Summary of Significant Accounting Policies | 2. Summary of Significant Accounting Policies Principles of Consolidation — The accompanying condensed consolidated financial statements include the results of operations of the Company and its wholly-owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation. The Company has prepared the accompanying condensed consolidated financial statements in conformity with accounting principles generally accepted in the United States of America, or GAAP. Unaudited Interim Condensed Consolidated Financial Statements — The accompanying condensed consolidated financial statements and the related interim information contained within the notes to the condensed consolidated financial statements are unaudited and have been prepared in accordance with GAAP and applicable rules and regulations of the Securities and Exchange Commission for interim financial information. Accordingly, they do not include all of the information and notes required by GAAP for complete financial statements. The accompanying unaudited condensed consolidated financial statements should be read along with the Company’s audited financial statements included in the Company’s Annual Report on Form 10-K, filed with the Securities and Exchange Commission on February 20, 2018. The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited financial statements and in the opinion of management, reflect all adjustments, consisting of normal and recurring adjustments, necessary for the fair presentation of the Company’s financial position, results of operations and cash flows for the interim periods presented. The results for the interim periods presented are not necessarily indicative of future results. The Company considers events or transactions that occur after the balance sheet date but before the financial statements are issued to provide additional evidence relative to certain estimates or to identify matters that require additional disclosure. Use of Estimates — The preparation of condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. By their nature, estimates are subject to an inherent degree of uncertainty. Actual results could differ from those estimates. Recently Adopted Accounting Pronouncements In January 2017, the Financial Accounting Standards Board, or FASB, issued ASU 2017-04, Intangibles—Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment On January 1, 2018, the Company adopted ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash (a consensus of the FASB’s EITF) Cash and cash equivalents subject to contractual restrictions and not readily available for use are classified as restricted cash. The Company’s restricted cash balances are primarily made up of cash posted as collateral for its worldwide facility leases. The following table provides a reconciliation of cash, cash equivalents and restricted cash as reported in the condensed consolidated balance sheet as of December 31, 2015, 2016 and 2017 and September 30, 2017 and 2018, to the total of the amounts reported in the condensed consolidated statement of cash flows included herein (in thousands): As of December 31, As of September 30, 2015 2016 2017 2017 2018 Cash and cash equivalents $ 123,143 $ 140,756 $ 252,402 $ 262,051 $ 167,626 Restricted cash, current, included in prepaid expenses and other current assets — 98 12 218 — Restricted cash, net of current portion 2,468 2,481 1,795 1,661 1,825 Cash, cash equivalents and restricted cash $ 125,611 $ 143,335 $ 254,209 $ 263,930 $ 169,451 In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers Revenue Recognition Other Assets and Deferred Costs—Contracts with Customers Revenue recognition from the Company’s primary revenue streams remained substantially unchanged following adoption of ASC 606 and therefore did not have a material impact on its revenues. The Company also considered the impact of ASC 606 subtopic ASC 340-40. Prior to the adoption of ASC 606, the Company expensed commission costs and related fringe benefits as incurred. Under ASC 340-40, the Company is required to capitalize and amortize incremental costs of obtaining a contract, such as sales commissions and related fringe benefits, over the period of benefit, which the Company has calculated to be three years. Incremental costs of obtaining a contract are recognized as an asset if the costs are expected to be recovered. The period of benefit was determined based on an average customer contract term, technology changes, and the company’s ability to retain customers. Sales commissions for renewal contracts are deferred and amortized on a straight-line basis over the related contractual renewal period. Amortization expense is included in sales and marketing expense on the condensed consolidated statements of operations. On January 1, 2018, the Company adopted ASC 606 using the modified retrospective transition method which resulted in an adjustment to retained earnings for the cumulative effect of applying the standard to all contracts not completed as of the adoption date. Upon adoption, prepaid expenses and other current assets increased by $10.7 million due to the capitalization of the current portion of sales commissions and other assets increased by $17.3 million due to the capitalization of the noncurrent portion of sales commissions. Deferred tax liabilities increased by $6.6 million due to temporary differences between the accounting and tax carrying values of the capitalized commissions. Retained earnings increased by $21.4 million as a net result of these adjustments. The comparative information has not been restated and continues to be reported under the accounting standards in effect for those periods. The Company has elected the use of practical expedients in its adoption of the new standard, which includes continuing to record revenue reported net of applicable taxes imposed on the related transaction and the application of the standard to all contracts not completed as of the adoption date. The following tables summarize the impact of adopting ASC 606 on the Company’s condensed consolidated financial statements during the three and nine months ended September 30, 2018 (in thousands, except per share data): As of September 30, 2018 As Reported Adjustments Balance Without Adoption of ASC 606 Condensed Consolidated Balance Sheet Assets Prepaid expenses and other current assets $ 61,926 $ (26,633 ) $ 35,293 Other assets 38,006 (28,331 ) 9,675 Liabilities Deferred tax liabilities $ 218,396 $ (13,013 ) $ 205,383 Equity Retained earnings (accumulated deficit) $ 73,957 $ (41,951 ) $ 32,006 Three Months Ended September 30, 2018 Nine Months Ended September 30, 2018 As Reported Adjustments Balance Without Adoption of ASC 606 As Reported Adjustments Balance Without Adoption of ASC 606 Condensed Consolidated Statement of Operations Sales and marketing $ 95,041 $ 12,018 $ 107,059 $ 282,599 $ 27,648 $ 310,247 (Provision for) benefit from income taxes $ (2,570 ) $ 2,942 $ 372 $ (14,269 ) $ 6,577 $ (7,692 ) Net income (loss) $ 12,717 $ (9,077 ) $ 3,640 $ 48,983 $ (21,072 ) $ 27,911 Net income (loss) per share: Basic $ 0.25 $ (0.18 ) $ 0.07 $ 0.94 $ (0.40 ) $ 0.54 Diluted $ 0.24 $ (0.17 ) $ 0.07 $ 0.93 $ (0.40 ) $ 0.53 Nine Months Ended September 30, 2018 As Reported Adjustments Balance Without Adoption of ASC 606 Condensed Consolidated Statement of Cash Flows Cash flows from operating activities Net income (loss) $ 48,983 $ (21,072 ) $ 27,911 Benefit from deferred income taxes (34,062 ) (6,577 ) (40,639 ) Prepaid expenses and other current assets 8,474 16,395 24,869 Other assets (12,830 ) 11,254 (1,576 ) Net cash provided by operating activities 330,864 — 330,864 Costs to Obtain and Fulfill a Contract — The Company’s incremental costs of obtaining a contract consist of sales commissions and their related fringe benefits. Sales commissions and fringe benefits paid on renewals are not commensurate with sales commissions paid on the initial contract, but they are commensurate with each other. Sales commissions and fringe benefits are deferred and amortized on a straight-line basis over the period of benefit, which the Company has estimated to be three years, for initial contracts and are amortized over the renewal period for renewal contracts, typically one year. The period of benefit was determined based on an average customer contract term, expected contract renewals, changes in technology and the Company’s ability to retain customers. Deferred commissions are classified as current or noncurrent assets based on the timing the expense will be recognized. The current and noncurrent portions of deferred commissions are included in prepaid expenses and other current assets and other assets, respectively, in the Company’s condensed consolidated balance sheets. As of September 30, 2018, the Company had $26.6 million of current deferred commissions and $28.3 million of noncurrent deferred commissions. Commissions expense is primarily included in sales and marketing expense on the condensed consolidated statements of operations. The Company had amortization expense of $5.8 million and $13.5 million related to deferred commissions during the three and nine months ended September 30, 2018, respectively. Other costs incurred to fulfill contracts have been immaterial to date. Revenue Recognition — The Company derives its revenue primarily from subscription fees for its premium subscription software services and, to a lesser extent, usage fees from audio services. Revenue is reported net of applicable sales and use tax, value-added tax and other transaction taxes imposed on the related transaction including mandatory government charges that are passed through to the Company’s customers. Revenue is recognized when control of these services is transferred to the Company’s customers, in an amount that reflects the consideration the Company expects to be entitled to in exchange for those services. The Company determines revenue recognition through the following five steps: • Identification of the contract, or contracts, with a customer • Identification of the performance obligations in the contract • Determination of the transaction price • Allocation of the transaction price to the performance obligations in the contract • Recognition of revenue when, or as, performance obligations are satisfied The Company accounts for a contract when it has approval and commitment from both parties, the rights of the parties are identified, payment terms are identified, the contract has commercial substance and collectability of consideration is probable. Disaggregated Revenue — The Company disaggregates revenue from contracts with customers by geography and product grouping, as it believes it best depicts how the nature, amount, timing and uncertainty of revenue and cash flows are affected by economic factors. The Company’s revenue by geography (based on customer address) is as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2017 2018 2017 2018 Revenues: United States $ 204,831 $ 241,630 $ 545,117 $ 690,097 United Kingdom 13,371 13,883 37,318 42,336 International — all other 51,065 53,414 131,315 161,361 Total revenue $ 269,267 $ 308,927 $ 713,750 $ 893,794 The Company’s revenue by product grouping is as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2017 2018 2017 2018 Revenues: Communications and collaboration $ 146,808 $ 175,045 $ 377,780 $ 498,142 Identity and access 76,380 89,762 208,487 262,197 Customer engagement and support 46,079 44,120 127,483 133,455 Total revenue $ 269,267 $ 308,927 $ 713,750 $ 893,794 Performance Obligations Premium Subscription Services As each day of providing access to the software is substantially the same and the customer simultaneously receives and consumes the benefits as access is provided, the Company has determined that its premium subscription services arrangements include a single performance obligation comprised of a series of distinct services. Revenue from the Company’s premium subscription services is recognized over time on a ratable basis over the contract term beginning on the date that our service is made available to the customer. Subscription periods range from monthly to multi-year, with the majority of contracts being one year, billed annually in advance and non-cancelable. Audio Services Accounts Receivable, Net — Accounts receivable, net, are amounts due from customers where there is an unconditional right to consideration. Unbilled receivables of $5.1 million and $3.2 million are included in this balance at December 31, 2017 and September 30, 2018, respectively. The payment of consideration related to these unbilled receivables is subject only to the passage of time. Contract Assets and Contract Liabilities — Contract assets and contract liabilities (deferred revenue) are reported net at the contract level for each reporting period. Contract Assets Contract Liabilities (Deferred Revenue) For the three and nine months ended September 30, 2018, revenue recognized related to deferred revenue at January 1, 2018 was approximately $62 million and $312 million, respectively. Approximately $493 million of revenue is expected to be recognized from remaining performance obligations as of September 30, 2018. Changes in contract balances for the nine months ended September 30, 2018 are as follows (in thousands): Deferred Revenue Current Non-Current Balance as of January 1, 2018 $ 340,570 $ 6,735 Increase (decrease), net 24,297 1,720 Balance as of September 30, 2018 $ 364,867 $ 8,455 Concentrations of Credit Risk and Significant Customers — The Company’s principal credit risk relates to its cash, cash equivalents, restricted cash and accounts receivable. Cash, cash equivalents and restricted cash are deposited primarily with financial institutions that management believes to be of high-credit quality. To manage accounts receivable credit risk, the Company regularly evaluates the creditworthiness of its customers and maintains allowances for potential credit losses. To date, losses resulting from uncollected receivables have not exceeded management’s expectations. For the three and nine months ended September 30, 2017 and 2018, no customer accounted for more than 10% of revenue. As of December 31, 2017 and September 30, 2018, no customer accounted for more than 10% of accounts receivable. Segment Data — Operating segments are identified as components of an enterprise for which separate discrete financial information is available for evaluation by the chief operating decision-maker or decision-making group when making decisions regarding resource allocation and assessing performance. The Company’s chief operating decision maker is its Chief Executive Officer. The Company, whose management uses consolidated financial information in determining how to allocate resources and assess performance, has determined that it operates in one segment. Marketable Securities — The Company’s marketable securities are classified as available-for-sale and are carried at fair value with the unrealized gains and losses, net of tax, reported as a component of accumulated other comprehensive income in equity. Realized gains and losses and declines in value judged to be other than temporary are included as a component of earnings based on the specific identification method. Fair value is determined based on quoted market prices. At September 30, 2017, marketable securities consisted of U.S. government agency securities and corporate bonds that had remaining maturities within two years and have an aggregate amortized cost and an aggregate fair value of $14.0 million, including $11,000 of unrealized losses. The Company did not have any marketable securities as of December 31, 2017 or September 30, 2018. Goodwill — Goodwill is the excess of the acquisition price over the fair value of the tangible and identifiable intangible net assets acquired. The Company does not amortize goodwill but performs an impairment test of goodwill annually or whenever events and circumstances indicate that the carrying amount of goodwill may exceed its fair value. The Company operates as a single operating segment with one reporting unit and consequently evaluates goodwill for impairment based on an evaluation of the fair value of the Company as a whole. As of November 30, 2017, our measurement date, the fair value of the Company as a whole exceeded the carrying amount of the Company. Through September 30, 2018, no events have been identified indicating an impairment. Long-Lived Assets and Intangible Assets — The Company records intangible assets at their respective estimated fair values at the date of acquisition. Intangible assets are being amortized based upon the pattern in which their economic benefit will be realized, or if this pattern cannot be reliably determined, using the straight-line method over their estimated useful lives, which range up to eleven years. The Company reviews long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of the assets, including intangible assets, may not be recoverable. 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 is impairment, the amount of the impairment is calculated as the difference between the carrying value and fair value. Through September 30, 2018, the Company recorded no material impairments. Foreign Currency Translation — The functional currency of operations outside the United States of America is deemed to be the currency of the local country, unless it is otherwise determined that the United States dollar would serve as a more appropriate functional currency given the economic operations of the entity. Accordingly, the assets and liabilities of the Company’s foreign subsidiaries are translated into United States dollars using the period-end exchange rate, and income and expense items are translated using the average exchange rate during the period. Cumulative translation adjustments are reflected as a separate component of equity. Foreign currency transaction gains and losses are charged to operations. Derivative Financial Instruments — The Company’s earnings and cash flows are subject to fluctuations due to changes in foreign currency exchange rates. The Company uses foreign currency forward contracts to manage exposure to fluctuations in foreign exchange rates that arise from receivables and payables denominated in foreign currencies. The Company does not designate foreign currency forward contracts as hedges for accounting purposes, and changes in the fair value of these instruments are recognized immediately in earnings. Because the Company enters into forward contracts only as an economic hedge, any gain or loss on the underlying foreign-denominated balance would be offset by the loss or gain on the forward contract. Gains and losses on forward contracts and foreign denominated receivables and payables are included in net foreign currency gains and losses. As of December 31, 2017 and September 30, 2018, the Company had outstanding forward contracts with notional amounts equivalent to the following (in thousands): Currency Hedged December 31, 2017 September 30, 2018 Euro / Canadian Dollar $ 556 $ 456 Euro / U.S. Dollar 4,208 4,038 Euro / British Pound 5,926 5,199 British Pound / U.S. Dollar — 638 Israeli Shekel / Hungarian Forint 8,008 — U.S. Dollar / Brazilian Real — 2,488 U.S. Dollar / Canadian Dollar — 4,385 Total $ 18,698 $ 17,204 Net realized and unrealized foreign currency gains and losses was a net gain of $47,000 and a net loss of $28,000 for the three and nine months ended September 30, 2017, respectively, and net losses of $0.1 million and $0.4 million for the three and nine months ended September 30, 2018, respectively, which are included in other income (expense), net in the condensed consolidated statements of operations. Excluding the underlying foreign currency exposure being hedged, net realized and unrealized gains and losses on forward contracts included in foreign currency gains and losses was a net loss of $0.4 million and $0.3 million for the three and nine months ended September 30, 2017, respectively, and a net loss of $40,000 and a net gain of $0.5 million for the three and nine months ended September 30, 2018, respectively. Stock-Based Compensation — The Company values all stock-based compensation awards, primarily restricted stock units, at fair value on the date of grant and recognizes the expense over the requisite service period, which is generally the vesting period, on a straight-line basis. Income Taxes — Deferred income taxes are provided for the tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes and operating loss carryforwards and credits using enacted tax rates expected to be in effect in the years in which the differences are expected to reverse. At each balance sheet date, the Company assesses the likelihood that deferred tax assets will be realized and recognizes a valuation allowance if it is more likely than not that some portion of the deferred tax assets will not be realized. This assessment requires judgment as to the likelihood and amounts of future taxable income by tax jurisdiction. The Company evaluates its uncertain tax positions based on a determination of whether and how much of a tax benefit taken by the Company in its tax filings is more likely than not to be realized. Potential interest and penalties associated with any uncertain tax positions are recorded as a component of income tax expense. Guarantees and Indemnification Obligations — As permitted under Delaware law, the Company has agreements whereby the Company indemnifies certain of its officers and directors for certain events or occurrences while the officer or director is, or was, serving at the Company’s request in such capacity. The term of the indemnification period is for the officer’s or director’s lifetime. As permitted under Delaware law, the Company also has similar indemnification obligations under its certificate of incorporation and bylaws. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is unlimited; however, the Company has directors’ and officers’ insurance coverage that the Company believes limits its exposure and enables it to recover a portion of any future amounts paid. In the ordinary course of business, the Company enters into agreements with certain customers that contractually obligate the Company to provide indemnifications of varying scope and terms with respect to certain matters including, but not limited to, losses arising out of the breach of such agreements, from the services provided by the Company or claims alleging that the Company’s products infringe third-party patents, copyrights, or trademarks. The term of these indemnification obligations is generally perpetual. The maximum potential amount of future payments the Company could be required to make under these indemnification obligations is, in many cases, unlimited. Through September 30, 2018, the Company has not experienced any losses related to these indemnification obligations. Net Income (Loss) Per Share — Basic net income (loss) per share is computed by dividing net income (loss) by the weighted average number of common shares outstanding for the period. Diluted net income (loss) per share is computed by dividing net income (loss) by the sum of the weighted average number of common shares outstanding during the period and, if dilutive, the weighted average number of potential common shares outstanding from the assumed exercise of stock options and the vesting of restricted stock units. The Company excluded the following options to purchase common shares and restricted stock units from the computation of diluted net income (loss) per share because they had an anti-dilutive impact (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2017 2018 2017 2018 Options to purchase common shares — — — — Restricted stock units 36 853 59 113 Total options and restricted stock units 36 853 59 113 Basic and diluted net income (loss) per share was calculated as follows (in thousands, except per share data): Three Months Ended September 30, Nine Months Ended September 30, 2017 2018 2017 2018 Net income (loss) $ 9,920 $ 12,717 $ 6,202 $ 48,983 Basic: Weighted average common shares outstanding, basic 52,706 51,652 49,697 52,090 Net income (loss) per share, basic $ 0.19 $ 0.25 $ 0.12 $ 0.94 Diluted: Weighted average common shares outstanding 52,706 51,652 49,697 52,090 Add: Common stock equivalents 900 414 1,038 739 Weighted average common shares outstanding, diluted 53,606 52,066 50,735 52,829 Net income (loss) per share, diluted $ 0.19 $ 0.24 $ 0.12 $ 0.93 Recently Issued Accounting Pronouncements On February 25, 2016, the FASB issued ASU 2016-02, Leases Along with ASU 2016-02, the Company is also evaluating Accounting Standards Update 2018-10, Codification Improvements to Topic 842 Leases, or ASU 2018-10, and Accounting Standards Update 2018-11, Targeted Improvements to Topic 842 Leases, or ASU 2018-11, which Upon adoption, the Company also expects to elect the transition package of practical expedients permitted within the new standard, which among other things, allows the carryforward of the historical lease classification. The Company has formed a project team focused on the implementation of the new accounting standard. The Company continues to evaluate which other, if any, practical expedients will be elected and is currently formalizing processes and controls to identify, classify, and measure its leases in accordance with ASU 2016-02. While the Company continues to evaluate the effect of adopting this guidance on its consolidated financial statements and related disclosures, it is expected that at a minimum, the obligations under existing operating leases, as disclosed in Note 11 to the condensed consolidated financial statements, will be reported in the consolidated balance sheet upon adoption. On February 15, 2018, the FASB issued ASU 2018-02, Income Statement—Reporting Comprehensive Income—Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income (Topic 220), |