cost Unrealized Gains Unrealized Losses Aggregate Fair Value (in thousands) Commercial paper $ 5,874 $ — $ (7 ) $ 5,867 Corporate bonds 81,947 — (279 ) 81,668 U.S. government agency obligations 4,000 — (13 ) 3,987 U.S. Treasury securities 356,671 8 (144 ) 356,535 Total $ 448,492 $ 8 $ (443 ) $ 448,057 December 31, 2016 Amortized Cost Unrealized Gains Unrealized Losses Aggregate Fair Value (in thousands) Commercial paper $ 12,446 $ — $ (7 ) $ 12,439 Corporate bonds 67,126 — (179 ) 66,947 U.S. government agency obligations 10,998 — (18 ) 10,980 Total $ 90,570 $ — $ (204 ) $ 90,366 For all of our securities for which the amortized cost basis was greater than the fair value at December 31, 2017 and 2016, the Company has concluded that there is no plan to sell the security nor is it more likely than not that the Company would be required to sell the security before its anticipated recovery. In making the determination as to whether the unrealized loss is other-than-temporary, the Company considered the length of time and extent the investment has been in an unrealized loss position, the financial condition and near-term prospects of the issuers, the issuers’ credit rating and the time to maturity. Contractual Maturities The contractual maturities of short-term and long-term investments held at December 31, 2017 and 2016 are as follows: December 31, 2017 December 31, 2016 Amortized Cost Basis Aggregate Fair Value Amortized Cost Basis Aggregate Fair Value (in thousands) Due within one year $ 416,932 $ 416,663 $ 54,694 $ 54,648 Due after 1 year through 2 years 31,560 31,394 35,876 35,718 Total $ 448,492 $ 448,057 $ 90,570 $ 90,366

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2017
Property Plant And Equipment [Abstract]
Property and Equipment	4. Property and Equipment Property and equipment as of December 31, 2017 and December 31, 2016 consists of the following: December 31. 2017 2016 (in thousands) Computer equipment & purchased software $ 4,571 $ 3,237 Employee computer equipment 4,260 1,534 Furniture and fixtures 11,083 8,174 Office equipment 2,620 2,326 Leasehold improvements 33,446 23,693 Equipment under capital lease 3,450 2,412 Internal-use software 2,892 1,301 Construction in progress 3,198 322 Total property and equipment 65,520 42,999 Less accumulated depreciation (22,226 ) (12,798 ) Property and equipment, net $ 43,294 $ 30,201 Depreciation and amortization expense was $9.4 million in 2017, $5.9 million in 2016, and $2.7 million in 2015. Accumulated depreciation for equipment under capital lease was $2.4 million as of December 31, 2017 and $1.2 million as of December 31, 2016. The Company capitalized asset retirement costs of $1.1 million at December 31, 2017 and $561 thousand at December 31, 2016 within leasehold improvements on the consolidated balance sheets, and recorded the related liability to other long-term liabilities. These costs represent future lease restoration obligations as required by Company’s leases.

Business Acquisition and Purcha

Business Acquisition and Purchase of Technology	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Business Acquisition and Purchase of Technology	5. Business Acquisition and Purchase of Technology On September 20, 2017, the Company acquired 100% of the equity interests of Motion AI, Inc., a Delaware technology corporation that allows users to scale one-to-one communications. The acquisition strengthens the Company’s position in the one-to-one communication space. Under the terms of the purchase agreement, the Company paid $9.0 million. The excess of the purchase consideration over the fair value of net tangible and identifiable intangible assets and liabilities acquired was recorded as goodwill and is primarily attributable to expanded market opportunities. The goodwill recognized is not deductible for U.S. income tax purposes. The fair values assigned to tangible and identifiable intangible assets acquired and liabilities assumed as part of the business combination were determined based on the replacement costs and present value of expected after-tax cash flows attributable to the business which were derived from management’s estimates and assumptions. The sole intangible asset acquired in the business combination was developed technology and the estimate of fair value of the developed technology was determined using a replacement cost approach and the useful life of the technology was estimated to be two years. The Company will begin amortizing the acquired technology when the technology is placed in use, which is expected to be 2018. The acquired technology will be amortized over its useful life of two year. The amortization expense will be recorded to cost of subscription revenue in the consolidated statements of operations. The preliminary allocation of the purchase price to the estimated fair value of acquired assets and assumed liabilities is $32 thousand of tangible assets, $6.0 million of acquired technology, and $5.2 million of goodwill. As part of the purchase price allocation, the Company recorded a deferred tax benefit of $2.2 million from a partial release of its deferred tax asset valuation allowance. The net deferred tax liability from this acquisition provided a source of additional income to support the realizability of the Company’s pre-existing deferred tax assets and as a result, the Company released a portion of its valuation allowance. Lastly, there was approximately $4.0 million of potential consideration that was not included in the purchase price allocation as it is not associated with pre-combination services. If earned, this will be recorded in the consolidated statement of operations over a period of approximately three years. The Company has included the operating results of the business combination in its consolidated financial statements since the date of the acquisition. The acquisition did not have a material effect on the revenue or earnings in the consolidated income statement for the reporting periods presented. The pro forma results of the Company as if the acquisition had taken place on the first day of 2016 were not materially different from the amounts reflected in the accompanying consolidated financial statements. During the third quarter of 2017 the Company also acquired technology for $400 thousand. The estimated useful life of the acquired technology is two years.

Intangible Assets

Intangible Assets	12 Months Ended
	Dec. 31, 2017
Goodwill And Intangible Assets Disclosure [Abstract]
Intangible Assets	6. Intangible Assets Intangible assets as of December 31, 2017 and 2016 consist of the following: Weighted Average Remaining Useful Life December 31, 2017 2016 (in thousands) Acquired technology 19 Months $ 7,252 $ 852 Acquired intellectual property — 80 80 Accumulated amortization (1,020 ) (916 ) Total $ 6,312 $ 16 The estimated useful life of acquired technology and intellectual property is two to three years. The Company evaluates the useful lives of these assets on an annual basis and tests for impairment whenever events or changes in circumstances occur that could impact the recoverability of these assets. Amortization expense related to intangible assets was $103 thousand in 2017, $84 thousand in 2016, and $96 thousand in 2015. Amortization expense of acquired technology is included in cost of subscription revenue in the consolidated statements of operations. Amortization expense of acquired intellectual property is included in sales and marketing expense in the consolidated statements of operations. Estimated future amortization expense for intangible assets, currently being amortized, as of December 31, 2017 is as follows: Years ended December 31, Amortization Expense (in thousands) 2018 200 2019 112 Total $ 312 The estimated amortization does not include the amortization of the $6.0 million of acquired technology from the acquisition of Motion AI, Inc. as the intangible asset has not been placed into service as of December 31, 2017. The Company expects that the acquired technology will be placed into service during 2018 and will be amortized through 2020.

0.25% Convertible Senior Notes,

0.25% Convertible Senior Notes, Convertible Note Hedge and Warrant	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
0.25% Convertible Senior Notes, Convertible Note Hedge and Warrant	7. 0.25% Convertible Senior Notes, Convertible Note Hedge and Warrant In May 2017, the Company issued $350 million aggregate principal amount of 0.25% convertible senior notes due June 1, 2022 (the “Maturity Date”) in a private offering and an additional $50 million aggregate principal amount of such notes pursuant to the exercise in full of the over-allotment options of the initial purchasers (the “2022 Notes”). The interest rates are fixed at 0.25% per annum and are payable semi-annually in arrears on June 1 and December 1 of each year, commencing on December 1, 2017. The total net proceeds from the debt offering, after deducting initial purchase discounts and debt issuance costs, were approximately $389.2 million. Each $1,000 principal amount of the 2022 Notes will initially be convertible into 10.5519 shares of the Company’s common stock (the “Conversion Option”), which is equivalent to an initial conversion price of approximately $94.77 per share, subject to adjustment upon the occurrence of specified events. The 2022 Notes will be convertible at the option of the holders at any time prior to the close of business on the business day immediately preceding February 1, 2022, only under the following circumstances: (1) during any calendar quarter commencing after the calendar quarter ending on June 30, 2017, if the last reported sale price of the Company’s common stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price on each applicable trading day; (2) during the five business day period after any five consecutive trading day period (the “Measurement Period”) in which the trading price per $1,000 principal amount of notes for each trading day of the Measurement Period was less than 98% of the product of the last reported sale price of the Company’s common stock and the conversion rate on each such trading day; or (3) upon the occurrence of specified corporate events. On or after February 1, 2022 until the close of business on the second scheduled trading day immediately preceding the Maturity Date, holders may convert their 2022 Notes at any time, regardless of the foregoing circumstances. Upon conversion, the Company will pay or deliver, as the case may be, cash, shares of the Company’s common stock or a combination of cash and shares of the Company’s common stock, at the Company’s election. If the Company undergoes a fundamental change prior to the maturity date, holders of the notes may require the Company to repurchase for cash all or any portion of their notes at a repurchase price equal to 100% of the principal amount of the notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date. In addition, if specific corporate events occur prior to the applicable maturity date, the Company will increase the conversion rate for a holder who elects to convert their notes in connection with such a corporate event in certain circumstances. During the year ended December 31, 2017, the conditions allowing holders of the 2022 Notes to convert have not been met. The 2022 Notes are therefore not convertible during the year ended December 31, 2017 and are classified as long-term debt. In accounting for the issuance of the convertible senior notes, the Company separated the 2022 Notes into liability and equity components. The carrying amount of the liability component was calculated by measuring the fair value of a similar debt instrument that does not have an associated convertible feature. The carrying amount of the equity component representing the Conversion Option was $106 million and was determined by deducting the fair value of the liability component from the par value of the 2022 Notes. The equity component is not remeasured as long as it continues to meet the conditions for equity classification. The excess of the principal amount of the liability component over its carrying amount (the "Debt Discount") is amortized to interest expense over the term of the 2022 Notes expense at an effective interest rate of 6.95% over the contractual term of the 2022 Notes. In accounting for the debt issuance costs of $10.8 million related to the 2022 Notes, the Company allocated the total amount incurred to the liability and equity components of the 2022 Notes based on their relative values. Issuance costs attributable to the liability component were $7.9 million and will be amortized to interest expense using the effective interest method over the contractual terms of the 2022 Notes. Issuance costs attributable to the equity component were $2.9 million and are netted with the equity component in stockholders’ equity. The net carrying amount of the liability component of the 2022 Notes is as follows: As of December 31, 2017 As of December 31, 2016 (in thousands) Principal $ 400,000 $ — Unamortized debt discount (94,498 ) — Unamortized issuance costs (7,055 ) — Net carrying amount $ 298,447 $ — The net carrying amount of the equity component of the 2022 Notes is as follows: As of December 31, 2017 As of December 31, 2016 (in thousands) Debt discount for conversion option $ 106,006 — Issuance costs (2,854 ) — Net carrying amount $ 103,152 $ — Interest expense related to the 2022 Notes is as follows: Year Ended December 31, 2017 2016 2015 (in thousands) Contractual interest expense $ 639 $ — $ — Amortization of debt discount 859 — — Amortization of issuance costs 11,507 — — Total interest expense $ 13,005 $ — $ — In connection with the offering of the 2022 Notes, the Company entered into convertible note hedge transactions (the “Convertible Note Hedges”) with certain counterparties in which the Company has the option to purchase (subject to adjustment for certain specified events) a total of approximately 4.2 million shares of the Company’s common stock at a price of approximately $94.77 per share. The Convertible Note Hedges will be settled in cash or shares, or any combination thereof, in accordance with the settlement method of the 2022 Notes in excess of the par amount, and are expected to settle upon conversion of the 2022 Notes. The total cost of the Convertible Note Hedges was $78.9 million. In addition, the Company sold warrants to certain bank counterparties whereby the holders of the warrants have the option to purchase initially (subject to adjustment for certain specified events) a total of approximately 4.2 million shares of the Company’s common stock at a price of $115.8 per share. The amount by which the settlement price exceeds the strike price may be settled in shares or cash at the Company’s election. The warrants are expected to settle three business days from each trading day commencing on September 1, 2022 and ending on the 79th trading day thereafter. The Company received $58.9 million in cash proceeds, net of issuance costs of $200 thousand, from the sale of these warrants. Taken together, the purchase of the Convertible Note Hedges and the sale of warrants are intended to offset any actual dilution from the conversion of these notes and to effectively increase the overall conversion price from $94.77 to $115.83 per share. As these transactions meet certain accounting criteria, the Convertible Note Hedges and warrants are recorded in stockholders’ equity and are not accounted for as derivatives. The net cost of $20 million incurred in connection with the Convertible Note Hedges and warrant transactions was recorded as a reduction to additional paid-in capital on the consolidated balance sheet. The difference between the Debt Discount and the total cost of the Convertible Note Hedges, and the difference between the calculation of the book and tax allocation of debt issuance costs between the liability and equity components of the 2022 Notes, resulted in a difference between the carrying amount and tax basis of the 2022 Notes. This taxable temporary difference resulted in the Company recognizing a $9.4 million deferred tax liability which was recorded as an adjustment to additional paid-in capital on the consolidated balance sheet. The creation of the deferred tax liability is recognized as a component of equity and represents a source of future taxable income which supports realization of a portion of the income tax benefit associated with the 2017 loss from operations. Therefore, the Company recorded a corresponding income tax benefit in its consolidated statement of operations in 2017. The net equity impact, included in additional paid-in capital, of the above components of the 2022 Notes is as follows: (in thousands) Conversion Option $ 106,006 Purchase of Convertible Note Hedges (78,920 ) Sales of warrants 59,080 Issuance costs (3,054 ) Deferred tax liability (9,399 ) Total $ 73,713

Geographic Data

Geographic Data	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Geographic Data	8. Geographic Data As more fully described in the Company’s Summary of Significant Accounting Policies, the Company operates in one operating segment. Revenue and long-lived assets by geographic region, based on physical location of the operations recording the sale or the assets are as follows: Revenues by geographical region: Year Ended December 31, 2017 2016 2015 (In thousands) Americas $ 283,696 $ 219,422 $ 154,625 Europe 70,895 41,616 23,487 Asia Pacific 21,021 9,929 3,831 Total $ 375,612 $ 270,967 $ 181,943 Percentage of revenues generated outside of the Americas 24 % 19 % 15 % In 2017, revenue derived from customers outside the United States (international) was approximately 33% of total revenue. In 2016, revenue derived from customers outside the United States (international) was approximately 28% of total revenue. Total long-lived assets by geographical region: As of December 31, 2017 As of December 31, 2016 (In thousands) Americas $ 29,764 $ 23,205 Europe 11,257 4,716 Asia Pacific 2,273 2,280 Total long lived assets $ 43,294 $ 30,201 Percentage of long lived assets held outside of the Americas 31 % 23 %

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	9. Commitments and Contingencies The Company leases its office facilities under non-cancelable operating leases that expire at various dates through October 2027. Rent expense for non-cancellable operating leases with free rental periods or scheduled rent increases is recognized on a straight-line basis over the terms of the leases. Certain leases contain optional termination dates. The table below only includes payments up to the optional termination date. If the Company were to extended leases beyond the optional termination date the future commitments would increase by approximately $31.6 million. Improvement reimbursements from landlords of $7.3 million are being amortized on a straight-line basis into rent expense over the terms of the leases. The difference between required lease payments and rent expense has been recorded as deferred rent. Rent expense was $18.9 million in 2017, $13.8 million in 2016, and $7.4 million in 2015. Deferred rent was $19.0 million as of December 31, 2017 and $10.2 million as of December 31, 2016. Future minimum payments under all operating and capital lease agreements as of December 31, 2017, are as follows: Operating Capital (in thousands) 2018 $ 19,345 $ 771 2019 19,752 290 2020 19,997 30 2021 21,433 — 2022 21,729 — Thereafter 99,644 — Total $ 201,900 1,091 Less: Portion representing interest (34 ) Capital lease obligation $ 1,057 In January 2018, the Company entered into a new 18 year property lease in Dublin, Ireland, with an option to break the lease after 10 years, for approximately 13,000 square feet of space. The lease commenced in January 2018 and the Company will pay an aggregate of approximately $8.5 million in rent over the initial 10 year lease period. The Company has entered into certain non-cancelable arrangements (“Vendor Commitments”), which require the future purchase of goods or services. Future minimum payments under all Vendor Commitments as of December 31, 2017, are as follows: Product related obligations INBOUND event obligations (in thousands) 2018 15,852 475 2019 10,826 316 2020 1,500 316 2021 — 653 2022 — 653 Thereafter — 653 Total $ 28,178 $ 3,066 Legal Contingencies From time to time the Company may become involved in legal proceedings or be subject to claims arising in the ordinary course of its business. Although the results of litigation and claims cannot be predicted with certainty, the Company currently believes that the final outcome of these ordinary course matters will not have a material adverse effect on its business, operating results, financial condition or cash flows. Regardless of the outcome, litigation can have an adverse impact on the Company because of defense and settlement costs, diversion of management resources and other factors.

Changes in Accumulated Other Co

Changes in Accumulated Other Comprehensive Loss	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Changes in Accumulated Other Comprehensive Loss	10. Changes in Accumulated Other Comprehensive Loss The following table summarizes the changes in accumulated other comprehensive loss, which is reported as a component of stockholders’ equity, for the years ended December 31, 2017 and 2016: Cumulative Translation Adjustment Unrealized L on Investments Total (in thousands) Beginning balance at January 1, 2016 $ (417 ) $ (388 ) $ (805 ) Other comprehensive (loss) income before reclassifications (172 ) 113 (59 ) Amounts reclassified from accumulated other comprehensive loss — — — Ending balance at December 31, 2016 $ (589 ) $ (275 ) $ (864 ) Other comprehensive income (loss) before reclassifications 968 (161 ) 807 Amounts reclassified from accumulated other comprehensive loss — — — Ending balance at December 31, 2017 $ 379 $ (436 ) $ (57 )

Stockholders' Equity and Stock-

Stockholders' Equity and Stock-Based Compensation	12 Months Ended
	Dec. 31, 2017
Stockholders Equity And Stock Based Compensation [Abstract]
Stockholders' Equity and Stock-Based Compensation	11. Stockholders’ Equity and Stock-Based Compensation Common Stock Reserved —As of December 31, 2017 and 2016, the Company has authorized 500 million shares of common stock. The number of shares of common stock reserved for the vesting of RSUs, exercise of common stock options, and ESPP are as follows (in thousands): December 31, 2017 December 31, 2016 RSUs 2,085 2,264 Common stock options 2,315 2,709 ESPP 10 11 4,410 4,984 Equity Incentive Plan —The Company’s 2007 Equity Incentive Plan (the “2007 Plan”) was terminated in connection with the IPO, and accordingly, no shares are available for issuance under the 2007 Plan. The 2007 Plan will continue to govern outstanding awards granted thereunder, The 2007 Plan provided for the grant of qualified incentive stock options and nonqualified stock options or other awards such as RSUs to the Company’s employees, officers, directors and outside consultants. The term of each option is fixed by the Company’s compensation committee and may not exceed 10 years from the date of grant. As of December 31, 2017, 1.7 million options to purchase common stock and 49 thousand RSUs remained outstanding under the 2007 Plan. On September 25, 2014, the Company’s board of directors adopted and the Company’s stockholders approved the 2014 Stock Option and Incentive Plan (the “2014 Plan”). The 2014 Plan became effective upon the closing of the Company’s IPO. The Company initially reserved 1,973,551 shares of its common stock, or the Initial Limit, for the issuance of awards under the 2014 Plan. The 2014 Plan provides that the number of shares reserved and available for issuance under the plan automatically increases each January 1, beginning on January 1, 2015, by 5% of the outstanding number of shares of the Company’s common stock on the immediately preceding December 31 or such lesser number of shares as determined by the compensation committee. This number is subject to adjustment in the event of a stock split, stock dividend or other change in the Company’s capitalization. The term of each option is fixed by the Company’s compensation committee and may not exceed 10 years from the date of grant. As of December 31, 2017, 582 thousand options to purchase common stock and 2.0 million RSUs remained outstanding under the 2014 Plan. Equity Compensation Expense —The Company’s equity compensation expense is comprised of awards of options to purchase common stock, RSUs, and stock issued under the Company’s ESPP. The following two tables show stock compensation expense by award type and where the stock compensation expense is recorded in the Company’s consolidated statements of operations: Year Ended December 31, 2017 2016 2015 (in thousands) Options $ 4,948 $ 5,202 $ 6,349 ESPP 1,233 1,093 1,035 RSUs 41,136 26,380 13,924 Total stock-based compensation $ 47,317 $ 32,675 $ 21,308 2017 2016 2015 (in thousands) Cost of revenue, subscription $ 658 $ 512 $ 341 Cost of revenue, service 2,327 1,640 1,216 Research and development 12,816 8,828 6,327 Sales and marketing 19,016 13,352 7,658 General and administrative 12,500 8,343 5,766 Total stock-based compensation $ 47,317 $ 32,675 $ 21,308 Excluded from stock-based compensation expense is $1.6 million of capitalized software development costs in 2017, $1.2 million in 2016, and $492 thousand in 2015. Stock Options —The fair value of employee options is estimated on the date of each grant using the Black-Scholes option-pricing model with the following assumptions: Year Ended December 31, 2017 2016 2015 Risk-free interest rate (%) 1.74-2.09 1.38 - 1.41 1.36 - 1.53 Expected term (years) 5.18-6.21 5.08 - 6.21 6.18 - 6.22 Volatility (%) 39.4-43.7 38.0 - 41.0 43.0 - 51.6 Expected dividends — — — The weighted-average grant-date fair value of options granted was $24.56 per share in 2017, $16.97 per share in 2016, and $16.53 per share in 2015. The interest rate was based on the U.S. Treasury bond rate at the date of grant with a maturity approximately equal to the expected term. The expected term of options granted to employees was calculated using the simplified method, which represents the average of the contractual term of the option and the weighted-average vesting period of the option. The expected term of options granted to nonemployees is equal to the remaining contractual term as of the measurement date. Expected volatility for the Company’s common stock was based on an average of the historical volatility of a peer group of similar public companies. The assumed dividend yield is based upon the Company’s expectation of not paying dividends in the foreseeable future. Forfeitures of share-based awards prior to vesting results in a reversal of previously recorded stock-compensation expense associated with such forfeited awards Prior to the Company’s IPO, the fair value of the Company’s common stock was determined by the Board of Directors at each award grant date based upon a variety of factors, including the results obtained from independent third-party valuations, the Company’s financial position and historical financial performance, the status of technological developments within the Company’s products, the composition and ability of the engineering and management team, an evaluation of benchmark of the Company’s competition, the climate in the marketplace, the illiquid nature of the common stock, arm’s-length sales of the Company’s capital stock (including redeemable convertible preferred stock), the effect of the rights and preferences of the preferred stockholders and the prospects of a liquidity event, among others. After the Company’s IPO, the fair value of the Company’s common stock is the closing price of the stock on the date of grant. The stock option activity for the year ended December 31, 2017 is as follows: Options (in thousands) Weighted- Average Exercise Price Weighted- Average Remaining Life (in years) Aggregate Intrinsic Value (in thousands) Outstanding—January 1, 2017 2,709 $ 13.99 6.1 $ 89,411 Granted 180 56.67 Exercised (543 ) 16.07 Forfeited/expired (31 ) 24.12 Outstanding—December 31, 2017 2,315 16.69 5.3 $ 165,974 Options vested or expected to vest—December 31, 2017 2,315 $ 16.69 5.3 $ 165,974 Options exercisable—December 31, 2017 1,945 $ 11.39 4.8 $ 149,803 Total unrecognized compensation cost related to the nonvested options was $5.4 million at December 31, 2017. That cost is expected to be recognized over a weighted-average period of 2.2 years as of December 31, 2017. Restricted Stock Units —RSUs vest upon achievement of a service condition and, prior to six months after the Company’s IPO, a performance condition. As soon as practicable following each vesting date, the Company will issue to the holder of the RSUs the number of shares of common stock equal to the aggregate number of RSUs that have vested. Notwithstanding the foregoing, the Company may, in its sole discretion, in lieu of issuing shares of common stock to the holder of the RSUs, pay the holder an amount in cash equal to the fair market value of such shares of common stock. The service condition is a time-based condition met over a period of four years, with 25% met after one year, and then in equal monthly or quarterly installments over the succeeding three years, or over a period of four years, with equal quarterly installments over those four years. The performance condition was met six months following the Company’s IPO. Upon completion of the Company’s IPO the Company began recording stock-based compensation expense based on the grant-date fair value of the RSUs using the accelerated attribution method for RSUs granted prior to its IPO and using the straight-line method for RSUs granted following its IPO. The total stock-based compensation expense expected to be recorded over the remaining life of outstanding RSUs is approximately $102.3 million at December 31, 2017. That cost is expected to be recognized over a weighted-average period of 2.7 years as of December 31, 2017. As of December 31, 2017, there are 2.1 million RSUs expected to vest with an aggregate intrinsic value of $184.1million. The total fair value of RSUs vested was approximately $48.6 million in the year ended December 31, 2017, $24.0 million in the year ended December 31, 2016, and $11.9 million in the year ended December 31, 2015. The following table summarizes the activity related to RSUs for the year ended December 31, 2017: RSUs Outstanding Shares (in thousands) Weighted- Average Grant Date Fair Value Per Share Unvested and outstanding at January 1, 2017 2,264 $ 42.04 Granted 1,189 64.59 Vested (1,151 ) 42.24 Canceled (217 ) 48.13 Unvested and outstanding at December 31, 2017 2,085 $ 54.12

Employee Stock Purchase Plan

Employee Stock Purchase Plan	12 Months Ended
	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Employee Stock Purchase Plan	12. Employee Stock Purchase Plan On September 25, 2014, the Company’s board of directors adopted and the Company’s stockholders approved the 2014 Employee Share Purchase Plan (the “ESPP”). The ESPP became effective upon the closing of the Company’s IPO. The ESPP authorizes the issuance of up to a total of 1,409,988 shares of common stock to participating employees, and allows eligible employees to purchase shares of common stock at a 15% discount from the fair market value of the stock as determined on specific dates at six-month intervals. The offering periods generally start on the first trading day on or after January 1st and July 1st of each year. In December 2017, the Company’s board of directors amended and restated the ESPP. In conjunction with the amendment of the ESPP, the Company amended the offering periods, which will now commence on June 1 and November 1 of each year starting with the offering period beginning with offering period in June 2018. The following table summarizes the activity related to ESPP: Shares Issued (in thousands) Weighted- Average Purchase Price Total Cash Proceeds (in thousands) 2017 94 38.83 3,635 2016 70 38.98 2,721 2015 29 28.46 814

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	13. Income Taxes (Loss) income before provision for income taxes was as follows: Year Ended December 31, 2017 2016 2015 (in thousands) United States $ (54,894 ) $ (47,112 ) $ (47,911 ) Foreign 4,855 2,083 2,270 Total $ (50,039 ) $ (45,029 ) $ (45,641 ) The benefit (provision) for income taxes consists of the following: Year Ended December 31, 2017 2016 2015 (in thousands) Current income tax provision Federal $ — $ — $ — State (144 ) (95 ) (61 ) Foreign (1,077 ) (579 ) (401 ) Total current income tax provision (1,221 ) (674 ) (462 ) Deferred income tax benefit Federal 10,435 61 (10 ) State 977 — — Foreign 134 80 60 Total deferred income tax benefit 11,546 141 50 Total income tax benefit (provision) $ 10,325 $ (533 ) $ (412 ) The following reconciles the differences between income taxes computed at the federal statutory rate of 35% and the provision for income taxes: Year Ended December 31, 2017 2016 2015 (in thousands) Expected income tax benefit at the federal statutory rate $ 17,166 $ 15,761 $ 15,974 State taxes net of federal benefit 5,150 916 2,257 Stock-based compensation 10,939 (2,001 ) (1,685 ) Difference in foreign tax rates 988 415 482 U.S. tax credits 1,717 1,609 2,738 Convertible debt and acquisition 11,573 — — Federal rate change (49,123 ) — — Transition tax (1,063 ) Change in valuation allowance 13,988 (16,413 ) (19,421 ) Other (1,010 ) (820 ) (757 ) Income tax benefit (provision) $ 10,325 $ (533 ) $ (412 ) On December 22, 2017, the United States of America signed tax legislation (the “2017 Act”) which enacts a wide range of changes to the U.S. corporate income tax system. The 2017 Act reduces the U.S. corporate tax rate to 21% effective in 2018, broadens the tax base and changes rules for expensing and capitalizing business expenditures, establishes a territorial tax system for foreign earnings as well as a minimum tax on certain foreign earnings, provides for a one-time transition tax on previously undistributed foreign earnings, and introduces new rules for the treatment of certain export sales. At December 31, 2017, the Company has not completed the accounting for the tax effects of enactment of the 2017 Act; however, in certain cases, as described below, the Company has made a reasonable estimate of the effects on existing deferred tax balances and the one-time transition tax. For the items for which the Company was not able to determine a reasonable estimate, no net income tax expense or benefit was recognized. The Company remeasured certain deferred tax assets and liabilities based on the rates at which they are expected to reverse in the future, which is generally 21% for U.S. federal tax purposes. However, the Company is still analyzing certain aspects of the Act and refining its calculations, which could potentially affect the measurement of these balances or potentially give rise to new deferred tax amounts. The provisional amount recorded related to the remeasurement of deferred tax balances was $49.1 million, which was offset by a corresponding reduction in the valuation allowance. The one-time transition tax is based on the Company’s total post-1986 earnings and profits (E&P) for which the Company previously deferred from U.S. income taxes. The one-time transition tax results in an estimated inclusion of $6.9 million of foreign earnings in U.S. taxable income, which reduces U.S. federal and state net operating losses generated during 2017. The Company has not yet completed the calculation of the total post-1986 foreign E&P for these foreign subsidiaries, and therefore this estimate may change as additional clarifying and interpretative technical guidance is issued related to the calculation of our one-time transition tax. The changes included in the 2017 Act are broad and complex. The final transition impacts of the 2017 Act may differ from the above estimates, possibly materially, due to, among other things, changes in interpretations of the 2017 Act, any legislative action to address questions that arise because of the 2017 Act, actions taken by U.S. state governments and taxing authorities in response to the 2017 Act, any changes in accounting standards for income taxes or related interpretations in response to the 2017 Act, or any updates or changes to estimates that have been utilized to calculate the transition impacts, including impacts from changes to current year earnings estimates and foreign exchange rates of foreign subsidiaries. The Securities Exchange Commission has issued rules that allow for a measurement period of up to one year after the enactment date of the 2017 Act to finalize the recording of the related tax impacts. The Company currently anticipate finalizing and recording any resulting adjustments during 2018. Deferred Tax Assets and Liabilities —Deferred income taxes reflect the net effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Significant components of the Company’s deferred tax assets and liabilities were as follows: Year Ended December 31, 2017 2016 (in thousands) Deferred tax assets: Net operating loss carryforwards $ 87,521 $ 73,750 Research and investment credits 9,402 6,674 Accruals and reserves 6,627 6,699 Depreciation 911 744 Intangible assets — 215 Stock-based compensation 4,146 8,115 Total deferred tax assets $ 108,607 $ 96,197 Deferred tax liabilities: Intangible assets (1,273 ) — Convertible debt (5,664 ) — Capitalized costs (4,648 ) (4,843 ) Total deferred tax liabilities (11,585 ) (4,843 ) Valuation allowance (96,630 ) (91,132 ) Net deferred tax assets $ 392 $ 222 The Company reviews all available evidence to evaluate its recovery of deferred tax assets, including its recent history of accumulated losses in all tax jurisdictions over the most recent three years as well as its ability to generate income in future periods. The Company has provided a valuation allowance against its U.S. net deferred tax assets as it is more likely than not that these assets will not be realized given the nature of the assets and the likelihood of future utilization. The valuation allowance increased by $5.5 million in 2017, $16.5 million in 2016 and $19.4 million in 2015, primarily due to the increase in the U.S. net operating loss deferred tax asset. The Company does not expect any significant changes in its valuation allowance positions within the next 12 months. At December 31, 2017, undistributed foreign earnings of approximately $6.9 million have been taxed due to the one-time transition tax on previously undistributed foreign earnings required by the 2017 Act. For any future foreign earnings, the Company will generally be free of additional U.S. federal tax consequences due to a dividends received deduction implemented as part of the move to a territorial tax system for foreign subsidiary earnings. No provision has been made for additional deferred taxes related to any remaining historical outside basis differences in our non-U.S. subsidiaries, which could include U.S. state taxes and foreign withholding taxes. The Company continues to assess the impact of the 2017 Act on its indefinite reinvestment in these outside basis differences generated on or before December 31, 2017 and intends to finalize this assessment within the one-year measurement period as allowed for by the Securities and Exchange Commission. The Company had federal and state net operating loss carryforwards of $352.5 million and $224.7 million, respectively at December 31, 2017, which expire at various dates through 2037 The Company had federal research and development credit carryforwards of $5.8 million at December 31, 2017 that expire at various dates through 2037. The Company also has state research and investment credit carryforwards of $2.5 million and $756 thousand, respectively that expire at various dates through 2032. Under Section 382 of the Internal Revenue Code of 1986, as amended, substantial changes in the Company's ownership may limit the amount of net operating loss carryforwards that could be utilized annually in the future to offset taxable income. Specifically, this limitation may arise in the event of a cumulative change in ownership of the Company of more than 50% within a three-year period. Any such annual limitation may significantly reduce the utilization of net operating loss carryforwards before they expire. The Company performed an analysis through December 31, 2016, and determined any potential ownership change under Section 382 during the year would not have a material impact on the future utilization of US net operating losses and tax credits. There was no material change to this conclusion in 2017. However, future transactions in the Company's common stock could trigger an ownership change for purposes of Section 382, which could limit the amount of net operating loss carryforwards and other attributes that could be utilized annually in the future to offset taxable income, if any. Any such limitation, whether as the result of sales of common stock by our existing stockholders or sales of common stock by the Company, could have a material adverse effect on results of operations in future years. Uncertain Tax Positions —The Company accounts for uncertainty in income taxes using a two-step process. The Company first determines whether it is more likely than not that a tax position will be sustained upon examination by the tax authority, including resolutions of any related appeals or litigation processes, based on technical merit. If a tax position meets the more-likely-than-not recognition threshold it is then measured to determine the amount of benefit to recognize in the financial statements. The tax position is measured as the largest amount of benefit that is greater than 50% likely of being realized upon ultimate settlement. The following summarizes activity related to unrecognized tax benefits: Year Ended December 31, 2017 2016 2015 (in thousands) Unrecognized benefit—beginning of the year $ 1,742 $ 673 $ 1,713 Gross increases—current period positions 983 1,069 171 Gross decrease—prior period positions — — (1,211 ) Unrecognized benefit—end of period $ 2,725 $ 1,742 $ 673 All of the gross unrecognized tax benefits represent a reduction to the research and development tax credit carryforward. The gross decrease to prior period positions, for the period ending December 31, 2015 is a result of the Company completing IRS documentation of all credits generated since inception. All of the unrecognized tax benefits decrease deferred tax assets with a corresponding decrease to the valuation allowance. None of the unrecognized tax benefits would affect the Company’s effective tax rate if recognized in the future. The Company has elected to recognize interest and penalties related to uncertain tax positions as a component of income tax expense. No interest or penalties have been recorded through December 31, 2017. The Company does not expect any significant change in its unrecognized tax benefits within the next 12 months. The Company files tax returns in the United States, Ireland, Australia, Singapore, Japan, Germany and various state jurisdictions. All of the Company’s tax years remain open to examination by major taxing jurisdictions to which the Company is subject, as carryforward attributes generated in past years may still be adjusted upon examination by the Internal Revenue Service or state and foreign tax authorities if they have or will be used in future periods. The Company is routinely examined by various taxing authorities. The IRS completed a federal income tax audit for the tax year 2013 during 2016

Employee Benefit Plan

Employee Benefit Plan	12 Months Ended
	Dec. 31, 2017
Compensation And Retirement Disclosure [Abstract]
Employee Benefit Plan	14. Employee Benefit Plan In July 2008, the Company established a defined contribution savings plan under Section 401(k) of the Internal Revenue Code. This plan covers substantially all employees who meet minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pretax basis, subject to legal limitations. Total contributions were $2.9 million in 2017, $2.1 million in 2016, and $1.2 million in 2015.

Quarterly Financial Results (un

Quarterly Financial Results (unaudited)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Results (unaudited)	15. Quarterly Financial Results (unaudited) Fourth Quarter Third Quarter Second Quarter First Quarter (in thousands, except per share amounts) Year ended December 31, 2017 Revenue $ 106,541 $ 97,726 $ 89,093 $ 82,252 Cost of revenue 21,056 19,010 18,591 17,072 Gross profit 85,485 78,716 70,502 65,180 Net loss (11,535 ) (10,583 ) (9,521 ) (8,075 ) Basic and diluted net loss per share $ (0.31 ) $ (0.29 ) $ (0.26 ) $ (0.22 ) Year ended December 31, 2016 Revenue $ 76,444 $ 70,589 $ 64,974 $ 58,960 Cost of revenue 16,887 15,812 15,195 13,971 Gross profit 59,557 54,777 49,779 44,989 Net loss (13,829 ) (10,515 ) (11,064 ) (10,154 ) Basic and diluted net loss per share $ (0.39 ) $ (0.30 ) $ (0.32 ) $ (0.29 )

Summary of Significant Accoun26

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation —The consolidated financial statements have been prepared in U.S. dollars, in accordance with accounting principles generally accepted in the United States of America (“GAAP”). The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates —The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expenses during the reporting period. Actual results could differ from those estimates.
Operating Segments	Operating Segments — The Company operates as one operating segment. Operating segments are defined as components of an enterprise for which separate financial information is regularly evaluated by the chief operating decision makers (“CODMs”), which are the Company’s chief executive officer and chief operating officer, in deciding how to allocate resources and assess performance. The Company’s CODMs evaluate the Company’s financial information and resources and assess the performance of these resources on a consolidated basis. Since the Company operates in one operating segment, all required financial segment information can be found in the consolidated financial statements.
Loss Per Share	Loss Per Share — Basic net loss per share is computed by dividing net loss by the weighted average number of common shares outstanding for the period. Diluted net loss per share is computed by giving effect to all potential dilutive common stock equivalents outstanding for the period. For purposes of this calculation, options to purchase common stock, restricted stock units (“RSUs”), Employee Stock Purchase Plan (“ESPP”), and the Conversion Option of the 2022 Notes (Note 7) are considered to be potential common stock equivalents. A reconciliation of the denominator used in the calculation of basic and diluted loss per share is as follows: Year Ended December 31, 2017 2016 2015 (in thousands, except per share amounts) Net loss $ (39,714 ) $ (45,562 ) $ (46,053 ) Weighted-average common shares outstanding—basic 36,827 35,197 33,222 Dilutive effect of share equivalents resulting from stock options, RSUs, ESPP and the Conversion Option of the 2022 Notes — — — Weighted-average common shares outstanding-diluted 36,827 35,197 33,222 Net loss per common share, basic and diluted $ (1.08 ) $ (1.29 ) $ (1.39 ) Additionally, since the Company incurred net losses for each of the periods presented, diluted net loss per share is the same as basic net loss per share. The Company’s outstanding stock options, RSUs, ESPP, and Conversion Option of the 2022 Notes were not included in the calculation of diluted net loss per share as the effect would be anti-dilutive. The following table contains all potentially dilutive common stock equivalents. Year Ended December 31, 2017 2016 2015 (in thousands) Options to purchase common shares 2,085 2,709 3,331 RSUs 2,315 2,264 1,703 ESPP 10 11 — The Company expects to settle the principal amount of the 2022 Notes in cash, and therefore, the Company uses the treasury stock method for calculating any potential dilutive effect of the Conversion Option on diluted net income per share, if applicable. The Conversion Option will have a dilutive impact on net income per share of common stock when the average market price of the Company’s common stock for a given period exceeds the conversion price of the 2022 Notes of $94.77 per share. During the year ended December 31, 2017, the Company's weighted average common stock price was below the conversion price of the 2022 Notes.
Cash and Cash Equivalents	Cash and Cash Equivalents — The Company considers all highly liquid investments purchased with original maturity of three months or less to be cash equivalents. Cash and cash equivalents consist of cash held in bank deposit accounts and short-term, highly-liquid investments with remaining maturities of three months or less at the date of purchase, consisting of money-market funds.
Investments	Investments — Investments consist of corporate debt securities, U.S. government agency obligations, and U.S. Treasury securities. Securities having remaining maturities of more than three months at the date of purchase and less than one year from the date of the balance sheets are classified as short-term, and those with maturities of more than one year from the date of the balance sheet are classified as long-term in the consolidated balance sheets. The Company classifies its debt investments with readily determinable market values as available-for-sale. These investments are classified as investments on the consolidated balance sheets and are carried at fair market value, with unrealized gains and losses considered to be temporary in nature reported as accumulated other comprehensive loss, a separate component of stockholders’ equity. The Company reviews all investments for reductions in fair value that are other-than-temporary. When such reductions occur, the cost of the investment is adjusted to fair value through recording a loss on investments in the consolidated statements of operations. Gains and losses on investments are calculated on the basis of specific identification. Investments are considered to be impaired when a decline in fair value below cost basis is determined to be other-than-temporary. The Company periodically evaluates whether a decline in fair value below cost basis is other-than-temporary by considering available evidence regarding these investments including, among other factors: the duration of the period that, and extent to which, the fair value is less than cost basis; the financial health of, and business outlook for the issuer, including industry and sector performance and operational and financing cash flow factors; overall market conditions and trends and the Company’s intent and ability to retain its investment in the security for a period of time sufficient to allow for an anticipated recovery in market value. Once a decline in fair value is determined to be other-than-temporary, a write-down is recorded and a new cost basis in the security is established.
Strategic Investments	Strategic investments — Strategic investments consist of non-controlling equity investments in privately held companies. These investments without readily determinable fair values for which the Company does not have the ability to exercise significant influence are accounted for using the cost method of accounting. Under the cost method of accounting, the non-marketable securities are carried at cost and are adjusted only for other-than-temporary impairments, certain distributions and additional investments.
Accounts Receivable and Allowance for Doubtful Accounts	Accounts Receivable and Allowance for Doubtful Accounts —Accounts receivable are carried at the original invoiced amount less an allowance for doubtful accounts based on the probability of future collection. When management becomes aware of circumstances that may decrease the likelihood of collection to a point where a receivable is no longer probable of being collected, it records an allowance against amounts due, which reduces the receivable to the amount that management reasonably believes will be collected. For all other customers, management determines the adequacy of the allowance based on historical loss patterns, the number of days that billings are past due and an evaluation of the potential risk of loss associated with specific accounts. To date, losses resulting from uncollected receivables have not exceeded management’s expectations. The following is a roll forward of the Company’s allowance for doubtful accounts (in thousands): Balance Beginning of Period Charged to Statement of Operations Deductions (1) Balance at End of Period Allowance for doubtful accounts Year ended December 31, 2017 $ 617 $ 3,353 $ (3,332 ) $ 638 Year ended December 31, 2016 $ 371 $ 2,517 $ (2,271 ) $ 617 Year ended December 31, 2015 $ 218 $ 1,367 $ (1,214 ) $ 371 (1) Deductions include actual accounts written-off, net of recoveries.
Restricted Cash	Restricted Cash — The Company had restricted cash of $5.1 million at December 31, 2017 and $483 thousand at December 31, 2016 related to leased facilities.
Property and Equipment	Property and Equipment —Property and equipment are stated at cost and depreciated using the straight-line method over the estimated useful lives of the related assets. Expenditures for maintenance and repairs are charged to expense as incurred, whereas major betterments are capitalized as additions to leasehold improvements. Depreciation is recorded over the following estimated useful lives: Estimated Useful Life Employee related computer equipment 2 – 3 years Computer equipment and purchased software 3 years Office equipment 5 years Furniture and fixtures 5 years Internal use software 5 years Leasehold improvements Lesser of lease
Internal Use Software	Internal use software The Company capitalizes certain payroll and stock compensation costs incurred to develop functionality for certain of the Company’s internally built software platforms. The costs incurred during the preliminary stages of development are expensed as incurred. Once a piece of incremental functionality has reached the development stage certain internal costs are capitalized until the functionality is ready for its intended use. Internal use software is included within property and equipment on the balance sheet. The costs are generally amortized on a straight-line basis over an estimated useful life of approximately five years.
Asset Retirement Obligations	Asset Retirement Obligations — The Company recognizes Assets Retirement Obligations (“AROs”) for any significant lease restoration obligation, if required by a lease agreement. The fair values of these AROs are recorded on a discounted basis, at the time the obligation is incurred, and accreted over time for the change in present value. Additionally, the Company capitalizes asset retirement costs by increasing the carrying amount of the related long-lived assets and depreciating these assets over their remaining useful life. The changes in these obligations during the year ending December 31, 2017 and December 31, 2016 are as follows: Year Ended December 31, 2017 2016 (in thousands) Beginning balance $ 591 $ — Additions 580 561 Accretion 46 30 Settlements (26 ) — Ending balance $ 1,191 $ 591
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets — Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable or that the useful lives of those assets are no longer appropriate. Management considers the following potential indicators of impairment of its long-lived assets (asset group): a substantial decrease in the Company’s stock price, a significant adverse change in the extent or manner in which a long-lived asset (asset group) is being used, a significant adverse change in legal factors or in the business climate that could affect the value of the long-lived asset (asset group), an accumulation of costs significantly in excess of the amount originally expected for the acquisition or construction of a long-lived asset (asset group), and a current expectation that, more likely than not, a long lived asset (asset group) will be sold or otherwise disposed of significantly before the end of its previously estimated useful life. When such events occur, the Company compares the carrying amounts of the assets to their undiscounted expected future cash flows. If this comparison indicates that there may be an impairment, the amount of the impairment is calculated as the difference between the carrying value and fair value. For the years presented, the Company did not recognize an impairment charge. Intangible Assets — Intangible assets consist acquired technology and intellectual property. We record acquired intangible assets at fair value on the date of acquisition. and amortize such assets using the straight-line method over the expected useful life of the asset. The estimated useful life of acquired technology and intellectual property is two to three years. The Company evaluates the useful lives of these assets on an annual basis and tests for impairment whenever events or changes in circumstances occur that could impact the recoverability of these assets. If the estimate of an intangible asset’s remaining useful life is changed, we amortize the remaining carrying value of the intangible asset prospectively over the revised remaining useful life.
Intangible Assets	Intangible Assets — Intangible assets consist acquired technology and intellectual property. We record acquired intangible assets at fair value on the date of acquisition. and amortize such assets using the straight-line method over the expected useful life of the asset. The estimated useful life of acquired technology and intellectual property is two to three years. The Company evaluates the useful lives of these assets on an annual basis and tests for impairment whenever events or changes in circumstances occur that could impact the recoverability of these assets. If the estimate of an intangible asset’s remaining useful life is changed, we amortize the remaining carrying value of the intangible asset prospectively over the revised remaining useful life.
Goodwill	Goodwill — Goodwill represents the excess of cost over the fair value of the net tangible and identifiable intangible assets acquired in a business combination. The Company has no other intangible assets with indefinite useful lives. Goodwill is not subject to amortization, but is monitored annually for impairment or more frequently if there are indicators of impairment. Management considers the following potential indicators of impairment: significant underperformance relative to historical or projected future operating results, significant changes in the Company’s use of acquired assets or the strategy of the Company’s overall business, significant negative industry or economic trends and a significant decline in the Company’s stock price for a sustained period. The Company performs its annual impairment test on November 30. Currently, the Company’s goodwill is evaluated at the entity level as it is determined there is only one reporting unit. The Company performs a two-step impairment test. In the first step, the fair value of each reporting unit is compared to its carrying amount. If the fair value exceeds the carrying value of the net assets assigned, goodwill is not considered impaired and the second step is not required. If the carrying value exceeds the fair value, then the second step of the impairment test is performed in order to determine the implied fair value of the reporting unit’s goodwill. If the carrying value of the goodwill exceeds the fair value, then an impairment charge is recorded. On November 30, 2017, the fair value of the Company’s single reporting unit exceeded its carrying amount. Because the fair value of the Company’s single reporting unit was in excess of its carrying value and there were no indicators that the Company’s goodwill had become impaired since that date, there was no impairment as of November 30, 2017 or December 31, 2017. For the years ended December 31, 2017, 2016 and 2015, the Company did not recognize an impairment charge.
Advertising Expense	Advertising Expense — The Company expenses advertising as incurred, which is included in sales and marketing expense in the accompanying consolidated statements of operations. The Company incurred $5.5 million of advertising expense in 2017, $4.2 million in 2016, and $4.9 million in 2015.
Revenue Recognition	Revenue Recognition —The Company primarily generates revenue from multiple-element arrangements, which typically include subscriptions to its online software solution and professional services which includes on-boarding and training services. The Company’s customers do not have the right to take possession of the online software solution. The Company recognizes revenue when all of the following have occurred: • persuasive evidence of an arrangement with the customer exists; • service has been or is being provided; • the fees are fixed or determinable; and • collectability of the fees is reasonably assured. The Company’s arrangements do not contain general rights of return. In order to treat elements in a multiple-element arrangement as separate units of accounting, the delivered elements must have standalone value and delivery of the undelivered element is probable and within control of the Company. The Company has determined that subscriptions for its online software solution have standalone value because, once a customer launches its initial site, the online software solution is fully functional and does not require any additional development, modification, or customization. Professional services consists primarily of on-boarding and web-based and in-person training, are not required to use the online software solution, and are determined to have stand-alone value from the related subscription services because they are sold separately by the Company and third parties. When multiple-element arrangements are separated into different units of accounting, the arrangement consideration is allocated to the identified separate units based on a relative selling price hierarchy. The estimated fair value of each element is determined based upon the following hierarchy: (1) vendor specific objective evidence (“VSOE”) of fair value, (2) third party evidence of selling price (“TPE”), or (3) the Company’s best estimate of selling price (“BESP”). There is not an available measure of TPE of selling price and, as such, arrangement consideration is allocated amongst multiple deliverable arrangements using VSOE, if VSOE can be established, and BESP if VSOE cannot be established. The Company establishes VSOE and BESP for each deliverable primarily considering the median or average of actual sales prices (stand-alone sales prices for VSOE) of each type of subscription and other professional services sold. The Company considers each type of subscription and service as well as pricing and geographic information when establishing VSOE and BESP. Arrangement consideration is allocated such that the revenue recognized does not exceed the fee subject to refund. Revenue from subscriptions is recognized ratably over the subscription period beginning on the date the Company’s subscription is made available to customers. Substantially all subscription contracts are one year or less. The Company recognizes revenue from on-boarding and training services as the services are provided. The Company pays its marketing and sales agency partners (“Partners”) a commission of the subscription sales price for sales to customers. The classification of the commission paid on the Company’s consolidated statements of operations depends on who is purchasing its subscription. In instances where the customer is purchasing the subscription, the Company is the primary obligor and records the commission paid to the Partners as sales and marketing expense. When the Partner purchases the subscription directly from the Company, the Company nets the consideration paid to the Partner against the associated revenue it recognizes, as in these instances the Company’s customer is the Partner and the Company’s remaining obligations are to the Partner. The Company does not believe that it receives a tangible benefit from the payment back to the Partner. Sales taxes collected from customers and remitted to government authorities are excluded from revenue. Amounts that have been invoiced are recorded in accounts receivable and deferred revenue or revenue, depending on whether the revenue recognition criteria have been met. Deferred revenue represents amounts billed for which revenue has not yet been recognized. Deferred revenue that will be recognized during the succeeding 12-month period is recorded as current deferred revenue and the remaining portion is recorded as long-term deferred revenue.
Concentrations of Credit Risk and Significant Customers	Concentrations of Credit Risk and Significant Customers —Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, investments and accounts receivable. A significant portion of the Company’s cash and cash equivalents is held at four financial institutions that management believes to be of high credit quality. Although the Company deposits it cash and cash equivalents with multiple financial institutions, its deposits exceed federally insured limits. The Company’s investments consist of highly rated corporate debt securities and U.S. government agency obligations, and U.S. Treasury securities . The Company limits the amount of investments in any single issuer. The Company believes that, as of December 31, 2017, its concentration of credit risk related to investments was not significant. The Company has no significant off-balance sheet risk such as foreign exchange contracts, option contracts, or other hedging arrangements. The Company generally does not require collateral from its customers and generally requires payment 30 days from the invoice date. The Company maintains an allowance for doubtful accounts based on its assessment of the collectability of accounts receivable. Credit risk arising from accounts receivable is mitigated as a result of transacting with a large number of geographically dispersed customers spread across various industries. At December 31, 2017 and 2016 there were no customers that represented more than 10% of the net accounts receivable balance. There were no customers that individually exceeded 10% of the Company’s revenue in any of the periods presented.
Foreign Currency	Foreign Currency —The functional currency of the Company’s foreign subsidiaries is the local currency. Assets and liabilities denominated in a foreign currency are translated into U.S. dollars at the exchange rates in effect at the balance sheet dates; with the resulting translation adjustments directly recorded to a separate component of accumulated other comprehensive loss. Income and expense accounts are translated at the weighted-average exchange rates during the period. Foreign currency transaction gains and losses are recorded in other income (expense).
Research and Development	Research and Development —Research and development expenses include payroll, employee benefits and other expenses associated with product development.
Capitalized Software Development Costs	Capitalized Software Development Costs — Certain payroll and stock compensation costs incurred to develop functionality for the Company’s software and internally built software platforms, as well as certain upgrades and enhancements that are expected to result in increased functionality are capitalized. The costs incurred in the preliminary stages of development are expensed as incurred. Once an application has reached the development stage, certain internal costs are capitalized until the software is substantially complete and ready for its intended use. Capitalized software development costs are amortized on a straight-line basis over their estimated useful life of two to five years. Management evaluates the useful lives of these assets on a quarterly basis and tests for impairment whenever events or changes in circumstances occur that could impact the recoverability of these assets. Capitalized software development costs, exclusive of those costs recorded within property and equipment, consisted of the following: December 31, 2017 December 31, (in thousands) Gross capitalized software development costs $ 33,360 $ 25,152 Accumulated amortization (24,600 ) (18,629 ) Capitalized software development costs, net $ 8,760 $ 6,523 The Company capitalized software development costs, exclusive of costs recorded within property and equipment, of $8.2 million in 2017, $6.4 million in 2016, and $4.5 million in 2015. Stock-based compensation costs included in capitalized software were $1.6 million in 2017, $1.2 million in 2016, and $492 thousand in 2015. Amortization of capitalized software development costs, exclusive of costs recorded within property and equipment, was $6.3 million in 2017, $5.1 million in 2016, and $4.6 million in 2015. Amortization expense is included in cost of revenue in the consolidated statements of operations.
Income Taxes	Income Taxes —Deferred tax assets and liabilities are recognized for the differences between the financial statement carrying amounts and the tax bases of existing assets and liabilities using tax rates expected to be in effect in the years in which the differences are expected to reverse. Deferred tax assets are reduced by a valuation allowance if it is more likely than not that some portion or all of the deferred tax assets will not be realized. Accounting for uncertainty in income taxes recognized in the financial statements is in accordance with accounting authoritative guidance, which prescribes a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination. If the tax position is deemed “more-likely-than-not” to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50 percent likelihood of being realized upon ultimate settlement. Undistributed foreign earnings of approximately $6.9 million have been taxed in 2017 due to a one-time transition tax on previously undistributed foreign earnings. For any future foreign earnings, the Company will generally be free of additional U.S. federal tax consequences due to a dividends received deduction implemented as part of the move to a territorial tax system for foreign subsidiary earnings.
Stock-Based Compensation	Stock-Based Compensation —The Company accounts for all stock options and awards granted to employees and nonemployees using a fair value method. Stock-based compensation is recognized as an expense and is measured at the fair value of the award. The measurement date for employee awards is generally the date of the grant. The measurement date for nonemployee awards is generally the date the awards vest. Stock-based compensation costs are recognized as expense over the requisite service period, which is generally the vesting period for awards, on a straight-line basis for awards with only a service condition, and using the graded-method for awards with both a performance and service that were granted prior to our IPO, and on a straight-line basis for the awards that were granted following our IPO, which only have service conditions.
Recent Accounting Pronouncements	Recent Accounting Pronouncements — Recent accounting standards not included below are not expected to have a material impact on our consolidated financial position and results of operations. The Company adopted updated guidance related to certain aspects of share-based payments to employees. The guidance requires the recognition of the income tax effects of awards in the income statement when the awards vest or are settled, thus eliminating additional paid-in capital pools. As a result of the adoption, we recorded an increase to deferred tax assets with a corresponding increase to the valuation allowance of $30.4 million to recognize net operating loss carryforwards attributable to excess tax benefits on stock compensation that had not been previously recognized as additional paid-in capital. In addition, the Company changed its policy election to account for forfeitures as they occur rather than on an estimated basis. The change in the policy election related to forfeitures resulted in the Company reclassifying $452 thousand from additional paid-in capital to accumulative deficit for the net cumulative-effect adjustment in stock compensation expense related to prior periods. In January 2017, the Financial Accounting Standards Board (“FASB”) In January 2017, the FASB issued guidance simplifying the accounting for goodwill impairment by removing Step 2 of the goodwill impairment test. Under current guidance, Step 2 of the goodwill impairment test requires entities to calculate the implied fair value of goodwill in the same manner as the amount of goodwill recognized in a business combination by assigning the fair value of a reporting unit to all of the assets and liabilities of the reporting unit. The carrying value in excess of the implied fair value is recognized as goodwill impairment. Under the new standard, goodwill impairment is recognized based on Step 1 of the current guidance, which calculates the carrying value in excess of the reporting unit’s fair value. The new standard is effective beginning in January 2020, with early adoption permitted. We do not believe the adoption of this guidance will have a material impact on our consolidated financial statements. In November 2016, the FASB issued guidance related to the presentation of restricted cash within the statement of cash flows. The guidance requires entities to show the changes in cash, cash equivalents, and restricted cash in the statement of cash flows. Entities will no longer present transfers between cash and cash equivalents and restricted cash in the statement of cash flows. As of December 31, 2017, we had $5.1 million in restricted cash. The new standard is effective beginning in the first quarter of 2018, with early adoption permitted. The impact of including restricted cash with cash and cash equivalents when reconciling the beginning-of-year and end-of-year total amounts presented on the consolidated statement of cash flows would increase net cash flows for the year ended December 31, 2017 by approximately $4.6 million. In February 2016, the FASB issued guidance that requires lessees to recognize most leases on their balance sheets but record expenses on their income statements in a manner similar to current accounting. For lessors, the guidance modifies the classification criteria and the accounting for sales-type and direct financing leases. The guidance is effective in 2019 with early adoption permitted. The Company is currently evaluating the impact of this guidance on the consolidated financial statements. In June 2016, the FASB issued guidance that introduces a new methodology for accounting for credit losses on financial instruments, including available-for-sale debt securities. The guidance establishes a new "expected loss model" that requires entities to estimate current expected credit losses on financial instruments by using all practical and relevant information. Any expected credit losses are to be reflected as allowances rather than reductions in the amortized cost of available-for-sale debt securities. This guidance will be effective for the Company on January 1, 2020. The Company is currently evaluating the impact of this guidance on the consolidated financial statements. In May 2014, the FASB issued updated guidance and disclosure requirements for recognizing revenue. The new revenue recognition standard provides a five-step analysis of transactions to determine when and how revenue is recognized. The core principle is that a company should recognize revenue 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. The standard also provides guidance on the recognition of costs related to obtaining customer contracts. The new standard is effective for the Company for its annual reporting periods beginning January 1, 2018. The Company will adopt the standard on January 1, 2018, using the modified retrospective method, which will result in a cumulative effect adjustment as of the date of adoption. The Company established a team that has assessed the impact of the standard including the timing of revenue recognition and the accounting for deferred commission costs and related balances. The Company has determined that there will be a change to the period over which sales commissions will be amortized to incorporate an estimated customer life and the amortization period over which internally developed new features and increased functionality for our software platform is recorded, in addition to the initial contract period. This will result in a longer amortization period for deferred sales commissions, which will reduce the expense in any one period compared to today. There will also be a change to the scope of capitalized sales commissions based on the definition of incremental costs of obtaining a contract. This will result in a higher capitalized commissions balance upon adoption. In addition, there will be a change in relation to the timing of revenue recognition for certain sales contracts, where free or discounted services are bundled with our subscription offering due primarily to the removal of the current limitation on contingent revenue. This will accelerate revenue recognition on these contracts when these services are provided up front as compared to today. The change in the period over which sales commissions will be amortized will have a material impact to the consolidated financial statements and disclosures. The change in the timing of revenue recognition for certain sales contracts, where free or discounted services are bundled with our subscription offering, will not have a material impact to the consolidated financial statements and disclosures.

Summary of Significant Accoun27

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Reconciliation of Denominator Used in Calculation of Basic and Diluted Loss Per Share	A reconciliation of the denominator used in the calculation of basic and diluted loss per share is as follows: Year Ended December 31, 2017 2016 2015 (in thousands, except per share amounts) Net loss $ (39,714 ) $ (45,562 ) $ (46,053 ) Weighted-average common shares outstanding—basic 36,827 35,197 33,222 Dilutive effect of share equivalents resulting from stock options, RSUs, ESPP and the Conversion Option of the 2022 Notes — — — Weighted-average common shares outstanding-diluted 36,827 35,197 33,222 Net loss per common share, basic and diluted $ (1.08 ) $ (1.29 ) $ (1.39 )
Schedule of Share Totals with Potentially Dilutive Impact	. The following table contains all potentially dilutive common stock equivalents. Year Ended December 31, 2017 2016 2015 (in thousands) Options to purchase common shares 2,085 2,709 3,331 RSUs 2,315 2,264 1,703 ESPP 10 11 —
Schedule of Roll Forward of Company's Allowance for Doubtful Accounts	The following is a roll forward of the Company’s allowance for doubtful accounts (in thousands): Balance Beginning of Period Charged to Statement of Operations Deductions (1) Balance at End of Period Allowance for doubtful accounts Year ended December 31, 2017 $ 617 $ 3,353 $ (3,332 ) $ 638 Year ended December 31, 2016 $ 371 $ 2,517 $ (2,271 ) $ 617 Year ended December 31, 2015 $ 218 $ 1,367 $ (1,214 ) $ 371 (1) Deductions include actual accounts written-off, net of recoveries.
Schedule of Property Plant and Equipment Useful Life	Depreciation is recorded over the following estimated useful lives: Estimated Useful Life Employee related computer equipment 2 – 3 years Computer equipment and purchased software 3 years Office equipment 5 years Furniture and fixtures 5 years Internal use software 5 years Leasehold improvements Lesser of lease
Schedule of Changes in Asset Retirement Obligations	The changes in these obligations during the year ending December 31, 2017 and December 31, 2016 are as follows: Year Ended December 31, 2017 2016 (in thousands) Beginning balance $ 591 $ — Additions 580 561 Accretion 46 30 Settlements (26 ) — Ending balance $ 1,191 $ 591
Summary of Capitalized Software Development Costs Exclusive of Costs Recorded within Property and Equipment	Capitalized software development costs, exclusive of those costs recorded within property and equipment, consisted of the following: December 31, 2017 December 31, (in thousands) Gross capitalized software development costs $ 33,360 $ 25,152 Accumulated amortization (24,600 ) (18,629 ) Capitalized software development costs, net $ 8,760 $ 6,523

Fair Value of Financial Instr28

Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Schedule of Fair Value Measurements of Financial Assets and Liabilities	The following table details the fair value measurements within the fair value hierarchy of the Company’s financial assets and liabilities at December 31, 2017 and December 31, 2016: December 31, 2017 Level 1 Level 2 Level 3 Total (in thousands) Cash equivalents and investments: Money market funds $ 12,845 $ — $ — $ 12,845 Commercial paper — 5,867 — 5,867 Corporate bonds — 81,668 — 81,668 U.S. government agency obligations — 3,987 — 3,987 U.S. Treasury securities — 356,535 — 356,535 Restricted cash: Certificates of deposit — 5,105 — 5,105 Total $ 12,845 $ 453,162 $ — $ 466,007 December 31, 2016 Level 1 Level 2 Level 3 Total (in thousands) Cash equivalents and investments: Money market funds $ 32,260 $ — $ — $ 32,260 Commercial paper — 12,439 — 12,439 Corporate bonds — 66,947 — 66,947 U.S. government agency obligations — 10,980 — 10,980 Total $ 32,260 $ 90,366 $ — $ 122,626
Summary of Composition of Short and Long Term Investments	The following tables summarize the composition of our short- and long-term investments at December 31, 2017 and 2016: December 31, 2017 Amortized Cost Unrealized Gains Unrealized Losses Aggregate Fair Value (in thousands) Commercial paper $ 5,874 $ — $ (7 ) $ 5,867 Corporate bonds 81,947 — (279 ) 81,668 U.S. government agency obligations 4,000 — (13 ) 3,987 U.S. Treasury securities 356,671 8 (144 ) 356,535 Total $ 448,492 $ 8 $ (443 ) $ 448,057 December 31, 2016 Amortized Cost Unrealized Gains Unrealized Losses Aggregate Fair Value (in thousands) Commercial paper $ 12,446 $ — $ (7 ) $ 12,439 Corporate bonds 67,126 — (179 ) 66,947 U.S. government agency obligations 10,998 — (18 ) 10,980 Total $ 90,570 $ — $ (204 ) $ 90,366
Summary of Contractual Maturities of Short and Long Term Investments	The contractual maturities of short-term and long-term investments held at December 31, 2017 and 2016 are as follows: December 31, 2017 December 31, 2016 Amortized Cost Basis Aggregate Fair Value Amortized Cost Basis Aggregate Fair Value (in thousands) Due within one year $ 416,932 $ 416,663 $ 54,694 $ 54,648 Due after 1 year through 2 years 31,560 31,394 35,876 35,718 Total $ 448,492 $ 448,057 $ 90,570 $ 90,366

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2017
Property Plant And Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment as of December 31, 2017 and December 31, 2016 consists of the following: December 31. 2017 2016 (in thousands) Computer equipment & purchased software $ 4,571 $ 3,237 Employee computer equipment 4,260 1,534 Furniture and fixtures 11,083 8,174 Office equipment 2,620 2,326 Leasehold improvements 33,446 23,693 Equipment under capital lease 3,450 2,412 Internal-use software 2,892 1,301 Construction in progress 3,198 322 Total property and equipment 65,520 42,999 Less accumulated depreciation (22,226 ) (12,798 ) Property and equipment, net $ 43,294 $ 30,201

Intangible Assets (Tables)

Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Goodwill And Intangible Assets Disclosure [Abstract]
Intangible Assets	Intangible assets as of December 31, 2017 and 2016 consist of the following: Weighted Average Remaining Useful Life December 31, 2017 2016 (in thousands) Acquired technology 19 Months $ 7,252 $ 852 Acquired intellectual property — 80 80 Accumulated amortization (1,020 ) (916 ) Total $ 6,312 $ 16
Estimated Future Amortization Expense for Intangible Assets	Estimated future amortization expense for intangible assets, currently being amortized, as of December 31, 2017 is as follows: Years ended December 31, Amortization Expense (in thousands) 2018 200 2019 112 Total $ 312

0.25% Convertible Senior Note31

0.25% Convertible Senior Notes, Convertible Note Hedge and Warrant (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Instrument [Line Items]
Schedule of Interest Expense	Interest expense related to the 2022 Notes is as follows: Year Ended December 31, 2017 2016 2015 (in thousands) Contractual interest expense $ 639 $ — $ — Amortization of debt discount 859 — — Amortization of issuance costs 11,507 — — Total interest expense $ 13,005 $ — $ —
Schedule of Net Equity Impact, Included in Additional Paid-in Capital, of the Liability and Equity Components	The net equity impact, included in additional paid-in capital, of the above components of the 2022 Notes is as follows: (in thousands) Conversion Option $ 106,006 Purchase of Convertible Note Hedges (78,920 ) Sales of warrants 59,080 Issuance costs (3,054 ) Deferred tax liability (9,399 ) Total $ 73,713
0.25% Convertible Senior Notes Due 2022 as Liability Component [Member]
Debt Instrument [Line Items]
Schedule of Net Carrying Amount of Notes	The net carrying amount of the liability component of the 2022 Notes is as follows: As of December 31, 2017 As of December 31, 2016 (in thousands) Principal $ 400,000 $ — Unamortized debt discount (94,498 ) — Unamortized issuance costs (7,055 ) — Net carrying amount $ 298,447 $ —
0.25% Convertible Senior Notes Due 2022 as Equity Component [Member]
Debt Instrument [Line Items]
Schedule of Net Carrying Amount of Notes	The net carrying amount of the equity component of the 2022 Notes is as follows: As of December 31, 2017 As of December 31, 2016 (in thousands) Debt discount for conversion option $ 106,006 — Issuance costs (2,854 ) — Net carrying amount $ 103,152 $ —

Geographic Data (Tables)

Geographic Data (Tables)	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Revenues by Geographical Region	Revenues by geographical region: Year Ended December 31, 2017 2016 2015 (In thousands) Americas $ 283,696 $ 219,422 $ 154,625 Europe 70,895 41,616 23,487 Asia Pacific 21,021 9,929 3,831 Total $ 375,612 $ 270,967 $ 181,943 Percentage of revenues generated outside of the Americas 24 % 19 % 15 %
Long Lived Assets by Geographical Region	Total long-lived assets by geographical region: As of December 31, 2017 As of December 31, 2016 (In thousands) Americas $ 29,764 $ 23,205 Europe 11,257 4,716 Asia Pacific 2,273 2,280 Total long lived assets $ 43,294 $ 30,201 Percentage of long lived assets held outside of the Americas 31 % 23 %

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Schedule of Future Minimum Payments	Future minimum payments under all operating and capital lease agreements as of December 31, 2017, are as follows: Operating Capital (in thousands) 2018 $ 19,345 $ 771 2019 19,752 290 2020 19,997 30 2021 21,433 — 2022 21,729 — Thereafter 99,644 — Total $ 201,900 1,091 Less: Portion representing interest (34 ) Capital lease obligation $ 1,057
Schedule of Future Minimum Payments Under Vendor Commitments	Future minimum payments under all Vendor Commitments as of December 31, 2017, are as follows: Product related obligations INBOUND event obligations (in thousands) 2018 15,852 475 2019 10,826 316 2020 1,500 316 2021 — 653 2022 — 653 Thereafter — 653 Total $ 28,178 $ 3,066

Changes in Accumulated Other 34

Changes in Accumulated Other Comprehensive Loss (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Changes in Accumulated Other Comprehensive Loss	The following table summarizes the changes in accumulated other comprehensive loss, which is reported as a component of stockholders’ equity, for the years ended December 31, 2017 and 2016: Cumulative Translation Adjustment Unrealized L on Investments Total (in thousands) Beginning balance at January 1, 2016 $ (417 ) $ (388 ) $ (805 ) Other comprehensive (loss) income before reclassifications (172 ) 113 (59 ) Amounts reclassified from accumulated other comprehensive loss — — — Ending balance at December 31, 2016 $ (589 ) $ (275 ) $ (864 ) Other comprehensive income (loss) before reclassifications 968 (161 ) 807 Amounts reclassified from accumulated other comprehensive loss — — — Ending balance at December 31, 2017 $ 379 $ (436 ) $ (57 )

Stockholders' Equity and Stoc35

Stockholders' Equity and Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2017
Stockholders Equity And Stock Based Compensation [Abstract]
Summary of Number of Shares of Common Stock Reserved	The number of shares of common stock reserved for the vesting of RSUs, exercise of common stock options, and ESPP are as follows (in thousands): December 31, 2017 December 31, 2016 RSUs 2,085 2,264 Common stock options 2,315 2,709 ESPP 10 11 4,410 4,984
Schedule of Stock Compensation Expense by Award Type	The following two tables show stock compensation expense by award type and where the stock compensation expense is recorded in the Company’s consolidated statements of operations: Year Ended December 31, 2017 2016 2015 (in thousands) Options $ 4,948 $ 5,202 $ 6,349 ESPP 1,233 1,093 1,035 RSUs 41,136 26,380 13,924 Total stock-based compensation $ 47,317 $ 32,675 $ 21,308
Effect of Stock-Based Compensation on Income by Line Item	The following two tables show stock compensation expense by award type and where the stock compensation expense is recorded in the Company’s consolidated statements of operations: 2017 2016 2015 (in thousands) Cost of revenue, subscription $ 658 $ 512 $ 341 Cost of revenue, service 2,327 1,640 1,216 Research and development 12,816 8,828 6,327 Sales and marketing 19,016 13,352 7,658 General and administrative 12,500 8,343 5,766 Total stock-based compensation $ 47,317 $ 32,675 $ 21,308
Schedule of Assumptions Used for Estimation of Fair Value of Options Granted to Employees	Stock Options —The fair value of employee options is estimated on the date of each grant using the Black-Scholes option-pricing model with the following assumptions: Year Ended December 31, 2017 2016 2015 Risk-free interest rate (%) 1.74-2.09 1.38 - 1.41 1.36 - 1.53 Expected term (years) 5.18-6.21 5.08 - 6.21 6.18 - 6.22 Volatility (%) 39.4-43.7 38.0 - 41.0 43.0 - 51.6 Expected dividends — — —
Summary of Stock Option Activity	The stock option activity for the year ended December 31, 2017 is as follows: Options (in thousands) Weighted- Average Exercise Price Weighted- Average Remaining Life (in years) Aggregate Intrinsic Value (in thousands) Outstanding—January 1, 2017 2,709 $ 13.99 6.1 $ 89,411 Granted 180 56.67 Exercised (543 ) 16.07 Forfeited/expired (31 ) 24.12 Outstanding—December 31, 2017 2,315 16.69 5.3 $ 165,974 Options vested or expected to vest—December 31, 2017 2,315 $ 16.69 5.3 $ 165,974 Options exercisable—December 31, 2017 1,945 $ 11.39 4.8 $ 149,803
Summary of Activity Related to RSUs	The following table summarizes the activity related to RSUs for the year ended December 31, 2017: RSUs Outstanding Shares (in thousands) Weighted- Average Grant Date Fair Value Per Share Unvested and outstanding at January 1, 2017 2,264 $ 42.04 Granted 1,189 64.59 Vested (1,151 ) 42.24 Canceled (217 ) 48.13 Unvested and outstanding at December 31, 2017 2,085 $ 54.12

Employee Stock Purchase Plan (T

Employee Stock Purchase Plan (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Activity Related to Employee Stock Purchase Plan	The following table summarizes the activity related to ESPP: Shares Issued (in thousands) Weighted- Average Purchase Price Total Cash Proceeds (in thousands) 2017 94 38.83 3,635 2016 70 38.98 2,721 2015 29 28.46 814

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of (Loss) Income Before Provision for Income Taxes	(Loss) income before provision for income taxes was as follows: Year Ended December 31, 2017 2016 2015 (in thousands) United States $ (54,894 ) $ (47,112 ) $ (47,911 ) Foreign 4,855 2,083 2,270 Total $ (50,039 ) $ (45,029 ) $ (45,641 )
Components of Income Tax Benefit (Provision)	The benefit (provision) for income taxes consists of the following: Year Ended December 31, 2017 2016 2015 (in thousands) Current income tax provision Federal $ — $ — $ — State (144 ) (95 ) (61 ) Foreign (1,077 ) (579 ) (401 ) Total current income tax provision (1,221 ) (674 ) (462 ) Deferred income tax benefit Federal 10,435 61 (10 ) State 977 — — Foreign 134 80 60 Total deferred income tax benefit 11,546 141 50 Total income tax benefit (provision) $ 10,325 $ (533 ) $ (412 )
Schedule of Differences Between Income Taxes Computed at the Federal Statutory Rate and the Provision for Income Taxes	The following reconciles the differences between income taxes computed at the federal statutory rate of 35% and the provision for income taxes: Year Ended December 31, 2017 2016 2015 (in thousands) Expected income tax benefit at the federal statutory rate $ 17,166 $ 15,761 $ 15,974 State taxes net of federal benefit 5,150 916 2,257 Stock-based compensation 10,939 (2,001 ) (1,685 ) Difference in foreign tax rates 988 415 482 U.S. tax credits 1,717 1,609 2,738 Convertible debt and acquisition 11,573 — — Federal rate change (49,123 ) — — Transition tax (1,063 ) Change in valuation allowance 13,988 (16,413 ) (19,421 ) Other (1,010 ) (820 ) (757 ) Income tax benefit (provision) $ 10,325 $ (533 ) $ (412 )
Components of the Company's Deferred Tax Assets and Liabilities	Significant components of the Company’s deferred tax assets and liabilities were as follows: Year Ended December 31, 2017 2016 (in thousands) Deferred tax assets: Net operating loss carryforwards $ 87,521 $ 73,750 Research and investment credits 9,402 6,674 Accruals and reserves 6,627 6,699 Depreciation 911 744 Intangible assets — 215 Stock-based compensation 4,146 8,115 Total deferred tax assets $ 108,607 $ 96,197 Deferred tax liabilities: Intangible assets (1,273 ) — Convertible debt (5,664 ) — Capitalized costs (4,648 ) (4,843 ) Total deferred tax liabilities (11,585 ) (4,843 ) Valuation allowance (96,630 ) (91,132 ) Net deferred tax assets $ 392 $ 222
Summary of Activity Related to Unrecognized Tax Benefits	The following summarizes activity related to unrecognized tax benefits: Year Ended December 31, 2017 2016 2015 (in thousands) Unrecognized benefit—beginning of the year $ 1,742 $ 673 $ 1,713 Gross increases—current period positions 983 1,069 171 Gross decrease—prior period positions — — (1,211 ) Unrecognized benefit—end of period $ 2,725 $ 1,742 $ 673

Quarterly Financial Results (38

Quarterly Financial Results (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Results	Fourth Quarter Third Quarter Second Quarter First Quarter (in thousands, except per share amounts) Year ended December 31, 2017 Revenue $ 106,541 $ 97,726 $ 89,093 $ 82,252 Cost of revenue 21,056 19,010 18,591 17,072 Gross profit 85,485 78,716 70,502 65,180 Net loss (11,535 ) (10,583 ) (9,521 ) (8,075 ) Basic and diluted net loss per share $ (0.31 ) $ (0.29 ) $ (0.26 ) $ (0.22 ) Year ended December 31, 2016 Revenue $ 76,444 $ 70,589 $ 64,974 $ 58,960 Cost of revenue 16,887 15,812 15,195 13,971 Gross profit 59,557 54,777 49,779 44,989 Net loss (13,829 ) (10,515 ) (11,064 ) (10,154 ) Basic and diluted net loss per share $ (0.39 ) $ (0.30 ) $ (0.32 ) $ (0.29 )

Summary of Significant Accoun39

Summary of Significant Accounting Policies - Additional Information (Detail)	Nov. 30, 2017USD ($)	Sep. 30, 2017	Dec. 31, 2017USD ($)SegmentReporting_UnitCustomer$ / shares	Dec. 31, 2016USD ($)Customer	Dec. 31, 2015USD ($)
Schedule Of Accounting Policies [Line Items]
Number of operating segment | Segment			1
Cash and cash equivalents, maturity description			Three months or less at the date of purchase, consisting of money-market funds.
Restricted cash related to leased facilities			$ 5,100,000	$ 483,000
Impairment charges of long lived assets			0
Intangible assets with indefinite useful lives			$ 0
Number of reporting unit | Reporting_Unit			1
Goodwill impairment	$ 0		$ 0	0	$ 0
Advertising expense			$ 5,500,000	4,200,000	4,900,000
Revenue subscription contract period			One year or less
Off-balance sheet risk amount			$ 0
Accounts receivable payment period			30 days
Capitalized software development costs, exclusive of costs recorded within property and equipment			$ 8,200,000	6,400,000	4,500,000
Amortization of software development costs, exclusive of costs recorded within property and equipment			$ 6,300,000	5,100,000	4,600,000
Minimum percentage chances of tax benefit to be realized on examination			50.00%
Undistributed foreign earnings			$ 6,900,000
Increase in valuation allowance			30,400,000
Reclassification from additional paid in capital to accumulative deficit due to change in policy			452,000
Restricted cash			5,100,000
Net increase in cash flows			27,978,000	$ 4,122,000	(68,141,000)
Pro Forma [Member]
Schedule Of Accounting Policies [Line Items]
Net increase in cash flows			$ 4,600,000
Accounts Receivable [Member] | Customer Concentration Risk [Member]
Schedule Of Accounting Policies [Line Items]
Number of customers represented more than 10% | Customer			0	0
Revenue [Member] | Customer Concentration Risk [Member]
Schedule Of Accounting Policies [Line Items]
Number of customers represented more than 10% | Customer			0	0
Acquired Technology [Member]
Schedule Of Accounting Policies [Line Items]
Estimated useful life		2 years
Minimum [Member] | Acquired Technology [Member]
Schedule Of Accounting Policies [Line Items]
Estimated useful life			2 years
Minimum [Member] | Acquired Intellectual Property [Member]
Schedule Of Accounting Policies [Line Items]
Estimated useful life			2 years
Maximum [Member] | Acquired Technology [Member]
Schedule Of Accounting Policies [Line Items]
Estimated useful life			3 years
Maximum [Member] | Acquired Intellectual Property [Member]
Schedule Of Accounting Policies [Line Items]
Estimated useful life			3 years
Internal Use Software [Member]
Schedule Of Accounting Policies [Line Items]
Property and equipment, estimated useful life			5 years
Stock-based compensation in capitalized software development costs			$ 1,600,000	$ 1,200,000	$ 492,000
Software Development Costs [Member] | Minimum [Member]
Schedule Of Accounting Policies [Line Items]
Property and equipment, estimated useful life			2 years
Software Development Costs [Member] | Maximum [Member]
Schedule Of Accounting Policies [Line Items]
Property and equipment, estimated useful life			5 years
0.25% Convertible Senior Notes Due 2022 as Liability Component [Member]
Schedule Of Accounting Policies [Line Items]
Common stock conversion price | $ / shares			$ 94.77

Summary of Significant Accoun40

Summary of Significant Accounting Policies - Summary of Reconciliation of Denominator Used in Calculation of Basic and Diluted Loss Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share Basic And Diluted [Abstract]
Net loss	$ (11,535)	$ (10,583)	$ (9,521)	$ (8,075)	$ (13,829)	$ (10,515)	$ (11,064)	$ (10,154)	$ (39,714)	$ (45,562)	$ (46,053)
Weighted-average common shares outstanding - basic									36,827	35,197	33,222
Weighted-average common shares outstanding - diluted									36,827	35,197	33,222
Net loss per common share, basic and diluted	$ (0.31)	$ (0.29)	$ (0.26)	$ (0.22)	$ (0.39)	$ (0.30)	$ (0.32)	$ (0.29)	$ (1.08)	$ (1.29)	$ (1.39)

Summary of Significant Accoun41

Summary of Significant Accounting Policies - Schedule of Potentially Dilutive Common Stock Equivalents (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Options to Purchase Common Shares [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	2,085	2,709	3,331
RSUs [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	2,315	2,264	1,703
ESPP [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	10	11

Summary of Significant Accoun42

Summary of Significant Accounting Policies - Schedule of Roll Forward of Company's Allowance for Doubtful Accounts (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Receivables [Abstract]
Allowance for doubtful accounts, Beginning Balance	$ 617	$ 371	$ 218
Allowance for doubtful accounts, Charged to Statement of Operations	3,353	2,517	1,367
Allowance for doubtful accounts, Deductions	(3,332)	(2,271)	(1,214)
Allowance for doubtful accounts, Ending Balance	$ 638	$ 617	$ 371

Summary of Significant Accoun43

Summary of Significant Accounting Policies - Schedule of Property Plant and Equipment Useful Life (Detail)	12 Months Ended
	Dec. 31, 2017
Employee Related Computer Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, Estimated Useful Life	2 years
Employee Related Computer Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, Estimated Useful Life	3 years
Computer Equipment and Purchased Software [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, Estimated Useful Life	3 years
Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, Estimated Useful Life	5 years
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, Estimated Useful Life	5 years
Internal Use Software [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, Estimated Useful Life	5 years
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, Estimated Useful Life, Description	Lesser of lease term or useful life

Summary of Significant Accoun44

Summary of Significant Accounting Policies - Schedule of Changes in Asset Retirement Obligations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Asset Retirement Obligation Disclosure [Abstract]
Beginning balance	$ 591
Additions	580	$ 561
Accretion	46	30
Settlements	(26)
Ending balance	$ 1,191	$ 591

Summary of Significant Accoun45

Summary of Significant Accounting Policies - Summary of Capitalized Software Development Costs Exclusive of Costs Recorded within Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Capitalized Computer Software Net [Abstract]
Gross capitalized software development costs	$ 33,360	$ 25,152
Accumulated amortization	(24,600)	(18,629)
Capitalized software development costs, net	$ 8,760	$ 6,523

Fair Value of Financial Instr46

Fair Value of Financial Instruments - Schedule of Fair Value of Financial Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of short and long term investments	$ 448,057	$ 90,366
Fair value of financial assets	466,007	122,626
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of financial assets	12,845	32,260
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of financial assets	453,162	90,366
Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of cash and cash equivalents	12,845	32,260
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of cash and cash equivalents	12,845	32,260
Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of short and long term investments	5,867	12,439
Commercial Paper [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of short and long term investments	5,867	12,439
Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of short and long term investments	81,668	66,947
Corporate Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of short and long term investments	81,668	66,947
US Government Agency Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of short and long term investments	3,987	10,980
US Government Agency Obligations [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of short and long term investments	3,987	$ 10,980
US Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of short and long term investments	356,535
US Treasury Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of short and long term investments	356,535
Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of restricted cash	5,105
Certificates of Deposit [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of restricted cash	$ 5,105

Fair Value of Financial Instr47

Fair Value of Financial Instruments - Additional Information (Detail) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Other assets	$ 4,617,000	$ 950,000
Strategic Investments [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Other assets	3,500,000	$ 0
2022 Notes [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Fair value of notes	$ 460,000,000

Fair Value of Financial Instr48

Fair Value of Financial Instruments - Summary of Composition of Short and Long Term Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 448,492	$ 90,570
Unrealized Gains	8
Unrealized Losses	(443)	(204)
Aggregate Fair Value	448,057	90,366
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,874	12,446
Unrealized Losses	(7)	(7)
Aggregate Fair Value	5,867	12,439
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	81,947	67,126
Unrealized Losses	(279)	(179)
Aggregate Fair Value	81,668	66,947
US Government Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,000	10,998
Unrealized Losses	(13)	(18)
Aggregate Fair Value	3,987	$ 10,980
US Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	356,671
Unrealized Gains	8
Unrealized Losses	(144)
Aggregate Fair Value	$ 356,535

Fair Value of Financial Instr49

Fair Value of Financial Instruments - Summary of Contractual Maturities of Short and Long Term Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Amortized Cost Basis, Due within one year	$ 416,932	$ 54,694
Amortized Cost Basis, Due after 1 year through 2 years	31,560	35,876
Amortized Cost	448,492	90,570
Aggregate Fair Value, Due within one year	416,663	54,648
Aggregate Fair Value, Due after 1 year through 2 years	31,394	35,718
Aggregate Fair Value, Total	$ 448,057	$ 90,366

Property and Equipment - Schedu

Property and Equipment - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 65,520	$ 42,999
Less accumulated depreciation	(22,226)	(12,798)
Property and equipment, net	43,294	30,201
Computer Equipment and Purchased Software [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	4,571	3,237
Employee Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	4,260	1,534
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	11,083	8,174
Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	2,620	2,326
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	33,446	23,693
Equipment under Capital Lease [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	3,450	2,412
Internal Use Software [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	2,892	1,301
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 3,198	$ 322

Property and Equipment - Additi

Property and Equipment - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Depreciation and amortization	$ 9,400	$ 5,900	$ 2,700
Accumulated depreciation	2,400	1,200
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Capitalized asset retirement costs	$ 1,100	$ 561

Business Acquisition and Purc52

Business Acquisition and Purchase of Technology - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 20, 2017	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2015	Dec. 31, 2016
Business Acquisition [Line Items]
Cash consideration paid			$ 9,415	$ 600
Goodwill			$ 14,950		$ 9,773
Deferred tax benefit from release of deferred tax asset valuation allowance	$ 2,200
Acquired Technology [Member]
Business Acquisition [Line Items]
Estimated useful life		2 years
Intangible assets acquired		$ 400
Motion AI, Inc. [Member]
Business Acquisition [Line Items]
Acquisition effective date			Sep. 20, 2017
Business acquisition, description of acquired entity			On September 20, 2017, the Company acquired 100% of the equity interests of Motion AI, Inc., a Delaware technology corporation that allows users to scale one-to-one communications. The acquisition strengthens the Company’s position in the one-to-one communication space. Under the terms of the purchase agreement, the Company paid $9.0 million. The excess of the purchase consideration over the fair value of net tangible and identifiable intangible assets and liabilities acquired was recorded as goodwill and is primarily attributable to expanded market opportunities.
Percentage of equity interests acquired	100.00%
Cash consideration paid	$ 9,000
Business combination, assets acquired and liabilities assumed, tangible assets	32
Goodwill	5,200
Business combination, potential consideration not included in purchase price allocation	$ 4,000
Potential consideration recording period, if earned	3 years
Motion AI, Inc. [Member] | Developed Technology [Member]
Business Acquisition [Line Items]
Estimated useful life	2 years
Motion AI, Inc. [Member] | Acquired Technology [Member]
Business Acquisition [Line Items]
Estimated useful life	2 years
Intangible assets acquired	$ 6,000		$ 6,000

Intangible Assets - Schedule of

Intangible Assets - Schedule of Intangible Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Finite Lived Intangible Assets [Line Items]
Accumulated amortization	$ (1,020)	$ (916)
Intangible assets, net	6,312	16
Acquired Technology [Member]
Finite Lived Intangible Assets [Line Items]
Acquired intangible assets	$ 7,252	852
Acquired intangible assets, Weighted average remaining useful life	19 months
Acquired Intellectual Property [Member]
Finite Lived Intangible Assets [Line Items]
Acquired intangible assets	$ 80	$ 80

Intangible Assets - Additional

Intangible Assets - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 20, 2017	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite Lived Intangible Assets [Line Items]
Amortization expense			$ 103	$ 84	$ 96
Acquired Technology [Member]
Finite Lived Intangible Assets [Line Items]
Estimated useful life		2 years
Intangible assets acquired		$ 400
Acquired Technology [Member] | Motion AI, Inc. [Member]
Finite Lived Intangible Assets [Line Items]
Estimated useful life	2 years
Intangible assets acquired	$ 6,000		$ 6,000
Acquired Technology [Member] | Minimum [Member]
Finite Lived Intangible Assets [Line Items]
Estimated useful life			2 years
Acquired Technology [Member] | Maximum [Member]
Finite Lived Intangible Assets [Line Items]
Estimated useful life			3 years
Acquired Intellectual Property [Member] | Minimum [Member]
Finite Lived Intangible Assets [Line Items]
Estimated useful life			2 years
Acquired Intellectual Property [Member] | Maximum [Member]
Finite Lived Intangible Assets [Line Items]
Estimated useful life			3 years

Intangible Assets - Estimated F

Intangible Assets - Estimated Future Amortization Expense for Intangible Assets (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Goodwill And Intangible Assets Disclosure [Abstract]
2,018	$ 200
2,019	112
Total	$ 312

0.25% Convertible Senior Note56

0.25% Convertible Senior Notes, Convertible Note Hedge and Warrant - Additional Information (Detail) $ / shares in Units, shares in Millions	1 Months Ended	12 Months Ended
	May 31, 2017USD ($)d$ / shares	Dec. 31, 2017USD ($)$ / sharesshares
Debt Instrument [Line Items]
Net proceeds from the debt offering		$ 389,233,000
Sales of warrants		58,880,000
Common Stock [Member]
Debt Instrument [Line Items]
Warrants, issuance costs		$ 583,000
0.25% Convertible Senior Notes Due 2022 [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	0.25%
Debt instrument, maturity date		Jun. 1, 2022
Debt instrument, payment terms		The interest rates are fixed at 0.25% per annum and are payable semi-annually in arrears on June 1 and December 1 of each year, commencing on December 1, 2017.
Net proceeds from the debt offering	$ 389,200,000
Principal amount of each convertible note	$ 1,000
Debt instrument, conversion ratio	10.5519
Debt instrument, conversion price per share | $ / shares	$ 94.77
Debt Instrument, Redemption Price, Percentage	100.00%
Debt Instrument, Redemption, Description		Repurchase price equal to 100% of the principal amount of the notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date.
Carrying amount of equity component	$ 106,000,000
Debt instrument, effective interest rate	6.95%
Debt issuance costs	$ 10,800,000
Number of common shares to be repurchased under convertible note hedge transactions with certain counterparties | shares		4.2
Hedging option strike price per common stock | $ / shares		$ 94.77
Cost of convertible note hedge transactions		$ 78,900,000
Warrants expected to settle, description		The warrants are expected to settle three business days from each trading day commencing on September 1, 2022 and ending on the 79th trading day thereafter.
Settlement period of warrants excess price over strike price		3 days
Warrants expected to settle, commencement date		Sep. 1, 2022
Sales of warrants		$ 58,900,000
Warrants, issuance costs		200,000
Convertible notes hedge and warrant transactions cost net		20,000,000
Deferred tax liability adjustment to additional paid-in capital		$ 9,400,000
0.25% Convertible Senior Notes Due 2022 [Member] | Common Stock [Member]
Debt Instrument [Line Items]
Warrants holder’s option to purchase number of shares of company’s common stock | shares		4.2
Warrants exercise price per share | $ / shares		$ 115.8
0.25% Convertible Senior Notes Due 2022 [Member] | Liability Component [Member]
Debt Instrument [Line Items]
Debt issuance costs	7,900,000
0.25% Convertible Senior Notes Due 2022 [Member] | Equity Component [Member]
Debt Instrument [Line Items]
Debt issuance costs	$ 2,900,000
0.25% Convertible Senior Notes Due 2022 [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, conversion price per share | $ / shares		94.77
Percentage of closing price to trigger debt conversion	130.00%
0.25% Convertible Senior Notes Due 2022 [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, conversion price per share | $ / shares		$ 115.83
Percentage of closing price to trigger debt conversion	98.00%
0.25% Convertible Senior Notes Due 2022 [Member] | Scenario 1 [Member]
Debt Instrument [Line Items]
Debt instrument, convertible, threshold trading days | d	20
Debt instrument, convertible, threshold consecutive trading days | d	30
0.25% Convertible Senior Notes Due 2022 [Member] | Scenario Two [Member]
Debt Instrument [Line Items]
Debt instrument, convertible, threshold trading days | d	5
Debt instrument, convertible, threshold consecutive trading days | d	5
0.25% Convertible Senior Notes Due 2022 [Member] | Private Offering [Member]
Debt Instrument [Line Items]
Principal amount of long term debt	$ 350,000,000
0.25% Convertible Senior Notes Due 2022 [Member] | Over-Allotment Options [Member]
Debt Instrument [Line Items]
Principal amount of long term debt	$ 50,000,000

0.25% Convertible Senior Note57

0.25% Convertible Senior Notes, Convertible Note Hedge and Warrant - Schedule of Net Carrying Amount of Liability Component (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Debt Instrument [Line Items]
Net carrying amount	$ 298,447
0.25% Convertible Senior Notes Due 2022 as Liability Component [Member]
Debt Instrument [Line Items]
Principal	400,000
Unamortized debt discount	(94,498)
Unamortized issuance costs	(7,055)
Net carrying amount	$ 298,447

0.25% Convertible Senior Note58

0.25% Convertible Senior Notes, Convertible Note Hedge and Warrant - Schedule of Net Carrying Amount of Equity Component (Detail) - 0.25% Convertible Senior Notes Due 2022 as Equity Component [Member] $ in Thousands	Dec. 31, 2017USD ($)
Debt Instrument [Line Items]
Debt discount for conversion option	$ 106,006
Issuance costs	(2,854)
Net carrying amount	$ 103,152

0.25% Convertible Senior Note59

0.25% Convertible Senior Notes, Convertible Note Hedge and Warrant - Schedule of Interest Expense (Detail) - 0.25% Convertible Senior Notes Due 2022 [Member] $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Debt Instrument [Line Items]
Contractual interest expense	$ 639
Amortization of debt discount	859
Amortization of issuance costs	11,507
Total interest expense	$ 13,005

0.25% Convertible Senior Note60

0.25% Convertible Senior Notes, Convertible Note Hedge and Warrant - Schedule of Net Equity Impact, Included in Additional Paid-in Capital, of the Liability and Equity Components (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Debt Instrument [Line Items]
Total	$ 73,713
0.25% Convertible Senior Notes Due 2022 as Net Equity Impact [Member]
Debt Instrument [Line Items]
Conversion Option	106,006
Purchase of Convertible Note Hedges	(78,920)
Sales of warrants	59,080
Issuance costs	(3,054)
Deferred tax liability	(9,399)
Total	$ 73,713

Geographic Data - Additional In

Geographic Data - Additional Information (Detail) - Segment	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Number of operating segment	1
Revenue [Member] | Outside Of United States [Member] | Geographic Concentration Risk [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	33.00%	28.00%

Geographic Data - Revenues by G

Geographic Data - Revenues by Geographical Region (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Total Revenues	$ 106,541	$ 97,726	$ 89,093	$ 82,252	$ 76,444	$ 70,589	$ 64,974	$ 58,960	$ 375,612	$ 270,967	$ 181,943
Americas [Member]
Segment Reporting Information [Line Items]
Total Revenues									283,696	219,422	154,625
Europe [Member]
Segment Reporting Information [Line Items]
Total Revenues									70,895	41,616	23,487
Asia Pacific [Member]
Segment Reporting Information [Line Items]
Total Revenues									$ 21,021	$ 9,929	$ 3,831
Revenue [Member] | Outside Of Americas [Member] | Geographic Concentration Risk [Member]
Segment Reporting Information [Line Items]
Percentage of revenues generated outside of the Americas									24.00%	19.00%	15.00%

Geographic Data - Long Lived As

Geographic Data - Long Lived Assets by Geographical Region (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Total long lived assets	$ 43,294	$ 30,201
Americas [Member]
Segment Reporting Information [Line Items]
Total long lived assets	29,764	23,205
Europe [Member]
Segment Reporting Information [Line Items]
Total long lived assets	11,257	4,716
Asia Pacific [Member]
Segment Reporting Information [Line Items]
Total long lived assets	$ 2,273	$ 2,280
Outside Of Americas [Member] | Assets Total [Member] | Geographic Concentration Risk [Member]
Segment Reporting Information [Line Items]
Percentage of long lived assets held outside of the Americas	31.00%	23.00%

Commitments and Contingencies-

Commitments and Contingencies- Additional Information (Detail) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2018USD ($)ft²	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Operating And Capital Leased Assets [Line Items]
Increase in future lease commitments		$ 31,600
Improvement reimbursements from landlords		7,300
Rent expense		18,900	$ 13,800	$ 7,400
Deferred rent, net of current portion		19,000	$ 10,200
Rent payable		$ 201,900
Subsequent Event [Member] | Lease Commencement, January 2018 [Member]
Operating And Capital Leased Assets [Line Items]
Lease agreement period	18 years
Renewal term	10 years
Square feet of property leased | ft²	13,000
Lease commencement date	2018-01
Rent payable	$ 8,500

Commitments and Contingencies -

Commitments and Contingencies - Schedule of Future Minimum Payments (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Commitments And Contingencies Disclosure [Abstract]
Capital Leases, 2018	$ 771
Capital Leases, 2019	290
Capital Leases, 2020	30
Capital Leases, Total	1,091
Less: Portion representing interest	(34)
Capital lease obligation	1,057
Operating, 2018	19,345
Operating, 2019	19,752
Operating, 2020	19,997
Operating, 2021	21,433
Operating, 2022	21,729
Operating, Thereafter	99,644
Operating, Total	$ 201,900

Commitments and Contingencies66

Commitments and Contingencies - Schedule of Future Minimum Payments Under Vendor Commitments (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Product Related Obligations [Member]
Long Term Purchase Commitment [Line Items]
Vendor Commitments, 2018	$ 15,852
Vendor Commitments, 2019	10,826
Vendor Commitments, 2020	1,500
Vendor Commitments, Total	28,178
INBOUND Event Obligations [Member]
Long Term Purchase Commitment [Line Items]
Vendor Commitments, 2018	475
Vendor Commitments, 2019	316
Vendor Commitments, 2020	316
Vendor Commitments, 2021	653
Vendor Commitments, 2022	653
Vendor Commitments, Thereafter	653
Vendor Commitments, Total	$ 3,066

Changes in Accumulated Other 67

Changes in Accumulated Other Comprehensive Loss - Changes in Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance, Amount	$ 118,700	$ 121,708
Other comprehensive (loss) income before reclassifications	807	(59)
Ending Balance, Amount	210,360	118,700
Cumulative Translation Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance, Amount	(589)	(417)
Other comprehensive (loss) income before reclassifications	968	(172)
Ending Balance, Amount	379	(589)
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance, Amount	(275)	(388)
Other comprehensive (loss) income before reclassifications	(161)	113
Ending Balance, Amount	(436)	(275)
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance, Amount	(864)	(805)
Ending Balance, Amount	$ (57)	$ (864)

Stockholders' Equity and Stoc68

Stockholders' Equity and Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Sep. 25, 2014	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Common stock authorized		500,000,000	500,000,000
Number of Shares outstanding		2,315,000	2,709,000
Unrecognized compensation costs		$ 5,400
Unrecognized compensation costs, weighted average period		2 years 2 months 12 days
Software Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Capitalized software development costs excluded from stock based compensation		$ 1,600	$ 1,200	$ 492
RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Percentage of service condition met		25.00%
Service agreement period description		The service condition is a time-based condition met over a period of four years, with 25% met after one year, and then in equal monthly or quarterly installments over the succeeding three years, or over a period of four years, with equal quarterly installments over those four years.
The total stock-based compensation expense expected to be recorded		$ 102,300
Weighted average period of RSU		2 years 8 months 12 days
Number of RSUs expected to vest		2,100,000
Aggregate intrinsic value of RSUs expected to vest		$ 184,100
Total fair value of RSUs vested		$ 48,600	$ 24,000	$ 11,900
Common Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Weighted-average grant date fair value of options granted		$ 24.56	$ 16.97	$ 16.53
Maximum [Member] | RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Period of service condition met		4 years
Minimum [Member] | RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Period of service condition met		1 year
2007 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Number of shares available for issuance		0
2007 Equity Incentive Plan [Member] | Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Number of Shares outstanding		1,700,000
2007 Equity Incentive Plan [Member] | RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Number of Shares outstanding		49,000
2007 Equity Incentive Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Number of years fixed for each option		10 years
2014 Stock Option and Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Percentage of common stock outstanding	5.00%
2014 Stock Option and Incentive Plan [Member] | Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Number of shares available for issuance	1,973,551
Number of Shares outstanding		582,000
2014 Stock Option and Incentive Plan [Member] | RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Number of Shares outstanding		2,000,000
2014 Stock Option and Incentive Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Number of years fixed for each option	10 years

Stockholders' Equity and Stoc69

Stockholders' Equity and Stock-Based Compensation - Summary of Number of Shares of Common Stock Reserved (Detail) - shares	Dec. 31, 2017	Dec. 31, 2016	Sep. 25, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for the potential conversion	4,410,000	4,984,000
ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for the potential conversion	10,000	11,000	1,409,988
RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for the potential conversion	2,085,000	2,264,000
Common Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for the potential conversion	2,315,000	2,709,000

Stockholders' Equity and Stoc70

Stockholders' Equity and Stock-Based Compensation - Schedule of Stock Compensation Expense by Award Type (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 47,317	$ 32,675	$ 21,308
ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	1,233	1,093	1,035
Common Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	4,948	5,202	6,349
RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 41,136	$ 26,380	$ 13,924

Stockholders' Equity and Stoc71

Stockholders' Equity and Stock-Based Compensation - Effect of Stock-Based Compensation on Income by Line Item (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 47,317	$ 32,675	$ 21,308
Cost of Revenue, Subscription [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	658	512	341
Cost of Revenue, Service [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	2,327	1,640	1,216
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	12,816	8,828	6,327
Sales and Marketing [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	19,016	13,352	7,658
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 12,500	$ 8,343	$ 5,766

Stockholders' Equity and Stoc72

Stockholders' Equity and Stock-Based Compensation - Schedule of Assumptions Used for Estimation of Fair Value of Options Granted to Employees (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate (%)	1.74%	1.38%	1.36%
Expected term (years)	5 years 2 months 4 days	5 years 29 days	6 years 2 months 4 days
Volatility (%)	39.40%	38.00%	43.00%
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate (%)	2.09%	1.41%	1.53%
Expected term (years)	6 years 2 months 15 days	6 years 2 months 15 days	6 years 2 months 19 days
Volatility (%)	43.70%	41.00%	51.60%

Stockholders' Equity and Stoc73

Stockholders' Equity and Stock-Based Compensation - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Beginning balance	2,709
Number of Shares, Granted	180
Number of Shares, Exercised	(543)
Number of Shares, Forfeited/Expired	(31)
Number of Shares, Ending balance	2,315	2,709
Number of Shares, Vested and expected to vest	2,315
Number of Shares, Exercisable	1,945
Weighted Average Exercise Price, Beginning balance	$ 13.99
Weighted Average Exercise Price, Granted	56.67
Weighted Average Exercise Price, Exercised	16.07
Weighted Average Exercise Price, Forfeited/ Expired	24.12
Weighted Average Exercise Price , Ending balance	16.69	$ 13.99
Weighted Average Exercise Price, Vested and expected to vest	16.69
Weighted Average Exercise Price, Exercisable	$ 11.39
Weighted Average Remaining Life, Outstanding	5 years 3 months 18 days	6 years 1 month 6 days
Weighted Average Remaining Life, Options vested or expected to vest	5 years 3 months 18 days
Weighted Average Remaining Life, Options exercisable	4 years 9 months 18 days
Aggregate Intrinsic Value, Outstanding	$ 165,974	$ 89,411
Aggregate Intrinsic Value, Options vested or expected to vest	165,974
Aggregate Intrinsic Value, Options exercisable	$ 149,803

Stockholders' Equity and Stoc74

Stockholders' Equity and Stock-Based Compensation - Summary of Activity Related to RSUs (Detail) - RSUs [Member] shares in Thousands	12 Months Ended
	Dec. 31, 2017$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted Shares, Beginning balance | shares	2,264
Shares, Granted | shares	1,189
Shares, Vested | shares	(1,151)
Shares, Canceled | shares	(217)
Restricted shares, Ending balance | shares	2,085
Weighted average grant date fair value, Beginning balance | $ / shares	$ 42.04
Weighted- Average Grant Date Fair Value, Granted | $ / shares	64.59
Weighted- Average Grant Date Fair Value, Vested | $ / shares	42.24
Weighted- Average Grant Date Fair, Canceled | $ / shares	48.13
Weighted average grant date fair value, Ending balance | $ / shares	$ 54.12

Employee Stock Purchase Plan -

Employee Stock Purchase Plan - Additional Information (Detail) - shares	Sep. 25, 2014	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorizes for issuance		4,410,000	4,984,000
Percentage of discount allowed to employee to purchase common stock	15.00%
ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorizes for issuance	1,409,988	10,000	11,000

Employee Stock Purchase Plan 76

Employee Stock Purchase Plan - Summary of Activity Related to Employee Stock Purchase Plan (Detail) - ESPP [Member] - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Issued	94	70	29
Weighted-Average Purchase Price	$ 38.83	$ 38.98	$ 28.46
Total Cash Proceeds	$ 3,635	$ 2,721	$ 814

Income Taxes - Schedule of (Los

Income Taxes - Schedule of (Loss) Income Before Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
United States	$ (54,894)	$ (47,112)	$ (47,911)
Foreign	4,855	2,083	2,270
Total	$ (50,039)	$ (45,029)	$ (45,641)

Income Taxes - Components of In

Income Taxes - Components of Income Tax Benefit (Provision) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current income tax provision
State	$ (144)	$ (95)	$ (61)
Foreign	(1,077)	(579)	(401)
Total current income tax provision	(1,221)	(674)	(462)
Deferred income tax benefit
Federal	10,435	61	(10)
State	977
Foreign	134	80	60
Total deferred income tax benefit	11,546	141	50
Total income tax benefit (provision)	$ 10,325	$ (533)	$ (412)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation Of Income Taxes [Line Items]
Federal statutory income tax rate		35.00%
Remeasurement of deferred tax balances due to change in U.S. corporate tax rate		$ 49,123,000
Increase in valuation allowance		$ 5,500,000	$ 16,500,000	$ 19,400,000
Valuation allowance changes, description		The Company does not expect any significant changes in its valuation allowance positions within the next 12 months.
Undistributed foreign earnings		$ 6,900,000
Federal net operating loss carryforwards		352,500,000
State net operating loss carryforwards		$ 224,700,000
Federal and state net operating loss carryforwards, expiration year		Dec. 31, 2037
Research and development credits		$ 9,402,000	$ 6,674,000
Minimum percentage chances of tax benefit to be realized on examination		50.00%
Unrecognized tax benefits affect the Company's effective tax rate		$ 0
Interest or penalties recorded		$ 0
Expected significant change in unrecognized tax benefits, description		The Company does not expect any significant change in its unrecognized tax benefits within the next 12 months
Federal [Member]
Reconciliation Of Income Taxes [Line Items]
Research and development credits		$ 5,800,000
Research and development credit carryforwards, expiration year		Dec. 31, 2037
State [Member]
Reconciliation Of Income Taxes [Line Items]
Research and development credits		$ 2,500,000
Research and development credit carryforwards, expiration year		Dec. 31, 2032
Investments credits		$ 756,000
Scenario Forecast [Member]
Reconciliation Of Income Taxes [Line Items]
Federal statutory income tax rate	21.00%

Income Taxes - Schedule of Diff

Income Taxes - Schedule of Differences Between Income Taxes Computed at the Federal Statutory Rate and the Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Expected income tax benefit at the federal statutory rate	$ 17,166	$ 15,761	$ 15,974
State taxes net of federal benefit	5,150	916	2,257
Stock-based compensation	10,939	(2,001)	(1,685)
Difference in foreign tax rates	988	415	482
U.S. tax credits	1,717	1,609	2,738
Convertible debt and acquisition	11,573
Federal rate change	(49,123)
Transition tax	(1,063)
Change in valuation allowance	13,988	(16,413)	(19,421)
Other	(1,010)	(820)	(757)
Total income tax benefit (provision)	$ 10,325	$ (533)	$ (412)

Income Taxes - Components of th

Income Taxes - Components of the Company's Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating loss carryforwards	$ 87,521	$ 73,750
Research and investment credits	9,402	6,674
Accruals and reserves	6,627	6,699
Depreciation	911	744
Intangible assets		215
Stock-based compensation	4,146	8,115
Total deferred tax assets	108,607	96,197
Deferred tax liabilities:
Intangible assets	(1,273)
Convertible debt	(5,664)
Capitalized costs	(4,648)	(4,843)
Total deferred tax liabilities	(11,585)	(4,843)
Valuation allowance	(96,630)	(91,132)
Net deferred tax assets	$ 392	$ 222

Income Taxes - Summary of Activ

Income Taxes - Summary of Activity Related to Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Unrecognized benefit - beginning of the year	$ 1,742	$ 673	$ 1,713
Gross increases-current period positions	983	1,069	171
Gross decrease—prior period positions			(1,211)
Unrecognized benefit - end of period	$ 2,725	$ 1,742	$ 673

Employee Benefit Plan - Additio

Employee Benefit Plan - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Postemployment Benefits [Abstract]
Contribution to Defined contribution savings plan	$ 2.9	$ 2.1	$ 1.2

Quarterly Financial Results (84

Quarterly Financial Results (Unaudited) - Schedule of Quarterly Financial Results (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 106,541	$ 97,726	$ 89,093	$ 82,252	$ 76,444	$ 70,589	$ 64,974	$ 58,960	$ 375,612	$ 270,967	$ 181,943
Cost of revenue	21,056	19,010	18,591	17,072	16,887	15,812	15,195	13,971	75,729	61,865	47,923
Gross profit	85,485	78,716	70,502	65,180	59,557	54,777	49,779	44,989	299,883	209,102	134,020
Net loss	$ (11,535)	$ (10,583)	$ (9,521)	$ (8,075)	$ (13,829)	$ (10,515)	$ (11,064)	$ (10,154)	$ (39,714)	$ (45,562)	$ (46,053)
Basic and diluted net loss per share	$ (0.31)	$ (0.29)	$ (0.26)	$ (0.22)	$ (0.39)	$ (0.30)	$ (0.32)	$ (0.29)	$ (1.08)	$ (1.29)	$ (1.39)