Dropbox (DBX) 10-Q 11 May 18 2018 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2018	Apr. 30, 2018
Document Information [Line Items]
Entity Registrant Name	Dropbox, Inc.
Entity Central Index Key	1,467,623
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Document Type	10-Q
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1
Amendment Flag	false
Class A common stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		73,796,324
Class B common stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		326,601,175
Class C common stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		0

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($)		Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents		$ 665,300,000	$ 430,000,000
Short-term investments		180,700,000	0
Trade and other receivables, net		26,200,000	29,300,000
Prepaid expenses and other current assets		57,700,000	58,800,000
Total current assets		929,900,000	518,100,000
Property and equipment, net		345,600,000	341,900,000
Intangible assets, net		17,900,000	17,000,000
Goodwill		99,000,000	98,900,000
Other assets		46,300,000	44,000,000
Total assets		1,438,700,000	1,019,900,000
Current liabilities:
Accounts payable		29,400,000	31,900,000
Accrued and other current liabilities		143,100,000	129,800,000
Accrued compensation and benefits		36,200,000	56,100,000
Capital lease obligation	[1]	92,800,000	102,700,000
Deferred revenue		444,600,000	417,900,000
Total current liabilities		746,100,000	738,400,000
Capital lease obligation, non-current	[1]	77,200,000	71,600,000
Deferred rent, non-current		68,900,000	69,800,000
Other non-current liabilities		36,300,000	37,200,000
Total liabilities		928,500,000	917,000,000
Commitments and contingencies (Note 7)
Stockholders’ equity:
Preferred stock		0	0
Common stock		0	0
Additional paid-in capital		2,104,900,000	533,100,000
Accumulated deficit		(1,600,400,000)	(1,049,700,000)
Accumulated other comprehensive income		5,700,000	4,200,000
Total stockholders’ equity		510,200,000	102,900,000
Total liabilities and stockholders’ equity		1,438,700,000	1,019,900,000
Convertible preferred stock
Stockholders’ equity:
Preferred stock		$ 0	$ 615,300,000
[1]	Includes amounts attributable to related party transactions. See Note 11 for further details.

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Revenue		$ 316.3	$ 247.9
Cost of revenue	[1]	120.6	93.5
Gross profit		195.7	154.4
Operating expenses
Research and development	[1]	378.5	89.3
Sales and marketing	[1]	157	67.2
General and administrative	[1]	126.1	31.3
Total operating expenses	[1]	661.6	187.8
Loss from operations		(465.9)	(33.4)
Interest expense, net		(1.2)	(4.2)
Other income, net		3.4	4.8
Loss before income taxes		(463.7)	(32.8)
Provision for income taxes		(1.8)	(0.3)
Net loss		$ (465.5)	$ (33.1)
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)		$ (2.13)	$ (0.17)
Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted (in shares)		218.8	193.5
[1]	Includes stock-based compensation as follows (in millions) for the three months ended March 31, 2018 and 2017: Cost of revenues of 37.8 million and 3.1 million. Research and development of 282.9 million and 21.8 million. Sales and marketing 72.4 million and 7.7 million. General and administrative of 93.4 million and 6.2 million, respectively.

Condensed Consolidated Stateme4

Condensed Consolidated Statements of Operations (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cost of revenue
Allocated share-based compensation expense	$ 37.8	$ 3.1
Research and development
Allocated share-based compensation expense	282.9	21.8
Sales and marketing
Allocated share-based compensation expense	72.4	7.7
General and administrative
Allocated share-based compensation expense	$ 93.4	$ 6.2

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net loss	$ (465.5)	$ (33.1)
Other comprehensive income, net of tax:
Change in foreign currency translation adjustments	1.5	2.5
Change in net unrealized losses on short-term investments	(0.1)	0
Total other comprehensive income, net of tax	1.4	2.5
Comprehensive loss	$ (464.1)	$ (30.6)

Condensed Consolidated Stateme6

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Cash flow from operating activities
Net loss		$ (465.5)	$ (33.1)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization		35.9	48
Stock-based compensation		486.5	38.8
Amortization of deferred commissions		2.4	1.2
Other		(0.6)	(0.5)
Changes in operating assets and liabilities:
Trade and other receivables, net		3.6	(0.4)
Prepaid expenses and other current assets		(1.5)	7.1
Other assets		(5.7)	(1.8)
Accounts payable		(2.8)	0.8
Accrued and other current liabilities		8.8	5.7
Accrued compensation and benefits		(26.2)	(20.1)
Deferred revenue		26.7	18.9
Non-current liabilities		0.2	(3)
Net cash provided by operating activities		61.8	61.6
Cash flow from investing activities
Capital expenditures		(9.9)	(5.1)
Purchases of intangible assets		(2.5)	(0.3)
Cash received from equipment rebates		0.1	1.3
Purchases of short-term investments		(180.8)	0
Net cash used in investing activities		(193.1)	(4.1)
Cash flow from financing activities
Proceeds from initial public offering and private placement, net of underwriters' discounts and commissions		638.2	0
Payments of deferred offering costs		(0.9)	0
Shares repurchased for tax withholdings on release of restricted stock		(241.2)	(24)
Principal payments against capital lease obligations	[1]	(29.8)	(34.6)
Other		(1.3)	(1.2)
Net cash provided by (used in) financing activities		365	(59.8)
Effect of exchange rate changes on cash and cash equivalents		1.6	0.8
Change in cash and cash equivalents		235.3	(1.5)
Cash and cash equivalents—beginning of period		430	352.7
Cash and cash equivalents—end of period		665.3	351.2
Non-cash investing and financing activities:
Property and equipment acquired under capital leases		$ 25.5	$ 14.5
[1]	Includes amounts attributable to related party transactions. See Note 11 for further details.

Description of the Business and

Description of the Business and Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of the Business and Summary of Significant Accounting Policies	Description of the Business and Summary of Significant Accounting Policies Business Dropbox, Inc. (the “Company” or “Dropbox”) is a global collaboration platform. Dropbox was incorporated in May 2007 as Evenflow, Inc., a Delaware corporation, and changed its name to Dropbox, Inc. in October 2009. The Company is headquartered in San Francisco, California. Basis of presentation and consolidation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with the United States of America generally accepted accounting principles (“GAAP”) and applicable rules and regulations of the Securities and Exchange Commission ("SEC") regarding interim financial reporting. The accompanying unaudited condensed consolidated financial statements include the accounts of Dropbox and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The condensed consolidated balance sheet as of December 31, 2017 included herein was derived from the audited financial statements as of that date. The unaudited condensed consolidated financial statements reflect all normal recurring adjustments necessary to present fairly the balance sheet, statements of operations, statements of comprehensive loss and the statements of cash flows for the interim periods, but are not necessarily indicative of the results of operations to be anticipated for the full fiscal year ended December 31, 2018 or any future period. The unaudited condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements and the related notes thereto as of and for the year ended December 31, 2017, included in the Company's prospectus filed pursuant to Rule 424(b) under the Securities Act of 1933, as amended, on March 23, 2018, referred to as the Prospectus. Initial public offering and private placement On March 27, 2018, the Company closed its initial public offering ("IPO"), in which the Company issued and sold 26,822,409 shares of Class A common stock at $21.00 per share. The Company received aggregate proceeds of $538.2 million , net of underwriters' discounts and commissions, before deducting offering costs of $6.9 million , net of reimbursements. Immediately prior to the closing of the Company’s IPO, 147,310,563 shares of convertible preferred stock outstanding converted into an equivalent number of shares of Class B common stock. Further, pursuant to transfer agreements with certain of the Company’s stockholders, 258,620 shares of the Company’s convertible preferred stock and 2,609,951 shares of the Company’s Class B common stock automatically converted into an equivalent number of shares of Class A common stock. Immediately subsequent to the closing of the Company's IPO, Salesforce Ventures LLC purchased 4,761,905 shares of Class A common stock from the Company at $21.00 per share. The Company received aggregate proceeds of $100.0 million and did not pay any underwriting discounts or commissions with respect to the shares that were sold in the private placement. The Company’s net proceeds from the IPO and the concurrent private placement totaled $ 638.2 million , before deducting offering costs of $ 6.9 million , net of reimbursements. On March 28, 2018, the underwriters exercised their option to purchase an additional 5,400,000 shares of the Company's Class A common stock at $21.00 per share. This transaction closed on April 3, 2018, resulting in additional proceeds of $108.4 million , net of underwriters' discounts and commissions. The shares and proceeds from this transaction are not reflected in the condensed consolidated financial statements as of and for the three months ended March 31, 2018. Upon the effectiveness of the registration statement for the Company's IPO, which was March 22, 2018, the liquidity event-related performance vesting condition, referred to as the Performance Vesting Condition, associated with the Company's two-tier RSUs was satisfied. As a result, the Company recognized the cumulative unrecognized stock-based compensation related to its two-tier restricted stock units ("RSUs") using the accelerated attribution method of $418.7 million attributable to service prior to such effective date. As of March 31, 2018 , the remaining unamortized stock-based compensation related to the two-tier RSUs was $2.6 million , which will be recognized if the requisite service is provided over a weighted average period of 0.6 years. During the three months ended March 31, 2018, the Company's Board of Directors approved the acceleration of the Performance Vesting Condition for which the service condition was satisfied, to occur upon the effectiveness of the registration statement for the Company's IPO, rather than six months following an IPO. As a result, the Company released 26.8 million shares of common stock underlying the two-tier RSUs for which the Performance Vesting Condition was satisfied, and recorded $13.9 million in employer related payroll tax expenses associated with these same awards during the three months ended March 31, 2018. See “—Stock-Based Compensation” for further discussion regarding the Company's two-tier RSUs. Stock Split On March 7, 2018, the Company effected a 1-for-1.5 reverse stock split of its capital stock. All of the share and per share information referenced throughout the condensed consolidated financial statements and notes to the condensed consolidated financial statements have been retroactively adjusted to reflect this reverse stock split. Use of estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported and disclosed in the Company’s condensed consolidated financial statements and accompanying notes. These estimates are based on information available as of the date of the condensed consolidated financial statements. Management evaluates these estimates and assumptions on a regular basis. Actual results may differ materially from these estimates. The Company’s most significant estimates and judgments involve recognition of revenue, the measurement of the Company’s stock-based compensation, including the estimation of the underlying deemed fair value of common stock in periods prior to the date of the Company's IPO, the estimation of the fair value of market-based awards, and the valuation of acquired intangible assets and goodwill from business combinations. Financial information about segments and geographic areas The Company manages its operations and allocates resources as a single operating segment. Further, the Company manages, monitors, and reports its financials as a single reporting segment. The Company’s chief operating decision-maker is its Chief Executive Officer, who reviews financial information presented on a consolidated basis for purposes of making operating decisions, assessing financial performance, and allocating resources. For information regarding the Company’s long-lived assets and revenue by geographic area, see Note 12. Foreign currency transactions The assets and liabilities of the Company’s foreign subsidiaries are translated from their respective functional currencies into U.S. dollars at the exchange rates in effect at the balance sheet date. Revenue and expense amounts are translated at the average exchange rate for the period. Foreign currency translation gains and losses are recorded in other comprehensive income (loss). Gains and losses realized from foreign currency transactions (those transactions denominated in currencies other than the foreign subsidiaries’ functional currency) are included in other income (expense), net. Monetary assets and liabilities are remeasured using foreign currency exchange rates at the end of the period, and non-monetary assets are remeasured based on historical exchange rates. The Company recorded $0.7 million and $2.7 million in net foreign currency transaction gains in the three months ended March 31, 2018 and 2017 , respectively. Revenue recognition The Company derives its revenue from subscription fees from customers for access to its platform. The Company’s policy is to exclude sales and other indirect taxes when measuring the transaction price of its subscription agreements. The Company accounts for revenue contracts with customers through the following 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, the Company satisfies a performance obligation The Company’s subscription agreements generally have monthly or annual contractual terms and a small percentage have multi-year contractual terms. Revenue is recognized ratably over the related contractual term beginning on the date that the platform is made available to a customer. Access to the platform represents a series of distinct services as the Company continually provides access to, and fulfills its obligation to the end customer over the subscription term. The series of distinct services represents a single performance obligation that is satisfied over time. The Company recognizes revenue ratably because the customer receives and consumes the benefits of the platform throughout the contract period. The Company’s contracts are generally non-cancelable. The Company bills in advance for monthly contracts and typically bills annually in advance for contracts with terms of one year or longer. The Company also recognizes an immaterial amount of contract assets, or unbilled receivables, primarily relating to rights to consideration for services completed but not billed at the reporting date. Unbilled receivables are classified as receivables when the Company has the right to invoice the customer. The Company records contract liabilities when cash payments are received or due in advance of performance to deferred revenue. Deferred revenue primarily relates to the advance consideration received from the customer. The price of subscriptions is generally fixed at contract inception and therefore, the Company’s contracts do not contain a significant amount of variable consideration. As a result, the amount of revenue recognized in the periods presented from performance obligations satisfied (or partially satisfied) in previous periods was not material. The Company recognized $188.2 million and $155.0 million of revenue during the three months ended March 31, 2018 and 2017 , respectively, that was included in the deferred revenue balances at the beginning of the respective periods. As of March 31, 2018 , future estimated revenue related to performance obligations that are unsatisfied or partially unsatisfied at the end of the reporting period was $495.5 million . The substantial majority of the unsatisfied performance obligations will be satisfied over the next twelve months. Stock-based compensation The Company has granted RSUs to its employees and members of the Board of Directors under the 2008 Equity Incentive Plan (“2008 Plan”), the 2017 Equity Incentive Plan (“2017 Plan”), and the 2018 Equity Incentive Plan ("2018 Plan"). The Company had two types of RSUs outstanding as of March 31, 2018 : • One-tier RSUs, which have a service-based vesting condition over a four year period. These awards typically have a cliff vesting period of one year and continue to vest quarterly thereafter. The Company began granting one-tier RSUs under its 2008 Plan in August 2015 and it continues to grant one-tier RSUs under its 2018 Plan. The Company recognizes compensation expense associated with one-tier RSUs ratably on a straight-line basis over the requisite service period and accounts for forfeitures in the period in which they occur. • Two-tier RSUs, which have both a service-based vesting condition and a Performance Vesting Condition. The service-based vesting period for these awards is typically four years with a cliff vesting period of one year and continue to vest monthly thereafter. Upon satisfaction of the Performance Vesting Condition, these awards will vest quarterly. The Performance Vesting Condition is satisfied on the earlier of (i) an acquisition or change in control of the Company or (ii) the earlier of (a) six months after the Company’s initial public offering or (b) March 15 of the year following the Company’s initial public offering. During the quarter ended March 31, 2018, the Company's Board of Directors approved the acceleration of the Performance Vesting Condition for which the service condition was satisfied, to occur upon the effectiveness of the registration statement related to the Company's IPO. Prior to August 2015, the Company granted two-tier RSUs under the 2008 Plan. The last grant date for two-tier RSUs was in May 2015. The Company recognizes compensation expense associated with two-tier RSUs using the accelerated attribution method over the requisite service period. The Performance Vesting Condition for the two-tier RSUs was satisfied upon the effectiveness of the registration statement related to the Company's IPO, which was March 22, 2018. The Company recognized the cumulative unrecognized expense of the two-tier RSUs, using the accelerated attribution method, during the three months ended March 31, 2018 . See "—Initial Public Offering and Private Placement” for further discussion. Since August 2015, the Company has granted RSUs as the only stock-based payment awards to its employees, with the exception of awards granted to its co-founders, and has not granted any stock options since then. The fair values of the common stock underlying the RSUs granted in periods prior to the date of the Company's IPO were determined by the Board of Directors, with input from management and contemporaneous third-party valuations, which were performed at least quarterly. For valuations after the Company's IPO, the Board of Directors will determine the fair value of each share of underlying common stock based on the closing price of the Company's Class A common stock as reported on the Nasdaq Global Select Market on the date of the grant. In December 2017, the Board of Directors approved a grant to the Company’s co-founders of restricted stock awards (“RSAs”) with respect to 14.7 million shares of Class A Common Stock in the aggregate (collectively, the “Co-Founder Grants”), of which 10.3 million RSAs were granted to Mr. Houston, the Company’s co-founder and Chief Executive Officer, and 4.4 million RSAs were granted to Mr. Ferdowsi, the Company’s co-founder and Director. These Co-Founder Grants have service-based, market-based, and performance-based vesting conditions. The Co-Founder Grants comprise nine tranches that are eligible to vest based on the achievement of stock price goals, or, each, a Stock Price Target. The Company estimated the grant date fair value of the Co-Founder Grants using a model based on multiple stock price paths developed through the use of a Monte Carlo simulation that incorporates into the valuation the possibility that the Stock Price Targets may not be satisfied. The average grant date fair value of each Co-Founder Grant was estimated to be $10.60 per share, and the Company will recognize aggregate stock-based compensation expense of $156.2 million over the requisite service period of each tranche, which ranged from 2.9 to 6.9 years, using the accelerated attribution method. If the Stock Price Targets are met sooner than the derived service period, the Company will adjust its stock-based compensation to reflect the cumulative expense associated with the vested awards. The Company will recognize expense if the requisite service is provided, regardless of whether the market conditions are achieved. The Co-Founder Grants contain an implied performance-based vesting condition because the Stock Price Targets are based on the trailing 30-day average price of the shares from an established national securities exchange or automated quotation system. Accordingly, no vesting could occur until the completion of the Company’s IPO. The relevant performance-based vesting condition for the Co-Founder Grants was satisfied on the date the Company’s shares of Class A common stock commenced trading on the Nasdaq Global Select Market, in connection with the Company’s IPO, which was March 23, 2018. The Company recognized the cumulative unrecognized expense of $10.6 million for the Co-Founder Grants, using the accelerated attribution method, during the three months ended March 31, 2018 . See Note 8, “Stockholders’ Equity” for further discussion. Cash and cash equivalents Cash consists primarily of cash on deposit with banks and includes amounts in transit from payment processors for credit and debit card transactions, which typically settle within five days. Cash equivalents include highly liquid investments purchased with an original maturity date of 90 days or less from the date of purchase. Short-term investments The Company’s short-term investments are primarily comprised of U.S. treasury securities, corporate notes and obligations, U.S. agency obligations, commercial paper, and certificates of deposits. The Company determines the appropriate classification of its short-term investments at the time of purchase and reevaluates such designation at each balance sheet date. The Company has classified and accounted for its short-term investments as available-for-sale securities as the Company may sell these securities at any time for use in its current operations or for other purposes, even prior to maturity. As a result, the Company classifies its short-term investments, including securities with stated maturities beyond twelve months, within current assets in the condensed consolidated balance sheets. The Company's short-term investments are classified as available-for-sale securities and are recorded at fair value each reporting period. Unrealized gains and losses on these short-term investments are reported as a separate component of accumulated other comprehensive income (loss) in the condensed consolidated balance sheets until realized. Interest income is reported within interest expense, net in the condensed consolidated statements of operations. The Company periodically evaluates its short-term investments to assess whether those with unrealized loss positions are other-than-temporarily impaired. The Company considers various factors in determining whether to recognize an impairment charge, including the length of time the investment has been in a loss position, the extent to which the fair value is less than the Company’s cost basis, and the financial condition and near-term prospects of the investee. Realized gains and losses are determined based on the specific identification method and are reported in other income (expense), net in the condensed consolidated statements of operations. If the Company determines that the decline in an investment’s fair value is other-than-temporary, the difference is recognized as an impairment loss in the condensed consolidated statements of operations. Concentrations of credit risk Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash, cash equivalents, accounts receivable, and short-term investments. The Company places its cash and cash equivalents and short-term investments with well-established financial institutions. Trade accounts receivables are typically unsecured and are derived from revenue earned from customers located around the world. Two customers accounted for 17% and 31% of total trade and other receivables, net as of March 31, 2018 . Two customers accounted for 18% and 27% of total trade and other receivables, net as of December 31, 2017 . No customer accounted for more than 10% of the Company’s revenue in the periods presented. Non-trade receivables The Company records non-trade receivables to reflect amounts due for activities outside of its subscription agreements. Historically, the Company’s non-trade receivables have related primarily to receivables resulting from tenant improvement allowances. Non-trade receivables totaled $3.6 million and $5.2 million , as of March 31, 2018 and December 31, 2017 , respectively, and are classified within prepaid expenses and other current assets in the accompanying condensed consolidated balance sheets. Deferred commissions, net Deferred commissions, net is stated as gross deferred commissions less accumulated amortization. Sales commissions earned by the Company’s sales force and third-party resellers, as well as related payroll taxes, are considered to be incremental and recoverable costs of obtaining a contract with a customer. These amounts have been capitalized as deferred commissions within prepaid and other current assets and other assets on the condensed consolidated balance sheet. The Company deferred incremental costs of obtaining a contract of $9.8 million and $4.7 million during the three months ended March 31, 2018 and 2017 , respectively. Deferred commissions, net included in prepaid and other current assets were $9.5 million and $8.1 million as of March 31, 2018 and December 31, 2017 , respectively. Deferred commissions, net included in other assets were $30.8 million and $24.8 million as of March 31, 2018 and December 31, 2017 , respectively. Deferred commissions are amortized over a period of benefit of five years. The period of benefit was estimated by considering factors such as historical customer attrition rates, the useful life of the Company’s technology, and the impact of competition in its industry. Amortized costs were $2.4 million and $ 1.2 million for the three months ended March 31, 2018 and 2017 , respectively. Amortized costs are included in sales and marketing expense in the accompanying condensed consolidated statements of operations. There was no impairment loss in relation to the deferred costs for any period presented. Property and equipment, net Equipment is stated at cost less accumulated depreciation. Depreciation is computed using the straight-line method over the estimated useful life of the related asset, which is generally three to seven years. Leasehold improvements are amortized on a straight-line basis over the shorter of their estimated useful lives or the term of the related lease. In the first quarter of 2018, the Company determined that the useful lives of certain infrastructure equipment, which are depreciated through cost of revenue, should be increased from three to four years. The Company accounted for this as a change in estimate that will be applied prospectively, effective as of January 1, 2018. This change in depreciable life resulted in a reduction of $6.1 million in depreciation expense within cost of revenue during the three months ended March 31, 2018 . The following table presents the estimated useful lives of property and equipment: Property and equipment Useful life Buildings 20 to 30 years Datacenter and other computer equipment 3 to 5 years Office equipment and other 3 to 7 years Leasehold improvements Lesser of estimated useful life or remaining lease term Lease obligations The Company leases office space, datacenters, and equipment under non-cancelable capital and operating leases with various expiration dates through 2033. Certain of the Company’s operating lease agreements contain tenant improvement allowances from its landlords. These allowances are accounted for as lease incentive obligations and are amortized as reductions to rent expense over the lease term. In addition, certain of the operating lease agreements contain rent concession, rent escalation, and options to renew. Rent concession and rent escalation provisions are considered in determining the straight-line rent expense to be recorded over the lease term. The lease term begins on the date the Company has the right to use the leased property for purposes of recognizing lease expense on a straight-line basis over the term of the lease. The Company does not assume renewals in its determination of the lease term unless the renewals are deemed to be reasonably assured at lease inception. The Company leases certain equipment from various third parties, including from a related party, through equipment financing leases under capital leases. See Note 11, “Related Party Transactions” for additional details. These leases either include a bargain purchase option, a full transfer of ownership at the completion of the lease term, or the terms of the leases are at least 75 percent of the useful lives of the assets and are therefore classified as a capital leases. These leases are capitalized in property and equipment and the related amortization of assets under capital leases is included in depreciation and amortization expense in the Company’s condensed consolidated statements of operations. Initial asset values and lease obligations are based on the present value of future minimum lease payments. Long-lived assets, including goodwill and other acquired intangible assets, net The Company evaluates the recoverability of its property and equipment and finite-lived intangible assets for possible impairment whenever events or circumstances indicate that the carrying amount of such assets may not be recoverable. The evaluation is performed at the lowest level for which identifiable cash flows are largely independent of the cash flows of other assets and liabilities. Recoverability of these assets is measured by a comparison of the carrying amounts to the future undiscounted cash flows the assets are expected to generate. If such review determines that the carrying amount of specific property and equipment or intangible assets is not recoverable, the carrying amount of such assets is reduced to its fair value. The Company reviews goodwill for impairment at least annually in the fourth quarter, or more frequently if events or changes in circumstances would more likely than not reduce the fair value of its single reporting unit below its carrying value. The Company has not recorded impairment charges on property and equipment, goodwill, or intangible assets for the periods presented in these condensed consolidated financial statements. Acquired property and equipment and finite-lived intangible assets are amortized over their useful lives. The Company evaluates the estimated remaining useful life of these assets when events or changes in circumstances warrant a revision to the remaining period of amortization. If the Company reduces the estimated useful life assumption for any asset, the remaining unamortized balance is amortized or depreciated over the revised estimated useful life on a prospective basis. See "—Property and Equipment, Net” for further discussion regarding a change in useful life applied during the three months ended March 31, 2018. Income taxes Deferred income tax balances reflect the effects of temporary differences between the financial reporting and tax bases of the Company’s assets and liabilities using enacted tax rates expected to apply when taxes are actually paid or recovered. In addition, deferred tax assets are recorded for net operating loss and credit carryforwards. A valuation allowance is provided against deferred tax assets unless it is more likely than not that they will be realized based on all available positive and negative evidence. Such evidence includes, but is not limited to, recent cumulative earnings or losses, expectations of future taxable income by taxing jurisdiction, and the carry-forward periods available for the utilization of deferred tax assets. The Company uses a two-step approach to recognizing and measuring uncertain income tax positions. The first step is to evaluate the tax position for recognition by determining if the weight of available evidence indicates it is more likely than not that the position will be sustained on audit. The second step is to measure the tax benefit as the largest amount, which is more than 50% likely of being realized upon ultimate settlement. The Company recognizes interest and penalties related to unrecognized tax benefits as income tax expense. Although the Company believes that it has adequately reserved for its uncertain tax positions, it can provide no assurance that the final tax outcome of these matters will not be materially different. The Company evaluates its uncertain tax positions on a regular basis and evaluations are based on a number of factors, including changes in facts and circumstances, changes in tax law, such as the 2017 Tax Cuts and Jobs Act ("2017 Tax Reform Act"), correspondence with tax authorities during the course of an audit, and effective settlement of audit issues. To the extent that the final tax outcome of these matters is different than the amounts recorded, such differences will affect the provision for income taxes in the period in which such determination is made and could have a material impact on the Company’s financial condition and results of operations. Fair value measurement The Company applies fair value accounting for all financial assets and liabilities and non-financial assets and liabilities that are recognized or disclosed at fair value in the financial statements on a recurring basis. The Company defines fair value as the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. When determining fair value measurements for assets and liabilities, the Company considers the principal or most advantageous market in which it would transact and the market-based risk measurements or assumptions that market participants would use in pricing the asset or liability, such as risks inherent in valuation techniques, transfer restrictions, and credit risk. Fair value is estimated by applying the following hierarchy, which prioritizes the inputs used to measure fair value into three levels and bases the categorization within the hierarchy upon the lowest level of input that is available and significant to the fair value measurement: Level 1 —Quoted prices in active markets for identical assets or liabilities. Level 2 —Observable inputs other than quoted prices in active markets for identical assets and liabilities, quoted prices for identical or similar assets or liabilities in inactive markets, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 —Inputs that are generally unobservable and typically reflect management’s estimate of assumptions that market participants would use in pricing the asset or liability. Recently issued accounting pronouncements not yet adopted In February 2016, the Financial Accounting Standards Board ("FASB") issued ASU No. 2016-02, Leases (Topic 842) . Most prominent among the changes in the standard is the recognition of right of use assets and lease liabilities by lessees for those leases classified as operating leases under current GAAP. Under the standard, disclosures are required to meet the objective of enabling users of financial statements to assess the amount, timing, and uncertainty of cash flows arising from leases. The Company will be required to recognize and measure leases existing at, or entered into after, the beginning of the earliest comparative period presented using a modified retrospective approach, with certain practical expedients available. The new standard is effective for fiscal years beginning after December 15, 2018. Early adoption by public entities is permitted. The Company is in the initial stage of its assessment of the new standard and is currently evaluating the quantitative impact of adoption and the related disclosure requirements. The Company anticipates the adoption of this standard will result in a substantial increase in its non-current assets and liabilities recorded on the condensed consolidated balance sheets. The adoption of the standard is not expected to have a material impact on the consolidated statement of operations. While the Company is assessing all potential impacts of the adoption of the standard, it currently expects the most significant impact to be the capitalization of right-to-use assets and lease liabilities for its office space and datacenter operating leases. The Company expects its accounting for capital leases related to infrastructure equipment to remain substantially unchanged under the new standard. The Company expects to adopt the

Cash, Cash Equivalents and Shor

Cash, Cash Equivalents and Short-Term Investments	3 Months Ended
	Mar. 31, 2018
Cash and Cash Equivalents [Abstract]
Cash, Cash Equivalents and Short-Term Investments	Cash, Cash Equivalents and Short-Term Investments The amortized cost, unrealized gains and losses and estimated fair value of the Company's cash, cash equivalents and short-term investments as of March 31, 2018 consisted of the following: As of March 31, 2018 Amortized Cost Unrealized Gain Unrealized Loss Estimated Fair Value Cash $ 71.2 $ — $ — $ 71.2 Cash equivalents Money market funds 506.1 — — 506.1 U.S. Treasury securities 62.0 — — 62.0 U.S. agency obligations 12.1 — — 12.1 Commercial paper 10.8 — — 10.8 Corporate notes and obligations 2.6 — — 2.6 Certificates of deposit 0.5 — — 0.5 Total cash and cash equivalents $ 665.3 $ — $ — $ 665.3 Short-term investments U.S. Treasury securities 93.6 — — 93.6 Corporate notes and obligations 57.4 — (0.1 ) 57.3 U.S. agency obligations 14.4 — — 14.4 Commercial paper 10.3 — — 10.3 Certificates of deposit 5.1 — — 5.1 Total short-term investments 180.8 — (0.1 ) 180.7 Total $ 846.1 $ — $ (0.1 ) $ 846.0 The Company's cash and cash equivalents at December 31, 2017 consisted of cash of $62.9 million and money market funds of $367.1 million . The Company did no t have short-term investments as of December 31, 2017. Included in cash and cash equivalents is cash in transit from payment processors for credit and debit card transactions of $13.9 million and $13.3 million as of March 31, 2018 and December 31, 2017 , respectively. All short-term investments were designated as available-for-sale securities as of March 31, 2018 . The Company had 77 short-term investments in unrealized loss positions as of March 31, 2018 . There were no material gross unrealized losses from available-for-sale securities and no realized gains or losses from available-for-sale securities that were reclassified out of accumulated other comprehensive income for the three months ended March 31, 2018 . For investments in available-for-sale debt securities that have unrealized losses, the Company evaluates whether (i) it has the intention to sell any of these investments and (ii) whether it is not more likely than not that it will be required to sell any of these investments before recovery of the entire amortized cost basis. Based on this evaluation, the Company determined that there were no other-than-temporary impairments associated with short-term investments as of March 31, 2018 . The following table presents the contractual maturities of the Company’s short-term investments as of March 31, 2018 : As of March 31, 2018 Amortized Cost Estimated Fair Value Due within one year $ 105.1 $ 105.1 Due between one to four years 75.7 75.6 Total $ 180.8 $ 180.7

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The Company measures its financial instruments at fair value each reporting period using a fair value hierarchy that prioritizes the use of observable inputs and minimizes the use of unobservable inputs when measuring fair value. A financial instrument’s classification within the fair value hierarchy is based upon the lowest level of input that is significant to the fair value measurement. The following table presents information about the Company’s financial instruments that are measured at fair value on a recurring basis using the above input categories: As of March 31, 2018 Level 1 Level 2 Level 3 Total Cash equivalents Money market funds $ 506.1 $ — $ — $ 506.1 U.S. Treasury securities — 62.0 — 62.0 U.S. agency obligations — 12.1 — 12.1 Commercial paper — 10.8 — 10.8 Corporate notes and obligations — 2.6 — 2.6 Certificates of deposit — 0.5 — 0.5 Total cash equivalents $ 506.1 $ 88.0 $ — $ 594.1 Short-term investments U.S. Treasury securities $ — $ 93.6 $ — $ 93.6 Corporate notes and obligations — 57.3 — 57.3 U.S. agency obligations — 14.4 — 14.4 Commercial paper — 10.3 — 10.3 Certificates of deposit — 5.1 — 5.1 Total short-term investments $ — $ 180.7 $ — $ 180.7 Total cash equivalents and short-term investments $ 506.1 $ 268.7 $ — $ 774.8 The total cash equivalents held by the Company as of December 31, 2017 were $367.1 million and were entirely comprised of money market funds classified within Level 1 of the fair value hierarchy. The Company had no transfers between levels of the fair value hierarchy. The carrying amounts of certain financial instruments, including cash held in banks, accounts receivable and accounts payable approximate fair value due to their short-term maturities and are excluded from the fair value table above.

Property and Equipment, Net

Property and Equipment, Net	3 Months Ended
	Mar. 31, 2018
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	Property and Equipment, Net Property and equipment, net consisted of the following: As of March 31, 2018 December 31, 2017 Building $ 36.6 $ 36.6 Datacenter and other computer equipment 692.4 663.1 Furniture and fixtures 23.8 21.2 Leasehold improvements 129.0 118.6 Construction in process 2.0 7.2 Total property and equipment 883.8 846.7 Accumulated depreciation and amortization (538.2 ) (504.8 ) Property and equipment, net $ 345.6 $ 341.9 The Company leases certain infrastructure from various third parties, including from a related party, through equipment financing leases that are accounted for as capital leases. See Note 11, “Related Party Transactions” for additional details. Infrastructure assets as of March 31, 2018 and December 31, 2017 , respectively included a total of $413.2 million and $417.9 million acquired under capital lease agreements. These leases are capitalized in property and equipment, and the related amortization of assets under capital leases is included in depreciation and amortization expense. The accumulated depreciation of the infrastructure under capital leases totaled $253.4 million and $259.0 million as of March 31, 2018 and December 31, 2017 , respectively. Construction in process includes costs primarily related to construction of leasehold improvements for office buildings and datacenters. Depreciation expense related to property and equipment was $34.1 million and $44.5 million for the three months ended March 31, 2018 and 2017 , respectively.

Goodwill

Goodwill	3 Months Ended
	Mar. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	Goodwill Goodwill represents the excess of the purchase price in a business combination over the fair value of net tangible and intangible assets acquired. Goodwill amounts are not amortized, but tested for impairment on an annual basis. There was no impairment of goodwill as of March 31, 2018 and December 31, 2017 . The Company did not complete any business combinations in any of the periods presented.

Revolving Credit Facility

Revolving Credit Facility	3 Months Ended
	Mar. 31, 2018
Debt Disclosure [Abstract]
Revolving Credit Facility	Revolving Credit Facility In April 2017, the Company entered into an amended and restated credit and guaranty agreement which provided for a $600.0 million revolving loan facility (the “revolving credit facility”). In conjunction with the revolving credit facility, the Company paid upfront issuance fees of $2.6 million , which are being amortized over the five -year term of the agreement. In February 2018, the Company amended its revolving credit facility to, among other things, permit the Company to make certain investments, enter into an unsecured standby letter of credit facility and increase its standby letter of credit sublimit to $187.5 million . The Company increased its borrowing capacity under the revolving credit facility from $600.0 million to $725.0 million . The Company may from time to time request increases in its borrowing capacity under the revolving credit facility of up to $275.0 million , provided no event of default has occurred or is continuing or would result from such increase. In conjunction with the amendment, the Company paid upfront issuance fees of $0.4 million , which are being amortized over the remaining term of the agreement. Pursuant to the terms of the revolving credit facility, the Company may issue letters of credit under the revolving credit facility, which reduce the total amount available for borrowing. Pursuant to the terms of the revolving credit facility, the Company is required to pay an annual commitment fee that accrues at a rate of 0.20% per annum on the unused portion of the borrowing commitments under the revolving credit facility. In addition, the Company is required to pay a fee in connection with letters of credit issued under the revolving credit facility, which accrues at a rate of 1.5% per annum on the amount of such letters of credit outstanding. There is an additional fronting fee of 0.125% per annum multiplied by the average aggregate daily maximum amount available under all letters of credit. Borrowings under the revolving credit facility bear interest, at the Company’s option, at an annual rate based on LIBOR plus a spread of 1.50% or at an alternative base rate plus a spread of 0.50% . The revolving credit facility contains customary conditions to borrowing, events of default and covenants, including covenants that restrict the Company’s ability to incur indebtedness, grant liens, make distributions to holders of the Company or its subsidiaries’ equity interests, make investments, or engage in transactions with its affiliates. In addition, the revolving credit facility contains financial covenants, including a consolidated leverage ratio covenant and a minimum liquidity balance of $100.0 million , which includes any available borrowing capacity. The Company was in compliance with the covenants of the revolving credit facility as of March 31, 2018 and December 31, 2017 , respectively. The Company had an aggregate of $82.7 million of letters of credit outstanding under the revolving credit facility as of March 31, 2018 , and the Company’s total available borrowing capacity under the revolving credit facility was $642.3 million as of March 31, 2018 . The Company’s letters of credit expire between April of 2019 and April of 2022 .

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Leases The Company has entered into various non-cancelable operating lease agreements for certain offices and datacenters with contractual lease periods expiring at various dates through 2033. The facility lease agreements generally provide for escalating rental payments and for options to renew, which could increase future minimum lease payments if exercised. The Company recognizes rent expense on a straight-line basis over the lease period and accounts for the difference between straight-line rent and actual lease payments as deferred rent. Gross rent expense was $21.9 million and $16.0 million for the three months ended March 31, 2018 and 2017 , respectively. Sublease income, which is recorded as a reduction of rental expense, was $3.5 million and $1.9 million for the three months ended March 31, 2018 and 2017 , respectively. Sublease income in excess of the Company’s original lease obligation is split with the original lessor per the terms of the sublease agreement, with the Company’s portion recorded to other income (loss), net. In 2017, the Company entered into a new lease agreement for office space in San Francisco, California, to serve as its new corporate headquarters. The Company expects to start making recurring rental payments under the lease in the third quarter of 2019. Included in the operating lease commitments below are total expected minimum obligations under the lease agreement of $829.7 million , which exclude expected tenant improvement reimbursements from the landlord of approximately $73.8 million and variable operating expenses. The Company’s obligations under the lease are supported by a $34.2 million letter of credit, which reduced the borrowing capacity under the revolving credit facility. Other commitments Other commitments include payments to third-party vendors for services related to the Company’s infrastructure, infrastructure warranty contracts, payments related to the imputed financing obligation for its previous headquarters, asset retirement obligations for office modifications, and a note payable related to financing of infrastructure. Future minimum payments under the Company’s capital leases, non-cancelable operating leases, and other commitments as of December 31, 2017 , are as follows. There have been no material changes in our commitments and contingencies, as disclosed in the Prospectus. Capital lease commitments Operating lease commitments (1) Other commitments Year ended December 31: 2018 $ 108.3 $ 91.5 $ 64.0 2019 54.9 94.9 49.9 2020 18.4 126.0 34.7 2021 0.4 115.9 1.7 2022 — 109.0 — Thereafter — 812.6 4.8 Future minimum payments 182.0 $ 1,349.9 $ 155.1 Less interest and taxes (7.7 ) Less current portion of the present value of minimum lease payments (102.7 ) Capital lease obligations, net of current portion $ 71.6 (1) Consists of future non-cancelable minimum rental payments under operating leases for the Company’s offices and datacenters, excluding rent payments from the Company’s sub-tenants, variable operating expenses, and tenant improvement reimbursements. Non-cancelable rent payments from the Company’s sub-tenants as of December 31, 2017 , are expected to be $72.1 million through 2023. Legal matters From time to time, the Company is a party to a variety of claims, lawsuits, and proceedings which arise in the ordinary course of business, including claims of alleged infringement of intellectual property rights. The Company records a liability when it believes that it is probable that a loss will be incurred and the amount of loss or range of loss can be reasonably estimated. In its opinion, resolution of pending matters is not likely to have a material adverse impact on its consolidated results of operations, cash flows, or its financial position. Given the unpredictable nature of legal proceedings, the Company bases its estimate on the information available at the time of the assessment. As additional information becomes available, the Company reassesses the potential liability and may revise the estimate. Indemnification The Company’s arrangements generally include certain provisions for indemnifying customers against liabilities if its products or services infringe a third party’s intellectual property rights. It is not possible to determine the maximum potential amount under these indemnification obligations due to the limited history of prior indemnification claims.

Stockholders' Equity

Stockholders' Equity	3 Months Ended
	Mar. 31, 2018
Stockholders' Equity Note [Abstract]
Stockholders' Equity	Stockholders’ Equity Common stock The Company’s amended and restated certificate of incorporation authorizes the issuance of Class A common stock, Class B common stock, and Class C common stock. Holders of Class A common stock, Class B common stock, and Class C common stock are entitled to dividends on a pro rata basis, when, as, and if declared by the Company’s Board of Directors, subject to the rights of the holders of the Company’s preferred stock. Holders of Class A common stock are entitled to one vote per share, holders of Class B common stock are entitled to 10 votes per share, and holders of Class C common stock are entitled to zero votes per share. As of March 31, 2018 , the Company had authorized 2,400.0 million shares of Class A common stock, 475.0 million shares of Class B common stock, and 800.0 million shares of Class C common stock, each at par value of $0.00001 . As of December 31, 2017 , the Company had authorized 533.3 million shares of Class A common stock, and 466.7 million shares of Class B common stock, each with par value of $0.00001 . As of March 31, 2018 , 54.0 million shares of Class A common stock, 341.0 million shares of Class B common stock, and no shares of Class C common stock were issued and outstanding. Class A shares issued and outstanding as of March 31, 2018 and December 31, 2017 exclude 14.7 million unvested restricted stock awards granted to the Company’s co-founders. See "Co-Founder Grants" section below for further details. Convertible preferred stock Immediately prior to the closing of the Company’s IPO, all of the 147.3 million shares of convertible preferred stock converted into an equivalent number of shares of Class B common stock. Further, pursuant to transfer agreements with certain of the Company’s stockholders, 0.3 million shares of the Company’s convertible preferred stock automatically converted into an equivalent number of shares of Class A common stock. Preferred stock The Company's Board of Directors will have the authority, without further action by the Company's stockholders, to issue up to 240.0 million shares of undesignated preferred stock with rights and preferences, including voting rights, designated from time to time by the Board of Directors. Equity incentive plans Under the 2018 Plan, the Company may grant stock-based awards to purchase or directly issue shares of common stock to employees, directors, and consultants. Options are granted at a price per share equal to the fair market value of Dropbox’s common stock at the date of grant. Options granted are exercisable over a maximum term of 10 years from the date of grant and generally vest over a period of four years. No options have been granted since August of 2015. RSUs and RSAs are also granted under the 2018 Plan. The 2018 Plan will terminate 10 years after the later of (i) its adoption or (ii) the most recent stockholder-approved increase in the number of shares reserved under the 2018 Plan, unless terminated earlier by the Dropbox Board of Directors. The 2018 Plan was adopted on March 22, 2018 with a reserve of 41.4 million shares of our Class A common stock for future issuance. As of March 31, 2018 , there were 38.7 million shares issued and outstanding and 53.9 million available for issuance under the 2008 Equity Incentive Plan, the 2017 Equity Incentive Plan, and the 2018 Plan ("the Plans"). Stock option and restricted stock activity for the Company's Equity Incentive Plans was as follows for the three months ended March 31, 2018 : Options outstanding Restricted stock outstanding Number of shares available for issuance under the Plans Number of shares outstanding under the Plans Weighted- average exercise price per share Weighted- average remaining contractual term (In years) Number of shares outstanding under the Plans Weighted- average grant date fair value per share Balance at December 31, 2017 9.0 5.0 $ 10.52 5.5 54.9 $ 15.60 Reserved for issuance under the 2018 Plan 41.4 — — — — Additional shares authorized 1.3 — — — — Options exercised and RSUs released — (0.2 ) 6.20 (30.6 ) 14.85 Options and RSUs canceled 1.4 — — (1.4 ) 17.12 Shares repurchased for tax withholdings on release of restricted stock 11.8 — — — — Restricted stock granted (11.0 ) — — 11.0 17.20 Balance at March 31, 2018 53.9 4.8 $ 10.62 2.7 33.9 $ 16.76 Vested at March 31, 2018 4.7 $ 10.31 2.6 — $ — Unvested at March 31, 2018 0.1 $ 24.12 33.9 $ 16.76 The following table summarizes information about the pre-tax intrinsic value of options exercised during the three months ended March 31, 2018 and 2017 : Three months ended March 31, 2018 2017 Intrinsic value of options exercised $ 1.7 $ 1.0 As of March 31, 2018 , unamortized stock-based compensation related to unvested stock options, restricted stock awards (excluding the Co-Founder Grants), and RSUs was $500.1 million . The weighted-average period over which such compensation expense will be recognized if the requisite service is provided is approximately 3.1 years as of March 31, 2018 . Co-Founder Grants In December 2017, the Board of Directors approved a grant to the Company’s co-founders of non-Plan RSAs with respect to 14.7 million shares of Class A Common Stock in the aggregate (collectively, the “Co-Founder Grants”), of which 10.3 million RSAs were granted to Mr. Houston, the Company’s co-founder and Chief Executive Officer, and 4.4 million RSAs were granted to Mr. Ferdowsi, the Company’s co-founder and Director. These Co-Founder Grants have service-based, market-based, and performance-based vesting conditions. The Co-Founder Grants are excluded from Class A common stock issued and outstanding until the satisfaction of these vesting conditions. The Co-Founder Grants also provide the holders with certain stockholder rights, such as the right to vote the shares with the other holders of Class A common stock and a right to cumulative declared dividends. However, the Co-Founder Grants are not considered a participating security for purposes of calculating net loss per share attributable to common stockholders in Note 9 as the right to the cumulative declared dividends is forfeitable if the service condition is not met. The Co-Founder Grants are eligible to vest over the ten -year period following the date the Company’s shares of Class A common stock commenced trading on the Nasdaq Global Select Market in connection with the Company’s IPO. The Co-Founder Grants comprise nine tranches that are eligible to vest based on the achievement of stock price goals, or, each, a Stock Price Target, measured over a consecutive thirty-day trading period during the Performance Period. The Performance Period begins on the first trading day following the later of (a) the expiration of the lock-up period following the first date the Company’s shares are traded on an established national securities exchange or automated quotation system (the “IPO Date”) and (b) January 1, 2019 and ends on the earliest to occur of: (i) the date on which all shares subject to the Co-Founder Grants vest, (ii) the date the applicable co-founder ceases to satisfy the service-based vesting condition, (iii) the tenth anniversary of the IPO Date, and (iv) the occurrence of an acquisition of the Company prior to the IPO Date. During the first four years of the Performance Period, no more than 20% of the shares subject to each Co-Founder Grant would be eligible to vest in any calendar year. After the first four years, all shares are eligible to vest based on the achievement of the Stock Price Targets. The Performance Vesting Condition for the Co-Founder Grants was satisfied on the date the Company’s shares of Class A common stock commenced trading on the Nasdaq Global Select Market in connection with the Company’s IPO, which was March 23, 2018. As of March 31, 2018 , unamortized stock-based compensation expense related to the Co-Founder Grants was $145.6 million . The Company calculated the grant date fair value of the Co-Founder Grants based on multiple stock price paths developed through the use of a Monte Carlo simulation. A Monte Carlo simulation also calculates a derived service period for each of the nine vesting tranches, which is the measure of the expected time to achieve each Stock Price Target. A Monte Carlo simulation requires the use of various assumptions, including the underlying stock price, volatility, and the risk-free interest rate as of the valuation date, corresponding to the length of time remaining in the performance period, and expected dividend yield. The weighted-average grant date fair value of each Co-Founder Grant was estimated to be $10.60 per share. The weighted-average derived service period of each Co-Founder Grant was estimated to be 5.2 years, and ranged from 2.9 - 6.9 years. The Company will recognize aggregate stock-based compensation expense of $156.2 million over the derived service period of each tranche using the accelerated attribution method as long as the co-founders satisfy their service-based vesting conditions. If the Stock Price Targets are met sooner than the derived service period, the Company will adjust its stock-based compensation to reflect the cumulative expense associated with the vested awards. The Company will recognize expense if the requisite service is provided, regardless of whether the market conditions are achieved.

Net Loss Per Share

Net Loss Per Share	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Net Loss Per Share	Net Loss Per Share The Company computes net loss per share using the two-class method required for multiple classes of common stock and participating securities. The rights, including the liquidation and dividend rights, of the Class A common stock and Class B common stock are substantially identical, other than voting rights. Accordingly, the Class A common stock and Class B common stock share equally in the Company’s net losses. Before the IPO, the Company’s participating securities also included convertible preferred stock. The holders of convertible preferred stock did not have a contractual obligation to share in the Company’s losses, and as a result net losses were not allocated to these participating securities. The following table sets forth the calculation of basic and diluted net loss per share attributable to common stockholders during the periods presented. The shares issued in the IPO and the private placement and the shares of Class A and Class B common stock issued upon conversion of the outstanding shares of convertible preferred stock in the IPO are included in the table below weighted for the period outstanding in the quarter ended March 31, 2018: Three months ended March 31, 2018 2017 Class A Class B Class A Class B Numerator: Net loss attributable to common stockholders $ (30.8 ) $ (434.7 ) $ (0.9 ) $ (32.2 ) Denominator: Weighted-average number of common shares outstanding used in computing basic and diluted net loss per common share 14.5 204.3 5.5 188.0 Net loss per common share, basic and diluted $ (2.13 ) $ (2.13 ) $ (0.17 ) $ (0.17 ) Since the Company was in a loss position for all periods presented, basic net loss per share attributable to common stockholders is the same as diluted net loss per share for all periods as the inclusion of all potential common shares outstanding would have been anti-dilutive. The weighted-average impact of potentially dilutive securities that were not included in the diluted per share calculations because they would be anti-dilutive was as follows: Three months ended March 31, 2018 2017 Convertible preferred stock — 147.6 Restricted stock units 56.3 49.0 Options to purchase shares of common stock 4.9 5.2 Co-Founder Grants 14.7 — Shares subject to repurchase from early-exercised options and unvested restricted stock — 0.4 Total 75.9 202.2

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Company computed the year-to-date income tax provision by applying the estimated annual effective tax rate to the year-to-date pre-tax loss and adjusted for discrete tax items in the period. The Company's income tax expense was $1.8 million and $0.3 million for the three months ended March 31, 2018 and 2017 , respectively. The income tax expense for the first quarter of 2018 was primarily attributable to U.S. state income taxes, foreign taxes, and increases in uncertain tax positions. For the periods presented, the difference between the U.S. statutory rate and the Company's effective tax rate is primarily due to the full valuation allowance on its U.S. and Irish deferred tax assets. The effective tax rate is also impacted by earnings realized in foreign jurisdictions with statutory tax rates lower than the federal statutory tax rate. The Company periodically evaluates the realizability of its net deferred tax assets based on all available evidence, both positive and negative. The realization of net deferred tax assets is dependent on the Company's ability to generate sufficient future taxable income during periods prior to the expiration of tax attributes to fully utilize these assets. As of March 31, 2018 , the Company continues to maintain a full valuation allowance on its deferred tax assets in the U.S. and Ireland. However, the Company has partially benefited from its deferred tax assets due to the recognition of forecasted future income which is more likely than not to be earned in one of its foreign jurisdictions. The Company is subject to income tax audits in the U.S. and foreign jurisdictions. The Company records liabilities related to uncertain tax positions and believes that it has provided adequate reserves for income tax uncertainties in all open tax years. Unrecognized tax benefits increased by approximately $7.8 million for the three months ended March 31, 2018 , of which $0.3 million , if recognized, would affect the Company's effective tax rate. Impact of the Tax Cuts and Jobs Act ("2017 Tax Reform Act") The 2017 Tax Reform Act was enacted on December 22, 2017 and provides for significant changes to U.S. tax law. Among other provisions, the 2017 Tax Reform Act reduces the U.S. corporate income tax rate to 21% effective in 2018. The 2017 Tax Reform Act also contains a number of provisions that may impact the Company in future years. Since ongoing guidance and accounting interpretation is expected in the 12 months following enactment, the Company has made certain provisional accounting estimates, as permitted under Staff Accounting Bulletin No. 118, and continues to analyze its accounting policies in this area. The U.S. Treasury Department, the IRS, and other standard-setting bodies could interpret or issue guidance on how provisions of the 2017 Tax Reform Act will be applied or otherwise administered that is different from the Company’s interpretation. As the Company completes its analysis of the 2017 Tax Reform Act, collects and prepares necessary data, and interprets any additional guidance, the Company may make adjustments to provisional amounts that it has recorded that may materially impact the provision for income taxes in the period in which the adjustments are made. The final accounting analysis will occur no later than one year from the date the 2017 Tax Reform Act was enacted. As a result of the reduction in the corporate rate, the Company remeasured its U.S. deferred tax assets and liabilities as of December 31, 2017 to reflect the lower rate expected to apply when these temporary differences reverse. The Company provisionally estimated that the remeasurement resulted in a reduction in deferred tax assets of $63.1 million , which was fully offset by a corresponding change to the Company’s valuation allowance. Although the tax rate reduction was known, the Company had not collected the necessary data to complete its analysis of the effect of the 2017 Tax Reform Act on the underlying deferred taxes and as such, the amounts recorded as of December 31, 2017 were provisional. However, the Company anticipates that any adjustment to provisional amounts recorded would be fully offset by a corresponding change to the Company’s valuation allowance. The Company has not made any additional measurement-period adjustments related to these items during the quarter because the Company is continuing to gather additional information and expects to complete its accounting within the prescribed measurement period. The Company has also considered and estimated a number of provisions of the 2017 Tax Reform Act effective January 1, 2018 as part of the estimated annual effective tax rate as of March 31, 2018. Due to forecasted tax losses and a full valuation allowance in the U.S., these provisions had no material impact to the income tax provision as of March 31, 2018. The 2017 Tax Reform Act also repealed the corporate alternative minimum tax (“AMT”) effective beginning in 2018, and permits AMT credit carryforwards to be refunded to the extent unused through 2021. Since the Company does not anticipate the use of these credits to reduce future federal taxes, the Company was able to reasonably estimate the income tax benefit and income tax receivable of $1.4 million during the year ended December 31, 2017. The Company had not collected the necessary data to complete its analysis of the classification of the AMT credit as a receivable and as such, the amounts recorded as an income tax receivable as of December 31, 2017 were provisional. There have not been material changes to the provisional amounts as of March 31, 2018. The 2017 Tax Reform Act also provides for a transition to a new territorial system of taxation and generally requires companies to include certain untaxed foreign earnings of non-U.S. subsidiaries into taxable income in 2017 (“Transition Tax”). As a result of the cumulative deficits in the Company’s foreign subsidiaries, the Company estimated that it has no Transition Tax inclusion. As of March 31, 2018, the Company has made no changes to its estimated Transition Tax inclusion. The 2017 Tax Reform Act subjects a US shareholder to tax on global intangible low-taxed income (“GILTI”) earned by certain foreign subsidiaries. The FASB Staff Q&A, Topic 740, No. 5 Accounting for GILTI, states that an entity can make an accounting policy election to either recognize deferred taxes for temporary basis differences expected to reverse as GILTI in future years or provide for the tax expense related to GILTI in the year the tax is incurred as a period expense only. Given the complexity of this provision, the Company is still evaluating the effects of the provision on its condensed consolidated financial statements and has not yet determined its accounting policy as of March 31, 2018. The Company has, however, included the estimated impact related to current year operations only in its annual effective tax rate for 2018 and has not provided for additional impact on deferred items. The Company expects to complete its accounting within the prescribed measurement period.

Related Party Transactions

Related Party Transactions	3 Months Ended
	Mar. 31, 2018
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions Dropbox Charitable Foundation During the year ended December 31, 2016, two of the Company’s controlling shareholders formed the Dropbox Charitable Foundation, a Delaware non-stock corporation (the “Foundation”). The primary purpose of the Foundation is to engage in charitable and educational activities within the meaning of Section 501(c)(3) of the Code. The Foundation is governed by a Board of Directors, a majority of which are independent. Both shareholders made contributions to the Foundation during the year ended December 31, 2016, comprised entirely of shares of Dropbox common stock. The Company has not consolidated the Foundation in the accompanying condensed consolidated financial statements, as the Company does not have control of the entity. During the three months ended March 31, 2018 , the Company did not make made cash contributions to the Foundation and during the three months ended March 31, 2017 , the Company made cash contributions to the Foundation of $0.1 million . Hewlett Packard Enterprise The Company has engaged in various commercial relationships with Hewlett Packard Enterprise (“HPE”), whose chief executive officer was appointed to the Dropbox Board of Directors in September 2017. The chief executive officer of HPE resigned effective February 1, 2018. The Company's commercial relationships with HPE include infrastructure equipment under capital leases, the purchase of commercial products and other services, and a multi-year subscription agreement for access to the Dropbox platform. During the three months ended March 31, 2018 and through the date of the resignation of the former chief executive officer of HPE, the Company made payments of $5.5 million for infrastructure equipment under capital leases and commercial products and services provided by HPE. As of March 31, 2018 , the Company had a remaining obligation of $94.7 million for equipment under capital lease from HPE. Related to the multi-year subscription agreement, the Company recognized an immaterial amount of revenue during the three months ended March 31, 2018 , and had an immaterial balance of deferred revenue and outstanding trade receivables as of March 31, 2018 .

Geographic Areas

Geographic Areas	3 Months Ended
	Mar. 31, 2018
Segment Reporting [Abstract]
Geographic Areas	Geographic Areas Long-lived assets The following table sets forth long-lived assets by geographic area: As of March 31, 2018 December 31, 2017 United States $ 325.9 $ 323.7 International (1) 19.7 18.2 Total property and equipment, net $ 345.6 $ 341.9 (1) No single country other than the United States had a property and equipment balance greater than 10% of total property and equipment, net, as of March 31, 2018 and December 31, 2017 . Revenue Revenue by geography is generally based on the address of the customer as defined in the Company’s subscription agreement. The following table sets forth revenue by geographic area for the three months ended March 31, 2018 and 2017 . Three months ended March 31, 2018 2017 United States $ 161.6 $ 129.9 International (1) 154.7 118.0 Total revenue $ 316.3 $ 247.9 (1) No single country outside of the United States accounted for more than 10% of total revenue during the three months ended March 31, 2018 and 2017 .

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2018
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events On March 28, 2018, the underwriters exercised their option to purchase an additional 5,400,000 shares of the Company's Class A common stock. This transaction closed on April 3, 2018, resulting in additional proceeds of $108.4 million , net of underwriters' discounts and commissions. The shares and proceeds are not reflected in the condensed consolidated financial statements as of and for the three months ended March 31, 2018.

Description of the Business a20

Description of the Business and Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of presentation	The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with the United States of America generally accepted accounting principles (“GAAP”) and applicable rules and regulations of the Securities and Exchange Commission ("SEC") regarding interim financial reporting. The accompanying unaudited condensed consolidated financial statements include the accounts of Dropbox and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.
Basis of consolidation	The condensed consolidated balance sheet as of December 31, 2017 included herein was derived from the audited financial statements as of that date. The unaudited condensed consolidated financial statements reflect all normal recurring adjustments necessary to present fairly the balance sheet, statements of operations, statements of comprehensive loss and the statements of cash flows for the interim periods, but are not necessarily indicative of the results of operations to be anticipated for the full fiscal year ended December 31, 2018 or any future period. The unaudited condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements and the related notes thereto as of and for the year ended December 31, 2017, included in the Company's prospectus filed pursuant to Rule 424(b) under the Securities Act of 1933, as amended, on March 23, 2018, referred to as the Prospectus.
Use of estimates	The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported and disclosed in the Company’s condensed consolidated financial statements and accompanying notes. These estimates are based on information available as of the date of the condensed consolidated financial statements. Management evaluates these estimates and assumptions on a regular basis. Actual results may differ materially from these estimates. The Company’s most significant estimates and judgments involve recognition of revenue, the measurement of the Company’s stock-based compensation, including the estimation of the underlying deemed fair value of common stock in periods prior to the date of the Company's IPO, the estimation of the fair value of market-based awards, and the valuation of acquired intangible assets and goodwill from business combinations.
Financial information about segments and geographic areas	The Company manages its operations and allocates resources as a single operating segment. Further, the Company manages, monitors, and reports its financials as a single reporting segment. The Company’s chief operating decision-maker is its Chief Executive Officer, who reviews financial information presented on a consolidated basis for purposes of making operating decisions, assessing financial performance, and allocating resources.
Foreign currency transactions	The assets and liabilities of the Company’s foreign subsidiaries are translated from their respective functional currencies into U.S. dollars at the exchange rates in effect at the balance sheet date. Revenue and expense amounts are translated at the average exchange rate for the period. Foreign currency translation gains and losses are recorded in other comprehensive income (loss). Gains and losses realized from foreign currency transactions (those transactions denominated in currencies other than the foreign subsidiaries’ functional currency) are included in other income (expense), net. Monetary assets and liabilities are remeasured using foreign currency exchange rates at the end of the period, and non-monetary assets are remeasured based on historical exchange rates.
Revenue recognition	The Company derives its revenue from subscription fees from customers for access to its platform. The Company’s policy is to exclude sales and other indirect taxes when measuring the transaction price of its subscription agreements. The Company accounts for revenue contracts with customers through the following 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, the Company satisfies a performance obligation The Company’s subscription agreements generally have monthly or annual contractual terms and a small percentage have multi-year contractual terms. Revenue is recognized ratably over the related contractual term beginning on the date that the platform is made available to a customer. Access to the platform represents a series of distinct services as the Company continually provides access to, and fulfills its obligation to the end customer over the subscription term. The series of distinct services represents a single performance obligation that is satisfied over time. The Company recognizes revenue ratably because the customer receives and consumes the benefits of the platform throughout the contract period. The Company’s contracts are generally non-cancelable. The Company bills in advance for monthly contracts and typically bills annually in advance for contracts with terms of one year or longer. The Company also recognizes an immaterial amount of contract assets, or unbilled receivables, primarily relating to rights to consideration for services completed but not billed at the reporting date. Unbilled receivables are classified as receivables when the Company has the right to invoice the customer. The Company records contract liabilities when cash payments are received or due in advance of performance to deferred revenue. Deferred revenue primarily relates to the advance consideration received from the customer. The price of subscriptions is generally fixed at contract inception and therefore, the Company’s contracts do not contain a significant amount of variable consideration. As a result, the amount of revenue recognized in the periods presented from performance obligations satisfied (or partially satisfied) in previous periods was not material.
Stock-based compensation	The Company has granted RSUs to its employees and members of the Board of Directors under the 2008 Equity Incentive Plan (“2008 Plan”), the 2017 Equity Incentive Plan (“2017 Plan”), and the 2018 Equity Incentive Plan ("2018 Plan"). The Company had two types of RSUs outstanding as of March 31, 2018 : • One-tier RSUs, which have a service-based vesting condition over a four year period. These awards typically have a cliff vesting period of one year and continue to vest quarterly thereafter. The Company began granting one-tier RSUs under its 2008 Plan in August 2015 and it continues to grant one-tier RSUs under its 2018 Plan. The Company recognizes compensation expense associated with one-tier RSUs ratably on a straight-line basis over the requisite service period and accounts for forfeitures in the period in which they occur. • Two-tier RSUs, which have both a service-based vesting condition and a Performance Vesting Condition. The service-based vesting period for these awards is typically four years with a cliff vesting period of one year and continue to vest monthly thereafter. Upon satisfaction of the Performance Vesting Condition, these awards will vest quarterly. The Performance Vesting Condition is satisfied on the earlier of (i) an acquisition or change in control of the Company or (ii) the earlier of (a) six months after the Company’s initial public offering or (b) March 15 of the year following the Company’s initial public offering. During the quarter ended March 31, 2018, the Company's Board of Directors approved the acceleration of the Performance Vesting Condition for which the service condition was satisfied, to occur upon the effectiveness of the registration statement related to the Company's IPO. Prior to August 2015, the Company granted two-tier RSUs under the 2008 Plan. The last grant date for two-tier RSUs was in May 2015. The Company recognizes compensation expense associated with two-tier RSUs using the accelerated attribution method over the requisite service period. The Performance Vesting Condition for the two-tier RSUs was satisfied upon the effectiveness of the registration statement related to the Company's IPO, which was March 22, 2018. The Company recognized the cumulative unrecognized expense of the two-tier RSUs, using the accelerated attribution method, during the three months ended March 31, 2018 . See "—Initial Public Offering and Private Placement” for further discussion. Since August 2015, the Company has granted RSUs as the only stock-based payment awards to its employees, with the exception of awards granted to its co-founders, and has not granted any stock options since then. The fair values of the common stock underlying the RSUs granted in periods prior to the date of the Company's IPO were determined by the Board of Directors, with input from management and contemporaneous third-party valuations, which were performed at least quarterly. For valuations after the Company's IPO, the Board of Directors will determine the fair value of each share of underlying common stock based on the closing price of the Company's Class A common stock as reported on the Nasdaq Global Select Market on the date of the grant. In December 2017, the Board of Directors approved a grant to the Company’s co-founders of restricted stock awards (“RSAs”) with respect to 14.7 million shares of Class A Common Stock in the aggregate (collectively, the “Co-Founder Grants”), of which 10.3 million RSAs were granted to Mr. Houston, the Company’s co-founder and Chief Executive Officer, and 4.4 million RSAs were granted to Mr. Ferdowsi, the Company’s co-founder and Director. These Co-Founder Grants have service-based, market-based, and performance-based vesting conditions. The Co-Founder Grants comprise nine tranches that are eligible to vest based on the achievement of stock price goals, or, each, a Stock Price Target. The Company estimated the grant date fair value of the Co-Founder Grants using a model based on multiple stock price paths developed through the use of a Monte Carlo simulation that incorporates into the valuation the possibility that the Stock Price Targets may not be satisfied. The average grant date fair value of each Co-Founder Grant was estimated to be $10.60 per share, and the Company will recognize aggregate stock-based compensation expense of $156.2 million over the requisite service period of each tranche, which ranged from 2.9 to 6.9 years, using the accelerated attribution method. If the Stock Price Targets are met sooner than the derived service period, the Company will adjust its stock-based compensation to reflect the cumulative expense associated with the vested awards. The Company will recognize expense if the requisite service is provided, regardless of whether the market conditions are achieved. The Co-Founder Grants contain an implied performance-based vesting condition because the Stock Price Targets are based on the trailing 30-day average price of the shares from an established national securities exchange or automated quotation system. Accordingly, no vesting could occur until the completion of the Company’s IPO. The relevant performance-based vesting condition for the Co-Founder Grants was satisfied on the date the Company’s shares of Class A common stock commenced trading on the Nasdaq Global Select Market, in connection with the Company’s IPO, which was March 23, 2018. The Company recognized the cumulative unrecognized expense of $10.6 million for the Co-Founder Grants, using the accelerated attribution method, during the three months ended March 31, 2018 . See Note 8, “Stockholders’ Equity” for further discussion.
Cash and cash equivalents	Cash consists primarily of cash on deposit with banks and includes amounts in transit from payment processors for credit and debit card transactions, which typically settle within five days. Cash equivalents include highly liquid investments purchased with an original maturity date of 90 days or less from the date of purchase.
Short-term investments	The Company’s short-term investments are primarily comprised of U.S. treasury securities, corporate notes and obligations, U.S. agency obligations, commercial paper, and certificates of deposits. The Company determines the appropriate classification of its short-term investments at the time of purchase and reevaluates such designation at each balance sheet date. The Company has classified and accounted for its short-term investments as available-for-sale securities as the Company may sell these securities at any time for use in its current operations or for other purposes, even prior to maturity. As a result, the Company classifies its short-term investments, including securities with stated maturities beyond twelve months, within current assets in the condensed consolidated balance sheets. The Company's short-term investments are classified as available-for-sale securities and are recorded at fair value each reporting period. Unrealized gains and losses on these short-term investments are reported as a separate component of accumulated other comprehensive income (loss) in the condensed consolidated balance sheets until realized. Interest income is reported within interest expense, net in the condensed consolidated statements of operations. The Company periodically evaluates its short-term investments to assess whether those with unrealized loss positions are other-than-temporarily impaired. The Company considers various factors in determining whether to recognize an impairment charge, including the length of time the investment has been in a loss position, the extent to which the fair value is less than the Company’s cost basis, and the financial condition and near-term prospects of the investee. Realized gains and losses are determined based on the specific identification method and are reported in other income (expense), net in the condensed consolidated statements of operations. If the Company determines that the decline in an investment’s fair value is other-than-temporary, the difference is recognized as an impairment loss in the condensed consolidated statements of operations.
Concentrations of credit risk	Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash, cash equivalents, accounts receivable, and short-term investments. The Company places its cash and cash equivalents and short-term investments with well-established financial institutions. Trade accounts receivables are typically unsecured and are derived from revenue earned from customers located around the world.
Non-trade receivables	The Company records non-trade receivables to reflect amounts due for activities outside of its subscription agreements. Historically, the Company’s non-trade receivables have related primarily to receivables resulting from tenant improvement allowances. Non-trade receivables totaled $3.6 million and $5.2 million , as of March 31, 2018 and December 31, 2017 , respectively, and are classified within prepaid expenses and other current assets in the accompanying condensed consolidated balance sheets.
Deferred commissions, net	Deferred commissions, net is stated as gross deferred commissions less accumulated amortization. Sales commissions earned by the Company’s sales force and third-party resellers, as well as related payroll taxes, are considered to be incremental and recoverable costs of obtaining a contract with a customer. These amounts have been capitalized as deferred commissions within prepaid and other current assets and other assets on the condensed consolidated balance sheet. The Company deferred incremental costs of obtaining a contract of $9.8 million and $4.7 million during the three months ended March 31, 2018 and 2017 , respectively. Deferred commissions, net included in prepaid and other current assets were $9.5 million and $8.1 million as of March 31, 2018 and December 31, 2017 , respectively. Deferred commissions, net included in other assets were $30.8 million and $24.8 million as of March 31, 2018 and December 31, 2017 , respectively. Deferred commissions are amortized over a period of benefit of five years. The period of benefit was estimated by considering factors such as historical customer attrition rates, the useful life of the Company’s technology, and the impact of competition in its industry. Amortized costs were $2.4 million and $ 1.2 million for the three months ended March 31, 2018 and 2017 , respectively. Amortized costs are included in sales and marketing expense in the accompanying condensed consolidated statements of operations. There was no impairment loss in relation to the deferred costs for any period presented.
Property and equipment, net	Equipment is stated at cost less accumulated depreciation. Depreciation is computed using the straight-line method over the estimated useful life of the related asset, which is generally three to seven years. Leasehold improvements are amortized on a straight-line basis over the shorter of their estimated useful lives or the term of the related lease. In the first quarter of 2018, the Company determined that the useful lives of certain infrastructure equipment, which are depreciated through cost of revenue, should be increased from three to four years. The Company accounted for this as a change in estimate that will be applied prospectively, effective as of January 1, 2018. This change in depreciable life resulted in a reduction of $6.1 million in depreciation expense within cost of revenue during the three months ended March 31, 2018 . The following table presents the estimated useful lives of property and equipment: Property and equipment Useful life Buildings 20 to 30 years Datacenter and other computer equipment 3 to 5 years Office equipment and other 3 to 7 years Leasehold improvements Lesser of estimated useful life or remaining lease term
Lease obligations	The Company leases office space, datacenters, and equipment under non-cancelable capital and operating leases with various expiration dates through 2033. Certain of the Company’s operating lease agreements contain tenant improvement allowances from its landlords. These allowances are accounted for as lease incentive obligations and are amortized as reductions to rent expense over the lease term. In addition, certain of the operating lease agreements contain rent concession, rent escalation, and options to renew. Rent concession and rent escalation provisions are considered in determining the straight-line rent expense to be recorded over the lease term. The lease term begins on the date the Company has the right to use the leased property for purposes of recognizing lease expense on a straight-line basis over the term of the lease. The Company does not assume renewals in its determination of the lease term unless the renewals are deemed to be reasonably assured at lease inception. The Company leases certain equipment from various third parties, including from a related party, through equipment financing leases under capital leases. See Note 11, “Related Party Transactions” for additional details. These leases either include a bargain purchase option, a full transfer of ownership at the completion of the lease term, or the terms of the leases are at least 75 percent of the useful lives of the assets and are therefore classified as a capital leases. These leases are capitalized in property and equipment and the related amortization of assets under capital leases is included in depreciation and amortization expense in the Company’s condensed consolidated statements of operations. Initial asset values and lease obligations are based on the present value of future minimum lease payments.
Long-lived assets, including goodwill and other acquired intangible assets, net	The Company evaluates the recoverability of its property and equipment and finite-lived intangible assets for possible impairment whenever events or circumstances indicate that the carrying amount of such assets may not be recoverable. The evaluation is performed at the lowest level for which identifiable cash flows are largely independent of the cash flows of other assets and liabilities. Recoverability of these assets is measured by a comparison of the carrying amounts to the future undiscounted cash flows the assets are expected to generate. If such review determines that the carrying amount of specific property and equipment or intangible assets is not recoverable, the carrying amount of such assets is reduced to its fair value. The Company reviews goodwill for impairment at least annually in the fourth quarter, or more frequently if events or changes in circumstances would more likely than not reduce the fair value of its single reporting unit below its carrying value. The Company has not recorded impairment charges on property and equipment, goodwill, or intangible assets for the periods presented in these condensed consolidated financial statements. Acquired property and equipment and finite-lived intangible assets are amortized over their useful lives. The Company evaluates the estimated remaining useful life of these assets when events or changes in circumstances warrant a revision to the remaining period of amortization. If the Company reduces the estimated useful life assumption for any asset, the remaining unamortized balance is amortized or depreciated over the revised estimated useful life on a prospective basis. See "—Property and Equipment, Net” for further discussion regarding a change in useful life applied during the three months ended March 31, 2018.
Income taxes	Deferred income tax balances reflect the effects of temporary differences between the financial reporting and tax bases of the Company’s assets and liabilities using enacted tax rates expected to apply when taxes are actually paid or recovered. In addition, deferred tax assets are recorded for net operating loss and credit carryforwards. A valuation allowance is provided against deferred tax assets unless it is more likely than not that they will be realized based on all available positive and negative evidence. Such evidence includes, but is not limited to, recent cumulative earnings or losses, expectations of future taxable income by taxing jurisdiction, and the carry-forward periods available for the utilization of deferred tax assets. The Company uses a two-step approach to recognizing and measuring uncertain income tax positions. The first step is to evaluate the tax position for recognition by determining if the weight of available evidence indicates it is more likely than not that the position will be sustained on audit. The second step is to measure the tax benefit as the largest amount, which is more than 50% likely of being realized upon ultimate settlement. The Company recognizes interest and penalties related to unrecognized tax benefits as income tax expense. Although the Company believes that it has adequately reserved for its uncertain tax positions, it can provide no assurance that the final tax outcome of these matters will not be materially different. The Company evaluates its uncertain tax positions on a regular basis and evaluations are based on a number of factors, including changes in facts and circumstances, changes in tax law, such as the 2017 Tax Cuts and Jobs Act ("2017 Tax Reform Act"), correspondence with tax authorities during the course of an audit, and effective settlement of audit issues. To the extent that the final tax outcome of these matters is different than the amounts recorded, such differences will affect the provision for income taxes in the period in which such determination is made and could have a material impact on the Company’s financial condition and results of operations.
Fair value measurement	The Company applies fair value accounting for all financial assets and liabilities and non-financial assets and liabilities that are recognized or disclosed at fair value in the financial statements on a recurring basis. The Company defines fair value as the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. When determining fair value measurements for assets and liabilities, the Company considers the principal or most advantageous market in which it would transact and the market-based risk measurements or assumptions that market participants would use in pricing the asset or liability, such as risks inherent in valuation techniques, transfer restrictions, and credit risk. Fair value is estimated by applying the following hierarchy, which prioritizes the inputs used to measure fair value into three levels and bases the categorization within the hierarchy upon the lowest level of input that is available and significant to the fair value measurement: Level 1 —Quoted prices in active markets for identical assets or liabilities. Level 2 —Observable inputs other than quoted prices in active markets for identical assets and liabilities, quoted prices for identical or similar assets or liabilities in inactive markets, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 —Inputs that are generally unobservable and typically reflect management’s estimate of assumptions that market participants would use in pricing the asset or liability.
Recently issued accounting pronouncements not yet adopted and Recently adopted accounting pronouncements	In February 2016, the Financial Accounting Standards Board ("FASB") issued ASU No. 2016-02, Leases (Topic 842) . Most prominent among the changes in the standard is the recognition of right of use assets and lease liabilities by lessees for those leases classified as operating leases under current GAAP. Under the standard, disclosures are required to meet the objective of enabling users of financial statements to assess the amount, timing, and uncertainty of cash flows arising from leases. The Company will be required to recognize and measure leases existing at, or entered into after, the beginning of the earliest comparative period presented using a modified retrospective approach, with certain practical expedients available. The new standard is effective for fiscal years beginning after December 15, 2018. Early adoption by public entities is permitted. The Company is in the initial stage of its assessment of the new standard and is currently evaluating the quantitative impact of adoption and the related disclosure requirements. The Company anticipates the adoption of this standard will result in a substantial increase in its non-current assets and liabilities recorded on the condensed consolidated balance sheets. The adoption of the standard is not expected to have a material impact on the consolidated statement of operations. While the Company is assessing all potential impacts of the adoption of the standard, it currently expects the most significant impact to be the capitalization of right-to-use assets and lease liabilities for its office space and datacenter operating leases. The Company expects its accounting for capital leases related to infrastructure equipment to remain substantially unchanged under the new standard. The Company expects to adopt the standard on January 1, 2019. In February 2018, the FASB issued ASU No. 2018-02, Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income . Under existing U.S. GAAP, the effects of changes in tax rates and laws on deferred tax balances are recorded as a component of income tax expense in the period in which the law was enacted. When deferred tax balances related to items originally recorded in accumulated other comprehensive income are adjusted, certain tax effects become stranded in accumulated other comprehensive income. The amendments in ASU No. 2018-02 allow a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the 2017 Tax Reform Act. The amendments in ASU No. 2018-02 also require certain disclosures about stranded tax effects. The guidance is effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years. Early adoption in any period is permitted. The Company is currently evaluating the timing and impact of adopting ASU No. 2018-02. In January 2016, the FASB issued ASU No. 2016-01, Financial Instruments Overall: Recognition and Measurement of Financial Assets and Financial Liabilities (Subtopic 825) , which primarily affects the accounting for equity investments, financial liabilities under the fair value option and the presentation and disclosure requirements for financial instruments. In addition, the FASB clarified guidance related to the valuation allowance assessment when recognizing deferred tax assets resulting from unrealized losses on available-for-sale debt securities. The accounting for other financial instruments, such as loans, investments in debt securities and financial liabilities is largely unchanged. The Company adopted ASU No. 2016-01 on January 1, 2018. The adoption of the standard did not have a material impact on the Company's condensed consolidated financial statements. In October 2016, the FASB issued ASU No. 2016-16, Income Taxes: Intra-Entity Transfers Other than Inventory (Topic 740) , which requires entities to recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs. The Company adopted ASU No. 2016-16 on January 1, 2018. The adoption of the guidance did not have a material impact on the Company's condensed consolidated financial statements.
Goodwill	Goodwill represents the excess of the purchase price in a business combination over the fair value of net tangible and intangible assets acquired. Goodwill amounts are not amortized, but tested for impairment on an annual basis.
Net loss per share	The Company computes net loss per share using the two-class method required for multiple classes of common stock and participating securities. The rights, including the liquidation and dividend rights, of the Class A common stock and Class B common stock are substantially identical, other than voting rights. Accordingly, the Class A common stock and Class B common stock share equally in the Company’s net losses. Before the IPO, the Company’s participating securities also included convertible preferred stock. The holders of convertible preferred stock did not have a contractual obligation to share in the Company’s losses, and as a result net losses were not allocated to these participating securities.

Description of the Business a21

Description of the Business and Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Estimated Useful Lives of Property and Equipment	The following table presents the estimated useful lives of property and equipment: Property and equipment Useful life Buildings 20 to 30 years Datacenter and other computer equipment 3 to 5 years Office equipment and other 3 to 7 years Leasehold improvements Lesser of estimated useful life or remaining lease term Property and equipment, net consisted of the following: As of March 31, 2018 December 31, 2017 Building $ 36.6 $ 36.6 Datacenter and other computer equipment 692.4 663.1 Furniture and fixtures 23.8 21.2 Leasehold improvements 129.0 118.6 Construction in process 2.0 7.2 Total property and equipment 883.8 846.7 Accumulated depreciation and amortization (538.2 ) (504.8 ) Property and equipment, net $ 345.6 $ 341.9

Cash, Cash Equivalents and Sh22

Cash, Cash Equivalents and Short-Term Investments (Tables)	3 Months Ended
	Mar. 31, 2018
Cash and Cash Equivalents [Abstract]
Schedule of Cash, Cash Equivalents and Short-Term Investments	The amortized cost, unrealized gains and losses and estimated fair value of the Company's cash, cash equivalents and short-term investments as of March 31, 2018 consisted of the following: As of March 31, 2018 Amortized Cost Unrealized Gain Unrealized Loss Estimated Fair Value Cash $ 71.2 $ — $ — $ 71.2 Cash equivalents Money market funds 506.1 — — 506.1 U.S. Treasury securities 62.0 — — 62.0 U.S. agency obligations 12.1 — — 12.1 Commercial paper 10.8 — — 10.8 Corporate notes and obligations 2.6 — — 2.6 Certificates of deposit 0.5 — — 0.5 Total cash and cash equivalents $ 665.3 $ — $ — $ 665.3 Short-term investments U.S. Treasury securities 93.6 — — 93.6 Corporate notes and obligations 57.4 — (0.1 ) 57.3 U.S. agency obligations 14.4 — — 14.4 Commercial paper 10.3 — — 10.3 Certificates of deposit 5.1 — — 5.1 Total short-term investments 180.8 — (0.1 ) 180.7 Total $ 846.1 $ — $ (0.1 ) $ 846.0
Contractual Maturities of Short Term Investments	The following table presents the contractual maturities of the Company’s short-term investments as of March 31, 2018 : As of March 31, 2018 Amortized Cost Estimated Fair Value Due within one year $ 105.1 $ 105.1 Due between one to four years 75.7 75.6 Total $ 180.8 $ 180.7

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Schedule of Fair Value Assets Measured On Recurring Basis	The following table presents information about the Company’s financial instruments that are measured at fair value on a recurring basis using the above input categories: As of March 31, 2018 Level 1 Level 2 Level 3 Total Cash equivalents Money market funds $ 506.1 $ — $ — $ 506.1 U.S. Treasury securities — 62.0 — 62.0 U.S. agency obligations — 12.1 — 12.1 Commercial paper — 10.8 — 10.8 Corporate notes and obligations — 2.6 — 2.6 Certificates of deposit — 0.5 — 0.5 Total cash equivalents $ 506.1 $ 88.0 $ — $ 594.1 Short-term investments U.S. Treasury securities $ — $ 93.6 $ — $ 93.6 Corporate notes and obligations — 57.3 — 57.3 U.S. agency obligations — 14.4 — 14.4 Commercial paper — 10.3 — 10.3 Certificates of deposit — 5.1 — 5.1 Total short-term investments $ — $ 180.7 $ — $ 180.7 Total cash equivalents and short-term investments $ 506.1 $ 268.7 $ — $ 774.8

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	3 Months Ended
	Mar. 31, 2018
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment, Net	The following table presents the estimated useful lives of property and equipment: Property and equipment Useful life Buildings 20 to 30 years Datacenter and other computer equipment 3 to 5 years Office equipment and other 3 to 7 years Leasehold improvements Lesser of estimated useful life or remaining lease term Property and equipment, net consisted of the following: As of March 31, 2018 December 31, 2017 Building $ 36.6 $ 36.6 Datacenter and other computer equipment 692.4 663.1 Furniture and fixtures 23.8 21.2 Leasehold improvements 129.0 118.6 Construction in process 2.0 7.2 Total property and equipment 883.8 846.7 Accumulated depreciation and amortization (538.2 ) (504.8 ) Property and equipment, net $ 345.6 $ 341.9

Commitments and Contingencies (

Commitments and Contingencies (Tables)	3 Months Ended
	Mar. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Payments	Future minimum payments under the Company’s capital leases, non-cancelable operating leases, and other commitments as of December 31, 2017 , are as follows. There have been no material changes in our commitments and contingencies, as disclosed in the Prospectus. Capital lease commitments Operating lease commitments (1) Other commitments Year ended December 31: 2018 $ 108.3 $ 91.5 $ 64.0 2019 54.9 94.9 49.9 2020 18.4 126.0 34.7 2021 0.4 115.9 1.7 2022 — 109.0 — Thereafter — 812.6 4.8 Future minimum payments 182.0 $ 1,349.9 $ 155.1 Less interest and taxes (7.7 ) Less current portion of the present value of minimum lease payments (102.7 ) Capital lease obligations, net of current portion $ 71.6 (1) Consists of future non-cancelable minimum rental payments under operating leases for the Company’s offices and datacenters, excluding rent payments from the Company’s sub-tenants, variable operating expenses, and tenant improvement reimbursements. Non-cancelable rent payments from the Company’s sub-tenants as of December 31, 2017 , are expected to be $72.1 million through 2023

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	3 Months Ended
	Mar. 31, 2018
Stockholders' Equity Note [Abstract]
Schedule of Stock Option and Restricted Stock Activity	Stock option and restricted stock activity for the Company's Equity Incentive Plans was as follows for the three months ended March 31, 2018 : Options outstanding Restricted stock outstanding Number of shares available for issuance under the Plans Number of shares outstanding under the Plans Weighted- average exercise price per share Weighted- average remaining contractual term (In years) Number of shares outstanding under the Plans Weighted- average grant date fair value per share Balance at December 31, 2017 9.0 5.0 $ 10.52 5.5 54.9 $ 15.60 Reserved for issuance under the 2018 Plan 41.4 — — — — Additional shares authorized 1.3 — — — — Options exercised and RSUs released — (0.2 ) 6.20 (30.6 ) 14.85 Options and RSUs canceled 1.4 — — (1.4 ) 17.12 Shares repurchased for tax withholdings on release of restricted stock 11.8 — — — — Restricted stock granted (11.0 ) — — 11.0 17.20 Balance at March 31, 2018 53.9 4.8 $ 10.62 2.7 33.9 $ 16.76 Vested at March 31, 2018 4.7 $ 10.31 2.6 — $ — Unvested at March 31, 2018 0.1 $ 24.12 33.9 $ 16.76
Schedule of Pre-Tax Intrinsic Value	The following table summarizes information about the pre-tax intrinsic value of options exercised during the three months ended March 31, 2018 and 2017 : Three months ended March 31, 2018 2017 Intrinsic value of options exercised $ 1.7 $ 1.0

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	The following table sets forth the calculation of basic and diluted net loss per share attributable to common stockholders during the periods presented. The shares issued in the IPO and the private placement and the shares of Class A and Class B common stock issued upon conversion of the outstanding shares of convertible preferred stock in the IPO are included in the table below weighted for the period outstanding in the quarter ended March 31, 2018: Three months ended March 31, 2018 2017 Class A Class B Class A Class B Numerator: Net loss attributable to common stockholders $ (30.8 ) $ (434.7 ) $ (0.9 ) $ (32.2 ) Denominator: Weighted-average number of common shares outstanding used in computing basic and diluted net loss per common share 14.5 204.3 5.5 188.0 Net loss per common share, basic and diluted $ (2.13 ) $ (2.13 ) $ (0.17 ) $ (0.17 )
Schedule of Potentially Dilutive Securities Excluded from Computation of Earnings Per Share	The weighted-average impact of potentially dilutive securities that were not included in the diluted per share calculations because they would be anti-dilutive was as follows: Three months ended March 31, 2018 2017 Convertible preferred stock — 147.6 Restricted stock units 56.3 49.0 Options to purchase shares of common stock 4.9 5.2 Co-Founder Grants 14.7 — Shares subject to repurchase from early-exercised options and unvested restricted stock — 0.4 Total 75.9 202.2

Geographic Areas (Tables)

Geographic Areas (Tables)	3 Months Ended
	Mar. 31, 2018
Segment Reporting [Abstract]
Long-lived Assets by Geographic Areas	The following table sets forth long-lived assets by geographic area: As of March 31, 2018 December 31, 2017 United States $ 325.9 $ 323.7 International (1) 19.7 18.2 Total property and equipment, net $ 345.6 $ 341.9 (1) No single country other than the United States had a property and equipment balance greater than 10% of total property and equipment, net, as of March 31, 2018 and December 31, 2017 .
Revenue by Geographic Areas	The following table sets forth revenue by geographic area for the three months ended March 31, 2018 and 2017 . Three months ended March 31, 2018 2017 United States $ 161.6 $ 129.9 International (1) 154.7 118.0 Total revenue $ 316.3 $ 247.9 (1) No single country outside of the United States accounted for more than 10% of total revenue during the three months ended March 31, 2018 and 2017 .

Description of the Business a29

Description of the Business and Summary of Significant Accounting Policies - Narrative (Details)	Apr. 03, 2018USD ($)$ / sharesshares	Mar. 28, 2018$ / sharesshares	Mar. 27, 2018USD ($)$ / sharesshares	Mar. 26, 2018shares	Mar. 22, 2018USD ($)	Mar. 07, 2018	Dec. 31, 2017USD ($)tranche$ / sharesshares	Mar. 31, 2018USD ($)award$ / sharesshares	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)tranche
Conversion of Stock [Line Items]
Stock issued in IPO (in shares) | shares			26,822,409
Share price of stock issued in IPO (in dollars per share) | $ / shares			$ 21
Proceeds from initial public offering and private placement			$ 538,200,000					$ 638,200,000	$ 0
Offering costs			$ 6,900,000					900,000	0
Reverse stock split ratio						0.6667
Net foreign currency transaction gain								(700,000)	(2,700,000)
Revenue recognized								188,200,000	155,000,000
Non-trade receivables							$ 5,200,000	$ 3,600,000		$ 5,200,000
Deferred contract costs, amortization period								5 years
Amortization of deferred commissions								$ 2,400,000	1,200,000
Impairment loss related to deferred costs								0		$ 0
Reduction in depreciation expense								(34,100,000)	(44,500,000)
Change in Accounting Method Accounted for as Change in Estimate
Conversion of Stock [Line Items]
Reduction in depreciation expense								$ 6,100,000
Infrastructure Equipment
Conversion of Stock [Line Items]
Property and equipment, useful life								4 years		3 years
Incremental Costs
Conversion of Stock [Line Items]
Deferred contract costs								$ 9,800,000	$ 4,700,000
Deferred Commissions | Prepaid Expenses and Other Current Assets
Conversion of Stock [Line Items]
Deferred contract costs							8,100,000	9,500,000		$ 8,100,000
Deferred Commissions | Other Assets
Conversion of Stock [Line Items]
Deferred contract costs							24,800,000	$ 30,800,000		$ 24,800,000
Customer Concentration Risk | Trade and Other Receivables | Customer A
Conversion of Stock [Line Items]
Concentration risk, percentage								17.00%		18.00%
Customer Concentration Risk | Trade and Other Receivables | Customer B
Conversion of Stock [Line Items]
Concentration risk, percentage								31.00%		27.00%
Two-Tier RSUs
Conversion of Stock [Line Items]
Recognized cumulative unrecognized stock-based compensation					$ 418,700,000
Remaining unamortized stock-based compensation								$ 2,600,000
Unamortized stock-based compensation, requisite service period								7 months 6 days
Shares released (in shares) | shares								26,800,000
Employer related payroll expense								$ 13,900,000
Vesting period								4 years
Two-Tier RSUs | Tranche One
Conversion of Stock [Line Items]
Vesting period								1 year
Restricted Stock Units (RSUs)
Conversion of Stock [Line Items]
Number of award types | award								2
One-Tier RSU
Conversion of Stock [Line Items]
Vesting period								4 years
One-Tier RSU | Tranche One
Conversion of Stock [Line Items]
Vesting period								1 year
Restricted Stock
Conversion of Stock [Line Items]
Shares granted (in shares) | shares								11,000,000
Shares granted (in dollars per share) | $ / shares								$ 17.20
Restricted Stock | Co-Founder Grants
Conversion of Stock [Line Items]
Recognized cumulative unrecognized stock-based compensation								$ 10,600,000
Remaining unamortized stock-based compensation							$ 156,200,000	$ 145,600,000		$ 156,200,000
Shares granted (in shares) | shares							14,700,000	14,700,000
Number of tranches | tranche							9			9
Shares granted (in dollars per share) | $ / shares							$ 10.60
Award requisite period							5 years 2 months 12 days
Restricted Stock | Co-Founder Grants | Tranche One
Conversion of Stock [Line Items]
Vesting period							4 years
Restricted Stock | Co-Founder Grants | Chief Executive Officer
Conversion of Stock [Line Items]
Shares granted (in shares) | shares							10,300,000
Restricted Stock | Co-Founder Grants | Director
Conversion of Stock [Line Items]
Shares granted (in shares) | shares							4,400,000
Minimum
Conversion of Stock [Line Items]
Property and equipment, useful life								3 years
Minimum | Restricted Stock | Co-Founder Grants
Conversion of Stock [Line Items]
Award requisite period							2 years 10 months 25 days
Maximum
Conversion of Stock [Line Items]
Property and equipment, useful life								7 years
Maximum | Restricted Stock | Co-Founder Grants
Conversion of Stock [Line Items]
Award requisite period							6 years 10 months 25 days
Convertible preferred stock | Conversion of Convertible Preferred Stock to Class B Common Stock
Conversion of Stock [Line Items]
Shares converted in conversion (in shares) | shares				147,310,563
Convertible preferred stock | Conversion of Convertible Preferred Stock to Class A Common Stock
Conversion of Stock [Line Items]
Shares converted in conversion (in shares) | shares				258,620
Class B common stock | Conversion of Convertible Preferred Stock to Class B Common Stock
Conversion of Stock [Line Items]
Shares issued in conversion (in shares) | shares				147,310,563
Class B common stock | Conversion of Class B Common Stock to Class A Common Stock
Conversion of Stock [Line Items]
Shares converted in conversion (in shares) | shares				2,609,951
Class A common stock | Conversion of Convertible Preferred Stock to Class A Common Stock
Conversion of Stock [Line Items]
Shares issued in conversion (in shares) | shares				258,620
Class A common stock | Conversion of Class B Common Stock to Class A Common Stock
Conversion of Stock [Line Items]
Shares issued in conversion (in shares) | shares				2,609,951
Private Placement
Conversion of Stock [Line Items]
Proceeds from initial public offering and private placement								$ 100,000,000
Private Placement | Class A common stock
Conversion of Stock [Line Items]
Sale of stock (in shares) | shares		4,761,905
Share price of stock sold in shares) | $ / shares		$ 21
Subsequent Event | Underwriters Over-allotment Option | Class A common stock
Conversion of Stock [Line Items]
Sale of stock (in shares) | shares	5,400,000
Share price of stock sold in shares) | $ / shares	$ 21
Proceeds received in sale of stock	$ 108,400,000

Description of the Business a30

Description of the Business and Summary of Significant Accounting Policies - Performance Obligations (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Unsatisfied or partially unsatisfied performance obligations	$ 495.5
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligation satisfaction period	12 months

Description of the Business a31

Description of the Business and Summary of Significant Accounting Policies - Schedule of Estimated Useful Lives of Property and Equipment (Details)	3 Months Ended
	Mar. 31, 2018
Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	3 years
Minimum | Buildings
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	20 years
Minimum | Datacenter and other computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	3 years
Minimum | Office equipment and other
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	3 years
Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	7 years
Maximum | Buildings
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	30 years
Maximum | Datacenter and other computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	5 years
Maximum | Office equipment and other
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	7 years

Cash, Cash Equivalents and Sh32

Cash, Cash Equivalents and Short-Term Investments - Schedule of Cash, Cash Equivalents and Short-Term Investments (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 665.3	$ 430	$ 351.2	$ 352.7
Total cash equivalents	665.3
Short-term investments, amortized cost	180.8
Short-term investments, unrealized gain	0
Short-term investments, unrealized loss	(0.1)
Short-term investments, estimated fair value	180.7
Total cash, cash equivalents, and short term investments, before unrealized gains (losses) on investments	846.1
Total cash, cash equivalents, and short term investments	846
U.S. Treasury securities
Cash and Cash Equivalents [Line Items]
Short-term investments, amortized cost	93.6
Short-term investments, unrealized gain	0
Short-term investments, unrealized loss	0
Short-term investments, estimated fair value	93.6
Corporate notes and obligations
Cash and Cash Equivalents [Line Items]
Short-term investments, amortized cost	57.4
Short-term investments, unrealized gain	0
Short-term investments, unrealized loss	(0.1)
Short-term investments, estimated fair value	57.3
U.S. agency obligations
Cash and Cash Equivalents [Line Items]
Short-term investments, amortized cost	14.4
Short-term investments, unrealized gain	0
Short-term investments, unrealized loss	0
Short-term investments, estimated fair value	14.4
Commercial paper
Cash and Cash Equivalents [Line Items]
Short-term investments, amortized cost	10.3
Short-term investments, unrealized gain	0
Short-term investments, unrealized loss	0
Short-term investments, estimated fair value	10.3
Certificates of deposit
Cash and Cash Equivalents [Line Items]
Short-term investments, amortized cost	5.1
Short-term investments, unrealized gain	0
Short-term investments, unrealized loss	0
Short-term investments, estimated fair value	5.1
Cash
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	71.2	62.9
Total cash equivalents	71.2
Money market funds
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	506.1	$ 367.1
Total cash equivalents	506.1
U.S. Treasury securities
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	62
Total cash equivalents	62
U.S. agency obligations
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	12.1
Total cash equivalents	12.1
Commercial paper
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	10.8
Total cash equivalents	10.8
Corporate notes and obligations
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	2.6
Total cash equivalents	2.6
Certificates of deposit
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	0.5
Total cash equivalents	$ 0.5

Cash, Cash Equivalents and Sh33

Cash, Cash Equivalents and Short-Term Investments - Narrative (Details)	3 Months Ended
	Mar. 31, 2018USD ($)investment	Dec. 31, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 665,300,000	$ 430,000,000	$ 351,200,000	$ 352,700,000
Short-term investments	180,700,000	0
Cash in transit for credit and debit card transactions	$ 13,900,000	13,300,000
Number of investments in unrealized loss positions | investment	77
Gross unrealized gains (losses) on available-for-sale securities reclassified out of AOCI	$ 0
Gross realized gains (losses) on available-for-sale securities reclassified out of AOCI	0
Other-than-temporary impairment loss	0
Cash
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	71,200,000	62,900,000
Money market funds
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 506,100,000	$ 367,100,000

Cash, Cash Equivalents and Sh34

Cash, Cash Equivalents and Short-Term Investments - Contractual Maturities of Short Term Investments (Details) $ in Millions	Mar. 31, 2018USD ($)
Amortized Cost
Due within one year	$ 105.1
Due between one to four years	75.7
Total	180.8
Estimated Fair Value
Due within one year	105.1
Due between one to four years	75.6
Total	$ 180.7

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	$ 665.3
Total short-term investments	180.7
U.S. Treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total short-term investments	93.6
Corporate notes and obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total short-term investments	57.3
U.S. agency obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total short-term investments	14.4
Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total short-term investments	10.3
Certificates of deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total short-term investments	5.1
Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	506.1
U.S. Treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	62
U.S. agency obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	12.1
Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	10.8
Corporate notes and obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	2.6
Certificates of deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	0.5
Fair Value, Measurements, Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total short-term investments	180.7
Total cash equivalents and short-term investments	774.8
Fair Value, Measurements, Recurring | U.S. Treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total short-term investments	93.6
Fair Value, Measurements, Recurring | Corporate notes and obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total short-term investments	57.3
Fair Value, Measurements, Recurring | U.S. agency obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total short-term investments	14.4
Fair Value, Measurements, Recurring | Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total short-term investments	10.3
Fair Value, Measurements, Recurring | Certificates of deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total short-term investments	5.1
Fair Value, Measurements, Recurring | Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	506.1
Fair Value, Measurements, Recurring | U.S. Treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	62
Fair Value, Measurements, Recurring | U.S. agency obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	12.1
Fair Value, Measurements, Recurring | Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	10.8
Fair Value, Measurements, Recurring | Corporate notes and obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	2.6
Fair Value, Measurements, Recurring | Certificates of deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	0.5
Fair Value, Measurements, Recurring | Cash equivalents
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	594.1
Fair Value, Measurements, Recurring | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total short-term investments	0
Total cash equivalents and short-term investments	506.1
Fair Value, Measurements, Recurring | Level 1 | U.S. Treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total short-term investments	0
Fair Value, Measurements, Recurring | Level 1 | Corporate notes and obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total short-term investments	0
Fair Value, Measurements, Recurring | Level 1 | U.S. agency obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total short-term investments	0
Fair Value, Measurements, Recurring | Level 1 | Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total short-term investments	0
Fair Value, Measurements, Recurring | Level 1 | Certificates of deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total short-term investments	0
Fair Value, Measurements, Recurring | Level 1 | Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	506.1	$ 367.1
Fair Value, Measurements, Recurring | Level 1 | U.S. Treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	0
Fair Value, Measurements, Recurring | Level 1 | U.S. agency obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	0
Fair Value, Measurements, Recurring | Level 1 | Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	0
Fair Value, Measurements, Recurring | Level 1 | Corporate notes and obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	0
Fair Value, Measurements, Recurring | Level 1 | Certificates of deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	0
Fair Value, Measurements, Recurring | Level 1 | Cash equivalents
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	506.1
Fair Value, Measurements, Recurring | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total short-term investments	180.7
Total cash equivalents and short-term investments	268.7
Fair Value, Measurements, Recurring | Level 2 | U.S. Treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total short-term investments	93.6
Fair Value, Measurements, Recurring | Level 2 | Corporate notes and obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total short-term investments	57.3
Fair Value, Measurements, Recurring | Level 2 | U.S. agency obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total short-term investments	14.4
Fair Value, Measurements, Recurring | Level 2 | Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total short-term investments	10.3
Fair Value, Measurements, Recurring | Level 2 | Certificates of deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total short-term investments	5.1
Fair Value, Measurements, Recurring | Level 2 | Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	0
Fair Value, Measurements, Recurring | Level 2 | U.S. Treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	62
Fair Value, Measurements, Recurring | Level 2 | U.S. agency obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	12.1
Fair Value, Measurements, Recurring | Level 2 | Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	10.8
Fair Value, Measurements, Recurring | Level 2 | Corporate notes and obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	2.6
Fair Value, Measurements, Recurring | Level 2 | Certificates of deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	0.5
Fair Value, Measurements, Recurring | Level 2 | Cash equivalents
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	88
Fair Value, Measurements, Recurring | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total short-term investments	0
Total cash equivalents and short-term investments	0
Fair Value, Measurements, Recurring | Level 3 | U.S. Treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total short-term investments	0
Fair Value, Measurements, Recurring | Level 3 | Corporate notes and obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total short-term investments	0
Fair Value, Measurements, Recurring | Level 3 | U.S. agency obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total short-term investments	0
Fair Value, Measurements, Recurring | Level 3 | Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total short-term investments	0
Fair Value, Measurements, Recurring | Level 3 | Certificates of deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total short-term investments	0
Fair Value, Measurements, Recurring | Level 3 | Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	0
Fair Value, Measurements, Recurring | Level 3 | U.S. Treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	0
Fair Value, Measurements, Recurring | Level 3 | U.S. agency obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	0
Fair Value, Measurements, Recurring | Level 3 | Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	0
Fair Value, Measurements, Recurring | Level 3 | Corporate notes and obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	0
Fair Value, Measurements, Recurring | Level 3 | Certificates of deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	0
Fair Value, Measurements, Recurring | Level 3 | Cash equivalents
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash equivalents	$ 0

Property and Equipment, Net - S

Property and Equipment, Net - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 883.8	$ 846.7
Accumulated depreciation and amortization	(538.2)	(504.8)
Property and equipment, net	345.6	341.9
Building
Property, Plant and Equipment [Line Items]
Total property and equipment	36.6	36.6
Datacenter and other computer equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	692.4	663.1
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total property and equipment	23.8	21.2
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment	129	118.6
Construction in process
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 2	$ 7.2

Property and Equipment, Net - N

Property and Equipment, Net - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 883.8		$ 846.7
Accumulated depreciation	538.2		504.8
Depreciation	34.1	$ 44.5
Infrastructure Assets Held under Capital Leases
Property, Plant and Equipment [Line Items]
Property and equipment, gross	413.2		417.9
Accumulated depreciation	$ 253.4		$ 259

Goodwill (Details)

Goodwill (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill impairment	$ 0	$ 0

Revolving Credit Facility (Deta

Revolving Credit Facility (Details) - Credit And Guarantee Agreement - Line of Credit - USD ($)	Apr. 30, 2017	Mar. 31, 2018	Feb. 28, 2018
Line of Credit Facility [Line Items]
Aggregate letters of credit outstanding amount		$ 82,700,000
Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 600,000,000		$ 725,000,000
Debt issuance fees	$ 2,600,000		400,000
Debt instrument, term	5 years
Line of credit facility, accordion feature, increase limit			275,000,000
Unused capacity, commitment fee percentage	0.20%
Covenant terms, minimum liquidity balance	$ 100,000,000
Remaining borrowing capacity		$ 642,300,000
Revolving Credit Facility | LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.50%
Revolving Credit Facility | Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.50%
Letter of Credit
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity			$ 187,500,000
Commitment fee percentage	1.50%
Fronting fee	0.125%

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Loss Contingencies [Line Items]
Gross rent expense	$ 21.9	$ 16
Sublease income	$ 3.5	$ 1.9
Operating lease, minimum obligation			$ 829.7
Tenant improvement reimbursements			73.8
Letter of credit
Loss Contingencies [Line Items]
Letter of credit supporting obligations			$ 34.2

Commitments and Contingencies41

Commitments and Contingencies - Schedule of Future Minimum Payments (Details) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Capital lease commitments
2,018			$ 108.3
2,019			54.9
2,020			18.4
2,021			0.4
2,022			0
Thereafter			0
Future minimum payments			182
Less interest and taxes			(7.7)
Less current portion of the present value of minimum lease payments	[1]	$ (92.8)	(102.7)
Capital lease obligations, net of current portion	[1]	$ 77.2	71.6
Operating lease commitments
2,018			91.5
2,019			94.9
2,020			126
2,021			115.9
2,022			109
Thereafter			812.6
Future minimum payments			1,349.9
Other commitments
2,018			64
2,019			49.9
2,020			34.7
2,021			1.7
2,022			0
Thereafter			4.8
Future minimum payments			155.1
Rent payments from sub-tenants			$ 72.1
[1]	Includes amounts attributable to related party transactions. See Note 11 for further details.

Stockholders' Equity - Common S

Stockholders' Equity - Common Stock, Convertible Preferred Stock, Preferred Stock (Details)	Mar. 26, 2018shares	Dec. 31, 2017$ / sharesshares	Mar. 31, 2018vote$ / sharesshares
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)			240,000,000
Class A common stock
Class of Stock [Line Items]
Votes per share | vote			1
Common stock, shares authorized (in shares)		533,300,000	2,400,000,000
Common stock, par value (in dollars per share) | $ / shares		$ 0.00001	$ 0.00001
Common stock, shares issued (in shares)			54,000,000
Common stock, shares outstanding (in shares)			54,000,000
Class B common stock
Class of Stock [Line Items]
Votes per share | vote			10
Common stock, shares authorized (in shares)		466,700,000	475,000,000
Common stock, par value (in dollars per share) | $ / shares		$ 0.00001	$ 0.00001
Common stock, shares issued (in shares)			341,000,000
Common stock, shares outstanding (in shares)			341,000,000
Class C common stock
Class of Stock [Line Items]
Votes per share | vote			0
Common stock, shares authorized (in shares)			800,000,000
Common stock, par value (in dollars per share) | $ / shares			$ 0.00001
Common stock, shares issued (in shares)			0
Common stock, shares outstanding (in shares)			0
Restricted Stock
Class of Stock [Line Items]
Shares granted (in shares)			11,000,000
Conversion of Convertible Preferred Stock to Class B Common Stock | Class B common stock
Class of Stock [Line Items]
Shares issued in conversion (in shares)	147,310,563
Conversion of Convertible Preferred Stock to Class B Common Stock | Convertible preferred stock
Class of Stock [Line Items]
Shares converted in conversion (in shares)	147,310,563
Conversion of Convertible Preferred Stock to Class A Common Stock | Class A common stock
Class of Stock [Line Items]
Shares issued in conversion (in shares)	258,620
Conversion of Convertible Preferred Stock to Class A Common Stock | Convertible preferred stock
Class of Stock [Line Items]
Shares converted in conversion (in shares)	258,620
Co-Founder Grants | Restricted Stock
Class of Stock [Line Items]
Shares granted (in shares)		14,700,000	14,700,000

Stockholders' Equity - Equity I

Stockholders' Equity - Equity Incentive Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 22, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares reserved for future issuance (in shares)	41,400,000
Additional shares available for grant (in shares)	1,300,000
Shares issued and outstanding (in shares)	4,800,000		5,000,000
2018 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period	10 years
Vesting period	4 years
Options granted (in shares)	0
Shares issued and outstanding (in shares)	38,700,000
Shares available for grant (in shares)	53,900,000
Remaining unamortized stock-based compensation	$ 500.1
Unamortized stock-based compensation, requisite service period	3 years 1 month 6 days
2018 Plan | Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period	10 years
Class A common stock | 2018 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares reserved for future issuance (in shares)		41,400,000

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Stock Option and Restricted Stock Activity (Details) - $ / shares shares in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2018
Number of shares available for issuance under the Plans
Beginning balance (in shares)	9
Reserved for issuance under the 2018 Plan (in shares)			41.4
Additional shares authorized (in shares)	1.3
Options and RSUs canceled (in shares)	1.4
Shares repurchased for tax withholdings on release of restricted stock (unaudited) (in shares)	11.8
Restricted stock granted (in shares)	(11)
Ending balance (in shares)	53.9	9
Options Outstanding, Number of shares outstanding under the Plans
Beginning balance (in shares)	5
Options exercised (in shares)	(0.2)
Ending balance (in shares)	4.8	5
Vested during period (in shares)	4.7
Unvested at end of period (in shares)			0.1
Options Outstanding, Weighted- average exercise price per share
Beginning balance (in dollars per share)	$ 10.52
Options exercised (in dollars per share)	6.20
Ending balance (in dollars per share)	10.62	$ 10.52
Vested during period (in dollars per share)	$ 10.31
Unvested at end of period (in dollars per shares)			$ 24.12
Options Outstanding, Weighted- average remaining contractual term (In years)
Weighted-average contractual term	2 years 8 months 12 days	5 years 6 months
Vested during period	2 years 7 months 6 days
Restricted Stock
Restricted Stock Outstanding, Number of Plan shares outstanding
Beginning balance (in shares)	54.9
RSUs released (in shares)	(30.6)
RSUs canceled (in shares)	(1.4)
Restricted stock granted (in shares)	11
Ending balance (in shares)	33.9	54.9
Unvested at end of period (in shares)	54.9	54.9	33.9
Restricted Stock Outstanding, Weighted- average grant date fair value per share
Beginning balance (in dollars per share)	$ 15.60
RSUs released (in dollars per share)	14.85
RSUs canceled (in dollars per share)	17.12
Restricted stock granted (in dollars per share)	17.20
Ending balance (in dollars per share)	16.76	$ 15.60
Unvested at end of period (in dollars per share)	$ 15.60	$ 15.60	$ 16.76

Stockholders' Equity - Schedu45

Stockholders' Equity - Schedule of Pre-Tax Intrinsic Value (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Stockholders' Equity Note [Abstract]
Intrinsic value of options exercised	$ 1.7	$ 1

Stockholders' Equity - Co-Found

Stockholders' Equity - Co-Founder Grants (Details) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended	3 Months Ended
	Dec. 31, 2017USD ($)tranche$ / sharesshares	Mar. 31, 2018USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant date fair value (in dollars per share) | $ / shares		$ 24.12
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)		11
Co-Founder Grants | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	14.7	14.7
Expiration period	10 years
Number of tranches | tranche	9
Remaining unamortized stock-based compensation | $	$ 156.2	$ 145.6
Weighted-average grant date fair value (in dollars per share) | $ / shares	$ 10.60
Award requisite period	5 years 2 months 12 days
Co-Founder Grants | Restricted Stock | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award requisite period	6 years 10 months 25 days
Co-Founder Grants | Restricted Stock | Tranche One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
Co-Founder Grants | Restricted Stock | Tranche One | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage vested maximum	20.00%
Co-Founder Grants | Chief Executive Officer | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	10.3
Co-Founder Grants | Director | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	4.4

Net Loss Per Share - Schedule o

Net Loss Per Share - Schedule of Earnings Per Share, Basic and Diluted (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Class of Stock [Line Items]
Net loss attributable to common stockholders	$ (465.5)	$ (33.1)
Weighted-average number of common shares outstanding used in computing basic and diluted net loss per common share (in shares)	218.8	193.5
Net loss per common share, basic and diluted (in dollars per share)	$ (2.13)	$ (0.17)
Class A
Class of Stock [Line Items]
Net loss attributable to common stockholders	$ (30.8)	$ (0.9)
Weighted-average number of common shares outstanding used in computing basic and diluted net loss per common share (in shares)	14.5	5.5
Net loss per common share, basic and diluted (in dollars per share)	$ (2.13)	$ (0.17)
Class B
Class of Stock [Line Items]
Net loss attributable to common stockholders	$ (434.7)	$ (32.2)
Weighted-average number of common shares outstanding used in computing basic and diluted net loss per common share (in shares)	204.3	188
Net loss per common share, basic and diluted (in dollars per share)	$ (2.13)	$ (0.17)

Net Loss Per Share - Schedule48

Net Loss Per Share - Schedule of Potentially Dilutive Securities Excluded from Computation of Earnings Per Share (Details) - shares shares in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	75.9	202.2
Convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	0	147.6
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	56.3	49
Options to purchase shares of common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	4.9	5.2
Co-Founder Grants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	14.7	0
Shares subject to repurchase from early-exercised options and unvested restricted stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	0	0.4

Income Taxes (Details)

Income Taxes (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income tax expense	$ 1,800,000	$ 300,000
Unrecognized tax benefits	7,800,000
Unrecognized tax benefits that would impact effective tax rate	$ 300,000
Estimated reduction in deferred tax assets due to remeasurement			$ 63,100,000
Estimated tax benefit from repealed corporate AMT			1,400,000
Estimated transition tax inclusion			$ 0

Related Party Transactions (Det

Related Party Transactions (Details)		3 Months Ended		12 Months Ended
		Mar. 31, 2018USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016shareholder
Controlling Shareholders | Dropbox Charitable Foundation
Related Party Transaction [Line Items]
Number of controlling shareholders in related party transaction | shareholder				2
Payments to related party		$ 0	$ 100,000
Affiliated Entity | Infrastructure Equipment Under Capital Leases and Commercial Products and Services
Related Party Transaction [Line Items]
Payments to related party	[1]	5,500,000
Capital lease remaining obligation		$ 94,700,000
[1]	Includes amounts attributable to related party transactions. See Note 11 for further details.

Geographic Areas (Details)

Geographic Areas (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Property and equipment, net	$ 345.6		$ 341.9
Total revenue	316.3	$ 247.9
United States
Segment Reporting Information [Line Items]
Property and equipment, net	325.9		323.7
Total revenue	161.6	129.9
International
Segment Reporting Information [Line Items]
Property and equipment, net	19.7		$ 18.2
Total revenue	$ 154.7	$ 118

Subsequent Events (Details)

Subsequent Events (Details) - Class A common stock - Underwriters Over-allotment Option - Subsequent Event $ in Millions	Apr. 03, 2018USD ($)shares
Subsequent Event [Line Items]
Sale of stock (in shares) | shares	5,400,000
Proceeds received in sale of stock | $	$ 108.4